(6 MARKERS)A Level OCR A Biology

Messenger RNA (mRNA) is used during translation to form polypeptides. Describe how mRNA is produced in the nucleus of a cell.

[6 marks]

1. Helicase;

2. Breaks hydrogen bonds;

3. Only one DNA strand acts as template;

4. RNA nucleotides attracted to exposed bases; 5. (Attraction) according to base pairing rule;

6. RNA polymerase joins (RNA) nucleotides together;

7. Pre-mRNA spliced to remove introns;

Describe the structure of proteins.

[5 marks]

1. Polymer of amino acids;

2. Joined by peptide bonds;

3. Formed by condensation;

4. Primary structure is order of amino acids;

5. Secondary structure is folding of polypeptide chain due to hydrogen bonding;

6. Tertiary structure is 3-D folding due to hydrogen bonding and ionic/disulfide bonds;

7. Quaternary structure is two or more polypeptide chains;

Describe how proteins are digested in the human gut.

[4 marks]

1. Hydrolysis of peptide bonds;

2. Endopeptidases break polypeptides into smaller peptide chains;

3. Exopeptidases remove terminal amino acids;

4. Dipeptidases hydrolyse/break down dipeptides into amino acids;

Describe the mass flow hypothesis for the mechanism of translocation in plants.

[4 marks]

1. In source/leaf sugars actively transported into phloem;

2. By companion cells;

3. Lowers water potential of sieve cell/tube and water enters by osmosis;

4. Increase in pressure causes mass movement (towards sink/root);

5. Sugars used/converted in root for respiration for storage;

Stimulation of osmoreceptors can lead to secretion of the hormone ADH. Describe and explain how the secretion of ADH affects urine produced by the kidneys.

[4 marks]

1. Permeability of membrane/cells (to water) is increased;

2. More water absorbed from/leaves distal tubule/collecting duct;

3. Smaller volume of urine;

4. Urine becomes more concentrated;

Describe the roles of calcium ions and ATP in the contraction of a myofibril.

[5 marks]

1. Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum;

2. (Calcium ions) cause movement of tropomyosin (on actin);

3. (This movement causes) exposure of the binding sites on the actin;

4. Myosin heads attach to binding sites on actin;

5. Hydrolysis of ATP (on myosin heads) causes myosin heads to bend;

6. (Bending) pulling actin molecules;

7. Attachment of a new ATP molecule to each myosin head causes myosin heads to detach (from actin sites)

Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cells when using an optical (light) microscope.

[4 marks]

1. Add drop of water to (glass) slide;

2. Obtain thin section (of plant tissue) and place on slide / float on drop of water;

3. Stain with/add iodine in potassium iodide;

4. Lower cover slip using mounted needle;

Human papilloma virus (HPV) is the main cause of cervical cancer. A vaccine has been developed to protect girls and women from HPV.

Describe how giving this vaccine leads to production of antibody against HPV.

[4 marks]

1. Vaccine/it contains antigen (from HPV);

2. Displayed on antigen-presenting cells;

3. Specific helper T cell (detects antigen and) stimulates specific B cell;

4. B cell divides/goes through mitosis/forms clone to give plasma cells;

5. B cell/plasma cell produces antibody;

HIV attaches to a specific protein receptor on helper T cells. A low percentage of people have a mutation of the CCR5 gene which codes for this protein receptor. This mutation results in a non-functional protein receptor.

Explain how this mutation can result in the production of a non-functional protein receptor. [4 marks]

1. Change in DNA base/nucleotide (sequence);

2. Change in amino acid (sequence)/primary structure;

3. Alters (position of) hydrogen/ionic/disulfide bonds;

4. Change in tertiary structure (of receptor)

Describe how the structures of starch and cellulose molecules are related to their functions. [5 marks]

Starch (max 3)

1. Helical/ spiral shape so compact;

2. Large (molecule)/insoluble so osmotically inactive;

3. Branched so glucose is (easily) released for respiration;

4. Large (molecule) so cannot leave cell/cross cell-surface membrane;

Cellulose (max 3)

5. Long, straight/unbranched chains of β glucose; 6. Joined by hydrogen bonding;

7. To form (micro/macro)fibrils;

8. Provides rigidity/strength;

Describe the processes involved in the transport of sugars in plant stems. [5 marks]

1. (At source) sucrose is actively (transported) into the phloem/sieve element/tube;

2. By companion/transfer cells;

3. Lowers water potential in phloem/sieve element/tube and water enters by osmosis;

4. (Produces) high (hydrostatic) pressure;

5. Mass flow/transport towards sink/roots/storage tissue;

6. At sink/roots sugars are removed/unloaded;

describe how the PCR is carried out

- DNA heated

- strands separate

- cooled

- primer binds

- nucleotides attach

- by complementary base pairing

- DNA polymerase joins nucleotides together

describe how the technique of fingerprinting is carried out and explain how it can be sued to identify a person

