Year 12 AQA BIOLOGY (Complete) Flashcards
This is the complete set of cards for Year 12 (233 cards)
1
Q
Describe Semi-conservative replication.
A
- Strands separate / H-bonds break;
- DNA helicase (involved);
- Both strands/each strand act(s) as (a) template(s);
- (Free) nucleotides attach;
- Complementary/specific base pairing due to H bonds forming between bases/ Adenine to Thymine and GC;
- DNA polymerase joins nucleotides (on new strand) forming phoshodiester bonds by condensation;
- Semi-conservative replication / new DNA molecules contain one old strand and one new strand;
2
Q
An enzyme catalyses only one reaction. Explain why.
A
- (Enzyme has) active site is a specific shape;
2. Only one substrate fits / binds (the active site);
3
Q
Describe how the structure of a protein depends on the amino acids it contains.
A
- Structure is determined by (relative) position of amino acid/R group/interactions;
Accept for ‘interactions’, hydrogen bonds / disulfide bridges / ionic bonds / hydrophobichydrophilic interactions
- Primary structure is sequence/order of amino acids;
- Secondary structure formed by hydrogen bonding (between amino acids);
Accept alpha helix/β-pleated sheet for ‘secondary structure’
- Tertiary structure formed by interactions (between R groups);
Accept for ‘interactions’, hydrogen bonds / disulfide bridges / ionic bonds / hydrophobichydrophilic interactions
- Creates active site in enzymes
OR
Creates complementary/specific shapes in antibodies/carrier proteins/receptor (molecules);
- 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)
4
Q
Describe Transcription in Eukaryotes
A
- Hydrogen bonds (between DNA bases) break;
- (Only) one DNA strand acts as a template;
- (Free) RNA nucleotides align by complementary base pairing;
- (In RNA) Uracil base pairs with adenine (on DNA) OR (In RNA) Uracil is used in place of thymine;
- RNA polymerase joins (adjacent RNA) nucleotides;
- (By) phosphodiester bonds (between adjacent nucleotides);
- Pre-mRNA is spliced (to form mRNA) OR Introns are removed (to form mRNA);
5
Q
What are algae cell walls made from (Polymer)
A
CELLULOSE
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);
7
Q
Explain how the humoral response leads to immunity.
A
- B cells specific to the antigen reproduce by mitosis.
- B cells produce plasma and memory cells
- Second infection produces antibodies in larger quantities AND quicker.
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;
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;
10
Q
The action of endopeptidases and exopeptidases can increase the rate of protein digestion. Describe how.
A
- Exopeptidases hydrolyse peptide bonds at the ends of a polypeptide/protein AND endopeptidases hydrolyse internal peptide bonds within a polypeptide/protein;
- More ‘ends’ OR More surface area;
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
- Count unlikely to be accurate / repeatable / reproducible / reliable;
- Because too many cells; OR Because cells overlapping / not spread out;
12
Q
Explain why plants grown in soil with very little water grow only slowly
A
- Stomata close;
2. Less carbon dioxide (uptake) for less photosynthesis/glucose production;
13
Q
Describe the advantage of the Bohr effect during intense exercise.
A
- Increases dissociation of oxygen;
Accept unloading/ release/reduced affinity for dissociation
- 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;
14
Q
Describe a biochemical test to show that raffinose solution contains a non-reducing sugar.
A
- Heat with acid and neutralise with alkali. eg HCl, NaHCO3
- Heat with Benedict’s (solution);
- Red precipitate;
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
- DNA helicase;
- Breaks hydrogen bonds between base pairs/ AT and GC/complementary bases
OR
Breaks hydrogen bonds between polynucleotide strands;
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;
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
- Vaccine contains antigen from pathogen;
- Macrophage presents antigen on its surface;
- T (helper) cell with complementary receptor protein binds to antigen;
- T cell stimulates B cell;
- (With) complementary antibody on its surface;
- B cell divides to form clone secreting / producing same antibody;
- B cell secretes large amounts of antibody;
18
Q
State three differences between DNA in the nucleus of a plant cell and DNA in a prokaryotic cell.
