2024 bio a level q

Question 1

The ratio of saturated to unsaturated fatty acids in a cell-surface membrane
determines the extent of the membrane’s fluidity.

the scientists observed:
* an increase in the proportion of phospholipids in the phagocytes containing
unsaturated fatty acids
* more phagocytosis.
Suggest and explain why there was more phagocytosis.

Answer 1

more unsaturated fatty acids
more fluid
membrane more fluid
easy to engulf

Question 2

Describe the processes of facilitated diffusion and active transport.

Answer 2

fd- movement of polar/charged molecules down a conc gradient using carrier/channel proteins

at- atp against gradient using carrier proteins

Question 3

what are microvilli

Answer 3

large projections of a membrane

Question 4

itamin A is a fat-soluble substance.
Micelles are involved in the process of vitamin A absorption.
Describe the process of vitamin A absorption into cells lining the ileum

Answer 4

combine/mix W bile salt
-make more soluble in water
- micelles breakdown close to cells.
- diffuses into illeum

Question 5

Describe the appearance and behaviour of chromosomes during prophase and during
anaphase of mitosis

Answer 5

condense and become more visible

chromosomes on opposite sides
spindle fibres attached to them

Question 6

Give three structural differences between an mRNA molecule and a tRNA molecule.

Answer 6

mrna- linear, codon, no amino binding site

trna- clover, anticodon, amino binding sit

Question 7

9. 2Suggest one change the scientists could make to both frog populations to increase
   the number of mating calls

Answer 7

more sexually active females

Question 7

8.1 Give two structural features of an aorta wall and explain how they are related to the
function of an aorta.

Answer 7

elastic stretches and recoils to maintain smooth blood pressure

muscle withstands high pressure

smooth endothelium reduces friction

Question 8

10.2 Describe the role of organelles in the production and release of enzymes by
animal cells.
Do not include details of transcription in your answer.

Answer 8

dna in nucelus cpdes for enzyme/protein production

ribosome es produce enzyme/protein

rer modifies enzyme/protein

mitochondria produce atp

Golgi apparatus make/transport glyxoprotein

vesicle move protein to cell surface membrane

Question 9

10.3 Describe the structure of ATP.
Outline how named enzymes break down and resynthesise ATP.

Answer 9

ribose adenine and 3 phophstaes

atp to adp + piby atp hydrolase in hydrolsss

adp+pi - atp by atp syhtase in condejnsatoin reaxtoon

Question 10

mitotic index

Answer 10

number of cells in mitosis / number of cells In field of view

Question 11

EE2 is contained in human contraceptive pills. Some EE2 is released in human urine
and collects in sewage. Untreated sewage pollutes the water in frog habitats.
Suggest and explain the effect EE2 pollution in frog habitats will have on
frog breeding.

Answer 11

less mating/breeding
fewer adverts ent cells so females not attracted
fewer mating cells as more males not sexually active

Question 12

1.2 Following the release of acetylcholine into a neuromuscular junction, a muscle
contraction occurs.
Describe the sequence of events, following the release of acetylcholine, that leads to
stimulation of this contraction.
Do not include in your answer the events following the release of calcium ions in the
myofibril.

Answer 12

1. Acetylcholine/neurotransmitter diffuses (across
   synaptic cleft);
2. (Acetylcholine/neurotransmitter) attaches to
   receptors on the sarcolemma;
3. Sodium ions enter leading to
   depolarisation/action potential;
4. Calcium (ions) released by
   endoplasmic/sarcoplasmic reticulum;

Question 13

1.3 Inhibitory synapses cause hyperpolarisation in postsynaptic neurones.
Explain how this inhibits synaptic transmission.

Answer 13

1. (Inside postsynaptic neurone/membrane/axon)
   is more negative
2. More sodium ions (required to enter) for
   depolarisation

Question 14

2.3 Fast muscle fibres have a higher concentration of glycogen than slow muscle fibres.
Explain how the difference in glycogen concentration is related to the different
properties of these muscle fibres.

