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Cells and Cell Processes

Cell Theory

Cells were first described by Robert Hooke in 1665.In the 1830s two German scientists, Theodor Schwann and MatthiasSchleiden, using light microscopes, suggested the cell theory:

1. All organisms are composed of cells.They may be unicellular (one celled) or multicellular (many celled).

2. The cell is the basic ‘unit’ of life.

Scientists have modified the cell theory over time as new technology leadsto new discoveries. Additions to the original cell theory are:

3. Cells are formed from pre-existing cells during cell division.4. Energy flow (the chemical reactions that create life) occurs within cells.5. Hereditary information (DNA) is passed on from cell to cell when cell

division occurs.6. All cells have the same basic chemical composition.

Microscopy

Light MicroscopesLight microscopes allow you to see the image because light passes through it.The properties of light mean that it is impossible to magnify an image by morethan x1000.

Electron MicroscopesThe electron microscope was developed in the 1930s. Ituses a beam of electrons instead of light.It is possible to get much larger magnifications, up to x50,000,000.Because you can’t see electrons, the image is displayed on a monitor.The disadvantage of electron microscopes is that you cannot see colour, andcan only study dead cells.Electron microscopes allowed scientists to discover the internal structures ofcells.

Confocal Laser Scanning MicroscopyLasers build up an image via a computer by scanning an object in themicroscope.Highly detailed images can be built up using this technique.The technique does not produce as high a magnification as electronmicroscopy, but it produces clearer images than light microscopy.


Plant and Animal Cells

Part of cell Function

Cell membrane Controls substances entering and leaving the cell

Cytoplasm Where most chemical reactions take place Nucleus

Controls the activities of the cell

Cell wall Supports the cell

Chloroplast Absorb light for photosynthesis

Vacuole Space filled with cell sap (a dilute solution of sugars and

mineral salts)

Function of cell parts

Every organism, except viruses, contains one or more cells.The size of the organism depends on the number of cells and not the size of thecells.

Examiners also like to compare animal and plant cells: PlantCells Animal CellsCell wall present No cell wall present

Chloroplast present No chloroplasts present

Large permanent vacuole present No permanent vacuole present

Nucleus

Cell wall

Chloroplast

Vacuole

Cellmembrane

Cytoplasm


How are the activities of a cell controlled?

All the activities of a cell depend on chemical reactions, which are controlled byspecial molecules called enzymes.

Enzymes are proteins.Proteins have a number of important functions:

· enzymes,· hormones (e.g. insulin)· muscle tissue

The structure of proteinsProteins are made of different amino acids linked together to form a chain:

The chain is then folded to form a specific shape: Thespecific shape of an enzyme enables it to function.

The active site of an enzyme depends on the shape (of the protein), which isheld by the chemical bonds.

Active site of enzyme.A cleft in the protein where aspecific substrate ‘fits’

Fig. 1 – amino acid chain.Numbers refer to the sequence of the aminoacids in the protein chain.This is determined by the ‘triplet code’ of DNA.(See page 9. – How does the nucleus control the cell?)

Fig. 2 – amino acid chain foldedto form a protein (enzyme)


Enzymes

1. Enzymes are proteins2. Enzymes speed up/catalyse the rate of a chemical reaction.3. All enzymes are specific and can only catalyse one type of molecule.

(See lock and key model above).4. Enzymes work best at a particular temperature – the optimum

temperature.· If the temperature is higher or lower than this temperature the

enzymes will catalyse the molecule at a much slower rate.(See page 28 – Interpreting effect of temperature on enzymes.)

· If the temperature gets too high the enzyme’s active site will changeshape and stop working – this is called denaturation.

5. Enzyme work best at a particular pH – the optimum pH.

Properties of enzymes

At any one point in time, there areover 500 different chemicalreactions taking place in every cell.

These reactions are controlled by aspecial type of molecule called anenzyme.

An enzyme is a biological catalyst; it speeds up a reaction, but it does nottake part in the reaction.

How do enzymes work?The way enzymes work isdescribed by the lock and keymodel.

A substrate is held in an active site,this increases the probability that areaction will take place.

The Lock and Key Model

Fig. 1Enzyme and substrate

Fig. 2Enzyme/substratecomplex.Only a substrate with aspecific shape can ‘fit’into the active site. Theenzyme is specific to acertain substrate.

Fig. 3Enzyme and productsEnzyme unchanged atthe end of the reaction.

Enzyme

Substrate

Activesite

Enzyme/substratecomplex

Products


Commercial Application of Enzymes

Biological washing powders contain digestive enzymes.They allow clothes to be washed at comparatively low temperatures.Advantages

· They use less energy.Disadvantages

· Some peoples are allergic to these powders and they can cause skinproblems.

How do biological washing powders work?(This links with work on the digestive system. See pages 27 + 30)

The enzymes that are used are lipase, protease and carbohydrase. Theseenzymes break down large insoluble food molecules into small, solublemolecules that are easier to wash out of the clothes.

· Lipase breaks down fats to fatty acids and glycerol.· Protease breaks down proteins to amino acids.· Carbohydrase breaks down starch to glucose.

Effect of pH on amylase (a carbohydrase enzyme) –an example of an enzyme investigation.

starch agar aroundhole becomes clear

holes

agar jellycontainingstarch

· Three equal sized holes are cut in agar jellycontaining starch.

· Each hole is filled with the same volume andsame concentration of a different enzymesolution and left at 20OC.

· After 30 minutes the Petri dish is flooded withiodine solution.

Hole Result Explanation1

(1% amylaseat pH2)

Agar aroundhole staysblack

Starch notdigested. pHtoo low foramylase.

2(1% amylase

at pH7)

Starch agararound holebecomesclear

Starch hasbeen digested.Optimum pHfor amylase.

3(1% boiled,

cooledamylase)

Agar aroundhole staysblack

Starch notdigested.Amylase hasbeendenatured.

Petridish

most ofstarch agarturns black

Substances Enter and Leave Cells Through the Cell Membrane

Diffusion

Molecules diffuse from an area of high concentration to an area of lowconcentration.This process does not require energy.

The rate of diffusion can be affected by the following factors:1. ConcentrationThe greater the difference in concentration between two areas (theconcentration gradient), the faster the rate diffusion happens.

2. TemperatureAs the temperature increases, the rate of diffusion increases too (moleculeshave more kinetic energy).

3. PressureIf there is high pressure, the molecules will quickly move from the area of highpressure to low pressure.

Molecules are constantlymoving.

Molecules of liquids andgases collide against eachother all the time.

We see this process ofmixing and moving indiffusion.

Oxygen and carbon dioxide pass through thecell membrane by diffusion.

Fig. 1Diffusion.All liquid and gasmolecules havekinetic energy; theyare constantlymoving and mixing.

Cell membrane

CO2O2

Substances•Enter•and•Leave•Cells•Through•the•Cell•Membrane

Osmosis

Osmosis is•the diffusion•of•water•molecules from•an•area•of•high•waterconcentration•to•an•area•of•low•water concentration•through a•selectivelypermeable•membrane.

The•cell•membrane•is a selectively•permeable•membrane;it•lets•some•molecules•through•but•not•others.

Concentratedsolution

Low waterconcentration

Dilutesolution

High waterconcentration

Selectively•permeablemembrane

Solute•moleculese.g.•salts,•sugars

Water•molecules

Pores•in•themembrane

The•pores•in•the•membrane•allow•small•water•molecules•to•pass•through.The•solutes•are•too•large•to•pass•through•the•pores•in•the•membrane.

Fig.1The movement of water is from an areaof high water concentration to an area oflow water concentration through aselectively permeable membrane.

Fig. 2No net movement of water.The concentration of water on both sidesof the membrane is equal. The samenumbers of water molecules move inboth directions.


Osmosis Investigations 1 – Modelling Living Material

Visking tubing is very similar to the cell membrane.It is also a selectively permeable membrane.It has tiny holes (pores), which allow small molecules through, but stopmolecules that are too large to fit through them.You will also come across visking tubing in experiments to do with the digestive system(See page 29).

Selectivelypermeablemembrane

Sugarsolution Water

Most water movesin this direction

Solutionmoves up thecapillary tube

Water

Sugar solution Visking tube

Investigation 1

The concentration ofwater outside thevisking tubing is higherthan the concentrationof water inside thevisking tubing.Water moves inthrough the pores inthe selectivelypermeable membraneby osmosis.This increases thepressure inside thevisking tubing causingthe solution to move upthe capillary tube.

Capillary tube

5% sucrose solution

20% sucrose solution

Tube 1

Visking tubing

Distilled water

Tube 2

Investigation 2

Tube 1Gets bigger (becomes turgid).The concentration of water outside thevisking tubing is higher than theconcentration of water inside. Waterhas moved in through the selectivelypermeable membrane by osmosis.

