2.Patterns in Natureweb2.cheltenham-h.schools.nsw.edu.au/moodle/pluginfile.php/988/mod...Preliminary Biology Topic 2 PATTERNS in NATURE Cell Division Vital Body Systems Cell structure

copyright © 2005-2006 keep it simple sciencePreliminary Biology Topic 2

Cheltenham Girls High School SL#609279

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What is this topic about?To keep it as simple as possible, (K.I.S.S.) this topic involves the study of:1. LIVING CELLS & THEIR STRUCTURE

2. CHEMICALS MOVE IN & OUT THROUGH MEMBRANES3. NUTRITION IN PLANTS & ANIMALS

4. GAS EXCHANGE & INTERNAL TRANSPORT5. CELL DIVISION FOR GROWTH & REPAIR

but first, an introduction...CellsAll living things are composed of microscopic “lumps”called cells.

Some organisms are composed of just one single cell.

All familiar organisms are made of many cells;for example, your body is composed of approximately 300billion cells... you are “multicellular”.

Each cell is a tiny sac of “protoplasm”... water with acomplex mixture of chemicals dissolved in it, plus manystructures called “organelles” (little organs).

Plants and animals have cells with a few importantdifferences. Organisms such as fungi are different again,while bacteria have a totally different cell structure.

Organization of a Multicellular OrganismA building is not just a pile of bricks, and an army is not justa rabble of soldiers. Each has a structure, and levels oforganization so everything works together.

Similarly, your body is not just a big heap of cells. It haslevels of organization...a CELL is the basic unit of any living thing.

a number of similar cells working together is a...

TISSUE examples: muscle tissue, bone tissue.

various tissues are combined to make an...

ORGAN examples: heart, kidney, liver.

a number of organs work together for a specificpurpose. This forms a...

SYSTEM example: digestive system.

Finally, all the body systems working together form...

YOU

In this topic you will study the basics of the structure andfunctioning of living things:

GENERALIZED DIAGRAM OF A LIVING CELL

“Membrane” on theoutside contains thecell , and controlswhat goes in or out

Organelles

Cytoplasmjelly-likeliquid fillsthe cell

Preliminary Biology Topic 2

PATTERNS in NATURE

CellDivision

Vital Body

Systems

Cell structure &

Chemistry



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CONCEPT DIAGRAM (“Mind Map”) OF TOPICSome students find that memorizing the OUTLINE of a topic helps them learn and remember the concepts andimportant facts. As you proceed through the topic, come back to this page regularly to see how each bit fits thewhole. At the end of the notes you will find a blank version of this “Mind Map” to practise on.

Cell Theory

Cell Organelles

Structure of

Membranes

Diffusion &

Osmosis

Surface Areato

VolumeRatio

Digestionin

Animals

Photosynthesis&

Respiration

Structure &Function of

Leaf

Gas Exchangein

Animals

Circulation in Animals

Gas Exchange &Transport in

Plants

Processof

Mitosis

Cell Chemicals

Types ofMicroscope

Major OrganellesStructure &

Function

History of ourknowledge of

cells

Differencesbetween Plant &

Animal cells

Comparisons:Structure

compared to diet

IdentifyingTests

Stomates& Lenticels

OpenSystems

Outcomes

Xylem & Phloem

Stages

The need &Purposes of Cell

Division

Mammal

Frog Insect

Fish

PPAATTTTEERRNNSSiinn

NNAATTUURREE

Living Cells&

Their Structure

ChemicalsMove In & Out

ThroughMembranes

Nutritionin

Plants &Animals

Gas Exchange&

Internal Transport

Cell Divisionfor

Growth & Repair

Closed Systems



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1. LIVING CELLS & THEIR STRUCTURE

The Cell TheoryThe “Cell Theory” is one of the fundamental concepts inBiology. It simply states:

• All living organisms are composed of cells

• All cells are produced from pre-existing cells.

The evidence supporting the Cell Theory has come almostentirely from the use of microscopes to examine livingthings.

Our knowledge of cell structure and function hasdeveloped as the technology of microscopes advanced overthe last 300 years or so.

Initially, only light microscopes were available, but from the1930’s electron microscopes began to reveal more detail ofcell structure and function.

Comparison: Light & Electron Microscopes

Light Electron‘scope ‘scope

How the beam of light beam of electronsimage focused by focused by magneticis formed glass lenses fields

Magnification generally about up to 1,000,000 X500 X. (500 times moreMaximum powerful)about 2,000 X

Resolution about 0.2 μm about 0.0002 μm(ability to see (1,000 times betterfine details) detail)

micrometres (μm) 1 μm = 0.000001(10-6)metre.

1 micrometre is 1/1000 of a millimetre

How Big Are Cells Anyway?

Typical Plant Cell50-100 μm

Typical Animal Cell5 - 20 μm

Bacterial Cells1 - 5 μm

History of Our Knowledge of Cells

Robert Hooke, 1665Hooke is credited with being the first person to see cellsand name them. Using a primitive microscope, he lookedat a piece of cork (dead tree bark) and saw tiny “boxes” likethe rooms and compartments of a gaol or monastery.(hence “cells”)

Anton van Leeuwenhoek, 1676van Leeuwenhoek used a very simple microscope, but itwas equipped with an excellent lens, through which he sawliving micro-organisms swimming around in a drop ofwater.

Over the next 150 years, microscopes improved, and it wassuspected that cells were present in all living things.

Robert Brown, 1827Brown was the first to discover structures inside cells. Hediscovered and described the nucleus inside plant cells.

By about 1840, the “Cell Theory” was becoming acceptedby most biologists, because cells were observed in everyorganism studied. Louise Pasteur’s discoveries showedthat all infectious diseases were caused by “germs”, whichwere microscopic, cellular organisms.

Rudolf Virchow, 1859 and Walther Flemming, 1879Between them, these two German scientists clarified theprocess of cell division, by which cells produce more cells.This established the principle that all cells come from pre-existing cells.

In the 20th century, the electron microscope opened up ourknowledge of the fine detail of cell structures and theirfunctions.

SCALE: 100 μm



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Cell Organelles Visible with a Light MicroscopeYou will have done practical work in class to use a light microscope to view cells in living things.

The Major Differences Between Plant & Animal Cells• Plant cells have a tough CELL WALL on the outside of their cell membrane.• Many plant cells contain CHLOROPLASTS. These are green in colour because they contain the pigment chlorophyll.

Chloroplasts are the sites of PHOTOSYNTHESIS, where plants make food.

Note: not all plant cells have chloroplasts... for example, cells in the underground roots cannot photosynthesize, so do notcontain any chloroplasts.

• Many plant cells contain a large VACUOLE. Animal cells rarely have vacuoles, and if present they are small.

What the Electron Microscope RevealsThe superior magnifying power and resolution of the electron microscope has given us a much more detailed knowledge ofthe cell and its organelles. The diagram below is a sketch of a plant cell similar to the one above, but with the added detailsthat the electron microscope has revealed. The extra organelles shown are generally NOT visible with a light microscope.

Generalized GeneralizedANIMAL CELL PLANT CELL

NUCLEUS

CYTOPLASM

CELLMEMBRANE

LargeVACUOLE

SmallVacuoles(only seen insingle celledanimals)

CELL WALL(on outside of membrane)

CHLOROPLASTS(green colour)

Cell WallCell MembraneVacuole

Chloroplast internalstructure

Stacks of flat membranes(grana) contain thechlorophyll

MitochondrionSite of cellularrespiration

Lysosomes

Golgi apparatus

NucleusExtra detail revealed

Endoplasmic Reticulum

A network of membranestructures connected tonucleus & extendingthroughout the cytoplasm

Often has the tinyRibosomes attached



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The Organelles... Structure & Function

The Nucleus is the control centre of the cell.Inside the nucleus are the chromosomes containing DNA,the genetic material. There is often a nucleolus present.This is the site for production of RNA, a “messenger”chemical which leaves the nucleus carrying instructions toother organelles. The nuclear membrane has holes or“pores” to allow RNA to exit.

The Cell Membrane is not only the boundary of the cell,but also controls what goes in or out of the cell. This isstudied in more detail in the next section.

The Mitochondria (singular: mitochondrion) are the sitesof cellular respiration.

Glucose + Oxygen Carbon + Water + ATP(sugar) Dioxide

The ATP produced by respiration carries chemical energyall over the cell to power all the processes of life. Themitochondria are therefore, the “power stations” of thecell, converting the energy of food into the readily usableform of ATP.

Inside a mitochondrion is a folded membrane with manyprojections (“cristae”). This structure provides a greatersurface area, where the enzymes (control chemicals) forrespiration are attached in correct sequence for the steps ofthe process. Hence, the structure helps the organelledo its job more efficiently.

Endoplasmic Reticulum (E.R.) is a network ofmembranes which form channels and compartmentsthroughout the cytoplasm of the cell. Its function can becompared to the internal walls of an office building whichdivide the space into “rooms” where different operationscan be kept separate so that each is efficient and does notinterfere with other operations.

The E.R. structure provides channels for chemicals and“messengers” to travel accurately to the correct locations,and for chemical production to occur in isolation fromother operations. Once again, structure matches function.

Often found attached to the E.R. are the tiny Ribosomes.These are the sites of production of proteins, the mainstructural and functional chemicals of living cells. RNA“messengers” from the nucleus control each ribosome tomanufacture the specific proteins that the cell needs.

The Chloroplasts are found only in photosynthetic plantcells. The electron microscope has revealed that thechloroplast is not just a bag of chlorophyll, but has anorganized internal structure which makes its functioningmore efficient.

