Paper 1 Long Recall Questions

Topics 1-4 A01 recall from PMT

Describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers. Give two named examples of polymers and their associated monomers to illustrate your answer. (5)

Ignore reference to dimers.

1. A condensation reaction joins monomers together and forms a (chemical) bond and releases water;

2. A hydrolysis reaction breaks a (chemical) bond between monomers and uses water;

3. A suitable example of polymers and the monomers from which they are made; 3. and 4. Polymers must contain many monomers. 3. and 4: suitable examples include • amino acid and polypeptide, protein, enzyme, antibody or specific example • nucleotide and polynucleotide, DNA or RNA • Alpha glucose and starch/glycogen • Beta glucose and cellulose. If neither specific carbohydrate example is given, allow monosaccharide/glucose and polysaccharide. 3. and 4. Reject (once) reference to triglycerides.

4. A second suitable example of polymers and the monomers from which they are made;

5. Reference to a correct bond within a named polymer; Reject reference to ester bond

Describe the structure of DNA (5)

1. Polymer of nucleotides; Accept ‘Polynucleotide’ Accept for ‘phosphate’. phosphoric acid

2. Each nucleotide formed from deoxyribose, a phosphate (group) and an organic/nitrogenous base;

3. Phosphodiester bonds (between nucleotides);

4. Double helix/2 strands held by hydrogen bonds;

5. (Hydrogen bonds/pairing) between adenine, thymine and cytosine, guanine;

Describe the role of two named enzymes in the process of semiconservative replication of DNA. (3)

1. (DNA) helicase causes breaking of hydrogen/H bonds (between DNA strands); Reject ‘helicase hydrolyses hydrogen bonds’.

2. DNA polymerase joins the (DNA) nucleotides; Reject if suggestion that DNA polymerase joins the complementary nucleotides or forms H bonds. Reject if joining RNA nucleotides or forming RNA.

3. Forming phosphodiester bonds;

During DNA replication, the two DNA strands separate and each acts as a template for the production of a new strand. As new DNA strands are produced, nucleotides can only be added in the 5’ to 3’ direction. Use your knowledge of enzyme action and DNA replication to explain why new nucleotides can only be added in a 5’ to 3’ direction. (4)

1. Reference to DNA polymerase;

2. (Which is) specific;

3. Only complementary with / binds to 5’ end (of strand); Reject hydrogen bonds / base pairing

4. Shapes of 5’ end and 3’ end are different / description of how different

Describe how an ATP molecule is formed from its component molecules (4)

1. and 2. Accept for 2 marks correct names of three components adenine, ribose/pentose, three phosphates;; Accept for 1 mark, correct name of two components Accept for 1 mark, ADP and phosphate/Pi Ignore adenosine Accept suitably labelled diagram

3. Condensation (reaction); Ignore phosphodiester

4. ATP synthase; Reject ATPase

Explain five properties that make water important for organisms. (5)

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 (specific) heat capacity so buffers changes in temperature; For ‘buffer’ accept ‘resist’.

4. Large latent heat of vaporisation so provides a cooling effect (through evaporation); Reject latent heat of evaporation

5. Cohesion (between water molecules) so supports columns of water (in plants); For ‘columns of water’ accept ‘transpiration stream’. Do not credit ‘transpiration’ alone but accept description of ‘stream’. For ‘columns of water’ accept ‘cohesion-tension (theory)’.

6. Cohesion (between water molecules) so produces surface tension supporting (small) organisms; For cohesion accept hydrogen bonding Ignore reference to pH. Allow other suitable properties but must have a valid explanation. For example • ice floating so maintaining aquatic habitat beneath • water transparent so allowing light penetration for photosynthesis

(5 max)

Describe the roles of iron ions, sodium ions, and phosphate ions in cells. (5)

Iron ions

1. Haemoglobin binds/associates with oxygen OR Haemoglobin transports/loads oxygen; Ignore reference to 2+ or 3+ in Fe2+ or Fe3+

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; Accept 5. OR 6. – not both

7. Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides;

8. Used in/to produce ATP; Reject ‘energy produced’

9. Phosphorylates other compounds (usually) making them more reactive;

10. Hydrophilic/water soluble part of phospholipid bilayer/membrane; Accept for 1 mark, Sodium ions cause water reabsorption in kidneys OR Sodium ions establish resting potential (in neurones) OR Sodium ion diffusion creates action potential

(5 max)

Describe how a sample of chloroplasts could be isolated from leaves. (4)

1. Break open cells/tissue and filter OR Grind/blend cells/tissue/leaves and filter; Accept homogenise and filter

2. In cold, same water potential/concentration, pH controlled solution; Accept for ‘same water potential/ concentration’, isotonic Accept for ‘pH controlled’, buffered

