Marking Schemes for Topic 3 Stafford Papers

TOPIC THREE THE VOICE OF THE GENOME

SAQ 286

(a) (i) Chloroplast; 1 (ii) Photosynthesis; Uses light (energy); To produce carbohydrates/starch/glucose/sugars/ATP/reduced NADP; max 2 Note that candidates cannot be expected to have a detailed knowledge of photosynthesis. (b) (i) A; 1 (ii) C; 1 (c) (i) Slows enzymes/prevents enzymes being denatured/ prevents/stops self-digestion; 1 Ignore references to bacteria. Reject enzymes not working (ii) To remove organelle C/nuclei; Which are larger/more dense; 2

AQA/BYA1/JAN06

SAQ 287

2 (a) A = capsule / slime/mucus (layer); 1 B = flagellum;1 2 (b) Ribosome; 1 2 (c) (Electrons have) shorter wavelength; 1 Greater resolution / can distinguish between close objects; 1 Reference to magnification = neutral 2 (d) Contains DNA; 1 Ribosomes; 1 Folded (inner) membrane / cristae / double membrane; 1 Dont contain membrane-bound

organelles/named example1

AQA/BYBI/JUN08

SAQ 288

(a) (i) Ribosomes; Cytoplasm; DNA; 1 max (ii) Any three suitable answers For example, No nuclear envelope/nucleus; No mitochondria; No chloroplasts; No vacuole;

Mesosomes present / folded cell (surface) membrane; Plasmids/loops of DNA / non-linear DNA; Capsule not in plant cells; Different composition of cell wall; DNA does not associate with proteins/form chromosome; No Golgi; No SER/RER; Smaller/70S ribosomes; 3 max (allow one mark for no membrane-bound organelles if no named organelle in answer) (b) Smooth endoplasmic reticulum/SER Synthesis of lipids/transport of lipids or polypeptides/drug detoxification; OR Rough endoplasmic reticulum/RER; Attachment of ribosomes/protein synthesis/protein transport; OR Golgi (body); Formation of lysosomes or (secretory) vesicles / adding sugars to proteins or lipids / secretion of enzymes/hormones; OR Lysosome; Digestion of damaged/worn-out organelles / autolysis; 2 max (As ribosomes are often referred to as membrane-bound, if ribosome is the named organelle, give no mark for name of organelle, but allow one mark for the correct function i.e.Protein synthesis/translation)

Total 6 AQA/BYB1/JUN07

SAQ 289

c) The length of mitochondria can vary from 1.5 m to 10 m but their width never exceeds 1 m. Explain the advantage of the width of mitochondria being no more than 1 m. (1) The uniformly narrow width of the mitochondria ensures that the diffusion distance is very low. The distance from the centre to the outer membrane of mitochondria is very less (about 0.5 m).

(Total 1marks) January 2004 BYB1, AQA

SAQ 290

b) (i) ice-cold (1) The low temperature will reduce enzyme action. This will help to keep the organelles

intact and prevent lysosomal enzymes from hydrolysing the organelles. (ii) isotonic (1) Isotonic means that the water potential of the solution is the same as the water potential of the cell contents. This helps to prevent osmosis and does not allow the organelles to shrink or swell and burst. c) Pellet A. The nucleus is the largest organelle. During centrifugation, the largest, more dense organelles sediment at lower speeds. To obtain smaller organelles, centrifugation will have to be carried out at higher speeds for longer intervals of time. (2) d) Incubate the mitochondria with pyruvate. The mitochondria will start to use up oxygen and produce carbon dioxide and ATP. The rate of oxygen absorption can be measured using a respirometer or the rate of carbondioxide production can be measured using a hydrogen carbonate indicator.

(Total 8 marks) June 2002 BYB1, AQA

SAQ 291

(a) ONE correct function; and explanation;

e.g. emulsifies fats / described; increases

surface area for lipase / faster rate of digestion

by lipase; OR bile (is alkaline) neutralises

acidic material / chyme from the stomach;

provides optimum pH for (digestive) enzymes;

(b) (i) cold - no / reduced enzyme action /

e.g. stops autolysis; (reject "cell activity

reduced") isotonic . stops osmotic effects /

description of effect on cells or organelles;

buffer . prevents damage to enzymes /

proteins; 3

(ii) break open the cells / release the cell

contents; 1

(iii) supernatant / liquid above the pellet; spun

at a high(er) speed; 2(mark as independent

points) Total 8 AQA GCE Mark Scheme, 2006

January. BYB1

SAQ 292 a)A - rough endoplasmic reticulum B - nuclear envelope

C - mitochondria D - golgi bodies or golgi apparatus E - secretory vesicles F - vacuole b)The ribosomes attached to the rough endoplasmic reticulum produce polypeptide chains by translation. The polypeptide chains are packed into transport vesicles and transported to the cis region or forming face of the golgi bodies. The polypeptides are modified in the cisternae of the golgi bodies and released in secretory vesicles from the trans region or the forming face of the golgi bodies. The secretory vesicles fuse with the cell membrane and release their contents by exocytosis. (Total 5 marks)

Cambridge Specimen Paper 2002 SAQ 293 (a) (i) A mitochondrion and B nucleus; 1 (need both for one mark) (ii) increased surface a rea; for respiration/enzymes; 2 (b) any suitable feature 1 e.g. plasmid/capsule/70S ribosomes/smaller ribosomes/complex cell wall/mesosome/no nucleus; (c) use of differential centrifugation/or description; first/low-spin pellet discarded / spin at low speed to remove cell wall material/cell debris; supernatant re-spun at higher speed / until pellet with chloroplasts is found; method of identifying chloroplasts e.g. microscopy; 3 max


SAQ294 (a) A Carries the (genetic) code / genetic instructions / DNA / makes mRNA / transcription / makes ribosomes; B Links amino acids / synthesises / makes protein; C Involved in modifying / packaging protein / forms glycoproteins / forms vesicles; 3 (b) (i) Mitochondrion; 0.01% as opposed to 0.003%; 2 Accept any valid approach but must be clear as to what the calculations relate

(ii) With electron microscopes sections must be cut; Cisternae are joined to each other; Outside plane of section; 2 max (iii) Protein synthesis requires energy / ATP; Mitochondria release energy / make ATP; From respiration; 3 Do not award credit for second point if candidate refers to mitochondria making / producing energy

Total 10 AQA/BYB1/JAN02 SAQ 295 (a) Red blood cell Bacterial cell Does not contain ribosomes Contains ribosomes; No cell wall Cell wall; No capsule Capsule; No flagellum Flagellum; No mesosomes Mesosomes; No plasmid Plasmid; No genetic material/ DNA Genetic material/ DNA; max 2 [Note: Must compare like with like] (b) No nucleus/ DNA; (Nucleus) codes for protein/ can't make RNA; OR No ribosomes/ rough endoplasmic reticulum; Protein is made/ synthesised/ translated (on ribosomes); OR No mitochondria; (Mitochondria) supply energy/ ATP for making proteins; max 2 (c) (i) Red blood cells do not contain endoplasmic reticulum/ do not have membrane-bound organelles; 1 [Note: not enough to say 'because there aren't any'] (ii) Water potential inside cell more negative/ lower; Water moves in by osmosis/ diffusion; 2 (d) (i) Have a greater surface area to volume ratio/ shorter distance to centre; 1 (ii) Cell membrane of abnormal cell not as strong/ spectrin strengthens membrane; 1 (e) 1 Amino acid based on carbon with four groups attached; 2 Amino/ NH2 and carboxyl/ COOH; 3 R-group/ side chain + hydrogen; 4 R-group differs from one amino acid to another; 5 Amino acids joined by condensation; 6 Bond formed between NH2 and COOH; 7 Involves removal of molecule of water; 8 H from NH2 and OH from COOH; max 6

Total 15 marks AQA/BYA1/JAN03 SAQ 296

9. a) A Nucleus B Chloroplast C Circular DNA

b) The bacterial cell wall is made up of murein or peptidoglycan, where as, the in a leaf cell the cell wall is made up of cellulose.

c) The flagellum (D) in bacterial cells is made up of a protein called flagellin. The flagellum spins like the propeller of a boat (cork screw motion) to help the bacteria to swim in water. (Total 6 marks)

June 2005 Unit 1, EdexcL SAQ 297

a) (i) A Glycoprotein B Phospholipid.

(ii) A acts as a receptor for hormones and also helps in cell to cell recognition .

(iii) The phospholipid molecules have a hydrophilic phosphate head which is attracts to water molecules in the membrane surface. The fattyacis tails are non-polar and hydrophobic so they face away from the water molecules on the membrane surface and form a barrier to polar molecules. (3)

b) The cell surface membrane is made up of a fluid mosaic model. Fluid means that the proteins can change places within the membrane. Mosaic means that the proteins are randomly embedded in the phospholipid bilayer. So when the two membranes are fused together , the proteins change places and arrange themselves randomly. (Total 8 marks)

June 2005 Unit 1, Edexcel

SAQ 298 SAQ 299 a) (i) A Flagellum

B Circular DNA

(ii) Glycogen

(iii) The plant cell wall is made up of cellulose but the bacterial cell wall is made up of peptidoglycan or murein.

SAQ 300

a) (i) The outer nuclear membrane is continuous with the endoplasmic reticulum, where as the mitochondrial membrane is not associated with the endoplasmic reticulum. The outer nuclear envelope has ribosomes attached to it, where as the outer mitochondrial membrane does not. The nuclear envelope has pores, but mitochondria does not. The inner membrane of mitochondria has ATP synthase (ATPase or stalked particles), but the nuclear envelope does not. The inner membrane of mitochondria is folded into cristae, but the nuclear envelope is not folded.

