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AQA A Level Biology > Year 13 AQA BIOLOGY 2022 > Flashcards

Year 13 AQA BIOLOGY 2022 Flashcards

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1
Q

Describe the light dependent reaction

A
  • Chlorophyll absorbs light energy & Excites electrons
  • Chlorophyll loses electrons (Oxidation of chlorophyll) via photoionisation;
  • Electrons move along carriers/electron transport chain releasing energy (Series of REDOX reactions)
  • Energy released (by electrons) used to form proton gradient;
  • H+ ions move through ATP synthase;
  • providing energy to join ADP and Pi to form ATP;
  • Photolysis of water produces 2 protons, 2 electrons and ½ oxygen;
  • NADP reduced by electrons / electrons and protons / hydrogen;
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2
Q

Describe the light independent reaction (Calvin Cycle)

A
  • Carbon dioxide combines with ribulose bisphosphate/RuBP;
  • Produces two glycerate (3-)phosphate/GP;
  • GP reduced to triose phosphate;
  • Using reduced NADP;
  • Using energy from ATP;
  • Triose phosphate converted to glucose/RuBP/ other named organic substance;
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3
Q

ATP is produced in the light dependant reaction, suggest why this is not their (plants) only source of ATP.

A
  • Plants don’t photosynthesis in the dark;
  • Not all the parts (e.g. roots) of the plants photosynthesise;
  • Plants require more ATP than is produced in the light dependant reaction;
  • ATP used in Active Transport (accept other named processes)
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4
Q

Describe the effect of introducing a herbicide/inhibitor on the electron transport chain

A

• Reduced transfer of protons across thylakoid membrane
OR
• Reduced chemiosmotic gradient/proton gradient across thylakoid membrane;
• (So) less ATP produced;
• (So) less reduced NADP produced;
• (So) light-independent reaction rate decreases / slows / stops
OR
• Less reduction of GP to triose phosphate;

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5
Q

Describe what happens during PHOTOIONISATION in the light dependent reaction.

A
  • Chlorophyll absorbs light OR Light excites/moves electrons in chlorophyll;
  • Electron/s are lost OR (Chlorophyll) becomes positively charged OR Chlorophyll is OXIDISED

Accept electrons go to electron transport/carrier chain for ‘electrons lost’.

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6
Q

When producing a chromatogram explain why the origin is marked using a pencil rather than ink.

A

• Ink and (leaf) pigments would mix OR (With ink) origin/line in different position
OR
• (With pencil) origin/line in same position OR (With pencil) origin/line still visible;

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7
Q

While making a chromatogram, describe the method used to separate the pigments after the solution of pigment had been applied to the origin.

A
  • Level of solvent below origin/line;
  • Remove/stop before (solvent) reaches top/end;
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8
Q

Suggest and explain the advantage to plants of having different colour pigments in leaves.

A

• Absorb different/more wavelengths of light for faster rates of photosynthesis;

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9
Q

Describe the need for plants to both photosynthesise AND respire

A
  • In the dark no ATP production in photosynthesis;
  • Some tissues (e.g. roots) unable to photosynthesise/produce ATP;
  • ATP cannot be moved from cell to cell/stored;
  • Plant uses more ATP than produced in photosynthesis;
  • ATP for active transport;
  • ATP for synthesis (of named substance);
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10
Q

Describe the process of succession

A
  • (Colonisation by) pioneer species;
  • Pioneers cause change in environmental abiotic / biotic factors(give an example);
  • Pioneers make the environment less hostile for new species;
  • New species change/make conditions less suitable for previous species;
  • Change/increase in diversity/biodiversity;
  • Stability increases [population/richness/abiotic factors];
  • Climax community;
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11
Q

Explain how succession results in a wide variety of fish living on coral reefs.

A
  • Increase in variety/diversity of species/plants/animals; OR Increase in number of species/populations; OR Increase in species richness / biodiversity
  • Provides more/different habitats/niches OR Provides greater variety/types of food OR becomes less hostile;
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12
Q

Describe random sampling
[estimation of population density]

A
  • Use a grid / split area into squares/sections;
  • Method of obtaining random coordinates / numbers, e.g. calculator/computer/random numbers table/random number generator;
  • Count number/frequency of plants in a quadrat;
  • Large sample (20+ quadrats) AND Calculate mean/average number (per quadrat/section);
  • Valid method of calculating total number of ……… e.g. mean number of plants per quadrat/section/m2 multiplied by number of quadrats/sections/m2 in wood;
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13
Q

Describe systematic sampling

A
  • Transect/lay line/tape measure (from one side of the dune to the other);
  • Place quadrats at regular intervals along the line;
  • Count plants/percentage cover/abundance scale (in quadrats) OR Count plants and record where they touch line/transect;
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14
Q

Describe how you would determine the mean percentage cover for beach grass on a sand dune.

A
  • Method of randomly determining position (of quadrats) e.g. random numbers table/generator;
  • Large number/sample of quadrats; (min 20)
  • Divide total percentage by number of quadrats/samples/readings;
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15
Q

Describe a method that could be used to determine the mean percentage cover of algae on a coral reef.

A
  • Method of randomly determining position (of quadrats) e.g. random numbers table/generator;
  • Large number/sample of quadrats; (>20)
  • Divide total percentage by number of quadrats/samples/readings;
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16
Q

Describe the mark, release, recapture technique

A
  • Capture sample, mark and release;
  • Appropriate method of marking suggested / method of marking does not harm fish;
  • Take second sample and count marked organisms;
  • No in No in Population = [No in sample1 × No in sample2] / Number marked in sample2;
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17
Q

The mark-release-recapture method can be used to estimate the size of a fish population.

Explain how.

A
  • Capture/collect sample, mark and release;
  • Ensure marking is not harmful (to fish) OR Ensure marking does not affect survival (of fish);
  • Allow (time for) fish to (randomly) distribute before collecting a second sample;
  • (Population =) number in first sample × number in second sample divided by number of marked fish in second sample/number recaptured;
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18
Q

Suggest why the mark-release-recapture method can produce unreliable results in very large lakes

A
  • Less chance of recapturing fish OR Unlikely fish distribute randomly/evenly;
  • Fish may remain in one area OR fish may congregate
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19
Q

Describe how you would determine how many quadrats to use when investigating a habitat.

A
  • Calculate running mean/description of running mean;
  • When enough quadrats, this shows little change/levels out (if plotted as a graph);
  • Enough to carry out a statistical test;
  • A large number to make sure results are reliable;
  • Need to make sure work can be carried out in the time available;
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20
Q

HSW:

Valid conclusions

A
  • Large sample size SO representative
  • Long study SO can allow…. / see effect of X
  • Control used SO comparison can be made.
  • Mean & SD SO significant differences can be determined.
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21
Q

Limitations:

You can only use the information provided.