Tube 2Gets smaller (becomes flaccid). Theconcentration of water inside thevisking tubing is higher than theconcentration of water outside.Water has moved out through theselectively permeable membrane byosmosis.

Sugar molecule

Water molecule


Osmosis and Living Cells

Plant cells

Concentrated solution(Low concentration of water)Water moves out of the cellthrough the selectivelypermeable cell membrane.The cell shrivels.

What happens to living cells in solutions with different concentrations?

Dilute solution(High concentration of water)Water moves in to the cellthrough the selectivelypermeable cell membrane.The cell swells and may burstbecause there is no cell wall.

Concentrated solution(Low concentration of water)Water moves out of the cellthrough the selectivelypermeable cell membrane.The cell becomes flaccid. (Itdoesn’t shrivel because ithas a cell wall.)

Dilute solution(High concentration of water)Water moves in to the cellthrough the selectivelypermeable cell membrane.The cell becomes turgid.(The cell wall prevents it frombursting)

Waterin Water

out

Waterin Water

out

Animal cells

Substances•Enter•and•Leave•Cells•Through•the•Cell•Membrane

More•Osmosis•Investigations

Investigation•4

· Identical•visking•tubes•are•filledwith•the•same•volume•(10ml)•of•asugar•(or•salt) solution.

· Each•bag•contains•a•differentconcentration•of•the•solution.

· The•ends•of•the•bags•are•tied.· The outside•of•the bags•are•dried

and•then•weighed.· They•are•left•for•the same•length

of•time•(30•minutes).· The•outside•of•the•bags are•dried

and•then•weighed•again.· The•%•change•in•mass•is

calculated•(because•all•bags•havea•different•mass – this•allows•afair•comparison).

· The•results•are•plotted•as•a•linegraph.

8.0

6.0

4.0

2.0

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Crynodiad•(M)

Mass hasincreased becauseconcentration ofwater outsidecylinder or bag ishigher than theconcentrationinside.Water has movedinthrough theselectivelypermeablemembrane byosmosis.

Mass hasdecreased

becauseconcentration of

water outsidecylinder or bag is

lower than theconcentration

inside.Water has moved

out through theselectivelypermeable

membrane byosmosis.

Mass has not changed.Concentration of potato cellsor solution inside bag isequal to the concentrationof the solution outside.

Investigation•3

· Potato•cylinders•of the•samelength•(30mm) are dried andthen weighed.

· They•are•placed•in•differentconcentrations•of•blackcurrantsquash•(a•sugar•solution).

· They•are•left•for•the same•lengthof•time•(30•minutes).

· They•are•dried•and•then•weighedagain.

· The•%•change•in•mass•iscalculated•(because•all•cylindershave•a•different•mass – thisallows•a•fair•comparison).

· The•results•are•plotted•as•a•linegraph.

Both•investigations•produce•a•similar•graph•and•the•conclusions•are•identical.

% c

hang

e in

mas

s

Concentration of cell orsolution in bag = 0.55M

Concentration•of•blackcurrant•solution•(M)


Active Transport

When the concentration of a material is lower outside the cell it must beactively transported into the cell (sometimes referred to as active uptake).

During active transport, salts or ions are pumped from an area of lowconcentration to an area of higher concentration.This process requires energy released by the cell.

Example – Uptake of nitrate ions by root hair cells

Fig. 1Diagram of a plantroot with enlargedview of a root haircells.

Highconcentrationof nitrate ionsinside plant

cells.

Lowconcentration of

nitrate ions insoil water.

· Nitrate ions cannot move in by diffusion.· Nitrate ions must be actively transported from the soil water (an area of

low nitrate concentration) to the inside of the plant cells (an area of highnitrate concentration).

Other examples of active transport include:

· Glucose actively transported from the small intestine into the blood.

· Marine algae can use active transport to concentrate iodine in their cellsto concentrations a million times greater than surrounding sea water.

Factors affecting active transport· Active transport needs energy.· Energy is released during respiration.

Any factor that affects the rate of respiration will affect the rate of activetransport:

· Glucose concentration – respiration needs glucose.· Oxygen – aerobic respiration needs oxygen.· Temperature – affects the enzymes controlling respiration.· Toxic substances – e.g. cyanide stops respiration.

Photosynthesis

Photosynthesis

Photosynthesis is the process that ‘produces food’ in green plants and otherphotosynthetic organisms (e.g. algae)

Photosynthesis takes place in the green parts of plants – mostly in leaves.

· Chlorophyll (found in thechloroplasts) absorbs lightenergy.

· This energy is used toconvert carbon dioxideand water into glucose.

· Oxygen is produced as aby-product.

The word equation for photosynthesis:

Carbon dioxide + Water Glucose + Oxygen

Light

Chlorophyll

Enzymes control the chemical reactions of photosynthesis.(See factors affecting enzymes on page 7)

Photosynthesis

Investigating the Conditions Needed for Photosynthesis

As oxygen is given off during photosynthesis, its rate of production can beused to measure the rate of photosynthetic activity.

This is made possible by using aplant that grows in water,e.g. Elodea (also called pondweed)and measuring:

· The volume of oxygenproduced per minute

OR· The number of oxygen bubbles

produced per minute

This allows us to compare resultsunder different conditions.

Investigation – Effect of Light Intensity on the Rate of Photosynthesis

· Measure and record thedistance of the lamp from theplant (e.g. 10cm);

· Count the number of bubblesgiven off every minute;

ORMeasure volume of gasproduced every minute.

· Repeat experiment to check the repeatability of the results;

· Redo the experiment at different distances by moving the lamp a further10cm from the plant each time.

The rate of photosynthesis can also bemeasured by using oxygen or carbondioxide sensors and data loggers tomeasure:

· Oxygen produced per minute;

· Carbon dioxide used up per minute;

Beaker ofwater

Lamp

Elodea(pondweed)

Photosynthesis

Some other factors we can investigate with this experiment:Independentvariable

How to changeindependentvariable

Dependentvariable

Controlled variables

Carbon dioxidelevels

Differentconcentrations ofpotassiumhydrogencarbonatesolutions.

· Temperature.· Distance of light· Same species of

plant.

Temperature Carry out experimentin water baths atdifferenttemperatures.

· Distance of light.· Same species of

plant.· Mass of potassium

hydrogencarbonatein water.

Species of plant Using differentspecies, e.g. Elodea(pondweed),Cabomba, etc.

Volume ofoxygenproducedevery minuteOR Number ofbubbles ofoxygenproducedevery minute · Distance of light.

· Mass of sodiumhydrogencarbonatein water.

· Temperature.

TemperatureThis affects the enzymes controllingphotosynthesis.

(See page 28 for explanation of effects oftemperature

on enzymes)

Light intensityThis provides energy forphotosynthesis. Increasing lightintensity will increase rate ofphotosynthesis (1) up to a point whenanother factor will be limiting (2).

Carbon dioxide concentrationIncreasing carbon dioxideconcentration will increase rate ofphotosynthesis (1) up to a point whenanother factor will be limiting (2).

A limiting factor is the factor that is controlling the rate of photosynthesis at agiven time. Increasing this factor will increase the rate of photosynthesis.

Environmental Factors Affecting the Rate of Photosynthesis

Rate cannot increase further.Temperature or CO2

concentration is a limitingfactor.

Rate cannot increase further.Temperature or light intensityis a limiting factor.

Photosynthesis

Testing a Leaf for the Presence of Starch

1. The leaf is placed in a beaker ofboiling water for 1 minute. (Thisbreaks down the cell membrane,making it easier for iodine to enterthe cell and to remove thechlorophyll in step 3).

2. The leaf is removed from thewater and put into a boilingtube half full of ethanol.

3. The boiling tube containing the leafand ethanol is placed in the hotwater for 10 minutes.(The boiling ethanol will dissolve thechlorophyll. This removes the greencolour from the leaf.)

4. The leaf is removed from the boilingtube and washed in the beaker ofwater.(This softens the leaf)

5. The leaf is placed on a white tile andcovered in iodine.(Any parts containing starch will becoloured dark blue-black).

You need to learn how this experiment works and explain the importance of each step.

· Glucose produced during photosynthesis cannot be stored and is eitherused up or stored as insoluble starch.

· We can test a leaf to see if photosynthesis has happened by testingfor the presence of starch.

· The plant must me kept in the dark for 24-48 before the experiment.This is so that the plant will use up its store of starch.

· Any starch found afterwards must have been formed by photosynthesisduring the experiment.

Photosynthesis

Identifying the Conditions Needed for Photosynthesis

Testing leaves for the presence of starch can be used to show howphotosynthesis is affected by:

· the presence of chlorophyll in the cells of a leaf;· light reaching a leaf;· carbon dioxide in the atmosphere around a leaf.

Experiment 1 – To show that chlorophyll is needed for photosynthesis Wecan test a plant to show it needs chlorophyll for photosynthesis by using avariegated leaf and testing it for the presence of starch.