(ii) Chloroplast (1)

b) The centriole is a hollow cylindrical structure, made up of nine triplets of microtubules. The centrioles always occur in pairs. The centrioles lie perpendicular to each other. The main function of the centrioles is to organize the spindle fibres during cell division. Tubulin subunits are assembled by the centrioles, resulting in spindle formation.

(Total 6 marks) January 2005 Unit 1, Edexcel

SAQ 301

Name of organelle

Two features of structure

One function

Golgi apparatus

1. Stack of curved cisternae 2. Surrounded by many vesicles

Modification of proteins

Rough endoplasmic reticulum

1. Network of flattened membranes (cisternae) 2. Ribosomes found on outer surface

Isolation, transport and packaging of proteins.

Chloroplast

1. Surrounded by double membrane (envelope) 2. Filled with stroma, which contains thylakoid membranes, circular DNA, ribosomes.

Site of photosynthesis

(Total 6 marks) June 2004 Unit 1, Edexcel

SAQ 302

a) (i)Palisade and spongy mesophyll layer , lower or upper epidermis, xylem and phloem tissues. (2) (ii) It is made up of several tissue, working together to perform a specific function (photosynthesis).

(Total 6 marks) June 2004 Unit 1, EdexcLl

SAQ 303

a) The root tip or the stem tip are suitable, because they contain rapidly dividing cells. These rapidly dividing tissues are called as meristems or meristematic tissue. (2) b) (i) To make the chromosomes visible. (1) (ii) Acetocarmine, acetic orcein, Feulgens or schiffs stain. c) Squashing spreads the cells out so that a single layer of cells is obtained on the slide. (1)


SAQ 304

a) Tissues and organs. (2)

Tissues are groups of similar cells performing a similar function, where as organs are groups of tissues that perform a specific function.

b) Not in syllabus ignore Magnification and resolution. (2)

Magnification is the ratio of the size of image to the size of the object, where as resolution is the degree of detail that is visible under the microscope.

(Total 4 marks)

January 2004 Unit 1, Edexcel

SAQ 305

The proteins that are synthesised on the rough endoplasmic reticulum pass into the cisternae and are packed into transport vesicles. These vesicles, fuse

with the cis-region of the Golgi bodies and are concentrated and modified by the addition of carbohydrate chains, to form glycoproteins. The modified proteins are then packed into secretory vesicles and released from the trans-region of the Golgi bodies. The secretory vesicles move towards the cell membrane and fuse with the membrane to release the contents by exocytosis.

Part of January 2004 Unit 1, Edexcel

SAQ 306

20. The table below refers to some features of

prokaryotic and eukaryotic cells.

If the feature is present, place a tick () in the

appropriate box and if the feature is absent,

place a cross (X) in the appropriate box.

Feature

Prokaryotic cell

Eukaryotic cell

Nuclear envelope

X

Cell surface membrane

Ribosome

Microtubules X

Mitochondria X

(Total 5 marks) January 1996, (B/HB1), Edexcel

SAQ 307

A) Anaphase

B) The spindle fibres are involved in pulling

the chromosomes towards the poles during

cell division and also for holding the

chromosomes in position. (2)

Centrioles: The centrioles organize the spindle

fibres during cell division and help to

assemble tubulin for the formation of spindle

fibres. (Total 13 marks)

June 2003 Unit 1, Edexcel

SAQ 308

a) Phospholipids are made up of two fatty acid tails and a phosphate head. The fatty acid tails are non polar and hydrophobic (water hating), while the phosphate heads are polar and hydrophilic (water loving). So the polar phosphate heads are attracted to water molecules on the membrane surfaces and the fatty acid tails face away from the water on the membrane surfaces, forming a bilayer. c) Carbohydrate : The carbohydrates may help in cell recognition, as in the case of antigens. They also play a role in adhesion of cells to each other. Protein: Some proteins may act as carriers or channels for the transport of specific substances across the cell membrane; some proteins may serve as receptors for hormones, helping hormones to recognize and affect only target cells; other proteins may serve as enzymes, as in the epithelial cells in the ileum of humans. (Total 8 marks)

January 2003 Unit 1, Edexcel SAQ309

a) (i) These are spherical bodies, about 0.5 nm

in diameter. They are filled with about fifty

different hydrolytic enzymes, in acidic

solutions. These are found only in animal cells.

(ii) The lysosome isolates the hydrolytic

enzymes from the rest of the cytoplasm.

These enzymes are used to hydrolyse bacteria

or other substances engulfed by the cells. The

lysosome fuses with the phagocytic vesice

and releases enzymes into the vesicle, where

hydrolysis takes place. These enzymes may be

used in a similar way to hydrolyse old or

damaged organelles within the cells.

Sometimes the lysosome may rupture and

destroy the entire cell. This is called as

autolysis and the lysosome is sometimes

called as the suicide bag or scavenger of the

cell.

b) During the first eight hours, there is a rapid

increase in the radioactivity inside the WBCs.

Between 8 hours to 14 hours, the level of

radioactivity remains relatively constant.

However, after 14 hours there is a decrease in

the level of radioactivity in the WBCs. Ven at

24 hours, there is some amount of radioactivity

inside the WBCs.

c) The bacteria is being hydrolysed by the

hydrolytic enzymes of the lysosome.

d) The products from the hydrolysis of the

bacterial molecules will still be radioactive.

These radioactive amino acids are expelled

from the cell by exocytosis.

e) All the bacteria may not have been taken up

by the cells. Also the bacterial cells may not

have taken up all the amino acids from the

supernatant solution.


SAQ 310

a) A Flagellum B Circular DNA C Cell wall / peptidoglycan / murein

b) Prokaryotic cell Eukaryotic cell

Smaller cells Larger cells

Do not have a nucleus

Have a nucleus

Do not have membrane bound organelles

Have membrane bound organelles

Have 70S ribosomes Have 80S ribosomes

Have mesosomes No mesosomes present

Circular DNA Linear DNA

Histones absent Histones present

Cell walls made of murein

Cell walls, if present, made of cellulose

Flagellum with no microtubules

Flagellum with 9+2 arrangement of microtubules

(Total 6 marks) May 2002 Unit 1, Edexcel

SAQ 311

Feature

Prokaryotic cell

Eukaryotic cell


Plasmids X Ribosomes Mitochondria X


SAQ312

a) This will prevent the entry or exit of water by osmosis. Thus the organelles will remain intact and there will be no osmotic effect. b)

Pellet Organelle

A Nuclei

B Mitochondria

C Ribosomes

c) Glucose, glycogen, proteins, ions, lipids, microtubules, microfilaments or RNA d)

d) The mitochondria produce large amounts of ATP by aerobic respiration, via the Krebs cycle and electron transport chain. Large amounts of ATP are used for the metabolic reactions in the liver cells, as liver cells are metabolically very active. (2) (Total 12 marks)

January 2002 Unit 1, Edexcel

SAQ 313

Name of organelle

Description One function

Golgi

apparatus

Made up of curved stacks of membranes called cisternae, surrounded by many vesicles.

Modification of proteins

Centrioles

Cylindrical organelles made up of microtubules

Involved in spindle organization during cell division in animal cells

Mitochondria

Rod-shaped structures with a double membrane, the inner one folded to form cristae.

Site of aerobic respiration for the production of ATP

(Total 5 marks) June 2001 Unit 1/Module B1,

Edexcel

SAQ 314

Feature

Prokaryotic cell

Eukaryotic cell

Endoplasmic reticulum

X

Mesosome X Ribosome Golgi apparatus X

(Total 4 marks) January 1999 Module BHB1,

EdexceL

SAQ 315

Statements Liver cell Leaf palisade cell

Mitochondria Starch grains X Microtubule Golgi apparatus

Glycogen granules

X

(Total 5 marks) June 2000 Module Test B/HB1, Edexcel

SAQ 316

a) (i)A Phospholipid layer B Glycoprotein C Carrier or Channel protein D Carbohydrate chain E Glycolipid (5) (ii) 7 nm (2) b) (i) The cytoplasm is on side Y. (1) (ii) The carbohydrate chains (glycocalyx) is always found on the outer surface of the cell membrane. Component 1 : Carrier or channel proteins Function : Transport of specific substances across the membrane. Component 2 : Glycoproteins Function: Help in cell to cell recognition. Component 3: Phospholipid bilayer Function: Forms a barrier to polar molecules and ions. (6) d) The phospholipid bilayer is impermeable to large polar molecules and ions. However, non polar molecules, like oxygen and carbon dioxide; and lipid soluble substances, like cholesterol can pass the phosphlipid bilayer. The larger polar molecules and ions can only enter the cells through specific proteins in the cell surface membrane. Since most biological molecules are large and polar, their movement across the membrane is restricted and determined by the carrier and channel proteins in the cell surface membrane.

(Total 19 marks) Specimen Materials OCR 2000

SAQ317

a) They have a cell wall made up of murein or peptidoglycan. They lack membrane bound organelles. They have 70 S ribosomes and lack a membrane bound nucleus. (3)

b) Lysosome: isolates the hydrolytic enzymes from the rest of the cytoplasm. These enzymes are used to hydrolyse bacteria or other substances engulfed by the cells. The lysosome fuses with the phagocytic vesicle and releases enzymes into the vesicle, where hydrolysis takes place. These enzymes may be

used in a similar way to hydrolyse old or damaged organelles within the cells. Sometimes the lysosome may rupture and destroy the entire cell.

Ribosomes: they are the sites of protein synthesis. The information from mRNA is translated into a polypeptide chain.

Centrioles: Involved in spindle organization during cell division in animal cells.