A
  • Small sample size, not representative;
  • Only sampled males, females may respond differently to treatment;
  • Only tested on …….. in a lab, in the wild, may obtain different pattern in data;
  • Only tested on …….. species, might not be true for all species;
  • No STATS test so differences could be due to chance;
  • Data is SUBJECTIVE, some people may have lied.
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22
Q

HSW:

Null hypothesis

A
  • [x] will have no effect on [y]
  • E.g. Temperature will have no effect on rate of reaction
  • There will be no correlation between age and weight
  • There will be no difference between the observed and expected ratio of 3:1 brown eyes to blue eyes
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23
Q

Name the two products of the light-dependent reaction that are required for the light-independent reaction.

A
  1. ATP;
  2. Reduced NADP;
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24
Q

Where precisely is rubisco found in a cell?

A

Stroma

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25
Q

Explain why scientists measure the rate of production of oxygen in this investigation. (Rate of photosynthesis)

A
  1. Oxygen produced in light-dependent reaction;
  2. The faster (oxygen) is produced, the faster the light-dependent reaction.
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26
Q

Explain why plants that have more chlorophyll will grow faster than plants with less chlorophyll.

A
  1. Have faster production of ATP and reduced NADP;
  2. (So) have faster / more light-independent reaction;
  3. (So) produce more sugars that can be used in respiration;
  4. (So) have more energy for growth;
  5. Have faster / more synthesis of new organic materials.
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27
Q

Explain the relationship between stomatal opening and photosynthesis.

A
  1. Stomata allow uptake of carbon dioxide;
  2. Carbon dioxide used in / required for photosynthesis;
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28
Q

Describe what happens during photoionisation in the light dependent reaction.

A
  • Chlorophyll absorbs light

OR

Light excites/moves electrons in chlorophyll;

  • Electron/s are lost

OR

(Chlorophyll) becomes positively charged;

OR

Chlorophyll is oxidised;

Accept electrons go to electron transport/carrier chain for ‘electrons lost’.

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29
Q

Describe the process of glycolysis.

A
  • Phosphorylation of glucose using (2) ATP;
  • Oxidation of Triose phosphate to Pyruvate;
  • Net gain of ATP;
  • NAD is reduced;
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30
Q

Name two uses of ATP in a cell

A
  • Phosphorylation of (named substance) to make more reactive / Lowers activation energy;
  • Releases small manageable amounts of energy for (named process);
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31
Q

Describe how oxidation takes place in glycolysis and in the Krebs cycle.

A
  • Removal of hydrogen/dehydrogenation;
  • by enzymes/dehydrogenases;
  • H accepted by NAD/reduced NAD formed;
  • In Krebs cycle, FAD (used as well);
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32
Q

Water is a waste product of aerobic respiration. Describe how water is formed at the end of aerobic respiration.

A
  • Oxygen is terminal/final electron acceptor;
  • Combines with electrons and protons (to form water);
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33
Q

Explain how the amount of ATP is increased by reactions occurring inside a mitochondrion.

A

This is because:

  • oxidation of/removal of electrons and H+
  • from pyruvate
  • acetyl CoA / 6 carbon compound; (credit oxidative decarboxylation)
  • substrate level production of ATP / ATP produced in Krebs cycle;
  • production of reduced NAD / FAD (allow they take up hydrogen);
  • in matrix of mitochondria;
  • electrons fed into electron transport chain / used in oxidative phosphorlation
  • (Electrons) pass along carriers/through electron transport chain/through series of redox reactions;
  • Energy is released;
  • Protons move into intermembrane space;
  • ADP/ADP + Pi;
  • ATP synthase;
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34
Q

Describe the events of oxidative phosphorylation.

A
  • NAD/FAD reduced / hydrogen attached to NAD/FAD;
  • H+ ions/electrons transferred from coenzyme to coenzyme/carrier to carrier (ETC on cristae of inner membrane)
  • Energy released (from electrons) through series of redox reactions;
  • Energy released used to pump H+/ protons into intermembrane space forming an electro-chemical gradient (of protons);
  • H+/ protons flow back through ATP synthase to produce ATP from ADP and phosphate.
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35
Q

Describe the roles of the coenzymes and carrier proteins in the synthesis of ATP.

A
  • NAD/FAD reduced / hydrogen attached to NAD/FAD;
  • H+ ions/electrons transferred from coenzyme to coenzyme/carrier to carrier (ETC on cristae of inner membrane)
  • Energy released (from electrons) through series of redox reactions;
  • Energy released used to pump H+/ protons into intermembrane space forming an electro-chemical gradient (of protons);
  • H+/ protons flow back through ATP synthase to produce ATP from ADP and phosphate
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36
Q

In many mammals, ‘uncoupling proteins’ help to maintain a constant body temperature during hibernation.

Suggest and explain how.

A
  1. Allow passage of protons/H+;
  2. (Energy) released as heat;
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37
Q

The mitochondria in muscles contain many cristae. Explain the advantage of this.

A
  • larger surface area for electron carrier system / MORE oxidative phosphorylation;
  • provide MORE** ATP / energy **for contraction;
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38
Q

Give two reasons why the respirometer was left for 10 minutes when it was first placed in the water bath.

A
  • Equilibrium reached;
  • Allow for expansion (gases/liquids) /pressure change in apparatus;
  • Allow respiration rate of seeds to stabilise;
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39
Q

Explain why a log scale is used to record the number of cells/bacteria.

A
  • Large range**/difference/**increase in numbers (of cells/bacteria);
  • Accept reference to exponential (increase)
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40
Q

Explain why converting pyruvate to lactate allows the continued production of ATP by anaerobic respiration.

A
  • Regenerates NAD / Oxidises reduced NAD;
  • (So) glycolysis continues;
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41
Q

Malonate inhibits a reaction in the Krebs cycle.

Explain why malonate would decrease the uptake of oxygen in a respiring cell.

A
  • Less/no reduced NAD/coenzymes OR Fewer/no hydrogens/electrons removed (and passed to electron transfer chain);
  • Oxygen is the final/terminal (electron) acceptor;
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42
Q

Respirometer Question

The student found that the coloured liquid moved 1.5 cm in 24 hours. The diameter of the lumen (hole) of the capillary tubing was 1 mm.

The volume of a capillary tubing is given by πr2l, where π is 3.14 and l = length.

Calculate the volume of gas produced in cm3 hour–1.

Show your working.

Answer = ____________________ cm3 hour–1

A
  1. Correct answer in range of
  2. 9 × 10–4 to 4.91 × 10–4 = 2 marks;;
    * Accept any equivalent mathematical representation of this answer*
  3. Incorrect but shows division by 24 = 1 mark

OR

1175 to 1178 = 1 mark;

OR

49 = 1 mark;

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43
Q

Define Biomass

A
  • Mass of carbon (organic compounds)
    • Dry mass of tissue per given area
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44
Q

Suggest what you should do to ensure all water is removed from a tissue / sample.

A
  • Regularly weigh and Heat (less than 100 °C)
  • Until mass is constant
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45
Q

Define Gross Primary Productivity

A
  • Chemical energy store in plant biomass, in a given area or volume. (Rate of photosynthesis)
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46
Q

Define Net Primary Production

A
  • Chemical energy store in plant biomass after respiratory losses to the environment have been taken into account. NPP= GPP -R
  • NPP is available for new plant growth and reproduction OR available for other trophic levels in the ecosystem, such as herbivores and saprobionts.
    • kJ ha–1 year–1 OR kJ km–2 year–1 OR kJ km–3 year–1
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47
Q

The percentage of the light energy trapped by the producers is very low.