Before After

Result:Green parts containing chlorophyll- stained blue-black - starch is present.Light parts of plant with no chlorophyll the iodine remains orange – no starchpresent.Conclusion:Chlorophyll must be present in leaf cells for photosynthesis to occur.

Experiment 2 – To show that light is needed for photosynthesisWe can deprive a part of a leaf of light and then test it for the presence ofstarch.

A tin foil stencil is cut out and put on one of the leaves of a plant.This excludes all light, except at the edges and on the pattern.

Result:Parts exposed to light stained blue-black - starch is present.Parts excluded from light iodine remains orange – no starch present.Conclusion:Leaves must be exposed to light for photosynthesis to occur.

Before After

Photosynthesis

Experiment 3 – To show that carbon dioxide is needed for photosynthesisWe can deprive a plant of carbon dioxide and then test it for the presence ofstarch.

Result:Leaves of plant from bell jar with sodium bicarbonate (plenty of carbondioxide) stained blue-black - starch is present.Leaves of plant from bell jar with sodium hydroxide (no carbon dioxide)iodine remains orange – no starch present.Conclusion:Plants need carbon dioxide to be able to photosynthesise.

Does the presence or absence of water affect photosynthesis?It is difficult to set up an experiment to prove that water is needed forphotosynthesis because you cannot easily remove water from the system. Ifyou remove water from a plant it will die.To follow how water is used in photosynthesis you need to use water containingradioactive isotopes of hydrogen or oxygen.

Uses of glucose produced in photosynthesis:

1. Glucose is used to release energy in respirationRespiration is taking place all the time in plant cells.

2. Glucose can be changed to starch and stored.

3. Glucose can be used to make cellulose which make up the body of plants(e.g. cell walls)

4. Glucose can be used to make proteins, which also make up the body ofplants.

Airtight seal using Vaseline

Respiration

Aerobic Respiration

Releasing energy from food (glucose) using oxygen

Through aerobic respiration, a cell gets its energy to do work or grow.Respiration occurs all the time (day and night) in all plant and animal cells.

You need to le arn the f ormula f or respir at i on:

Glucose + Oxygen Carbon Dioxide + Water + ENERGY

Water and carbon dioxide are the waste products that are removedfrom the body.

In animals, muscle cells use the energy to contract, and move their bodies.Some energy is released as heat, and this keeps the body temperatureconstant.

Investigating the energy released as heat during respiration.

Three flasks were set up(as shown) and theirtemperature wasmeasured at the beginningand the end of a week.

Thermometer

Cotton wool bung(Allows air to passthrough. A rubberstopper wouldprevent air passingthrough.)

Thermos flask(Prevents heatloss)

Flask A Flask B Flask C

Flask temperature (oC)Flask Contents of flaskAt start At the

endA Pea seeds 20 32B Boiled pea seeds 20 28C Boiled pea seeds in disinfectant 20 20

Flask A – Temperature has increased because heat is released duringrespiration from the living cells of the peas.Flask B – Temperature has increased because microbes such as bacteriaare present. These release heat during respiration in their cells.Flask C – A control flask. It shows the difference between living and deadpeas. (The disinfectant has killed any bacteria).

Peas

Respiration

Anaerobic•Respiration

Releasing•energy•from•food•without•using•oxygen

This•is•what•happens•when•there•is•not•enough•oxygen•available.It•releases•much•less•energy•from•each•molecule•of•glucose than•aerobicrespiration because•the•glucose•molecule•is•not•completely•broken•down.

You also need to learn this equation:

Glucose Lactic•acid

Disadvantage•of•anaerobic•respiration· Lactic•acid•is•released•in•the•muscles,•which•can•cause•pain•(cramp).

Advantage•of•anaerobic•respiration· Muscles•can•release•energy•for•a•short•period•when•not•enough•oxygen•is

available,•e.g.•100m•sprints.

What•is•an•‘oxygen•debt’?

After•using•anaerobic•respiration•to•release•energy,•an•‘oxygen•debt’ iscreated.Breathing•deeply•after•finishing•exercise,•to•get•oxygen•to•the•muscle,•breaksdown•lactic acid•to•water•and•carbon•dioxide.

It•is•a•good•measure•of•fitness•to•see•how•quickly•you•can•recover•from•an‘oxygen•debt’.A•fit•person•can:

o Breathe•in•a•greater•volume•of•air.o Produce•less•lactic•acid,o Break•down•lactic•acid•faster.

Anaerobic•Respiration•in•Yeast•(Fermentation)

Anaerobic•respiration•in•yeast•results•in•different•products•compared•to•animals:

Another equation you also need to learn:

Glucose Ethanol•+•Carbon•dioxide

Humans,•who•brew•alcoholic•drinks•by•growing•yeast•in•anaerobic•conditions,use•the•reaction.

The Digestive System


To be of use to the body, food must move from the digestive system into theblood.· The molecules of food must be small enough and soluble to pass through:

e.g. vitamins, minerals, water

· Other molecules are too large and insoluble:e.g. starch, proteins, fats

Before these molecules can be absorbed into the blood, they must be digestedto small, soluble molecules.

Fibre is excreted from the body as faeces as it is not possible to digest andabsorb it into the blood.

Functions of the Digestive System:· Digest large insoluble molecules to small soluble ones by using

enzymes.· Absorb small soluble molecules into the blood.

Food Digestive Enzyme Product Used for StarchCarbohydrase · Glucose Provide energy

Proteins Protease · Amino acids Making proteinsfor growth andrepair

Fats Lipase · Fatty acids

· Glycerol

Provide energy

Digestive EnzymesEnzymes speed the process of breaking down large insoluble molecules tosmall, soluble molecules. Every enzyme is specific to only one food group.(See page 7). (See page 7 – lock and key model)

1. Ingestion

2. Digestion(Large insolublemolecules brokendown into smallsoluble molecules)

4. Egestion(Undigested foodpassed out)

3. Absorption(Small soluble moleculestaken into blood stream)


The Effect of Temperature on Enzyme Action

The effect of temperature on enzymes can be demonstrated using the followinginvestigation.

Investigating effect of temperature on the activity of lipaseThis investigation shows:

· how lipase activity changes with temperature· how indicators can help us to follow chemical reactions.

2ml lipase

· 5ml milk· 7ml sodium

carbonate· 5 drops of

phenolphthalein

1. Place test tubes containing milk, sodiumcarbonate and phenolphthalein in differentwater baths until the contents reach thesame temperature as the water bath.

2. Add 2 ml of lipase and start timing.

3. The time taken for the solution to lose itspink colour is recorded.

How is rate of reaction calculated(s-1)?= 1

time taken for solution to lose colour.

Why does the phenolphthalein change colour?· When the fat in milk breaks down, fatty acids and glycerol are produced.· The fatty acids lower the pH of the mixture, which changes the colour of

the phenolphthalein from pink to colourless.

Rat

e of

reac

tion

(s-1

)

Temperature OC

Interpreting effect of temperature on enzymes

Enzyme and substrate have morekinetic energy and collide more often.The rate of reaction increases.

Optimumtemperature

High temperaturescause active site ofenzyme to changeshape.Enzyme is denatured.

Kineticenergy islow.There arefewercollisionsbetweenenzyme andsubstrate.


Evaluating Visking tubing as a model for a gut

Example of a visking tubing modelThese experiments very often combine theory from different parts of Biology 2.

· Understanding how a selectively permeable membrane works;· Understanding how enzymes work;· Food tests;· Diffusion and osmosis.

1. A visking tube is filled with a mixture ofstarch, glucose, fats and proteins andleft for 30 minutes.

2. The water is then tested for starch, glucose,fats and proteins.

ResultsContent of water

At start After 30minutes

Starch - -Glucose - +Fat - -Protein - -

ConclusionStarch, fat and protein molecules are too big to pass through the holesin the Visking membrane.Glucose molecules are small enough to pass through the holesin the Visking tubing.Similarities of model Limitations of the modelThe food molecules are contained in atube whose walls are permeable only tosmall molecules.

The Visking tubing membrane is smooth,a gut lining is folded and folded againwith a larger surface area for its length

The food in the tube is a mixture of largeand small molecules.

A real gut is surrounded by blood flowingin vessels that take away the solubleproducts of digestion. This maintains aconcentration gradient between the gutcontents and the surrounding blood.

The tube is surrounded by liquid thatcontains a low concentration of foodmolecules.

The visking tubing does not move thefood around by muscular contractions.

- = absent+ = present

Visking tubing is a smooth selectively permeable membrane with pores in it.These pores are small holes that are large enough to allow water and othersmall molecules through. They are too small to allow large molecules through.(See page 15 and 17 for its use in osmosis investigations)

(gut contents)

(gut wall)

(blood)


Digestion of Fats, Proteins and Carbohydrates

Testing for Products of Digestion

Food Reagent Method Positive ResultProtein Biuret · Add blue Biuret to some food in Lilac colour a

test tube.Glucose Benedict’s · Add blue Benedict’s to some

food in a test tube.· Place the test tube in boiling

water bath for 5 minutes.