Answer 14

1. Fast (fibres) contract quickly whereas
   slow (fibres) contract slowly
2. Fast (fibres mainly) use anaerobic respiration
3. Fast (fibres) produce ATP quickly
4. Glycogen is a store of glucose

Question 15

3.2 Give three environmental factors that should be controlled when measuring the rate
of photosynthesis in this investigation.
Do not include features of the plant in your answer.

Answer 15

1. Intensity/brightness of light (at each wavelength)
2. Carbon dioxide concentration
3. Temperature
4. Water

Question 16

3.3 Describe how the products of the light-dependent reaction are used in the
light-independent reaction to produce triose phosphate.

Answer 16

1. ATP and reduced NADP;
2. ATP provides energy;
3. GP reduced to triose phosphate;

Question 17

4.1 In fruit flies, a gene for body colour has a dominant allele for grey body, G, and a
recessive allele for black body, g.
Explain how you would determine if the genotype of a grey fly is homozygous or
heterozygous for body colour.

Answer 17

1. Cross with homozygous recessive (fly)
2. Black offspring/flies then is heterozygous/G

Question 18

4.2 In fruit flies, males are XY and females are XX.
A cross between a grey-bodied male fly and a black-bodied female fly produced some
black-bodied females. Explain how this shows that the gene for body colour is not
sex-linked.

Answer 18

(If sex-linked) grey/male fly would only have / pass
on grey/dominant allele

Question 19

5.1 A weed is a plant growing where it is not wanted. Fat hen is a weed which grows in
some crop fields.
Describe how you could estimate the number of fat hen plants in a field.

Answer 19

1. Use a grid
2. Method of obtaining random
   coordinates/numbers e.g.
   calculator/computer/random numbers
   table/generator;
3. Count number/frequency in a quadrat;
4. Large sample and calculate mean
   number (per quadrat);
5. Multiply mean number of plants per m2 by area
   of field

Question 20

5.2 In potato plant fields, fat hen plants can grow up to a height of 2 m and absorb large
quantities of nutrients from the soil.
Fat hen has a negative effect on the growth of potato plants.
Use the information provided to explain why.
In your answer, name the type of competition occurring between fat hen plants and
potato plants

Answer 20

1. Interspecific (competition);
2. Less/no light (for potato plant) so less/no
   photosynthesis;
3. Less nitrates/nitrogen to produce
   amino acids/protein/DNA/RNA/ATP

Question 21

8.3 A technician produced the different concentrations of GA solution from a stock
10–1 mol dm–3 concentration of GA.
Describe how the technician produced the 10–3 mol dm–3 solution.

Answer 21

0.1 parts/cm3 of 10–1/stock/GA and/to 9.9 parts/cm3
of (distilled) water;

Question 22

7.4 Describe how restriction endonuclease and DNA ligase are used to insert a gene into
a plasmid.

Answer 22

1. Restriction endonucleases/enzymes cuts
   plasmid
2. Ligase joins gene/DNA and plasmid

Question 23

Read the following passage.
The wall gecko is a medium-sized lizard. In an isolated habitat of southern
Italy, the wall gecko shows phenotypic diversity. Scientists investigated
whether disruptive selection was leading to sympatric speciation in the
wall gecko.
Pale geckos live only on walls and are nocturnal (active at night). Dark geckos
live mainly on the dark trunks of olive trees and are diurnal (active during the
day). These diurnal geckos can change skin colour when occupying different
surfaces during the day.
Comparison of mitochondrial genes indicated that the diurnal geckos formed a
distinct genetic group. This comparison also confirmed that all the geckos in
the habitat were of the same species.
The scientists used the mark-release-recapture method to estimate the size of
the population of geckos in the habitat.
5
10
Use the information in the passage and your own knowledge to answer the
following questions.
1 0 . 1 The wall gecko shows phenotypic diversity (lines 1–2).
Suggest two factors that have resulted in this phenotypic diversit

Answer 23

1.Mutations/genotype/alleles;
2. Environment/habitat
3. Epigenetics;
4. Crossing over;
5. Independent segregation/assortment (of
homologous chromosomes);
6. Random fusion of gametes