A
Plant v prokaryote
- (Associated with) histones/proteins v no histones/proteins;
- Linear v circular;
- No plasmids v plasmids;
- Introns v no introns;
- Long(er) v short(er);
19
Q
Describe two precautions the student should take when clearing away after the dissection.
A
- Carry/wash sharp instruments/scalpel by holding handle OR Carry/wash sharp instruments by pointing away (from body)/down;
- Disinfect instruments/surfaces;
- Disinfect/sanitise hands OR Wash hands with soap (and water);
- Put organ/gloves/paper towels in a (separate) bag/bin/tray to dispose;
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
- Polar molecule;
- Acts as a (universal) solvent;
OR - (Universal) solvent;
- (Metabolic) reactions occur faster in solution;
OR - Reactive;
- Takes place in hydrolysis / condensation / named reaction;
Polar molecule so acts as (universal) solvent so (metabolic reactions are faster = 3 marks
21
Q
Explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake
A
- Large(r) organisms have a small(er) surface area:volume (ratio); OR Small(er) organisms have a large(r) surface area:volume (ratio);
- Overcomes long diffusion pathway OR Faster rate of diffusion;
22
Q
Describe the role of DNA polymerase in the semi-conservative replication of DNA.
A
- Joins (adjacent DNA) nucleotides; 5’ to 3’
- (Catalyses) condensation (reactions);
- (Catalyses formation of) phosphodiester bonds (between adjacent nucleotides);
23
Q
Describe the role of antibodies in producing a positive result in an ELISA test.
A
- (First) antibody binds/attaches /complementary (in shape) to antigen; 2. (Second) antibody with enzyme attached is added;
- (Second) antibody attaches to antigen;
- (Substrate/solution added) and colour changes;
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;
25
Describe the process of complete digestion of starch
```
(salivary/pancreatic) Amylase;
Maltose;
Maltase;
Maltose to glucose;
Hydrolysis;
Glycosidic bonds;
```
26
Describe Transcription in Eukaryotes
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);
27
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.
1. Examine large number of fields of view / many cells; [20 or more]
2. To ensure representative sample;
OR
3. Repeat count;
4. To ensure figures are correct;
OR
5. Method to deal with part cells shown at edge /count only whole cells;
6. To standardise counting;
28
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.
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;
29
Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind.
Explain why.
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;
30
Describe the absorption of glucose (Cotransport)
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;
31
Suggest two ways the student could improve the quality of his scientific drawing
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;
32
What is the function of Cell surface membrane
Made of a Phospholipid Bilayer;
Controls what enters the cell/ is selectively permeable;
Can be folded to increase Surface Area;
33
What is the role of the disulfide bridge in forming the quaternary structure of an antibody?
Joins two (different) polypeptides;
34
Name the protein associated with DNA in a chromosome.
Histone;
35
Describe the features of Telophase
Nuclear membrane begins to reform;
| Chromosomes unwind;
36
What is a homologous pair of chromosomes?
Two chromosomes that carry the same genes in the same loci / location
37
Explain why death of alveolar epithelium cells reduces gas exchange in human lungs.
1. Reduced surface area;
2. Increased distance for diffusion;
3. Reduced rate of gas exchange;
38
Other than the distribution of stomata, suggest and explain two xerophytic features the leaves of this plant might have.
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;
39
The structure of cellulose is related to its role in plant cell walls. Explain how.
* Long, straight, unbranched chains of Beta glucose;
* (Joined by) many WEAK hydrogen bonds;
* Form microfibrils / macrofibrils;
* Provide rigidity/strength/support;
40
Describe binary fission in bacteria.
1. Replication of (circular) DNA;
Accept nucleoid
2. Replication of plasmids;
3. Division of cytoplasm (to produce daughter cells);
41
Compare and contrast the processes by which water and inorganic ions enter cells.
