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AQA A Level Biology > Year 12 AQA BIOLOGY (Complete) > Flashcards

Year 12 AQA BIOLOGY (Complete) Flashcards

This is the complete set of cards for Year 12

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1
Q

Describe Semi-conservative replication.

A
  1. Strands separate / H-bonds break;
  2. DNA helicase (involved);
  3. Both strands/each strand act(s) as (a) template(s);
  4. (Free) nucleotides attach;
  5. Complementary/specific base pairing due to H bonds forming between bases/ Adenine to Thymine and GC;
  6. DNA polymerase joins nucleotides (on new strand) forming phoshodiester bonds by condensation;
  7. Semi-conservative replication / new DNA molecules contain one old strand and one new strand;
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2
Q

An enzyme catalyses only one reaction. Explain why.

A
  1. (Enzyme has) active site is a specific shape;

2. Only one substrate fits / binds (the active site);

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3
Q

Describe how the structure of a protein depends on the amino acids it contains.

A
  1. Structure is determined by (relative) position of amino acid/R group/interactions;

Accept for ‘interactions’, hydrogen bonds / disulfide bridges / ionic bonds / hydrophobichydrophilic interactions

  1. Primary structure is sequence/order of amino acids;
  2. Secondary structure formed by hydrogen bonding (between amino acids);

Accept alpha helix/β-pleated sheet for ‘secondary structure’

  1. Tertiary structure formed by interactions (between R groups);

Accept for ‘interactions’, hydrogen bonds / disulfide bridges / ionic bonds / hydrophobichydrophilic interactions

  1. Creates active site in enzymes

OR

Creates complementary/specific shapes in antibodies/carrier proteins/receptor (molecules);

  1. Quaternary structure contains >1 polypeptide chain

OR

Quaternary structure formed by interactions/bonds between polypeptides;

Accept for ‘intereactions’, hydrogen bonds/ disulfide bridges/ionic bonds/hydrophobichydrophilic interactions

Accept prosthetic (group)

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4
Q

Describe Transcription in Eukaryotes

A
  1. Hydrogen bonds (between DNA bases) break;
  2. (Only) one DNA strand acts as a template;
  3. (Free) RNA nucleotides align by complementary base pairing;
  4. (In RNA) Uracil base pairs with adenine (on DNA) OR (In RNA) Uracil is used in place of thymine;
  5. RNA polymerase joins (adjacent RNA) nucleotides;
  6. (By) phosphodiester bonds (between adjacent nucleotides);
  7. Pre-mRNA is spliced (to form mRNA) OR Introns are removed (to form mRNA);
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5
Q

What are algae cell walls made from (Polymer)

A

CELLULOSE

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6
Q

A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange.

A

1 Large surface area provided by many lamellae over many gill filaments;
2 Increases diffusion/makes diffusion efficient;
3 Thin epithelium/distance between water and blood;
4 Water and blood flow in opposite directions/countercurrent;
5 (Point 4) maintains concentration gradient (along gill)/equilibrium not reached;
6 As water always next to blood with lower concentration of oxygen;
7 Circulation replaces blood saturated with oxygen;
8 Ventilation replaces water (as oxygen removed);

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7
Q

Explain how the humoral response leads to immunity.

A
  1. B cells specific to the antigen reproduce by mitosis.
  2. B cells produce plasma and memory cells
  3. Second infection produces antibodies in larger quantities AND quicker.
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8
Q

Describe how a person infected with HIV will develop AIDS (if untreated) and die of secondary infections.

A
  • High viral load leads to increased destruction of helper T/CD4 cells;
  • Less activation of B cells/cytotoxic T cells/phagocytes;
  • Less production of plasma cells/antibodies OR (With cytotoxic T cells) less able to kill virus infected cells;
  • (Less able to) destroy other microbes/pathogens OR (Less able to) destroy mutated/cancer cells;
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9
Q

Hydrogen bonds are important in cellulose molecules. Explain why

A
  • Holds chains/cellulose molecules together/forms cross links between chains/cellulose molecules/forms microfibrils;
  • Providing strength/rigidity (to cellulose/cell wall);
  • Weak Hydrogen bonds provide strength in large numbers;
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10
Q

The action of endopeptidases and exopeptidases can increase the rate of protein digestion. Describe how.

A
  1. Exopeptidases hydrolyse peptide bonds at the ends of a polypeptide/protein AND endopeptidases hydrolyse internal peptide bonds within a polypeptide/protein;
  2. More ‘ends’ OR More surface area;
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11
Q

HSW:

The student looked at cells in a 1 in 10 dilution during his preliminary work. He decided not to use this dilution to determine the number of cells in the undiluted liquid culture.

Suggest an explanation for the student’s decision.

A
  1. Count unlikely to be accurate / repeatable / reproducible / reliable;
  2. Because too many cells; OR Because cells overlapping / not spread out;
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12
Q

Explain why plants grown in soil with very little water grow only slowly

A
  1. Stomata close;

2. Less carbon dioxide (uptake) for less photosynthesis/glucose production;

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13
Q

Describe the advantage of the Bohr effect during intense exercise.

A
  1. Increases dissociation of oxygen;

Accept unloading/ release/reduced affinity for dissociation

  1. For aerobic respiration at the tissues/muscles/cells

OR

Anaerobic respiration delayed at the tissues/muscles/cells

OR

Less lactate at the tissues/muscles/cells;

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14
Q

Describe a biochemical test to show that raffinose solution contains a non-reducing sugar.

A
  1. Heat with acid and neutralise with alkali. eg HCl, NaHCO3
  2. Heat with Benedict’s (solution);
  3. Red precipitate;
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15
Q

In the process of semi-conservative DNA replication, the two strands within a DNA molecule are separated. Each then acts as a template for the formation of a new complementary strand.

Describe how the separation of strands occurs.

A
  1. DNA helicase;
  2. Breaks hydrogen bonds between base pairs/ AT and GC/complementary bases

OR

Breaks hydrogen bonds between polynucleotide strands;

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16
Q

Describe and explain the advantage of the counter-current principle in gas exchange across a fish gill.

A

1.   Water and blood flow in opposite directions;

2.   Maintains diffusion/concentration gradient of oxygen OR equilibrium not reached OR
Oxygen concentration always higher (in water);

3.   (Diffusion) along (whole) length of lamellae/filament/gill/capillary;

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17
Q

When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how

A
  1. Vaccine contains antigen from pathogen;
  2. Macrophage presents antigen on its surface;
  3. T (helper) cell with complementary receptor protein binds to antigen;
  4. T cell stimulates B cell;
  5. (With) complementary antibody on its surface;
  6. B cell divides to form clone secreting / producing same antibody;
  7. B cell secretes large amounts of antibody;
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18
Q

State three differences between DNA in the nucleus of a plant cell and DNA in a prokaryotic cell.

A

Plant v prokaryote

  1. (Associated with) histones/proteins v no histones/proteins;
  2. Linear v circular;
  3. No plasmids v plasmids;
  4. Introns v no introns;
  5. Long(er) v short(er);
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19
Q

Describe two precautions the student should take when clearing away after the dissection.

A
  1. Carry/wash sharp instruments/scalpel by holding handle OR Carry/wash sharp instruments by pointing away (from body)/down;
  2. Disinfect instruments/surfaces;
  3. Disinfect/sanitise hands OR Wash hands with soap (and water);
  4. Put organ/gloves/paper towels in a (separate) bag/bin/tray to dispose;
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20
Q

Give two properties of water that are important in the cytoplasm of cells.
For each property of water, explain its importance in the cytoplasm.

A
  1. Polar molecule;
  2. Acts as a (universal) solvent;
    OR
  3. (Universal) solvent;
  4. (Metabolic) reactions occur faster in solution;
    OR
  5. Reactive;
  6. Takes place in hydrolysis / condensation / named reaction;
    Polar molecule so acts as (universal) solvent so (metabolic reactions are faster = 3 marks
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21
Q

Explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake

A
  1. Large(r) organisms have a small(er) surface area:volume (ratio); OR Small(er) organisms have a large(r) surface area:volume (ratio);
  2. Overcomes long diffusion pathway OR Faster rate of diffusion;
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22
Q

Describe the role of DNA polymerase in the semi-conservative replication of DNA.

A
  1. Joins (adjacent DNA) nucleotides; 5’ to 3’
  2. (Catalyses) condensation (reactions);
  3. (Catalyses formation of) phosphodiester bonds (between adjacent nucleotides);
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23
Q

Describe the role of antibodies in producing a positive result in an ELISA test.

A
  1. (First) antibody binds/attaches /complementary (in shape) to antigen; 2. (Second) antibody with enzyme attached is added;
  2. (Second) antibody attaches to antigen;
  3. (Substrate/solution added) and colour changes;
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24
Q

Give one advantage of viewing a biological specimen using a transmission electron microscope compared with using a scanning electron microscope.