- DNA is cut

- using restriction endonucleases

- electrophoresis

- separates according to mass

- DNA made single- stranded

- transfer to membrane

- add probe

- radioactive

- bind to VNTRs as complementary

- pattern is unique

describe how bacteria may be produced which have the resistance gene in their plasmid

- desired gene cut from DNA

- using restriction endonucleases

- cut plasmid open

- with same restriction endonucleases

- sticky ends form

- DNA ligase joins pieces of DNA together

- returns plasmid to cells

- use Ca^2+

describe how a cell from a mouse uses injected DNA to synthesis jararhagin protein

- DNA separates

- assembly of mRNA

- using mRNA nucleotides

- using RNA polymerase

- joins nucleotides together

- mRNA joins ribosome

- tRNA carries specific amino acid

- codon complementary to anti-codon on tRNA

- peptide bonds form between amino acids

Describe the appearance and behaviour of chromosomes during mitosis.

[5 marks]

(During prophase)

1. Chromosomes coil/condense/shorten/thicken/become visible;

2. (Chromosomes) appear as (two sister) chromatids joined at the centromere;

(During metaphase)

3. Chromosomes line up on the equator/centre of the cell;

4. (Chromosomes) attached to spindle fibres;

5. By their centromere;

(During anaphase)

6. The centromere splits/divides;

7. (Sister) chromatids/chromosomes are pulled to opposite poles/ends of the cell/separate;

(During telophase)

8. Chromatids/chromosomes uncoil/unwind/become longer/thinner;

Describe and explain the processes that occur during meiosis that increase genetic variation. [5 marks]

1. Homologous chromosomes pair up;

2. Independent segregation;

3. Maternal and paternal chromosomes are reshuffled in any combination;

4. Crossing over leads to exchange of parts of (non-sister) chromatids/alleles between homologous chromosomes;

5. (Both) create new combinations of alleles;

Describe two aseptic techniques she would have used when transferring a sample of broth culture on to an agar plate. Explain why each was important. [4 marks]

1. Keep lid on Petri dish OR Open lid of Petri dish as little as possible;

2. To prevent unwanted bacteria contaminating the dish OR L. monocytogenes may be dangerous/may get out; OR

3. Wear gloves OR Wear mask OR Wash hands; 4. To prevent contamination from bacteria on hands/mouth OR Prevent spread of bacteria outside the lab; OR

5. Use sterile pipette OR Flame the loop OR Flame the neck of the container of the culture;

6. To maintain a pure culture of bacteria;

In the UK, children are vaccinated against this disease. Describe how vaccination can lead to protection against bacterial meningitis. [6 marks]

1. Antigen/epitope on surface of N. meninigitidis / bacterium binds to surface protein / surface receptor on a (specific/single) B cell; 2. (Activated) B cell divides by mitosis / produces clone; 3. (Division) stimulated by cytokines / by T cells; 4. B cells/plasma cells release antibodies; 5. (Some) B cells become memory cells; 6. Memory cells produce plasma / antibodies faster;

Describe how a population of Neisseria meningitidis (Nm) can become resistant to these antibiotics. [4 marks]

1. Mutation;

2. Results in Nm cell with allele for resistance to one antibiotic/to named antibiotic;

3. (This) cell survives and passes the allele for resistance to offspring;

4. Process repeated with different genes conferring resistance to each of the other (two) antibiotics;

Contrast the structure of a bacterial cell and the structure of a human cell. [5 marks]

1. Bacterial cell is much smaller than a human cell; 2. Bacterial cell has a cell wall but human cell does not;

3. Bacterial cell lacks a nucleus but human cell has a nucleus;

4. Bacterial cell lacks membrane-bound organelles but human cell has membranebound organelles;

5. Bacterial ribosomes smaller than human ribosomes / bacteria have 70S ribosomes whereas humans have 80S ribosomes;

6. Bacterial DNA is circular but human DNA is linear;

7. Bacterial DNA is 'naked' whereas human DNA is bound to histones/proteins;

Explain how microorganisms in the soil produce a source of nitrates from the remains of crop plants

1) Protein/amino acids/DNA, into ammonium compounds/ ammonia

2) By saprobionts

3) Ammonium/ammonia into nitrite

4) Nitrite into nitrate

5) By nitrifying bacteria

6) Nitrogen to ammonium/ ammonia

7) By nitrogen-fixing bacteria in soil

Describe advantages and disadvantages of using chemical pesticides to control pests of crops

(Advantages)

1) Acts quickly

2) Can apply to particular area

3) Kills wide variety of plants

(Disadvantages)

4) Needs to be reapplied

5) Not specific

6) Pests can develop resistance

7) (Bio)accumulation

IGNORE ref. to leaching/eutrophication

Describe how plants use light energy in the light-dependent reaction

1) Excites electrons/ removes electrons from chlorophyll

2) Electrons move along carriers/ electron transfer chain, releasing energy

3) Energy used to join ADP and Pi to form ATP

4) Photolysis of water produces protons, electrons and oxygen

5) NADP reduced by electrons/electrons and protons/ hydrogen

Describe competitive and non-competitive inhibition of an enzyme

1) Inhibitors reduce binding of enzyme to substrate

(Competitive)

