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Name : _________________________________________________
Marking Tracker – please record your scores for all completed sections below.
Section Name Marks achieved
Cell structure self assessment questions /26
Cell structure homework questions /19
Transport across membranes self assessment questions /28
Transport across membranes homework questions /21
Atomic structure self assessment questions /29
Atomic structure homework questions /21
Biological molecules self assessment questions /29
Biological molecules homework questions /21
DNA structure self assessment questions /32
DNA structure homework questions /20
Head Start to A Level
Biology
2
Please note – this document is really big!
You are welcome to print this document if you are able – but you do not have to. If you do
print the document, we would prefer that you only print the following 21 pages:
1;
19 – 21;
36 – 39;
53 – 56;
72 – 75;
90 – 94.
These pages correspond to the mark tracker to record your scores for each question section
from the cover and the ‘homework’ questions for each section (which should have a star in
the top right hand corner.) The remaining pages are useful notes (to provide help with the
work if you need it), the practice questions, and mark schemes for self-assessment and
review before you complete the homework questions. Please try to print these pages half
size (‘2 pages per sheet’) and double sided where you can, which will then only run to 5
sheets of paper.
If you don’t have access to a printer, that’s OK as most of us don’t at home either! It’s fine to
complete all of your work on paper. Please ensure each page of your work is titled with the
correct section heading (from the table on the front cover) and you write the correct
question numbers in the margin so your teacher will be able to recognise which question is
which when they review it with you. To keep your work in the correct order, please ensure
each page is numbered. It would be really useful if you could complete the ‘self-assessment
questions’ as separate sheets to the ‘homework questions’ so you can hand in the
homework questions easily!
3
Welcome to A Level Biology at Wyke Sixth Form College!
This booklet reviews what we think are the five most important concepts you should have
covered already to help support your transition from GCSE Science to A Level Biology.
For each section, you will find:
Information sheets covering the topic content
Relevant examination questions from GCSE Science, with the corresponding
mark schemes so that you can self-assess your own knowledge and
understanding of each topic area
Links to online resources that can review the topic content more thoroughly
Homework questions indicated with a ‘star!’
We have written each section to provide just a little bit more than what you need at GCSE to
help you see the links between what you already know and what we’ll cover together.
You will be expected to sit an entrance exam within the first 3 weeks of the Biology course
to assess your initial understanding in both Biology and Maths, therefore you must read
through this booklet, answering all questions to prepare for this. Bring the booklet to the
first lesson and every subsequent lesson, as many questions will be marked in class. The
more you use this resource, the more effectively you can revise for this examination.
We have arranged this booklet into sections so that you can organise your time more
effectively. We think it is important to plan your work so that it does not become
overwhelming. The sections begin on the following pages:
1. Cell structure pg. 4
2. Transport across membranes pg. 22
3. Atomic structure and bonding pg. 40
4. Biological molecules and enzymes pg. 57
5. DNA structure and cell division pg. 76
We would recommend completing approximately one section of this booklet a week –
reading the material, answering and marking the self-assessment questions before
attempting the homework questions to bring to class. Take care – we slipped a few naughty
A Level questions in there! As the first day of term is 10th September, if you would like to
follow this structure the last day to begin the first section is 6th August.
Take care, and enjoy your summer!
Lee, Sophie, Kim, Zoe and Sadie
4
Prokaryotic cells
Prokaryotes are singled celled organisms such
as bacteria, and are usually much smaller than
eukaryotic cells (1/10th the size)
The term prokaryote means before (pro) the
nucleus (karyote). Which means that these
cells do not contain a nucleus or any other
organelles that are bound by a membrane
(e.g, chloroplasts or mitochondria)
What do they have?
Prokaryotic DNA is circular and can be
found floating free in the cytoplasm
or in smaller loops called plasmids.
A cell wall composed of peptidoglycan
(sometimes referred to as murein),
not cellulose like plants.
A cell membrane
Ribosomes
Mesosomes (folding of the cell
membrane as a site of respiration)
Slime capsule
In addition, some also have flagella
for movement and pili for
attachment.
Eukaryotic cells
Eukaryotic cells are more complex and
can be single celled (e.g. some algae,
some fungi and a group called the
protists) or multi-cellular organisms
(e.g plants and animals).
The term ‘eukaryotic’ means true (eu)
nucleus (karyote). Meaning these cells
have a nucleus, and organelles that
are bound by membranes.
To the right are diagrams of an animal
and plant cell that you should be
familiar with from your GCSE Biology
course.
5
Eukaryotic cells at A-level
As we step into A-level Biology we start to
understand that cells are much more complex
than this and have other organelles that are
specially adapted to carry out very specific
functions.
To the right you will see an animal cell (top)
and a plant cell (bottom), with the additional
organelles that we will learn about in the A-
level course.
Let’s discuss some of the functions (and
structures) of these organelles, starting with
the ones you know.
Cell surface membrane (both animal and
plant cell) – to control the movement of
specific molecules and ions in and out of the
cell. We will look at the structure of this in
great detail in the first year of the course.
Cytoplasm (both) – the site of many cellular
reactions (such as anaerobic respiration)
Cell wall (plant) – made of a long chain
carbohydrate (polysaccharide) called
cellulose. This is rigid and prevents the cell
from bursting due to osmotic pressure from
the cytoplasm.
Nucleus (both) – contains genetic material in
the form of DNA. The DNA is wound around a
series of proteins called histones. This DNA-
protein complex forms a material called
chromatin.
The nucleus is surrounded by a membrane
called the nuclear envelope, which has gaps
in it called nuclear pores.
The nucleolus is a dense region of the nucleus
that is responsible for producing ribosomes.
See diagram on the left for its structure.
6
Mitochondria (both) - site of aerobic
respiration, which produces a molecule called
ATP. ATP is a store of chemical energy that
can be used by the cell in many processes.
Mitochondria have a double membrane,
which is very selectively permeable. They also
have infoldings of the inner membrane called
cristae. These give a large surface area for a
very important process that occurs during
aerobic respiration. The fluid filling the
mitochondria is known as the matrix – this is
the site of some of the stages of aerobic
respiration. They also contain their own genes
in the form of circular mitochondrial DNA,
and ribosomes so they can produce the
proteins needed in respiration.
Vacuole (both) – large ones found
permanently in plant cells, and temporary
smaller ones in animal cells.
The vacuole is surrounded by a membrane
called the tonoplast.
In plant cells, the large vacuole acts as a
storage of cell sap (water with dissolved salts
and sugars in it). This helps to keep the cell
turgid.
Vacuoles also act as a waste storage.
Ribosomes (both) – these are very small
organelles made of 2 sub-units: 1 attaches to
mRNA (a copy of a gene) and 1 joins amino
acids together. Each unit is made of just 2
things: RNA and protein.
Ribosomes are the site of protein synthesis.
7
And now for some new organelles…
Endoplasmic reticulum (both) – sometimes
referred to as the ER, the endoplasmic
reticulum is made of a series of membrane
folds, which are actually just extensions of the
nuclear envelope.
There are 2 types, which each have different
functions:
Rough ER – this is closest to the nucleus and
has ribosomes attached to it. It’s function
therefore is protein synthesis and transport.
Smooth ER – this does not have ribosomes
attached, and its function is the synthesis and
transport of lipids.
Chloroplasts (plant) – these are the site of
photosynthesis, a process in which plants
convert light energy into chemical energy
using water and carbon dioxide to produce
oxygen and glucose.
They have a double membrane which is highly
selective, and a fluid centre called the stroma,
where one of the reactions in photosynthesis
occurs.
They have discs made of membrane called
thylakoids, that stack together to form grana.
These give a large surface area for one of the
processes in photosynthesis.
They also contain large starch grains, which
are a store of glucose.
Like mitochondria, they also have their own
circular DNA and ribosomes.
Golgi body / apparatus (both) -
The Golgi body is made of sacs of flattened
membrane called cisternae.
Functions include:
Modifying and packaging proteins into
vesicles
The formation of lysosomes
Formation of glycoproteins
8
Centrosomes (both) – these are involved in
spindle fibre formation during mitosis and
meiosis (see later section of this booklet).
Centrosomes consist of two centrioles, which
are filaments made of protein.
Lysosomes (both) – these are specialised
vesicles.
They are small membrane enclosed
organelles that contain digestive (hydrolytic)
enzymes called lysozymes.
Functions include:
Digesting dead cells and worn out
organelles
Digesting engulfed pathogens
9
Practise Questions Q1. The diagram shows a cell.
(a) (i) Use words from the box to name the structures labelled A and B .
cell membrane chloroplast cytoplasm nucleus
A ___________________________
B ___________________________
(2)
(ii) The cell in the diagram is an animal cell.
How can you tell it is an animal cell and not a plant cell?
Give two reasons.