A

Higher resolution OR View internal structures;

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25
Q

Describe the process of complete digestion of starch

A 
(salivary/pancreatic) Amylase;
Maltose;
Maltase; 
Maltose to glucose;
Hydrolysis;
Glycosidic bonds;
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26
Q

Describe Transcription in Eukaryotes

A
  1. Hydrogen bonds (between DNA bases) break;
  2. (Only) one DNA strand acts as a template;
  3. (Free) RNA nucleotides align by complementary base pairing;
  4. (In RNA) Uracil base pairs with adenine (on DNA) OR (In RNA) Uracil is used in place of thymine;
  5. RNA polymerase joins (adjacent RNA) nucleotides;
  6. (By) phosphodiester bonds (between adjacent nucleotides);
  7. Pre-mRNA is spliced (to form mRNA) OR Introns are removed (to form mRNA);
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27
Q

HSW:

Describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for this root tip was accurate.

A
  1. Examine large number of fields of view / many cells; [20 or more]
  2. To ensure representative sample;

OR

  1. Repeat count;
  2. To ensure figures are correct;

OR

  1. Method to deal with part cells shown at edge /count only whole cells;
  2. To standardise counting;
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28
Q

Heat from respiration helps mammals to maintain a constant body temperature.
Use this information to explain the relationship between the surface area to volume ratio of mammals and the oxygen dissociation curves of their haemoglobins.

A
  1. Smaller mammal has greater surface area to
    volume ratio;
  2. Smaller mammal/larger SA:Vol ratio more
    heat lost (per unit body mass);
  3. Smaller mammal/larger SA:Vol ratio has
    greater rate of respiration/metabolism;
  4. Oxygen required for respiration;
    (Haemoglobin) releases more oxygen / oxygen released more readily / haemoglobin has lower affinity;
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29
Q

Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind.

Explain why.

A
  1. Binding of first oxygen changes tertiary / quaternary (structure) of haemoglobin; [conformational shift caused]
  2. Creates / leads to / uncovers second / another binding site OR Uncovers another iron / Fe / haem group to bind to;
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30
Q

Describe the absorption of glucose (Cotransport)

A
  1. Sodium ions actively transported from ileum cell to blood;
  2. Maintains / forms diffusion gradient for sodium to enter cells from gut (and with it, glucose);
  3. Glucose enters by facilitated diffusion with sodium ions;
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31
Q

Suggest two ways the student could improve the quality of his scientific drawing

A
  1. Only use single lines/do not use sketching (lines)/ensure lines are continuous/connected;
  2. Add labels/annotations/title;
  3. Add magnification/scale (bar);
  4. Draw all parts to same scale/relative size;
  5. Do not use shading/hatching;
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32
Q

What is the function of Cell surface membrane

A

Made of a Phospholipid Bilayer;
Controls what enters the cell/ is selectively permeable;
Can be folded to increase Surface Area;

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33
Q

What is the role of the disulfide bridge in forming the quaternary structure of an antibody?

A

Joins two (different) polypeptides;

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34
Q

Name the protein associated with DNA in a chromosome.

A

Histone;

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35
Q

Describe the features of Telophase

A

Nuclear membrane begins to reform;

Chromosomes unwind;

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36
Q

What is a homologous pair of chromosomes?

A

Two chromosomes that carry the same genes in the same loci / location

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37
Q

Explain why death of alveolar epithelium cells reduces gas exchange in human lungs.

A
  1. Reduced surface area;
  2. Increased distance for diffusion;
  3. Reduced rate of gas exchange;
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38
Q

Other than the distribution of stomata, suggest and explain two xerophytic features the leaves of this plant might have.

A
  1. Hairs so ‘trap’ water vapour and water potential gradient decreased;
  2. Stomata in pits/grooves so ‘trap’ water vapour and water potential gradient decreased;
  3. Thick (cuticle/waxy) layer so increases diffusion distance;
  4. Waxy layer/cuticle so reduces evaporation/transpiration.
  5. Rolled/folded/curled leaves so ‘trap’ water vapour and water potential gradient decreased;
  6. Spines/needles so reduces surface area to volume ratio;
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39
Q

The structure of cellulose is related to its role in plant cell walls. Explain how.

A
  • Long, straight, unbranched chains of Beta glucose;
  • (Joined by) many WEAK hydrogen bonds;
  • Form microfibrils / macrofibrils;
  • Provide rigidity/strength/support;
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40
Q

Describe binary fission in bacteria.

A
  1. Replication of (circular) DNA;

Accept nucleoid

  1. Replication of plasmids;
  2. Division of cytoplasm (to produce daughter cells);
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41
Q

Compare and contrast the processes by which water and inorganic ions enter cells.

A
  1. Comparison: both move down concentration gradient;
  2. Comparison: both move through (protein) channels in membrane;
    Accept aquaporins (for water) and ion channels
  3. Contrast: ions can move against a concentration gradient by active transport
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42
Q

Describe the structure of proteins.

A
  • Polymer of amino acids;
  • Joined by peptide bonds;
  • Formed by condensation reactions;
  • Primary structure is number AND order of amino acids;
  • Secondary structure is folding of polypeptide chain into Alpha-helix and Beta-pleated sheets due to hydrogen bonding;
  • Tertiary structure is 3-D folding due to hydrogen bonding and ionic bonding and disulfide bridges;
  • Quaternary structure is two or more polypeptide chains joined together;
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43
Q

What is the function of Plasmid

A

Circular DNA;

Contains antibiotic resistance genes;

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44
Q

Explain how oxygen is loaded, transported and unloaded in the blood.

A
  • Haemoglobin carries oxygen / has a high affinity for oxygen / oxyhaemoglobin;
  • In red blood cells;
  • Loading/uptake/association in lungs at high p.O2;
  • Unloads/ dissociates / releases to respiring cells/tissues at low p.O2;
  • Unloading linked to higher carbon dioxide (concentration);
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45
Q

Describe Translation

A
  1. (mRNA attaches) to ribosomes OR (mRNA attaches) to rough endoplasmic reticulum;
  2. (tRNA) anticodons (bind to) complementary (mRNA) codons;
  3. tRNA brings a specific amino acid;
  4. Amino acids join by peptide bonds;
  5. (Amino acids join together) with the use of ATP;
  6. tRNA released (after amino acid joined to polypeptide);
  7. The ribosome moves along the mRNA to form the polypeptide;
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46
Q

A student investigated variation in snail shell height in two populations of snails.

Give two ways in which the student could ensure his samples would provide a reliable measure of the variation between individuals in each population.

A
  1. Select at random to remove bias

2. Large sample/number (of snails)/>10;

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47
Q

HSW:

Why do we use RATIOS ?

A

Allows valid comparisons between two numbers

Original numbers may vary

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48
Q

Describe how you would use the student’s results (dilution series and % change in mass) to find the water potential of the potato tissue.

A
  1. Plot a graph with concentration on the x-axis and percentage change in mass on the y-axis;
  2. Find concentration where curve crosses the x-axis / where percentage change is zero;
  3. Use (another) resource to find water potential of sucrose concentration (where curve crosses x-axis).
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49
Q

What are the differences between a triglyceride and a phospholipid?

A
  1. Fatty acid removed;

2. Replaced with a phosphate group;

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50
Q

Describe the difference between active and passive immunity.

A
  1. Active involves memory cells, passive does not;
  2. Active involves production of antibody by plasma cells/memory cells;
  3. Passive involves antibody introduced into body from outside/named source;
  4. Active long term, because antibody produced in response to antigen;
  5. Passive short term, because antibody (given) is broken down;
  6. Active (can) take time to develop/work, passive fast acting;
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51
Q

Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin.

A
  1. Increases/more oxygen dissociation/unloading OR Deceases haemoglobin’s affinity for O2;
  2. (By) decreasing (blood) pH/increasing acidity;
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52
Q

HSW:

Why do we use STANDARD DEVIATIONS?

A

Shows spread of data around the mean
Reduces the effect of outliers
See if differences between mean values are significant (SD don’t overlap ) or not (SD do overlap) / calculate T value for the T test
Allows STATS test to be completed to determine if differenes are significant

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53
Q

Describe how the movement of the diaphragm leads to air movement into the lungs

A
  1. Diaphragm contracts and flattens.
  2. Volume of lungs increases.
  3. Pressure inside the lungs is lower than atmospheric pressure.
  4. Air moves into the lungs.
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54
Q

Explain how oxygen is loaded, transported and unloaded in the blood.

A
  • Haemoglobin carries oxygen / has a high affinity for oxygen / oxyhaemoglobin;
  • In red blood cells;
  • Loading/uptake/association in lungs at high p.O2;
  • Unloads/ dissociates / releases to respiring cells/tissues at low p.O2;
  • Unloading linked to higher carbon dioxide (concentration);
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55
Q

Describe the gross structure of the human gas exchange system and how we breathe in and out.

A
  1. Named structures – trachea, bronchi, bronchioles, alveoli;
  2. Above structures named in correct order OR Above structures labelled in correct positions on a diagram;
  3. Breathing in – diaphragm contracts and external intercostal muscles contract;
  4. (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric, resulting in air moving in);
  5. Breathing out - Diaphragm relaxes and internal intercostal muscles contract;
  6. (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting in air moving out);
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56
Q

A forest was cleared to make more land available for agriculture.
After the forest was cleared the species diversity of insects in the area decreased.