2) Inhibitor similar tertiary structure to substrate

3) Binds to active site

4) Inhibition can be overcome by more substrate added

(Non-competitive)

5) Inhibitor binds to side other than active site (allosteric) on enzyme

6) Changes shape of active site

7) Cannot be overcome by adding more substrate

Explain why maltase:

- only breaks down maltose

- allows this reaction to take place at normal body temperature

1) *Tertiary* structure of enzyme (means)

2) Active site is complementary to maltose

3) Description of *induced fit*

4) Enzyme is a catalyst

5) Lowers activation energy required

6) By forming enzyme-substrate complexes

Explain how the diet of a person can increase the risk of coronary heart disease

1) Too much saturated fat/ cholesterol in diet

2) Increase in cholesterol in blood

3) Atheroma plaques in artery walls

4) Reduces diameter of *coronary* arteries

5) Less oxygen/glucose to heart tissue

6) Increase in blood pressure

7) (Increased risk of) clot/ thrombosis/ embolism/ aneurysm

Describe how the heart controls and coordinates the regular contraction of the atria and ventricles

1) SAN -> AVN -> bundle of His

2) Impulses/ electrical activity (over atria)

3) Atria contract

4) Non-conduction tissue (between atria and ventricles)

5) Delay (at AVN) ensures atria empty before ventricles contract

6) Ventricles contract from apex upwards

Describe the processes involved in the absorption of the products of starch digestion

1) Glucose moves in with sodium (into epithelial cell)

2) Via. (carrier/channel) protein

3) Sodium removed (from epithelial cell) by active transport

4) Into blood

5) Maintaining low sodium concentration (in epithelial cell)/ sodium concentration gradient (between lumen and epithelial cell)

6) Glucose moves into blood

7) By (facilitated) diffusion

Describe the role of the enzymes of the digestive system in the complete breakdown if starch

1) Amylase

2) (Starch) to maltose

3) Maltase

4) Maltose to glucose

5) Hydrolysis

6) Of glycosidic bonds

Explain how the epithelial cells that line the small intestine are adapted for absorption of glucose

1) Microvilli

2) Large/increased surface area

3) Many mitochondria

4) (Mitochondria/ respiration) produce ATP (for active transport)

5) Carrier protein for active transport

6) Channel/ carrier proteins for facilitated diffusion

7) *Co-transport* of sodium (ions) and glucose or symport/ carrier proteins for sodium (ions) and glucose

8) Membrane-bound enzymes digest disaccharides/ produce glucose

Describe how trees convert carbon dioxide into organic substances during photosynthesis.

1) Carbon dioxide combines with ribulose bisphosphate/ RuBP

2) Produces two molecules of glycerate (3-) phosphate/ GP

3) Reduced to triose phopshate/ TP

4) Using reduced NADP

5) Using energy from ATP

6) Triose phosphate converted to other organic substances/ named organic substances/ ribulose bisphosphate

7) In light independent reaction/ Calvin cycle

Explain how the use of pesticides can result in resistant strains of insect pests

1) *Variation*/ *variety* in pest population

2) Due to mutation

3) *Allele* for resistance

4) Reference to selection

5) Pests with resistance (survive and) breed/ differential reproductive success

6) Increase in frequency of allele

Explain how farming practises increase the productivity of agricultural crops

1) Fertilisers/ mineral/ named ion (added to soil)

2) Role of named nutrient/ element e.g. nitrate/ nitrogen for proteins /

phosphate/ phosphorus for ATP/DNA

3) Pesticides/biological control prevents damage/consumption of crop

4) Pesticides/weed killers/herbicides/weeding remove competition

5) Selective breeding / genetic modification (of crops)

6) Glass/greenhouses enhance temp/CO2/light

7) Ploughing aerates soil/improves drainage

8) Ploughing/aerates allows nitrifcation

9) Benefit of crop rotation in terms of soil nutrients/fertility/pest reduction

10) Irrigation/water to remove limiting factor

11) Protection of crops from birds/pests/frost by covers/netting etc.

Explain how nitrates may cause the death of fish in fresh water.

1) Growth of algae/surface plants blocks light

2) Reduced/no photosynthesis so (submerged) plants die

3) *Saprobiotic* (microorganisms/bacteria)

4) Aerobically respire / use oxygen in respiration

5) Less oxygen for fish to respire / aerobic organisms die

Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells/enzyme

1) Cell homogenisation to break open cells

2) Filter to remove (large) debris/whole cells

3) Use isotonic solution to prevent damage to mitochondria/organelles

4) Keep cold to prevent/reduce damage by enzymes / use buffer to prevent protein/enzyme menstruation

5) Centrifuge (at lower speed/1000g) to separate nuclei/cell fragments/heavy organelles

6) Re-spin (supernatant / after nuclei/pellet removed) at higher speed to get mitochondria in pellet/at bottom