1. ____________________________________________________________
______________________________________________________________
2. ____________________________________________________________
______________________________________________________________(2)
(b) Oxygen will diffuse into the cell in the diagram.
Why?
Use information from the diagram.
___________________________________________________________________
___________________________________________________________________(1)
(c) The cell shown in the diagram is usually found with similar cells.
Draw a ring around the correct answer to complete the sentence.
10
an organ.
Scientists call a group of similar cells a system.
a tissue.
(1)
(Total 6 marks)
Q2. This question is about cell structures.
(a) Draw one line from each cell structure to the type of cell where the structure is found.
Cell Structure Type of cell where
the structure is found
Nucleus Prokaryotic cells
Permanent vacuole Plant cells only
Plasmid Eukaryotic cells
(2)
(b) Figure 1 shows a plant cell.
What are the names of structures A, B and C? Tick one box.
Structure A Structure B Structure C
Chloroplast Vacuole Cell wall
Nucleus Chloroplast Cell membrane
Vacuole Mitochondrion Cell membrane
Vacuole Ribosome Cell wall
(1)
11
A student observed slides of onion cells using a microscope.
Figure 2 shows two of the slides the student observed.
Figure 2
The cells on the slides are not clear to see.
(c) Describe how the student should adjust the microscope to see the cells on Slide A more clearly.
___________________________________________________________________
___________________________________________________________________(1)
(d) Describe how the student should adjust the microscope to see the cells on Slide B more clearly.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________(2)
(e) The student made the necessary adjustments to get a clear image.
Figure 3 shows the student’s drawing of one of the cells.
Figure 3
12
The real length of the cell was 280 micrometres (µm).
Calculate the magnification of the drawing.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
Magnification = × _________________________(3)
(Total 9 marks)
Q3. Diagrams A, B and C show cells from different parts of the human body, all drawn to the same
scale.
(a) Which cell, A, B or C, appears to have adaptations to increase diffusion into or out
of the cell?
Give one reason for your choice.
___________________________________________________________________
___________________________________________________________________(1)
(b) (i) Cell C is found in the pancreas.
Name one useful substance produced by the pancreas.
______________________________________________________________(1)
(ii) Use information from the diagram to explain how cell C is adapted for producing this substance.
______________________________________________________________
______________________________________________________________
______________________________________________________________(2)
(Total 4 marks)
13
Q4. (a) The diagrams show the structures of a yeast cell and a bacterial cell.
(i) Both the yeast cell and the bacterial cell have structures A and B.
Name structures A and B.
A ___________________________
B ___________________________
(2)
(ii) The yeast cell and the bacterial cell have different shapes and sizes.
Give one other way in which the structure of the bacterial cell is different from the structure of the yeast cell.
______________________________________________________________
______________________________________________________________(1)
(b) Sourdough bread is light in texture and tastes slightly sour. The bread is made using two types of microorganism, a yeast and a bacterium. The bacterium can make acids such as lactic acid. The acid makes the bread taste sour.
The graph shows how the growth rates of the yeast and the bacteria change with temperature.
Temperature in °C
14
(i) Sourdough bread rises fastest at 27°C.
Use information from the graph to explain why.
______________________________________________________________
______________________________________________________________
______________________________________________________________
____________________________________________________________(2)
(ii) The bread tastes most sour if it rises at 32°C.
Use information from the graph to explain why.
______________________________________________________________
______________________________________________________________
______________________________________________________________
____________________________________________________________(2)
(Total 7 marks)
15
Practise Questions – Mark schemes Q1.
(a) (i) A = nucleus 1
B = (cell) membrane 1
(ii) any two from:
ignore shape
• no (cell) wall
• no (large / permanent) vacuole
• no chloroplasts / chlorophyll 2
(b) because high to low oxygen / concentration or down gradient
allow ‘more / a lot of oxygen molecules outside’
ignore along / across gradient 1
(c) a tissue 1
[6]
Q2. (a)
allow 1 mark for one or two correct links 2
(b)
vacuole ribosome cell wall
tick box takes precedence if no tick is given, look at both the figure and the circling of words in the table if writing is seen on the figure and in the table both must be correct
1
16
(c) turn the (fine focusing) knob until the cells are in focus
allow focus it
do not accept increase magnification
ignore decrease magnification ignore clear ignore references to resolution / illumination ignore zoom in / out
1
(d) (rotate the) nosepiece / objective lens
allow change the (objective / eyepiece) lens 1
to a higher power (lens)
allow (to) increase the magnification
a comparator is required
ignore change / adjust the magnification
allow stronger or more powerful lens
ignore references to resolution / illumination unqualified
ignore zoom in / out
ignore references to an electron microscope 1
(e) conversion of units: (112 mm ⟶) 112 000 (µm) or
(280 µm ⟶) 0.28 (mm) 1
or
allow 1 mark for no conversion of units 112 / 280 or incorrect value from step 1 correctly substituted
1
400 (×)
do not accept if units are given
if no other mark scored allow 1 mark for:
a triangle with words or letters in is insufficient, as the correct rearrangement is needed
1
an answer of 400 (×) scores 3 marks
[9]
17
Q3. (a) B no mark for ‘B’ alone
large(r) surface / area or large(r) membrane
accept reference to microvilli
accept reasonable descriptions of the surface
do not accept wall / cell wall
ignore villi / hairs / cilia 1
(b) (i) any one from:
• insulin / hormone
if named hormone / enzyme must be correct for pancreas
• enzyme / named enzyme 1
(ii) many ribosomes 1
(ribosomes) produce protein
accept insulin / hormone / enzyme named is (made of) protein
or
allow many mitochondria (1)
provide energy to build protein or to make protein (1)
accept ATP for energy 1
[4]
Q4. (a) (i) A = (cell) wall
ignore cellulose 1
B = cytoplasm 1
(ii) any one from:
accept has DNA instead of a nucleus, but not just has DNA
• bacterial cell / it has no nucleus
allow no mitochondria
• DNA free in cytoplasm
ignore size
• has no vacuole / no vesicles
ignore strands of DNA 1
(b) (i) yeast grows best / better / well or optimum temperature for yeast / more yeast present
allow yeast works best / better / well 1
(yeast) makes CO2 or respires / respiration; allow fermentation
18
1
(ii) bacterium grows best / better / well / more bacteria present or optimum temperature for bacterium
ignore microorganisms / microbes
allow works / respires best / better / well 1
(bacterium) makes (lactic) acid
do not allow wrong acid 1
[7]
Cell structure: /26
Identify three key areas for further study and revision:
If you scored less than 20, review the material presented again before completing the homework questions.
If you scored less than 10, the following videos may help with your work.
Prokaryotic and Eukaryotic Cells: https://www.youtube.com/watch?v=HBZcpzr5B2g
Plant cells: https://www.youtube.com/watch?v=EAoeI2gXBRg
Animal Cells: https://www.youtube.com/watch?v=GuY0n7-zfds
19
Homework Questions
Q1. Some infections are caused by bacteria.
The genetic material is arranged differently in the cells of bacteria compared with animal and plant cells.
Describe two differences.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(Total 2 marks)
Q2. The image below shows some muscle cells from the wall of the stomach, as seen through a light
microscope.
(a) Describe the function of muscle cells in the wall of the stomach.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
________________________________________________________________(2)
(b) The figure above is highly magnified.
The scale bar in the figure above represents an actual size of 0.1 mm. The scale bar was measured using a ruler to be 40mm long.
Calculate the magnification of the figure above.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
Magnification = _______________ times
(2)
20
(c) The muscle cells in Figure above contain many mitochondria.
What is the function of mitochondria?
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(d) The muscle cells also contain many ribosomes. The ribosomes cannot be seen in the figure above.
(i) What is the function of a ribosome?
______________________________________________________________
______________________________________________________________
(1)
(ii) Suggest why the ribosomes cannot be seen through a light microscope.
______________________________________________________________
______________________________________________________________
(1)
(Total 8 marks)
Q3. The figure below shows four different types of cell.
(a) Which cell is a plant cell?
Give one reason for your answer.
Cell _________
Reason ____________________________________________________________
(2)
21
(b) Which cell is an animal cell?
Give one reason for your answer.
Cell _________
Reason ____________________________________________________________
(2)
(c) Which cell is a prokaryotic cell?
Give one reason for your answer.
Cell _________
Reason ____________________________________________________________
(2)
(d) A scientist observed a cell using an electron microscope.
The size of the image was 25 mm.
The magnification was × 100 000
Calculate the real size of the cell.
Use the equation:
Give your answer in micrometres.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
Real size = __________________ micrometres
(3)
(Total 9 marks)
(Total 19 marks)
22
Cell Surface Membrane
The cell surface membrane can be found around
every cell, whether that’s a plant cell, animal cell
or bacterial cell. It allows the movement of
substances into and out of the cell. It can
prevent certain substances from entering
because it is a partially permeable membrane.