(Total 9 marks) Specimen Materials OCR 2000

SAQ 318

SAQ 319

Nuclear envelope


Ribosomes

Microtubules

Mitochondria

Prokaryotic cell Eukaryotic cellFeature

;

;

;

;

;

SAQ 320 a) A.Flagellum / flagella; B. (peptidoglycan) / cell wall; C.(circular) DNA / chromosome / nucleoid

SAQ 321 -

SAQ322 (a) A mitochondria; B ribosomes (accept ribosomes and rER); 2 (b) idea of sections or cuts; idea of mitochondria orientated differently or in different positions / description of 3D structure of mitochondria, e.g. sausage-shaped; 2

(c) translation / protein/polypeptide synthesis; 1 (d) provide/produce energy or ATP (reject create energy); (disqualify first mark if .for respiration.) high respiration (rate) (accept lots); for active uptake / transport (accept description); absorption of digested food/substances/products/correctly named product (only accept monosaccharides, amino acids, dipeptides); 3 max

Total 8 AQA/BYB1/JAN05 SAQ 323

(a) central C with R and H attached by single bonds ;

NH2 and COOH attached to carbon by

single bonds ; [accept NH3+ an/or COO] 2

(b) (i) A -Ribosomes ; B- Rough ER ; C -Golgi apparatus ; 3

(ii) (Rises by 15 units in 15 minutes) Rate = 15 15 ; [accept other correct figures] = 1 ; unit per min ; [allow unit mark if figures from incorrect curve] 3

(c) Radioactivity will continue to drop in (all) organelles ;

Reference to half life (of isotope) / natural drop in radioactivity over time ;

Moved out of cell / exocytosis / secreted ; As protein / named example ;

Radioactivity will not reach zero ; Because some, amino acids / proteins, incorporated ;max 3

[11]

SAQ 324 (a) (i) Golgi body (ii)cell surface membrane/ phospholipid bilayer (iii)exocytosis /endocytosis (b) Production of protein ; Secretion of proteins (hormones, enzymes) ;Exocytosis (from the cell) ;Endocytosis (intocell) SAQ325 (a) Endoplasmic reticulum / mitochondrion / mitochondria / membrane-bound organelles / internal membranes ;

1 mark (ii) Bacterium! named bacterium / bacteria / blue-green algae -I cyanobacteria ; 1 mark (b) (i) Ribosome ; (ii) Protein synthesis ; OR (I) (Rough) endoplasmic reticulum / intermembranal space ; (ii) {Transporting / trafficking / folding! synthesising} proteins ; 2 marks (c) B (Outer mitochondria!) membrane / double membrane! intramembranal space! double envelope ; Crista / infokling of (inner mitochondria!) membrane / inner mitochondria! membrane ; 2 marks

Total 6 marks SAQ 326

(7 MARKS MAX) SAQ 327

(a) ii Mitochondrion / mitochondria ; iii Ribosomes / rough endoplasmic reticulum / RER; iv Golgi body / golgi apparatus / smooth endoplasmic reticulum / SER; v Vacuole ; vi Centriole ; 5 marks

SAQ 328

(a) A Plasma membrane / cell membrane / cell surface membrane;

B Centriole(s) / microtubule(s) / centrosome;

C Golgi apparatus / Golgi body / smooth ER;

D Rough ER / ribosome; 4 SAQ 329

The table below refers to three organic compounds found in cell organelles.If the compound is found in the organelle, place a tick () in the appropriate box and if the compound is not found in the organelle, place a cross (x) in the appropriate box. [Total 4 marks

Organelle

Ribosome

Chloroplast

Smooth endoplasmicreticulum

Mitochondrion

Phospholipid DNA

;

;

;

;

RNA

SAQ 330 (a) Cell S has more rough endoplasmic reticulum; Ribosomes are site of protein/enzyme synthesis/ where enzymes are made; 2 (b) (i) Inner membrane folded/forms cristae; 1 (ii) Fewer folds/cristae in cell R; 1 Accept converse; unqualified descriptions refer to cell R. (c) Only eukaryotic cells have membrane bound organelles; Nucleus/nuclear envelope Endoplasmic reticulum; Mitochondria; Lysosomes; Smaller percentage of membrane is plasma membrane; Do not have mesosomes; 2 Accept converse; unqualified descriptions relate to cell R. Note that this is an animal cell. Do not accept general statement about membrane-bound organelles in addition to rough endoplasmic reticulum/mitochondria and lysosomes.

(d) Rate of uptake increases then levels out; At approximately 3 (mmol dm-3 ); 2 (e) Limited by carrier molecules/ proteins/ carriers are saturated; 1 (f) 1 Homogenise/chop (or otherwise crudely break) leaves; 2 Suspend in/mix with buffer; 3 Cold and isotonic; 4 Filter and centrifuge filtrate; 5 At low speed; 6 Discard pellet/keep supernatant; 7 Centrifuge again at faster speed 8 Chloroplasts are in pellet (formed by second centrifugation); 6 max

Total 15 AQA/BYA1/JAN08 SAQ 331- SAQ 332 (a) (i) Golgi body (ii)cell surface membrane/ phospholipid bilayer (iii)exocytosis /endocytosis (b) Production of protein ; Secretion of proteins (hormones, enzymes) ;Exocytosis (from the cell) ;Endocytosis (intocell) (c) (i) digestive enzymes / protease /lipase (ii) ref to rough endo plasmic reticulum Ref to passage through reticulam Ref to golgi bodies in vesicles lysosomes

SAQ333

(a) (i) A transcription; B translation; (2 marks)

(ii) exocytosis / reverse pinocytosis;

(1 marks)

(c) tRNA has an unpaired triplet of bases / anticodon; attaches to / binds to mRNA codon / complementary bases; tRNA carries a specific amino acid; which becomes part of polypeptide / reference to formation of peptide bonds;

(3 marks)

[Total 6 marks] SAQ 334

Question 7 Maximum mark

(a) (i) Produced {on / by} {ribosomes /rough endoplasmic reticulum} ; 1 marks (ii) Transported by the (smooth) ER (to Golgi bodies) ; [accept rough ER] Correct reference to vesicles ; Correct reference to (vesicles) fuse with (cell) membrane /(protein secreted by) exocytosis ; 2 marks

SAQ 335

(a) (i) Name the processes taking place during stages A and B. A transcription;

B translation;

(2 marks)

(ii) Name the process by which protein is secreted in stage F. exocytosis / reverse pinocytosis;

(1 marks)

(b)tRNA has an unpaired triplet of bases / anticodon; attaches to / binds to mRNA codon / complementary bases; tRNA carries a specific amino acid; which becomes part of polypeptide / reference to formation of peptide bonds;

(3 marks) [Total 6 marks]

SAQ336

a) name the parts labelled A, B, C, and D. A cell wall;

B spindle (fibre) / microtubule:

C centromere;

D chromatid / (daughter) chromosome;

(4 marks)

(b) name the stage of meiosis shown in this diagram. Anaphase;

(1 mark) [Total 5 marks]

SAQ 337-

SAQ 338-

SAQ 339 (a) (i) Golgi; 1 (ii) Exocytosis; 1 (b) (i) Joining together of amino acids / synthesis/production of thyroglobulin / makes protein; 1 Do not credit synthesis of amino acids (ii) Electron microscope has high/greater resolution; Because it uses electrons; Which have smaller wave(length); max 2 (c) (i) (structure) made up of similar cells; 1 (ii) (structure) made up of (different) tissues; 1 In part (c) ignore references to function Total 7 marks

AQA/BYA1/JUN04 SAQ .340 (a) Interphase/S-phase; 1 (b) A D C E B; 1 (c) Attachment of centromeres/chromosomes/chromatids; Separation of centromeres/chromatids/chromosomes; 2 (d) Halves chromosome number/haploid; Diploid/full number restored at fertilisation; Allow correct reference to variation max 2

Total 6 AQA/BYA2/JAN06 SAQ 341

SAQ 342 (a) (i) (D) B E A C; 1 (ii) metaphase; 1 (b) interphase/S phase; 1 (c) (i) 0.06 x 100; 6(%); 2 (correct answer 2 marks) (ii) more (cancer cells) killed, cancer cells divide more (often) (so are more likely to be killed, more susceptible); 1 (iii) longer time to recover; reduced rate of mitosis / divide more slowly/increased doubling time; 2

Total 8 AQA/BYB2/JAN08

SAQ343

(a) Centromeres divide/chromatids separate; One chromatid/chromosome moves to each pole; Spindle fibres shorten; 2 max (b) Rate of removal (of tubulin) proportional to shortening of spindle fibres/ speed of movement of chromatids/fibres control speed of movement; Provides force/pulls chromatids or chromosomes apart/movement linked to shortening of fibres; 2


SAQ 344 -

SAQ 345

(a) (I) anaphase (II) the cells have just formed / newly formed cells (ii) this stage of mitosis is very short/finishes quickly/ faster than other stages of mitosis/ only a small part of mitosis (iv) cells are in interphase / between G1 and G2 (b) (i) existing DNA is copied / new DNA formed / ref to base pairing /ref to semiconservative replication /ref to DNA polymerase (ii) interphase / S phase

SAQ 346

(a) name the parts labelled A, B, C, and D. A cell wall;

B spindle (fibre) / microtubule:

C centromere;

D chromatid / (daughter) chromosome;

(4 marks)

(b)Anaphase; (1 mark)

[Total 5 marks]

SAQ 347 (a) CDBEA;; [Two error = 1 mark, more than two errors = 0 marks] [Allow one mark for DBEA C] 2 marks (b) (i) Root fip / (just behind) last 4-5 mm of root ; 1 mark (ii) (Ethanoic / acetic / propionic) orcein / feulgen / toluidene blue / haemotoxalin 1 mark (c) (i) (DNA) replication / Si; [do not credit reference to prophase / interphase] 1 mark (ii) [DNA / chromosomes) [doubled / copied) / new set of [chromosomes / DNA] forms / eq [Allow replication if not given in part (i)] 1 mark

Total 6 marks SAQ 348 (a) (i) Shorten/thicken /coil/condense; 1 (ii) (Line up) at equator (of spindle)/centromeres attach to spindle; 1 (accept move towards middle of the cell) (iii) Chromosomes or chromatids moving apart/centromere divides; 1 (b) Telophase; 1 (c) (Cells with 9.4) replicated DNA/chromatids joined together / late interphase/prophase/metaphase/before cell division; 1 (Cells with 4.7) single chromatids/DNA is not replicated/telophase/early interphase; 1 (must be clear reference to which cells are being discussed)

Total 6AQA/BYB2/JAN7

SAQ 349

(a)Interphase is made up of two growth phases, G1 and G2 separated by an intermediate phase, S.