Describe the principles and the limitations of using a transmission electron microscope to investigate cell structure

*Principles*

1) Electrons pass through/enter (thin) specimen

2) Denser parts absorb more electrons

3) (So) denser parts appear darker

4) Electrons have short wavelength so give high resolution

*Limitations*

5) Cannot look at living material / must be in a vacuum

6) Specimen must be (very) thin

7) Artefacts present

8) Complex straining method / complex/long preparation time

9) Image not in 3D / only 2D images produced

Describe how a vaccine leads to the production of antibodies against a disease-causing organism

1) Vaccine contains antigen from pathogen

2) Macrophage presents antigen on its surface

3) T cell with complementary receptor protein binds to antigen

4) T cell stimulates production of B cells

5) (With) complementary antibody on its surface

6) B cells secrete large amounts of antibody

7) B cells divide to form clones all producing same antibody

Describe the difference between active and passive immunity

1) Active involves memory cells, passive does not

2) Active involves production of antibody by plasma/memory cells

3) Passive involves antibody introduced into body from outside

4) Active long term, because antibody produced in response to antigen

5) Passive short term, because (given) antibody is broken down

6) Active can take time to develop/work, passive fact acting

Describe what happens to chromosomes in meiosis

1) Chromosomes shorten/thicken/condense

2) Chromosomes associate in homologous pairs / form bivalents

3) Crossing over

4) Join to *spindle* fibres

5) (At) equator/middle of cell

6) (Join via.) centromere

7) (Homologous) chromosomes mive to opposite poles

8) (Pairs of) chromatids separated in 2nd division

Explain how microorganisms in the soil produce a source of nitrates from the remains of crop plants

1) Protein/amino acids/DNA, into ammonium compounds/ ammonia

2) By saprobionts

3) Ammonium/ammonia into nitrite

4) Nitrite into nitrate

5) By nitrifying bacteria

6) Nitrogen to ammonium/ ammonia

7) By nitrogen-fixing bacteria in soil

Describe advantages and disadvantages of using chemical pesticides to control pests of crops

(Advantages)

1) Acts quickly

2) Can apply to particular area

3) Kills wide variety of plants

(Disadvantages)

4) Needs to be reapplied

5) Not specific

6) Pests can develop resistance

7) (Bio)accumulation

IGNORE ref. to leaching/eutrophication

Describe how plants use light energy in the light-dependent reaction

1) Excites electrons/ removes electrons from chlorophyll

2) Electrons move along carriers/ electron transfer chain, releasing energy

3) Energy used to join ADP and Pi to form ATP

4) Photolysis of water produces protons, electrons and oxygen

5) NADP reduced by electrons/electrons and protons/ hydrogen

Describe competitive and non-competitive inhibition of an enzyme

1) Inhibitors reduce binding of enzyme to substrate

(Competitive)

2) Inhibitor similar tertiary structure to substrate

3) Binds to active site

4) Inhibition can be overcome by more substrate added

(Non-competitive)

5) Inhibitor binds to side other than active site (allosteric) on enzyme

6) Changes shape of active site

7) Cannot be overcome by adding more substrate

Explain why maltase:

- only breaks down maltose

- allows this reaction to take place at normal body temperature

1) *Tertiary* structure of enzyme (means)

2) Active site is complementary to maltose

3) Description of *induced fit*

4) Enzyme is a catalyst

5) Lowers activation energy required

6) By forming enzyme-substrate complexes

Explain how the diet of a person can increase the risk of coronary heart disease

1) Too much saturated fat/ cholesterol in diet

2) Increase in cholesterol in blood

3) Atheroma plaques in artery walls

4) Reduces diameter of *coronary* arteries

5) Less oxygen/glucose to heart tissue

6) Increase in blood pressure

7) (Increased risk of) clot/ thrombosis/ embolism/ aneurysm

Describe how the heart controls and coordinates the regular contraction of the atria and ventricles

1) SAN -> AVN -> bundle of His

2) Impulses/ electrical activity (over atria)

3) Atria contract

4) Non-conduction tissue (between atria and ventricles)

5) Delay (at AVN) ensures atria empty before ventricles contract

6) Ventricles contract from apex upwards

Describe the processes involved in the absorption of the products of starch digestion

1) Glucose moves in with sodium (into epithelial cell)

2) Via. (carrier/channel) protein

3) Sodium removed (from epithelial cell) by active transport

4) Into blood

5) Maintaining low sodium concentration (in epithelial cell)/ sodium concentration gradient (between lumen and epithelial cell)

6) Glucose moves into blood

7) By (facilitated) diffusion

Describe the role of the enzymes of the digestive system in the complete breakdown if starch

1) Amylase

2) (Starch) to maltose

3) Maltase

4) Maltose to glucose

5) Hydrolysis

6) Of glycosidic bonds

Explain how the epithelial cells that line the small intestine are adapted for absorption of glucose

1) Microvilli

2) Large/increased surface area

3) Many mitochondria

4) (Mitochondria/ respiration) produce ATP (for active transport)

5) Carrier protein for active transport

6) Channel/ carrier proteins for facilitated diffusion

7) *Co-transport* of sodium (ions) and glucose or symport/ carrier proteins for sodium (ions) and glucose

8) Membrane-bound enzymes digest disaccharides/ produce glucose

Describe how trees convert carbon dioxide into organic substances during photosynthesis.