Explain why

A
  1. Decrease in variety of plants / fewer plant species;
  2. Fewer habitats/niches;
  3. Decrease in variety of food / fewer food sources;
  4. Aspect of clearing forest (killing insects) eg machinery, pesticides;
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57
Q

What is the function of Chloroplasts

A

Contain thylakoids, stacked into Granum;
Site of photosynthesis;

Grana (Light dependent reaction)
Stroma (Light independent reaction)

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58
Q

Name the 7 bonds found within biological molecules

A

Carbohydrates: Glycosidic / Hydrogen (cellulose)
Polypeptides: Peptide / Ionic / Hydrogen / Disulphide
Lipids: Ester
Nucleic acids: Phosphodiester / Hydrogen
Water: Hydrogen
ATP: Phosphoric anhydride

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59
Q

Name the two scientists who proposed models of the chemical structure of DNA and of DNA replication.

A

Crick and Watson;

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60
Q

Describe and explain the mechanism that causes lungs to fill with air.

A
  1. Diaphragm (muscle) contracts and external intercostal muscles contract ribs move up and out
  2. (Causes volume increase and) pressure decrease;
  3. Air moves down a pressure gradient

OR

Air enters from higher atmospheric pressure;

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61
Q

Explain how one feature of an alveolus allows efficient gas exchange to occur.

A
  1. (The alveolar epithelium) is one cell thick;

2. Creating a short diffusion pathway / reduces the diffusion distance;

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62
Q

Describe binary fission in bacteria.

A
  1. Replication of (circular) DNA;
  2. Replication of plasmids;
  3. Division of cytoplasm (to produce daughter cells);
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63
Q

Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind.

Explain why.

A
  1. Binding of first oxygen changes tertiary / quaternary (structure) of haemoglobin; [conformational shift caused]
  2. Creates / leads to / uncovers second / another binding site OR Uncovers another iron / Fe / haem group to bind to;
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64
Q

Sucrase does not hydrolyse lactose. Use your knowledge of the way in which enzymes work to explain why.(3)

A
  1. Lactose has a different shape/structure;
  2. Does not fit/bind to active site of enzyme/sucrase;
    OR
  3. Active site of enzyme/sucrase has a specific shape/structure;
  4. Does not fit/bind to lactose so no Enzyme-Substrate Complexes formed.
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65
Q

Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them.

A

• Many alveoli/ alveoli walls folded provide a large surface area;
• Many capillaries provide a large surface area (So) fast diffusion;
Alveoli or capillary walls/ epithelium/ lining are thin/ one cell thick / short distance between alveoli and blood;
• Flattened/ squamous epithelium (So) short diffusion distance/ pathway / (So) fast diffusion;
• Ventilation / circulation; So Maintains a diffusion / concentration gradient (So) fast diffusion;

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66
Q

Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution.

A
  1. Filter and dry (the precipitate);

2. Find mass/weight;

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67
Q

Eukaryotic cells produce and release proteins. Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells.

A
  1. DNA in nucleus is code (for protein);
  2. Ribosomes/rough endoplasmic reticulum produce (protein);
  3. Mitochondria produce ATP (for protein synthesis);
    4 Golgi apparatus package/modify; OR Carbohydrate added/glycoprotein produced by Golgi apparatus;
    5 Vesicles transport OR Rough endoplasmic reticulum transports;
  4. (Vesicles) fuse with cell(-surface) membrane;
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68
Q

Compare & Contrast Eukaryotic and Prokaryotic DNA

A

Comparisons
1. Nucleotide structure is identical;
2. Nucleotides joined by phosphodiester bond;
OR Deoxyribose joined to phosphate (in sugar, phosphate backbone);
3. DNA in mitochondria / chloroplasts same / similar (structure) to DNA in prokaryotes;
Contrasts
4. Eukaryotic DNA is longer;
5. Eukaryotic DNA contain introns, prokaryotic DNA does not;
6. Eukaryotic DNA is linear, prokaryotic DNA is circular;
7. Eukaryotic DNA is associated with / bound to protein / histones, prokaryotic DNA is not;

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69
Q

Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf.

A
  1. (Carbon dioxide enters) via stomata;
  2. (Stomata opened by) guard cells;
  3. Diffuses through air spaces;
  4. Down diffusion gradient;
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70
Q

Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin.

A
  1. Increases/more oxygen dissociation/unloading OR Deceases haemoglobin’s affinity for O2;
  2. (By) decreasing (blood) pH/increasing acidity;
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71
Q

Which stats test would you use if the data is categoric?

E.g. Difference between ‘Number of yellow shelled snails and pink shelled snails’

A

CHI Squared

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72
Q

When a pathogen causes an infection, plasma cells secrete antibodies which destroy this pathogen.
Explain why these antibodies are only effective against a specific pathogen.(2)

A
  • Antigens (on pathogen) are a specific shape/ have specific tertiary / 3D structure;
  • Antibody fits/binds / is complementary to antigen/ antibody-antigen complex forms; OR Antibodies are a specific shape / have specific tertiary/ 3D structure;
  • Antigens (on pathogen) fit/ bind/ are complementary to antibody / antibody-antigen complex forms;
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73
Q

Describe how tissue fluid is formed and how it is returned to the circulatory system.

A

Formation

  1. High blood / hydrostatic pressure / pressure filtration;
  2. Forces water / fluid out;
  3. Large proteins remain in capillary;

Return

  1. Low water potential in capillary / blood;
  2. Due to (plasma) proteins;
  3. Water enters capillary / blood;
  4. (By) osmosis;
  5. Correct reference to lymph;
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74
Q

Define ‘non-coding base sequences’ and describe where the non-coding multiple repeats are positioned in the genome.

A
  1. DNA that does not code for protein/polypeptides OR DNA that does not code for (sequences of) amino acids OR DNA that does not code for tRNA/rRNA;
  2. (Positioned) between genes;
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75
Q

Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein

A
  • Glucose and galactose
  • Joined by condensation
  • Joined by glycosidic bond
  • Added to polypeptide in Golgi
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76
Q

What is the proteome of a cell?

A

(The proteome is the full) range of / number of different proteins that a cell is able to produce (at a given time);
OR
(The proteome is the full) range of / number of different proteins the genome / DNA is able to code for;

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77
Q

Polluted air contains more particulate matter than clean air.

A high concentration of particulate matter results in the death of some alveolar epithelium cells. If alveolar epithelium cells die inside the human body they are replaced by non-specialised, thickened tissue.

Explain why death of alveolar epithelium cells reduces gas exchange in human lungs.

A
  1. Reduced surface area;
  2. Increased distance for diffusion;
  3. Reduced rate of gas exchange;
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78
Q

Describe how an ester bond is formed in a phospholipid molecule.

A
  1. Condensation (reaction) OR Loss of water;

2. Between of glycerol and fatty acid;

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79
Q

Describe the induced fit model of enzyme action.(2)

A
  1. Active site not complementary;
  2. Active site changes (shape) / is flexible;
  3. (Change in enzyme allows) substrate to able to fit / Enzyme-Substrate complex to form;
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80
Q

Describe how haemoglobin normally loads oxygen in the lungs and unloads it in a tissue cell.

A
  • Oxygen combines (reversibly) to produce oxyhaemoglobin;
  • each haemoglobin molecule/ one haemoglobin may transport 4 molecules of oxygen;
  • higher partial pressure of oxygen / oxygen tension / concentration in lungs;
  • haemoglobin (almost) 95% / 100% saturated;
  • unloads at low oxygen tension (in tissues);
  • presence of carbon dioxide displaces curve further to right / increases oxygen dissociation;
  • allows more O2 to be unloaded;
  • increase temp/ acidity allows more O2 to be unloaded;
  • low pO2 / increase CO2 / increase term / increase acidity occur in vicinity of respiring tissue;
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81
Q

Name a factor that can affect transpiration

A

Light (intensity) / temperature / air movement / humidity;

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82
Q

Describe & explain how you could use the biuret test to distinguish a solution of enzyme, lactase, from a solution of lactose(2)

A
  1. Add Biuret reagent to both solutions) – no
    mark;
  2. Lactase / enzyme will give purple / lilac / mauve;
    OR
  3. Lactose / reducing sugar will not give purple /
    lilac /mauve / will remain blue;
  4. Because Lactase is a protein;
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83
Q

Describe and explain two features you would expect to find in a cell specialised for absorption.

A
  1. Folded membrane/microvilli so large surface area (for absorption);
    Accept ‘brush border’ for ‘microvilli’.
  2. Large number of co-transport/carrier/channel proteins so fast rate (of absorption) OR
    Large number of co-transport/carrier proteins for active transport OR
    Large number of co-transport/carrier/channel proteins for facilitated diffusion;
  3. Large number of mitochondria so make (more) ATP (by respiration) OR
    Large number of mitochondria for aerobic respiration OR
    Large number of mitochondria to release energy for active transport;
  4. Membrane-bound (digestive) enzymes so maintains concentration gradient (for fast absorption);
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84
Q

What is the formula for percentage change?

A

[Difference / Original] x 100

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85
Q

HSW: Define Standard deviation

A

Spread of data around the mean

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86
Q

Which stats test would you use if there is a relationship between 2 (continuous) variables?

E.g. Age and Height

A

Correlation Coefficient

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87
Q

The student used a sharp scalpel to cut the specimen.

Describe how she should ensure she handled the scalpel safely during this procedure.

A
  1.    Cut away from body; Accept description of cutting technique to avoid cutting fingers
  2.    Against hard/non-slip/flat surface; Accept named hard surface eg tile/board
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88
Q

Explain how oxygen in a red blood cell is made available for respiration in active tissues.