(i)Explain what is happening within the cell during phase S. quantity of DNA doubles;replication of DNA / chromosomes;preparation for mitosis / nuclear division / cell division / asexual reproduction;

(2 marks)

(ii)State one process other than cell growth which occurs during phase G2.

mitochondria divide / energy stores increase / ATP produced / respiration / duplication of centrioles / spindle begins to form / protein

synthesis;

(1 marks)

(b)Account for the changes in the quantity of DNA in the cell during mitosis. DNA content halves / returns to original level;DNA / chromosomes / chromatids shared between (daughter) cells / nuclei;during cell division / cytokinesis;

(2 marks) [Total 5 markS

SAQ 350

(a) B D A C F E / D A C F E B : (1 marks)

(b) 1 ,pairing of homologous chromosomes / eq; chiasmata formation / crossing over occurs; 2 chromosome number halved / haploid cells formed; two divisions to complete process / four cells formed; The converse of these points allowed if a clear reference to mitosis was made.

(2 marks (d) production of genetically identical cells; daughter cells have same function as parent cell; for growth / repair; for asexual reproduction / clone formation; rapid reproduction in favourable conditions;

(3 marks) [Total 6 marks]

SAQ 351

(a) (i)Cell B Type of division Mitosis;

Reason no reduction in chromosome number / same number of chromosomes / both diploid / still diploid / identical to Cell A; Cell C Type of division meiosis / reduction division; ReasoN chromosome number halved / crossing over has occurred / haploid / chromosomes different from A; (2 marks)

(ii) homologous chromosomes pair / synapsis occurs / bivalents formed; chiasma formed / crossing over took place;

exchange of materials / genes / genetic information between chromatids; 3 marks)

SAQ 352

Read through the following passage on the cell cycle and mitosis, then write on the dotted lines themost appropriate word or words to complete the passage.

In the cell cycle, replication of DNA takes place during .interphase / S phase;.

At the beginning of prophase the chromosomes become visible and can be seen to consist

of two . chromatids;. joined at the ............centromere;....... .

The ...........nucleolus / nucleoli;......... and nuclear membrane disappear and a spindle

develops in the cell.

The chromosomes become attached to the spindle at the equator during

..........metaphase;............ . At anaphase one copy of each chromosome is pulled

towards each ...........pole / end / aster;........... of the spindle. The final phase, called

telophase, involves the formation of two new nuclei. In plant cells the two daughter

cells are separated by the formation of a .... cell plate / cell wall / phragmoplast /

middle lamella;... . [Total 7 marks]

SAQ 353 (a) (B)DAC; 1 (b) Chromatids/chromosomes separating (accept splitting); (They are) pulled; by spindle fibres; Ignore references to phases 2 max (c) (i) Chromosomes visible / can be counted ; 1 (ii) To stop cells during mitosis/in prophase/metaphase; To stop cells getting to anaphase; Chromosomes are visible in many cells; To ensure chromosomes are spread out; 1

Total 5AQA/BYA2/JUN8

SAQ 354 (a) (i) 20 1 (ii) 10 1 (iii) 10 1 (b) (i) (Daughter) chromatids will not separate / centromere wont divide; Centromere attaches to spindle fibres; 2 NOT chromosomes cant be pulled apart. Ignore references to stages of mitosis. (ii) Red blood cells formed / produced by mitosis; 1

Total 6 marksAQA/BYA2 JUN02

SAQ 355 (a) (i) Prophase; 1 (ii) Chromosomes/chromatids moved apart; 1 (iii) A wide range of processes occurs during interphase. This list is by no means exhaustive, but we would expect to see answers such as: Increase in volume of cell/volume of cytoplasm / increase in mass / cell bigger; increase in number of organelles; synthesis of protein/named protein; DNA replication/increase / chromosomes copied; ATP synthesis / respiration; max 2 (b) Divide real length of bar (in mm)/10 by 0.02; 1 (c) 12/200 x 24 / single error in otherwise correct method; 1.44 hours (1 hour 26 min); 2

Total 7 marks AQA /BYB2/JAN5

SAQ 356 (a) (i) where mitosis/division/growing/ occurs 1 (reject growing cells) (ii) to distinguish chromosomes/chromosomes not visible without stain; 1 (iii) to let light through/thin layer; 1 (b) (i) 74 + 18/982; = 9.4% / 9%; 2 (allow 1 mark for identifying prophase & metaphase i.e. 92 or correct method using wrong figures) (ii) genetic differences/different types of garlic; time of day; chance; age of root tip; water availability; temperature; nutrient availability; 2 maX (environmental factors = 1 but cannot be awarded in addition to a name environmental factor)


SAQ 357-

SAQ 358 (a) (i) onion / garlic / other suitable species; (ii) root tip; 2 marks (b) (acidic/acidified/acetic/ethanoic/propanoic) orcein / feulgen / toluidene blue; 1 mark (c) to macerate them/to separate the cells; 1 mark (d) A = centromere; B = chromatids; 1 mark Total 6 marks

SAQ359

(a) anaphase ; prophase ; telophase ; metaphase ; [if I or II, penalise ONCE] 4 (b) (i) (G lasts) 7.0 hrs (and cell cycle time is 14 hrs) / 18-11 ;

7 100 14 ; = 50 % ; 3

(ii) B ; DNA replication / DNA mass beginning to, increase / double ; 2

[9] SAQ 360

a) Reference to named stain (acetic orcein / acetocarmine / Feulgens / Schiffs) ; Warm / heat ; Break open tip with (mounted) needle /eq ; Mount in stain / acid / water ; (gently) squash under coverslip / eq ; max 4

(b) (i) A ; 1

(ii) C ; 1

(c) Synthesis / division / multiplication of organelles (or named organelle) ; Growth ; Replication of DNA/ chromosomes ; Protein synthesis / name of specific protein being synthesised ; Any normal cell activities, named example (e.g. respiration) ; max 2

[8]

SAQ 361

(a) Correct measurement 78 / 79 ; Measurement 1000 (to give m) ; 50 ; [if final answer is incorrect maximum marks = 2] 3

(b) Drawing marks:

D1 Chromosomes drawn correctly ; D2 Centrioles drawn correctly ;

Label marks: Chromosomes ; Centrioles ;

Spindle fibres ; 5

(c) Anaphase ; [ignore reference to I or II] 1

(d) Spindle fibres:Pull {centromeres / chromatids / chromosomes} {apart / to opposite poles} OR {Pull / hold} chromosomes into position ;

Centrioles: {Produce / organise / assemble} spindle (fibres) / microtubules ; OR Organise / assemble} tubulin ; 2

[11] SAQ 362

(a) (i) BDAC; 1

(ii) Metaphase; [ignore I and II] 1

(b) (i) DNA replicates; Cell division / cytokinesis; 2

(ii) Mitosis / G2 and mitosis; 1

(iii) {l5/20} hours; 1 SAQ 363 a). The root tip or the stem tip are suitable, because they contain rapidly dividing cells. These rapidly dividing tissues are called as meristems or meristematic tissue. (2)

b) (I).To make the chromosomes visible. (1)

(ii)Acetocarmine, acetic orcein, Feulgens or schiffs stain. (1)

c) Squashing spreads the cells out so that a single layer of cells is obtained on the slide. (1)


SAQ 364

(a) 1. Reference to named stain (acetic orcein / acetocarmine / Feulgens / Schiffs);

2. {Warm / heat} (with the stain / acid);

3. Break open tip (with needle / eq);

4. {Mount / eq} in {stain / acid / water / glycerol};

5. (Gently) squash under coverslip

/ eq;

6. Warm (gently to intensify stain); 4

(b) 1. Telophase is the longest stage;

2. Anaphase is the shortest stage;

3. Correct manipulation of figures to compare any two phases;

4. Any two actual times given e.g. {prophase 29.16 mins / metaphase 16.80 mins / anaphase 8.40 mins / telophase 33.36 mins}; 3

(c) (Use the equation to) work out actual time of each phase;

Total all four times; OR

Add up all 4 percentages; {Substitute into

equation / eq} / Multiply by 100

1200; 2 [9]

SAQ 365

(a) A Metaphase ;

B Prophase ;

C Telophase ; 3

(b) 1. Chromatids separate / centromere splits ;

2. Moved to (opposite) {poles / ends / centrioles} ;

3. By spindle fibres / microtubules ;

4. Shortening / eq ; 2

(c) Daughter cells genetically identical to parent cell / maintains chromosome number / eq ; 1

[6] SAQ 366

(a) (i) 4 ;

(ii) 4 ; 2

(b) 1. Idea of using a short length of root tip ; 2. Ref. to acidification ; 3. Add {acetic orcein / acetocarmine / Feulgens stain / Schiffs reagent / Toluidine Blue / Lactoproprionic Acid} ;

4. Warm / heat ; 5. Break open tip (with mounted needle / eq) ; 6. Mount/ eq in {stain / acid / water} ; 7. (Gently) squash under coverslip or slide ; 8. Warm slide (to intensify staining) ; 5

(c) (i) Metaphase /prophase ; 1 (ii) Spindle is made during prophase ; 2 (if there is no spindle) {there is nothing for the chromosomes to attach to(in metaphase)} / {chromatids cannot be pulled apart(in anaphase)} ; [10]

