Cell structure - Textbook chapter 1

Key objectives: What are cells? How do we measure cells? What is the difference between Magnification and Resolution? How do you calculating magnification? What are the different types of microscope?

Background The history of microscopy dates back to Hooke (1665) and van Leeuwenhoek (1676) whose observations ultimately lead to development of the cell theory. The cell theory has four basic ideas:

1. Cells are the smallest unit capable of independent life.2. Cells are the basic unit of all living organisms i.e. all living things are made of cells.3. Cells arise from other cells by a process of cell division.4. The cell contains information that acts as the instructions for growth. This information is passed on to

new cells.

There 3 types of microscope used to study cells: light microscope, transmission electron microscope (TEM) and Scanning electron microscope (SEM). Modern light microscopes can achieve an effective magnification of up to 1500x and have a maximum resolving power of 200nm. Electron microscopes can achieve magnifications of up to 500000x and resolutions of 1nm.

The “power” of a microscope depends both on its magnification and resolution, the higher the resolution of a microscope the greater the detail you can see. The maximum resolution achievable with a microscope is equal to half the energy source used to create the image.

Cell Theory

1) What is a cell? [2]

Units of measurement

1) Complete the diagram below to show: names of the units of measurement, unit symbols, mathematical operations for converting between units.

2) Complete the table below to show the corresponding value nanometres, micrometres and millimetres for the measurements given in each row. The first row has been completed for you. Ensure that your answers use the correct unit symbols.

Nanometre Micrometre Millimetre5 0.005 0.0000051

11

37

0.5

3) When studying cells structure using a microscope the smallest unit of measurement commonly used to describe findings is the nanometre. Explain why.

Magnification and Resolution

1) Define the following terms:

Magnification:

Resolution:

2) Visible light has a wavelength of 400-700 nm. Calculate the best resolution achievable with a light microscope? Show your working out:

3) If the electron gun produces an electron beam with 2 nm wavelength, what is the best resolution achievable?

Calculating total Magnification of a compound light microscope

Eyepiece Magnification

Objective Magnification

Overall Magnification

X10 X4X10 X10X10 X40X10 X100

Calculating Cell Magnification from images

The diagram below shows the general structure of an animal cell as seen under an electron microscope.

_________5m

1) Calculate the magnification factor of the diagram

2) Calculate the length of structure G

3) Calculate the diameter of the nucleolus (structure B)

4) Calculate the diameter of the nucleus

5) Calculate the diameter of the cell at its widest point

The diagram below shows the general structure of a plant cell when viewed under and electron microscope.

___________ 40m

1) Calculate the magnification factor of the diagram

2) Calculate the thickness of the cellulose cell wall.

3) Calculate the length of the cell.

4) Calculate the length of structure C.

5) Calculate the length of the vacuole.

Types of microscope

1) Why is the maximum effective magnification of a light microscope said to be 1500x when it is possible to

produce higher magnifications with improved lenses?

2) Use a named example to explain the need for staining when using a light microscope.

3) State a possible disadvantage of staining a specimen for observation when using a light microscope

4) State 2 advantages of using electron microscopes to study cells over a light microscope.

Feature Light Microscope Transmission electron microscope (TEM)

Scanning electron microscope (SEM)

Source of image

How is the beam focused

Maximum effectivemagnification

Maximum resolution

Can a live specimen be used?

Section or external view of the specimen

Cost

Can the image be viewed directly

Is staining of the specimen required?

5) State 2 disadvantages of using electron microscopes to study cells.

6) Describe with reference to the role of staining how the transmission electron microscope differs from a scanning electron microscope?

7) Explain why a vacuum necessary in an electron microscope?Which microscope?

1) State which type of microscope has been used to create the image below, give a reason for your answer.

2) The two images below of human chromosomes were produced using a light microscope and SEM. State which is which; give a reason for your answer.

3) The image below was produced by staining a section of gut epithelium. The image is not shown in false colour. Which type of microscope was used to produce the image? Explain your answer.