This means that it is permeable (open) to only
some molecules.
The cell membrane has been shown on all of
your diagrams before as a line. It is actually a lot
more complicated than that.
Structure of the cell surface membrane
The main body of the membrane is made up of a
double layer called the phospholipid bilayer.
The reason it is called this is because it is made
up of two layers (bi means two) of molecules
known as phospholipids.
Within the bilayer are large proteins which are
also responsible for transport and for cell
recognition.
There are two ways that the proteins can sit in
the bilayer. First, we have peripheral proteins
which sit on one side of the bilayer (on the
periphery), peripheral proteins are usually
helpful for cell recognition. We also have
integral proteins which span the full width of
the bilayer. Integral proteins are the ones which
are involved in transport of molecules.
There are two main types of integral proteins.
There are channel proteins, which as their name
suggests has a channel going through the middle
of it, this allows small molecules to pass through
them. We also have carrier proteins, these
don’t have a channel through them, and will
move larger molecules.
The combination of phospholipids and proteins
being closely packed together in a random
pattern. Leads to this being called the fluid
mosaic model (it looks like a mosaic).
23
Transport into and out of cells
There are 4 modes of transport you need to
be aware of;
Simple Diffusion
You should have covered diffusion at GCSE.
What you talked about most of the time was
simple diffusion (we’re going to talk about a
process called facilitated diffusion later on).
Simple diffusion can be talking about gas or
liquid particles. They move from an area of
high concentration to an area of low
concentration down a concentration
gradient. The key thing with simple diffusion,
is that these molecules don’t need to be
transported by a protein, they pass straight
over the phospholipid bilayer. They can do
this because they are small molecules.
Particles also don’t need an input of extra
energy to move this way. Molecules such as
oxygen, water and carbon dioxide can pass
through the phospholipid bilayer by simple
diffusion.
Osmosis
Osmosis should be another method of
transport that you covered at GCSE. Osmosis
occurs only with water.
The definition you had at GCSE may have
been: The water particles move from an area
of high water concentration to an area of low
water concentration, down a concentration
gradient, across a partially permeable
membrane.
That’s GCSE level. We want you to be talking
about it with correct A-Level terms. Instead of
‘water concentration’ which is a thing that
doesn’t exist. We instead are going to use the
term ‘water potential’. A high water potential
is a very dilute solution (lots of water, little
dissolved solute.) A low water potential is
when there’s not a lot of water present.
So, our A-Level definition is:
Water particles moving from a higher water
potential to a lower water potential, down a
water potential gradient, across a partially
permeable membrane.
Another key thing to remember about
osmosis is that it doesn’t require an input of
extra energy for it to happen – it uses the
kinetic energy the particles already have.
24
Facilitated diffusion
Some particles are too large to fit through the
phospholipid bilayer, so can’t move by simple
diffusion. This is where facilitated diffusion
comes in. Facilitated diffusion can use either
of our integral proteins to help move
molecules across the bilayer. The channel
proteins and carrier proteins within the
bilayer change shape when they come into
contact with a specific molecule (i.e. Glucose).
Facilitated diffusion is another transport
mechanism that it doesn’t require an input of
extra energy for it to happen, as particles are
still moving down a concentration gradient.
Active transport
The final transport mechanism is active
transport. This will be another method that
you will have looked at during GCSE, we’re
just adding a bit more information.
Active transport moves substances from an
area of low concentration to an area of high
concentration against a concentration
gradient. For active transport to happen, an
input of extra energy is required in the form
of a molecule called ATP (Adenosine
Triphosphate).
Another extra piece of information you need
to know is that the carrier proteins which
span the phospholipid bilayer are also
required for active transport to be able to
occur.
Page 25 of 94
Practice Questions
Q1. The diagram shows a cell from a plant leaf.
(a) Name the part of this cell that:
(i) controls the passage of substances in and out of the cell
______________________________________________________________
(1)
(ii) is filled with cell sap.
______________________________________________________________
(1)
(b) The chloroplasts produce oxygen.
Draw a ring around the correct answer to complete the sentence.
diffusion.
The oxygen produced by the chloroplasts passes out of the cell by digestion.
respiration.
(1)
(Total 3 marks)
Page 26 of 94
Q2. The digestive system breaks down food into small molecules.
The small molecules can be absorbed into the blood.
The diagram below shows the human digestive system.
(a) Glucose is absorbed into the blood in the small intestine.
Most of the glucose is absorbed by diffusion.
How does the glucose concentration in the blood compare to the glucose concentration in the small intestine?
Tick (✔) one box.
The concentration in the blood is higher.
The concentration in the blood is lower.
The concentration in the blood is the same.
(1)
Page 27 of 94
Substances can move into and out of cells.
(b) (i) How does oxygen move into and out of cells?
Draw a ring around one answer.
diffusion digestion photosynthesis
(1)
(ii) Diagram 1 shows the percentage concentration of oxygen in three cells, A, B and C.
Diagram 1
Oxygen can move from cell to cell.
Into which cell, A, B or C, will oxygen move the fastest?
(1)
(c) (i) How does water move into and out of cells?
Draw a ring around one answer.
breathing osmosis respiration
(1)
(ii) Differences in the concentration of sugars in cells cause water to move into or out of cells at different rates.
Diagram 2 shows three different cells, P, Q and R.
The information shows the percentage concentration of sugar solution in cells P, Q and R.
Diagram 2
Page 28 of 94
Water can move from cell to cell.
Into which cell, P, Q or R, will water move the fastest?
(1)
(Total 5 marks)
Q3. The diagram shows part of a plant root. A large number of structures like the ones labelled X grow out of the surface of the root.
(a) (i) What is the name of structure X?
Draw a ring around one answer.
root hair stoma villus
(1)
(ii) Name two substances which structure X absorbs from the soil.
1. ____________________________________________________________
2. ____________________________________________________________
(2)
Page 29 of 94
(b) The substances in (a)(ii) are transported from the roots to the leaves. Carbon dioxide also enters the leaves.
Draw a ring round the correct answer to complete the sentence.
active transport.
Carbon dioxide enters leaf cells by diffusion.
reabsorption.
(1)
(Total 4 marks)
Q4. Cells, tissues and organs are adapted to take in different substances and get rid of different substances.
The table shows the concentration of four ions outside cells and inside cells.
Ion Concentration
outside cells in mmol per dm3
Concentration inside cells in mmol per dm3
Sodium 140 9
Potassium 7 138
Calcium 2 27
Chloride 118 3
(a) Use information from the table above to complete the following sentences.
Sodium ions will move into cells by the process
of __________________________________ .
Potassium ions will move into cells by the process
of __________________________________ .
(2)
Page 30 of 94
(b) Some students investigated the effect of the different concentrations of sugar in four drinks, A, B, C and D, on the movement of water across a partially permeable membrane.
The students:
• made four bags from artificial partially permeable membrane
• put equal volumes of 5% sugar solution in each bag
• weighed each bag containing the sugar solution
• placed one bag in each of the drinks, A, B, C and D
• after 20 minutes removed the bags containing the sugar solution and weighed them again.
The diagram below shows how they set up the investigation.
(i) The bag in drink A got heavier after 20 minutes.
Explain why.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(3)
(ii) In which drink, A, B, C or D, would you expect the bag to show the smallest change in mass?
Tick (✔) one box.
A
B
C
D
(1)
Page 31 of 94
(iii) Explain why you think the bag you chose in part (b)(ii) would show the smallest change.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(Total 8 marks)
Q5. The image below shows an epithelial cell from the lining of the small intestine.
(a) (i) In the image above, the part of the cell labelled A contains chromosomes.
What is the name of part A?
______________________________________________________________
(1)
(ii) How are most soluble food molecules absorbed into the epithelial cells of the small intestine?
Draw a ring around the correct answer.
diffusion osmosis respiration
(1)
(b) Suggest how the highly folded cell surface helps the epithelial cell to absorb soluble food.
___________________________________________________________________
________________________________________________________________ (1)
Page 32 of 94
(c) Epithelial cells also carry out active transport.
(i) Name one food molecule absorbed into epithelial cells by active transport.
______________________________________________________________
(1)
(ii) Why is it necessary to absorb some food molecules by active transport?
______________________________________________________________
______________________________________________________________
(1)
(ii) Suggest why epithelial cells have many mitochondria.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(d) Some plants also carry out active transport.
Give one substance that plants absorb by active transport.
___________________________________________________________________
(1)
(Total 8 marks)
Page 33 of 94
Practice Questions Mark scheme
Q1. (a) (i) (cell) membrane
1
(ii) vacuole 1
(b) diffusion 1
[3]
Q2.