The “grana” are stacked membrane sacs containingchlorophyll, which absorbs the light energy forphotosynthesis. This light-capturing step is kept separatefrom the “stroma” zone, where the chemical reactions tomake food are finalized.

Nuclear membrane

with pores, for RNA exit

Nucleolus

RNA manufacture

Nuclear material“chromatin”Chromosomesunwound andspread out

NUCLEUS

MITOCHONDRION

Outer membrane

Inner membranefolded into“cristae”

Respirationenzymes attached

CHLOROPLAST

Doublemembraneenvelope

Membranestacks (“grana”)containing chlorophyll

“Stroma” zone

ENDOPLASMICRETICULUM

RIBOSOMESattached to membranes

Membranes

Membranesenclosechannels and“rooms”



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The Golgi Apparatus is a semi-circular arrangement ofmembranes which are concerned with packaging chemicalsinto small membrane sacs (“vesicles”) for either storage orsecretion from the cell.

One type of “vesicle” produced by a Golgi Body is theLysosome. These membrane sacs contain digestiveenzymes which can destroy any foreign proteins whichenter the cell. Lysosome enzymes also rapidly digest thecontents of a cell which has died, so that your body canclean up the remains and replace the dead cell.

A Summary... MembranesExcept for the tiny ribosomes, all the cell organelles arebuilt from, and surrounded by, membranes. Themembranes provide:-

• the infrastructure of the cell• channels for chemicals and “messengers” to move along• packaging for chemicals which need to be kept separate• points of attachment for control chemicals (“enzymes”)• control over what moves in or out of each organelle, andin or out of the entire cell.

The structure of the “membrane-bound” organelles helpthe cell’s various functions to be carried out with greatefficiency.

Having these membrane-based organelles is the definingcharacteristic of the “Eucaryotic” group of organisms,which includes all plants and animals.

Bacteria cells do NOT have all the membrane-typeorganelles, and can only operate efficiently by being verysmall.

GOLGI BODYCurvedmembranesacs

Vesicles pinch-offfor storage orsecretion

Lysosomesform thisway

Worksheet 1Fill in the blank spaces and diagram labels.Check your answers in the “Answer Section” at the back.

The “Cell Theory” states that (a)..........................................are composed of cells, and that all cells are produced from(b)................................................................

Our knowledge of cells is due mainly to the technology of(c)........................................................

The (d)....................................... of a microscope refers to itsability to distinguish fine details. The (e).................................‘scope is far superior in both (d) and (f)...................................

The man credited with being the first to see cells was(g).........................................................................

Label the parts of this plant cell seen with a simple lightmicroscope.

Which TWO parts of this plant cell would definitely notever be seen in an animal cell? (n)..........................................&(o)....................................................................

List 5 additional organelles normally only visible with anelectron microscope. (p)........................................................q).............................................. r)..............................................s)............................................... (t)..............................................

Complete these lists to describe functions of organelles.Organelle FunctionCell membrane (u)

(v) Partitions cell into channels & compartments

Golgi apparatus (w)

(x) Cellular respiration.

(y) Photosynthesis

Cell wall (z)

(k)............................................................

(l) inside (k).........................................................

(m)....................................................................(jj).........................................

(i)...................................

(h).....................................

WHEN COMPLETED, WORKSHEETS BECOME SECTION SUMMARIES

Cell Chemistry... What Cells Are Made From

CARBOHYDRATESinclude the sugars and starch.

monosaccharides (mono = one)are simple sugars such as glucose C6H12O6

disaccharides (di = two)are sugars made from TWO monosaccharidesjoined together, such as “table sugar”(sucrose).

polysaccharides (poly = many)are huge molecules made from thousands ofsugar molecules joined in chains or networks.Examples are:Starch...made by plants, to store excess sugar.Glycogen... made by animals, to store sugar.Cellulose... made by plants as a structuralchemical. The CELL WALL of a plant cell ismade from cellulose.

Uses of Carbohydrates in Living Things:Sugars are energy chemicals. Glucose is made byplants in photosynthesis, and is the “fuel” forcellular respiration to make ATP to power allcells.Starch & Glycogen are polymer molecules usedto store sugars as a food reserve. Starch is themain nutrient chemical in the plant foods we eat.Cellulose & Lignin are polymers of sugar used byplants structurally. Cellulose makes the toughcell wall of all plant cells. Lignin is a strongmaterial used to reinforce the walls of “veins” inplants.



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2. CHEMICALS MOVE IN & OUT THROUGH MEMBRANES

INORGANIC CHEMICALSThese include small simple molecules like water(H2O) and carbon dioxide (CO2), as well as mineralions such as calcium, nitrate, phosphate, chlorideand so on.

Although these are often considered of lesserimportance, you should remember that all livingthings are about 75% water.

ORGANIC CHEMICALS“Organic” chemicals are based on the elementcarbon, which can form chains, rings andnetworks and so build into the extremely complexmolecules needed to make a living cell. Many are“polymers” made by joining together manysmaller molecules.

There are four main categories to know about...

Monosaccharidesugarmolecules

Disaccharidesugar

Polysaccharide.Small part of aStarch molecule

PROTEINSare the main structural chemicals of organelles,cells, bone, skin & hair. Life is built fromprotein.

Proteins are polymers, made from amino acidmolecules joined in chains.

Amino acidmolecules

Part of a protein molecule...a chain of amino acids

LIPIDSare the fats and oils.

All cell membranes are built fromlipid & protein.

Lipids are used as a way to storeexcess energy food. Carbohydratescan be converted to fat for storage.

NUCLEIC ACIDS (DNA & RNA)are the most complex of all. DNA is the geneticinformation of every cell. RNA is the “messenger” sentout from the nucleus to control all cell activities.

DNA is a huge polymer of sugars, phosphate and“bases” coiled in a double helix shape.



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Identifying Chemicals in TissuesYou will have done laboratory work to learn some simplechemical tests which identify important substances. Thesetests all rely on a “reagent” which changes colour.

To keep it simple (K.I.S.S.) these are the ones to know:-

Cell Test Colour in PositiveChemical Reagent Pure water Result

Glucose Benedict’s pale blue yellow or solution orange

Starch Iodine yellow dark blue orsolution brown black

Protein Biuret blue purple

You will have used one or more of these tests on livingtissue and possibly examined the cells with a microscope.For Example: if tissue scraped from a fresh potato ismounted on a slide with a simple “contrast stain” (likemethylene blue) the cells look like this:

If a drop of iodine solution is added, the same cells changeas shown:

Once you have an understanding of the main chemicalsthat cells are made from, you need to realize that all ofthese substances, or their raw materials or waste products,are constantly moving in or out of a living cell.

To do this

CHEMICALS MUST CROSS THE CELL MEMBRANE.

The Structure of the Cell MembraneThe electron microscope and other modern analysismethods have revealed the structure of the membraneswhich surround a cell and form most of the cell organelles.

The membrane is extremely thin; just two molecules thick.The basic chemical unit is a “phospholipid” molecule; alipid (fat) with phosphate groups attached. Each moleculehas two distinct ends; one which is attracted to watermolecules (“hydrophilic”) and the other is repelled by water(“hydrophobic”).“Hydro”=water. “philic”=to like. “phobic”=hate / fear.

Two layers of phospholipids form each membrane. Themolecules cling to each other, and line up with theirhydrophilic ends on the outside attracted to the watersolution of the cytoplasm inside the cell, and to the wateryenvironment outside the cell.

Their hydrophobic ends are repelled from the waterysurroundings, and cling together inside the membrane itself.

It is like a thin layer of oil floating on water... it is fluid andflexible, but clings together forming an unbroken “skin” onthe surface.

Other molecules are embedded in the phospholipid bilayer.Various proteins, many with carbohydrates attached, floataround among the membrane molecules

These other molecules serve purposes including:

• “receptors” for messenger chemicals from other cells• identification markers, so your body knows its own cells

from any foreign invaders• helping chemicals get through the membrane.

POTATO CELLS

POTATO CELLSWITH IODINE

Organellesvisible

Cell wall

Organelles turn black

This indicates the presenceof starch inside theorganelles(these are storage vacuoles)

Outside of cell

Inside of cell

Membrane proteins

One phospholipid

hydro--philic

-phobic

MEMBRANE STRUCTURE

Outside of cell

Inside of cell Double layer ofphospholipid molecules



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How Chemicals Get Through the MembraneThe cell membrane as the boundary of a cell is a bit likegrowing a plant hedge as the boundary of a field. It stopsthe cows and horses getting out, but a small mouse, or alizard can easily crawl through it.

Similarly, a membrane is “semi-permeable”; it preventsmost (especially large) molecules getting through, butallows others to pass through easily. Small molecules likewater (H2O), oxygen (O2) and carbon dioxide (CO2) passfreely through the membrane like a lizard through a hedge.

To understand why these molecules move at all, you need tolearn about the processes of DIFFUSION & OSMOSIS.

Diffusionoccurs in every liquid or gas because the atoms andmolecules are constantly moving... the particles “jiggle”about at random in what is called “Brownian motion”.(Named for its discoverer Robert Brown, the same manwho discovered the cell nucleus. Revise page 2)

Imagine a water solution containing a dissolved chemical,but it is NOT evenly distributed... it is more concentratedin one place than elsewhere. As the molecules jiggle aboutat random, they will automatically spread out to make theconcentration (eventually) even. This process is calledDIFFUSION.

In a living cell, there is often a “concentration gradient”from the outside to the inside of the cell. For example,because a cell keeps consuming oxygen for cellularrespiration, the inside of the cell usually has a lowconcentration of O2 dissolved in the water of thecytoplasm. On the outside, there can be plenty of O2.