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
42
Describe the structure of proteins.
* 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;
43
What is the function of Plasmid
Circular DNA;
| Contains antibiotic resistance genes;
44
Explain how oxygen is loaded, transported and unloaded in the blood.
* 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);
45
Describe Translation
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;
46
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.
1. Select at random to remove bias
| 2. Large sample/number (of snails)/>10;
47
HSW:
Why do we use RATIOS ?
Allows valid comparisons between two numbers
| Original numbers may vary
48
Describe how you would use the student’s results (dilution series and % change in mass) to find the water potential of the potato tissue.
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).
49
What are the differences between a triglyceride and a phospholipid?
1. Fatty acid removed;
| 2. Replaced with a phosphate group;
50
Describe the difference between active and passive immunity.
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;
51
Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin.
1. Increases/more oxygen dissociation/unloading OR Deceases haemoglobin’s affinity for O2;
2. (By) decreasing (blood) pH/increasing acidity;
52
HSW:
Why do we use STANDARD DEVIATIONS?
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
53
Describe how the movement of the diaphragm leads to air movement into the lungs
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.
54
Explain how oxygen is loaded, transported and unloaded in the blood.
* 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);
55
Describe the gross structure of the human gas exchange system and how we breathe in and out.
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);
56
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
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;
57
What is the function of Chloroplasts
Contain thylakoids, stacked into Granum;
Site of photosynthesis;
Grana (Light dependent reaction)
Stroma (Light independent reaction)
58
Name the 7 bonds found within biological molecules
Carbohydrates: Glycosidic / Hydrogen (cellulose)
Polypeptides: Peptide / Ionic / Hydrogen / Disulphide
Lipids: Ester
Nucleic acids: Phosphodiester / Hydrogen
Water: Hydrogen
ATP: Phosphoric anhydride
59
Name the two scientists who proposed models of the chemical structure of DNA and of DNA replication.
Crick and Watson;
60
Describe and explain the mechanism that causes lungs to fill with air.
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;
61
Explain how one feature of an alveolus allows efficient gas exchange to occur.
1. (The alveolar epithelium) is one cell thick;
| 2. Creating a short diffusion pathway / reduces the diffusion distance;
62
Describe binary fission in bacteria.
1. Replication of (circular) DNA;
2. Replication of plasmids;
3. Division of cytoplasm (to produce daughter cells);
63
Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind.
Explain why.
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;
64
Sucrase does not hydrolyse lactose. Use your knowledge of the way in which enzymes work to explain why.(3)
1. Lactose has a different shape/structure;
2. Does not fit/bind to active site of enzyme/sucrase;
OR
1. Active site of enzyme/sucrase has a specific shape/structure;
2. Does not fit/bind to lactose so no Enzyme-Substrate Complexes formed.
65
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.
• 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;
66
Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution.
1. Filter and dry (the precipitate);
| 2. Find mass/weight;
67
Eukaryotic cells produce and release proteins. Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells.
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;
6. (Vesicles) fuse with cell(-surface) membrane;
68
Compare & Contrast Eukaryotic and Prokaryotic DNA
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;
69
Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf.
1. (Carbon dioxide enters) via stomata;
2. (Stomata opened by) guard cells;
3. Diffuses through air spaces;
4. Down diffusion gradient;
70
Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin.
1. Increases/more oxygen dissociation/unloading OR Deceases haemoglobin’s affinity for O2;
2. (By) decreasing (blood) pH/increasing acidity;
71
Which stats test would you use if the data is categoric?
E.g. Difference between 'Number of yellow shelled snails and pink shelled snails'
CHI Squared
72
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)
* 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;
73
Describe how tissue fluid is formed and how it is returned to the circulatory system.