3. Centrifuge/spin and remove nuclei/cell debris;

4. (Centrifuge/spin) at high(er) speed, chloroplasts settle out;

Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells. Do not include details of transcription and translation in your answer. (4)

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

(4 max)

Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells. (6)

1. TEM use electrons and optical use light;

2. TEM allows a greater resolution;

3. (So with TEM) smaller organelles / named cell structure can be observed OR greater detail in organelles / named cell structure can be observed;

4. TEM view only dead / dehydrated specimens and optical (can) view live specimens;

5. TEM does not show colour and optical (can);

6. TEM requires thinner specimens;

7. TEM requires a more complex/time consuming preparation;

8. TEM focuses using magnets and optical uses (glass) lenses;

3. ‘clearer’ is not equivalent to ‘detail’ 4. Accept ‘Only optical can view live specimens’ 5. Accept ‘Only optical can show colour’ 7. Accept ‘TEM requires a more difficult preparation’

Ignore references to artefacts

max 6

Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cells when using an optical (light) microscope. (4)

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

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

3. Stain with / add iodine in potassium iodide. 3. Allow any appropriate method that avoids trapping air bubbles

4. Lower cover slip using mounted needle.

Describe binary fission in bacteria. (3)

1. Replication of (circular) DNA; Accept nucleoid Reject chromosome Reject mitosis

2. Replication of plasmids;

3. Division of cytoplasm (to produce daughter cells); Ignore genetically identical

Describe two aseptic techniques that a biologist would have used when transferring a sample of broth culture on to an agar plate. Explain why each was important. (4)

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

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

3. Wear gloves OR Wear mask OR Wash hands;

4. To prevent contamination from bacteria on hands / mouth OR Prevent spread of bacteria outside the lab;

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

6. To maintain a pure culture of bacteria

Describe the appearance and behaviour of chromosomes during mitosis. (5)

(During prophase)

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

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

(During metaphase)

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

4. (Chromosomes) attached to spindle fibres;

5. By their centromere;

(During anaphase)

6. The centromere splits / divides;

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

(During telophase)

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

No marks for naming the stages Reject references to homologous chromosomes / pairing of chromosomes Ignore references to spindle formation during prophase

max 5

Name and describe five ways substances can move across the cell-surface membrane into a cell. (5)

1. (Simple) diffusion of small/non-polar molecules down a concentration gradient; If no reference to 'small/ non-polar' for 1. accept this idea from 'large/charged' given in description of 2.

2. Facilitated diffusion down a concentration gradient via protein carrier/channel; Reject if active rather than passive

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

For any answer accept a correct example For ‘carrier protein’ accept symport OR cotransport protein

The movement of substances across cell membranes is affected by membrane structure. Describe how. (5)

1. Phospholipid (bilayer) allows movement/diffusion of nonpolar/lipid-soluble substances; 1. and 2. Accept correct named examples 1. and 2. Ignore water Accept phospholipid (bilayer) allows movement/diffusion of O2/CO2 Accept water-insoluble

2. Phospholipid (bilayer) prevents movement/diffusion of polar/ charged/lipid-insoluble substances OR (Membrane) proteins allow polar/charged substances to cross the membrane/bilayer; Accept water-soluble

3. Carrier proteins allow active transport;

4. Channel/carrier proteins allow facilitated diffusion/co-transport; Accept aquaporins allow osmosis

5. Shape/charge of channel / carrier determines which substances move;

6. Number of channels/carriers determines how much movement;

7. Membrane surface area determines how much diffusion/movement; 6. and 7. Accept correct reference to faster/slower/rate for ‘how much movement’ Accept microvilli / Golgi (apparatus) / ER / rER Accept surface area to volume for ‘surface area’

8. Cholesterol affects fluidity/rigidity/permeability; Accept cholesterol affects vesicle formation/ endocytosis/exocytosis/phagocytosis;

5 max

Compare and contrast the processes by which water and inorganic ions enter cells. (3)

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

Describe how HIV is replicated. (4)

1. Attachment proteins attach to receptors on helper T cell/lymphocyte;

2. Nucleic acid/RNA enters cell;

3. Reverse transcriptase converts RNA to DNA;

4. Viral protein/capsid/enzymes produced;

5. Virus (particles) assembled and released (from cell);

5 max

Describe how a phagocyte destroys a pathogen present in the blood. (3)

1. Engulfs; Accept endocytosis OR Description Ignore ‘taken in’

2. Forming vesicle/phagosome and fuses with lysosome;

3. Enzymes digest/hydrolyse; Accept lysozymes for ‘enzymes’

Describe the role of antibodies in producing a positive result in an ELISA test. (4)

1. (First) antibody binds/attaches /complementary (in shape) to antigen;

2. (Second) antibody with enzyme attached is added;

3. (Second) antibody attaches to antigen; Accept (second) antibody attaches to (first) antibody (indirect ELISA test).