DIFFUSION DRIVES MOLECULES THROUGH THEMEMBRANES.

Osmosisis a special case of diffusion, which occurs when theconcentration gradient involves dissolved molecules orions which CANNOT get through the membrane.

For example, consider a cell which is surrounded by a solutioncontaining a lot of dissolved sugar. The sugar cannot diffusethrough the membrane to equalize the concentrations. In sucha situation, water (which can go through the membrane) willdiffuse toward the high sugar concentration, as if attemptingto equalize by diluting the sugar.

In this case, the cell will lose water and might shrink andshrivel up.

The opposite situation could happen too. A cell’scytoplasm contains many dissolved chemicals. If theoutside environment around the cell is more watery (lessconcentrated in dissolved substances) then osmosis willcause water to diffuse into the cell.

Comparison of Diffusion and Osmosis

Diffusion is the movement of dissolved solutes, from anarea of higher concentration toward a lower concentrationarea. The movement follows the “concentration gradient”.

Osmosis is the diffusion of WATER through a semi-permeable membrane, against the concentration gradientof solutes. It occurs whenever the solutes cannot penetratethe membrane, but water can.

later

DIFFUSION of SMALLMOLECULES into a CELL

Lowerconcentration

Equal concentrationthroughout

Higherconcentrationoutside cell

Lowerconcentrationinside

Sugar cannotget in throughmembrane

OSMOSIS

Highconcentrationof sugaroutside cell

Water diffuses OUTof cell

Dissolved chemicals cannotdiffuse out...

...so waterdiffusesinto thecell.

This is how plantsabsorb water intotheir roots, evenwhen the soilseems almost dry.

Highconcentration



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Other Ways Substances Get Through Membranes

Diffusion and Osmosis are vitally important for manychemicals (especially water) to get in and out of cells. Theseprocesses happen automatically without any effort by thecell... we say these are “passive transport” processes.

What about all the other important chemicals which cannotget through the membrane? How do they get in or out?

Be aware that cells have a variety of ways that they candeliberately move substances across the membrane apartfrom simple diffusion and osmosis. One such processinvolves the membrane proteins... revise membranestructure on page 8.

These “other” ways to transport materials acrossmembranes all require the cell to use energy (ATP fromcellular respiration) to transport substances forcibly. We saythese are “active transport” processes. You do not need toknow the details at this stage.

The Importance of theSurface Area to Volume Ratio

Why are cells so small? The answer requires a mathematical study...

Consider a series of cubes of increasing size:

Notice that as the cubes get bigger:• Surface Area increases, and...• Volume increases, but...• SA / Vol Ratio DECREASES,

because the volume grows faster than the surface area.

This pattern is the same for any shape... as any shapedobject gets bigger, the ratio between its Surface Area andits Volume gets smaller.

What’s this got to do with cells?The amount of food, oxygen or other substances a cellneeds depends on its volume... the bigger the cell, the moreit needs according to its volume.

But, all cells have to get whatever they need in throughtheir cell membrane, and the size of the membrane is allabout surface area.

As any cell gets bigger, it becomes more and more difficultfor it to get enough food, water and oxygen because itsSA/Vol. ratio keeps shrinking. Similarly, getting rid ofwaste products also becomes more difficult.

Large cells are impossible... all single-celled organisms aremicroscopic, and all larger organisms are multi-cellular.The only way to be big is to have lots of small cells.

In a later section, the process by which cells divide to makemore cells will be covered.1 unit

sides2 unitsides

3 unitsides

4 unitsides

Surface Area:Six squares, each 1x1

SA = 6x1x1= 6 sq.units

Volume = lxbxh= 1x1x1= 1 cu.unit

Ratio of SA to Volume

SA/V = 6 / 1

SA = 6vol





SA/V = 24 / 8

SA = 3vol





SA/V = 54 / 27

SA = 2vol





SA/V = 96 / 64

SA = 1.5vol

Cells must feed their volume,through their Surface area



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Worksheet 2

Simple, small molecules and ions (e.g. water, nitrate) areknown as (a)..................................................... compounds,as opposed to “organic” compounds which are basedon the element (b)..................................., and include:-

• (c)..............................which are polymers of amino acids

• Lipids, which are found structurally in the cell (d)........................................and are also used as

(e)............................................................................

• (f)....................................................................... whichinclude the sugars & starches.One of this group, glucose, has chemical formula(g)............................................. and is the “food” madeduring (h)............................................................ and thefuel for (i)......................................................... (organelle)tomake ATP.• Nucleic acids, of which (j)...................................is thebest known.

If Benedict’s solution turns from blue to yellow, thisproves that (k)..................................................... is present.

Protein can be identified by (l)....................................reagent, and if starch is present iodine solution will turnfrom (m) ................................ to (n)......................................

The cell membrane is made from a double layer of(o).............................................................. molecules, withvarious proteins embedded.The membrane is “semi- (p)........................................”

Diffusion is a process where molecules move from aplace of (q).................................... concentration,towards a (r)........................................... concentration.

Osmosis is the diffusion of (s).......................................molecules only, against the solute concentration(t)..............................................., when the solute isunable to get through a membrane.

Diffusion & Osmosis are both examples of(u)................................................................ transport,because the cell does not need to use(v)............................................... to make things move.

As any shape gets larger, its (w).........................................ratio gets smaller. This is why all cells are small. A largecell needs chemicals in proportion to itsx).............................................. However, it must getsubstances in through its y)...............................................,the size of which is measured by its z).................................................................

The only way for living things to be large, is to haveaa).................................... cells, NOT by havingab)................................... cells.




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Autotrophs & Heterotrophs“Auto-”= self.“Hetero-”= other... not self.“troph-”= feeding

An autotroph is an organism that makes its own food. Allplants are autotrophic, making their own food byPHOTOSYNTHESIS.(There are also certain single-celled bacteria-relatedmicrobes that make their own food, but to keep it simple(K.I.S.S.) only plants will be dealt with here.)

Any organism that cannot make its own food must be aheterotroph. All animals are heterotrophic, and so are thefungi and most bacteria. A heterotrophic animal eats plantsor other animals which have eaten plants, and so onaccording to the food chain involved.

Photosynthesis in PlantsAll plants make their own food from the simple, low-energyraw materials water (H2O) and carbon dioxide (CO2) usingthe energy of sunlight, to make the high-energy sugarglucose (C6H12O6), with oxygen gas (O2) as a by-product.

This brief summary equation is very deceptive.Photosynthesis actually occurs as a complex series ofchemical steps inside the chloroplast.

Photosynthesis & Cellular RespirationYou will have noticed that these two vital processes, whenwritten as summary equations, are exact opposites.

What is really happening is ENERGY FLOW through thefood chains of an ecosystem. Photosynthesis captures theenergy of light and stores it in a high energy food compoundlike glucose. Cellular respiration releases that stored energy inthe form of ATP which can power all cellular and lifeactivities... growing, moving, keeping warm etc.

As you learned in Topic 1, in all ecosystems there is aconstant input and flow of energy via the food chains,while the chemicals such as H2O, O2, and CO2 simply getre-cycled over and over.

The Most Important Process on EarthPhotosynthesis makes all the food on Earth, for all thefood chains. It also makes all the oxygen in the atmospherefor us animals to breathe.

For these two good reasons, Photosynthesis has got to beconsidered the most important biological process on the planet.

3. NUTRITION IN PLANTS & ANIMALS

WATER + CARBON GLUCOSE + OXYGENDIOXIDE

6H22O + 6CO22 C66H1122O66 + 6O22

chlorophyll

light energy

light

PPhhaassee 11In the grana,chlorophyllabsorbs lightenergy and usesit to split water

into hydrogen andoxygen

PHOTOSYNTHESIS in the CHLOROPLAST

PPhhaassee 22In thestroma, acycle ofreactionsbuildsglucosefrom CO2and thehydrogenfrom water

Light energy

CHLOROPLAST - site ofphotosynthesis

MITOCHONDRIA - site ofcellular respiration

GLUCOSE+

OXYGEN

CARBONDIOXIDE

+WATER

ATP

green pigmentin chloroplastsof plant cells

toair

high-energy

sugar (food)fromair

fromsoil



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What Happens to Glucose in a Plant?If photosynthesis only makes glucose, where do all theother biological chemicals in a plant come from?

Glucose is a monosaccharide sugar, a member of thecarbohydrate group. (Revise page 7) It is easy for a plant toconvert glucose into other types of carbohydrate.

Glucose can also be converted chemically into lipids... fatsand oils, since they contain exactly the same chemicalelements (carbon, hydrogen & oxygen only - CHO).

GLUCOSE LIPIDS (oils)

Making proteins and nucleic acids is more difficult, sincethese contain additional chemical elements, especiallynitrogen, phosphorus and sulfur.

This is where the “minerals” such as nitrate, phosphate and sulfatecome in. Soil minerals are often called “plant nutrients”, and agardener may say he/she is “feeding” the plants when applyingfertilizer, but these minerals are NOT food.

They are the essential ingredients needed so plants canmake proteins and DNA etc, fromthe real food... glucose.

Experiments with PhotosynthesisThe classic experiment you have probably done, is where aleaf is partly covered with light-proof aluminium foil, andthen exposed to light for several days. The aim of thisexperiment is to prove that light is needed forphotosynthesis to occur.

After several days, the leaf is decolourized (so the test canbe seen more easily) and then tested with IODINEsolution.

Why Iodine? It detects STARCH, not glucose.