A
  • CO2 (increased) respiration;
  • (increased) dissociation oxygen from haemoglobin;
  • Low partial pressure in tissues/plasma;
  • Oxygen diffuses from r.b.c. to tissues;
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89
Q

Define ‘gene mutation’ and explain how a gene mutation can have:
• no effect on an individual
• a positive effect on an individual.

A

(Definition of gene mutation)
1. Change in the base/nucleotide (sequence of chromosomes/DNA);
2. Results in the formation of new allele;
(Has no effect because)
3. Genetic code is degenerate (so amino acid sequence may not change); OR
Mutation is in an intron (so amino acid sequence may not change);
Accept description of ‘degenerate’, eg some amino acids have more than one triplet/codon.
4. Does change amino acid but no effect on tertiary structure;
5. (New allele) is recessive so does not influence phenotype;
(Has positive effect because)
6. Results in change in polypeptide that positively changes the properties (of the protein) OR Results in change in polypeptide that positively changes a named protein; For ‘polypeptide’ accept ‘amino acid sequence’ or ‘protein’.
7. May result in increased reproductive success OR May result in increased survival (chances);

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90
Q

Describe the features of Metaphase

A

Spidle fibres form;
Spindle fibres attach;
To the centromere of chromosomes;
Chromosomes align at the equator;

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91
Q

Arteries and arterioles take blood away from the heart. Explain how the structures of the walls of arteries and arterioles are related to their functions. (6)

A

Elastic tissue
1 Elastic tissue stretches under pressure/when heart contracts;
2 Recoils/springs back;
3 Evens out pressure/flow;
Muscle
4 Muscle contracts;
5 Reduces diameter of lumen/vasoconstriction/constricts vessel;
6 Changes flow/pressure;
Epithelium
7 Epithelium smooth;
8 Reduces friction/blood clots/less resistance;

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92
Q

Explain what the term non-overlapping DNA means.

A

A base from one triplet cannot be used in an adjacent triplet

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93
Q

The movement of substances across cell membranes is affected by membrane structure.

Describe how.

A
  • Phospholipid (bilayer) allows movement/diffusion of non-polar/lipid-soluble substances;
  • Phospholipid (bilayer) prevents movement/diffusion of polar/ charged/lipid-insoluble substances OR (Membrane) proteins allow polar/charged substances to cross the membrane/bilayer;
  • Carrier proteins allow active transport;
  • Channel/carrier proteins allow facilitated diffusion/co-transport;
  • Shape/charge of channel / carrier determines which substances move;
  • Number of channels/carriers determines how much movement;
  • Membrane surface area determines how much diffusion/movement;
  • Cholesterol affects fluidity/rigidity/permeability;
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94
Q

Describe how a peptide bond is formed between two amino acids to form a dipeptide

A
  1. Condensation (reaction) / loss of water;

2. Between amine / NH2 and carboxyl / COOH;

95
Q

Tests using monoclonal antibodies are specific. Use your knowledge of protein structure to explain why.

A
  • (Specific) primary structure / order of amino acids;
  • (Specific) tertiary / 3D structure / shape;
  • (So) Only binds to / fits / complementary to one antigen;
96
Q

Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them.

A

• Many alveoli/ alveoli walls folded provide a large surface area;
• Many capillaries provide a large surface area (So) fast diffusion;
Alveoli or capillary walls/ epithelium/ lining are thin/ one cell thick / short distance between alveoli and blood;
• Flattened/ squamous epithelium (So) short diffusion distance/ pathway / (So) fast diffusion;
• Ventilation / circulation; So Maintains a diffusion / concentration gradient (So) fast diffusion;

97
Q

Explain how oxygen in a red blood cell is made available for respiration in active tissues.

A
  • CO2 (increased) respiration;
  • (increased) dissociation oxygen from haemoglobin;
  • Low partial pressure in tissues/plasma;
  • Oxygen diffuses from r.b.c. to tissues;
98
Q

Many different substances enter and leave a cell by crossing its cell surface membrane.
Describe how substances can cross a cell surface membrane.

A

1 (Simple / facilitated) diffusion from high to low concentration / down concentration gradient;
2 Small / non-polar / lipid-soluble molecules pass via phospholipids / bilayer;
OR
Large / polar / water-soluble molecules go through proteins;
3 Water moves by osmosis / from high water potential to low water potential / from less to more negative water potential;
4 Active transport is movement from low to high concentration / against concentration gradient;
5 Active transport / facilitated diffusion involves proteins / carriers;
6 Active transport requires energy / ATP;
7 Ref. to Na+ / glucose co-transport;

99
Q

Give one reason why eggs produced by meiosis are genetically different.

A

Independent segregation

OR

Crossing over;

100
Q

Describe and explain two features you would expect to find in a cell specialised for absorption.

A
  1. Folded membrane/microvilli so large surface area (for absorption);
  2. Large number of co-transport/carrier/channel proteins so fast rate (of absorption)

OR Large number of co-transport/carrier proteins for active transport

OR Large number of co-transport/carrier/channel proteins for facilitated diffusion;

  1. Large number of mitochondria so make (more) ATP (by respiration) OR Large number of mitochondria for aerobic respiration OR Large number of mitochondria to release energy for active transport;
  2. Membrane-bound (digestive) enzymes so maintains concentration gradient (for fast absorption);
101
Q

Describe the structure of a phospholipid molecule and explain how phospholipids are arranged in a plasma membrane (3 marks).

A
  1. Glycerol joined to two fatty acid tails Phosphate group joined to glycerol on opposite side. (joined by condensation reaction with ester bond).;
  2. Phospholipid has hydrophilic head (phosphate and glycerol) and hydrophobic tails (fatty acid chains)
  3. Arrange to form a phospholipid bilayer; (Hydrophilic head facing out. Hydrophobic fatty acid chains facing in)
102
Q

Describe the features of Prophase

A

Nuclear membrane begins to breakdown;
Centrioles move to poles of the cell;
Chromatin supercoils and condense in chromosomes;

103
Q

Describe the structure of DNA relates to its functions

A
  1. Sugar-phosphate (backbone)/double stranded/helix so provides strength/stability /protects bases/protects hydrogen bonds;
  2. Long/large molecule so can store lots of information;
  3. Helix/coiled so compact;
  4. Base sequence allows information to be stored/ base sequence codes for amino acids/protein;
  5. Double stranded so replication can occur semi-conservatively/ strands can act as templates;
  6. Complementary base pairing / A-T and G-C so accurate replication/identical copies can be made;
  7. (Weak) hydrogen bonds for replication/ unzipping/strand separation;
  8. Many weak hydrogen bonds so stable/strong molecule;
104
Q

Describe how you could use the emulsion test to show that a seed contains lipids. (3)

A
  1. Crush/grind;
  2. With ethanol/ alcohol, to dissolve the lipid;
  3. Then add water then shake;
  4. Forms a white emulsion / goes white;
105
Q

Give two precautions the students should have taken when setting up the potometer to obtain reliable measurements of water uptake by the plant shoot.

A
  1. Seal joints / ensure airtight / ensure watertight;
  2. Cut shoot under water;
  3. Cut shoot at a slant;
  4. Dry off leaves;
  5. Insert into apparatus under water;
  6. Ensure no air bubbles are present;
  7. Shut tap;
  8. Note where bubble is at start / move bubble to the start position;
106
Q

Give one feature of starch and explain how this feature enables it to act as a storage
substance.

A
  • Helical / spiral So compact / tightly packed / can fit (lots) into a small space;
  • Insoluble So no osmotic effect / does not leave cell / does not affect water potential;
  • Large molecule / long chain (So) does not leave cell / contains large number of glucose units;
  • Branched chains (So) rapid hydrolysis to remove glucose for respiration;
107
Q

Describe how courtship behaviour increases the probability of successful mating.

A
  1. Attracts/recognises same species;
  2. Attracts/recognises mate/opposite sex;
  3. Indication of sexual maturity/ fertility / synchronises mating;
  4. Stimulates release of gametes;
  5. Form pair bond;
108
Q

Suggest two ways the student could improve the quality of his scientific drawing

A
  1. Only use single lines/do not use sketching (lines)/ensure lines are continuous/connected;
  2. Add labels/annotations/title;
  3. Add magnification/scale (bar);
  4. Draw all parts to same scale/relative size;
  5. Do not use shading/hatching;
109
Q

Describe and explain the advantage of the counter-current principle in gas exchange across a fish gill.

A
  1. Water and blood flow in opposite directions;
  2. Maintains diffusion/concentration gradient of oxygen OR Oxygen concentration always higher (in water);
  3. (Diffusion) along length of lamellae/filament/gill/capillary;
110
Q

Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange.

A
  1. Tracheoles have thin walls so short diffusion distance to cells;
  2. Highly branched / large number of tracheoles so short diffusion distance to cells;
  3. Highly branched / large number of tracheoles so large surface area (for gas exchange);
    4.Tracheae provide tubes full of air so fast diffusion (into insect tissues);
  4. Fluid in the end of the tracheoles that moves out (into tissues) during exercise so faster diffusion through the air to the gas exchange surface;
    OR
    Fluid in the end of the tracheoles that moves out (into tissues) during exercise so larger surface area (for gas exchange);
  5. Body can be moved (by muscles) to move air so maintains diffusion / concentration gradient for oxygen / carbon dioxide;
111
Q

Describe and explain the mechanism that causes forced expiration.