Give two reasons why.

A
  • Reflected / absorbed by water vapour;
  • Reflected from producers / wrong wavelength;
    • Transmitted / passes between chloroplasts/ between plants / too few chloroplasts;
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48
Q

In natural ecosystems, most of the light falling on producers is not used in photosynthesis.

Suggest two reasons why.

A
  1. (Light is) reflected;

Light is not absorbed on its own is not enough.

  1. (Light is) wrong wavelength;

Accept frequency for wavelength.

Accept reference to absorbing specified wavelengths/frequencies.

  1. (Light) misses chlorophyll/ chloroplasts/photosynthetic tissue;
  2. CO2 concentration or temperature is a limiting factor.
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49
Q

The biomass of primary consumers is less than the biomass of producers. Explain why.

A
  • Loss of energy/heat / use of energy / less energy to be passed on;
  • In respiration;
  • In excreta / excretion / urine / carbon dioxide;
  • Inedible parts / indigestible parts / egesta / egestion / to decomposers;
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50
Q

Describe how and explain why the efficiency of energy transfer is different at different stages in the transfer.

A
  • Some light energy fails to strike/is reflected/not of appropriate wavelength;
  • Efficiency of photosynthesis in plants is low/approximately
  • 2% efficient;
  • Respiratory loss / excretion / faeces / not eaten;
  • Loss as heat;
  • Efficiency of transfer to consumers greater than transfer to producers/approximately 10%;
  • Efficiency lower in older animals/herbivores/ primary consumers/warm blooded animals;
  • Carnivores use more of their food than herbivores;
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51
Q

Explain how the intensive rearing of domestic livestock increases net productivity

A
  • Slaughtered when still growing/before maturity/while young so more energy transferred to biomass/tissue/production;
  • Fed on concentrate /controlled diet /controlled conditions/so higher proportion of (digested) food absorbed/lower proportion lost in faeces / valid reason for addition;
  • Movement restricted so less respiratory loss / less energy used;
  • Kept inside/heating/shelter / confined so less heat loss / no predators;
  • Genetically selected for high productivity;
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52
Q

Describe the need for plants to both photosynthesise AND respire

A
  • In the dark no ATP production in photosynthesis;
  • Some tissues unable to photosynthesise/produce ATP;
  • ATP cannot be moved from cell to cell/stored;
  • Plant uses more ATP than produced in photosynthesis;
  • ATP for active transport;
  • ATP for synthesis (of named substance);
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53
Q

Describe the role of saprobionts in the nitrogen cycle

A
  • (use enzymes to) decompose proteins / DNA / RNA / urea;
  • Producing / releasing ammonia / ammonium ions;
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54
Q

Explain how carbon-containing compounds present in the pine leaves that fall from the trees are absorbed and used for growth by saprobionts/fungi that live in the soil.

A
  • extracellular digestion;
  • by secretion of enzymes;
  • absorption of digested/soluble products;
  • synthesis of structural compounds/named compound;.
  • respiration provide energy for growth
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55
Q

Nitrogen compounds in the plants are made available for the main crop after ploughing in spring.

Describe the role of microorganisms in this process.

A
  • proteins/amino acids broken down;
  • deamination/ammonification/ release of ammonium compounds;
  • By saprophytes/saprobionts/decomposers;
  • conversion to nitrates via nitrites;
  • by nitrifying bacteria/named bacterium;
  • nitrates absorbed into roots via active transport
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56
Q

Give two examples of biological molecules containing nitrogen that would be removed when a crop is harvested.

A
  1. Amino acid/protein/ polypeptide/peptide;
  2. nucleic acid/nucleotide/base;
  3. DNA;
  4. RNA / pre-mRNA / mRNA / rRNA / tRNA
  5. ATP/ADP;
  6. NAD/NADP (reduced or not);
  7. Cyclic AMP/cAMP;
  8. Chlorophyll;
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57
Q

Plants absorb a number of other nutrients from the soil including phosphates. Describe why phosphates are needed by a growing plant.

A
  • production of phospholipids;
  • in cell membranes;
  • synthesis of ATP;
  • production of DNA;
  • production of RNA;
  • production of NADP
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58
Q

Describe how a lack of phosphates in the soil surrounding a plant can affect its growth

A
  • (Required to) make ATP/glucose phosphate, soless respiration/less energy for growth;
  • (Required to) make nucleotides, so less DNA/mRNA/tRNA for cell division/production of protein (for growth);
  • (Required to) make RuBP/NADP, so less CO2 fixed/reduced into sugar;
  • (Required to) make phospholipids for membranes;
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59
Q

Outline the advantages of having Mycorrhizae

growth near plants

A
  • Mycorrhizae help plants to defend themselves (causing an increase in crop yield);
  • Mycorrhizae help plants to take up nitrates/phosphates (causing an increase in crop yield);
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60
Q

You are given samples of water from three different rivers.

Describe how you would obtain a quantitative measurement of their cloudiness.

A
  • Use of colorimeter;
  • Measure the absorbance/transmission (of light);
  • Example of how method can be standardised eg same volume of water, zeroing colorimeter, same wavelength of light, shaking the sample;
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61
Q

Describe the process of eutrophication.

A
  • Nitrates / Phosphates / Ammonium ions flushed/leached into waterway
  • Increased algal bloom
  • Light blocked out
  • Submerged aquatic plant unable to photosynthesise and die
  • Increase in saprobionts so increases rate of aerobic respiration
  • Saprobionts / aero.resp organismsn die as lack of oxygen (anoxic)
  • Increase in anaerobic microorganisms
  • Production of toxins
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62
Q

State three causes of genetic variation

A
  • Mutation
  • Crossing over
  • Independent segregation / assortment (of homologous chromosomes)
  • Random fusion of gametes / fertilisation / mating
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63
Q

What is meant by a genome?

A
  • ‘(all) the ‘genes’/alleles’ ‘genetic material/code’ in a cell/organism/ person’
  • ‘the total number of DNA bases in a cell/organism’
  • the full base sequence of all the genetic material of an organism
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64
Q

What is a ‘gene pool’?

A

All the alleles in a population.

Reject: Community;

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65
Q

How do multiple alleles of a gene arise?

A
  • mutations;
  • which are different / at different positions within the same gene;
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66
Q

In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios.

Suggest two reasons why.

A
  • Small sample size;
  • Fusion/fertilisation of gametes is random;
  • Linked Genes; Sex-linkage / crossing over;
  • Epistasis;
  • Lethal genotypes;
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67
Q

What is meant by a recessive allele?

