June 2002 U4a

1. One main function

Letter

Initiating and controlling voluntary muscle movement

A

Co-ordination of skeletal muscle movement, balance and posture

C

Contains centres controlling heart and breathing rate

Region Cerebral hemispheres / cerebrum / cortex ;

;

B

Cerebellum ;

Medulla (oblongata) / brain stem ;

1 mark only for correct letters ; [4]

2.

(a)

Pyruvate / pyruvic acid ;

1

(b)

Pyruvate / pyruvic acid / substance X, reduced / accepts hydrogen / protons / electrons (to lactic acid) ; NADH + H+ / reduced NAD / NADH2 (used in this reduction) is oxidised to NAD ;

2

(c)

Ethanol / ethyl alcohol, and carbon dioxide / CO2 ;

1

(d)

1. 2. 3. 4.

Transfers electrons / H+ / hydrogen (ions), to electron transfer chain / FAD ; Reference to inner membrane of mitochondrion / cristae ; Oxidative phosphorylation ; Generation of ATP (from ADP) ;

3 [7]

3.

(a)

(b)

1. 2. 3. 4. 1. 2. 3. 4. 5. 6. 7. 8.

Schwann cells ; Wrap / fold / roll, around axon ; Fatty / lipid / phospholipid, nature ; Reference to nodes as, gaps in the sheath, / naked / exposed / uncovered, axon ;

2

(myelination) increases speed of, conduction / impulse ; When diameters, same / both 15 m, myelinated faster than non-myelinated ; (Both) myelinated speeds faster than non-myelinated at 700 m even though diameters much smaller / eq ; Correct manipulation of figures to compare the effect of the myelin sheath on speed of conduction ; Myelin sheath prevents (initiation of), action potential / depolarisation / acts as an insulator ; Action potential / depolarisation, only possible at nodes / gaps ; Reference to, impulse jumping from node to node / saltatory effect ; No Na+ channels except at nodes / reference to inward movement Na+ involved in action potential ; 5 [7]

Edexcel Unit 4A June 2002 MS

1

4.

(a)

1. 2. 3. 4. 5.

(b)

1. 2. 3. 4.

(c)

(d)

In regions A and B, both concentrations the same / both decrease by same value between A and B ; Falls then rises again when ADH high but always falls when ADH low ; When ADH high concentration never falls as far as when ADH low ; High ADH no change overall, low ADH lower at E than A / eq ; Credit comparative use of figures for any change between regions for high ADH and low ADH ; 3 (Rise in) ADH increases permeability of (cells in), collecting ducts / DCT regions C / D / E ; More water moves out into blood / is reabsorbed ; By osmosis ; (shown by) reference to increase, in concentration of fluid between, C and E / C and D / D and E ; 3

1. 2. 3. 4.

Concentration of blood increases / eq ; Reference to detection by, osmoreceptors / hypothalamus ; Reference to (nerve) impulses ; ADH released from (posterior) pituitary ;

3

1. 2. 3.

Need to conserve water / reduce water loss as much as possible ; Reference to counter current multiplier ; (Long loop means that) a higher concentration of, Na+ / Cl- / ions, in medulla / eq, can be generated ; So more water reabsorbed (from, fluid / urine) in collecting duct ; Produces more concentrated urine ;

3

4. 5.

[12]

5.

ACCEPT POINTS ONLY IN CORRECT CONTEXT 1.

Absorption of light causes changes in / of photosensitive / photoreceptive, pigments ;

2.

Reference to phytochrome (pigments) in, plants / leaves ;

3.

P660 / PR and P730 / PFR ;

4.

P660 / PR converted to P730 / PFR when red light / eq absorbed, P730 / PFR converted to P660 / PR when far-red light absorbed ;

5.

P730 / PFR high during daytime because more red light present in daylight / white light ;

6.

Reference to slow conversion of, P730 / PFR, back to, P660 / PR, in darkness ;

7.

Reference to phytochromes involved in, initiation of germination / flowering / photomorphogenesis ;

8.

Reference to, visual pigments / iodopsin / rhodopsin / visual purple, in retina (of mammals) ;

9.

Rhodopsin / visual purple in rod cells ;

10.

(Rhodopsin consists of) opsin combined with, retinal / retinene / retinine ;

11.

Cis form of, retinal / retinene / retinine, changes to trans form in light ;

Edexcel Unit 4A June 2002 MS

2

12.

(This causes rhodopsin) to split ;

13.

Iodopsin (thought to be) in cone cells ;

14.

Three types (of iodopsin) respond to different, wavelengths / colours, / reference to trichromatic theory ;

15.

Changes in (retinal) pigments lead to, generator potential / hyperpolarisation / action potential / changes in membrane potential ; [10]

6. Name of virus

Type of nucleic acid

Structure

Example of host cell

TMV (Tobacco mosaic virus)

RNA ;

(naked) Helical ;

Leaf cells in tobacco plant

Lambda phage ()

DNA ;

Complex

Bacterium

HIV (Human immunodeficiency virus)

RNA ;

Polyhedral ;

T-lymphocyte/T-cell /T4/T-helper ; [6]

7.

(a) (b)

Substance / chemical, that can, kill / inhibit growth, of an organism ; Produced by, microorganisms / fungi / other organism ;

2

Reference to penicillin targeting cell wall ; During growth of bacterial cell ; By interfering with synthesis (of cell wall); By preventing formation of, cross links / bonds, between peptidoglycan molecules ; Makes bacteria more susceptible to osmotic shock / eq ;

3 [5]

8.

(a)

(i)

(ii)

(b)

Step 4 Both Gram negative and Gram positive / all bacteria, appear dark blue / purple / eq ; Step 6 Gram negative bacteria appear, pink / red ; Gram positive bacteria, appear / stay, dark blue / purple / eq ;

3

In Gram positive bacteria the stain penetrates more ; In Gram negative bacteria the crystal violet washes out; (Because) Gram positive bacteria have thicker walls / Gram negative bacteria have extra phospholipid layer ;

2

Stain a sample before and after adding the chemical ; Incubate the bacteria with the chemical ; Compare changes in, relative number / proportion, of Gram negative to Gram positive ;

2 [7]

Edexcel Unit 4A June 2002 MS

3

9.

(a)

n=

3.0 – 1.0 ; 0.301

= 6.64 ; Number of generations = 6 ; Allow consequential error (b)

(c)

Reference to the level line ; No increase in number of cells / no growth / second lag phase / eq ; No reproduction / death rate = birth rate ; Glucose exhausted / eq ; No available respiratory substrate ; Bacteria synthesising, enzyme / lactase ; (needed for) hydrolysis of lactose ; Reference to diauxic growth ; (i) (ii)

3

5

Rate between 18-24 hours greater than that between 6-12 hours ; Credit calculation of growth rates ;

2

Using lactose ; Two monosaccharides / glucose and galactose, available ; Reference to greater concentration of substrates ;

2 [12]

Edexcel Unit 4A June 2002 MS

4