Turns green,orange thenbrick red.(Colour changedepends onconcentrationof glucose)

Starch Iodine · Add brown iodine to somefood.

Blue-black colour.

Starch Glucose

Fat Glycerol + Fatty acids

Protein Amino acids


Organs of the Digestive System and their Functions

MouthStarch digestion beginsby carbohydrase insaliva.

Small intestine· Continued digestion

of carbohydrates bycarbohydrase toglucose and proteinsby protease to aminoacids. Lipase digestfats to fatty acids andglycerol.

· Soluble products ofdigestion absorbedinto blood.

Large intestineAbsorption ofwater

PancreasSecretes lipase,protease andcarbohydrase intothe small intestine.

StomachSecretesprotease,which digestsprotein.

Oesophagus

AnusEgestion of waste

LiverProduction andsecretion of bile.

Gall bladderStores bileproduced bythe liver.

Bile ductCarries bile tosmall intestine.

The•Digestive•System

How•is•food•moved•along•the•digestive•system?

Food•is•moved•along•the•digestive•system•by•the•contraction•of•muscles•in•thegut•wall.•This•movement•is•called peristalsis.

The•gut•walls•contain•two•layers•of•muscles•running•in•different•directions:

Ball•of•food(bolus)

1. Muscles inthe•wall•of•thegut contract.

2. Food•ispushedalong•thedigestivesystem.

What•does•bile•do?

Bile•is•produced•in•the•liver•and•stored•in•the•gall•bladder.Bile•is•not•an•enzyme.Bile emulsifies fats,•which•means•breaking•down•large•droplets•of•fat•to•smallerdroplets•(a•physical•change•not•a•chemical•change).This•increases•the•surface•area•of•the•fats•for•the•enzyme•lipase•to•work•on.

Large•oil droplet(Oil is a type of fat)

Small droplets of•oil•have•alarger•surface•area•for•enzymesto•work•on•and•digest.

· Bile will speed up the rate ofreaction of any investigation usinglipase.

Fig. 1Peristalsis intheoesophagus.

Bile

Respiratory System

The Respiratory System

Nasal Cavity

Diaphragm

LungAlveolus

Bronchiole

Bronchus

TracheaRib

Intercostal muscles

Heart

The function of the respiratory system is to:· get oxygen into the blood· remove carbon dioxide from the blood.

Respiratory System

Breathing

1. Intercostalmuscles contract.Rib cage movesup and out.

2. Diaphragmcontracts,

moves downand flattens.

5. Lungs inflateand draw air into

the lungs

3. Volume ofthorax

increases

4. Pressure insidethorax decreases

Breathing in(Inspiration)

1. Intercostal musclesrelax.Rib cage moves downand in.

2. Diaphragmrelaxes andmoves up

5. Air pushedout of the

lungs

3. Volume ofthorax

decreases

4. Pressure insidethorax increases

Breathing out(Expiration)

Respiratory System

Model of the Respiratory System

Part of model Part of realbody

How model isthe same as thebody

How the model isdifferent from thebody

Bell jar Ribcage Approximately thesame shape.

Has no musclesattached to ‘ribs’ andso is rigid and cannotmove up and down/ inand out.

Balloon Lung Inflates anddeflates.

· Single bag, not aseries of tubes withterminal alveoli;

· balloon does not fillthe space, or stickto the inside of theribcage.

Rubber sheet Diaphragm Domed upposition matchesposition when airis exhaled.

· pulls down furtherthan flat;

· has to be pushed inand out by us;

Tube into balloon Trachea The windpipe is arelatively widetube conductingair into the lungs.

Is not held open byhorseshoe shapedstiffening rings.

Rubber sheet

Bell jar

Balloon

Glass tube through cork

Respiratory System

Gaseous Exchange in the Alveoli

The alveoli are the respiratory surface of the lungs.The alveoli are full of air and are covered on the outside by blood capillaries.

Oxygen diffuses across the walls of the alveoli from the air into the blood.Carbon dioxide diffuses across the walls of the alveoli from the blood into theair in the alveoli.

How are alveoli adapted for gaseous exchange?

O2

CO2

Red blood cells(carry oxygen)

2. Large surface areaIncreases gaseous

exchange.(Provided by a largenumber of alveoli.)

3. Thin walls Gasescan pass

through by diffusionmuch easier.4. Moist lining

To dissolveoxygen so that it

can diffusethrough the

alveolus wall.

1. Good blood supplySo that more gases can

be exchanged.

Fig.1 Outside view of alveolus. Alveolus

Alveoluscut open

Bronchiole

Air in and out

Wall ofalveolus

Bloodcontaining

oxygen

Blood withoutoxygen

Fig.2View of alveolus cutopen.

Respiratory System

Keeping the Lungs Clean

The air youbreathecontains dust,bacteria andviruses.The alveoli arevery delicate,so the air hasto be ‘cleaned’before itreaches them.

Mucusproducing

cells

Trachealcells with

cilia

Cilia move the mucus.

The mucus traps any dust and bacteria in the air.· The cilia move the mucus out of the lungs into

the back of your throat in a wave like motion (like aMexican wave).

· You swallow the mucus and acid in the stomachdestroys any bacteria.

Electron micrographshowing tracheal

cells with cilia.

Differences between inspired air and expired air

Limewater test forcarbon dioxide

The limewaterturns cloudy

Inspired air is breathed in and expired air is breathed out.The body absorbs oxygen from inspired air and adds carbon dioxideand water vapour to expired air.

· Expired air has less oxygen than inspired air.· Expired air has more carbon dioxide than inspired air.· Expired air has more water vapour than inspired air.

Inspiredair

Expiredair

Oxygen 21% 16%Carbon dioxide 0.04% 4%Water vapour Varies

SaturatedNitrogen 79% 79%

Respiratory System

Effects of tobacco smoke on the body

Effects of smoking on cilia and mucus

Smoke from tobacco paralyses cilia in the trachea and bronchi for aboutan hour after a cigarette has been smoked.

Dry dust and chemicals in the smoke irritate the lungs, and clog up the mucus.Cilia normally sweep this mucus away, but smoke has paralysed them. Mucusbuilds up and if this becomes infected it can cause bronchitis.

Coughing causes damage to the alveolar walls, this reduces their surface areafor gas exchange and results in the sufferer being short of oxygen.

Tobacco smoke contains many chemicals

Tar is a dark brown, sticky substance, which collects in the lungs as thesmoke cools. It contains carcinogens – chemical substances known tocause cancer.

Carbon monoxide is a gas that combines with haemoglobin, and reduces theoxygen-carrying capacity of the blood by as much as 15% in heavy smokers.

Nicotine is the addictive drug that makes smoking such a hard habit to give up.Nicotine makes the heart beat faster and the blood pressure rise.

Lung cancer90% of lung cancers are thoughtto be caused by smoking.One in ten moderate smokers,and one in five heavy smokersdie from the disease.

EmphysemaThe chemicals in tobacco smokedamage the walls of the alveoli,and they eventually break down.This reduces their surface area forgas exchange and results in thesufferer being short of oxygen.

Canceroustumour

EmphysemaWalls of alveoli have

broken down.

Smoking related diseases

Respiratory•System

What’s•in•cigarette•smoke?

How•have•attitudes•to•smoking•changed?· Less people smoke now;· More smokers are trying to give up;· There•are•more•help•lines•and•advertising•to•encourage•people•not•to

or to stop smoking;· Smoking is socially unacceptable;· There are no cigarette advertisements;· Sponsorship of sports by tobacco companies has been banned;· Cigarette packets carry health warnings;· Cigarettes for sale are no longer displayed in large shops;· Smoking•has•been banned•in•public•places.

Why•have•attitudes•to•smoking•changed?· People know that nicotine is an addictive drug;· People know that smoking can cause lung cancer and emphysema;· The•dangers•of•smoking•are•now•recognised,•e.g.•passive•smoking.

The•following•apparatus•can be•used•to•analyse•the•smoke•from•cigarettes:The following•apparatus•can•be•used•to•analyse•the•smoke•from•cigarettes:

Cigarette

Whitecottonwool pH•indicator

Thermometer

Result· The•white•cotton•wool•will•turn•brown•as•it•filters•tar•from•the•tobacco

smoke.· The pH indicator will turn red; this shows tobacco smoke is acidic.

The•air•is•drawn•through•the•apparatus•before•the•cigarette•is•lit.This•is•the control•experiment.This•is•to•show•that•it•is•the•smoke•from•burning•tobacco•that•causesany•changes•and•not•drawing•air•through•unlit•tobacco.