SAQ367-

SAQ 368

(a) (i) 95 - 100 minutes; 1 (ii) It shows the distance between the (sister) chromatids increases at this point; As they begin to separate/ move to opposite poles; 2 (b) Chromatids cannot be seen; Valid reason, e.g. chromosomes have not condensed / too diffuse / still in interphase; 2 (c) (i) Zygote; 1 (ii) Avoids doubling of chromosomes number at each generation / maintains chromosome number from generation to generation/ diploid/correct number/ 46 restored at fertilisation; 1

Total 7 AQA/BYA2/JAN7

SAQ 369

(a) (i) 6; 1 (ii) On graph: .F. on vertical rise from 3 to 6 pg; .S. on vertical fall from 6 to 3 pg; 2 (b) Crossing over / described; Independent/random assessment / independent/random segregation / described clearly (e.g. not just alignment); 2 Ignore reference to name of phase Total 5 AQA/BYA5/JAN7 SAQ 370

(a) (i) 1 OR 2; (ii) 3; 2

(b) (i) 6.5; (ii) 3.25; 2 (c) Any two from: A , B , C , D and E; 1 (d) Only nucleus from sperm / (more) cytoplasm from 2o oocyte / from egg; Mitochondria (in cytoplasm) contain DNA; 2 Total 7 AQA/BYA7/JUN8 SAQ 371

(a) Chromosomes attach to equator/middle of cell/spindle; Prophase; Anaphase; DNA replication/synthesis / chromosome copying/duplication; Telophase; 5 (b) (i) Meiosis; 1 (ii) 32; 1 Total 7 marks AQA/BYA2/JUN4

SAQ372 (a) Later fertilisation/cell fusion; (NOT just .sexual reproduction.) Restoring diploid/original number/not doubling chromosome number; 2 [ALLOW ref . + .] (b) Any three pairs from need comparison of meiosis and mitosis each time

SAQ 373

(a) Stage C / formation of secondary spermatocyte; and two of Occurs during meiosis; Shows anaphase of meiosis I / anaphase I; Shows chromosome number halved/reduced / diploid to haploid; max 3 (b) Addition of water molecules / hydrolysis; Protein to amino acids / break peptide bonds; Carbohydrate to monosaccharides / break gycosidic bonds; Glycoprotein attaches to active site / forms E-S complex; Because it has complementary/matching shape; [reject same shape] [allow 1 mark for glycoprotein broken down to amino acids/monosaccharides]

max 2 Total 5 marks AQA /BYA7/ JUN4

SAQ 374

(a) Three marks for three of: Produced my mitosis; DNA replicates; DNA / chromosomes divided equally between daughter cells; Idea of semi-conservative replication and base pairing / complementary strands; No crossing over; No random segregation; 3 max (b) Two marks for two of: (for female) Polar bodies produced / only one ovum produced (reject fewer ova produced) / unequal cell division; Primary oocytes formed before birth / growth phase before birth; Pause in meiosis at prophase I / eq.; Pause in meiosis at metaphase II / eq. / meiosis not complete until fertilisation occurs; 2 max Allow reverse argument for male.

Total 5 marks AQA/BYA7/JUN02

SAQ 375

a) (i) 1. (waxy layer) is waterproof ; 2. {enzyme / pectinase} in (aqueous) solution ; 3. (therefore) {enzyme / pectinase} unable to pass through (waxy layer) / unable to get to {pectin / polysaccharide / carbohydrate} / eq ; 4. pectinase is specific and will not digest lipid / waxy surface ; (ii) 1. shape of (enzyme / pectinase) active site ; 2. fits pectin / does not fit cellulose / reference to specificity of enzymes ; (b) (i) 1. increases the surface area ; 2. more {substrate /pectin} available / increases the number of {enzyme-substrate complexes / collisions between enzyme / eq and substrate / eq} ; (b)(ii)1. hydrolysis uses up water ; 2. evaporation of water /eq ; 3. idea of same number of the {enzyme / pectinase} molecules but in less {solvent/water} ; 4. pectinase released from orange tissues/eq ; 5. correct reference to osmosis (into

orange) ; {12 MARKS SNAB }

SAQ376

(a) (i) BBhh black, long hair ; bbHH white, short hair ; 1 mark (ii) BbHh ; 1 mark (b) (i) BbHh x bbhh; bh BH BbHh Bh Bbhh bH bbHh bh bbhh 1 for gametes correct ; 1 for offspring correct ; 1 for phenotypes: black short, black long, white short, white long ; 4 marks (ii) new combinations of characteristics/alleles ; in offspring but not parents ; example ; 2 marks (c) mutation produces new alleles/changes DNA /eq ; independent assortment mixes alleles/ new combinations of alleles ; 2 marks (d) provides new alleles / new combinations of alleles / keeps large gene pool ; allows adaptations / allows natural selection /allows response to changes in environment / reduces inbreeding / avoids homozygosity and consequent problems ; 2 marks

Total 12 marks

SAQ377-

SAQ378

(a) A . granum/thylakoid; chlorophyll molecules to trap light / light absorbing pigments/ light dependent reaction / part of light dependent reaction; 2 B . stroma; (contains enzymes for) carbon dioxide fixation/light-independent reaction/ part of light-independent reaction; (allow ribosome role of protein in photosynthesis) 2 (b) (i) C . starch; 1 (ii) from glucose in a condensation/polymerisation reaction / many glucose molecules joined together; 1

Total 6 AQA/BYB4/JAN 05

SAQ379

(a) Two linked points:

Crossing over/exchange of material (between chromatids); Different combinations of alleles/linkage groups changed/broken; OR Independent assortment/alignment of (homologous) chromosomes; Different combinations of (maternal and paternal) chromosomes/alleles; 2 max

TOTAL 5 AQA/BYB4/JAN7

SAQ 380

(a) (i) 8 .chromatids. each side; spindle drawn; 2 (ii) 4 chromosomes; 1 from each homologous pair; 2 (b) produces haploid cells / chromosome number halved; fertilisation; maintains the diploid / chromosome number (in next generation); 2 max

Total 6 AQA /BYB2/JAN 05

AQA 381

(a) (i) TB Tb tB tb; 1 (ii) homologous chromosomes appropriately labelled; 1 (iii) separation of chomatids; 1 (b) (i) crossing over occurs; between D and G; sections of chromatids/chromosomes/DNA/genes exchanged; 3 (ii) crossing over is infrequent (between close genes); 1


SAQ 382

(a) A- mitosis B- meiosis (b) (i) fertilization /syngamy (ii) zygote /diploid cell (b) 1 carcinogens /chemical that cause mutation 3. Uncontrolled mitosis/ cell divison 4. Ref to mutation and DNA damage 5. Ref to disruption of mechanisms wich controls cell didvision- cuses cells to multiply faster hence then die (c) X Acrosome Y nucleus Z mitochondria (10 marks max)

SAQ 383

(a) negative / inverse correlation / as age increases sperm motility decreases; 1 (b) tail / undulipodium beats / waves; (accept flagellum) Mitochondria provide ATP / energy; (not .make. energy) 2 (c) crossing over; independent / random assortment / segregation; 2 (ignore mutation)


SAQ 385-

SAQ384

(a) First meiotic division (A) will show cells with chromosomes appearing as double structures/two chromatids still joined / chromosomes in A and chromatids in B /homologous pairs are separating; Must be in context of anaphase Diploid number of chromosomes /appropriate number for A and B; Allow reverse argument for second meiotic division If answer is unqualified, assume that it refers to cells at A, since this is the logic of the question. 2 (b) Crossing over / chromatids exchange sequences of DNA / chiasmata;

Random/independent segregation/assortment (of chromosomes) / chromosomes from

homologous pairs move independently at meiosis I; And meiosis II; max 2

AQA/BYA5/JAN6 SAQ 386 (a) (i) Difference; Example, Sperm has flagellum; 1

(ii) Explanation; Example, (Flagellum), so it can swim to the egg; 1 (b) (i) Homologous chromosomes/chromosomes form pairs; One (of each pair) goes to each cell produced; 2 (ii) Restores diploid number at fertilisation; Maintain chromosome number (from one generation to next); 2

Total 6 AQA/BYB2/JAN8 SAQ 387

(a) (i) 800 = x 20 (principle, sperm magnified more than ovum) 40 OR 33/34/35 =11.0-11.7 (principle, ovum measured diameter more than sperm); 3 answer 220-234 (x); (correct answer 2 marks) 2 (ii) (provide) nutrients, organelles, cytoplasm, stored food, resparatory substrate (for embryo); 1 (b) prevent entry of (more) sperm / further fertilisation; (ensure only) diploid number of chromosomes / transfer of 1 set of chromosomes; 2

Total 5 AQA/BYB2/JAN 06

SAQ 388

(a) One/different form of a gene (positioned in the same locus/relative position); 1 (b) (Homologous chromosomes) have same genes; At the same loci; Different alleles (usually) only small differences in base sequence; 2 max (c) (i) 125: 1 (ii) Egg contains a store of energy/food/nutrients for the developing embryo (after fertilisation); 1


SAQ 389

SAQ 390

1. Tail / flagellum ; {To swim / to propel it) to the {egg / ovum / vitelline membrane}; 2. Small(er) size ; Makes it easier for it to swim Ito aid mobility / makes it possible to produce them in large numbers ;

3. Haploid number of chromosomes / only one of each chromosome / (only) 23 chromosomes rather than 46; So {normal /diploid) number restored at fertilisation ; 4. Acrosame / sac of enzymes ; To digest way (in)to egg ; 5. Mitochondria ; Energy for swimming / eq ; 4 marks (b) (Mitosis and) meiosis ; 1 mark (c) (Produces) {biological / genetic} variation ; No two sperms the same ; Many sperms do not reach egg / increases chances of fertilising eggs ; Selection for {fittest / eq} sperm ; Some sperms defective ; 2 marks Total 7 marks