4) The three images below are of human cheek cells. One image has been produced using a light microscope, one using a SEM and one using a TEM. For each image identify the microscope used and justify your choice

. Cell structure

Key objectives: What is the role of the cytoskeleton? Which organelles may be present in a cell and why? How can we recognise organelles in micrographs / diagrams? What are the differences between plant and animal cells? How do organelles in a cell work together? What are the differences between prokaryotic and eukaryotic cells?

Background All living things are cells or are made of cells. From your GCSE course you should be familiar with the basic structure of plant and animal cells. Since the development of the electron microscope a large number of structures have been identified within cells; those structures with a specialised function are termed organelles. Organelles within a cell work together to enable the cell to carry out its function. The fact that each organelle performs a different function within the cell is referred to as division of labour. The type, number and position of organelles will vary between cells dependent upon the cells role, environment and “life stage”.

CytoskeletonThere is a network of fine filaments or fibres that run through the cytoplasm of the cell. This is known as the cytoskeleton. There are three types of fibre:1) microfilaments2) intermediate filaments3) microtubules

Complete the table to compare the structure and functions of the components of the cytoskeleton:

Cytoskeleton Component FunctionMicrotubule

Size:

Composition:

1) Describe two ways in which the cytoskeleton can aid the movement of an entire cell.

2) Name a type of human cell (not a sperm cell) that is able to move and explain why this is important to the cells function

3) Why might chloroplasts need to be moved around a plant cell

4) Many of the cells that line the human respiratory system are ciliated. Explain why

Which organelles may be present in a cell and what do they do?

Organelle Diagram Structure Function Animal cell?

Plant cell?

Visible under a light microscope

Nucleus

Nucleolus

The nucleus is the largest organelle (10-20m diameter)Roughly spherical.Surrounded by a double membrane called the nuclear envelopeThe nuclear envelope contains openings called nuclear pores.Outer membrane joins up to the endoplasmic reticulumThe nucleoplasm contains chromatin (DNA + histones) which can be seen as dark blobs or fibre.)

Nucleolus is not surrounded by A membraneDense spherical structure inside the nucleus

Contains nearly all of a cells genetic material; instructions for making proteinsControls protein synthesis (makes mRNA)

Nucleolus makes RNA and Ribsosmes.These pass into the cytoplasm through the nuclear pores

Yes Yes Yes

Ribosome

Rough endoplasmic reticulum

Smooth endoplasmic reticulum

Golgi apparatus

Mitochondrion

(mitochondria)

Chloroplast

Lysosome

Centrioles

Plasma membrane

Cellulose cell wall

Vacuole

Vesicle

1) Describe three structures / organelles present in generalised plant cells but absent from animal cells.

A)B)C)

2) Name the structures in the diagram below

3) Sperm cells contain large numbers of mitochondria. Explain why?

4) What evidence can be seen in the diagram that suggests that the cell is:

o metabolically active and involved in secretion of enzymes [3]

o involved in production or modification of lipids? [1]

The diagram is a line drawing of a cell as seen with an electron microscope.

Complete the table by matching the label to the function and then naming the appropriate part. The first one has been completed for you.

Function of Structure Label Name of Part of the Cell

Controls the activity of the cell. A Nucleus

HGF

E

B

D

C

A

20 μm

Protein/polypeptides are made here.

Aerobic respiration takes place here.

Produces secretary vesicles.

Controls the entry of substances into the cell.

Contains hydrolytic enzymes.

Makes lipids, including steroids.

By reference to the diagram: Is the cell that of an animal or a plant? Give a reason for your answer.