Suction•pump

Smoking – Ethical•Issues

Blood and Circulation

Harvey’s ApproachPrior to Harvey’s discovery, it was thoughtthat the blood was formed in the liver, andwas used up as it went around the body.

Harvey used a scientific approach, whichincluded:

· Dissection of humans and otheranimals.

· A detailed study of the structure of theheart.

· Observation of living hearts in fish.· Experiments on human circulation.· Mathematical models.

Fig. 1WilliamHarvey

A Historical PerspectiveIn the early 1600s William Harvey, a physician toKing Charles I. suggested that blood circulatedaround the body, flowing from the heart througharteries and returning through veins.

Fig. 2 Harvey’s experiment onhuman circulation.

The PulmonarycirculationBlood pumpedform the heart tothe lungs andback to the heart.

The SystemicCirculationBlood pumpedform the heart tothe body andthen back to theheart.

The Human Circulatory System - A double circulatory system.The blood must pass through the heart twice before completing one wholecircuit of the body.

Oxygen entersthe blood in thelungs.

Oxygen entersthe blood in thelungs.

Rightside

Leftside

Fig. 3Diagram showinga doublecirculatorysystem.

Oxygenated blood

Deoxygenated blood


Blood

Blood is made up of

Red bloodcellscarry oxygen

White bloodcells defendthe bodyagainstpathogens

Plateletsclotting ofblood

Plasmacarriesdissolvedsubstances

Red blood cell

Fig.3 – Illustration of blood smear

PlateletWhite blood cell

Fig 2. Micrograph of a bloodsmear.The centre of red blood cellsappear paler because theyhave no nucleus and thereforemore light from the microscopepasses through them.

Fig. 1 – Illustration of the components of blood.

Examining blood smears(These are diagrams you should be able to label).


Blood

Red Blood Cells.These cells carry oxygen around the body.

They are flattened, biconcave, disc shapedcells; they are red in colour because of apigment called haemoglobin. This joins withoxygen to transport it around the body.Red blood cells don’t have a nucleus.

Iron is needed to produce haemoglobin. If there is a shortage of iron a personwon’t have enough red blood cells, this is called anaemia, less oxygen will becarried around the body.

Fig. 1 – micrograph of redblood cells

White blood cellsThese cells defend the body against pathogens (microbes that cause disease).

They are bigger than red blood cells, and have a nucleus, but don’t contain apigment so are colourless.If you have an infection the number of white blood cells in you body increasesrapidly.There are many types pf white blood cells, but you only need to learn about twoof them:

· Phagocytes – ingest and digest ‘foreign’ cells.· Lymphocytes – produce antibodies and antitoxins.

Comparing red and white blood cells(You should be able to draw, label and compare a red and white blood cell)

Red blood cellsFig. 2 – side view (left )and front view (right) ofred blood cell (not to scale)

White blood cellsFig. 3 –white blood cell (phagocyte)(not to scale)

No nucleus present Nucleus presentRegular disc shaped Irregular shapeSmaller than white blood cells Larger than red blood cells

cellmembrane

cell membrane

nucleus

Blood and Circulation.

PlateletsPlatelets clot the blood.

When the skin is cut you bleed.Platelets make the blood clot, forminga thick jelly. This hardens to form a scab,preventing bleeding and blood loss. Thescab keeps the wound clean as new skingrows underneath.This prevents pathogens from entering the body and bacterial infection.

Fig. 1 – micrograph showingred blood cells clotting.

Fig 2. – Illustration of bloodclotting in a wound

Plasma

Plasma carries dissolved substances.

This is the liquid part of blood. It is pale yellow in colour and is 90% water.

Plasma carries many dissolved substances around the body:

· Small soluble food molecules, e.g. glucose, amino acids, etc.· Waste chemicals produced by the body, e.g. carbon dioxide from

respiration and urea produced by the liver.· Hormones carried from the endocrine glands to their target organs,

e.g. insulin.· Antibodies produced by lymphocytes (white blood cells).· Mineral salts, e.g. sodium ions.

Blood•and•Circulation

The•Heart

Structure•of the Heart

The•function•of•the•heart•is•to•pump•blood.The•heart•is•made•of•a•special•muscle called•cardiac•muscle.

There•are•blood•vessels•on•the•outside•of•theheart – the coronary•arteries.These•supply•oxygen•and•glucose•to•the•heartmuscle.Without a•steady•supply•of•oxygenated•bloodthe•heart•muscle•couldn’t•keep•contractingand•pumping•blood.

If•a•blood•clot•blocks•a•coronary•artery,•theheart•muscles•won’t•get•enough•oxygen•andwill•stop•working – this•is•a•heart•attack.

Fig. 1 – Illustration showing the outside of a humanheart. The blood vessels shown are the coronaryarteries.

Valves preventbackflow•of•bloodwhen•ventricles•relax.

Aortaan artery•carryingblood•to•the•body.

Pulmonaryvein carryingoxygenatedblood•from•thelungs•to•theheart.

Left atrium

Valvepreventsbackflow•ofblood•to•atriumwhen•theventriclecontracts.

Left•ventricle

Pulmonary•arterycarrying•deoxygenatedblood•from•the•lungs•tothe•heart.

Vena•Cavavein•carryingblood•fromthe•bodyback•to•theheart.

Right•atrium

Right•ventricle

Fig. 2 – illustration showinginternal structure of the heart.


Facts you must learn about the heart:

· The heart is divided into 2 halves.· Blood flows in one direction through each half of the heart.· There are valves between the atria and ventricles. These can close to

stop backflow of blood when the ventricles contract.· There are valves at the bottom of the bottom of the pulmonary artery and

aorta to prevent backflow of blood to the ventricles when they relax.· There are tendons attached to the valves so they don’t get pushed inside

out.· The right side of the heart pumps blood to the lungs.· The left side of the heart pumps blood to the body.· The atria (more than one atrium) have thin walls because they only pump

blood to the ventricles.· The ventricles have thick muscular walls, because when they contract

they have to pump blood out of the heart.· The left ventricle has a thicker muscular wall than the right ventricle

because it pumps blood to all parts of the body – the right ventricle onlypumps blood to the lungs.

Flow of Blood Through the Heart

· The vena cava carries blood from the organs of the body to the rightatrium.

· Blood passes through a valve to the right ventricle.· The right ventricle contracts, pumping blood through the valve into the

pulmonary artery.· The pulmonary artery carries the blood to the lungs where it is

oxygenated.· The pulmonary vein carries blood back from the lungs to the left

atrium.· Blood passes through the valve into the left ventricle.· The left ventricle contracts, pumping blood through the valve into the

aorta.· The aorta carries blood form the heart to the organs of the body.

QWC questions sometimes ask you to describe the flow of blood through the heart. Always check to see whereyou need to start and finish.Remember, you will lose marks by including irrelevant information!


Blood Vessels

Fig.1 – (Left to right) Illustration of an artery, capillary and vein (not drawn to scale).

· Arteries have thick walls because they carry blood under pressure awayfrom the heart.

· Veins have thins walls because they carry blood under low pressure backto the heart.

Artery

Arteriole

Capillaries

Vein

Venule

Fig. 2 Illustration showing structural relationship between blood vessels.

CapillaryBody cells

12

Fig. 3Diffusion betweencells andcapillaries.1 Oxygen andglucose.2. Carbon dioxide.

Capillaries are the smallest blood vessels that carry blood through the organs ofthe body.

· They form extensive networks so that no cell is far away from a capillary.· Their walls are very thin to allow materials to diffuse easily between the

blood and the body cells.

Plants, Water and Nutrients

Investigation 1

1. Tie a polythene bag around the stem and pot of a plant.(This prevents water evaporating from the soil in the pot.)

2. Place it inside a large bell jar that stands on a vaselined glass plate.(This prevents exchange of gases with the outside of the jar.)3. Leave in a partly exposed, sunny site.4. Observe the bell jar after 24 hours.

Investigating Water Loss in Plants

Bell jar Plant

Glassplate

Polythene bag

Droplets

ResultDroplets of water have formed on the inside of the bell jar.

ConclusionThe water on the inside of the jar must have come from the plant becauseno water can pass into the jar or evaporate from the soil.


Investigation 2 – Estimating the rate of transpiration from a plant cutting

Method1. Cut a shoot from a plant and place

it in a measuring cylinder.2. Pour a thin layer of oil over the

surface of the water.(This prevents evaporation ofwater directly from the surface ofthe water.)

3. Weigh the whole apparatus.4. Record the results in a table.5. Leave for a period of time.6. Weigh the apparatus again.7. Calculate the change in mass.

(This experiment can be carried out bystudying change in volume of water,however it is not as accurate.)

ResultsThe mass of the apparatus will have decreased.