A
  1. Contraction of internal intercostal muscles;
  2. Relaxation of diaphragm muscles / of external intercostal muscles;
  3. Causes decrease in volume of chest / thoracic cavity;
  4. Air pushed down pressure gradient.
112
Q

HSW:

How would you use the equation
M1 x V1 = M2 x V2
to make a solution of known concentration?

A 
M1 = desired conc
V1 = desired volume
M2 = original/stock conc
V2 = volume stock needed
113
Q

HSW:

Use of a colorimeter in this investigation would improve the repeatability of the student’s results.

Give one reason why

A
  1.    Quantitative values are not subjective / More accurate / More precise
  2.    Standardises (the) method;
114
Q

What is the function of Lysosomes

A

Contains digestive enzymes;

Digests worn out organelles/autolysis;

115
Q

Describe the structure of the human immunodeficiency virus (HIV).

A
  1. RNA (as genetic material);
  2. Reverse transcriptase;
  3. (Protein) capsomeres/capsid;
  4. (Phospho)lipid (viral) envelope OR Envelope made of membrane;
  5. Attachment proteins;
116
Q

Describe how you would use a 1.0 mol dm−3 solution of sucrose to produce 30 cm3 of a 0.15 mol dm−3 solution of sucrose.

A

Add 4.5 cm3 of (1.0 mol dm–3) solution to 25.5 cm3 (distilled) water.
Mix

117
Q

Describe how a non-competitive inhibitor works

A
  1. Attaches to the enzyme at a site other than the active site (allosteric site);
  2. Changes (shape of) the active site OR Changes tertiary structure (of enzyme);
  3. (So active site and substrate) no longer complementary so less/no substrate can fit/bind (‘no longer complementary so less/no enzyme-substrate complexes form’);
118
Q

When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how

A
  1. Vaccine contains antigen from pathogen;
  2. Macrophage presents antigen on its surface;
  3. T (helper) cell with complementary receptor protein binds to antigen;
  4. T cell stimulates B cell;
  5. (With) complementary antibody on its surface;
  6. B cell divides to form clone secreting / producing same antibody;
  7. B cell secretes large amounts of antibody;
119
Q

The structure of cellulose is related to its role in plant cell walls. Explain how. (3)

A
  • Long, straight, unbranched chains of Beta glucose;
  • (Joined by) many WEAK hydrogen bonds;
  • Form microfibrils / macrofibrils;
  • Provide rigidity/strength/support;
120
Q

A mutation in a gene coding for an enzyme

could lead to the production of a non-functional enzyme. Explain how

A
  1. Change in base sequence (of DNA/gene);
  2. Change in amino acid sequence / primary structure (of enzyme);
  3. Change in hydrogen/ionic/ disulphide bonds;
  4. Change in the tertiary structure/active site (of enzyme);
  5. Substrate not complementary/cannot bind (to enzyme / active site) / no enzyme-substrate complexes form;
121
Q

Explain the arrangement of phospholipids in a cell-surface membrane.

A
  • Bilayer OR Water is present inside and outside a cell;
  • Hydrophobic (fatty acid) tails point away/are repelled from water OR Hydrophilic (phosphate) heads point to/are in/are attracted to water;
122
Q

Describe one way that the lock and key model is different from the induced fit model(2)

A
  1. Active site does not change (shape) / is fixed (shape) / is rigid / does not wrap around
  2. substrate / (already) fits the substrate / is
  3. complementary (before binding);
123
Q

HSW: Why can some conclusions NOT be made ?

A

No Standard Deviation given for the means

124
Q

Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample.

A

Lipid

  1. Add ethanol/alcohol then add water and shake/mix OR Add ethanol/alcohol and shake/mix then pour into/add water;
  2. White/milky emulsion OR emulsion test turns white/milky;

Non-reducing sugar

  1. Do Benedict’s test and stays blue/negative;
  2. Boil with acid then neutralise with alkali;
  3. Heat with Benedict’s and becomes red/orange (precipitate);

Amylase

  1. Add biuret (reagent) and becomes purple/violet/mauve/lilac;
  2. Add starch, (leave for a time), test for reducing sugar/absence of starch;
125
Q

Many different substances enter and leave a cell by crossing its cell surface membrane.
Describe how substances can cross a cell surface membrane.

A

1 (Simple / facilitated) diffusion from high to low concentration / down concentration gradient;
2 Small / non-polar / lipid-soluble molecules pass via phospholipids / bilayer;
OR
Large / polar / water-soluble molecules go through proteins;
3 Water moves by osmosis / from high water potential to low water potential / from less to more negative water potential;
4 Active transport is movement from low to high concentration / against concentration gradient;
5 Active transport / facilitated diffusion involves proteins / carriers;
6 Active transport requires energy / ATP;
7 Ref. to Na+ / glucose co-transport;

126
Q

Root pressure moves water through the xylem. Describe what causes root pressure. (4)

A
  1. Active transport by endodermis;
  2. ions/salts into xylem;
  3. Lowers water potential (in xylem);
  4. (Water enters) by osmosis;
127
Q

Describe how a student could use an eyepiece graticule to determine the mean diameter of stomata.

A
  1. Measure (each stoma) using eyepiece graticule;
  2. Calibrate eyepiece graticule against stage micrometer / ruler / graph paper;
  3. Take a large number of measurements (to calculate a mean);
128
Q

What is the function of Cell Wall

A

Provides rigid shape / structure;

Stops osmotic lysis;

129
Q

What is the function of Capsule

A

Protects cell from immune systems;

Aids bacteria sticking together;

130
Q

Explain why a cell membrane may be described as a fluid-mosaic?

A
  • The position of the molecules within the membrane is fluid – they are able to move around within the membrane.
  • Membrane is made up from a variety of different molecules arranged into a mosaic.
131
Q

Describe the gross structure of human gas exchange system and how we breathe in and out

A
  • Named structures – trachea, bronchi, bronchioles, alveoli
  • Above structures named in correct order OR Above structures labelled in correct positions on a diagram
  • Breathing in – Diaphragm contract and external intercostal muscles contract
  • Volume increases and pressure decreases in thoracic cavity.
  • Breathing out – Diaphragm relaxes and internal intercostal muscles contract
  • Volume decrease and pressure increase in thoracic cavity
132
Q

Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels.

A
  1. Micelles contain bile salts and fatty acids/monoglycerides;
  2. Make fatty acids/monoglycerides (more) soluble (in water)

OR Bring/release/carry fatty acids/monoglycerides to cell/lining (of the iluem)

OR Maintain high(er) concentration of fatty acids/monoglycerides to cell/lining (of the ileum);

  1. Fatty acids/monoglycerides absorbed by diffusion;
  2. Triglycerides (re)formed (in cells);

Accept chylomicrons form

  1. Vesicles move to cell membrane;

Accept exocytosis for ‘vesicles move’

133
Q

Name and describe five ways substances can move across the cell-surface membrane into a cell.

A
  1. (Simple) diffusion of small/non-polar molecules down a concentration gradient;
  2. Facilitated diffusion down a concentration gradient via protein carrier/channel;
  3. Osmosis of water down a water potential gradient;
  4. Active transport against a concentration gradient via protein carrier using ATP;
  5. Co-transport of 2 different substances using a carrier protein;
134
Q

What is the function of the Ribsosomes

A

Site of Protein synthesis (Translation)

135
Q

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

A
  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;
136
Q

Describe how an ester bond is formed in a phospholipid molecule.

A
  1. Condensation (reaction) OR Loss of water;

2. Between of glycerol and fatty acid;

137
Q

What is the function of the Nucleus

A

Contains genetic material / DNA;

Controls cell activity;

138
Q

Describe how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta.

A
  1. Atrium has higher pressure than ventricle (due to filling / contraction);
  2. Atrioventricular valve opens;
  3. Ventricle has higher pressure than atrium (due to filling / contraction);
  4. Atrioventricular valve closes;
  5. Ventricle has higher pressure than aorta;
    Points 1, 3, 5, and 7 must be comparative: eg higher
  6. Semilunar valve opens;
    Marks 2, 4, 6, 8 given in the correct sequence can gain 4 marks
  7. Higher pressure in aorta than ventricle (as heart relaxes);
  8. Semilunar valve closes;
  9. (Muscle / atrial / ventricular) contraction causes increase in pressure;
139
Q

The number of species present is one way to measure biodiversity.

Explain why an index of diversity may be a more useful measure of biodiversity.

A

Also measures number of individuals in a species / different proportions of species;
Some species may be present in low/high numbers;

140
Q

Explain how oxygen is loaded, transported and unloaded in the blood.

A
  • Haemoglobin carries oxygen / has a high affinity for oxygen / oxyhaemoglobin;
  • In red blood cells;
  • Loading/uptake/association in lungs at high p.O2;
  • Unloads/ dissociates / releases to respiring cells/tissues at low p.O2;
  • Unloading linked to higher carbon dioxide (concentration);
141
Q

Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst.

A
  1. Substrate binds to the active site/enzyme OR Enzyme-substrate complex forms;
  2. Active site changes shape (slightly) so it is complementary to substrate OR Active site changes shape (slightly) so distorting/breaking/forming bonds in the substrate;
  3. Reduces activation energy;
142
Q

Describe the role of enzymes in the digestion of proteins in a mammal.