Formation
1. High blood / hydrostatic pressure / pressure filtration;
2. Forces water / fluid out;
3. Large proteins remain in capillary;
Return
4. Low water potential in capillary / blood;
5. Due to (plasma) proteins;
6. Water enters capillary / blood;
7. (By) osmosis;
8. Correct reference to lymph;
74
Define ‘non-coding base sequences’ and describe where the non-coding multiple repeats are positioned in the genome.
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;
75
Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein
* Glucose and galactose
* Joined by condensation
* Joined by glycosidic bond
* Added to polypeptide in Golgi
76
What is the proteome of a cell?
(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;
77
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.
1. Reduced surface area;
2. Increased distance for diffusion;
3. Reduced rate of gas exchange;
78
Describe how an ester bond is formed in a phospholipid molecule.
1. Condensation (reaction) OR Loss of water;
| 2. Between of glycerol and fatty acid;
79
Describe the induced fit model of enzyme action.(2)
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;
80
Describe how haemoglobin normally loads oxygen in the lungs and unloads it in a tissue cell.
* 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;
81
Name a factor that can affect transpiration
Light (intensity) / temperature / air movement / humidity;
82
Describe & explain how you could use the biuret test to distinguish a solution of enzyme, lactase, from a solution of lactose(2)
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;
83
Describe and explain two features you would expect to find in a cell specialised for absorption.
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);
84
What is the formula for percentage change?
[Difference / Original] x 100
85
HSW: Define Standard deviation
Spread of data around the mean
86
Which stats test would you use if there is a relationship between 2 (continuous) variables?
E.g. Age and Height
Correlation Coefficient
87
The student used a sharp scalpel to cut the specimen.
Describe how she should ensure she handled the scalpel safely during this procedure.
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
88
Explain how oxygen in a red blood cell is made available for respiration in active tissues.
* CO2 (increased) respiration;
* (increased) dissociation oxygen from haemoglobin;
* Low partial pressure in tissues/plasma;
* Oxygen diffuses from r.b.c. to tissues;
89
Define ‘gene mutation’ and explain how a gene mutation can have:
• no effect on an individual
• a positive effect on an individual.
(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);
90
Describe the features of Metaphase
Spidle fibres form;
Spindle fibres attach;
To the centromere of chromosomes;
Chromosomes align at the equator;
91
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)
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;
92
Explain what the term non-overlapping DNA means.
A base from one triplet cannot be used in an adjacent triplet
93
The movement of substances across cell membranes is affected by membrane structure.
Describe how.
* 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;
94
Describe how a peptide bond is formed between two amino acids to form a dipeptide
1. Condensation (reaction) / loss of water;
| 2. Between amine / NH2 and carboxyl / COOH;
95
Tests using monoclonal antibodies are specific. Use your knowledge of protein structure to explain why.
* (Specific) primary structure / order of amino acids;
* (Specific) tertiary / 3D structure / shape;
* (So) Only binds to / fits / complementary to one antigen;
96
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.
• 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
Explain how oxygen in a red blood cell is made available for respiration in active tissues.
* CO2 (increased) respiration;
* (increased) dissociation oxygen from haemoglobin;
* Low partial pressure in tissues/plasma;
* Oxygen diffuses from r.b.c. to tissues;
98
Many different substances enter and leave a cell by crossing its cell surface membrane.
Describe how substances can cross a cell surface membrane.
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
Give one reason why eggs produced by meiosis are genetically different.
Independent segregation
OR
Crossing over;
100
Describe and explain two features you would expect to find in a cell specialised for absorption.
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;
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);
101
Describe the structure of a phospholipid molecule and explain how phospholipids are arranged in a plasma membrane (3 marks).
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
Describe the features of Prophase
Nuclear membrane begins to breakdown;
Centrioles move to poles of the cell;
Chromatin supercoils and condense in chromosomes;
103
Describe the structure of DNA relates to its functions
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
Describe how you could use the emulsion test to show that a seed contains lipids. (3)
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
Give two precautions the students should have taken when setting up the potometer to obtain reliable measurements of water uptake by the plant shoot.