A
  • Only expressed (in the phenotype) when homozygous
  • Not expressed in the heterozygote
  • Not expressed if dominant present
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68
Q

Define dominant allele

A

Always expressed within the phenotype

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69
Q

What does Hardy Weinberg’s equation predict? [3]

A
  • The frequency of alleles (of a particular gene);
  • Will stay constant from one generation to the next/over generations / no genetic change over time;
  • (3 of the following) Providing no mutation/no selection / population large / population genetically isolated / mating at random / no migration;
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70
Q

Define gene linkage

A

(Genes/loci) on same chromosome

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71
Q

Define epistasis

A
  • The allele of one gene affects the expression of another in the phenotype;
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72
Q

Define codominance

A

Both alleles (equally) expressed in the phenotype;

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73
Q

Rules for Dominant alleles

A
  • Affected offspring MUST have at least one affected parent.
  • Unaffected parents ONLY have unaffected offspring.
  • If both parents are affected and have an unaffected offspring, both parents must be Heterozygous
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74
Q

Rules for recessive alleles

A
  • Unaffected parents can have an affected offspring (if they are Heterozygous)
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75
Q

Male offspring (XY) are more likely than females (XX) to show recessive sex-linked characteristics.

Explain why.

A
  • (Recessive) allele is always expressed in males / males have one (recessive) allele;
  • Females need two recessive alleles / females need to be homozygous recessive / females could have dominant and recessive alleles / be heterozygous;
76
Q

Expected offspring phenotype ratio from heterozygous parents:

Monohybrid

A

3 : 1

77
Q

Expected offspring phenotype ratio from heterozygous parents:

Dihybrid

A

9 : 3 : 3 : 1

78
Q

Expected offspring phenotype ratio from heterozygous parents:

Epistasis

A

9 : 4 : 3

or

15 : 1 (Ratio adds to 16 but is not 9 : 3 : 3 : 1)

or

9 : 7

79
Q

Expected offspring phenotype ratio from heterozygous parents:

Autosomal linkage

A

3:1 (if no crossing over)

(no other pattern other than 4 phenotypes with recombination of alleles)

80
Q

What is meant by the term phenotype

A
  • (Expression / appearance / characteristic due to) genetic constitution / genotype / allele(s);
  • (Expression / appearance / characteristic due to) interaction with environment;
81
Q

Explain how a single base substitution causes a change in the structure of a polypeptide.

A
  • Change in sequence of amino acid(s) / primary structure (of polypeptide);
  • Change in (position of) hydrogen, ionic, disulfide bonds;
  • Alters tertiary structure;
82
Q

Describe the process of crossing over and explain how it increases genetic diversity.

A
  1. Homologous pairs of chromosomes associate / form a bivalent;
  2. Chiasma(ta) form;
  3. (Equal) lengths of (non-sister) chromatids / alleles are exchanged;
  4. Producing new combinations of alleles;

THIS IS ‘RARE’ = Unequal chance of recombinant alleles forming.

Less recombinant gametes form.

83
Q

Give two differences between mitosis and meiosis.

A

Mitosis given first

  1. One division, two divisions in meiosis;
  2. (Daughter) cells genetically identical, daughter cells genetically different in meiosis;
  3. Two cells produced, (usually) four cells produced in meiosis;
  4. Diploid to diploid/haploid to haploid, diploid to haploid in meiosis;
  5. Separation of homologous chromosomes only in meiosis;
  6. Crossing over only in meiosis;
  7. Independent segregation only in meiosis;
84
Q

A population of fruit flies contained 64% grey-bodied flies.

Body colour is controlled by gene G which has 2 alleles. G produces Grey and is dominant to g, which produces black.

Use the Hardy–Weinberg equation to calculate the percentage of flies heterozygous for gene G. [2]

A

48% [2]

q2=0.36 or (36/100)

so, q=0.6 and P=0.4

Therefore, 2 x 0.4 x 0.6 x [100] = 48%

2Pq [1]

0.48 [1]

85
Q

There were 850 fruit flies in one population. In this population, 510 fruit flies had the genotype WNWN, 255 had the genotype WNWV and 85 had the genotype WVWV.

Calculate the actual frequency of the allele WV. Do not use the Hardy-Weinberg equation in your calculation. [1]

A

0.25; [1]

WNWV = 1x 255 = 255

WNWV = 2 x 85 = 170

Therefore, (255 + 170) divided by (1700) = 0.25

Frequency is always shown as a proportion of 1.

86
Q

In a population, the frequency of the allele for tongue-rolling, T, is 0.4.

Use the Hardy-Weinberg equation to calculate the percentage of people in this population that are heterozygous for tongue-rolling.

A

48% [2]

P=0.4 so, q=0.6

2Pq [1]

0.48 [1]

= 2 x 0.4 x 0.6 x [100] = 48% [2]

87
Q

In a species of snail, shell colour is controlled by a gene with three alleles. The shell may be brown, pink or yellow. The allele for brown, CB, is dominant to the other two alleles. The allele for pink, CP, is dominant to the allele for yellow, CY.

Give all the genotypes which would result in a brown-shelled snail.

A

CBCB, CBCP and CBCY;

88
Q

What are the most common LIMITATIONS to a conclusion?

A
  • No STATISTICAL TEST: Differences could be due to CHANCE
  • Data is for only ONE (named) species
  • Data only collected in a lab / In vitro
  • Only tested on males / females. Observations may differ in females / males
  • Data is subjective
  • Data only collected for ………….days / weeks / years
  • Long term side effects are not known
  • At no point is the ……… 100% effective.
89
Q

Explain what is meant by the terms totipotent and pluripotent?

A
  • Totipotent cells can give rise to all cell types;
  • Pluripotent can only give some cell types;
90
Q

Explain how cells produced from stem cells can have the same genes yet be of different types.

A
  • {not all / different} genes are switched {on / off} /active / activated ;
  • correct and appropriate reference to factors / mechanisms for gene switching ;

e.g. reference to promoters / transcription factors

91
Q

Describe the mechanism by which a signal protein causes the synthesis of mRNA.

A
  • signal protein {binds to / joins to / interacts with / activates}
  • receptor on surface membrane;
  • messenger molecule moves from cytoplasm and enters nucleus;
  • {produces / activates} transcription factor;
  • binds to promoter region;
  • RNA polymerase transcribes target gene;
92
Q

Explain how oestrogen enables RNA polymerase to transcribe its target gene.

A
  • Oestrogen is lipid soluble so diffuses through the Oestrogen diffuses through the phospholipid cell membrane;
  • attaches to ERα receptor;
  • ERα receptor changes shape / Tertiary structure;
  • ERα receptor leaves protein complex which inhibited it’s action;
  • oestrogen receptor binds to promoter region;
  • enables RNA polymerase to transcribe target gene.
93
Q

Compare the structure of dsRNA and DNA.

A
  • Similarities; 2 max
  • Polynucleotides/polymer of nucleotides;
  • Contain Adenine, Guanine, Cytosine;
  • Have pentose sugar/5 carbon sugar;
  • Double stranded/hydrogen bonds/base pairs.
  • Differences; 2 max
  • dsRNA contains uracil, DNA contains thymine;
  • dsRNA contains ribose DNA contains Deoxyribose;
  • dsRNA is Shorter than DNA; fewer base pairs in length;
94
Q

Explain how the methylation of tumour suppressor genes can lead to cancer.