Sure enough, you probably found that any part of the leafexposed to light turned black when soaked in iodine, whileparts under the foil did not go black. This proves that anypart of a leaf allowed to photosynthesize will build up astore of starch from the glucose it makes. The first productof photosynthesis is glucose, but it is rapidly converted toother things.

Variations on this same method can be used to experimentwith other aspects of photosynthesis, such as proving thatchlorophyll is needed. In this experiment you might haveused “variegated” plant leaves which have chloroplasts onlyin parts of each leaf... guess where the starch is detected?

GLUCOSEmolecules

joined in pairs

joined in 1000’s

(polymerization)

Other sugars, such as sucrose

CELLULOSEfor building newcell walls STARCH

for storage of foodIn fact, plants convert glucose to STARCHso rapidly that the chloroplasts in a plantleaf become packed with starch grainswhen it is photosynthesizing.

THIS IS THE BASIS OF EXPERIMENTS YOUHAVE DONE

Soil mineralsnitrate, sulfate etc

GLUCOSE Polymerization

Aminoacids PROTEIN

chemicalconversion

Aluminium foil

Light

Iodine testshows lots ofstarch here

No light,no starch



14

Structure & Function...How Plants Get Water & Carbon DioxideIn order to photosynthesize, plants must collect water andcarbon dioxide. In a land plant, water is collected by theroots from the soil, and carbon dioxide is collected fromthe air into the leaves.

Both roots and leaves require special structures to gatherthese vital chemicals.

Plants Absorb Waterthrough special outgrowths on the roots called “root hairs”.Each root hair is part of one, very elongated cell. Root hairshelp absorption of water by greatly increasing the surfacearea of the root in contact with the soil.

The actual absorption of water is achieved by OSMOSIS.(Revise page 9) The cell cytoplasm is kept at a higher soluteconcentration than the water solution in the soil, so waterdiffuses into the cell through the cell membrane of the roothair cells.

Once absorbed into the root hair cells, water diffuses fromcell to cell towards the central XYLEM tubes which carrythe water (and dissolved minerals) upwards to the leaves.This upward flow is achieved by the plant constantlyallowing water vapour to evaporate from each leaf(“Transpiration”). This creates a “suction” at the top of thexylem tube, rather like drinking through a straw.

Alongside the xylem tubes are the PHLOEM tubes whichcarry food from the leaves to any part of the plant whichcannot photosynthesize... especially the roots.

Together the Xylem and Phloem tubes form the “veins” ina plant. They not only carry substances around the plant,but are important as reinforcement and support structures.

The Structure of the LeafA plant leaf is a factory for photosynthesis. A typical leaf isbuilt so that every part of its design is suited to theachievement of that one objective... making food. It is aclassic case of Structure matches Function.

The general shape of a leaf... broad, flat and thin,gives it maximum surface area for absorbing light and

carbon dioxide from the air. A leaf is thin enough that lightpenetrates to reach each layer of cells within, for maximumphotosynthesis.

The “veins” contain xylem tubes for carrying waterand minerals up from the roots, and phloem tubes for

carrying manufactured food away. Being speciallyreinforced with tough “lignin”, the veins also support theflimsy leaf, and keep it in shape and positioned to catchmaximum light.

The cuticle is a layer of clear, waxy material. It allowslight through, but is waterproof to prevent excessive

water loss.

The epidermis layer of cells is transparent like awindow, to let light through to the cells underneath.

MICROSCOPIC VIEW NEAR A ROOT TIP

LLOONNGGIITTUUDDIINNAALL TTRRAANNSSVVEERRSSEESSEECCTTIIOONN SSEECCTTIIOONN

XYLEM TUBES

ROOT HAIRSOutgrowths fromepidermis cells

Phloemtubes

Epidermis layer

1

1

2

2

MICROSCOPIC CROSS SECTION THROUGH A LEAF

Poreopening

SURFACE VIEWOF A STOMATE

3

4

5

6

7

8

9

4

3

magnified



15

The Palisade Layer of cells are tightly packed in anorderly row immediately under the top epidermis where

there is maximum light. Each cell contains manychloroplasts. This is the “engine room” for photosynthesis.

The Spongy Layer has very loosely packed cells, withlots of spaces around them. This allows gases (CO2 & O2)and water to easily move around by diffusion.

The lower leaf surface has many openings, called“stomates”. Through these openings or “pores”:

• water evaporates from the leaf (Transpiration).This ensures that water and minerals continue tobe “sucked up” from the roots.

• CO2 diffuses into the leaf for photosynthesis.• O2 diffuses out of the leaf into the air.

A magnified surface view of a stomate is shown at

Veins run throughout each leaf. The Xylem tubesbring water and minerals from the roots and release them

into the spongy layer. From there, some diffuses into thecells for photosynthesis, while the rest evaporates throughthe stomates.

There are Phloem tubes as well, which collect the foodmanufactured in the leaf cells and carry it away to feedother parts of the plant, such as roots, stem and flowerswhich might not be able to photosynthesize.

Veins also act as reinforcing, helping to keep the flimsy leafdeployed to catch maximum light.

Each stomate pore is an opening formed between twospecial “guard cells”. These cells can change shape to

open the pore, or close it up to minimize water loss in dryconditions. The guard cells change shape by using osmosisto either pump-up full of water (pore open), or deflate andshrivel (pore closed).

The Importance of Surface AreaNotice that in both the roots absorbing water, and theleaves absorbing light and CO2, the plant maximizes therate of photosynthesis by maximizing surface area.

It is generally true of all processes such as absorption andmany chemical reactions, that the greater the surface area,the faster the rate of the process.

You may have done a simple experiment similar to this:-

The more finely divided a solid is, the greater its surfacearea, so the powder has more surface area than the lumps.This experiment demonstrates the principle that thingshappen faster when more surface area is available forreaction or absorption.

5

6

7

8

9

9

Same quantity of same strength acid

Same quantity of solid calcium carbonate

Lumps Powder

Both lumps andpowder reactwith acid inexactly thesame way, butthe ppoowwddeerrrreeaaccttss ffaasstteerr..



16

Nutrition in AnimalsAnimals are Heterotrophs... they must eat energy-rich foodmade by other organisms, either plants or other animals.

The food an animal eats is composed largely of complexcarbohydrates, proteins and fats which must be digestedbefore being absorbed into the body and used by the cells.Digestion involves chemically breaking large moleculesdown into smaller units which can be carried around thebody and transported across cell membranes.

Digestion is carried out by the digestive system... you havestudied the human digestive system in the past. Here’s aquick revision:-

Once again Surface Area is important. The chewing offood by the teeth breaks the food into smaller pieces, so itssurface area is increased. This allows digestive enzymes toattack and digest it faster.

Different Animals Have Different Systems

The digestive systems of different animals are often quitesimilar, but certainly not identical. Once again, the principleof “structure matches function” can be noticed.

Digestion in HerbivoresPlant-eaters face a problem... a lot of plant material has alow nutrient value and contains a lot of fibrous matterwhich is difficult to digest. The fibre is mostly the plant cellwalls, made of cellulose... a polymer of glucose, but animalslack the necessary digestive enzymes to break the cellulosedown.

Herbivores usually have:-• flat, grinding teeth to chew the food thoroughly to

increase the surface area exposed to digestive enzymes• relatively long intestines and caecum, so there is more

surface area and longer time available for digestion• bacteria living in their gut which have the enzymes to

digest cellulose. This is an example of “mutualism”.

Digestion in CarnivoresFlesh eaters don’t need such huge digestive systems. Theirfood is much more concentrated in its nutritional value, andrelatively easy to digest.

Carnivores usually have:-• sharp, tearing teeth to cut flesh into chunks for

swallowing... chewing is not so important• relatively short intestines• highly elastic stomach, which allows them to swallow a

large meal. The stomach acid and enzymes are vital fordigesting their high protein meat diet.

More on Surface Area: the small intestines of every animalhas a highly folded inner surface, so there is a greater areafor absorbing nutrients into the blood stream.

ENZYME

Starch molecule Sugarmolecules

Protein moleculeENZYME

Amino acidmolecules

SSaalliivvaarryy GGllaannddss. Enzyme in saliva beginsdigesting starch

CChheewwiinngg the foodbegins thedigestion process

OOeessoopphhaagguuss carriesfood to stomach

SSttoommaacchh churnsfood with acid.Enzyme digestsprotein

PPaannccrreeaass adds acocktail ofenzymes to food

LLiivveerr receives andprocesses digestednutrients after theyare absorbed intoblood stream

GGaallll bbllaaddddeerr addsbile to dissolvefats so enzymescan digest them

SSmmaallll IInntteessttiinneeCompletes digestionwith cocktail ofenzymes, thenabsorbs nutrients intoblood stream

DDuuooddeennuummFirst part of intestine

LLaarrggee IInntteessttiinneeAbsorbs water,vitamins & mineralsinto blood stream

RReeccttuumm storesundigested wastes(faeces) for laterelimination

HUMAN DIGESTIVE SYSTEM

CCaaeeccuumm && AAppppeennddiixx have nospecial function in humans

long LLaarrggee IInntteessttiinnee

huge CCaaeeccuumm

SSttoommaacchh

SSmmaallll IInntteessttiinnee

Grindingteeth

Tearingteeth

Shorter intestinesSSttoommaacchhmore important



17

Digestion in a Nectar FeederSome animals eat a diet that requires very little digestion atall. Many birds (eg honey-eaters, humming birds) andinsects (eg butterflies) feed largely on the sugary nectar offlowers.

Sugar does not require any digestion at all, so their digestivesystem can be very short and simple.