4. (Substrate/solution added) and colour changes; Only award if enzyme mentioned.

Describe how presentation of a virus antigen by a phagocyte leads to the secretion of an antibody against this virus antigen. (3)

1. Helper T cell / TH cell binds to the antigen (on the antigen-presenting cell / phagocyte);

2. This helper T / TH cell stimulates a specific B cell;

3. B cell clones OR B cell divides by mitosis;

4. (Forms) plasma cells that release antibodies;

1. and 2. ‘Helper’ is required once only. 2. Accept ‘This (helper) T cell stimulates a competent B cell’ ‘T cell stimulates B cell to undergo clonal selection’. This statement achieves mp2 and mp3.

max 3

In the UK, children are vaccinated bacterial meningitis. This is a potentially fatal disease. Describe how vaccination can lead to protection against bacterial meningitis. (6)

1. Antigen / epitope on surface of N. meninigitidis / bacterium binds to surface protein / surface receptor on a (specific / single) B cell. If answered in context of T cell, allow Antigen binds to (specific / single) T cell

2. (Activated) B cell divides by mitosis / produces clone; If answered in context of T cell, allow (Activated) T cell releases cytokine.

3. (Division) stimulated by cytokines / by T cells; If answered in context of T cell, allow (Cytokine) stimulates production of plasma cells;

4. B cells / plasma cells release antibodies;

5. (Some) B cells become memory cells;

6. Memory cells produce plasma / antibodies faster

Describe the difference between active and passive immunity. (5)

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.

Max 5

Mammals such as a mouse and a horse are able to maintain a constant body temperature. Use your knowledge of surface area to volume ratio to explain the higher metabolic rate of a mouse compared to a horse. (3)

Accept converse answers in relation to the horse.

Mouse

1. (Smaller so) larger surface area to volume ratio; Accept larger SA:V. Must be comparative.

2. More/faster heat loss (per gram/in relation to body size); Ignore heat lost more easily/readily. Must be comparative.

3. (Faster rate of) respiration/metabolism releases heat; Accept respiration/metabolism replaces heat. Reject produce/generate heat/energy.

Describe and explain the advantage of the counter-current principle in gas exchange across a fish gill. (3)

1. Water and blood flow in opposite directions;

2. Maintains diffusion/concentration gradient of oxygen Accept: converse for carbon dioxide Accept: equilibrium not reached OR Oxygen concentration always higher (in water);

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

Describe the gross structure of the human gas exchange system and how we breathe in and out. (6)

1. Named structures – trachea, bronchi, bronchioles, alveoli; Reject mp1 if structures from other physiological systems are named but award mp2 if the correct structures are in the correct order.

2. Above structures named in correct order OR Above structures labelled in correct positions on a diagram; Reject mp1 if structures from other physiological systems are named but award mp2 if the correct structures are in the correct order.

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); For thoracic cavity accept ‘lungs’ or ‘thorax’. Reference to ‘thoracic cavity’ only required once.

5. Breathing out - Diaphragm relaxes and internal intercostal muscles contract; Accept diaphragm relaxes and (external) intercostal muscles relax and lung tissue elastic (so recoils).

6. (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting in air moving out);

For thoracic cavity accept ‘lungs’ or ‘thorax’. Reference to ‘thoracic cavity’ only required once. If idea of thoracic cavity is missing or incorrect, allow ECF for mark point 6.

Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels. (5)

1. Micelles contain bile salts and fatty acids/monoglycerides; Ignore other correct components of micelles

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); Accept lipid/fat for fatty acid/ monoglyceride

3. Fatty acids/monoglycerides absorbed by diffusion; Reject if absorbed by facilitated diffusion Ignore if micelles themselves are being absorbed

4. Triglycerides (re)formed (in cells); Accept chylomicrons form

5. Vesicles move to cell membrane; Accept exocytosis for ‘vesicles move’

Describe the role of enzymes in the digestion of proteins in a mammal. (4)

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;

Accept chain/chain of amino acids/peptide for polypeptide Accept digest/breakdown/ break for ‘act’ Mark points 2, 3 and 4 reject answers where substrate or product is incorrect eg ‘Endopeptidase produces dipeptides’ Ignore references to source and location of enzymes

Cells lining the ileum of mammals absorb the monosaccharide glucose by co-transport with sodium ions. Explain how. (3)

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;

Tissue fluid is formed from blood at the arteriole end of a capillary bed. Explain how water from tissue fluid is returned to the circulatory system. (4)

1. (Plasma) proteins remain; Accept albumin/globulins/fibrinogen for (plasma) protein

2. (Creates) water potential gradient OR Reduces water potential (of blood);