1) Carbon dioxide combines with ribulose bisphosphate/ RuBP

2) Produces two molecules of glycerate (3-) phosphate/ GP

3) Reduced to triose phopshate/ TP

4) Using reduced NADP

5) Using energy from ATP

6) Triose phosphate converted to other organic substances/ named organic substances/ ribulose bisphosphate

7) In light independent reaction/ Calvin cycle

Explain how the use of pesticides can result in resistant strains of insect pests

1) *Variation*/ *variety* in pest population

2) Due to mutation

3) *Allele* for resistance

4) Reference to selection

5) Pests with resistance (survive and) breed/ differential reproductive success

6) Increase in frequency of allele

Explain how farming practises increase the productivity of agricultural crops

1) Fertilisers/ mineral/ named ion (added to soil)

2) Role of named nutrient/ element e.g. nitrate/ nitrogen for proteins /

phosphate/ phosphorus for ATP/DNA

3) Pesticides/biological control prevents damage/consumption of crop

4) Pesticides/weed killers/herbicides/weeding remove competition

5) Selective breeding / genetic modification (of crops)

6) Glass/greenhouses enhance temp/CO2/light

7) Ploughing aerates soil/improves drainage

8) Ploughing/aerates allows nitrifcation

9) Benefit of crop rotation in terms of soil nutrients/fertility/pest reduction

10) Irrigation/water to remove limiting factor

11) Protection of crops from birds/pests/frost by covers/netting etc.

Explain how nitrates may cause the death of fish in fresh water.

1) Growth of algae/surface plants blocks light

2) Reduced/no photosynthesis so (submerged) plants die

3) *Saprobiotic* (microorganisms/bacteria)

4) Aerobically respire / use oxygen in respiration

5) Less oxygen for fish to respire / aerobic organisms die

Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells/enzyme

1) Cell homogenisation to break open cells

2) Filter to remove (large) debris/whole cells

3) Use isotonic solution to prevent damage to mitochondria/organelles

4) Keep cold to prevent/reduce damage by enzymes / use buffer to prevent protein/enzyme menstruation

5) Centrifuge (at lower speed/1000g) to separate nuclei/cell fragments/heavy organelles

6) Re-spin (supernatant / after nuclei/pellet removed) at higher speed to get mitochondria in pellet/at bottom

Describe the principles and the limitations of using a transmission electron microscope to investigate cell structure

*Principles*

1) Electrons pass through/enter (thin) specimen

2) Denser parts absorb more electrons

3) (So) denser parts appear darker

4) Electrons have short wavelength so give high resolution

*Limitations*

5) Cannot look at living material / must be in a vacuum

6) Specimen must be (very) thin

7) Artefacts present

8) Complex straining method / complex/long preparation time

9) Image not in 3D / only 2D images produced

Describe how a vaccine leads to the production of antibodies against a disease-causing organism

1) Vaccine contains antigen from pathogen

2) Macrophage presents antigen on its surface

3) T cell with complementary receptor protein binds to antigen

4) T cell stimulates production of B cells

5) (With) complementary antibody on its surface

6) B cells secrete large amounts of antibody

7) B cells divide to form clones all producing same antibody

Describe the difference between active and passive immunity

1) Active involves memory cells, passive does not

2) Active involves production of antibody by plasma/memory cells

3) Passive involves antibody introduced into body from outside

4) Active long term, because antibody produced in response to antigen

5) Passive short term, because (given) antibody is broken down

6) Active can take time to develop/work, passive fact acting

Describe what happens to chromosomes in meiosis

1) Chromosomes shorten/thicken/condense

2) Chromosomes associate in homologous pairs / form bivalents

3) Crossing over

4) Join to *spindle* fibres

5) (At) equator/middle of cell

6) (Join via.) centromere

7) (Homologous) chromosomes mive to opposite poles

8) (Pairs of) chromatids separated in 2nd division

Describe an experiment you could carry out to test how temperature affects membrane permeability

+Cut beetroot into 5 identical pieces that have the same surface area, and rinse them to remove any pigment that leaked while cutting.

+Add the pieces into 5 separate test tubes, each containing 5cm cubed of water.

+Place the test tubes in water baths of different temperatures for the same length of time.

+Remove the beetroot from the test tubes, leaving the coloured liquid.

+Using a colorimeter, measure how much of the light is absorbed when passing through the 5 liquids.The higher the absorbance, the more pigment has been released, therefore the higher the membrane permeability.