SAQ 391

SAQ392

(5 max)

SAQ 393

(a)(i)Comment on the changes in the percentage of men with high sperm counts during the period 1930 to 1990. percentage falling / fall of 35%; biggest drop in sixties / between 1951-1970; some evidence of flattening / ref to figures; (2 marks)

(ii)Compare the figures for men with low sperm counts with those with high sperm counts over the same period. lower percentage of men with low sperm counts at beginning;

numbers increasing during the period / increased by 13%; both fall 1971 - 80; fall in percentage of men with high sperm counts in greater than rise in percentage of men with low sperm counts / converse; biggest rise in numbers in sixties / corresponds with drop in numbers of men with high sperm counts / fluctuations in numbers of men with low sperm counts; after 1980 figures similar;

(3 marks)

(b) Explain why it is necessary for large numbers of sperms to be produced when only one sperm is required to bring about fertilisation. large numbers do not reach fallopian tubes / site of fertilisation; many sperm die; ref to conditions / pH in vagina; enzymes needed for activation of sperm / ref capacitation; many sperm may be abnormal / reduced mobility; (2 marks

AQA 394

1. Tail / flagellum ; To swim / to propel it) to the {egg / ovum / vitelline membrane}; 2. Small(er) size ; Makes it easier for it to swim Ito aid mobility / makes it possible to produce them in large numbers ; 3. Haploid number of chromosomes / only one of each chromosome / (only) 23 chromosomes rather than 46; So {normal /diploid) number restored at fertilisation ; 4. Acrosame / sac of enzymes ; To digest way (in)to egg ; 5. Mitochondria ; Energy for swimming / eq ; 4 marks (b) (Mitosis and) meiosis ; 1 mark (c) (Produces) {biological / genetic} variation ; No two sperms the same ; Many sperms do not reach egg / increases chances of fertilising eggs ; Selection for {fittest / eq} sperm ; Some sperms defective ; 2 marks Total 7 marks AQA

395

(a) (i) A / identified (e.g. 7):

has mass of DNA in B / mass of DNA in C / would have chromosome number of B / contains least DNA / has 23 chromosomes; 1 Reject haploid (ii) 14 (arbitrary units); Diploid number of chromosomes re-established; Gametes are haploid (or concept explained) / each gamete will contain 7 units; 2 max (b) Separation of chromatid pairs / chromatids within a pair / chromosomes; Reject homologous chromosomes 1


SAQ 396-

SAQ397

5(a)(i) reference to {chemical / air / gravity / light / eq} ; 5(a)(ii) 1. idea of {breakdown / digestion / eq} of style ; 2. (breaks down) protein / pectin / middle lamella ; 3. reference to hydrolysis / eq ; 4. easier for pollen tube to grow / reduced resistance / eq ; 5. supplies {nutrients / named nutrient / energy} for (pollen tube) growth / eq ; 5(b) 1. photosynthesis ; 2. {component / eq} of {cytoplasm / sap} ; 3. water as a solvent /eq ; 4. water as a transport medium /eq ; 5. involved in thermoregulation / eq ; 6. reference to role in structural support ; 7. reference to involvement in hydrolysis ; 8. reference to turgor changes ;

SAQ 398

(a) Anaphase and telophase as cell is shown at metaphase;

Meiosis II as chromosomes not homologous pairs / as chromatids will be split by this division; 2 Allow one mark for all correct stages if both points not made (b) Hollow ball of cells; With inner cell mass (at one end); Secretes hCG; Stage at which implantation into uterine lining occurs; 2 max (c) Only produced by embryo/placenta; After implantation; 2

Total 6 AQA/BYA7/JUN07

SAQ 399 SAQ 400 Meiosis ; Halved / ; Random(ly) / independently ; (Digestive) enzymes / lysozyme / eq ; Acrosome ; Zygote ; Mitosis ; Total 7 marks SAQ 401 (a) (Receptor) proteins different / specific shape; Due to tertiary structure; Complementary nature of two proteins; Different proteins present in different species; 2 max (b) (i) Acrosome / acrosome reaction; Releases enzymes / named enzyme (hyaluronidase); Digests outer layer of egg / zona pellucida; Fusion of egg and sperm membranes; 3 max (ii) Formation of fertilisation membrane / cortical reaction (or described) / destruction of ZP3 receptors; 1 (c) ATP formed directly from Krebs cycle; Production of reduced NAD / FAD or hydrogen attached to NAD / FAD; H+ or electrons passed through series of coenzymes / carriers / redox reactions / electron transport chain; Energy released in transfer / energy made available;

Used to combine ADP and phosphate (to form ATP); 4 max (Allow H+ moved across inner mitochondrial membrane and pass through stalked particles forming ATP)

Total 10 AQA/BYB8A/JUN8 SAQ 402 2(a) 0.008 / 0.8% / 1000 8 / 125 1 / 8 10-3 2 Correct method but arithmetic mistake gains 1 mark (b) Cytoplasm of egg contains yolk / food stores; Needed for nourishment / development of (embryo / zygote). 2

Total 4AQA/BYB2/JUN1

SAQ403 3(a) (Allow labelled features on diagrams) (i) Chromosomes or chromatids on equator / in middle of cell; Of spindle (once); No nuclear membrane (once only). (ii) Chromatids moving towards poles / centrioles; Of spindle (once); Two centromeres per chromosome/ centromeres are being pulled; No nuclear membrane (once only). max 3 (b) (i) T 8 U 16 2 (ii) (No) Both derived by mitosis / clones; From same cell; U has two of each allele, but these are identical. max 2 (iii) 24 1


SAQ 404

(a) suggestion and explanation;; examples: no capacitation (of sperm); so unable to bind to egg; OR tail / flagellum not working / not present; so unable to swim / move / travel to egg; OR acrosome not developed / does not contain enzymes; unable to digest path to egg / egg coating / zona pellucida; OR lack of / fewer mitochondria; so not enough energy / ATP for movement; (b) cut up / homogenise (testis tissue); in cold / isotonic / buffer solution; centrifuge at

different speeds / low speed; remove pellet and) spin supernatant at higher speed; 3 max

Total 5 AQA/BYB8A/JUN06

SAQ 405

(a) (i) ovulation; mark)

(ii) mitosis; (1 mark)

(iii) corpus luteum / yellow body; (1 mark)

(iv) progesterone / oestrogen; (1 mark)

SAQ 406

The diagram below shows a germinating pollen grain and a mature ovule from a flower of the Papilionaceae. Some nuclei have been labelled.

(a) insect attracted / eq. / to flower by scent / colour / nectar;

lands on wing petals / depresses keel petal;

anthers / stamens dust / eq. pollen on to insects abdomen;

pollen carried to another stigma / carpel;

(2 marks)

(b) The zygote D;

The endosperm G;

Describe one mechanism which prevents self-fertilisation in flowering plants. any two

nature; is stigma before shed pollen eg.; / protanding

times; different at nature parts female and male / dichogamy

any two

shed; pollen before ripe / witheredstigma eg.; / protogyny

times; different at nature parts female and male / dichogamy

Paired marking points

y;heterostyl of nexplanatio

stigma; on landing pollen prevents flower of structure

ref. to dioecious plants; self-pollination impossible;

self-incompatibility / sterility; no pollen germination;

(2 marks) [Total 6 marks

SAQ 407

(a) A Pollen tube ; B Tube nucleus ; 2

(b) One, fuses / fertilises / combines, with female nucleus / egg cell / eq ; To form zygote ; Which is diploid ; One fuses with polar nuclei / fusion nucleus / primary endosperm nucleus ; To form endosperm (nucleus) ; Which is triploid / 3n ; 4

(c) (i) 15% ; 1

(ii) (Germination rate of) both decreases ; (Germination rate of) Bauhinia always greater than that of Camellia / / converse ; [greater at all concentrations must be implied] (Germination rate of) Camellia reaches zero at 25%, Bauhinia minimum at 30% / does not reach zero / eq ; Above 30 % / this (germination rate of) Bauhinia (starts to) increase (Camellia stays at zero) ; 3

[10] SAQ 408

(a) A = Pollen (grain) / microspore ;

B = Embryo sac / megaspore ;

C = Micropyle ; 3

(b) Mitosis / mitotic ; 1

(c) One male nucleus fuses with egg cell

/ female gamete / ovum / female nucleus /eq ; Forms a 2n / diploid / zygote ;

One male nucleus fuses with polar nuclei / fusion nucleus ;

Forms a 3n / triploid endosperm nucleus ; Max 3 [7]

SAQ 409

Meiosis ; Halved / ; Random(ly) / independently ; (Digestive) enzymes / lysozyme / eq ; Acrosome ; Zygote ; Mitosis ; Total 7 marks

SAQ 410

SAQ 411

SAQ412

(a) bone marrow; (1 mark)

(b) 1 granulocyte / granular polymorph / neutrophil / eosinophil; 2 monocyte; (2 marks)

(c) Platelet / thrombocyte; (1 mark)

(d) Suggest why, when a stem cell divides, it is important that one daughter cell remains a stem cell. to enable continued formation of blood cells / eq;

(1 mark) [Total 5 marks]

SAQ 413

(a) Two suitable reasons;; with explanation;; They can divide (to form new blood cells); So can replace existing (faulty) cells; OR They can form (any type of) white blood cell; So restore

ability to fight infection; OR Childs own cells; So no/little risk of rejection; 4 max (b) Description of sigmoid curve; Reference to specific time and event; Few modified cells to start with/mainly non-functional white cell present; (Modified) stem cells replace non-functional cells/form new population of (functional) cells; (Levels off because) the number of (white) cells reaches the normal level; 3


SAQ 414

(a) Stem cells are able to develop into a variety of different cells / other cells of the body have become already specialized (b) 1. Embryonic stem cells come from human embryos

2. most likely source would be spare embryos from in vitro fertilization

3. parents of spare embryo may object to them being used

4. some people regard embryos as unborn children

5. have ethical (religious) objections to killing embryos

6a. other people consider embryos can be used to alleviate human suffering

6b. some people on the other hand would consider that this type of research offers so much potential to alleviate human suffering that it would be ethically wrong not to attempt it.