A short-lived butterfly might need only nectar for theenergy its sugar supplies, but a bird needs more nutrients.Most eat the plant pollen which is rich in protein and oil.Therefore, their short little digestive system does need todo some work, apart from simply absorbing sugar.

Nectar & Pollen feeding lorikeet

Very short iinntteessttiinneess

SSttoommaacchh digests pollen(rich in protein)eaten with thesugary nectar

Long bbeeaakk && ttoonngguueereaches deep intoflowers

Photo by Diana



18

Worksheet 3Fill in the blank spaces.Check your answers in the “Answer Section” at the back

Part A(a).......................................... (e.g. plants) are organismsthat can make their own food, while(b)............................................... (such as animals) cannot.

The process of photosynthesis can be summarized as

(c)............... + (d)............ (e)............. + (f).................

Photosynthesis occurs in the (g)..........................................(organelle) in plant cells. The green pigment(h).......................................... absorbs (i).............................energy for the process. This energy is stored as chemicalenergy in the (j)..........................................moleculesproduced.

Thousands of Glucose molecules can be joinedtogether by the process of (k)..............................................to form (l)........................................ (used for storage) orcellulose which is used to build (m).....................................

Glucose can also be chemically converted into(n).................................. To convert sugar to amino acids,the plant needs a supply of (o)...........................................Amino acids can then be joined together to form(p)...................................................

The structures mainly responsible for absorbing waterinto a plant are the (q)....................................... which areoutgrowths of root cells and greatly increase the(r)........................................ of the roots. Water isabsorbed by the process of (s)............................................then transported up to the leaves through(t).................................................... tubes.

In a leaf, there are many examples of “structurematching function”, such as:• The shape of the leaf gives maximum surface area for(u)..................................................................................

• The (v)................................................ layer of cells,packed together & full of chloroplasts for maximumphotosynthesis.

• The “spongy layer” of loosely packed cells to allow(w)............................................................................................

• The (x)................................................ which can openand close and allow water to evaporate out (called(y).....................................................) and to let the gas(z).................................................... in for photosynthesis.

Part B

Animals have to digest the food they eat. This is carried out by digestive (a)..................................... which,for example, break starch into (b)....................................and proteins into (c).........................................................

There are 4 organs in the mammal digestive systemthat produce digestive enzymes. Name them all.(d)......................................... ............................................................................................. ...............................................

Digestion begins with chewing food which increasesthe (e).................................................... of the food, soenzymes can attack it faster.

Digested nutrients are absorbed into the blood streamfrom the (f).............................................., then carried inthe blood to the (g)................................... for processing.

Herbivorous animals usually have:

• (h)........................................ teeth to chew thoroughly

• relatively (i)................................. intestines and caecum

• mutualistic (j)................................... living in their gutto help them digest (k)......................................... which isa major part of their diet.

Compared to them, carnivores usually have:

• (l)..................................... teeth

• relatively (m)............................................ intestines

Nectar feeders, such as (n).................................................have digestive systems which are very(o)......................................and......................................




19

Organisms Need What Cells NeedEvery living cell, plant or animal, has certain requirements:-

A single-celled organism exchanges these chemicals withthe environment directly through its cell membrane.However, in all multicellular organisms most of the cellsare located deep within the body. There have to be bodysystems to:-

• absorb nutrients, water and oxygen• excrete wastes• transport all these chemicals between the cells

and the environment.

In animals the body systems involved are:Digestive system absorbs nutrients and water.Respiratory system (e.g. lungs) exchanges gases,absorbing oxygen, and excreting carbon dioxide.Excretory system (kidneys) removes other wastes such asurea.Circulatory system (blood, heart, veins etc) transports allthese things around the body.

Plants also have systems for exchanging gases, and fortransporting substances around their bodies.

Requirements for Efficient Gas ExchangePlant or animal, large or small, all organisms need toexchange gases with their environment. Efficient gasexchange requires:-

• large surface areain contact with the environment

• moist gas exchange membranebecause the gases must dissolve in water before passing through the membrane by diffusion

• close contact with the blood supply(or other transport system) to carry gases between cellsand the gas exchange organs.

Gas Exchange in AnimalsThere are many ways that animals carry out gas exchange.This section will compare four different systems... mammal,frog, fish and insect.

Lungs in a MammalUsing the human as a typical example:

The lung is not just a hollow space like a balloon. If it was, thesurface area for gas exchange would be about the size of thispage. By dividing into millions of alveoli, the total surface areainside your lungs is about the same size as a tennis court!

The inside surface is always moist, for gases to dissolve anddiffuse, and each alveolus is in intimate contact with ablood capillary to transport the gases to and from the bodycells.

The requirements for efficient gas exchange havebeen met.

4. GAS EXCHANGE & INTERNAL TRANSPORT

FOOD WATER OXYGEN

WASTE PRODUCTS such as CO2 must be excreted

HUMAN RESPIRATORY SYSTEM

Trachea (Windpipe)

Bronchi(sing: bronchus)carry air to eachlung

Each bronchus sub-divides intoBronchioles

Each bronchioleends in a clusterof tiny air sacs...the Alveoli

Each Alveolus has awall just 1 cell thick, andthe internal surface iskept moist

BronchioleAIR flowsin and out

BloodcapillaryBlood flow

OO2

CCOO2

Lungis not hollow,but sponge-like



20

Gas Exchange in a FrogAmphibians hatch from their egg as“tadpoles” which live in water andbreathe with gills. Later theyundergo metamorphosis anddevelop into the adult form which breathes with lungs.

However, a frog’s lungs are much simpler than a mammal’s,and don’t have as many alveoli.

Doesn’t this mean less surface area and less efficiency?Yes, but a “cold-blooded” frog doesn’t need to carry outcellular respiration just to make body heat the waymammals do. So the need for O2 intake and CO2 excretionis a lot less. Also, the frog doesn’t just do gas exchange inits lungs...

The frog makes up for its inefficient lungs by carrying outgas exchange through other body surfaces which are keptmoist and are lined with blood vessels... its mouth andthroat cavity and the skin all over its body.

Gas Exchange in an InsectInsects don’t have lungs at all. Along the sides of theirbodies is a series of holes called spiracles. Each spiracleallows air to move into a network of tubes (“trachea”)which infiltrate their whole body.

This system is quite efficient in a small animal, but rapidlybecomes inadequate as the animal grows larger, because ofthe Surface Area to Volume Ratio getting smaller.(see p.10)That’s why there’s no such thing as a really big bug!Hollywood fantasies cannot actually happen.

Gas Exchange in a FishLand-dwelling, air-breathing animals always must have theirgas exchange organs inside their bodies so the moistmembranes won’t dry out. In water this can’t happen, so afishes gills are exposed to the water environment, butshielded by a tough “gill cover” to protect the delicatebreathing organs.

The gills are a series of feather-like plates around which thewater flows. Each gill plate consists of thousands of tiny“filaments” each one a thin leaf-shaped structure packedwith blood capillaries.

Note that the direction of blood flow in the capillaries isopposite to the flow of water around the gill filaments. Thisis called “counter-current flow”, and (without going intodetail... KISS Principle) makes the gas exchange processmuch more efficient.

It needs to be efficient, because remember from Topic 1,that the level of oxygen dissolved in most aquaticenvironments is much lower than the concentration in air.

Study again each system compared... mammal, frog, insectand fish and take note of how each system achieves thethree essential features of any gas exchange system...

• LARGE SURFACE AREA

• MOIST MEMBRANE SURFACE for diffusion

• CLOSE CONTACT WITH BLOOD STREAM or body cells.

FROG RESPIRATORY SYSTEM

Simple Lung

Mouth andthroat cavity.Moist & lined withblood vesselsMoist Skin

also acts as a gas exchange surface

GAS EXCHANGE IN AN INSECT

Spiracles

TracheaThe trachea tubes are moist insidefor gas exchange. Gases diffusedirectly to the body cells, which arenever far from a trachea tube.The network of tubes increases thesurface area for gas exchange.

FISH BREATHE WITH GILLS

Waterin

Gillsunder gill cover

Water out

Gases aredissolved inthe water

WATER FLOW GILL FILAMENTS

BLOOD FLOW IN CAPILLARIES



21

Internal Transport in AnimalsOnce nutrients and gases have been absorbed into the body,they need to be transported to every body cell. In animalsthis is the job of the Circulatory System, consisting of theheart, blood vessels and the blood itself.

Once again, different types of animals have all sorts ofvariations, but in this section only a broad comparisonbetween two general types of system will be made.

Closed Circulation SystemsAll vertebrate animals (fish, amphibians, reptiles, birds andmammals) have a blood system that is “closed”... the bloodis always flowing inside a blood vessel, pumped around bythe heart.

This system is highly efficient because the blood can bekept flowing within the vessels, guaranteeing a steady flowof nutrients, gases and wastes between body cells and theoutside environment. This efficiency allows vertebrates togrow very large and still function perfectly despite the poorSA/Vol ratio of a large body.

Be aware that fish, amphibians and most reptiles do nothave a system quite the same as a mammal, but in all casesthe system is “closed”.

Open Circulation SystemsInvertebrate animals (including insects, worms & snails)have much simpler circulatory systems in which the“blood” (or a fluid doing the same job) does not always stayinside a blood vessel.

The “open” system is not efficient, because the blood is notforced to keep flowing as in a closed system. However, in asmall insect, with its separate gas exchange system, this isobviously quite adequate... after all, insects are the mostnumerous animals on the planet!