Question 24

8.4 Describe a suitable procedure the student could follow to investigate the effect of
different concentrations of GA on the growth of stem segments.
In your answer, you should include the variables that should be controlled in this
investigation

Answer 24

1. (Use distilled) water (control) and different (GA)
   concentrations and 10 (stem) segments in each;
2. Measure (length of) stem/segments at start and
   at end (of investigation)
3. (Place stems in same) volume of solution/GA;
4. (Leave for same period of) time;
5. (Same) temperature;
6. (Same) species/type (of plant);
7. (Same) age (of plant);
8. (Same) diameter/thickness of stem/segments;

Question 25

10.2 The ability of diurnal geckos to change skin colour (lines 7–8) is advantageous.
Explain why.

Answer 25

1. Provides camouflage;
2. (So) not seen by predators/prey

Question 26

2.1 A student investigated the effect of temperature on the rate of aerobic respiration in
woodlice

The student altered the temperature of the water bath and measured how far the drop
of coloured liquid moved every minute for 5 minutes.

Other than those stated, suggest two variables the student should have kept constant
in this investigation

Answer 26

age of woodlive
same woodlice
xpeives of woodlice

Question 27

2.2 Describe how the student used the apparatus in Figure 1 to reset the drop of coloured
liquid back to the right-hand end of the tubing.

Answer 27

open the three way tap
push /press the syringe

Question 28

2.3 The student also set up a control experiment.
Suggest a suitable control experiment and explain why it was necessary

Answer 28

no woodlice and all other conditiosnare the same

to show that respiring woodlice
are causing the drop to move

Question 29

5 Leigh syndrome (LS) is a rare, recessive, inherited condition.
LS is caused by a mutation in any one of more than 75 different genes coding for
proteins involved in oxidative phosphorylation.
In 80% of people with LS, these mutations occur in nuclear DNA. In 20% of people
with LS, these mutations occur in mitochondrial DNA (mtDNA).
15% of the nuclear DNA mutations that cause LS occur in the SURF1 gene. A
mutated SURF1 gene codes for a shorter polypeptide than a non-mutated
SURF1 gene.
0 5 . 1 Name one type of SURF1 gene mutation and explain how this mutation could lead to
production of a shorter polypeptide

Answer 29

1. Deletion/translocation;
2. Could mean triplet(s)/codon(s) missing

Question 30

S usually causes death within the first three years of life.
Using all the information in this question, evaluate whether all people should be
genetically screened for LS.

Answer 30

1. Some people could be heterozygous/carriers;
2. Could prevent (human) suffering/death
3. It is rare (globally)
   OR
   (Only) 1 in 40 000 (globally);

Question 31

5.3 The frequency of LS is higher in the Faroe Islands than globally.
Suggest and explain one reason wh

Answer 31

1. Genetic drift;
2. Frequency is higher by chance

Question 32

Define the biological term population

Answer 32

1. A group (of organisms) of the same species in a
   (particular) space at a (particular) time;
2. That can (potentially) interbreed;

Question 33

Which statement correctly represents the species richness of the woodland

Answer 33

The number of all species present in the woodland

Question 34

A student studying the information in this question concluded that all woodlands
should be protected to increase the biodiversity of birds.
Evaluate the student’s conclusion.

Answer 34

1. The number of (bird) species increased (over 30
   years);
2. Long-term study;
3. (Bird) species did not increase every year;
4. Don’t know if the protection was for birds

Question 35

It is not possible to extrapolate the data for the number of bird species recorded
breeding each year beyond 1979

Answer 35

Not a linear relationship;

Question 36

Suggest how the changes in the index of similarity in the bird community provide
evidence for the process of succession.

Answer 36

1. (The bird community) becomes less similar (to
   the first year)
2. (Suggesting) biodiversity has changed/
   increased;
3. Due to changes/increases in the species/birds
   (present)

Question 37

The news website published the headline:
The LPI shows human activities cause significant decrease in biodiversity.
Suggest three reasons why this headline is not valid.
Use all the information provided.

Answer 37

1. No significant decrease/difference as shown by
   SD;
2. No idea if due to human activity
3. LPI/index above 1970/1.0/baseline4