Describe the experiment you could do to find the water potential of potato cells

+make different concentrations of sucrose solution in test tubes, making 15cm cubed of each

+Cut potatoes into identically sized chips, about 1cm in diameter

+divide the chips into groups of three and measure the masses of each group.+place one group into each sucrose solution

+leave the chips in the solutions for at least 20 minutes

+remove the chips and gently dab with paper towel

+weigh each group again and record the results

+calculate % mass change for each group

+Use the results to make a calibration curveThe potato chips will gain water in solutions with high water potential, and lose water in solutions with a lower water potential.

What factors affect the rate

The speed of the carrier proteins, the faster they work, the faster the rate of active transport.

The number of carrier proteins present, the more there are, the faster the rate of active transport will be

The rate of respiration in the cell, if respiration in inhibited, the production of ATP will slow down, so active transport will not have the energy to take place.

Explain how glucose is absorbed into the blood stream from the small intestine

In the last part of the small intestine, the concentration of glucose is too low for glucose to diffuse out into the blood, so it is absorbed from the middle by co-transport.

Sodium ions are actively transported out of the epithelial cells at the end of the intestine, into the blood by a sodium-potassium pump. This creates a concentration gradient, there is now a higher concentration of sodium ions in the middle of the intestine than inside the cell.

Sodium ions diffuse from the middle into the epithelial cell, via the sodium-glucose co-transporter proteins.

The co-transporter carries glucose into the cell with the sodium. As a result the concentration of glucose in the cell increases.

Glucose diffuses out of the cell, down its concentration gradient through a protein channel by facilitated diffusion.

What are the 4 main stages in an immune response?

Phagocytosis, Phagocytes activating the T-cells, T-cells activate B-cells which divide into plasma cells, plasma cells make more antibodies for the specific antigen

Explain the process of phagocytosis

1) A phagocyte recognises the antigens on a pathogene

2) The cytoplasm of the phagocyte moves round the pathogen, engulfing it.

3) The pathogen is now contained in a vacuole or a vesicle in the cytoplasm of the phagocyte.

4) A lysosome fuses with the phagocytic vacuole and the lytic enzymes break down with the pathogen

5) The phagocyte presents the pathogens antigens, it sticks the antigens on its surface to activate other immune system cells.

Explain how the phagocytes activate the T-cells

A T-cell is another type of white blood cell. It has receptor proteins on its surface that bind to complimentary antigens presented by the phagocytes.

This activates the T-cell.Different T-cells react in different ways. Helper T-cells release chemical signals that activate and stimulate phagocytes and cytotoxic T-cells which kill abnormal and foreign cells. They also activate B-cells.

Explain the role of B-cells in the immune response

B-cells are also a types of white blood cell that are covered in antibodies. Each B-cell has a different shaped antibody on its membrane, so only a complimentary antigen will produce an antigen-antibody complex.

When the antibody meets with a complimentary antigen, it binds to it. This, together with the substances from helper T-cells activates the B-cell. This is called clonal selection. The activated B-cell divides into plasma cells

Explain the role of plasma cells in the immune response(4th step of immune response)

Plasma cells are clones of B-cells. They secrete antibodies specific to the antigen. These are called monoclonal antibodies. They bind to the antigens surface to form an antigen-antibody complex.

An antibody has two binding sites so can bind to two pathogens at the same time. This means that pathogens become clumped- this is called agglutination. Phagocytes then bind to the antibodies and phagocytose many pathogens at once. This leads to the destruction of pathogens carrying this antigen in the body.

Outline the method of indirect ELISA as a HIV test

1) HIV antigen is bound to bottom of a well in a well plate.

2)A sample of a person's plasma is added to the well. If there are HIV specific antibodies they will bind to the HIV antigen. The well is washed out to remove other antigens and antibodies.

3)Another antibody that has an enzyme attached to it is added. This antibody binds to the HIV antibody. The well is washed again.

4)A solution is added to the well, containing a substrate, which can react with the enzyme attached to the secondary antibody. This reaction will produce a coloured product.

Explain the life cycle of HIV

1)The HIV binds to protein receptors on helper T-cells

2) The capsid is released into the cell, where it uncoats and releases the genetic information into the helper T-cell's cytoplasm

3)Inside the cell, reverse transcriptase is used to make a complimentary strand of DNA from the viral RNA strand

4)Double stranded DNA is made and inserted into the cell's DNA

5)Host cell enzymes are used to make viral proteins from the DNA

6)The viral proteins are assembled into new viruses, which bud from the cell and infect other cells

How are prokaryotic cells different to eukaryotic cells?

1) The cytoplasm has no membrane bound organelles.

2)The ribosomes are smaller than those in a eukaryotic cell

3)Some prokaryotes have a flagellum, a long hair-like structure that rotates to help the cell move.

4)A prokaryote lacks a nucleus. The DNA floats free in the cytoplasm. It is circular DNA, one long coiled up strand

5)Some prokaryotes have plasmids- small loops of DNA that aren't part of the main circular DNA molecule. They contain genes for antibiotic resistance.

6)Some prokaryotes have a capsule made up of secreted slime to help protect bacteria from attacks from the immune system.

