past papers

Question 1

function of nucleus

Answer 1

transcription
contains genetic material for polypeptide production

Question 2

why use biomass instead of no of individuals when collecting data to measure diversity?

Answer 2

too numerous to count

Question 3

how do properties of APs (hydrophobic and philic side) allow them to become positioned across the membrane and make a channel through which ions can pass?

Answer 3

• hydrophobic side next to fatty acid tails
• hydrophilic sides allow ion movement through membrane

Question 4

how many daughter cells does binary fission produce?

Answer 4

2

Question 5

how can 2 enzymes w diff amino acid seq catalyse same reaction?

Answer 5

active sites have sim tertiary structures
so form e-s complex

Question 6

diffs between DNA and tRNA

Answer 6

double stranded vs single
many nucleotides vs fe (NOT LONGER VS SHORTER)
thymine vs uracil (NOT T VS U)

Question 7

how to remove large organelles from cell contents

Answer 7

centrifuge
large organelles removed in early pellets

Question 8

why is a separate stain needed for rbc when og binds to DNA?

Answer 8

rbc dont have nucleus

Question 9

comp and cont starch vs cellulose

Answer 9

a glucose vs b
branched vs un
coiled vs straight
both glycosidic bonds
both polysaccharides
no microfibrils vs microfibrils

Question 10

describe complete digestion of starch by a mammal

Answer 10

1. Hydrolysis;
2. (Of) glycosidic bonds;
3. (Starch) to maltose by amylase;
4. (Maltose) to glucose by disaccharidase/maltase;
5. Membrane-bound (disaccharidase/maltase);

Question 11

explain how a mutation in DNA base seq could lead to the formation of non-functioning PAH.

Answer 11

change primary structure
change hydrogen bonds
substrate cant bind- not complimentary

Question 12

how could the structure of a chromosome differ over its length to result in a stain binding more in some areas?

Answer 12

difference in base sequences

Question 13

a sugar binds to an enzyme and rate increases more. how?

Answer 13

changes tertiary structure
changes shape of active site
more e-s complexes form

Question 14

what should scientists take into account to help accurately identify species that a bee belongs to after collecting them?

Answer 14

must allow close examination

Question 15

3 ways to improve method of data collection when investigating biodiversity of bees in diff areas

Answer 15

1. Collect at more times of the year so
   more points on graph/better line (of
   best fit) on graph;
2. Counted number of individuals in each
   species so that they could calculate
   index of diversity;
3. Collected from more sites/more years
   to increase accuracy of (mean) data;

Question 16

if value is greater than critical value, do you accept or reject the null?

Answer 16

reject

Question 17

compare and contrast structure and properties of triglycerides and phospholipids

Answer 17

1. Both contain ester bonds (between glycerol and
   fatty acid);
2. Both contain glycerol;
3. Fatty acids on both may be saturated or
   unsaturated;
4. Both are insoluble in water;
5. Both contain C, H and O but phospholipids also
   contain P;
6. Triglyceride has three fatty acids and
   phospholipid has two fatty acids plus phosphate
   group;
7. Triglycerides are hydrophobic/non-polar and
   phospholipids have hydrophilic and
   hydrophobic region;
8. Phospholipids form monolayer (on
   surface)/micelle/bilayer (in water) but
   triglycerides don’t;

Question 18

adaptations of tracheal system

Answer 18

tracheoles one cell thick- short diffusion pathway

tracheoles enter directly to the muscle- short diffusion pathway

tracheoles highly branched- large sa for rapid diffusion

Question 19

importance of xylem being kept open as a continuous tube

Answer 19

• water evaporates out through stomata creating tension
• water molecules are polar so attracted to each other
• form a continuous column of water and move up xylem by cohesion tension
• break column- cant move up

Question 20

2 investigations other than rats before drugs can be tested on human cancer patients

Answer 20

test on healthy humans to look for side effects
investigate diff concs to find the best dosage

Question 21

what is cotransport?

Answer 21

transport of 2 different substances using carrier proteins

Question 22

why cant ELISA be used to diagnose AIDS?

Answer 22

(To diagnose AIDS, need to look for/at)
1. (AIDS-related) symptoms
2. Number of helper T cells

Question 23

why can nucleotides only be added in 5’-3’ direction

Answer 23

1. Reference to DNA polymerase;
2. (Which is) specific;
3. Only complementary with/binds to 5’ end (of
   strand);
4. Shapes of 5’ end and 3’ end are
   different/description of how different;

Question 24

how does control show pregnancy test has worked?

Answer 24

blood sample has moved

Question 25

The dengue virus causes damage to capillaries so that blood proteins move out of the capillaries into the tissue fluid. Explain how this would affect the return of tissue fluid into the capillaries.

Answer 25

1. Increases water potential of blood/capillary OR Decreases water potential of tissue fluid; 2. (So) less water returns to blood/capillaries (by osmosis) OR (So) more water leaves blood/capillaries (by osmosis);

Question 26

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

Answer 26

1. Micelles contain bile salts and fatty acids/monoglycerides; 2. Make fatty acids/monoglycerides more soluble in water OR Bring/release/carry fatty acids/monoglycerides to cell/lining of the iluem 3. Fatty acids/monoglycerides absorbed by diffusion; 4. Triglycerides reformed (in cells); Accept chylomicrons form 5. Vesicles move to cell membrane; Accept exocytosis

Question 27

Explain the advantages of lipid droplet and micelle formation.

Answer 27

1. Droplets increase surface areas for lipase 2. (So) faster hydrolysis of triglycerides / lipids 3. Micelles carry fatty acids and glycerol / monoglycerides to membrane / to (intestinal epithelial) cell;

Question 28

Use your knowledge of surface area to volume ratio to explain the higher metabolic rate of a mouse compared to a horse.

Answer 28

1. larger surface area to volume ratio 2. More/faster heat loss 3. (Faster rate of) respiration releases heat; Accept respiration/metabolism replaces heat.

Question 29

Explain why death of alveolar epithelium cells reduces gas exchange in human lungs. (when die, replaced by thicker tissue)

Answer 29

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

Question 30

Describe binary fission in bacteria.

Answer 30

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

Question 31

Describe the process of crossing over and explain how it increases genetic diversity.

Answer 31

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;

Question 32

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

Answer 32

DNA that does not code for protein/polypeptides (Positioned) between genes;

Question 33

Explain the pattern shown by the results in the graph above. (conc of urine increases as thickness of medulla increases)

Answer 33

1. Thicker medulla means a longer loop (of Henle); 2. means increase in sodium ion concentration (in medulla) 3. (Therefore) water potential gradient maintained (for longer), so more water (re)absorbed (from loop and collecting duct);

Question 34

succession

Answer 34

hostile abiotic conditions pioneer species and rocks-> soil less harsh abiotic new species outcompete increased biodiversity climax community