ConclusionThe mass has decreased because water has been lost from the measuringcylinder.Because water couldn’t evaporate directly from the surface of the water itmust have travelled up the stem of the plant and evaporated from theleaves. This movement of water is called transpiration.

Factors that could affect the result of the investigation:

· The humidity of the air, or any breezes in the room could affect the rateof water loss from the cuttings.

· Healthy cuttings will lose water steadily; unhealthy ones may not workso well.

Plants,•Water•and•Nutrients

Investigation•3 – Investigating•Stomata

Method•for•an•epidermal•impression•of•leaf1. The•upper•surface•of•a•leaf•is•painted•with•a•thin•layer•of•clear•nail•varnish.2. Leave•for•10 – 15•minutes•to•allow•the•varnish•to•dry.3. Remove•the•layer•of•varnish•by•attaching•clear•sticky•tape•to•it,•peeling•it

from•the•leaf•surface•and•sticking•it•to•a•microscope•slide.4. Observe•the•slide•with a•microscope•and•count•the•number•of•stomata•in•the

field•of•view.5. Repeat•steps•1•to•4•for•the•lower•surface•of•a•leaf.6. Compare•the•results.

Fig. 1 Upper surface of a privet leafshowing no stomata present.

Fig. 2 Lower surface of a privet leafshowing stomata present.

The stomata are•pores•in•surface•of•a•leaf•that•allow•water•vapour•to•pass•out.They•also•allow•gaseous•exchange•to•occur.A pair•of•guard•cells controls•the size•of•a•stoma.•These•can•change•theirshape•causing•the•stoma•to•open•or•close.•This•allows•a•plant•to•control•howmuch•water is•lost.

Fig. 3 Illustration of stomata. The differences in the thickness of the cell walls of theguard cells cause them to change shape when their water content changes leading toopening and closing of the stomatal pore.

Guard•cell

Stoma

Nucleus

Thin•cell•wall

Chloroplast

Thick•cell•wall

ResultThe•lower•surface•contains•the•highest•number•of•stomata.ConclusionThe•function•of•stomata•is•to•allow•gas•exchange•between•the•cells•of•the leafand•the•air,•however•water•is•also•lost•by•diffusion•through•open•stomata.Having•most•of•the•stomata•on•the•lower•surface•of•the•leaf•shades•them•fromthe•heat•of•the•sun,•and•is•an•adaptation•to•reduce•water•loss.


Investigation 4 – Comparing Water Loss From Leaves

AnalysisLeaf Appearance after 10 days Explanation1 Slightly wrinkled As there are far less stomata on the upper

surface of a leaf the Vaseline has onlyprevented a small amount of water loss.

2 Almost fresh As most stomata are found on the lowersurface the Vaseline has prevented mostof the water being lost from the leaf.

3 Fresh The Vaseline has prevented water lossthrough the stomata on both surfaces.

4 Wrinkled and dried out Water has been lost through the stomataof both surfaces.

(This investigation can be done as a ‘stand alone’ or as a variation of “Investigation 2”and “Investigation 5”.)

Quantitative or Qualitative Result?The result in the table is a description and therefore can’t be graphed; this is aqualitative result.If the mass of the leaves were measured before and after 10 days and thepercentage change in mass was calculated we would have a result that could begraphed; this is a quantitative result.

Fig. 2 – Appearance of leaves after 10 days.

Fig. 1 – Appearance of leaves at start of investigation.

Method· Four leaves were removed from a green plant and their stalks covered with

Vaseline (this prevents water loss from the cut ends).· Their surfaces were treated as follows:

o Leaf 1 – Vaseline on upper surface of leaf,o Leaf 2 – Vaseline on lower surface of leaf,o Leaf 3 – Vaseline on upper and lower surface of leaf,o Leaf 4 – No Vaseline.


Investigation 5 – Using a Simple Potometer to Measure Transpiration Rate.

Fig. 1 A simple potometer.An air bubble is introduced into the capillary tube at the start of the investigation. Aswater evaporates through the stomata of the leaves water is drawn up the capillary tubecausing the bubble to move.The investigation makes the assumption that water uptake is equal to the transpirationrate. However not all water is lost from the leaves, some is taken up by leaf tissue or usedfor photosynthesis.

Plant shoot

BubbleScale

Tap

Water reservoir

Beaker of water

Capillary tube

Method1. Set the bubble to it’s starting position by using the tap to release water

from the water reservoir.2. Measure the time taken for the bubble to move a set distance

ORMeasure how far the bubble moves in a set period of time.

3. Record the results.4. Repeat the experiment.

Environmental factors that affect water loss from a plant· Temperature – as temperature increases water molecules have more

kinetic energy and therefore move faster. This increases transpiration.· Humidity - increasing humidity reduces the concentration gradient of

water between the air and the intercellular spaces in the spongy layer ofthe leaf – this decreases the diffusion of water out of the stomata.

· Wind speed – increasing wind speed carries away more water vapourfrom near the leaf surface and increases the rate of diffusion of watervapour out of the stomata.


Structure of a Leaf

1. Epidermis

3. Spongy layerC

ontains large airspaces to allowgaseous exchange.

4. Epidermis

5. Guard cells

6. Stoma

7. XylemTransports w

ater

8. PhloemTransports sugar

9. Air space

Allows gas

exchangew

ith leaf

10. Cuticle

Waxy, w

aterproof layerto reduce w

ater loss

2. Palisade layerC

ontains cells packedw

ith chloroplasts forphotosynthesis.

Tran section (T.S.) of a leaf


The Transpiration StreamThere is a constant flow of water through a plant; this is called thetranspiration stream.

Fig. 2 Annotated illustration of the transpiration stream

Observation of root hair cells

Fig. 3 Root with root hairs(left) and magnified view ofroot hair (above).

Water enters the plant from an areaof high concentration of water in thesoil to an area of lower waterconcentration inside the root hair cell,through it’s partially permeablemembrane, by osmosis.

The increased surface area of theroot hair cell allows the plant to takein more water faster by osmosis.

1. Water enters the plantthrough root hair cells byosmosis.

2. Water moves fromcell to cell in the rootby osmosis.

3. Water moves intothe xylem by osmosis

4. Water molecules sticktogether and this causes waterto be pulled up the xylem as acolumn.

7. Water diffuses from the airspaces in the spongy layerout of the stomata into theair.

6. Water evaporates from some ofthe leaf cells, causing more waterto be pulled up the xylem.

5. Water moves from cell to cellin the leaf by osmosis.

Water

2. Water is carried throughthe plant by the xylem.

Water enters the roothairs by osmosis.

Fig. 1 The transpiration stream

3. Water evaporates fromthe leaf through thestomata


Active Uptake of Mineral Ions by Plant Roots

When the concentration of a material is lower outside the cell it must be activelytransported into the cell (sometimes referred to as active uptake).

Example – Uptake of nitrate ions by root hair cells

Fig. 1

Diagram of a plantroot with enlargedview of a roothairǺcells.

Highconcentrationof nitrate ionsinside plant

cells.

Lowconcentration of

nitrate ions insoil water.

· Nitrate ions cannot move in by diffusion.· Nitrate ions must be actively transported from the soil water (an area of low

nitrate concentration) to the inside of the plant cells (an area of high nitrateconcentration).

During active transport, salts or ions are pumped from an area of lowconcentration to an area of higher concentration.

This process requires energy released by the cell during respiration.

Factors that affect active transport:

· Active transport needs energy.· Energy is released during respiration.

Any factor that affects the rate of respiration will affect the rate of activetransport, e.g.:

· Glucose concentration – respiration needs glucose.· Oxygen – aerobic respiration needs oxygen.· Temperature – affects the enzymes controlling respiration.· Toxic substances – e.g. cyanide stops respiration.

Factors that affect active transport will have an effect on the rate of uptake ofions from the soil into root hair cells.

Plants,•Water•and•Nutrition

Plant•Transport•SystemsPlants•have•two•separate•transport•systems.

· Phloem•vessels (tubes) – transport•sugar and•other•substances•thatare•produced•by•cells•to•all•the•other•parts•of•the•plant.

· Xylem•vessels (tubes) – transport•water and mineral•ions from•theroots•to•the•rest•of•the•plant.

Phloem•VesselsPhloem•carries•sugar•from•the•photosynthetic•areas•to•other•parts•of•the•plant.Sugar is•moved•to•other•parts•of•the•plant•for use•in•respiration and•convertedinto starch•for•storage.The•transport•of sugar•is•not•fully•understood•so•plant•scientists•are•stillinvestigating•it.

Phloem•and•xylem•vessels•usually•run•together•side•by•side.Groupings•of•phloem•and•xylem•vessels•are•called vascular•bundles.

Fig. 1 – T.S. of a sunflowerstem showing positions ofvascular bundles.

Vascular•bundle

Xylem•vesselsPhloem•vessels

Fig. 2 – T.S. of a sunflowerstem showing a singlevascular bundle.