(a) The concentration in the blood is lower. 1
(b) (i) diffusion
apply list principle 1
(ii) A
apply list principle 1
(c) (i) osmosis
apply list principle 1
(ii) R
apply list principle 1
[5]
Q3. (a) (i) root hair
1
(ii) any two from:
ignore food
• water
• ions / minerals / nutrients / salts / correct named eg nitrates
ignore N,P,K
• oxygen 2
(b) diffusion 1
[4]
Page 34 of 94
Q4. (a) diffusion
1
active transport 1
this order only
(b) (i) concentration (of sugar) in the bag was higher (than in the drink)
allow concentration (of sugar) in the drink was lower (than in the bag)
or
higher water potential outside the bag or in the drink / boiling tube
allow lower water potential inside the bag 1
(so) water moved in (to the tubing)
allow water moves down its concentration gradient
do not allow sugar moving 1
by osmosis
allow diffusion (of water)
do not allow sugar moving by osmosis or water moving by active transport
1
(ii) B 1
(iii) close(st) to the concentration in the bag or to 5%
allow small(est) diffusion gradient or close(st) to an equilibrium
1
(so rate of) diffusion / osmosis is slow
allow (so) less water moves in (to the bag)
ignore ref. to sugar 1
[8]
Q5. (a) (i) nucleus
1
(ii) diffusion 1
(b) increases / larger surface area (for diffusion)
ignore large surface area to volume ratio 1
(c) (i) sugar / glucose
accept amino acids / other named monosaccharides 1
Page 35 of 94
(ii) against a concentration gradient or from low to high concentration
1
(iii) (active transport requires) energy 1
(from) respiration 1
(d) minerals / ions
accept named ion ignore nutrients
do not accept water 1
[8]
Transport Across Membranes Total Score: /28 Identify three key areas for further study and revision:
If you scored less than 18, review the material presented again before completing the homework
questions.
If you scored less than 10, the following videos could help before you carry on:
Fluid Mosaic Model: https://www.youtube.com/watch?v=Qqsf_UJcfBc
Osmosis: https://www.youtube.com/watch?v=wFjnAc0zMGA
Facilitated Diffusion: https://www.youtube.com/watch?v=IX-kLh34KcQ
Active Transport: https://www.youtube.com/watch?v=eDeCgTRFCbA
Page 36 of 94
Homework Questions
Q1. The diagram shows the same plant cell:
• after 1 hour in distilled water
• after 1 hour in strong sugar solution.
(a) Describe two ways in which the cell in the strong sugar solution is different from the cell in distilled water.
1. _________________________________________________________________
___________________________________________________________________
2. _________________________________________________________________
___________________________________________________________________
(2)
(b) Explain how the differences between the cell in the strong sugar solution and the cell in distilled water were caused.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
Page 37 of 94
(c) Some sugar molecules are absorbed from the small intestine into the blood by active transport.
Explain why the rate of absorption of these sugar molecules can depend on the concentration of oxygen in the cells lining the small intestine.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(3)
(Total 7 marks)
Q2. (a) Contrast the processes of facilitated diffusion and active transport.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(3)
Page 38 of 94
(b) Putting bee honey on a cut kills bacteria. Honey contains a high concentration of sugar.
Use your knowledge of water potential to suggest how putting honey on a cut kills bacteria.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(3)
(Total 6 marks)
Q3. A group of students carried out an investigation to find the water potential of potato tissue.
The students were each given a potato and 50 cm3 of a 1.0 mol dm−3 solution of sucrose.
• They used the 1.0 mol dm−3 solution of sucrose to make a series of different concentrations.
• They cut and weighed discs of potato tissue and left them in the sucrose solutions for a set time.
• They then removed the discs of potato tissue and reweighed them.
The table below shows how one student presented his processed results.
Concentration of sucrose solution / mol
dm−3
Percentage change in mass of potato
tissue
0.15 +4.7
0.20 +4.1
0.25 +3.0
0.30 +1.9
0.35 −0.9
0.40 −3.8
Page 39 of 94
(a) Explain why the data in the table above are described as processed results.
___________________________________________________________________
___________________________________________________________________
(1)
(b) Describe how you would use a 1.0 mol dm−3 solution of sucrose to produce 30 cm3 of a 0.15 mol dm−3 solution of sucrose.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(c) Explain the change in mass of potato tissue in the 0.40 mol dm−3 solution of sucrose.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(d) Describe how you would use the student’s results in the table above to find the water potential of the potato tissue.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(3)
(Total 8 marks)
(Total 21 marks)
Page 40 of 94
A periodic table can give you the proton /
atomic number of an element, this also tells
you how many electrons are in the atom.
You will have used the rule of electrons shell
filling, where: The 1st shell holds up to 2
electrons, the 2nd up to 8, the 3rd up to 8 and
the 4th up to 18 (you may have been told 8).
For the example of Lithium (Li) Atomic
number =3, electrons = 3, arrangement 2 in
the first shell and 1 in the second or Li = 2,1
Atomic Structure
In GCSE Chemistry you will have learned that
an atom is a single unit of matter, composed
of 3 things:
Protons (positive charge)
Electrons (negative charge)
Neutrons (no charge)
The protons and neutrons make up the
nucleus of the atom and are surrounded by
shells / orbitals of electrons.
Some other key chemistry terms you should
be familiar with:
Molecule:
Two or more atoms chemically bonded
together (can be the same atoms or
different). Examples oxygen gas O2, hydrogen
gas H2, water H2O, glucose C6H12O6
Compound:
Two or more different atoms chemically
bonded together. Examples: water H2O,
glucose C6H12O6, methane CH4
Mixture:
Two or more different atoms or molecules
together but not chemically bonded. Example:
air (made up of O2, N2, Ar, CO2)
Page 41 of 94
Bonding in molecules.
Ionic bonds (r) form between a metal and a
non-metal element. Ionic bonding involves
the metal atom losing an electron(s)
(becoming a positively charged ion) and the
non-metal gaining this electron(s) (becoming
a negatively charged ion).
This loss or gain of electrons makes each ion
more stable than the original atom as they
have complete outer shells of electrons.
The metal ions and non-metal ions are held
together by strong electrostatic attractions
between the opposite charges. This is an ionic
bond.
Covalent compounds can contain single (1
shared pair of electrons), double (2 shared
pairs) or triple (3 shared pairs) bonds.
Covalent bonds form between 2 non-metals.
Covalent bonds (l) involve the sharing of
electrons between atoms, which completes
their outer shells, making them more stable.
The bond forms, and is very strong, because
the shared pair(s) of electrons are attracted to
the positive nuclei of both atoms.
Page 42 of 94
In some molecules that contain covalent
bonds, the shared pairs of electrons are not
distributed evenly.
If one atom has a stronger electronegativity
than the other, the shared electrons are
pulled closer to its nucleus than the other
atom.
This gives one atom a partial positive charge,
and one atom a partial negative charge.
The partial charges are represented by the
symbol δ
Molecules that do this are called polar
molecules, and a good example is water.
Examples of importance:
This cohesive property of water is
important in plants – allowing
continuous streams of water to be
pulled upwards through the xylem
vessels from root to leaf.
Important in providing surface tension
on bodies of water!
Actually, the fact that water is a polar
molecule gives it one of its very important
properties.
The partial charges on the hydrogen and
oxygen atoms make water molecules
cohesive.
This means that the partial positive charge of
a hydrogen of one water molecule, is
attracted to the partial negative charge of an
oxygen of another water molecule.
This attractive force forms a hydrogen bond,
making the molecules cohere together!
Page 43 of 94
Types of reaction
At GCSE you know that oxidation is adding
oxygen to an atom or molecule and that
reduction is removing oxygen
or
oxidation is removing hydrogen and reduction
is adding hydrogen.
You may have also learned that oxidation is
removing electrons and reduction is adding
electrons.
2. Condensation reactions
• These involve forming bonds between
small molecules to make larger ones.
In doing so, water is formed.
• For example, when 2 glucose
molecules form a glycosidic bond to
make maltose, water is released. This
is an example of a condensation
reaction.In A-level biology we study a
number of oxidation and reduction
reactions, and introduce you to two
other types of reactions that are
fundamental in living systems:
1. Hydrolysis reactions
• These involve breaking down a larger
molecule into smaller molecules,
using the addition of water.
• Example; breaking down the
carbohydrate maltose into 2 glucose
molecules. This involves the breaking
of the glycosidic bond between the
two glucose molecules, requiring
water to do so.
Page 44 of 94
Practise Questions
Q1.
An argon atom can be represented as
(a) What does the number 40 represent in ?
___________________________________________________________________
___________________________________________________________________
(1)
(b) How many protons does this atom of argon have?
Tick one box.
18
22
40
58
(1)
(c) How many neutrons does this atom of argon have?
Tick one box.
18
22
40
58
(1)
Page 45 of 94
The diagram below shows the energy levels (shells) in a neon atom.
(d) A neon atom has 10 electrons.
Complete the diagram above to show the electronic structure of a neon atom.