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
Give one feature of starch and explain how this feature enables it to act as a storage
substance.
* 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
Describe how courtship behaviour increases the probability of successful mating.
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
Suggest two ways the student could improve the quality of his scientific drawing
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
Describe and explain the advantage of the counter-current principle in gas exchange across a fish gill.
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
Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange.
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);
5. 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);
6. Body can be moved (by muscles) to move air so maintains diffusion / concentration gradient for oxygen / carbon dioxide;
111
Describe and explain the mechanism that causes forced expiration.
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
HSW:
How would you use the equation
M1 x V1 = M2 x V2
to make a solution of known concentration?
```
M1 = desired conc
V1 = desired volume
```
```
M2 = original/stock conc
V2 = volume stock needed
```
113
HSW:
Use of a colorimeter in this investigation would improve the repeatability of the student’s results.
Give one reason why
1. Quantitative values are not subjective / More accurate / More precise
2. Standardises (the) method;
114
What is the function of Lysosomes
Contains digestive enzymes;
| Digests worn out organelles/autolysis;
115
Describe the structure of the human immunodeficiency virus (HIV).
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
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.
Add 4.5 cm3 of (1.0 mol dm–3) solution to 25.5 cm3 (distilled) water.
Mix
117
Describe how a non-competitive inhibitor works
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
When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how
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
The structure of cellulose is related to its role in plant cell walls. Explain how. (3)
* Long, straight, unbranched chains of Beta glucose;
* (Joined by) many WEAK hydrogen bonds;
* Form microfibrils / macrofibrils;
* Provide rigidity/strength/support;
120
A mutation in a gene coding for an enzyme
| could lead to the production of a non-functional enzyme. Explain how
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
Explain the arrangement of phospholipids in a cell-surface membrane.
* 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
Describe one way that the lock and key model is different from the induced fit model(2)
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
HSW: Why can some conclusions NOT be made ?
No Standard Deviation given for the means
124
Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample.
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
3. Do Benedict’s test and stays blue/negative;
4. Boil with acid then neutralise with alkali;
5. Heat with Benedict’s and becomes red/orange (precipitate);
Amylase
6. Add biuret (reagent) and becomes purple/violet/mauve/lilac;
7. Add starch, (leave for a time), test for reducing sugar/absence of starch;
125
Many different substances enter and leave a cell by crossing its cell surface membrane.
Describe how substances can cross a cell surface membrane.
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
Root pressure moves water through the xylem. Describe what causes root pressure. (4)
1. Active transport by endodermis;
2. ions/salts into xylem;
3. Lowers water potential (in xylem);
4. (Water enters) by osmosis;
127
Describe how a student could use an eyepiece graticule to determine the mean diameter of stomata.
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
What is the function of Cell Wall
Provides rigid shape / structure;
| Stops osmotic lysis;
129
What is the function of Capsule
Protects cell from immune systems;
| Aids bacteria sticking together;
130
Explain why a cell membrane may be described as a fluid-mosaic?
* 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
Describe the gross structure of human gas exchange system and how we breathe in and out
* 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
Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels.
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);
Accept chylomicrons form
5. Vesicles move to cell membrane;
Accept exocytosis for ‘vesicles move’
133
Name and describe five ways substances can move across the cell-surface membrane into a cell.
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
What is the function of the Ribsosomes
Site of Protein synthesis (Translation)
135
Describe the mass flow hypothesis for the mechanism of translocation in plants.
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
Describe how an ester bond is formed in a phospholipid molecule.
1. Condensation (reaction) OR Loss of water;
| 2. Between of glycerol and fatty acid;
137
What is the function of the Nucleus
Contains genetic material / DNA;
| Controls cell activity;
138
Describe how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta.
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
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.
Also measures number of individuals in a species / different proportions of species;
Some species may be present in low/high numbers;
140
Explain how oxygen is loaded, transported and unloaded in the blood.
* 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
Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst.