7)The cell wall supports the cell and is made from a polymer called murein.

Outline the process of binary fission

1)The circular DNA and plasmids replicate. The circular DNA is only replicated once, but the smaller ones can be replicated several times.

2)The cells get bigger and the DNA loops move to opposite poles

3)The cytoplasm begins to divide and new cells walls begin to form.

4)The cytoplasm divides and two daughter cells are produced.

Explain how drugs are targeted towards cancer cells only

Antigens on cancerous cells have tumor markers. This means monoclonal antibodies can be produced to attach to the antigen. Anti-cancer drugs can be attached to the antibodies, so when the antibodies bind with the tumor markers, the drug accumulates where cancer cells are present. This lowers side effects of the drugs on other cells.

How are gases exchanged in insects?

- Terrestrial insects have microscopic air-filled pipes = tracheae = gas exchange.

- Air moves into tracheae through pores called spiracles.

- Oxygen travels down concentration gradient towards cells.

- Tracheae branch into tracheoles = have thin permeable walls that go to individual cells = means oxygen diffuses directly to respiring cells.

- CO2 from the cells moves down its concentration gradient towards spiracles to be released into atmosphere.

What the counter-current system?

Describes the exchange of oxygen in a fish.

Blood flows through the lamellae in one direction and water flows over them in the opposite direction = this means that the water with a relatively high oxygen concentration always flows next to blood with a lower concentration of oxygen = steep concentration gradient so as much oxygen as possible can diffuse from water into blood.

Describe and explain how the structure of the mammalian breathing system enablesefficient uptake of oxygen into the blood.

1. alveoli provide a large surface area;

2. walls of alveoli thin to provide a short diffusion pathway;

3. walls of capillary thin / close to alveoli provides a short diffusion pathway;

4. walls (of capillaries / alveoli) have flattened cells;

5. cell membrane permeable to gases;

6. many blood capillaries provide a large surface area;

7. intercostal / chest muscles / diaphragm muscles / to ventilate lungs / maintain a diffusion / concentration gradient;

8. wide trachea / branching of bronchi / bronchioles for efficient flow of air;

9. cartilage rings keep airways open; (reject moist and thin membranes)6 max

How is PCR carried out to produce large quantities of DNA? [6]

1. DNA heated to 90 degrees C.

2. strands separate

3. cooled to below 70 degrees C.

4. primers bind

5. nucleotides attach

6. by complementary base pairing

7. DNA polymerase joins nucleotides together

8. cycle is repeated

How do you transfer a specific gene into a bacterial cell? [4]

1. use restriction endonuclease...

2. ...to cut the plasmid, forming sticky ends.

3. Use ligase to join the gene to the plasmid.

4. Culture the bacteria in a medium containing plasmids...

5. ...to allow the uptake of plasmids.

Describe PCR [6]

1. heat DNA (to 90 degrees C)

2. break H bonds (separating strands)

3. add primers

4. add nucleotides

5. cool....

6. ...to allow binding

7. use DNA polymerase...

8. ... to join nucleotides

9. repeat many times.

Describe how altered DNA may lead to cancer? [6]

1. DNA is altered by mutation...

2. ... changing the base sequence....

3. ... of the gene that controls cell growth.

4. Change in the protein structure....

5. .... of tumour suppressor genes...

6. ... to tumour suppressor genes do not produce proteins that inhibit cell division.

7. So cell division is uncontrolled

8. via mitosis

9. leading to the production of a malignant tumour.

Use knowledge of photosynthesis and respiration to describe and explain how the concentration of CO2 in the air changes:

over a period of 24 hours

at different heights above the ground. [5]

1. high conc. of CO2 in dark due to respiration

2. no photosynthesis in the dark, photosynthesis only in light.

3. In light, net uptake of CO2. The rate of photosynthesis is greater than the rate of respiration.

4. Decrease in CO2 concentration with height.

5. Less photosynthesising tissue at ground level, more microorganisms.

During the light-independent reaction of photosynthesis, carbon dioxide is converted into organic substances. Describe how [6]

1. CO2 combines with RuBP

2. Producing 2GP molecules

3. GP is reduces to TP

4. Using reduced NADP

5. Using energy from ATP

6. TP converted to RUBP, 1C used to make other organic substance such as glucose.

ATP is useful in many biological processes. Explain why. [4]

1. Releases energy in small / manageable amounts.

2. Broken down in a single step - single bond broken, providing an immediate energy source, available rapidly.

3. Phosphorylates reactions, lowering activation energy.

4. Reformed / regeneration.

Describe how ATP is made in mitochondria [6]

1. Substrate level phosphorylation

2. Krebs cycle produces reduced NAD

3. Electrons released from reduced NAD

4. Electrons pass along ETC through a series of redox reactions.

5. energy released

6. ADP + Pi

7. Protons move into inter membrane space

8. ATP synthase channels

Explain why it is important for plants to produce ATP during respiration in addition to during photosynthesis. [5]