Use x to represent an electron.
(1)
(e) The nucleus of a neon atom has a charge.
What is the charge?
Tick one box.
Negative
Neutral
Positive
(1)
(f) A neon atom has 10 protons, 10 electrons and 10 neutrons.
Explain why there is no overall charge on a neon atom.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
Page 46 of 94
(g) There are two different types of neon atom.
What are these different types of atom called?
Tick one box.
Compounds
Ions
Isotopes
Molecules
(1)
(h) Neon is a gas.
The states of matter can be shown by a simple particle model.
Draw one line from each state of matter to the correct particle model.
State of matter Particle model
Gas
Liquid
Solid
(2)
(Total 10 marks)
Q2. The table below shows the relative mass and charge of the particles in an atom.
Name of particle Relative mass Charge
proton 1 +1
neutron
electron very small
(a) Complete the table above. (3)
Page 47 of 94
(b) The diagram below represents a lithium atom.
Give the number of protons, neutrons and electrons in the lithium atom shown in the diagram above.
Number of protons _________________
Number of neutrons _________________
Number of electrons _________________
(3)
(Total 6 marks)
Q3. This question is about calcium.
(a) What type of compound is calcium oxide?
Tick one box.
An acid
A base
A carbonate
A salt
(1)
(b) Ionic compounds, such as calcium oxide, have high melting points.
Complete the sentences. Use words from the box.
bonds forces ions layers
Calcium oxide has a giant ionic lattice in which there are strong electrostatic
______________________ of attraction in all directions.
(1)
Page 48 of 94
(c) The figure below shows the electronic structure of an oxygen atom and a calcium atom.
Describe how the calcium atom and the oxygen atom forms calcium oxide.
You should give the charge on each ion formed.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(4)
(Total 6 marks)
Q4. One step in the manufacture of lead is the reduction of lead oxide with carbon. Lead and carbon dioxide are the products of this reaction.
(a) Write a word equation for this reaction.
___________________________________________________________________
(1)
(b) What is meant by “reduction”?
___________________________________________________________________
(1)
(Total 2 marks)
Page 49 of 94
Q5. The word equation below shows a reaction used in an industrial process.
chromium oxide + aluminium → chromium + aluminium oxide
The reaction is highly exothermic.
(a) What is an exothermic reaction?
___________________________________________________________________
___________________________________________________________________
(2)
(b) Name the products of this reaction.
___________________________________________________________________
(1)
(c) In the reaction one substance is reduced.
(i) Name the substance which is reduced.
______________________________________________________________
(1)
(ii) What happens to the substance when it is reduced?
______________________________________________________________
______________________________________________________________
(1)
(Total 5 marks)
Page 50 of 94
Practise Questions – Mark schemes
Q1. (a) the mass number
or number of protons and neutrons
ignore (relative) atomic mass 1
(b) 18 1
(c) 22 1
(d)
ignore pairing of electrons 1
(e) positive 1
(f) equal number of protons and electrons
do not accept equal number of protons, electrons and neutrons
1
(therefore) the positive cancels out the negative charge
allow (therefore) equal number of positives and negatives
1
(g) isotopes 1
(h)
2
[10]
Page 51 of 94
Q2. (a)
name of particle
relative mass
charge
proton (1) (+1)
neutron 1 0 1 + 1
electron (very small) −1 1
allow words instead of numbers allow neutral or no charge for the neutron
(b) (protons) 3 1
(neutrons) 4 1
(electrons) 3 1
allow words instead of numbers
[6]
Q3. (a) A base
1
(b) forces 1
(c) calcium loses electrons and oxygen gains electrons
max 3 for incorrect reference to atom / ion or to oxygen / oxide
1
two electrons are transferred 1
calcium has a 2+ charge 1
oxide has a 2– charge 1
[6]
Q4. (a) lead oxide + carbon = lead + carbon dioxide
(A symbol equation was accepted if correct) 1
(b) oxygen removed (or addition of electrons) 1
[2]
Page 52 of 94
Q5. (a) gives out
heat
each for 1 mark 2
(b) chromium and aluminium oxide 1
(c) (i) chromium oxide 1
(ii) oxygen removed/gains electrons 1
[5]
Atomic structure, bonding and redox reactions: /29
Identify three key areas for further study and revision:
If you scored less than 20, review the material presented again before completing the homework
questions.
If you scored less than 10, the following videos could help before you carry on:
Atomic Structure https://www.youtube.com/watch?v=jNmNyy2BX4g
Ionic bonding: https://www.youtube.com/watch?v=Biq-e9hsbiI
Covalent bonding: https://www.youtube.com/watch?v=lenvZEcMc60
Page 53 of 94
Homework Questions
Q1. This question is about sodium and chlorine.
Figure 1 shows the positions of sodium and chlorine in the periodic table.
Figure 1
(a) State one difference and one similarity in the electronic structure of sodium and of chlorine.
Difference __________________________________________________________
___________________________________________________________________
Similarity ___________________________________________________________
___________________________________________________________________
(2)
(b) Sodium atoms react with chlorine atoms to produce sodium chloride (NaCl).
Describe what happens when a sodium atom reacts with a chlorine atom.
Write about electron transfer in your answer.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(4)
Page 54 of 94
(c) The reaction between sodium and chlorine is an exothermic reaction.
Complete the reaction profile for the reaction between sodium and chlorine.
Figure 2
(2)
(Total 8 marks)
Q2. Brine, a solution containing sodium chloride in water, can be used to manufacture chlorine,
hydrogen and sodium hydroxide. A student sets up a simplified model of the industrial cell.
Page 55 of 94
(a) The electron arrangements of some atoms are shown here.
H 1
O 2.6
Na 2.8.1
C1 2.8.7
(i) Use the relevant electron arrangements to describe the bonding in water.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(b) Use the atomic structures of and to explain the meaning of the term isotopes.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(3)
(Total 5 marks)
Page 56 of 94
Q3. This question is about fluorine.
(a) Calcium reacts with fluorine to produce calcium fluoride (CaF2).
Explain how oxidation and reduction have taken place in this reaction.
Write about electron transfer in your answer.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________ (4)
(b) Explain why calcium fluoride has a high melting point.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(4)
(Total 8 marks)
(Total 21 Marks)
Page 57 of 94
Biological Molecules
Carbohydrates
Three elements make up carbohydrate molecules – carbon, hydrogen and oxygen.
There are several types of carbohydrates;
Sugars: Small, sweet, water-soluble molecules.
The simplest sugars are monosaccharides. Monosaccharides are single units from which disaccharides or larger carbohydrates are built. Monosaccharides contain the elements carbon, hydrogen and oxygen in the ratio of 2 hydrogen atoms and 1 oxygen atom for each carbon atom. Glucose (shown in the first image, top right) and Fructose are monosaccharides.
Disaccharides are made of two monosaccharides joined together with a glycosidic bond. Glucose and Fructose join together to form the disaccharide sucrose. The joining together of 2 monosaccharides occurs to release a molecule of water in a condensation reaction. Breaking the glycosidic bond to form monosaccharides in digestion is a hydrolysis reaction, catalysed by the enzyme sucrase (shown in the second image on the right.)
Glucose occurs in 2 forms: alpha (α) glucose and beta (β) glucose, identified by the position of the hydroxyl (-OH) group on carbon 1 (shown in the third image on the right.)
Polysaccharides: large polymers made from many
monosaccharide monomers that are insoluble in
water (shown in the fourth image.)
Starch is a polysaccharide. Two different
polysaccharides of alpha glucose monomers are
used to make starch - amylose and amylopectin.
The starch polymers are helical and insoluble so it
is a good storage molecule in plants.
Cellulose is a polysaccharide made of beta glucose
monomers. Molecules are bonded in long straight
lines, with hydrogen bonds between the strands. It
forms microfibrils to provide strength to plant cell
walls.
Page 58 of 94
Lipids
Three elements make up the lipid molecule -
carbon, hydrogen and oxygen. This is the same as
in carbohydrates, but the ratio and bonding of
these atoms is different.
Lipids are fats and oils, predominantly made up of
a group of lipids called triglycerides. These contain
a molecule of glycerol bonded to 3 fatty acids in
three different condensation reactions. (Picture 1)
The fatty acid is a long chain of carbon atoms
with a carboxyl/carboxylic acid (-COOH)
group at the end. Hydrogen atoms are
attached to the remaining carbons with single
bond.
If the carbon atoms in the chain are joined
with single bonds, the structure is known as a
saturated fatty acid. If there are any carbon
to carbon double bonds, then the fatty acid is
unsaturated. If there are multiple carbon to
carbon double bonds, this forms a
polyunsaturated fatty acid. (Picture 2)
Cell membranes are formed from a bilayer of
phospholipids. These are structures made of
glycerol with 2 fatty acids instead of 3, with
the ‘missing’ fatty acid chain replaced with a
phosphate group. (Picture 3)
Proteins
Proteins are polymers, made of long chains of
amino acid monomers joined together in chains -
up to several hundred amino acids in length. There
are only 20 different amino acids and the
combination of these 20 in different orders
produces a wide range of complex proteins.
