2014 Flashcards
(32 cards)
What is meant by a hierarchy? [2 marks]
- Groups within groups;
2. No overlap (between groups);
Explain the role of independent segregation in meiosis.
[2 marks]
- (To provide) genetic variation;
- (Allows) different combinations of
maternal and paternal chromosomes/
alleles; - (To produce) haploid cells/half the
chromosome number; - (Allows) homologous chromosomes/
homologous pairs to arrange randomly
(at equator/middle of cell)/separate;
A zeedonk is the offspring produced from breeding a mountain zebra with a donkey.
l The body cells of a mountain zebra contain 32 chromosomes.
l The body cells of a donkey contain 62 chromosomes.
Use this information to suggest why zeedonks are usually infertile.
[2 marks]
- (Zeedonk has) 47/odd/uneven number of chromosomes;
- Chromosomes cannot pair/are not homologous/ chromosome number cannot be halved / meiosis cannot occur / sex cells/haploid cells are not produced;
What is selective breeding?
[1 mark]
(Humans breed) organisms with certain/chosen characteristics/alleles;
Explain one potential problem that can be caused by selective breeding.
[2 marks]
- Inbreeding / breed closely related organisms;
- (So higher probability of) mutations being passed on / recessive alleles being expressed / health problems/example given / increase in genetic disease;
- Reduced genetic variation/diversity / smaller gene pool / less variety of alleles;
- (So) can be killed by/susceptible to the same/a disease / reduces ability to adapt/survive (future) environmental changes / may not be beneficial to future breeding programmes;
The oxygen dissociation curve for haemoglobin shifts to the right during vigorous
exercise. Explain the advantage of this shift.
[3 marks]
1. Lower affinity for oxygen / releases more oxygen / oxygen is released quicker / oxygen dissociates/unloads more readily; 2. (To) muscles/tissues/cells; 3. (For) high/rapid respiration;
Explain how the body shape of a Weddell seal is an adaptation to living in a cold
environment.
[2 marks]
- Small SA:VOL;
2. (So) reduces heat loss / (more) heat retained;
Describe and explain the changes in the rate of blood flow to the different organs
during a long dive.
[3 marks]
- Brain is the same, others fall;
- Brain controls other organs/remains active/
needs constant supply of oxygen; - Lungs not used/are used less / seal is not
breathing; - Heart rate decreases / heart pumps less;
- Blood diverted to muscles;
- Oxygen (in blood) will last longer / less
oxygen used / oxygen is conserved;
Describe and explain how the countercurrent system leads to efficient gas exchange
across the gills of a fish.
[3 marks]
- Water and blood flow in opposite directions;
- Maintains concentration/diffusion gradient / equilibrium not reached / water always next to blood with a lower concentration of oxygen;
- Along whole/length of gill/lamellae;
Amoebic gill disease (AGD) is caused by a parasite that lives on the gills of some
species of fish. The disease causes the lamellae to become thicker and to fuse
together.
AGD reduces the efficiency of gas exchange in fish. Give two reasons why.
[2 marks]
- (Thicker lamellae so) greater/longer diffusion distance/pathway;
- (Lamellae fuse so) reduced surface area;
Calculate the volume of water that would have to pass over the gills each hour to
supply the oxygen required by the fish. Show your working.
[2 marks]
Correct answer of 5.1 or 5.14(2857) (dm3) = 2 marks;;
One mark for incorrect answers that show 36 or 0.4 x 90 or 90 ÷ 7;
The volume of water passing over the gills increases if the temperature of the water
increases. Suggest why.
[1 mark]
- Increased metabolism/respiration/enzyme activity;
2. Less oxygen (dissolved in water);
The antibiotic tetracycline binds to ribosomes in bacterial cells.
Explain how this causes the death of bacterial cells.
[2 marks]
- Prevents protein synthesis;
2. (So) enzymes not produced / any named process involving proteins/enzymes is inhibited;
Tetracycline can enter a bacterium through protein A. This protein is found in the
plasma membrane.
Suggest how a change in the amino acid sequence of this protein could make a
bacterium resistant to tetracycline.
[2 marks]
- Different tertiary structure/tertiary shape;
2. (So tetracycline) does not fit/bind/ is not complementary / does not enter/pass through (protein/into cell);
Evolutionary relationships between different primates can be found by comparing their
proteins and DNA.
6 (a) All primates produce a species-specific type of haemoglobin. An antibody against
human haemoglobin could be used to compare the evolutionary relationships between
different primates. Describe and explain how.
[3 marks]
1. Antibody and haemoglobin/blood (of different primates) mixed/added/bind; 2. Precipitate/complex/band formed; 3. Amount of precipitate/complex/ thickness of band shows relationship/similarity (in protein/DNA);;
These data suggest that gibbons are the most distantly related to humans. Explain
how.
[2 marks]
(Largest decrease in separation temperature) – no mark
1. (So) few(er) hydrogen/H bonds;
2. (So) few(er) complementary bases/ few(er)
base pairs;
There were differences in separation temperature of DNA formed from
single-stranded DNA of the same species of primate. Suggest why.
[1 mark]
(Same species) have different alleles/different base sequences/ (different) mutations/introns/ non-coding DNA/multiple repeats;
Use this information to calculate how long ago the evolutionary lines of humans and
chimpanzees separated. Show your working.
[2 marks]
Correct answer in range of 9.69 to 9.71(4286) = 2 marks;;
One mark for incorrect answers that show any of the following:
(1oC =) 5.7(14286) (million years)
OR:
20 000 000 ÷ 3.5
OR:
20 ÷ 3.5
What two measurements are needed to calculate an index of diversity?
[2 marks]
- Number of (individuals of) each species;
2. Total number of individuals / number of species;
Some fields acted as controls. They were sprayed with a solution that did not
contain the herbicide. Explain the purpose of these control fields.
[1 mark]
- (Shows) results are due to the herbicide/
are not due to another factor; - (To) compare the effect of using and not
using the herbicide / shows the effect of
adding the herbicide;
Suggest an explanation for the relationship between the concentration of herbicide
and the mean crop yield.
[2 marks]
- (More) weeds killed so more crops/plants
survive/higher yield/less competition; - High concentrations (of herbicide) harm/damage/kill/are toxic to crops/plants;
Explain the relationship between the concentration of herbicide and the mean index of
diversity of insects.
[3 marks]
- Reduced plant diversity / fewer plant species / fewer varieties of plant;
- Fewer habitats/niches;
- Fewer food sources/varieties of food;
Explain how the structure of DNA is related to its functions.
[6 marks]
- Sugar-phosphate (backbone)/double stranded/helix so provides strength/stability /protects bases/protects hydrogen bonds;
- Long/large molecule so can store lots of information;
- Helix/coiled so compact;
- Base sequence allows information to be stored/ base sequence codes for amino acids/protein;
- Double stranded so replication can occur semi-conservatively/ strands can act as templates;
- Complementary base pairing / A-T and G-C so accurate replication/identical copies can be made;
- (Weak) hydrogen bonds for replication/ unzipping/strand separation;
- Many hydrogen bonds so stable/strong;
What do these data suggest about the relative importance of the mutant alleles of
genes C, D and E on increasing the risk of developing lung cancer? Explain your
answer.
[3 marks]
- (Mutation) in E produces highest risk/1.78;
- (Mutation) in D produces next highest risk/1.45;
- (Mutation) in C produces least risk/1.30;