7. Correct reference to animal rights issuing appropriate context

SAQ

SAQ 416

(a) (i) (superovulation) from IVF treatment; 1 mark (ii) totipotent cells can give rise to a complete human/all cell types; pluripotent can only give some cell types; 2 marks

(b) (i) cells allowed to multiply / produce more cells; in petri dish/test tube / any reasonable attempt to refer to suitable culture vessel; reference to culture medium/incubator/sterile conditions; to produce more (identical) cells; 2 marks (ii) cell becomes specialised (in function)/stem cells develop into different types of cells;cells stop dividing;one type of cell can be used to produce a specific type of tissue / named example; one cell type can be sued to produce tissue / use of named example; 2 marks (c) This question is intended to test the candidates ability to deal thoughtfully with a moral dilemma and to balance scientific knowledge and ethical considerations. These are the kinds of skills developed through well-informed class discussion. Candidates must decide for or against - a candidate who does not make his or her choice clear is limited to a maximum of 3 marks. A candidate who presents points for and against without expressing an opinion is limited to a maximum of 3 marks for valid points either for or against (which ever is the greater) unless he or she presents a good case why the matter is too finely balanced to come down one way or the other. To gain 4 marks a candidate must include one of the points marked with an asterisk in the mark scheme which attempts to counter the opposing view. Against: Embryonic stem cells are (potential) people/babies; From the moment of conception; Objectional on religious/ethical grounds; [do NOT credit unqualified statements such as unnatural', against nature' 'playing God] Pressure on women to produce surplus embryos; Cloning/stem cell techniques may get into the wrong hands/regulation might be difficult to police* / might be the thin edge of a wedge like designer babies; It will soon be possible to use non-embryonic stem cells so research into the use of embryonic stein cells is unnecessary / eq; * Although there are some advantages there could be unexpected dangerous

consequences therefore not worth the risk / eq;*

SAQ 417

(a) For germination / early development ; (As a source of) energy ; Reference to dispersal ; Reference to high energy value of oil ; Reference to dormancy ; 2 marks (b) (i) Mitosis ; 1 mark (ii) Cells all the same ; Have not yet developed specialised features ; Still actively dividing ; 2 marks (iii) {Quicker / cheaper} than conventional means ; All have high yield /the desired characteristics / consistently good / less variation ; Virus free / sterile / (microbial) infection / disease free ; Easy to transport ; 2 marks (c) (i) (A plant cell) from which the cell wall has been removed ; 1 mark (ii) Easier to get DNA / gene in ; 1 mark

(d) 1. Any appropriate reference to pollination ; 2. The {wild / high yielding} strain would have been crossed with the original strain ; 3. By transferring pollen from one type to another ; 4. From {anther /stamen} to stigma ; 5. Selection (to isolate the best specimens for breeding) ; 6. Selection repeated for several generations ; 2 marks (e) Quicker (qualified) / taking genes from other species / {more reliable / less hit and miss} ; 1 mark For: Potential for alleviating human suffering / eq*; Specific example e.g. culturing patient's own cells to provide replacement tissues/organs; Stem cells from IVF would otherwise be discarded; Embryos should not be considered as human at an early stage (awareness that only cells at a very early stage are used)*. Use of non-embryonlc cells will need a development phase using embryonic cells / more can be done with embryonic stem cells;

Ethically questionable to use embryonic stem cells but these objections are outweighed by the greater evil of not using embryonic stein cells to alleviate human suffering*, Could be excesses but these can be regulated*;

4 marks Total 11 marks SAQ418

(a) (Lipid has) high energy value / eq ; To provide {nutrition / energy} (for the seed / embryo) ; [do not allow food] (To provide energy) for {growth / development / germination / eq} ; Until photosynthesis 2 marks (b) Reference to {seed dispersal / seeds dispersed} / eq ; Only a proportion of the seeds {mOved around / hidden / collected} are actually eaten ; Prevents overcrowding / colonisation of new areas / reference to competition 2 marks (c) (i) Induction ; 1 mark (ii) Gibberellic acid {produced / activated} when seed exposed to cold ; {Switches on / induces} (lipase) gene ; Correct reference to transcription ; Removes {inhibitor / repressor}; 2 marks (iii) 1. mRNA leaves the nucleus ; 2. Reference to {codon / anticodon} ; 3. Amino acids {joined / condensed) ; 4. On ribosomes ; 5. Amino acid sequence determined by base sequence (of RNA / DNA) ; 6. Any correct reference to tRNA ;

3 marks Total 10 marks SAQ 419

(a) (I) to control the ph (ii) 1. Ref to gene activation and switching of genes 3. Beta galactosidase is active 4. Subculture b has been exposed to lactose 5. Lactose binds to repaire molecule 6. Lactose prevents repressor molecule from binding with DNA 7. Initiating the production of mRNA for synthesis of beta galactosidase

8. Inactivated repressor substance prevented from (b) 1. Use water baths / incubator /control temperature 2.suitable range of temperature minimum value 5 one less than 30 and one more than 45 3. need to standardize the suspension of buffer 4. correct use of colorimeter

SAQ 420

(a) (i) (Gene) induction / activation ; 1 mark (ii) Reference to DNA {supercoiling / unwinding / eq} ; (DNA) transcription factors / correct reference to hormone / removal of repressor / removal of gene inhibitor / eq ; 2 marks (b) (i) RNA / mRNA / nucleotides / RNA polymerase ; [do not credit reference to tRNA or rRNA] 1 mark (ii) {Hormone / ecdysone} {switches on gene / induces gene / activates gene / initiates transcription / causes (DNA) uncoiling / eq} ; Causing another (unknown) {substance / protein / enzyme} to be produced which {starts off skin shedding / causes uncoiling of DNA / causes unzipping of DNA} ; 2 marks (c) Not enough males / change in sex ratio ; A {reduction / collapse} in population in context / increase in population justified ; Alternative answer: Appropriate reference to {increase in enzyme activity / decrease in enzyme activity due to denaturing / growth effects} ; Appropriate consequences leading to {increase / decrease} in crocodile population ; 2 marks Total 8 marks

SAQ421

(a) signal protein {binds to / joins to / interacts with / activates} receptor on surface membrane; messenger molecule crosses cytoplasm and enters nucleus; {produces / activates} transcription factor; reference to gene switching / gene promotion; so transcription occurs / description of transcription e.g. in terms of base pairing; 3 marks (b) DNA retained as master copy / eq; DNA molecules are {much larger (than RNA)/{unable/too big} to pass through nuclear pores}; DNA double helix while RNA single strand / eq; proteins cannot be made in nucleus /made in cytoplasm on ribosomes; amino acids must be assembled in the sequence specified by genetic / DNA code; 2 marks (c) pass through RER; vesicles made; vesicles fuse with Golgi apparatus; proteins modified to active form; vesicles budded off Golgi apparatus; ref to exocytosis / description e.g. fusing with membra 3 marksTotal 8 marks

SAQ 422

SAQ 423

SAQ 424

(a) Identify those at risk from developing cancer; So as to avoid relevant environmental factors / enable early diagnosis; Identify risk in families; 2 max (b) Mutation of suppressor gene up to 4 marks 1. Mutation is a change in the DNA / sense strand; 2. Base sequence altered / e.g.; 3. Suppressor gene produces wrong instructions / has different code; 4. (Therefore) different amino acid sequence; 5. Different protein structure / non-functional protein;

Malignant tumour up to 2 marks 6. Cell division by mitosis; 7. Tumour cells growth abnormal / continuous / uncontrolled / rapid; 8. Tumour cells spread / invade other tissues / form secondary tumours / metastasis; 9. Via blood / lymph system; 6 max (c) (i) Most lung cancer occurs in smokers / non-smokers also develop lung cancer; Smoking increases the risk of lung cancer; Smoking is an environmental factor for lung cancer; Smokers risk more than 4x that of non-smokers / correct ref to figures; (But) only a small proportion of smokers develop lung cancer; Smokers more likely to develop other lung disease than cancer; 3 max (ii) Do not know size of sample / might be small sample in study; Genetic differences / predisposition; Could be different age at which started to smoke; Could be different number of cigarettes smoked per day;Could be different tar levels in cigarettes smoked; Could be different sexes in sample;Other valid; 2 max (d) All exposed to same environmental conditions / factors / no regional variations; Same level of pollution / example; reject less pollution Similar diet / example; Same water supply; Easier to screen whole population; Easier to follow family history / people related; Identify genetic differences in those affected (since everything else the same) / less genetic diversity; 2 max


SAQ 425

(a) (i) Produced {on / by} {ribosomes /rough endoplasmic reticulum} ; 1 marks (ii) Transported by the (smooth) ER (to Golgi bodies) ; [accept rough ER] Correct reference to vesicles ; Correct reference to (vesicles) fuse with (cell) membrane /(protein secreted by) exocytosis ; 2 marks

(b) (i) These cells (from the embryo) are {undifferentiated / unspecialised / able to develop into other types of cells / eq} ; [do not credit references to pluripotent / totipotent unqualified] 1 mark (ii) Can differentiate / become specialised / so able to develop into beta cells ; 1 mark