A
  • Methylation prevents / inhibits transcription of (named) gene;
  • Protein not produced that prevents cell division / causes cell death / apoptosis;
  • No control of mitosis.
95
Q

Describe how alterations to tumour suppressor genes can lead to the development of tumours.

A
  • (Increased) methylation (of tumour suppressor genes);
  • Mutation (in tumour suppressor genes);
  • Tumour suppressor genes are not transcribed/expressed OR
  • Amino acid sequence/primary/ tertiary structure altered;
  • (Results in) rapid/uncontrollable cell division;
96
Q

Describe what is meant by a malignant tumour.

A
  • mass of undifferentiated / unspecialised / totipotent cells;
  • uncontrolled cell division
  • metastasis / (cells break off and) form new tumours / spread to other parts of body;
97
Q

Describe how altered DNA may lead to cancer.

A
  • (DNA altered by) mutation;
  • (mutation) changes base sequence;
  • of gene controlling cell growth / oncogene / that monitors cell division;
  • of tumour suppressor gene;
  • change protein structure / non-functional protein / protein not formed;
  • (tumour suppressor genes) produce proteins that inhibit cell division;
  • mitosis;
  • uncontrolled / rapid / abnormal (cell division);
  • malignant tumour;
98
Q

Describe how alterations to tumour suppressor genes can lead to the development of tumours.

A
  • (Increased) methylation (of tumour suppressor genes);
  • Mutation (in tumour suppressor genes);
  • Tumour suppressor genes are not transcribed / expressed OR Amino acid sequence / primary structure altered;
  • (Results in) rapid/uncontrollable cell division;
99
Q

Define epigenetics

A
  • Heritable phenotype changes (gene function) that do not involve alterations in the DNA sequence/mutation.
100
Q

Explain how carbon-containing compounds present in the pine leaves that fall from the trees are absorbed and used for growth by saprobionts/fungi that live in the soil.

A
  • extracellular digestion;
  • by secretion of enzymes;
  • absorption of digested/soluble products;
  • synthesis of structural compounds/named compound;.
  • respiration provide energy for growth
101
Q

Describe the process of eutrophication.

A
  • Nitrates / Phosphates / Ammonium ions flushed into waterway
  • Increased algal bloom light blocked out
  • Submerged aquatic plant unable to photosynthesise and die
  • Increase in saprobionts so increases rate of aerobic respiration
  • Saprobionts / aero.resp organismsn die as lack of oxygen (anoxic)
  • Increase in anaerobic microorganisms
  • Production of toxins
102
Q

Explain how a single base substitution causes a change in the structure of a polypeptide.

Do not include details of transcription and translation in your answer.

A
  1.    Change in (sequence of) amino acid(s)/primary structure;
    * Reject amino acids are formed.*
    * Reject amino acids code.*
  2.    Change in hydrogen & ionic & disulfide bonds;
  3.    Alters tertiary/30 structure;
103
Q

There are different types of gene mutation.

Which statement describes incorrectly the effect of the mutation in an exon of a gene.

A substitution may not result in a change to the encoded amino acid.

An inversion will result in a change in the number of DNA bases.

A deletion will result in a frame shift.

An addition will result in a frame shift.

A

An inversion will result in a change in the number of DNA bases.

104
Q

A type of malignant tumour cell divides every 8 hours.

Starting with one of these cells, how many tumour cells will be present after 4 weeks?

Assume none of these cells will die.

Give your answer in standard form.

A

1.9/1.93 × 1025

105
Q

What name is used for the non-coding sections of a gene?

A

Introns

106
Q

Explain why fragments of DNA from cancer cells may be present in blood plasma.

A

cancer cells die / break open releasing DNA;

107
Q

Describe how alterations to tumour suppressor genes can lead to the development of tumours.

A
  1. (Increased) methylation (of tumour suppressor genes);
    * Accept abnormal methylation or hypermethylation*
  2. Mutation (in tumour suppressor genes);
  3. Tumour suppressor genes are not transcribed/expressed

OR

Amino acid sequence/primary structure altered;

  1. (Results in) rapid/uncontrollable cell division;
108
Q

The time required for a cell to complete the cell cycle was 4 hours 18 minutes.

Calculate the time required in minutes for this cell to multiply to produce eight cells.

A

774 minutes / 12 hours 54mins

109
Q

Describe how DNA is replicated in a cell.

A
  • DNA strands separate / hydrogen bonds broken;
  • Parent strand acts as a template / copied / semi-conservative replication;
  • Nucleotides line up by complementary base pairing; (Adenine & Thymine etc)
  • Role of DNA polymerase: joins adjacent nucleotides on the developing strand via condensation and formation of phosphodiester bond;
  • 5’ to 3’ direction
  • Each new DNA molecule has 1 template and 1 new strand
  • Formed by semi-conservative replication.
110
Q

Why is the DNA heat to 95°C during PCR?

A
  • Produce single stranded DNA
  • Breaks WEAK hydrogen bonds between strands
111
Q

Why do you add primers during PCR?

A
  • Attaches to / complementary to start of the gene / end of fragment;
  • Replication of base sequence from here;
  • Prevents strands annealing
112
Q

Explain why ‘base-pairs’ is a suitable unit for measuring the length of a piece of DNA.

A
  • DNA = 2 chains / joined by linking of 2 bases / A with T and G with C/ purine pairs with pyrimidine;
  • Bases are a constant distance apart / nucleotides occupy constant distance/each base-pair is same length / sugar-phosphate is a constant distance;
113
Q

Name one mutagenic agent.

A
  • high energy radiation /ionising particles e.g. named particles/α, β, γ & X-rays;
  • benzene;
  • x rays/cosmic rays;
  • uv (light);
  • carcinogen / named carcinogen;
  • mustard gas / phenols / tar (qualified);
114
Q

A deletion mutation occurs in gene 1.

Describe how a deletion mutation alters the structure of a gene.

A
  • removal of one or more bases/nucleotide;
  • frameshift/(from point of mutation) base sequence change;
115
Q

Describe the main stages in the copying, cutting and separation of the DNA (fragments).

A
  • heat DNA to 95°C / 90°C;
  • strands separate;
  • cool so that primers bind to DNA;
  • add DNA polymerase/nucleotides;
  • use of restriction enzymes to cut DNA at specific base sequence/ breaks phosphodiester bonds
  • use of electric current and agar/gel;
  • shorter fragments move further;
116
Q

Describe the polymerase chain reaction.

A
  • Heat DNA (95 degrees C);
  • Breaks hydrogen bonds/separates strands;
  • Add primers;
  • Add nucleotides;
  • Cool to (50 d.C);
  • (to allow) binding of nucleotides/primers;
  • Heat to 70-75 degrees C to activate Taq DNA polymerase;
  • Role of (DNA) polymerase;
  • Repeat cycle many times;
117
Q

Describe a plasmid

A
  • circular DNA;
  • separate from main bacterial DNA;
  • contains only a few genes;
118
Q

Suggest one reason why DNA replication stops in the polymerase chain reaction.