CLOSED CIRCULATION IN A MAMMALSchematic Diagram

Capillarynetwork inLungs

Capillarynetwork inbody

Alveoli (air sacs)in lungs

CO2 O2

HEARTpumps bloodVe

ins

Arte

ries

Vein

BBooddyy cceellllssreceive O2 &nutrients, getrid of CO2 &other wastes

OPEN CIRCULATION IN AN INSECTSchematic diagram

HHeeaarrttpumps“blood”fluid

Arteries

BBooddyy cceellllssbathe in fluidcarrying thenutrients

Circulatoryfluid flows outof bloodvessels

Fluid slowly collects back into veins.Wastes (but not CO2) are taken awayfor excretion, and blood returns tothe heart.

Arte

ry

Photo by Kevin Walsh



22

Gas Exchange in PlantsThe structure and functioning of the leaf stomates wascovered earlier... revise pages 14-15.

What about other parts of a plant?

Lenticelsare simple structures on the stems and trucks of plantswhich allow gas exchange to the cells by simple diffusionfrom the air.

Root Hairswere covered earlier in connection with water absorption(revise page 14)Because they increase the surface area of the roots, roothairs are important for gas exchange as well as waterabsorption. Oxygen in soil spaces, or dissolved in soil watersimply diffuses into the root hair cells, and spreads to otherroot cells by further diffusion.

Internal Transport in PlantsPlants have two separate systems for transportingsubstances inside their bodies...

Xylemtubes carry water and dissolved minerals from the roots tothe leaves.

The upward movement of water in xylem tubes happenswithout any effort by the plant... it is “passive transport”.The evaporation of water from the leaves through thestomates, (“Transpiration”) causes a “suction” effect at thetop of each xylem tube. This draws more water from theroots.

Rate of TranspirationYou will have done experiments on transpiration tomeasure it, and the factors which affect its rate. A commonway to do this is with a “potometer”:-

Tightly packedstem cells

Lenticel opening

Loosely packedcells allow gasesto diffuse in andout

Hollow, deadcells, joinedend-to-endforming atube

Cell wallsre-inforcedwith ringsand spiralsof lignin

POTOMETER METHOD FORMEASURING TRANSPIRATION

Fresh plantshoots

Plastic tubefilled withwater

Ruler

Glass tube filled with water.As Transpiration occurs from the leaves anddraws water up from below, an air bubble issucked in at the end of the tube. A rulergives a scale to measure rates oftranspiration under different conditions.

Typically it is found that the rate of transpiration is increased by:-higher temperatures, air flow (wind), low humidity and light. (plantsopen their stomates when there is light, to get CO2 in for Photosynthesis)



23

PhloemPlants have a separate set of tubes for transporting sugarsand other food nutrients, the phloem tubes.

While the xylem tubes are formed from dead cells, thephloem are living cells joined end-to-end. The ends of eachcell are perforated (“sieve plates”) so each cell is open intothe next so they form a continuous tube.

The movement of food via the phloem is called“Translocation”. It is an “active transport” operation,meaning that the plant has to use energy to cause thematerial to flow. A “companion cell” beside the phloem cellsupplies ATP from cellular respiration to power the activetransport in the phloem tube.

While the xylem is a one-way flow system, the phloemsystem can carry food (especially sugars) in either direction.If a lot of photosynthesis is occurring, the phloem willcarry sugar to storage sites in roots or stem. Ifphotosynthesis is not possible for an extended time, thenthe phloem will carry sugars back from the storage sites tofeed the leaf cells, or supply a growing flower or fruit.

The Use of Radio-isotopesto Study Transport Systems

The atoms of each chemical element are not all exactly thesame. They have the same number of protons & electrons(that’s what makes them that element), but the number ofneutrons in the atom may vary. Such atoms of the sameelement, but with a different number of neutrons, are called“isotopes”. Some isotopes are “radio-active” and give offnuclear radiations... hence “radio-isotopes”.

The radiation they give off can be detected byphotographic paper or special instruments such as the“Geiger counter”. If a radio-isotope is introduced into aplant or animal, its transport through the body can befollowed by monitoring the radiation the isotope emits.

This “tracer” technique is one of the more importantmethods used to study the movement of substances inliving things. This is how a lot of our knowledge oftransport systems has been discovered.

For example:If a leaf is exposed to CO2 containing “carbon-14” (aradio-active isotope of carbon):

PHLOEM CELLalive and filled withcytoplasm Sieve plate

between cells

“Companion cell” hasmany mitochondria to provideATP to the phloem cell

Soon, radiation isdetected in starch grains

in leaf cells.

Next, radiation is found in sugars inphloem tubes

Later, it’s here

Later still, the radiation isdetected in starch storedhere

From studies likethis we learn the

details of thechemistry and

transport systemsinside living

things



24

Worksheet 4

Fill in the blank spaces and diagram labels.Check your answers in the “Answer Section” at the back

Part A AnimalsThe 3 requirements for an efficient Gas Exchange systemare:

• large (a)....................................................................

• gas exchange membrane which is kept (b)............................

• close contact with (c)..........................................................

In any gas exchange system, the gases move across themembrane by the process of (d)..............................................

Compared to a mammal’s lung, that of a frog is (i).........................................................................Frogs exchange gases through their (j)..................................and ........................................................... as well as lungs.

Insects have a series of holes called (k)................................along their body which lead into a network of tubes called(l)............................................... This works OK for smallinsects, but means no insect can ever be really large becauseits (m)............................................................... ratio would betoo small for sufficient gas exchange.

In a fish’s (n)....................................... there are thousands ofleaf-shaped (o).................................................. around whichwater flows. In each filament are blood capillaries in whichblood always flows (p)....................................................... tothe water flow. This “(q)...................................... current”flow is much more efficient.

In a “(r)............................................ circulatory system theblood is always inside blood vessels, and kept circulating bythe pumping of the (s)............................................................

(t)............................................... animals have “opencirculatory systems” in which the blood leaves the bloodvessels and flows directly in contact with the body cells.

Part B PlantsGases exchange in a plant occurs through the(a)........................................................... of the leaves, and viathe (b)........................................... of stems, and the(c)......................................................... in the roots.

Xylem tubes carry (d)............................................ and.......................................... from (e)................................ to(f)............................................................

The evaporation of water from the leaves is called(g).................................................................... It is increased byfactors such as (h).............................................. and(i).......................................................................

Food nutrients are carried by the (j).........................................tubes. This transport is called (k)...............................................and is considered “active” transport because(l)...............................................................................................In contrast, xylem transport is (m)............................................

(e)..............................

(f)............................

(g).......................................

(h)................................microscopicair sacs




25

The Need For Cell DivisionSingle-celled organisms reproduce by simply dividing intwo.

In a multicellular plant or animal cell division is vital forgrowth. Remember that individual cells cannot grow largebecause as they do, their SA/Vol ratio gets smaller, andthey cannot get materials in and out through their cellmembrane fast enough to survive. So, the only way to growis to produce MORE small cells.

Cell division is also used to replace damaged or worn outcells in the body. For example, your body is constantlyproducing new blood cells to replace those that wear outbecause of the battering they receive being pumped aroundall the time.

The Process of Cell DivisionCell division occurs as a sequence of steps or “phases” assummarized by this schematic diagram.

Steps ...more information

Mitosis Through the MicroscopeYou will have done a laboratory practical in which you useda microscope to examine a prepared slide of cellsundergoing cell division. Commonly the root tip of a plantseedling is viewed, and the sketch shows roughly what thecells may look like...

5. CELL DIVISION FOR GROWTH & REPAIR

The chromosomescondense togetherand becomevisible.They line up in themiddle of the cell,then separate into2 identical groups

Once separated, eachset of chromosomesforms a new nucleus

Finally, the cellmembrane growsto divide the cell in2 parts, with ashare of cytoplasmand organelles ineach

Genetic information isstored in the cellnucleus, as DNA.The DNA is containedin thread-like“chromosomes” whichare not normallyvisible.

The nuclear membranedissolves sochromosomes can moveright across the cell.They are moved bythreads called “thespindle” which act likefishing lines, reelingthem to opposite sidesof the cell

THIS

IS M

ITO

SIS .

.. TH

E D

IVIS

ION

OF

THE

CELL

NUC

LEUS

This final division iscalled

“CYTOKINESIS”

Most cells look like this one.No chromosomes visible,but DNA is being copiedready for mitosis to start

Thesehavejustfinisheddividing

Chromosomesjust becomingvisible. Mitosis isunder way

Chromosomeshave lined upin the middleof the cell.

Chromosomesbeing pulledapart into 2identicalgroups

Mitosis complete,Cytokinesis is next

These 3 diagrams shown how cells in mitosisare often drawn in textbooks, in a stylized way.If you need to sketch them, do it like this forgreater clarity

Chromosomes pulledapart

Chromosomes linedup in middle of cell

Chromosomes becomevisible after copying

Original “parent”cell makes a copyof its geneticinformation



26

The Results of Cell Division• One parent cell divides to form 2 “daughter” cells.

• Each daughter cell is genetically identical to the other,and to the parent cell. This is because the original DNAwas first duplicated (“replicated”) then divided into twoduplicate sets by mitosis.

• The daughter cells are not necessarily identical in size, buteach gets a share of cytoplasm, mitochondria, ribosomes and all the other organelles.

• Each daughter cell can then make more organelles, and grow in size, until it is full size. Each may then undergocell division again. This endless repetition of cell growthand cell division is called the “cell cycle”.

You began as a single cell. It divided by mitosis, thendivided again and again, until today you are a complexorganism of about 300 billion cells. Each of your cells isgenetically identical to every other, and to that original cellyou formed from.