(c) Against: Amounts to killing an unborn child / abortion / murder ; Interfering in nature / may have unforeseen consequences ; Example e.g. may have genetic consequences for future generations / may lead to wider abuses in future / may get out of control / technology may be used in eugenics ; Example e.g. pressure to harvest human eggs purely for medical use ; The money could be better used for other types of research ; For: Spare embryos from IVF would be destroyed anyway ; The potential to relieve human suffering is too great to ignore; unethical not to allow the research ; You cant undiscover something / its going to happen anyway ; Better that the research stays {in UK / Europe / N America / eq} ; where it can be regulated ; 3 marks (d) For one mark: Must have something to do with genetics and something to do with {environmental / other} factors / mixture of genetic and environmental factors ; For two marks: The {susceptibility / predisposition / eq} is {hereditary / genetic / genotype} / there is a genetic component ; AND It is {triggered off / also influenced by / eq} environmental {factor / factors} ; 2 marks Total 10 marks

SAQ 426

SAQ427

(a) Ribosomes / rough endoplasmic reticulum / cytoplasm 1 mark (b) {Stimulus / sunlight / UV} = {hormone / melanin} made ; [Stimulus / sunlight / UV} causes production of (MSH) receptors ; Correct and appropriate reference to gene activation Reference to {enzyme / protein} synthesis ; Reference to formation of melanosomes by melanocytes ; Reference to migration of melanosomes ; 2 marks (c) {Cannot make / do not have} {hormone / receptor / enzyme); Reference to {absent / defective / mutated} gene ; Correct reference to enzyme induction 2 marks (d) (i) Around the nucleus; 1 mark (ii) {Screens from / absorb} UV; Prevents [damage to DNA / mutation); Prevents uncontrolled division leading to cancer ; 2 marks

Total 8 marks

SAQ 428

(a) supercoiling / transcription factors /repressor molecules / hormones ; 1 mark (b) A suggestion to include two from: 1. (due to) uncontrolled mitosis / cell division ; 2. the rate of cell division greater than cell death / apopotosis ; 3. correct reference to mutation ; 2 marks (c) (i) A description to include four from: 1. animals / cell culture tested for humans ; 2. reference to female subjects ; 3. (phase I) preliminary (small scale) tests on healthy volunteers ; 4. {independent / official} body of {scientists / medics} / (UK) Medicines Control Agency decides whether work can progress (to phase 2} ; 5. (phase II) drug tested on small groups of (volunteer) {patients / people} who already have the disease ;

6. (phase III) {larger / 1000 to 3000 group of} {patients / people} who already have the disease ; [Accept if no reference to phase I and II] 7. placed randomly in two groups one to receive treatment the other not / as control ; 8. one group given medical product the other a placebo / dummy treatment / no active ingredient ; 9. (double blind test) neither patients nor doctors know who has the active compound ; 10. statistics used to analyse results / test for significance ; [Credit points 6-9 in context of animal testing]

4 marks 8048/9048 Mark Schemes 19

SAQ 429

(a) (i) height (partly) determined by genes; half of childs genes (for height) from each parent / children of tall parents more likely to inherit genes for tallness (than children in general); {taller children / children of tall parents}stronger / more likely to survive (in the past); tall {women/men} might be {more fertile / more able to survive child birth}; tall people tend to marry tall people; 3 marks (ii) protein/amino acids {important/needed/essential} for growth / making new cells; in the past growth of (many) children was limited by lack of protein (compared with today)/ adequate protein intake needed to reach genetic potential/eq / reference to dietary protein a source of amino acids to make human protein; improved quality of protein / all necessary amino acids; 2 marks (iii) children who are (frequently) unwell do not grow (as well as healthy ones); sick children use resources to fight disease instead of forgrowing; sick children have reduced appetite/vomit a lot/have poordigestion;1 mark (b) mutation / reference to tumour repression substance; triggered off by carcinogenic substances / tar in tobacco smoke; leading to uncontrolled cell division; leading to formation a mass of cells / tumour; cycle/rate of cell

formation exceeds rate of cell death/apotosis; NOT more cell division, damages DNA 3 marks Total 9 marks

SAQ 430

The answer to this question requires continuous prose. Quality of language should be considered in crediting points in the mark scheme. In order to gain credit, answers must be expressed logically in clear scientific terms. (a) 1 Feature / beak size due to effect of more than one gene; NOT ref. multiple alleles 2 Different alleles of each gene present in the population; 3 Meiosis gives new combinations of alleles / of genes / of DNA; 4 By crossing-over / described; 5 By independent assortment of chromosomes / in meiosis I; 6 By independent assortment of chromatids / in meiosis II; Independent assortment (unspecified) = 1 mark alternative to point 5 or 6 7 Meiosis gives new combinations of chromosomes; 8 Several / large number of combinations (of alleles / chromosomes) possible; 5 max (b) 1 Variation (in beak size) already present in population; 2 (Variation) due to inheritance / due to mutation; 3 Beak size relates to food size; (On Albermarle): 4 Competition between birds of similar beak size / birds with more extreme beak sizes get enough food / reduce competition; 5 OR converse _ best adapted survive / selected for / larger beak sizes (in G. fortis) survive / larger beak an advantage; (On 2nd island): 6 G. fortis has smaller seeds available (since no competition); 7 G. fortis does not need large beak to survive / to feed; 8 (Survivors) reproduce; 9 Pass on (relevant) allele(s) / gene(s) to offspring; Worth 2 marks, because subsumes survivors reproduce marking point

10 Increasing frequency of appropriate allele(s) / gene(s) (in population); 7 max (c) (i) Allopatric new spp. arise in separated areas AND sympatric in same area / no geographical barrier; 1 (ii) Allopatric separation by sea / on separate islands / by mountains; Sympatric: Temporal different breeding seasons / feeding times / Behavioural different courtship displays / different niches / habitats / feeding areas / Mechanical mismatch in reproductive parts / Gamete incompatibility sperm killed in females reproductive tract / Hybrid inviability / hybrid infertility; 2

Total 15 AQA/BYA5/JAN 2

SAQ 431

(a) polygenic inheritance / several genes; many categories / continuous range / single or multiple allele inheritance would produce discrete categories / eq.; 2 (b) (SE gives idea of) variability of mean; time / population mean would lie within these limits in 68% / 70% / 2/3 of samples; 2

Total 4AQA/ BYA5/JUN06

SAQ 432

(a) (i) Polygenic several different genes influence same feature; Multiple allele more than two alleles of one gene; 2 (ii) Influence of environment/suitable example; As they are genetically identical (with respect to flower length); 2 (iii) All heterozygous for flower-length genes; Parents were homozygous for long or short alleles / inherit (one) long allele from one parent and (one) short allele (for each gene) from the other; 2 Accept these points from LABELLED genetic diagrams. (iv) Crossing over; Independent assortment/random segregation; Random fertilisation; Environmental influence; 3 max (b) (i) Similarity carry genes for same features / same genes / made from two

identical chromatids; Difference different alleles (of some/all genes)/different sequences of bases/from different parents; 2 (ii) Crossing over / chiasma formation; 1 (iii) Prophase I; 1 (iv) Produces new combinations of alleles; Introduces (genetic) variation; Into gametes / offspring; 2 max


SAQ 433

(a) Prevents doubling of chromosome no. (at fertilisation) / restores diploid no. (at fertilisation); 1 accept numerical example if clearly n+n"2n/ +" whole number (b) (i) Prophase I; 1 (ii) 9; 1 (c) (i) Crossing over / chromosomes exchanging parts / chromatids exchanging parts / chiasma formation; Produces new combinations of alleles; 2 (ii) Independent/random AND assortment /segregation/described; 1


SAQ 434

(a) (i) Discrete groups / types / categories / explained e.g. large and small seed diameters / types exist; [ Reject: Bimodal] 1 (ii) Different survival advantages / explained e.g. size linked to location; selection against intermediate forms / in favour of extreme forms; 2 (b) Interbreed / cross the two types of flax plants; Offspring fertile (if same species)/ offspring can also interbreed/ or reasonable alternative; [Reject:Viable] 2

Total 5 marks AQA/BYA5/JAN3

SAQ 435

(a) one / two / few genes versus many / polygenic; limited / none versus significant; limited / few versus wide / many; 3

(b) named difference in environmental factor during pregnancy e.g. nutrient supply; 1


SAQ 436 (a) (i) Continuous variation . range of values/not discrete categories/many categories/ no gaps; 1 (ii) Crossing over / chiasmata; Random segregation / independent assortment; In meiosis I and meiosis II; max 2 (b) Range influenced by single .outlier. (accept anomaly) / converse for S.D.; S.D. shows dispersion/spread about mean; Range only shows highest and lowest values/extremes; S.D. allows statistical use; Tests whether or not differences are significant; max 2

Total 5 marks AQA/BYA5/JAN5 SAQ437. (a)1. Chromosomes shorten/thicken/condense; 2. Chromosomes associate in homologous/(described) pairs / formation of bivalents / tetrads; 3. Crossing-over / chiasma formation; 4. Join to spindle (fibres) / moved by spindle; 5. (At) equator/middle of cell; 6. (join via) centromere / kinetochore; 7. (Homologous) chromosomes move to opposite poles / chromosomes separate/move apart; (ALLOW are pulled apart) 8. (Pairs of) chromatids separated in 2nd division; max 6 (b) 1. Crossing-over; [IGNORE any wrong ref. to timing] 2. Independent/random assortment/orientation/segregation of (homologous) chromosomes in meiosis I; 3. Independent/random assortment/orientation/segregation of chromatids in meiosis II; + Any three from: 4. Different adaptations / some better adapted; 5. Some survive / example described; 6. To reproduce; 7. Pass on gene/allele;

8. Allows for changing environment/different environment/example described; max 5 (c) (i) 21; 1 (ii) 1. T. aestivum has 2 copies of each type of chromosome/is diploid; 2. T. aestivums chromosomes can form bivalents/can assort in meiosis/ can produce haploid gametes; 3. T. aestivums gametes receive a copy of every chromosome receive all the genetic information; 3 [ACCEPT converse argument for hybrid plants] Total 15 marks AQA/BYA5/JAN04

Marking Schemes for Topic 3 Stafford Papers

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