Xylem•VesselsThe•function•of•xylem•vessels•are:

1. Transport•of•water – from•the•roots•to•the•rest•of•the•plant.2. Transport•minerals – minerals•such•as•nitrates•phosphates•and

potassium•are•transported•by•xylem•around•the•plant•dissolved•in•water.3. Support•the•plant – the•xylem•vessels•in•the•shoots•and•roots•of•mature

plants•are•inflexible•and•strong•and•give•support•to•the•plant.

Fig. 3 Turgid cell Fig. 4 Flaccid cell

Fig. 1Flower atbeginning.

Fig. 2Flowerafter afewhours.

ExplanationWater•and•dye•are•pulled•up•through•xylem•vessels.When•they•reach•the•flower•petals•the•water•evaporates•from•pores•in•thepetal•surface•but•the•dye•remains•in•the•cells•of•the•petals.The•petals•become•coloured•as•dye•accumulates•in•them.This•procedure•could•be•useful•for•producing•quantities•of•unusuallycoloured•flowers.

The Importance•of•WaterWater•is•important•to•the•plant•for:

1. Use in photosynthesis;2. Transport of minerals;3. Support.

How•does•water•support•the•structure•of•plant?Water•provides•support•due•to•the•pressure•of•the•vacuoles•pushing•against•thecell•walls•and•this•keeps•the•cells•turgid•and•prevents•cells•becoming•flaccid•andplants•wilting.

Investigation•into•the•movement•of•a•dye•through•a•flowering•plant1. Take•a•white•flower•with•a•long•stalk,•e.g.•a•chrysanthemum•and•cut•the

stalk•carefully•lengthwise.2. Put•each•half•of•the•stalk•into•a•measuring•cylinder•(or•boiling•tube)

containing•either•plain•water•or•water•to•which•food•dye•has•been•added.3. Tape•the•measuring•cylinders•to•a•plastic•tray•so•that•they•don’t•fall•over.4. Leave•the•flower•for•a•few•hours.5. Observe•where•the•dye•ends•up•in•the•flower•head.


Healthy•Plant•Growth

Plants•can•only•grow•well•if•they•are•in•a•soil•rich•in mineral nutrients.Plant•roots•absorb•the•minerals•from•the•soil•and•use•them•to•produce•materialsthat•they•need•to•grow.

Three•main•minerals•are•needed:· Nitrates· Potassium· Phosphates

NPK fertilisers•that•contain•nitrates,•phosphates•andpotassium•can•be•added•to•soil•to•increase•the•mineralcontent.

Investigating•Plant•Nutrient•Requirements

1. Three•healthy•plants•of•the•same•species•and•age•are•grown•in•an•equalvolume•of•aerated•mineral•solutions.

2. After•eight•weeks•the•growth•of•the•plants•are•observed.

AnalysisPlant Description Explanation

1 Healthy growth Complete•solution•of•minerals2 Poor•growth Nitrogen•deficiency3 Yellowing•of•leaves Potassium•deficiency4 Poor•root•growth Phosphate•deficiency

Plant•1 Plant•2 Plant•3 Plant•4

Monitoring the Environment, Energy Flow and Nutrient Transfer

What effects do humans have on the environment ?

Assessing Environmental EffectsDuring the planning process, developers must carry out an environmentalimpact assessment for each development to show the local authority beforestarting work. There can be a large fine for failing to do this.

When the human population was less, the effect of human activity on theenvironment was lower and localised. As populations have increased, the effectson the environment have increased also.

These days more and more species are becoming extinct because man isdestroying their habitats.

Habitats are being destroyed because ofincreases in the use of land for :

· Building· Quarrying· Dumping rubbish· Agriculture

The purpose of the environmentalimpact assessment is:

1. ensure the timing of anydevelopment has the leastpossible impact on wildlife;

2. show if any rare orendangered species arepresent;

3. show if it is possible to reducethe environmental effectsthrough adapting the plans tosuit the habitat’s needs;

4. monitor long term changesthat might develop.

It is the job of Natural Resources Wales to monitor, protect and improvethe environment, as well as to promote sustainable development.


Intensive Farming

In order to feed the growing worldpopulation we need get as muchyield (from plants or animals) fromless land.We can do this by using intensivefarming methods.

You need to be able to name methods of intensive farming and describe theiradvantages and disadvantages:

Methods Advantages Disadvantages

Fertilisers Increase plant yield. Can wash out of soils andpollute rivers and streams.

PesticidesIncreases yield by stoppingpests from eating orcompeting with crop plants.

Can destroy non-pestspecies.Can lead to bioaccumulation.

Disease controlPrevents losses of plantsand animals.

Antibiotics given to animalsmay still be found in meatform treated animals.

Batterymethods

Less room to move. Lessenergy wasted. Less foodneeded. Reduced costs.

Poor quality of life for animal.

TB infection in cattle andbadgersBovine tuberculosis (bTB)is a very serious disease ofcattle in Britain.There is very strongevidence of a link betweenbTB in cattleand bTB in badgers.

Farmers believe that badgers should be culled to prevent the spread of bTB.Arguments supporting a cull Arguments against a cullBadgers carry bTB and pass it on tocattle.

Badger culls have not always beeneffective.

Many cattle die each year. Badgers that survive can move toother areas spreading the disease.Vaccination may be more effective.


Measuring pollution in rivers and streams

Populations can be upset by the introduction of harmful materials into theenvironment, which results in pollution.

Pollution in rivers and streamscan be measured using:

· Changes in pH levels· Changes in oxygen

levels· Indicator species

· Changes in pHAcidification of rivers and streams is due to acid rain and run-off fromsurrounding land. Below pH 4.5-5 aluminium is released from rocks. This istoxic to fish.

· Changes in oxygen levelsThe change in oxygen concentration shows how much bacteria there is in thewater. The more bacteria there are, the more polluted the water is.

· Indicator speciesYou can estimate the amount ofpollution by recording thepresence or absence of certainindicator species.

· Carrying out a surveyA survey should be a fair test. Therefore only one factor should change (theindependent variable).Everything else should stay the same.

Example of an annual survey· The independent variable is the year.

The variables that should stay the same:· Time of year the survey is carried out,· Same locations sampled,· Time of day the survey is carried out,· Volume of water sampled,· Method of sampling,· Same water conditions, e.g. temperature, flow rate, turbidity.


ZoneDescription Sulphur dioxide

content of the air(ug/m3)

0

1

2

3

4

5

6

Heavy Pollution

Clean Air

High sulphurdioxide

concentration

Low sulphurdioxide

concentration

Lichen can be used as indicator species for air pollution.Lichens are sensitive to sulphur dioxide gas (produced form burning fossilfuels).Some species are so sensitive that a very low concentration of the gas will killthem.Lichen found growing on trees or rocks could be used to indicate theconcentration of sulphur dioxide in the air.

Note, some of the species found in more polluted air can also be found in purerair. Always look for the lichen giving the highest zone reading on the scale.

Measuring Air Pollution


Pesticides in Food Chains

These are chemicals that farmers use to control pests and diseases on cropplants.

Insecticides kill insect pests feeding on plants.Herbicides (weed killers) reduce competition for water and lightbetween pest plants and crops.

Fungicides kill fungi that cause plant diseases.

Environmental Effects of Pesticides - Bioaccumulation

Pesticides can be sprayed on crops.Pesticides from crops may be washed into lakes, rivers and naturalunderground water stores and so contaminate drinking water.

Some chemicals are not broken down by the cells of living organisms andtherefore enter the food chain.The further along a food chain an organism is, the more chemicalsaccumulate in its tissues. The scientific name for this is bioaccumulation.The organism at the end of a food chain will receive a toxic dose that hasharmful effects, e.g. reducing fertility or death.

DDT – A Case Study for BioaccumulationBetween 1960 and 1970 seeds were often treated with pesticides, such asDDT to try and stop insects from eating them.Before long, the numbers of birds of prey, such as the Sparrowhawk weredecreasing. Many were found dead with high levels of pesticides in theirbodies.Scientific evidence has shown that DDT stays in the environment for a longtime.DDT has been banned in the USA since 1972 and in the UK since 1984.


Heavy Metals in Food Chains

In the year 2000 new laws were passed to reduce the level of pollution byindustry.Many industries (oil refineries, chemical works, steel plants and paper mills)used to release chemicals into rivers and the sea. These chemicals includedheavy metals such as lead, mercury, cadmium and tin.

A well-known case of industrial pollution is the tragedy of Minamata, a fishingvillage in Japan.

52 people died from mercury poisoning. Others were paralysed and babieswere born with brain damage. Mercury affects the nervous system.

ExplanationA plastics factory released mercury compounds into the sea.Plant plankton (microscopic plants) absorbed mercury.Animal plankton (microscopic animals) ate a lot of the plant plankton, andmercury built up inside them.