Even when you have finished growing, mitosis willcontinue in many parts of your body:

• skin, to replace the layers that constantly flake off.• hair follicles and finger-nails, which grow all your life• bone marrow, where blood cells are constantly being

produced to replace those that wear out.• anywhere else where injury or cell death requires replace-

ment, although this is very slow in nerve tissue.

Where Mitosis Occurs in Other OrganismsA human baby is more or less the same shape as an adult,and simply grows bigger, proportionally all over, to becomean adult. In other organisms though, cell division occursonly in certain parts of the body, and growth is notproportional.

Plantsgrow only at certain places known as “meristems”. Theseare located

• at the root tip• at the “buds” where new shoots & flowers will appear• in the cambium layer, between xylem & phloem

(cambium growth is how the stem/trunk gets larger)

Insectsgrow differently in two distinct stages.

Most insects hatch from their egg as a “larva”... caterpillar,grub or maggot. The larva does not undergo cell division atall, but grows rapidly by increasing the size of each cell.(within the limits imposed by the SA/Vol ratio, of course)

Next, the insect larva undergoes metamorphosis and totallychanges its body plan. This is achieved by special “disks” ofcells which begin mitosis in particular directions, eachforming a different body part such as a wing, leg or kidney.These “disks” correspond to the meristems of a plant, asspecial sites of mitosis.

A Final Note...The main store of genetic material is the DNA in the nucleus, but that’s not the only place in a cell where DNA is found.DNA is also located in the mitochondria, and in chloroplasts in plant cells. These organelles are able to reproducethemselves (at least in part) in mini-versions of cell division.

This occurrence of DNA in these two important organelles (both concerned with food & energy, and its flow inecosystems) will be dealt with in a later topic. The evidence points to a very interesting evolutionary origin for theseorganelles...

Nuclear DNA

Mitochondrial DNA Chloroplast DNA



Worksheet 5

Fill in the blanks. Check answers at the back.

In a multicellular organism, cell division is necessary for(a)................................................. and to replace damagedor worn out cells.

Mitosis refers to the division of the (b).............................,while the division of cytoplasm into 2 cells is called(c)............................................................

Before mitosis becomes visible in a cell the geneticinformation (d)......................................................................

The genetic information is contained in the chemical(e)................................... which is built into thread-likestructures called (f)................................................................

The visible sequence of mitosis is:• chromosomes thicken, become visible, and the nuclearmembrane (g).....................................................................

• chromosomes (h)......................................... in the middleof the cell

• chromosomes move to opposite ends of the cell,pulled by the threads of the (i)............................................

• Each group of chromosomes forms a new(j)........................................................ then cytokinesisdivides the cell itself.

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The results of cell division include that the daughtercells are genetically (k)........................................, andidentical to the (l)................................................. cell.

Apart from the nucleus, 2 other organelles containDNA. These are the (m)........................................ and........................................................................

Sites of mitosis in a plant are called “(n).............................located at (o)........................................................., and(p)............................................................. as well as thecambium layer in the stem.

Most insects hatch from their egg as a q)............................which grows by cell r)..............................................,without cell s).................................................. Later, theyundergo t)..............................................................................in which their body tissues totallyu)...................................................... and are re-built toform the totally different adult. During this process, celldivision occurs only in special “v)....................................”of cells.




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CONCEPT DIAGRAM (“Mind Map”) OF TOPICSome students find that memorizing the OUTLINE of a topic

helps them learn and remember the concepts and important facts.Practise on this blank version.

PPAATTTTEERRNNSSiinn

NNAATTUURREE



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Practice QuestionsThese are not intended to be "HSC style" questions, but tochallenge your basic knowledge and understanding of thetopic, and remind you of what you NEED to know at theK.I.S.S. principle level.

When you have confidently mastered this level, it is stronglyrecommended you work on questions from past exam papers.

Part A Multiple Choice1. The man credited with the discovery of the cell nucleus was:A.Robert HookeB. Anton van LeeuwenhoekC. Robert BrownD. Louise Pasteur

2. The organelle least likely to be seen with a light microscopeis:A. MitochondrionB. VacuoleC. NucleusD. Chloroplast

3. The cell structure never found in an animal cell is:A. cell membraneB. cell wallC. endoplasmic reticulumD. golgi body

4. The function of the ribosomes can be described as:A. storage of genetic informationB production of ATPC. packaging of substances for secretionD. manufacture of proteins

5. Starch, glycogen and cellulose are all:A. proteins, composed of amino acidsB. nucleic acids, related to DNA & RNAC. sugars, of the carbohydrate groupD. polymers of glucose

6. A food substance, which may be a mixture of variousorganic chemicals, was tested with the following results:Iodine solution gave a yellow, brown colour.Biuret reagent gave a purple colour.Benedict’s reagent resulted in a pale blue colour.From these results you would conclude that the food contains:A. protein, but no starch or sugarB. starch, but no protein or sugarC. sugar and protein, but no starchD. sugar and starch, but no protein

7. The diagram shows a cell surrounded by a solution whichhas a high concentration of largemolecules. You might expect:A. solute molecules to diffuse in...B. water to diffuse in...C. water to diffuse out...D. solute molecules to diffuse out... to/from the cell.

8. A brick was smashed into smaller pieces with a hammer.It would be true to say that the brick pieces, when comparedto the original brick, have:A. larger volumeB. larger SA/Vol ratioC. smaller surface areaD. smaller SA/Vol ratio

9. The chemical raw materials needed for photosynthesis are:A. glucose and oxygenB. water and carbon dioxideC. carbon dioxide and oxygenD. water and glucose

10. The chemical known as “ATP” is best described as:A. the carrier of genetic informationB. the product of cellular respirationC. the absorber of light for photosynthesisD. a waste product from the mitochondria

11. Soil minerals such as nitrates, phosphates and sulfates areessential to a plant for which purpose?A. To provide energy.B. To make starch from glucoseC. As raw materials for photosynthesisD. To make proteins from glucose.

The following diagram shows a cross-section through a leaf.Use the diagram for Q12 and 13.

12. A structural feature which helps the functioning of the leafis that the cells at “P”:A. are transparentB. are loosely packedC. contain many chloroplastsD. open up to let gases in/out

13. The “guard cells” are labeledA. Q B. R C. S D T

14. In a mammalian digestive system, the main chemicaldigestion in the stomach involves the breakdown ofA. starch B. proteinC. lipidsD. sugars

15. An animal with large, flat, grinding teeth and a very largecaecum (a blind “pocket” of the intestine) probably eatsmainly:A. nectar, pollen and flowersB. the flesh of other animalsC. plant leaves and grassD. fish & other seafood

P

Q

R

S

T



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16. Which of the following is NOT an essential feature of agas exchange system?A. close contact with the blood supplyB. large surface areaC. strong protective shieldingD. moist membrane

17. An animal’s respiratory system consists of a series of holesalong the body which allow air to circulate into a network oftiny tubes throughout the tissues. This animal is probably aA. spiderB. frogC. fishD. reptile

18. A plant would probably show the lowest rate oftranspiration under conditions of:A. hot & windyB. bright light & low humidityC. hot & bright lightD. high humidity & cool

19. Which of the following correctly gives a structural featureand a functional feature of xylem tubes?A. living cells which transport waterB. reinforced with lignin, carry out passive transportC. dead, hollow cells, carrying food nutrientsD. cells filled with cytoplasm, carrying out active transport

20. The diagramshows some plantcells which areundergoing celldivision.

The correctsequence of eventsis shown by the cellsA. SPQTRB. RSPTQC. RQPTSD. PQTSR

Part B Longer Response QuestionsMark values given are suggestions only, and are to give you anidea of how detailed an answer is appropriate.

21. ( 3 marks) Compare the light microscope to the electronmicroscope in terms of how each forms an image, themagnification, and the resolution of each.

22. (2 marks) Using either the nucleus or mitochondrion as yourexample, discuss the way that the structure of theorganelle relates to its function.

23. (10 marks) Name, and give a function, for each part of this plant cell.

24. (4 marks) Using examples, discuss the difference between the “organic”and “inorganic” chemicals found in living cells.

25 (2 marks) The cell membrane is described as being “semi-permeable”.Explain what this means.

26. (4 marks) Compare the processes of diffusion and osmosis, identifyingwhat substances are involved and the direction of movement(compared to any “concentration gradient”)

27. (4 marks) Explain why all living cells have to be very small in size.

28. (2 marks) Differentiate between “autotrophs” & “heterotrophs”,including examples in your answer.

29. (5 marks) a) Summarize the process of photosynthesis by a wordequation, including the energy source.b) Give two reasons why photosynthesis can be considered themost important biological process on Earth.

30. ( 5 marks) In experiments on photosynthesis, the presence of starch inleaves is often taken as proof that photosynthesis has takenplace.a) Explain why it is starch, not glucose, that the leaves are testedfor.b) Outline the method of testing for starch in a leaf, includingany preliminary treatment(s).

31. (4 marks) Discuss the relationship between structure and function shownby the leaf cell layers known as the “palisade layer” & the“spongy layer”.

P

Q

R

ST

(f)(g)(h)

(j)

(d)

(e)

(a)

(i)

(b)

(c)



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32. (6 marks) Compare & contrast the processes of Transpiration andTranslocation in a plant, includinga) the substances transportedb) the plant tissues involvedc) the basic mechanism of transport involved.

33. (3 marks) Briefly outline how the length and complexity of an animal’sdigestive system is related to its diet.Refer to 3 different types of diets in your answer.

34.(3 marks) Explain the roles of the respiratory, excretory and circulatorysystems of a mammal, and any connection between them.