1. In the dark, no ATP production in photosynthesis

2. Some tissues are unable to photosynthesise and produce ATP in this way.

3. ATP cannot be moved from cell to cell or stored

4. Plant uses more ATP than produced in photosynthesis

5. ATP for active transport / synthesis of glucose.

Describe the role of bacteria in making the nitrogen in dead leaves available to growing plants. [5]

1. Saprobionts...

2. ... break down proteins

3. extracellular digestion

4. ammonia produced

5. ammonia converted to nitrite to nitrate

6. by nitrifying bacteria / via nitrification

How do trees convert CO2 into organic substances during photosynthesis? [6]

1. CO2 combines with RuBP

2. Producing 2GP

3. Which is reduced to TP

4. Using reduced NADP

5. Using energy from ATP

6. TP is converted to other substances

7. in the light independent reaction.

Use your knowledge of photosynthesis to explain variation in CO2 concentration over 24hrs and at different heights? [5]

1. high concentration of CO2 linked with darkness

2. as no photosynthesis in the dark

3. In the dark, plants and other organisms respire

4. In light, net uptake of CO2 by plants. They use more CO2 than they produce. Rate of photosynthesis > rate of respiration.

5. Decreases in CO2 concentration with height

6. at ground level fewer leaves / less photosynthesising tissue.

In the LIR of photosynthesis, the carbon in carbon dioxide becomes carbon in TP. Describe how. [5]

1. CO2 combines with RuBP

2. to produce 2GP

3. reduced to TP

4. requires reduced NADP

5. energy from ATP.

In the LDR, light energy generates ATP. Describe how. [5]

1. Light energy excites electrons in chlorophyll

2. Electrons pass down the ETC

3. via a series of redox reactions

4. the ETC is in the thylakoid membrane of the grana

5. energy released

6. ATP is phosphorylated from ADP and Pi.

Describe the light independent reactions of photosynthesis and explain how they allow the continued synthesis of hexose sugars. [6]

1. RuBP combines with CO2

2. to form GP and then TP

3. Using (energy from) ATP

4. and reduced NADP

5. 2 molecules of TP form hexose

6. all RuBP is regenerated.

7. 10 molecules of TP form 6 molecules of RuBP

Describe the role of the ETC in the LDR of photosynthesis [6]

1. ETC accepts excited electrons

2. from the chlorophyll

3. electrons lose energy along the chain

4. ATP produced

5. from ADP and Pi

6. Reduced NADP formed

7. when electrons (from ETC) and H+ combine with NADP

8. H+ from phoyolsysis.

Describe how light energy absorbed by chlorophyll molecules is used to synthesise ATP [5]

1. Excitation of chlorophyll molecule raises the energy level

2. Electrons emitted from chlorophyll molecule

3. Electrons travel to the ETC

4. Loss of energy by electrons along the ETC.

5. Energy lost by electrons used to synthesis ATP

6. from ADP + Pi.

Explain how Caribbean species could evolve? [6]

1. geographical isolation

2. separate gene pools (no gene flow)

3. Variation due to mutation

4. Different selection pressures / different (a)biotic conditions

5. Differential reproductive success - selected organisms survive and reproduce

6. Lead to an increase in the allele frequency.

Describe the part played by the inner membrane of mitochondrion in producing ATP? [3]

1. electrons are transferred down the ETC

2. Providing energy to take protons into the space between membranes

3. Protons pass back through membrane through ATPase

4. Energy used to combine ADP + Pi to produce ATP.

Describe what happens to pyruvate in anaerobic conditions and explain why anaerobic respiration is advantageous to human skeletal muscle. [4]

1. Forms lactate

2. Use of reduced NAD

3. Regenerates NAD

4. NAD can be reused to oxidise more respiratory substrate

5. allows glycolysis to continue

6. can still form ATP

7. when oxygen in short supply.

Describe the roles of coenzymes and carrier proteins in the synthesis of ATP [3]

1. NADH -> NAD + e- + H+

2. Electrons transferred between carriers

3. energy used to synthesis ATP from ADP + Pi.

4. Protons passed into inter membrane space.

5. Protons flow back through ATPsynthase enzyme.

Explain how increased use of inorganic fertilisers on the fields may have led to death of marine organisms. [5]

1. runoff / leaching of nutrients

2. leads to increased growth of algae

3. competition for light

4. death of algae

5. increases microorganisms

6. respiration of microorganisms uses up oxygen

7. fish die due to lack of oxygen.

Explain how farming practices increase the productivity of agricultural crops. [5]

1. fertilisers

2. contain nitrogen for proteins

3. selective breeding of crops

4. Aeration allows nitrification

5. Crop rotation

Describe how the action of microorganisms in the soil produces a source of nitrates for crop plants. [5]

1. Protein broken into ammonia

2. by saprobionts

3. Ammonia into nitrite

4. Nitrite into nitrate

5. By nitrifying bacteria

6. Nitrogen to ammonia

7. by nitrogen fixing bacteria