All amino acids have the same structure; a central
carbon, with a hydrogen atom, carboxylic (-COOH)
acid group and amino (-NH3) group joined to that
carbon. The variation which produces 20 different
amino acids is that they each have a different
variable (‘R’) group. All amino acids contain
carbon, hydrogen, oxygen and nitrogen atoms –
some contain sulfur as well. (Picture 4)
Page 59 of 94
Protein structure
Amino acids are joined to each other in a chain
with covalent bonds called peptide bonds, formed
in condensation reactions. The order of the amino
acids determines the structure of the protein and
how it works.
The order of the amino acids in a polypeptide
chain forms the simplest level of structure, known
as the primary structure. The protein chain can
then coil or fold into pleats which are held
together by weak hydrogen bonds to form the
secondary structure. (Picture 1)
Proteins then experience further folding into a
more complex three-dimensional shape, held
together with stronger disulfide bonds. This is the
tertiary structure. Enzymes fold into a vaguely
spherical structure and are globular proteins.
(Picture 2)
Enzymes
Enzymes are globular proteins with a specific
primary structure, which leads to a specific tertiary
structure (or shape). The tertiary structure of an
protein is essential to its function.
Chemical reactions need some form of energy
input to take place. This input energy is called the
activation energy. Enzymes act as catalysts by
reducing the activation energy to speed up the
rate of these reactions. (Picture 3)
Enzymes can be catabolic (break substrates down
into smaller products) or anabolic (build substrates
up into larger products).
Enzymes have a specific site into which the
substrates can attach itself, this attachment site is
called the active site. The active site is
complementary to the shape of the substrate.
Once they attach together they form the enzyme-
substrate complex. The enzyme then causes
bonds within the substrate to break, or causes
bonds to form between multiple substrates. The
product of the reaction then leaves the enzyme’s
active site. After the product leaves the active site,
it is able to accept another substrate and catalyse
another reaction. (Picture 4)
Page 60 of 94
Self Assessment Practice Questions Q1. (a) Food molecules such as proteins cannot be absorbed unless they are digested.
Give one reason why.
___________________________________________________________________
___________________________________________________________________
(1)
A scientist investigated the effect of pH on the activity of two protease enzymes. Figure 2 shows the results.
Figure 2
(b) What is the optimum pH for enzyme Y?
pH ____________________
(1)
(c) Where in the digestive system might the two protease enzymes be produced? Tick one box.
Enzyme X Enzyme Y
Mouth Stomach
Pancreas Mouth
Small intestine
Pancreas
Stomach Small
intestine
(1)
Page 61 of 94
Figure 3 shows a model of an enzyme molecule.
Figure 3
(d) Which substrate fits the enzyme molecule in Figure 3?
Tick one box.
(1)
(e) The enzyme and substrate diagrams are used as a model for a theory of enzyme action.
What is the name of this theory?
Tick one box.
Evolution
Lock and key
Natural selection
Protein synthesis
(1)
Page 62 of 94
(f) Explain why pH affects enzyme activity.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(Total 7 marks)
Q2. Lipase is an enzyme that digests fat.
(a) (i) Complete the equation to show the digestion of fat.
Use the correct answer from the box.
glucose glycerol glycogen
fat fatty acids + ___________________
(1)
(ii) Name one organ that makes lipase.
______________________________________________________________
(1)
(b) Some students investigated the effect of bile on the digestion of fat by lipase.
The students: 1 mixed milk and bile in a beaker 2 put the pH sensor of a pH meter into the beaker 3 added lipase solution 4 recorded the pH at 2-minute intervals 5 repeated steps 1 to 4, but used water instead of bile.
Suggest two variables that the students should have controlled in this investigation.
1. _________________________________________________________________
___________________________________________________________________
2. _________________________________________________________________
___________________________________________________________________
(2)
Page 63 of 94
(c) The graph shows the students’ results.
(i) Why did the pH decrease in both investigations?
______________________________________________________________
______________________________________________________________
(1)
(ii) Bile helps lipase to digest fat.
What evidence is there in the graph to support this conclusion?
______________________________________________________________
______________________________________________________________
(1)
(iii) Suggest one reason why the contents of both beakers had the same pH at the end of the investigations.
______________________________________________________________
______________________________________________________________
(1)
(Total 7 marks)
Page 64 of 94
Q3. An athlete decides to try a new type of protein drink after he exercises.
(a) The athlete tests the protein drink to check it contains protein.
Which solution is used to test for protein in the drink?
Tick one box.
Benedict’s
Biuret
Iodine
Universal indicator
(1)
(b) What colour will the solution turn to if there is protein in the drink?
Tick one box.
Blue-black
Purple
Red
Yellow
(1)
Figure 1 shows the proportion of different nutrients in the protein drink.
Figure 1
Page 65 of 94
(c) What is the ratio of sugar to protein in the protein drink?
1:1
1:0:6
1:2
1:1:6
(1)
(d) Why is a high protein diet useful to an athlete?
Tick one box.
Provides amino acids to make new muscle.
Provides fatty acids to produce urea.
Provides glucose for energy.
Provides lactic acid for anaerobic respiration.
(1)
(Total 4 marks)
Q4.
(a) Draw one line from each digestive enzyme to the correct breakdown product.
Digestive enzyme Breakdown products
amino acids.
Amylase breaks down starch into……
bases.
Lipase breaks down fats into…
fatty acids and
glycerol.
Protease breaks down proteins into…
sugars.
(3)
(Total 3 marks)
Page 66 of 94
Q5. Amylase is an enzyme that digests starch.
A student investigated the effect of pH on the activity of amylase.
This is the method used.
1. Mix amylase solution and starch suspension in a boiling tube.
2. Put the boiling tube into a water bath at 25 °C.
3. Remove a drop of the mixture every 30 seconds and test it for the presence of starch.
4. Repeat the investigation at different pH values.
The table below shows the students’ results.
pH Time when no starch was
detected in minutes
5.0 7.0
5.5 4.5
6.0 3.0
6.5 2.0
7.0 1.5
7.5 1.5
8.0 2.0
(a) The student concluded pH 7.25 was the optimum pH for the amylase enzyme.
This is not a valid conclusion.
Suggest two reasons why.
1. _________________________________________________________________
___________________________________________________________________
2. _________________________________________________________________
___________________________________________________________________
(2)
Page 67 of 94
(b) The student did another investigation.
This is the method used.
1. Put amylase solution and starch suspension into a boiling tube.
2. Make the pH 7.25.
3. Put the boiling tube into a water bath at 25 °C.
4. Measure the amount of sugar produced every 30 seconds.
The results are shown in the figure below.
Calculate the mean rate of sugar produced per minute during the first 5 minutes.
___________________________________________________________________
___________________________________________________________________
Mean rate = ________________ units per minute
(2)
Page 68 of 94
(c) Iodine solution is added to a sample taken from the boiling tube after 10 minutes and 60 minutes.
Suggest what you would see in these samples.
After 10 minutes _____________________________________________________
___________________________________________________________________
.After 60 minutes _____________________________________________________
___________________________________________________________________
(2)
(d) The scientist repeated the investigation at 37 °C.
Draw a line on the figure above to show the predicted results.
(2)
(Total 8 marks)
(Total 29 marks)
Page 69 of 94
Self Assessment Practice Questions Mark schemes
Q1. (a) any one from:
• they are too big
• they are insoluble 1
(b) (pH) 7.5
allow answers in range 7.4 to 7.6 1
(c) (enzyme X) stomach
(enzyme Y) small intestine 1
(d) 1
(e) lock and key 1
(f) (some pH values):
change the shape of the active site
allow some pH values denature enzymes 1
(so) so substrate will no longer fit / bind to the active site 1
[7]
Q2.(a) (i) glycerol
1
(ii) pancreas / small intestine
accept duodenum / ileum
ignore intestine unqualified 1
(b) any two from: • type of milk • volume / amount of milk • vol. bile equals vol. water • volume of lipase • concentration of lipase • temperature
ignore time interval
ignore solution unqualified
do not allow pH
ignore starting pH
ignore volume / amount of bile / water
Page 70 of 94
ignore concentration of bile
accept amount of lipase if neither volume nor concentration given
2
(c) (i) fatty acid (production) 1
(ii) faster reaction / digestion (with bile) or pH decreases faster (with bile) or takes less time (with bile) or steeper fall / line (with bile)
allow use of data, ignore easier 1
(iii) all fat / milk digested or same amount of fatty acids present or (lower pH) denatures the enzyme / lipase
allow all reactants used up
ignore reference to neutralisation
allow enzyme won’t work at low pH
do not allow enzyme killed 1
[7]
Q3. (a) biuret
1
(b) purple 1
(c) 1:1.6 1
(d) provides amino acids to make new muscle 1
[4]
Q4. (a) Enzyme Breakdown products
3 [3]
Page 71 of 94
Q5. (a) any two from:
• same result at pH 7 and 7.5 or could be any pH between 7 and 7.5 or not tested at pH 7.25 or need to test at smaller pH intervals (between 7 and 7.5)
• accuracy of result only to nearest 0.5 minutes • no repeats • difficult to determine end point (colour)
2
(b) 2.7 / 5 1
0.54 (units per minute)
allow 0.52 with no working shown for 2 marks 1
allow 1 mark for 0.52 or 0.56
(c) (after 10 minutes) solution goes black 1
(after 60 minutes) solution stays the same or does not go black or goes slightly orange
1
(d) steeper curve 1
levels off at 11.8 units and before 45 minutes 1
[8]
Biological Molecules Total Score: /29
Identify three key areas for further study and revision:
If you scored less than 20, review the material presented again before completing the homework
questions.