35. (4 marks) One of the main features of any respiratory system is a largesurface area for gas exchange. Outline how a large surface isachieved in a a) mammalb) frogc) fishd) insect

36. (4 marks) Using simple schematic diagrams, contrast the circulatorysystems of vertebrate and invertebrate animals.

37. (4 marks) a) Identify THREE structures in a plant which are involved ingas exchange.b) Choose ONE of the structures listed in part (a) anddescribe one feature of it which aids gas exchange in theplant.

38. (4 marks) Outline the way in which technology, such as radio-isotope“tracing” is used to study the path of elements through aliving plant or animal.

39. (6 marks) Describe the sequence of steps that occur in the processes ofmitosis & cytokinesis.

40. (4 marks) a) Identify the parts of a plant where cell division occurs.b) Contrast the general pattern of growth of a plant with thatof a vertebrate animal such as a mammal.



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Answer Section

Worksheet 1a) all living things.... b) ...pre-existing cellsc) microscopes d) resolutione) electron f) magnificationg) Robert Hooke h) cytoplasmi) nucleus j) chloroplastk) cell wall l) cell membranem) vacuole n) cell wall & (o) chloroplast(p)-(t) (any order) golgi body, endoplasmic reticulum,mitochondria, ribosomes, lysosomes(u) controls substances going in/out of cellv) Endoplasmic reticulumw) packaging substances for storage or secretionx) mitochondria y) chloroplastz) strength/ rigidity/ protection on outside of plant cell

Worksheet 2a) inorganic b) carbonc) proteins d) membranee) energy storage compounds f) carbohydratesg) C6H12O6 h) photosynthesisi) cellular respiration j) DNAk) sugar (glucose) l) Biuret reagentm)yellow/brown n) black/dark blueo) phospholipid p) permeableq) high(er) r) lowers) water t) gradientu) passive v) energy or ATPw) Surface area / Volume x) volumey) cell membrane z) surface areaaa) many ab) large

Worksheet 3Part Aa) Autotrophs b) heterotrophsc) carbon dioxide d) watere) glucose f) oxygeng) chloroplasts h) chlorophylli) light j) glucosek) polymerization l) starchm) cell walls n) lipidso) minerals (inorganic ions) p) proteinsq) root hairs r) surface areas) osmosis t) xylemu) light absorption v) palisadew) circulation of water & gases throughout the leafx) stomates y) transpirationz) carbon dioxide

Part Ba) enzymes b) sugarsc) amino acidsd) salivary glands, stomach, pancreas & small intestinee) surface area f) small intestineg) liver h) large & flati) long j) bacteriak) cellulose l) sharp, tearingm) short n) hummingbirdso) short & simple

Worksheet 4Part Aa) surface area b) moistc) blood supply d) diffusione) trachea f) bronchig) bronchioles h) alveolii) simple/ less S.A. j) skin & mouth/throat cavityk) spiracles l) tracheam) SA/Vol n) gillso) filaments p) in opposite directionq) counter- r) closeds) heart t) invertebrate

Part Ba) stomates b) lenticelsc) root hairs d) water & mineralse) roots f) leavesg) transpirationh)& i) temperature/wind/humidity/lightj) phloem k)translocationl) the plant must expend energym) passive

Worksheet 5a) growth b) nucleusc) cytokinesis d) is copied/duplicated/replicatede) DNA f) chromosomesg) dissolves h) line upi) spindle j) nucleusk) identical l) parentm) mitochondria & chloroplastn) meristems o) root tipsp) shoot tips (buds) q) larvar) enlargement s) divisiont) metamorphosis u) break down / changev) disks

Practice QuestionsPart A Multiple Choice1. C 5. D 9. B 13. D 17. A2. A 6. A 10. B 14. B 18. D3. B 7. C 11. D 15. C 19. B4. D 8. B 12. A 16. C 20. C

Part B Longer Response QuestionsIn some cases there may be more than one correct answer. The following “model” answers are correct,but not necessarily perfect.

21.The light ‘scope forms images by focusing light beams with glasslenses. Electron ‘scopes focus beams of electrons using magneticfields.Light scopes achieve magnifications around 500X and resolutionof about 0.2 um. Electron scopes are 500-1,000 times better ineach department.

22.Nucleus- membrane has pores to allow RNA messengers to goout into the cell.ORMitochondrion- inner membrane is highly folded for moresurface area. The enzymes of cellular respiration are arranged onthese membranes for greater efficiency.



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31.Palisade layer: composed of cells neatly and tightly packedtogether under the upper epidermis where there is maximumlight. Each cell is packed with chloroplasts. These features all helpthe palisade layer carry out maximum photosynthesis.Spongy layer: composed of cells that are very loosely packed.This allows spaces for water & gases to more easily diffuseto/from stomates & veins and so helps supply photosynthesizingcells.

32. Transpiration Translocationa) water food nutrients (sugar)b) xylem phloemc) passive active

33.Grazing herbivores eat a diet high in cellulose fibre. They needvery long intestines & large caecum, so food has more time in thegut while mutualistic bacteria digest the cellulose to glucose.

Meat-eating carnivores do not need such long intestines becausemeat is easier to digest and more nutritious. They have shorterintestines but a stomach that can take in a large meal, less often,and digest the high protein meat.

Nectar feeders (e.g. honey-eater birds) eat a diet high in sugarwhich needs no digesting at all. They have very simple, shortsystems since they only need to absorb the sugar into theirbloodstream.

34.Respiratory system: carries out gas exchange.Excretory system: removal of wastes.Circulatory system: transports substances around the body,including gases and wastes... therefore connects with respiratoryand excretory systems.

35.a) Mammal’s lungs have millions of tiny air sacs (alveoli).b) Frog has very simple lungs, but increases respiratory surface byusing skin, mouth and throat membranes for gas exchange as well.c) Fish’s gills are made up of thousands of leaf-shaped filaments.Each is flat & thin, giving large contact area with water flowingpast.d) Insects have microscopic, branched air tubes (trachea) thatpenetrate throughout their body. This gives a large area of contactwith air for gas exchange.

36.Refer to diagrams on p21.The main thing is to show that vertebrates have a “closed” system(blood is always inside a blood vessel) while many invertebrateshave “open” systems, where the blood leaves blood vessels and“bathes” the cells at some part of the circulation.

37.a) stomates, lenticels & root hairsb) Root hairs: these microscopic outgrowths from root cellsincrease the surface area available. This helps gas exchange (as wellas water absorption).

23.a) Golgi body- packaging for storage or secretionb) Endoplasmic Reticulum- divides cell into compartments andchannels for separation of operations and transportingsubstances.c) Ribosomes- manufacture of proteinsd) Mitochondria- cellular respiration/ release energy from foode) Lysosomes- packages of digestive enzymes for destroyingforeign “germs”, or for breaking up dead cells.f) Cell wall- strength & rigidityg) Cell membrane- controls entry/exit of substancesh) Vacuole- storage of water/ pumps cell tight like a tyrei) Nucleus- control centre/ contains genetic instructions (DNA)j) Chloroplast- photosynthesis

24.Organic chemicals are mainly complex molecules, oftenpolymers, based on the element carbon. E.g. carbohydrates,proteins, lipids & nucleic acids.Inorganic chemicals in living cells are small, simple molecules ormineral ions E.g. water, oxygen, nitrate & chloride ions.

25.Semi-permeable means that some chemicals can diffuse throughit easily, while others cannot get through .

26.Diffusion is the movement of any solute, solvent or gas alongthe concentration gradient.Osmosis is the diffusion of WATER, against the concentrationgradient, through a semi-permeable membrane.

27.As any object gets larger, its SA/Vol ratio gets smaller. A cell needsnutrients, oxygen, etc in proportion to its volume, but must getthese substances in through its cell membrane, the size of whichis its surface area.Therefore, a large cell (with a smaller SA/Vol ratio) would not beable to take in necessary substances fast enough to survive.

28.Autotrophs are organisms that can make their own food.example: PlantsHeterotrophs have to eat food made by other organisms.example animals.

29. light energy

a) Carbon dioxide + water Glucose + Oxygenb) 1. It makes all the food, and is the basis of all the food chains

2. It makes all the oxygen in the atmosphere.

30a) Although glucose is the immediate product of photosynthesis,it is rapidly polymerized to form starch. Therefore, starch is foundin large quantities in a photosynthesizing leaf, but very littleglucose could be detected.b) First the leaf is boiled, then washed in hot alcohol todecolourize it, so colour tests can be seen. Then it can be soakedin iodine solution to test for starch. A black colour indicates thepresence of starch.



34

38.Chemicals containing radio-active “tracers” are introducedinto living things, and any movement is tracked by detectingthe radiation produced by the radio-isotope. For example,CO2 gas, containing radio-active carbon-14, is absorbed bya plant leaf, converted to sugar and transported to storagein the roots. This movement can be studied and tracked bythe radiations from the carbon-14.

39.(For 6 marks, try for 6 points)• Genetic information (DNA) is replicated.• Chromosomes condense and become visible in thenucleus. Nuclear membrane dissolves.• Chromosomes line up in centre of cell. Spindle forms.• Chromosomes pulled apart into 2 identical groups.• Each group forms a new, identical nucleus.• Cytokinesis now divides the cytoplasm & organelles into2 separate cells.

40.a) “Meristems” located at root tips, buds and cambium.b) Plants grow only at the meristems, and usually grow dis-proportionally in different parts of their body. This meansthey may drastically change their shape & proportions asthey grow. In contrast, mammals grow fairly evenly in everybody part and stay more or less in proportion all their life.

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