A
  • Limited number of primers/nucleotides; /

Primers / nucleotides ‘used up’.

  • DNA polymerase (eventually)denatures
119
Q

Suggest why a restriction enzyme has cut the human DNA in many places but has cut the plasmid DNA only once.

A
  • enzymes only cut DNA at specific base sequence/recognition site/specific point;
  • sequence of bases/recognition site/specific point (on which enzyme acts)
  • occurs once in plasmid and many times in human DNA;
  • (max 1 if no reference to base sequence or recognition site)
120
Q

Describe how the bacteria containing the insulin gene are used to obtain sufficient insulin for commercial use.

A
  • use of fermenters;
  • provides nutrients plus suitable conditions for optimum growth/named
  • environmental factor;
  • reproduction of bacteria;
  • insulin accumulates and is extracted;
121
Q

Explain what is meant by a vector.

A
  • Carrier;
  • DNA/gene; (context of foreign DNA)
  • Into cell/other organism/host;
122
Q

Explain how modified plasmids are made by genetic engineering and how the use of markers enable bacteria containing these plasmids to be detected.

A
  • isolate TARGET gene/DNA from another organism/mRNA from cell/organism;
  • using restriction endonuclease/restriction enzyme/reverse transcriptase to get DNA;
  • produce sticky ends;
  • use DNA ligase to join TARGET gene to plasmid;
  • also include marker gene; example of marker e.g. antibiotic resistance;
  • add plasmid to bacteria to grow (colonies);
  • (replica) plate onto medium where the marker gene is expressed;
  • bacteria/colonies not killed have antibiotic resistance gene and (probably) the TARGET gene;
  • bacteria/colonies expressing the marker gene have the TARGET gene as well;
123
Q

mRNA may be described as a polymer. Explain why.

A
  • Made up of many (similar) molecules/monomers/nucleotides/units;
124
Q

What is a DNA probe?

A
  • (Short) single strand of DNA;
  • Bases complementary (with DNA/allele/gene)
125
Q

Name three techniques used by scientists to compare DNA sequences.

A
  • Polymerase Chain Reaction
  • DNA fingerprinting
  • Gel electrophoresis
126
Q

What is meant by a genome?

A
  • (All) the DNA in a cell/organism;
  • ‘(all) the ‘genes’/alleles’ ‘genetic material/code’ in a cell/organism/ person’
  • the total number of DNA bases in a cell/organism’

Reject all the DNA/ genes within a species

127
Q

Describe the roles of two named types of enzymes used to insert DNA fragments into plasmids.

A
  1. Restriction (endonuclease/enzyme) to cut plasmid/vector;
  2. Ligase joins gene/DNA to plasmid/vector;
128
Q

Describe how enzymes could be used to insert the GH gene into a plasmid.

A
  1. Restriction endonucleases/enzymes cuts plasmid; OR

Restriction endonucleases/enzymes produces ‘sticky ends’;

  • Reject restriction enzymes cuts the gene.*
    2. Ligase joins gene/DNA and plasmid OR

Ligase joins ‘sticky ends’;

129
Q

After obtaining copies of the HGH gene, the geneticist will attempt to insert them into plasmid vectors.

Describe how the geneticist would attempt to insert copies of the HGH gene into these plasmids.

A
  1. Cut the plasmid with a restriction endonuclease;
    * Allow ‘add base sequences to blunt ends of plasmid and HGH gene’*
  2. (So that) both have complementary / sticky ends;
  3. (Mix together) and add ligase to join the complementary / sticky ends;
130
Q

Suggest why the plasmids were injected into the eggs of silkworms, rather than into the silkworms.

A
  1. (If injected into egg), gene gets into all / most of cells of silkworm;
  2. So gets into cells that make silk.
131
Q

Name the type of enzyme used to produce the cDNA.

A

Reverse transcriptase;

132
Q

Describe what is meant by speciation (allopatric)

A
  • Geographical isolation;
  • Separate gene pools / no interbreeding (between populations);
  • Variation due to mutation;
  • Different environmental/abiotic/biotic conditions / selection pressures;
  • Selection for different/advantageous, features/characteristics/mutation/ /allele;
  • Differential reproductive success / (selected) organisms survive and reproduce;
  • Leads to change in allelic frequencies;
  • Cannot breed/mate to produce fertile offspring.
133
Q

Describe what is meant by speciation (sympatric)

A
  • NOT Geographical isolation;
  • Leads to reproductive isolation
  • Separate gene pools / no interbreeding (between populations);
  • Selection for different/advantageous, features/characteristics/mutation/ /allele;
  • Differential reproductive success / (selected) organisms survive and reproduce;
  • Leads to change in allelic frequencies;
    Cannot breed/mate to produce fertile offspring.
134
Q

Describe how bacteria can become resistant to antibiotics

A
  • Variation/variety;
  • Mutation;
  • Some bacteria have allele to survive/grow/live in high concentration of named antibiotic
  • adapted bacteria survive and replicate by binary fission;
  • Increase in frequency of allele;
135
Q

Describe the process of succession

A
  • (Colonisation by) pioneer species;
  • Pioneers cause change in environmental abiotic / biotic factors(give an example);
  • Pioneers make the environment less hostile for new species;
  • New species change/make conditions less suitable for previous species;
  • Change/increase in diversity/biodiversity;
  • Stability increases [population/richness/abiotic factors];
  • Climax community;
136
Q

Describe the effect of IAA on root and shoot growth.

A
  • IAA synthesised in shoots tips.
  • IAA diffuses into growing (cell elongating) region.
  • Light causes movement of IAA from light side to shaded side.
  • Proportionally more IAA on shaded side.
  • Causes directional growth as there is greater cell elongation on shaded side.
  • Shaded side grows faster and causes shoot to bend towards the light.
  • IAA synthesised in root tips.
  • IAA diffuses into growing (cell elongating) region.
  • IAA moves towards underside/shaded side.
  • Inhibits cell elongation.
  • Uneven growth (more elongation on side with less IAA).
  • Causes directional growth away from light and downwards towards gravity.
137
Q

Describe what is meant by the term taxis

A
  • Moves towards or away from directional stimulus
138
Q

Describe what is meant by the term kinesis

A
  • Movement is random/non-directional response
    OR
  • Organism does not move towards a particular stimulus;
139
Q

Compare & Contrast taxis and tropism

A
  • Both are directional responses to stimuli
  • Taxis involves the movement of the entire organism whereas tropism is the movement of part of an organism
140
Q

Explain the advantages of simple reflex arcs

A
  • Rapid;
  • Protect against damage to body tissues;
  • Do not have to be learnt;
  • Help escape from predators;
  • Enable homeostatic control;
141
Q

As a neurone transmits an impulse, its rate of oxygen consumption increases.
Explain why.

A
  • ATP required for active transport;
  • Na+ (actively) moved out only at nodes in myelinated / Na+ (actively) moved out along whole length of axon in non-myelinated;
142
Q

Describe how a resting potential is maintained in a neurone.