If you scored less than 10, the following videos could help before you carry on:
Monosaccharides: https://youtu.be/xNP2jrm2iMo
Digestive enzymes: https://www.youtube.com/watch?v=VLK2wANjQm0
Factors affecting enzymes: https://youtu.be/Rfvh4LIsEEM
Page 72 of 94
Homework Questions
Q1. Scientists measured the mean amino acid concentration in white wines made from grapes
grown organically and white wines made from grapes that were not grown organically.
(a) Which test could the scientists have used to identify that there are amino acids in white wine?
___________________________________________________________________
(1)
(b) All amino acids have the same general structure. The image below shows the structure of the amino acid isoleucine.
Draw a box around the part of the molecule that would be the same in all amino acids.
(1)
(c) Name the chemical element found in all amino acids that is not found in triglycerides.
___________________________________________________________________
(1)
(Total 3 marks)
Q2. (a) Describe the difference between the structure of a triglyceride molecule and the
structure of a phospholipid molecule.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(1)
Page 73 of 94
(b) Animal fats contain triglycerides with a high proportion of saturated fatty acids. If
people have too much fat in their diet, absorption of the products of fat digestion can increase the risk of obesity. To help people lose weight, fat substitutes can be used to replace triglycerides in food.
Describe how a saturated fatty acid is different from an unsaturated fatty acid.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(1)
The diagram shows the structure of a fat substitute.
(c) This fat substitute cannot be digested in the gut by lipase.
Suggest why.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2) (Total 4 marks)
Page 74 of 94
Q3. (a) Maltose is hydrolysed by the enzyme maltase.
Explain why maltase catalyses only this reaction.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(3) (Total 3 marks)
Q4. The diagram shows one end of a cellulose molecule.
(a) (i) Name the monomers that form a cellulose molecule.
______________________________________________________________
(1)
(ii) Name bond Y.
______________________________________________________________
(1)
(iii) What chemical group is at position Z?
______________________________________________________________
(1)
(b) (i) Complete the table to show two ways in which the structure of cellulose is different from the structure of starch.
Starch Cellulose
(2) (Total 5 marks)
Q5. (a) Sucrose, maltose and lactose are disaccharides.
(i) Sucrase is an enzyme. It hydrolyses sucrose during digestion. Name the products of this reaction.
_________________________ and _________________________ (2)
Page 75 of 94
(ii) Sucrase does not hydrolyse lactose. Use your knowledge of the way in which enzymes work to explain why.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(b) A woman was given a solution of sucrose to drink. Her blood glucose concentration was measured over the next 90 minutes. The results are shown on the graph.
(i) Describe how the woman’s blood glucose concentration changed in the period shown in the graph.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(Total 6 marks)
(Total 21 marks)
Page 76 of 94
DNA Structure
DeoxyriboNucleic Acid is the genetic material of
most organisms. It’s a complex chemical, found in
the nucleus of eukaryotes and in the cytoplasm of
prokaryotes. DNA is a polymer. The monomer is
called a nucleotide, and is made up of;
a sugar molecule called deoxyribose,
a phosphate molecule and
one of four different nitrogenous bases.
The 4 different nitrogenous bases are;
A= Adenine
T= Thymine
C= Cytosine
G= Guanine
The monomers are joined together to form a long
chain, known as a polynucleotide. DNA is made of
two chains which run in opposite directions
causing the molecule to spiral forming a DOUBLE
HELIX. The two chains are joined by
complementary base pairing between the bases on
the two strands.
Complementary base pairing
A pairs with T; C pairs with G
The bases pair up in the formation stated above.
They are held together by hydrogen bonds.
A section of DNA that codes for a protein is called
a gene. The sequence of DNA bases in the gene
codes for the sequence of amino acids in that
specific protein.
In eukaryotic cells, DNA molecules are normally
found in the nucleus wrapped around histone
proteins to form chromosomes. Each
chromosome is one long piece of DNA with many
different genes located at specific positions or loci
along its length.
Page 77 of 94
Genetics and cell division
Each body cell in a human contains 46
chromosomes (diploid number) in 23 pairs
(haploid number), with one chromosome in each
pair from mother and one from father. This pair is
referred to as a homologous pair: both
chromosomes in the pair are the same size and
containing the same genes (these genes can be
different alleles).
In preparation for cell division, the chromosome
will make a copy of itself. A chromosome is often
seen as an X shaped molecule. The X shape is
actually one chromosome attached to an exact
copy of itself (2 identical sister chromatids) after
this replication. They are joined together by an
attachment called a centromere.
The cell cycle describes the series of events that
cells follow before division. Cells go through G1,
where they grow before division. They then
duplicate their DNA (S), before copying the cell
structures they will need (e.g. ribosomes,
mitochondria) after division in G2. These stages
are called interphase. Finally, they enter mitosis,
which includes a stage where the cells divide.
Mitosis
Prophase; The chromosomes become
supercoiled and compact and can now be
seen under a light microscope. They have the
X shape.
Metaphase; the nuclear envelope breaks
down, the chromosomes line up along the
equator of the cell and spindle fibres,
produced by the centrioles, attach to the
chromosomes.
Anaphase; The spindle fibres pull the the
chromatids apart by splitting the centromere,
separating the chromatids to the poles of the
cell.
Telophase; A nuclear envelope forms around
each set of chromatid at the poles.
Cytokinesis the cytoplasm divides forming 2
genetically identical daughter cells.
Page 78 of 94
Meiosis
This cell division is responsible for the production
of sex cells and introduces genetic variation. It
results in the formation of gametes containing half
of the original genetic information (haploid
number) as each daughter cell produced at the
end of meiosis ends up with one chromosome
from each homologous pair.
In meiosis the cell undergoes 2 cellular divisions.
1) Prophase I; The chromosomes condense and
the nuclear envelope breaks down. Homologous
chromosomes pair up and can cross over DNA
(Recombination).
2) Metaphase I; The homologous pairs arrange
themselves randomly along the equator.
3) Anaphase I; Spindle fibres attach to the
centromere and pull one chromosome from each
pair to opposites poles of the cell.
4) Telophase I; Two nuclear envelopes form to
surround the divided genetic information. Each
contains one chromosome from each pair. the
cytoplasm is normally divided between two new
daughter cells.
5) Prophase 2; New nucleus breaks down and
chromosomes coil and condense.
6) Metaphase 2; Chromosomes line up along the
equator of each daughter cell. Spindle fibres attach
to the centromeres.
7) Anaphase 2; The spindle fibres start to drag the
chromatids from each chromosome to opposite
sides of the cell.
8) Telophase 2; The nuclear envelopes start to
reform and the cytoplasm spits to form 4 haploid
cells that are genetically different to the parent
cells.
Comparison
Dead and damaged cells are replaced by mitosis,
as this produces genetically-identical daughter
cells (clones) with the same number of
chromosomes as the parent cell. Mitosis is used in
asexual reproduction and only requires one
parent.
Two parents are needed for sexual reproduction.
Meiosis halves the number of chromosomes (46
23 in humans) to produce gametes (sperm or eggs,
in humans). This mixes the DNA from two parents
and so creates variation. This is important because
when these gametes fuse in fertilisation, this
produces a zygote with the expected diploid
number of chromosomes (46).
This zygote will divide by mitosis to produce an
embryo where every cell is genetically identical
and has 46 chromosomes. Mitosis is also used for
growth.
Page 79 of 94
Self Assessment Questions Q1. Cells divide in a series of stages called the cell cycle.
Stage 2 of the cycle is mitosis.
The diagram below shows a simplified cell cycle for a human body cell.
(a) Draw one line from each stage in the cell cycle to what happens during that stage.