A
  1. (Reference to) hydrolysis of peptide bonds;
  2. Endopeptidase act in the middle of protein/polypeptide OR Endopeptidase produces short(er) polypeptides/ increase number of ends;
  3. Exopeptidases act at end of protein/polypeptide OR Exopeptidase produces dipeptides/amino acids;
  4. Dipeptidase acts on dipeptide/between two amino acids OR Dipeptidase produces (single) amino acids;
143
Q

Describe the role of enzymes in the digestion of proteins in a mammal.

A
  1. (Reference to) hydrolysis of peptide bonds;
  2. Endopeptidase act in the middle of protein/polypeptide OR Endopeptidase produces short(er) polypeptides/ increase number of ends;
  3. Exopeptidases act at end of protein/polypeptide OR Exopeptidase produces dipeptides/amino acids;
  4. Dipeptidase acts on dipeptide/between two amino acids OR Dipeptidase produces (single) amino acids;
144
Q

The oxygen dissociation curve of the foetus is to the left of that for its mother. Explain the advantage of this for the foetus.

A
  • Higher affinity / loads more oxygen;
  • At low/same/high partial pressure/pO2;
  • Oxygen moves from mother/to foetus;
145
Q

Explain how selection occurs in living organisms

A
  1. Variation due to mutation;
  2. Different environmental/abiotic/biotic conditions / selection pressures;
  3. Selection for different/advantageous, features/characteristics/mutation/ /allele;
  4. Differential reproductive success / (selected) organisms survive and reproduce;
  5. Leads to change in allele frequency;
  6. Occurs over a long period of time;
146
Q

State why some antibodies are referred to as monoclonal

A

(Antibodies) produced from a single clone of B cells / plasma cells;
OR

(Antibodies) produced from the same B cell / plasma cell;

147
Q

Suggest one economic argument for maintaining biodiversity.

A

A suitable example of how some species may be important financially e.g.

  1. medical / pharmaceutical uses;
  2. commercial products / example given;
  3. tourism;
  4. agriculture;
  5. saving local forest communities;
148
Q

Compare & Contrast Eukaryotic and Prokaryotic DNA

A

Comparisons
1. Nucleotide structure is identical;
2. Nucleotides joined by phosphodiester bond;
OR Deoxyribose joined to phosphate (in sugar, phosphate backbone);
3. DNA in mitochondria / chloroplasts same / similar (structure) to DNA in prokaryotes;
Contrasts
4. Eukaryotic DNA is longer;
5. Eukaryotic DNA contain introns, prokaryotic DNA does not;
6. Eukaryotic DNA is linear, prokaryotic DNA is circular;
7. Eukaryotic DNA is associated with / bound to protein / histones, prokaryotic DNA is not;

149
Q

Suggest how one antibody can be specific to two different proteins.

A
  1. (Part of both proteins) have a similar tertiary structure;
  2. Antibody is complementary to both OR Antigen-binding site is complementary to both (different proteins) OR Antibody can form antigen-antibody complex with both
150
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;
151
Q

Explain the decrease in mass of potato tissue in the 0.40 mol dm−3 solution of sucrose.

A
  1. Water potential of solution is less than / more negative than that of potato tissue; (Ψ as equivalent to water potential)
  2. Tissue loses water by osmosis.
152
Q

How does oxygen move through the insect?

A
  1. Oxygen diffuses in through the spiracles;
  2. Spiracle closes;
  3. Oxygen moves through the trachea into the tracheoles;
  4. Oxygen delivered directly to the respiring tissues;
153
Q

Describe how the human immunodeficiency virus (HIV) is replicated once inside helper T cells (TH cells).

A
  1. RNA converted into DNA using reverse transcriptase;
  2. DNA incorporated/inserted into (helper T cell) DNA/chromosome/genome/nucleus;
  3. DNA transcribed into (HIV m)RNA;
  4. (HIV mRNA) translated into (new) HIV/viral proteins (for assembly into viral particles);
154
Q

Two solutions often used to stain tissues are haematoxylin solution and iodine solution.

  • Haematoxylin solution stains DNA a blue colour.
  • Iodine solution stains starch a blue-black colour.

A scientist used haematoxylin solution and not iodine solution to stain the lung tissue.

Suggest why.

A
  1. Lung tissue does not contain starch;
  2. (Makes) nucleus visible;

OR

Nucleus contains DNA;

155
Q

Describe the roles of iron ions, sodium ions, and phosphate ions in cells.

A

Iron ions
1. Haemoglobin binds/associates with oxygen OR Haemoglobin transports/loads oxygen;
Sodium ions
2. Co-transport of glucose/amino acids (into cells);
3. (Because) sodium moved out by active transport/Na – K pump;
4. Creates a sodium concentration/diffusion gradient;
5. Affects osmosis/water potential;
Phosphate ions
6. Affects osmosis/water potential;
7. Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides;
8. Used in/to produce ATP;
9. Phosphorylates other compounds (usually) making them more reactive;
10. Hydrophilic/water soluble part of phospholipid bilayer/membrane

156
Q

Describe how a change in the base sequence of the DNA coding for an enzyme may result in a non-functional protein.

A
  1. Change in primary structure changes
    sequence of amino acids;
  2. Hydrogen bonds and Ionic bonds and Disulphide bonds form in different positions;
  3. Alters the tertiary structure of the enzyme / alters shape of active site;
  4. No Enzyme-Substrate complexes can be formed;
157
Q

Describe how comparisons of biological molecules in two species could be used to find out if they are closely related.

A

Compare DNA base sequence;
Compare RNA base sequence;
Compare sequence of amino acids /primary structure (of named / same protein);

158
Q

Describe and explain the role of antibodies in stimulating phagocytosis.

A
  • Bind to antigen OR Are markers;

* (Antibodies) cause (clumping) agglutination OR Attract phagocytes;

159
Q

What is the function of the Mitochondria

A

Site of AEROBIC respiration;

ATP production;

160
Q

What is the function of the Smooth Endoplasmic Reticulum

A

Site of lipid synthesis;

161
Q

Which stats test would you use to see the DIFFERENCE between two MEANS?

E.g. Difference between mean heights of males and females

A

STUDENT T Test

162
Q

Describe how an enzyme-substrate complex increases the rate of reaction

A
  1. Reduces activation energy

2. Due to bending bonds OR Without the enzyme, very few substrates have sufficient energy for the reaction.

163
Q

Suggest one ethical argument for maintaining biodiversity.

A

Prevent extinction
Loss of populations
Reduction in populations
Loss of habitats

164
Q

Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how.

A
  1. Homologous chromosomes pair up;
  2. maternal and paternal chromosomes are arranged in any order;
  3. Independent segregation;
  4. Crossing over;
  5. (Equal) Portions of chromatids are swapped between chromosomes;
  6. Produces new combination of alleles;
  7. Chromatids separated at meiosis II/ later;
165
Q

Describe how a phagocyte destroys a pathogen present in the blood.

A
  1. Engulfs;
  2. Forming vesicle/phagosome and fuses with lysosome;
  3. Enzymes hydrolyse;
166
Q

Describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for this root tip was accurate.

A

Description; Explanation;
E.g, 1. Examine large number of fields of view / many cells;
2. To ensure representative sample;

OR

  1. Repeat count;
  2. To ensure figures are correct;

OR

  1. Method to deal with part cells shown at edge /count only whole cells;
  2. To standardise counting;
167
Q

Describe the non-specific defence mechanisms the body may launch against pathogens (5 marks)

A

The process is called phagocytosis – No Mark
1. Pathogen is engulfed by the phagocyte.
2. Engulfed pathogen enters the cytoplasm of
the phagocyte in a vesicle;
3. Lysosomes fuse with vesicle releasing
digestive enzymes;
4. Lysosome enzymes break down the pathogen.
5. Waste materials are ejected from the cell by exocytosis;

168
Q

Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange.

A
  1. Tracheoles have thin walls so short diffusion distance to cells;
  2. Highly branched / large number of tracheoles so short diffusion distance to cells;
  3. Highly branched / large number of tracheoles so large surface area (for gas exchange);
    4.Tracheae provide tubes full of air so fast diffusion (into insect tissues);
  4. Fluid in the end of the tracheoles that moves out (into tissues) during exercise so faster diffusion through the air to the gas exchange surface;
    OR
    Fluid in the end of the tracheoles that moves out (into tissues) during exercise so larger surface area (for gas exchange);
  5. Body can be moved (by muscles) to move air so maintains diffusion / concentration gradient for oxygen / carbon dioxide;
169
Q

Scientists isolated mitochondria from liver cells. They broke the cells open in an ice-cold, buffered isotonic solution. Explain why the solution was:

a) Isotonic
b) Ice cold
c) buffered

A

a) Prevents osmosis / no (net) movement of water So organelle/named organelle does not burst/shrivel;
b) Reduce/prevent enzyme activity so organelles are not digested / damaged;
c) Maintain a constant pH so proteins do not denature;

170
Q

Describe how haemoglobin normally loads oxygen in the lungs and unloads it in a tissue cell.