3. Water moves (to blood) by osmosis;

4. Returns (to blood) by lymphatic system;

The mass flow hypothesis is used to explain the movement of substances through phloem. Use your understanding of the mass flow hypothesis to explain how pressure is generated inside this phloem tube. (3)

1. Sucrose actively transported (into phloem);

2. Lowering/reducing water potential OR More negative water potential;

3. Water moves (into phloem) by osmosis (from xylem);

Describe the cohesion-tension theory of water transport in the xylem (5)

1. Water lost from leaf because of transpiration / evaporation of water (molecules) / diffusion from mesophyll / leaf cells; OR Transpiration / evaporation / diffusion of water (molecules) through stomata / from leaves;

2. Lowers water potential of mesophyll / leaf cells;

3. Water pulled up xylem (creating tension);

4. Water molecules cohere / ‘stick’ together by hydrogen bonds;

5. (forming continuous) water column;

6. Adhesion of water (molecules) to walls of xylem;

max 5

Describe the mass flow hypothesis for the mechanism of translocation in plants. (4)

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.

4 max

Describe how a gene is a code for the production of a polypeptide. Do not include information about transcription or translation in your answer. (3)

1. (Because) base/nucleotide sequence;

2. (In) triplet(s);

3. (Determines) order/sequence of amino acid sequence/primary structure (in polypeptide);

Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells. (5)

Comparisons

1. Nucleotide structure is identical; Accept labelled diagram or description of nucleotide as phosphate, deoxyribose and base

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; Accept shorter than nuclear DNA/is circular not linear/is not associated with protein/histones unlike nuclear DNA

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;

max 5

Describe how mRNA is formed by transcription in eukaryotes (5)

1. Hydrogen bonds (between DNA bases) break; Ignore DNA helicase. Reject hydrolysing hydrogen bonds.

2. (Only) one DNA strand acts as a template;

3. (Free) RNA nucleotides align by complementary base pairing; For ‘align by complementary base pairing’, accept ‘align to complementary bases’ or ‘align by base pairing’.

4. (In RNA) Uracil base pairs with adenine (on DNA) OR (In RNA) Uracil is used in place of thymine; Do not credit use of letters alone for bases.

5. RNA polymerase joins (adjacent RNA) nucleotides; Reject suggestions that RNA polymerase forms hydrogen bonds or joins complementary bases.

6. (By) phosphodiester bonds (between adjacent nucleotides);

7. Pre-mRNA is spliced (to form mRNA) OR Introns are removed (to form mRNA);

5 max

Describe how a polypeptide is formed by translation of mRNA (6)

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;

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

• a positive effect on an individual.

(4)

(Definition of gene mutation)

1. Change in the base/nucleotide (sequence of chromosomes/DNA); For 4 marks at least one mark must be scored in each section of the answer. Accept named mutation for ‘change’.

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);

4 max

Crossing over greatly increases genetic diversity in this species of moss. Describe the process of crossing over and explain how it increases genetic diversity. (4)

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;

1. Accept descriptions of homologous pairs

2. Accept descriptions of chiasma(ta) e.g. chromatids / chromosomes entangle / twist

2. Neutral Crossing / cross over

3. Reject genes are exchanged

3. Accept lengths of DNA are exchanged

4. Do not accept references to new combinations of genes unless qualified by alleles

The ability to continue producing lactase (LP) as an adult and digest milk is controlled by a dominant allele. One hypothesis for LP in humans suggests that the selective pressure was related to some human populations farming cattle as a source of milk. Describe how farming cattle as a source of milk could have led to an increase in LP. (4)

1. LP due to mutation OR Allele due to mutation; Reject mutation caused by drinking milk. Reject (LP) gene

2. Milk provides named nutrient; Accept any correct named nutrient e.g. glucose, galactose, protein Ignore ‘sugar’ ‘lactose’ as named nutrient

3. Individuals with LP more likely to survive and reproduce OR Individuals with advantageous allele more likely to survive and reproduce; Reject (LP) gene Accept ‘individuals who produce lactase’ for ‘LP individuals’ Accept ‘pass on allele/LP/characteristic’ for reproduce.

4. Directional selection;

5. Frequency of allele increases (in the offspring/next generation); Accept description of increasing frequency of allele e.g. ‘higher proportion’, ‘more common’ but ignore increase in number of allele

max 4

Ecologists investigate changes in grassland communities. Outline a method the ecologists could have used to determine the plant species richness at one site (3)

1. A method of selecting sampling sites at random;

2. Use of quadrat;

3. Identify (plant) species (at site / in each quadrat) OR Count number of (different plant) species (at site / in each quadrat);

1. E.g. grid with coordinates selected using random number table

2. Frame or point

3. Reject refs to % cover, or counting individuals