A
  • active transport/pumping of sodium (ions across membrane);
  • out of neurone/higher concentration outside;
  • differential permeability to K+ and Na+;
  • Membrane more permeable to K+ ions;
143
Q

The potential across the membrane is reversed when an action potential is produced.

Describe how.

A
  • Sodium ion gates / channel (proteins) open;
  • Na+ (rapidly) diffuse in;
144
Q

SYNAPSE:

Describe the sequence of events leading to the release of acetylcholine and its binding to the postsynaptic membrane.

A
  • Depolarisation of presynaptic membrane;
  • Ca2+ channels open and calcium ions enter (synaptic knob);
  • (Calcium ions cause) synaptic vesicles move to/fuse with presynaptic membrane and release acetylcholine / neurotransmitter;
  • Acetylcholine/neurotransmitter diffuses across (synaptic cleft);
  • (Acetylcholine attaches) binds to receptors on the postsynaptic membrane;
  • Sodium ions enter (postsynaptic neurone) leading to depolarisation;
145
Q

When a nerve impulse arrives at a synapse, it causes the release of neurotransmitter from vesicles in the presynaptic knob.

Describe how.

A
  • (Nerve impulse/depolarisation of membrane) causes Ca2+ channel (proteins) to open;
  • Ca2+ enter by (facilitated) diffusion;
  • Causes (synaptic) vesicles to fuse with (presynaptic) membrane;
146
Q

The binding of GABA to receptors on postsynaptic membranes causes negatively charged chloride ions to enter postsynaptic neurones.

Explain how this will inhibit transmission of nerve impulses by postsynaptic neurones.

A
  • (Inside of postsynaptic) neurone becomes more negative/hyperpolarised;
  • More sodium ions required (to reach threshold) OR Not enough sodium ions enter (to reach threshold);
  • For depolarisation/action potential;
147
Q

Describe how the speed of the conduction could be increased in a neurone.

A
  • Axon is myelinated;
  • So shows saltatory conduction/impulses jump from node of Ranvier to node of Ranvier;
    OR
  • Axon has a larger diameter;
  • So less resistance to flow of ions;
148
Q

Myelination affects the rate of conduction of a nerve impulse. Explain how.

A
  • Actno potential jumps from node of Ranvier to node of Ranvier / depolarisation only at node of Ranvier;
  • Fewer jumps / depolarisations to travel length of axon;
149
Q

Describe how the inhibition of acetylcholinesterase affects the action of synapses.

A
  • Acetylcholine not broken down / stays bound to receptor;
  • Na+ ions (continue to) enter / (continued) depolarisation / Na+ channels (kept) open / action potentials;
150
Q

Describe what is meant by the term refractory period

A
  • (Refractory period) limits number of impulses per second/frequency of nerve impulses;
  • Maximum frequency of impulse transmission
  • Period of time between threshold and return to resting membrane potential.
  • When maximum frequency reached/exceeded, no further increase in information/ all (higher) stimuli seem the same;
151
Q

What is meant by a fatigued synapse?

A

When release (Fusion of vesicles with presynaptic membrane) of neurotransmitters exceeds production of vesicle bound neurtransmitters.

152
Q

Describe how synaptic transmission is unidirectional.

A
  • Vesicles with neurotransmitters are only ever produced in the terminal end branch of the presynaptic neuone
  • Neurotransmitter receptors are only ever located on the post synaptic membrane.
153
Q

Explain how the fovea increases the detail of an image.

A
  • High (visual) acuity
  • Each / single cone is connected to a single bipolar/neurone
  • Each cone sends separate impulse to the brain
154
Q

Explain how the connection of several rods to a single bipolar cell (Retinal convergence) influences visual acuity

A
  • (Spatial) Summation means cannot distinguish between stimuli from different rod cells linked to same bipolar cell;
  • Decreases acuity;
155
Q

Explain how the connection of several rods to a single bipolar cell (Retinal convergence) influences sensitivity

A
  • (Summation of) sub-threshold stimuli produces threshold stimulation;
  • Increases sensitivity;
156
Q

People with red-green colour blindness are unable to distinguish between red and green, and also between other colours

Explain why.

A
  • Green sensitive pigment/cones non-functional
    OR
    Cones that detect green light non-functional;
  • Three different types of pigment/cone;
  • Other/different colours (‘seen’) due to stimulation of more than one cone/pigment;
157
Q

Explain how pressure on the Pacinian corpuscle produces the changes in membrane potential recorded by microelectrode A.

A
  • (Pressure) deforms / opens (sodium) channels;
  • Sodium ions enter;
  • Causing depolarisation;
  • Increased pressure opens more channels / greater sodium entry;
  • [Size of generator potential determines frequency of action potentials]
158
Q

Exercise causes an increase in heart rate.

Describe the role of receptors and of the nervous system in this process.

A
  1. Chemoreceptors detect rise in CO2 / H+ / acidity / carbonic acid /f all in pH
    OR
    Baro / pressure receptors detect rise in blood pressure;
  2. Send impulses to cardiac centre/medulla;
  3. More impulses to SAN;
  4. By sympathetic (nervous system for chemoreceptors / CO2)
    OR
    By parasympathetic (nervous system for baro / pressure receptors / blood pressure);
159
Q

The rate of ATP consumption of a de-myelinated neurone is greater than that of a myelinated neurone when conducting impulses at the same frequency.

Explain why.

A
  • Greater entry of sodium ions / greater exit of K+
  • in de-myelinated neurone;
  • Ref. to active transport / ref. to ion pumps;
160
Q

Explain how nervous control in a human can cause increased cardiac output during exercise.

A
  • Coordination via medulla (of brain) / cardiac centre;
  • (Increased) impulses along sympathetic nerve;
  • To S.A. node;
  • Release of noradrenalin;
  • More impulses sent from S.A.N (across atria);
  • Increased heart rate / increased stroke volume;
161
Q

Explain why increased cardiac output is an advantage during exercise.

A
  • Higher cardiac output - Increases O2 supply (to muscles);
  • Increases glucose supply (to muscles);
  • More ATP produced by oxidative phosphorylation / more energy release / more aerobic respiration / actively respiring muscles
  • Increases CO2 removal (from muscles) / lactate removal;
  • Increases heat removal (from muscles) / for cooling;
  • Delays the formation of lactate
162
Q

Describe how the Pacinian corpuscle propagates an action potential.

A
  • (Pressure causes) membrane/lamellae to become deformed/stretched;
  • Sodium ion channels in membrane open and sodium ions move in;
  • Depolarisation leading to generator potential;
  • Greater pressure more channels open/sodium ions enter;
163
Q

Describe what is meant by the term threshold

A
  • When threshold has been reached;
  • (Threshold or above) causes maximal response / all or nothing principle;
164
Q

Describe the banding pattern in striated muscle.