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
Describe the role of enzymes in the digestion of proteins in a mammal.
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
Describe the role of enzymes in the digestion of proteins in a mammal.
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
The oxygen dissociation curve of the foetus is to the left of that for its mother. Explain the advantage of this for the foetus.
* Higher affinity / loads more oxygen;
* At low/same/high partial pressure/pO2;
* Oxygen moves from mother/to foetus;
145
Explain how selection occurs in living organisms
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
State why some antibodies are referred to as monoclonal
(Antibodies) produced from a single clone of B cells / plasma cells;
OR
(Antibodies) produced from the same B cell / plasma cell;
147
Suggest one economic argument for maintaining biodiversity.
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
Compare & Contrast Eukaryotic and Prokaryotic DNA
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
Suggest how one antibody can be specific to two different proteins.
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
Describe the process of crossing over and explain how it increases genetic diversity
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
Explain the decrease in mass of potato tissue in the 0.40 mol dm−3 solution of sucrose.
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
How does oxygen move through the insect?
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
Describe how the human immunodeficiency virus (HIV) is replicated once inside helper T cells (TH cells).
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
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.
1. Lung tissue does not contain starch;
2. (Makes) nucleus visible;
OR
Nucleus contains DNA;
155
Describe the roles of iron ions, sodium ions, and phosphate ions in cells.
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
Describe how a change in the base sequence of the DNA coding for an enzyme may result in a non-functional protein.
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
Describe how comparisons of biological molecules in two species could be used to find out if they are closely related.
Compare DNA base sequence;
Compare RNA base sequence;
Compare sequence of amino acids /primary structure (of named / same protein);
158
Describe and explain the role of antibodies in stimulating phagocytosis.
* Bind to antigen OR Are markers;
| * (Antibodies) cause (clumping) agglutination OR Attract phagocytes;
159
What is the function of the Mitochondria
Site of AEROBIC respiration;
| ATP production;
160
What is the function of the Smooth Endoplasmic Reticulum
Site of lipid synthesis;
161
Which stats test would you use to see the DIFFERENCE between two MEANS?
E.g. Difference between mean heights of males and females
STUDENT T Test
162
Describe how an enzyme-substrate complex increases the rate of reaction
1. Reduces activation energy
| 2. Due to bending bonds OR Without the enzyme, very few substrates have sufficient energy for the reaction.
163
Suggest one ethical argument for maintaining biodiversity.
Prevent extinction
Loss of populations
Reduction in populations
Loss of habitats
164
Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how.
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
Describe how a phagocyte destroys a pathogen present in the blood.
1. Engulfs;
2. Forming vesicle/phagosome and fuses with lysosome;
3. Enzymes hydrolyse;
166
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.
Description; Explanation;
E.g, 1. Examine large number of fields of view / many cells;
2. To ensure representative sample;
OR
3. Repeat count;
4. To ensure figures are correct;
OR
5. Method to deal with part cells shown at edge /count only whole cells;
6. To standardise counting;
167
Describe the non-specific defence mechanisms the body may launch against pathogens (5 marks)
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
Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange.
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);
5. 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);
6. Body can be moved (by muscles) to move air so maintains diffusion / concentration gradient for oxygen / carbon dioxide;
169
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) 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
Describe how haemoglobin normally loads oxygen in the lungs and unloads it in a tissue cell.
* 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
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.
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
Explain what is meant by a phylogenetic group
(Grouped according to) evolutionary links/history/relationships / common ancestry;
173
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.
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
Suggest two ways a student could improve the quality of their scientific drawing
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
The thickness of the aorta wall changes all the time during each cardiac cycle.
Explain why
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
Define the term exon.
Base/nucleotide/triplet sequence coding for polypeptide/sequence of amino acids/primary structure;
177
Give one advantage of using a SEM rather than a TEM.