Identifying organelles from micrographs

4) Name the large round organelle in the micrograph below 5) Is it found in animal or plant cells6) Name the structures A,B and C

7) Name the large organelle shown in the micrograph below8) Is it found in animal or plant cells?9) Suggest what structure D could be

10) Name the organelle shown in the micrograph below11) State the role of the organelle

12) Name the structures visible in the transmission electron micrographs below

13) Name the structure shown in the micrograph

14) Name the structure shown in the micrograph below

15) Name the structure shown in the micrograph below

Test yourself on a full cell micrograph

Is this an animal or plant cell? Can you name the structure 1-4

Use the word bank at the bottom of the page to label this plant cell

Parts of the cell working together

Complete the paragraph below to describe how organelles in a cell work together to produce and secrete proteins such as hormones

The nucleus carries all the necessary instructions for the cell to function. The code for protein synthesis is

carried in the ____________ which are made of ____________ or histones. The instructions are

____________ or copied into mRNA (messenger ribonucleic acid). The mRNA then leaves the nucleus via the

_________________ and travels to the ______________ where the message is read and translated into

protein. The newly manufactured proteins are transported to forming face of Golgi body/apparatus in

transport __________. Within the Golgi apparatus the proteins are processed. Vesicles are budded off from

the maturing face of Golgi and are transferred to the ___________________ for secretion. Glandular cells

(e.g. pancreas) contain large amounts of __________________ (this is encrusted with ribosomes and is

where protein synthesis takes place) and Golgi body. These cells also contain many mitochondria since

protein synthesis requires a lot of __________.

Nuclear envelope, Nucleolus, Chloroplast, Mitochondria, cytoplasmEndoplasmic reticulum, starch grain, Cell wall, plasma membrane, vacuole

(ii) State the function of structures B. [1]

(iii) Describe the role of structure C in secretion. [3]

Prokaryotes and Eukaryotes

1) The diagram below shows Staphylococcus, which is a prokaryotic cell. Label parts A to D

2) The following table compares some features of a prokaryotic and eukaryotic animal cell. Complete the table by using ‘present’, ‘absent’ or a short descriptive phrase. The first has been completed for you.

Cellular Feature Prokaryotic Cell Eukaryotic Animal Cell

Cell wall Present Absent

Cell surface membrane

Nucleus

Membrane bound organelles

DNA

Plasmids in the cytoplasm

Read p14-15 OCR Biology text book

1) Fill in the gaps

It was once common practice to classify all living organisms as either animals or plants. With improved

knowledge of living things it has become apparent that there are ______ fundamentally different types of

cell. The most obvious difference between the two types is that one possesses a nucleus and the other does

not.

The cells of animals, ___________ and fungi contain many organelles some of which are bound by a

membrane. These are referred to as ______________ cells. The cells of bacteria are very different, they lack

membrane bound organelles such as a _____________. This type of cell is referred to as a _______________

cell (meaning before nucleus). Prokaryotic cells are about 1000 to 10000 times smaller than eukaryotic cells

and are much simpler in structure. Biologists believe eukaryotes evolved from ________________.

2) Eukaryotic cells contain membrane bound organelles, give 5 examples:

3) Prokaryotic cells have one membrane, where is it?

4) Use table 1 to compare plant (eukaryote), animal (eukaryote) and prokaryotic cells. For each cell type indicate whether the feature is present or absent using a tick or cross.

Feature Plant cells Animal cells Prokaryote cellsChloroplasts

Large permanent vacuole

Cellulose cell wall

Peptidoglycan (murein) cell wall

Linear chromosome

Circular chromosome

Plasmids

Endoplastic Reticulum

Golgi body

DNA free in the cytoplasm

ATP is produced in the mitochondriaATP is produced at infolded

regions of the cell membrane called mesosomesUndulipodia contain 9 + 2 circular arrangement of microtubulesFlagella made form spiral protein called FlagellinRibosomes

Cell membrane

5) Give 2 ways in which prokaryotes are useful to humans

6) Mitochondria and chloroplasts contain small loops of DNA similar to the plasmids found in prokaryotic cells. These organelles also contain ribosomes that are the same size as prokaryotic ribosomes. Can you suggest an explanation for these features?

7) Give one way in which a eukaryotic plant cell is similar to a prokaryote.

8) Give two ways in which a eukaryotic plant cell is different from a prokaryote.

9) Label the highlighted features on the diagram of the bacterium E.coli shown in the diagram below.