A
  • Lightest band is I band, actin only
  • Darkest band is overlapping region, actin and myosin
  • Medium shading is H zone/band is myosin only.
165
Q

Describe the sliding filament theory

A
  • Attachment / cross bridges between actin and myosin heads;
  • ‘Power stroke’ / movement of myosin heads / pulling of actin (over myosin);
  • Detachment of myosin heads (requires ATP binding);
  • (Energy from ATP) Myosin heads move back/to original position / ‘recovery stroke’;
166
Q

Describe the function of calcium ions in muscle contraction.

A
  • Ca2+ Binding/changing shape/removing tropomyosin;
  • Exposes actin binding sites;
  • Myosin head attaches/cross-bridge formation;
  • Activates ATP hydrolase;
167
Q

Nerve impulses arriving at the presynaptic membrane at the neuromuscular junction
result in shortening of sarcomeres.

Describe how. [5 marks]

A
  • Entry of calcium ions (presynaptic membrane);
  • Vesicles fuse with membrane / exocytosis /release Ach (Acetylcholine);
  • Neurotransmitter diffuses;
  • Binds to receptors, postsynaptic / membrane / muscle membrane;
  • Depolarisation / sodium ions enter;
  • Release of calcium ions (from within the muscle);
  • Removes tropomyosin / bind to troponin;
  • Exposing binding sites on the actin;
  • Actinomyosin cross bridge formation / myosin binds;
  • Myosin head moves / pulls the actin along;
  • Rachet mechanism / description /detach and reattach;
  • ATP hydrolase activated;
168
Q

Explain the importance of ATP hydrolase during muscle contraction.

A
  • Hydrolysis of ATP releasing energy;
  • used to form / break actinomyosin cross-bridges;
169
Q

Muscle contraction requires ATP. What are the advantages of using aerobic rather than anaerobic respiration to provide ATP in a long-distance race?

A
  • Aerobic respiration releases more energy / produces more ATP;
  • Little/no lactate produced / does not accumulate;
  • Avoids cramp / muscle fatigue;
  • CO2 easily removed from the body / CO2 removed by breathing;
170
Q

A muscle fibre contracts when it is stimulated by a motor neurone. Describe how transmission occurs across the synapse between a motor neurone and a muscle fibre.

A
  • Ca2+ channels / gates open;
  • Ca2+ ions enter (pre-synaptic neurone);
  • Vesicles move towards / fuse with presynaptic membrane;
  • Release / exocytosis of transmitter substance / of acetylcholine;
  • Diffusion (of transmitter) across gap / cleft;
  • (Transmitter) binds to receptors in postsynaptic membrane;
  • Na+ channels open / Na+ ions enter (postsynaptic side);
171
Q

After death, cross bridges between actin and myosin remain firmly bound resulting in rigor mortis. Explain what causes the cross bridges to remain firmly bound.

A
  • respiration stops;
  • no ATP produced;
  • ATP required for separation of actin and myosin/cross bridges;
172
Q

Describe the role of calcium ions in the contraction of a sarcomere.

A
  • interact with/move/touch tropomyosin; (allow troponin as alternative)
  • to reveal binding sites on actin; (not active sites)
  • allowing myosin (heads) to bind/touch actin / actinomyosin formed;
  • activate ATP hydrolase / energy released from ATP;
173
Q

Describe slow twitch muscle fibres

A
  • have lots of mitochondria/ (slow fibres) respire aerobically;
  • More myoglobin
174
Q

Describe fast twitch muscle fibres

A
  • used for rapid/brief/powerful/strong contractions;
  • Phosphocreatine used up rapidly during contraction/to make ATP;
  • Anaerobic respiration involved;
  • ATP used to reform phosphocreatine;
  • Lots of phosphocreatine in fast twitch fibres;
  • No myoglobin
175
Q

Describe the role of phosphocreatine

A
  • Provides (energy and) phosphate / phosphorylates;
  • To make ATP from ADP & Pi;
176
Q

Homeostasis

Explain how insulin reduces the blood glucose concentration.

A
  • (More) insulin binds to receptors;
  • (Stimulates) uptake of glucose by channel/transport proteins
  • Activates enzymes which convert glucose to glycogen;
177
Q

Explain the action of Glucagon

A
  • Attaches to receptors on target cells and activates/stimulates enzymes;
  • Glycogen to glucose / glycogenolysis;
  • Gluconeogenesis;
178
Q

Explain the effect of sweating or panting on temperature control.

A
  • Evaporation (of water from lining of mouth or skin);
  • Heat transferred from blood;
179
Q

Describe how a change in blood pH or blood pressure can cause a change in heart rate.

A
  • (Carbon dioxide) detected by chemoreceptors / (pressure) detected by baroreceptors;
  • Medulla/cardiac centre involved;
  • More impulses to SAN/along sympathetic nerve;
  • (Decrease) pH detected by chemoreceptors in carotid artery /aorta;
  • Sends (more) impulses to medulla (oblongata);
  • More Nerve impulses sent by sympathetic nervous system to SAN;
180
Q

Less CO2 in the blood leads to a reduction in heart rate.

Describe how.

A
  • (less CO2 in blood) Detected by chemoreceptors;
  • (Chemoreceptors) located in aorta / carotid artery;
  • Fewer impulses to cardiac centre / medulla (oblongata);
  • (More) impulses along parasympathetic nerve OR less impulses along sympathetic nerve;
  • (To) SAN;
181
Q

Describe the secondary messenger model

A
  • Adenylate cyclase activated / cAMP produced / second messenger produced;
  • Activates enzyme(s) (in cell);
  • (So) glycogenolysis/ gluconeogenesis occurs / glycogenesis inhibited;
182
Q

Describe the role of glycogen formation and its role in lowering blood glucose levels.

A
  • Glucose concentration in cell/liver falls;
  • Below that in blood (plasma)/ higher in blood;
  • Creates/maintains glucose concentration/diffusion gradient;
  • Glucose enters cell/leaves blood by facilitated diffusion/via carrier(protein)/channel (protein);
183
Q

Describe how blood glucose levels can be increased using hormones.

A
  • Release of glucagon;
  • Leads to formation of glucose in liver (cells);
  • From non-carbohydrates/amino acids/fatty acids;
184
Q

Describe how ultrafiltration occurs in a glomerulus.

A
  • Higher than normal High blood/hydrostatic pressure;
  • Two named small substances pass out eg water, glucose, ions, urea;
  • (Through small) gaps/pores/fenestrations in (capillary) endothelium;
  • (And) through (capillary) basement membrane;
185
Q

Explain why a thicker medulla leads to more concentrated urine.

A
  • Thicker medulla means a longer loop of Henle;
  • (The longer the loop of Henle means) increase in sodium ion concentration (in medulla) so sodium ion gradient maintained for longer (in medulla);
  • (Therefore) water potential gradient maintained (for longer), so more water (re)absorbed (from loop and collecting duct) by osmosis;
186
Q

Describe the action of ADH in the kidney.

A
  • Permeability of membrane/cells (to water) is increased;
  • More water absorbed from/leaves distal tubule/collecting duct;
  • Smaller volume of urine;
  • Urine becomes more concentrated;

AQA A Level Biology (3 decks)

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