Thin sections do not need to be prepared / shows surface of specimen / can have 3-D images;
178
What is the function of the Rough Endoplasmic reticulum
Encrusted in Ribosomes;
Site of protein synthesis;
Transports and stores protein within the cell
179
Give one advantage of using a TEM rather than a SEM.
1. Higher resolution;
2. higher (maximum) magnification / higher detail (of image);
OR
2. Allows internal details / structures within (cells) to be seen / cross section to be taken;
180
The movement of Na+ out of the cell allows the absorption of glucose into the cell lining the ileum.
Explain how
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’.
2. Na+ moving (in) by facilitated diffusion, brings glucose with it
OR
Na+ moving (in) by co-transport, brings glucose with it;
181
Explain how HIV affects the production of antibodies when AIDS develops in a person.
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;
182
Describe how an enzyme can be phosphorylated.
* Attachment/association of (inorganic) phosphate (to the enzyme);
* 2. (Released from) hydrolysis of ATP OR (Released from) ATP to ADP + Pi;
183
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.
* 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
Explain how a competitive inhibitor works
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
What is a monomer?
A monomer is a smaller / repeating) unit / molecule from which larger molecules / polymers are made;
186
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
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
Explain what is meant by genetic diversity.
Difference in DNA/base sequence/alleles/genes;
188
Describe the features of Anaphase
Spindle fibres shorten;
Centromere splits;
Sister chromatids are separated;
Chromatids pulled to opposite poles of the cell;
189
Describe how you would test a liquid sample for the presence of lipid and how you would recognise a positive result.
1. (Mix / shake sample) with ethanol, then water and shake;
| 2. Cloudy White / milky (emulsion);
190
Describe how an ester bond is formed in a phospholipid molecule.
1. Condensation (reaction) OR Loss of water;
| 2. Between of glycerol and fatty acid;
191
Explain how an arteriole can reduce the blood flow into capillaries.
1. Muscle contracts;
| 2. Constricts/narrows arteriole/lumen;
192
Explain 3 properties that make water important for organisms.
1. A metabolite in condensation/hydrolysis/ photosynthesis/respiration; 2. A solvent so (metabolic) reactions can occur OR A solvent so allowing transport of substances;
3. High heat capacity so buffers changes in temperature;
4. Large latent heat of vaporisation so provides a cooling effect (through evaporation);
5. Cohesion (between water molecules) so supports columns of water (in plants);
6. Cohesion (between water molecules) so produces surface tension supporting (small) organisms;
193
Give two differences between mitosis and meiosis.
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
Name 3 dimers
```
Lactose
Sucrose
Maltose
Dipeptide
Dinucleotide
```
195
What is the function of Golgi Apparatus
Modifies/packages/sorts proteins;
| Produces vesicles;
196
Describe the gross structure of human gas exchange system and how we breathe in and out
* 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
Describe and explain how cell fractionation and centrifugation can be used to isolate mitochondria from a suspension of animal cells.
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;
6. Re-spin (supernatant / after nuclei/pellet removed) at higher speed to get mitochondria in pellet/at bottom;
7. Observe pellet with a microscope to identify mitochondria;
198
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.
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
Compare and contrast the structure and properties of triglycerides and phospholipids
* 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
What is the effect of substrate concentration on the rate of an enzyme controlled reaction(3)
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
HSW: What are some reasons for VARIATION in a data set?
1: Genetic differences
2: Gender / Ethnicity / Age
3: Metabolic rates differ
4: Different prior medical history
5: Previous exposure to pathogen
202
Eukaryotic cells produce and release proteins.
Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells
1. DNA in nucleus is code (for protein);
2. Ribosomes/rough endoplasmic reticulum produce (protein);
Accept rER for ‘rough endoplasmic reticulum’
3. Mitochondria produce ATP (for protein synthesis);
4. Golgi apparatus package/modify;
OR
Carbohydrate added/glycoprotein produced by Golgi apparatus;
Accept body for ‘apparatus’
5. Vesicles transport
OR
Rough endoplasmic reticulum transports;
6. (Vesicles) fuse with cell(-surface) membrane;
Accept exocytosis at cell membrane
203
Describe the pathway taken by an oxygen molecule from an alveolus to the blood
1. (Across) alveolar epithelium;
| 2. Endothelium of capillary;
204
Omega-3 fatty acids are unsaturated. What is an unsaturated fatty acid?