A
  • Oxygen combines (reversibly) to produce oxyhaemoglobin;
  • each haemoglobin molecule/ one haemoglobin may transport 4 molecules of oxygen;
  • high partial pressure of oxygen / oxygen tension / concentration in lungs;
  • haemoglobin (almost) 95% / 100% saturated;
  • unloads at low oxygen tension(in tissues);
  • presence of carbon dioxide displaces curve further to right / increases oxygen dissociation;
  • allows more O2 to be unloaded;
  • increase temp/ acidity allows more O2 to be unloaded;
  • low pO2 / increase CO2 / increase term / increase acid occur in vicinity of respiring tissue;
171
Q

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.

A
  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
  3. Wear gloves / Wear mask / Wash hands;
  4. To prevent contamination from bacteria on hands / mouth / Prevent spread of bacteria outside the lab;
    OR
  5. Use sterile pipette / Flame the loop / Flame the neck of the container of the culture;
  6. To maintain a pure culture of bacteria
172
Q

Explain what is meant by a phylogenetic group

A

(Grouped according to) evolutionary links/history/relationships / common ancestry;

173
Q

Scientists use optical microscopes and transmission electron microscopes to investigate cell structure. Explain the advantages and limitations of using a TEM to investigate cell structure.

A

Advantages:
1 Small objects can be seen;
2 TEM has high resolution;
3 Electron wavelength is shorter;

Limitations:
4 Cannot look at living cells;
5 Must be in a vacuum;
6 Must cut section / thin specimen;
7 Preparation may create artefact;
174
Q

Suggest two ways a student could improve the quality of their scientific drawing

A
  1. Don’t use shading;
  2. Only use single lines / don’t use sketching (lines) / ensure lines are continuous / connected;
  3. Add further labels / annotations;
  4. Don’t cross label lines;
  5. Add magnification / scale (bar);
175
Q

The thickness of the aorta wall changes all the time during each cardiac cycle.

Explain why

A
  1. (Aorta wall) stretches;
  2. Because ventricle/heart contracts / systole / pressure increases;
  3. (Aorta wall) recoils;
  4. Because ventricle relaxes / heart relaxes /diastole / pressure falls;
  5. Maintain smooth flow / pressure;
176
Q

Define the term exon.

A

Base/nucleotide/triplet sequence coding for polypeptide/sequence of amino acids/primary structure;

177
Q

Give one advantage of using a SEM rather than a TEM.

A

Thin sections do not need to be prepared / shows surface of specimen / can have 3-D images;

178
Q

What is the function of the Rough Endoplasmic reticulum

A

Encrusted in Ribosomes;
Site of protein synthesis;
Transports and stores protein within the cell

179
Q

Give one advantage of using a TEM rather than a SEM.

A
  1. Higher resolution;
  2. higher (maximum) magnification / higher detail (of image);
    OR
  3. Allows internal details / structures within (cells) to be seen / cross section to be taken;
180
Q

The movement of Na+ out of the cell allows the absorption of glucose into the cell lining the ileum.

Explain how

A
  1. (Maintains/generates) a concentration/diffusion gradient for Na+ (from ileum into cell);

Accept ‘(Maintains/generates) a lower concentration of Na+ inside the cell compared with outside the cell’.

  1. Na+ moving (in) by facilitated diffusion, brings glucose with it

OR

Na+ moving (in) by co-transport, brings glucose with it;

181
Q

Explain how HIV affects the production of antibodies when AIDS develops in a person.

A
  1. Less/no antibody produced;
  2. (Because HIV) destroys helper T cells;

Accept ‘reduces number’ for ‘destroys’

  1. (So) few/no B cells activated / stimulated

OR

(So) few/no B cells undergo mitosis/differentiate/form plasma cells;

182
Q

Describe how an enzyme can be phosphorylated.

A
  • Attachment/association of (inorganic) phosphate (to the enzyme);
    1. (Released from) hydrolysis of ATP OR (Released from) ATP to ADP + Pi;
183
Q

In classification, comparing the base sequence of a gene provides more information than comparing the amino acid sequence for which the gene codes. Explain why.

A
  • Reference to base triplet/triplet code / more bases than amino acids / longer base sequence than amino acid sequence;
  • Introns/non-coding DNA;
  • Same amino acid may be coded for / DNA code is degenerate;
184
Q

Explain how a competitive inhibitor works

A
  1. Inhibitor is a similar shape to substrate;
  2. Inhibitor enters active site / competes with substrate;
  3. Less substrate binds/fewer enzyme-substrate complexes form per second.
185
Q

What is a monomer?

A

A monomer is a smaller / repeating) unit / molecule from which larger molecules / polymers are made;

186
Q

The structure of a cholera bacterium is different from the structure of an epithelial cell from the small intestine. Describe how the structure of a cholera bacterium is different

A
  1. Cholera bacterium is prokaryote;
  2. Does not have a nucleus/nuclear envelope/ has DNA free in cytoplasm/has loop of DNA;

3 and 4 Any two from: [No membrane-bound organelles/no mitochondria / no golgi/no endoplasmic reticulum];
5 Small ribosomes only;
6 and 7 Any two from [Capsule/flagellum/plasmid / cell wall]

187
Q

Explain what is meant by genetic diversity.

A

Difference in DNA/base sequence/alleles/genes;

188
Q

Describe the features of Anaphase

A

Spindle fibres shorten;
Centromere splits;
Sister chromatids are separated;
Chromatids pulled to opposite poles of the cell;

189
Q

Describe how you would test a liquid sample for the presence of lipid and how you would recognise a positive result.

A
  1. (Mix / shake sample) with ethanol, then water and shake;

2. Cloudy White / milky (emulsion);

190
Q

Describe how an ester bond is formed in a phospholipid molecule.

A
  1. Condensation (reaction) OR Loss of water;

2. Between of glycerol and fatty acid;

191
Q

Explain how an arteriole can reduce the blood flow into capillaries.

A
  1. Muscle contracts;

2. Constricts/narrows arteriole/lumen;

192
Q

Explain 3 properties that make water important for organisms.

A
  1. A metabolite in condensation/hydrolysis/ photosynthesis/respiration; 2. A solvent so (metabolic) reactions can occur OR A solvent so allowing transport of substances;
  2. High heat capacity so buffers changes in temperature;
  3. Large latent heat of vaporisation so provides a cooling effect (through evaporation);
  4. Cohesion (between water molecules) so supports columns of water (in plants);
  5. Cohesion (between water molecules) so produces surface tension supporting (small) organisms;
193
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;
194
Q

Name 3 dimers

A 
Lactose
Sucrose
Maltose
Dipeptide
Dinucleotide
195
Q

What is the function of Golgi Apparatus

A

Modifies/packages/sorts proteins;

Produces vesicles;

196
Q

Describe the gross structure of human gas exchange system and how we breathe in and out

A
  • Named structures – trachea, bronchi, bronchioles, alveoli
  • Above structures named in correct order OR Above structures labelled in correct positions on a diagram
  • Breathing in – Diaphragm contract and external intercostal muscles contract
  • Volume increases and pressure decreases in thoracic cavity.
  • Breathing out – Diaphragm relaxes and internal intercostal muscles contract
  • Volume decrease and pressure increase in thoracic cavity
197
Q

Describe and explain how cell fractionation and centrifugation can be used to isolate mitochondria from a suspension of animal cells.

A
  1. Cell homogenisation to break open cells and release organelles;
  2. Filter to remove (large) debris/whole cells;
  3. Use isotonic solution to prevent osmotic damage to mitochondria / organelles;
  4. Keep cold to prevent/reduce damage to organelles by enzyme;
  5. Use buffer to maintain pH and prevent protein/enzyme denaturation;
  6. Use differential Centrifuge (at high speed/1000 g) to separate nuclei / cell fragments / heavy organelles;
  7. Re-spin (supernatant / after nuclei/pellet removed) at higher speed to get mitochondria in pellet/at bottom;
  8. Observe pellet with a microscope to identify mitochondria;
198
Q

It was important that the sampling procedures are standardised when collecting samples from two sites.

Give one way in which the sampling procedure could be standardised.

A

Same size of area (sampled) / Same size net/mesh / Same sampling time / Samples taken at same time of day/on same day;

Accept use of quadrat

199
Q

Compare and contrast the structure and properties of triglycerides and phospholipids

A
  • Both contain ester bonds
  • Both contain glycerol
  • Fatty acids on both may be saturated or unsaturated
  • Both are insoluble in water
  • Both contain C, H and O but phospholipids are also contain P
  • Triglyceride has three fatty acids and phospholipids have two fatty acids plus phosphate group
  • Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region
  • Phospholipids form monolayer/micelle/bilayer but triglycerides don’t.
200
Q

What is the effect of substrate concentration on the rate of an enzyme controlled reaction(3)

A
  1. Increases then plateaus / constant / steady / rate does not change;
  2. It plateaus as all active sites occupied / Saturated;
  3. (rate of reaction) / maximum number of Enzyme-Substrate complexes per second;
201
Q

HSW: What are some reasons for VARIATION in a data set?

A

1: Genetic differences
2: Gender / Ethnicity / Age
3: Metabolic rates differ
4: Different prior medical history
5: Previous exposure to pathogen

202
Q

Eukaryotic cells produce and release proteins.

Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells

A
  1. DNA in nucleus is code (for protein);
  2. Ribosomes/rough endoplasmic reticulum produce (protein);

Accept rER for ‘rough endoplasmic reticulum’

  1. Mitochondria produce ATP (for protein synthesis);
  2. Golgi apparatus package/modify;

OR

Carbohydrate added/glycoprotein produced by Golgi apparatus;

Accept body for ‘apparatus’

  1. Vesicles transport

OR

Rough endoplasmic reticulum transports;

  1. (Vesicles) fuse with cell(-surface) membrane;

Accept exocytosis at cell membrane

203
Q

Describe the pathway taken by an oxygen molecule from an alveolus to the blood

A
  1. (Across) alveolar epithelium;

2. Endothelium of capillary;

204
Q

Omega-3 fatty acids are unsaturated. What is an unsaturated fatty acid?

A 
Double bond(s);
(Bonds) between carbon atoms within the hydrocarbon chain;
205
Q

Describe the role of micelles in the absorption of fats into the cells of the ileum.

A
  1. Micelles include bile salts and fatty acids;
  2. Make the fatty acids (more) soluble in water;
  3. Bring/release/carry fatty acids to cell/lining (of the ileum);
  4. Maintain high(er) concentration of fatty acids to cell/lining (of the ileum);
  5. Fatty acids (absorbed) by diffusion;
206
Q

Explain how the active site of an enzyme causes a high rate of reaction.

A
  1.    Lowers activation energy;
  2.    Induced fit causes active site (of enzyme) to change shape;
  3.    (So) enzyme-substrate complex causes bonds to form/break;
207
Q

HSW:

Why do we use PERCENTAGE changes (e.g. % increase or % decrease)?

A

Measure the effect of X (e.g. red blood cells at sea level vs altitude)
Starting values differ / allows comparison of changes over time

208
Q

Explain how natural selection produces changes within a species.

A
  1. Variation [caused by mutation] between members of population / species;
  2. Predation / disease / competition results in differential survival;
  3. Some have adaptations that favour survival;
  4. Differential reproductive success / survive to reproduce/ have more offspring/
  5. Pass on their advantageous alleles /
  6. Changes allelic frequencies
209
Q

Explain what is meant by a heirarchy

A
  1. Groups within groups;

2. No overlap (between groups);

210
Q

HSW:

Describe how he made a 1 in 10 dilution and then used this to make a 1 in 1000 dilution of the original liquid culture of bacteria.

A
  1. Add 1 part (bacteria) culture to 9 parts (sterile) liquid (to make 10–1 dilution);

Accept water / nutrient / broth for liquid

  1. Mix (well);

Accept stir

  1. Repeat using 9 parts fresh (sterile) liquid and 1 part of 10–1 and 10–2 dilutions to make 10–3 dilution;

OR

Add 1 part 10–1 (suspension) to 99 parts (sterile) liquid (to make 10–3 dilution);

211
Q

Name the biological molecule

A

Beta glucose

212
Q

Scientists can use protein structure to investigate the evolutionary relationships between different species.

Explain why.

A
  1. Amino acid sequences / primary structure;
  2. Closer the (amino acid) sequence the closer the relationship;
  3. (Protein structure) related to (DNA) base/triplet sequence;
213
Q

HSW: How do we increase RELIABILITY?

A

More data collected / larger sample size
Over longer period of time / more time points
More independent variable values tested
Anomalies have less effect

214
Q

Farmers clear tropical forest and grow crops instead. Explain how this causes the
diversity of insects in the area to decrease.

A
  1. Lower diversity of plants/ few species of plants/less variety of plants/few plant layers;
  2. Few sources/types of food/feeding sites;
  3. Few habitats/ niches;
  4. Fewer (species of) herbivore so few (species of) carnivores;
  5. Aspect of agriculture (killing insects);
215
Q

Why would you use a LOG SCALE on the Y axis?

A

The is a large range / change in the [Dependent variable]

216
Q

Explain how HIV affects the production of antibodies when AIDS develops in a person.

A
  1. Less/no antibody produced;
  2. (Because HIV) destroys helper T cells; Accept ‘reduces number’ for ‘destroys’
  3. (So) few/no B cells activated / stimulated OR (So) few/no B cells undergo mitosis/differentiate/form plasma cells;
217
Q

Define degenerate code

A

More than one codon for one amino acid

218
Q

A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange.

A

1 Large surface area provided by many lamellae over many gill filaments;
2 Increases diffusion/makes diffusion efficient;
3 Thin epithelium/distance between water and blood;
4 Water and blood flow in opposite directions/countercurrent;
5 (Point 4) maintains concentration gradient (along gill)/equilibrium not reached;
6 As water always next to blood with lower concentration of oxygen;
7 Circulation replaces blood saturated with oxygen;
8 Ventilation replaces water (as oxygen removed);

219
Q

Explain five properties that make water important for organisms.

A
  1. A metabolite in condensation/hydrolysis/ photosynthesis/respiration; 2. A solvent so (metabolic) reactions can occur OR A solvent so allowing transport of substances;
  2. High heat capacity so buffers changes in temperature;
  3. Large latent heat of vaporisation so provides a cooling effect (through evaporation);
  4. Cohesion (between water molecules) so supports columns of water (in plants);
  5. Cohesion (between water molecules) so produces surface tension supporting (small) organisms;
220
Q

ATP is an energy source used in many cell processes. Give two ways in which ATP is a suitable energy source for cells to use.

A
  1. Releases relatively small amount of energy/ little energy is lost as heat;
  2. Releases energy instantaneously;
  3. Phosphorylates other compounds, making them more reactive;
  4. Can be rapidly re-synthesised;
  5. Is not lost from/ does not leave cells;
221
Q

Give two types of cell, other than pathogens, that can stimulate an immune response.

A
  1. (Cells from) other organisms/transplants;
  2. Abnormal/cancer/tumour (cells);
  3. (Cells) infected by virus;
222
Q

What is an allele?

A

(Different) form/type/version of a gene / different base sequence of a gene;

223
Q

Give two similarities in the movement of substances by diffusion and by osmosis.

A
  1. (Movement) down a gradient / from high concentration to low concentration;
  2. Passive / not active processes; OR Do not use energy from respiration / from ATP / from metabolism; OR Use energy from the solution;
224
Q

Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels.

A
  1. Micelles contain bile salts and fatty acids/monoglycerides;
  2. Make fatty acids/monoglycerides (more) soluble (in water) OR Bring/release/carry fatty acids/monoglycerides to cell/lining (of the iluem) OR Maintain high(er) concentration of fatty acids/monoglycerides to cell/lining (of the ileum);
  3. Fatty acids/monoglycerides absorbed by diffusion;
  4. Triglycerides (re)formed (in cells);
  5. Vesicles move to cell membrane;
225
Q

What is a dimer?

A

2 monomers chemically bonded together

226
Q

Define ‘gene mutation’ and explain how a gene mutation can have:

  • no effect on an individual

* a positive effect on an individual.

A

(Definition)
1. Change in the base/nucleotide (sequence of chromosomes/DNA);
2. Results in the formation of new allele;
3. Genetic code is degenerate (so amino acid sequence may not change);
OR Mutation is in an intron (so amino acid sequence may not change);
4. Does change amino acid but no effect on tertiary structure;
5. (New allele) is recessive so does not influence phenotype;
6. Results in change in polypeptide that positively changes the properties (of the protein) OR Results in change in polypeptide that positively changes a named protein;
7. May result in increased reproductive success OR May result in increased survival (chances);

227
Q

Describe how the student would show that reducing sugars were present in a solution.

A
  1. Add Benedict’s;
  2. Heat to 95°C;
  3. Red/orange/yellow/green precipitate (shows reducing sugar present);
228
Q

Describe how you would test a sample of food for the presence of starch.

A
  1. Add potassium iodide (KI) solution to the food sample;

2. Blue/black/purple indicates starch is present;

229
Q

Give two structural differences between a molecule of messenger RNA (mRNA) and a molecule of transfer RNA (tRNA).

A
  1. mRNA does not have hydrogen bonds / base pairing, tRNA does; OR mRNA is linear / straight chain, tRNA is cloverleaf;
  2. mRNA does not have an amino acid binding site, tRNA does;
  3. mRNA has more nucleotides;
  4. (Different) mRNAs have different lengths, all tRNAs are similar / same length;
  5. mRNA has codons, tRNA has an anticodon;
230
Q

What is meant by species richness

A

The number of different species in a community

231
Q

What is a species?

A
  1. Group of similar organisms / organisms with similar features / / organisms with same genes / chromosomes;
  2. Reproduce to produce fertile offspring;
232
Q

What are Fungi cell walls made from?

A

CHITIN

233
Q

Explain how water enters xylem from the endodermis in the root and is then transported to the leaves.

A

(In the root)

  1. Casparian strip blocks apoplast pathway / only allows symplast pathway;
  2. Active transport by endodermis;
  3. (Of) ions/salts into xylem;
  4. Lower water potential in xylem / water enters xylem by osmosis /down a water potential gradient;

(Xylem to leaf)

  1. Evaporation / transpiration (from leaves);
  2. (Creates) cohesion / tension / H-bonding between water molecules / negative pressure;
  3. Adhesion / water molecules bind to xylem;
  4. (Creates continuous) column of water

AQA A Level Biology (3 decks)

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