Stage in the cell cycle
What happens during
that stage
Stage 1 Nucleus divides
Stage 2 Cell divides into two
Stage 3 Copies of the DNA are
made
(2)
Page 80 of 94
(b) The mass of DNA in a human body cell at the start of the cell cycle is 6 picograms.
What mass of DNA will be in each of the new cells produced by this cell division?
Tick one box.
3 picograms
6 picograms
9 picograms
12 picograms
(1) (Total 3 marks)
Q2. Muscle cells divide to form new muscle cells.
(a) Which two cell components are copied before the muscle cells start to divide?
Tick two boxes.
Cytoplasm
Mitochondria
Plasmids
Ribosomes
Vacuole
(2)
Page 81 of 94
Mitosis is part of the cell cycle.
The diagram below shows the percentage of time taken by each stage of a cell cycle.
(c) The cell cycle shown in the diagram above takes 21 hours in total.
Cell division takes 5% of the total time.
Calculate how many hours cell division takes.
___________________________________________________________________
___________________________________________________________________
Time taken = _______________ hours
(2)
(d) What percentage of time is spent copying DNA in the cell cycle shown in the diagram above?
___________________________________________________________________
___________________________________________________________________
Percentage = _______________
(2)
Page 82 of 94
(e) A sperm cell from a dog contains 39 chromosomes.
How many chromosomes are there in each dog muscle cell?
Tick one box.
39
78
156
312
(1)
(f) A sperm cell fuses with an egg cell.
What is this process called?
Tick one box.
Fertilisation
Meiosis
Ovulation
Respiration
(1) (Total 8 marks)
Page 83 of 94
Q3. The genetic material in cells is made of DNA.
(a) Which two of the following describe the structure of DNA?
Tick two boxes.
A double helix
A monomer
A polymer
A protein
A single strand
(2)
(b) Complete the sentences.
Choose answers from the box.
clone disorder gene
genome mutation
A small section of DNA which codes for one protein is called a ________________ .
All the genetic material of an organism is called its _________________________ .
(2)
(c) Gametes (sex cells) contain half the amount of DNA compared to body cells.
Give the names of the two types of gametes in humans.
_______________________________ and _______________________________
(1)
(d) What is the process called when the gametes join?
___________________________________________________________________
(1)
Page 84 of 94
(e) The diagram below shows cell division by meiosis to form gametes.
Which two features in the diagram above show that this cell division is meiosis and not mitosis?
Tick two boxes.
The cell divides twice
The chromosomes pull apart into the new cells
The cytoplasm divides into new cells
The DNA is copied
The new cells have half the number of chromosomes
(2) (Total 8 marks)
Q4. This question is about reproduction.
(a) Complete the sentences. Choose answers from the box.
asexual clones eggs gametes
meiosis mitosis sexual variation
Identical offspring are produced by ____________________ reproduction.
These offspring are called ____________________ .
In another form of reproduction male and female ____________________ join at fertilisation.
This leads to ____________________ in the offspring.
The embryo grows by a type of cell division called ____________________ . (5)
Page 85 of 94
(b) The body cells of a kangaroo have 16 chromosomes.
How many chromosomes will an egg cell of a kangaroo have?
Tick one box.
4
8
16
32
(1)
(Total 6 marks)
Q5. Sexual reproduction in humans involves the joining together of an egg cell and a sperm cell.
The sex of an embryo is decided by the chromosomes they inherit from their mother and father.
(a) Where in the cell are the chromosomes?
Tick one box.
Cell membrane
Cytoplasm
Nucleus
Ribosomes
(1)
(b) Draw one line from each type of cell to the number of chromosomes in the cell.
Type of cell Number of
chromosomes
23
Sperm cell 26
46
Embryo cell 52
69
(2) (Total 3 marks)
Page 86 of 94
Q6. In sexual reproduction, an egg fuses with a sperm.
(a) (i) Draw a ring around the correct answer to complete the sentence.
An egg and a sperm fuse together in the process of
cloning.
fertilisation.
mitosis.
(1)
(ii) Egg cells and sperm cells each contain the structures given in the box.
chromosome gene nucleus
List these three structures in size order, starting with the smallest.
1 ____________________________________________________ (smallest)
2 ____________________________________________________________
3 _____________________________________________________ (largest)
(2)
(iii) The egg and the sperm contain genetic material.
Draw a ring around the correct answer to complete the sentence.
The genetic material is made of
carbohydrate.
DNA.
protein.
(1)
(Total 4 marks)
Page 87 of 94
Self Assessment Questions mark schemes Q1. (a)
allow 1 mark for 1 or 2 correct
credit can be given where students have matched the boxes correctly, for example numbering the boxes
2
(b) 6 picograms 1
[3]
Q2. (a) mitochondria
1
ribosomes 1
(c)
1
1.05 (hours)
allow for 2 marks 1 hour 3 minutes or 1:03 (hours)
1
an answer of 1.05 hours scores 2 marks
(d)
allow 5 × 7 1
35 (%) 1
an answer of 53 (%) scores 2 marks
(e) 78 1
(f) fertilisation 1 [8]
Page 88 of 94
Q3. (a) a double helix
1
a polymer 1
(b) gene 1
genome 1
in this order only
(c) sperm and egg(s) / ova / ovum
in either order 1
(d) fertilisation 1
(e) the cell divides twice 1
the new cells have half the number of chromosomes 1
[8]
Q4. (a) asexual
1
clones 1
gametes 1
variation 1
mitosis
in this order 1
(b) 8 1
[6]
Q5. (a) Nucleus
1
Page 89 of 94
(b) Type of cell Number of chromosomes
extra lines from left cancel the mark 2
[3]
Q6. (a) (i) fertilisation
1
(ii) in sequence:
accept 1 next to gene, 2 next to chromosome and 3 next to nucleus in box
1 gene 2 chromosome 3 nucleus
allow 1 mark for smallest or largest in correct position 2
(iii) DNA 1
[4]
DNA, Mitosis and Meiosis Total Score: /32
Identify three key areas for further study and revision:
If you scored less than 20, review the material presented again before completing the homework
questions.
If you scored less than 10, the following videos could help before you carry on:
DNA: https://youtu.be/TQ_iCf8mzMA
Mitosis: https://youtu.be/I0VdEiPWkHs
Meiosis: https://youtu.be/6MpYxrrATFY
Page 90 of 94
Homework Questions
Q1. DNA is the genetic material of human cells.
Figure 1 shows the structure of part of a DNA molecule.
(a) (i) Describe where DNA is found in a human cell.
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(ii) When a cell divides by mitosis the new cells are genetically identical.
What causes the cells to be genetically identical?
______________________________________________________________
______________________________________________________________
(1)
(Total 3 marks)
Page 91 of 94
Q2. The photograph shows some cells in the root of an onion plant.
By UAF Center for Distance Education [CC BY 2.0], via Flickr
(a) Cells X and Y have just been produced by cell division.
(i) Name the type of cell division that produced cells X and Y.
______________________________________________________________
(1)
(ii) What happens to the genetic material before the cell divides?
______________________________________________________________
(1)
(b) A gardener wanted to produce a new variety of onion.
Explain why sexual reproduction could produce a new variety of onion.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(3)
(Total 5 marks)
Page 92 of 94
Q3. The photographs show the flowers of two closely-related species of plant.
Species A Species B
Images: © iStock/Thinkstock
The drawings show chromosomes from one cell in the root of each plant during cell division.
Species A Species B
One chromosome
One
chromosome
(a) The drawings show that each chromosome has two strands of genetic material.
(i) How does a chromosome become two strands?
______________________________________________________________
______________________________________________________________
(1)
(ii) Explain why each chromosome must become two strands before the cell divides.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
Page 93 of 94
(b) For sexual reproduction, the plants produce gametes.
(i) Name the type of cell division that produces gametes. ___________________
(1)
(ii) How many chromosomes would there be in a gamete from each of these two plant species?
Species A Species B
(1)
(iii) It is possible for gametes from Species A to combine with gametes from Species B to produce healthy offspring plants.
How many chromosomes would there be in each cell of one of the offspring plants?
(1)
(c) (i) For successful gamete production to take place, chromosomes that contain the same genes must pair up.
The drawings showing the chromosomes of Species A and of Species B are repeated below.
Species A Species B
The offspring plants cannot reproduce sexually.
Suggest an explanation for this.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(Total 8 marks)
Page 94 of 94
Q4. (a) In humans there are two types of cell division: mitosis and meiosis.
The table below gives statements about cell division.
Tick ( ) one box in each row to show if the statement is true for mitosis only, for meiosis only, or for both mitosis and meiosis.
The first row has been done for you.
Statement Mitosis only
Meiosis only
Both mitosis and meiosis
How cells are replaced
How gametes are made
How a fertilised egg undergoes cell division
How copies of the genetic information are made
How genetically identical cells are produced
(4)
(Total 4 marks)
(Total 20 marks)