```
Double bond(s);
(Bonds) between carbon atoms within the hydrocarbon chain;
```
205
Describe the role of micelles in the absorption of fats into the cells of the ileum.
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
Explain how the active site of an enzyme causes a high rate of reaction.
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
HSW:
Why do we use PERCENTAGE changes (e.g. % increase or % decrease)?
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
Explain how natural selection produces changes within a species.
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/
4. Pass on their advantageous alleles /
5. Changes allelic frequencies
209
Explain what is meant by a heirarchy
1. Groups within groups;
| 2. No overlap (between groups);
210
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.
1. Add 1 part (bacteria) culture to 9 parts (sterile) liquid (to make 10–1 dilution);
Accept water / nutrient / broth for liquid
2. Mix (well);
Accept stir
3. 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
Name the biological molecule
Beta glucose
212
Scientists can use protein structure to investigate the evolutionary relationships between different species.
Explain why.
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
HSW: How do we increase RELIABILITY?
More data collected / larger sample size
Over longer period of time / more time points
More independent variable values tested
Anomalies have less effect
214
Farmers clear tropical forest and grow crops instead. Explain how this causes the
diversity of insects in the area to decrease.
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
Why would you use a LOG SCALE on the Y axis?
The is a large range / change in the [Dependent variable]
216
Explain how HIV affects the production of antibodies when AIDS develops in a person.
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
Define degenerate code
More than one codon for one amino acid
218
A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange.
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
Explain five properties that make water important for organisms.
1. A metabolite in condensation/hydrolysis/ photosynthesis/respiration; 2. A solvent so (metabolic) reactions can occur OR A solvent so allowing transport of substances;
3. High heat capacity so buffers changes in temperature;
4. Large latent heat of vaporisation so provides a cooling effect (through evaporation);
5. Cohesion (between water molecules) so supports columns of water (in plants);
6. Cohesion (between water molecules) so produces surface tension supporting (small) organisms;
220
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.
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
Give two types of cell, other than pathogens, that can stimulate an immune response.
1. (Cells from) other organisms/transplants;
2. Abnormal/cancer/tumour (cells);
3. (Cells) infected by virus;
222
What is an allele?
(Different) form/type/version of a gene / different base sequence of a gene;
223
Give two similarities in the movement of substances by diffusion and by osmosis.
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
Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels.
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
What is a dimer?
2 monomers chemically bonded together
226
# Define ‘gene mutation’ and explain how a gene mutation can have:
* no effect on an individual
| * a positive effect on an individual.
(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
Describe how the student would show that reducing sugars were present in a solution.
1. Add Benedict’s;
2. Heat to 95°C;
3. Red/orange/yellow/green precipitate (shows reducing sugar present);
228
Describe how you would test a sample of food for the presence of starch.
1. Add potassium iodide (KI) solution to the food sample;
| 2. Blue/black/purple indicates starch is present;
229
Give two structural differences between a molecule of messenger RNA (mRNA) and a molecule of transfer RNA (tRNA).
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
What is meant by species richness
The number of different species in a community
231
What is a species?
1. Group of similar organisms / organisms with similar features / / organisms with same genes / chromosomes;
2. Reproduce to produce fertile offspring;
232
What are Fungi cell walls made from?
CHITIN
233
Explain how water enters xylem from the endodermis in the root and is then transported to the leaves.
(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)
5. Evaporation / transpiration (from leaves);
6. (Creates) cohesion / tension / H-bonding between water molecules / negative pressure;
7. Adhesion / water molecules bind to xylem;
8. (Creates continuous) column of water