Fish ate a lot of the animal plankton. Because they could not excrete themercury (get rid of it from their bodies), the concentration increasedinside them.When people ate a lot of the fish they received a very high concentrationof mercury.This toxic or poisonous dose was enough to kill them or make them veryill.


Effect of Fertilisers and Sewage on the Environment

Fertilisers contain the minerals that crop plants needto grow, e.g. nitrates and phosphates. Chemicalfertilisers are important in intensive farming, but theymust be used carefully especially near streams, riversand ponds.

Algal bloom

Fertiliser beingwashed into the river. Some plants start dying because

of competition for light.

Fish die because decomposingbacteria have used up all the

oxygen for respiration

Explanation – (QWC question model answer)· Fertilisers containing nitrates and phosphates are washed into streams,

rivers, ponds and the sea.· Nitrates and phosphates cause an increase in the growth of water plants or

algal blooms.· Some plants start dying because there is increased competition for light.· Decomposing bacteria decompose (rot) the dead plants.· The number of decomposing bacteria increases.· The decomposing bacteria use up the oxygen in the water for respiration.· There is less oxygen in the water.· Animals, such as fish, die because there is not enough oxygen in the water.

What about sewage?· Untreated sewage causes an increase in the growth

of water plants. (It has the same effect as fertilisers).· Bacteria in the water also feed on untreated sewage,

using up the oxygen in the water for respiration.


Light energy from the sun is the source of all energy for all living things onthe planet.Green plants absorb only a small percentage of this energy (about 1%), usingthe chlorophyll in their chloroplasts. The rest of the light is either reflected or isat the wrong wavelength.

Energy and Nutrient Transfer

The absorbed energy is used for photosynthesis to produce substances thatbecome part of the cells. These increase the biomass of the plant.

· Biomass is the mass of living material in plants and animals.

· The arrows in a food chain show energy being passed from one livingthing to the next. (This is sometimes described as a flow of energy).

Producer Herbivore Carnivore

Third stageconsumer

Second stageconsumer

First stageconsumer

Food Chains – Glossary of terms

There are many terms to describe the organisms in a food chain. Someorganisms can be described using more than one label.E.g. an herbivore can also be described as a first stage consumer.

Producer Makes it’s own food by photosynthesis.Consumer An organism that eats other organisms.First stage consumer The first organism that is ‘eating’ in a food chain.Second stage consumer The second organism that is ‘eating’ in a food chain.Third stage consumer The third organism that is ‘eating’ in a food chain.Herbivore An organism that only eats plants.Carnivore An organism that only eats animals.Omnivore An organism that eats both animals and plants.

Carnivore


lettuce

hawk

fox owl

chaffinch

thrush

slugrabbit

cereal

Food Webs

In the exam, you may be asked to explain what happens if an animal isremoved from the chain.

ExampleAll the rabbits die from a disease.1. What effect would this have on the foxes?· The number of foxes would decrease.

b) Why?· There is less food for the foxes to eat.

2. a) What effect would this have on lettuce production?· The number of lettuce would increase.

b) Why?· There are less rabbits eating the lettuce.

3. Explain in full the effect on the mice. (Notice, the mouse is not part of the same food chain).

· The number of mice would decrease because the foxes have less rabbitsto eat therefore they eat more mice.

Remember to think carefully· what eats what, ?· which animals will have less food?· what will be the effect on other animals?

mouse

Food webs are made from a number of different food chains linked together.


Energy Flow Through a Food Chain

There•is•energy•lost•at•each•step•of•a•food•chain,•so•there’s•less•available•for thenext animal. This is why the numbers of organisms in a food chain is limited. Themore energy lost every step, the shorter the food chain.

Grasses Woodmice Foxes

Waste materials fromanimals:

· Dead animals,· Excretion (Urine);· Egestion (faeces).

Not used inphotosynthesis

Heat energy from respiration

Waste materials from plants:· Dead plants.

Energy is also ‘lost’ from the food chain for the repair of animal or plant cells.

Some things to consider about energy lost as heat during respiration.· Animals lose more heat than plants because their metabolism is higher (the

amount of chemical activity in cells).· Animals lose more heat than plants because they move around; plants don’t.· Warm-blooded animals (mammals and birds) lose more heat than

cold-blooded animals (all the others) because they need to keep their bodytemperature constant. (See homeostasis).

· Land animals lose more energy than animals in water, because they have tosupport their bodies. E.g. we humans have to stand, a jellyfish just floats!

Efficient Food ProductionMore food can be produced from an area of land if it isused for growing crops rather than grazing animals. Lessenergy is lost if people eat plants, because the foodchain is shorter.However,•potatoes•wouldn’t•grow•on•a mountain, butsheep can graze there, so no need to stop all animalproduction.


Pyramids of number show the number of organisms in a given area orvolume for every feeding level.

Pyramids of biomass shows the dry mass of organisms in a given area orvolume for every feeding level.

Food Pyramids

Rules for pyramids of number:1. The producer is always at the bottom.2. The size of every block (area or volume) shows the number of plants or

animals in the food chain.

Pyramids of numbers can be misleading.The pyramid on the left represents acabbage field, and the one on the rightwoodland. Their shapes are different eventhough they show the number of individualorganisms. A tree can support thousandsof animals; therefore the base of thepyramid is smaller than the levels above.

Rules for pyramids of biomass:1. The producer is always at the bottom.2. The size of every block (area or volume) shows the dry mass of the of

plants or animals in the food chain

The shape of a pyramid of biomasscan change during the year,depending on the time a survey iscarried out.

The pyramid on the right has beendrawn from grassland during May.

If a survey were carried out inDecember the mass of grass wouldbe less.During the winter it is colder andthere is less sunlight, therefore thegrass would be producing lessbiomass by photosynthesis.

417gm-2 Grass

1.25gm-2 Slugs

0.3gm-2 Robin

RememberA pyramid of biomass will always bepyramid shaped.


Building Food PyramidsOrganisms are represented as small squares on graph paper. Drawing a linearound all the small squares will give a box that represents the numbers orbiomass of an organism.

Organism Number in the Mass of eachfood chain organism (g)

Total biomassof organisms (g)

Rose plants 1 640640

Aphids 7000 0.05350

Ladybirds 400 0.25100

Chaffinch 1 25 25

Natural RecyclingNot every animal or plant gets eaten!

· Decomposers are bacteria andfungi.

· Decomposers digest and useanimal and plant waste for growthand respiration.

· Minerals such as nitrates arereleased to the soil, and are thenused by plants for growth.

Factors that affect the activity of decomposers (bacteria andfungi):

· Temperature· Oxygen· pH· Heavy metals

=Number x mass

Keep theheight of

each blockthe same

The length of the blockshould be drawn to scaleE.g. 1 small square = 10g

Rose plants

Chaffinch

Ladybirds

Aphids

Remember tolabel each level


The Carbon Cycle

· Carbon enters the food chain via photosynthesis.· Some of this carbon then becomes carbohydrates, fats and proteins in

plants.· The carbohydrates, fats and proteins are passed along the food chain when

animals are feeding (consuming).· Some carbon is converted to carbon dioxide during respiration by plants

and animals.· Carbon is returned to the environment when living things die or produce

waste material, e.g. faeces.· Decomposers (micro-organisms such as bacteria or fungi) feed on dead

organisms and the waste material for growth and other life processes. Thisis called decomposition or decay.

· Carbon is released to the atmosphere as carbon dioxide when decomposersrespire.

· When decay is prevented substances such as peat, coal, oil and gas areformed and these store energy in carbon compounds.

· Energy and carbon dioxide are released when these fossil fuels are burnt.

Respiration Photosynthesis

Feeding

Respiration

Decay

Combustion

Human effects on the carbon cycle· Combustion (burning) of fossil fuels has increased the concentration of

carbon dioxide in the environment.· Combustion of fossil fuels also releases sulphur dioxide that leads to acid

rain.


The Nitrogen Cycle

· Living organisms need nitrogen to make proteins.· 79%•of•the•air•is•nitrogen,•but•plants•and•animals•can’t•use•nitrogen•gas.· Nitrogen must be changed into nitrates before plants can use it.

Nitrates can be absorbed by plant roots and used to make proteins. This proteinthen becomes food for animals as it is passed on along food chains.

How does the nitrogen cycle work?· When a plant or animal dies,· Soil bacteria and fungi act as decomposers,· They convert protein (and urea from urine) into ammonia,· The ammonia is then converted to nitrates in a process called

nitrification.· Nitrifying bacteria carry out nitrification.· The nitrates are then absorbed (taken up) by plant roots.· The nitrates are used to make amino acids.· The amino acids are then used to make new proteins.

Absorption

Ureaseenzyme Decomposition

FeedingExcretion

urea

Nitrification

Death

cells and cell processes - alun school...cells and cell processes cell theory cells were first...

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