Topic 3 and 4 extras

Question 1

use of the Hardy-Weinberg equation allows scientists to determine whether evolution has occurred.

Answer 1

Identify changes in the allele frequency over time (
• if allele frequency stays the same, no evolution / if allele
frequency changes, evolution has occurred

Question 2

Species richness

Answer 2

number of species in a habitat

Question 3

genetic diversity

Answer 3

number of alleles in one species

Question 4

Percentage change

Answer 4

end - original = D

d/original x100 = percentage change

Question 5

bone marrow

Answer 5

contains unspecialised cells

has the ability to differentiate into heart cells

Question 6

pluripotent

Answer 6

pluripotent stem cells can differentiate and give rise to
many cell types
• because genes in pluripotent stem cells are inactivated
and therefore they cannot differentiate into all cell
types

Question 7

Why can stem cells from bone marrow/ own body repair damage

Answer 7

• stem cells are from same patient, therefore no rejection
• these stem cells receive stimulus from surrounding
  cells
• which causes some genes to be activated
  • these active genes are transcribed to mRNA
  • this mRNA is translated on ribosomes to produce
  polypeptide chains / proteins
  • these proteins ensure that these cells develop into the appropriate cell

Question 8

Describe how society controls the use of embryonic stem cells in medical research

Answer 8

• regulatory bodies / laws / High Court (1)
  • setting or considering ethical / moral aspects (1)
  • judging what is acceptable / follow a code of practice (1)
  • checking that source of stem cells is acceptable (1)
  • decide on maximum age of embryo allowed for research
  / nervous system develops / feels pain (1)
  • human cloning is illegal (1)

Question 9

To calculate the size of an electron micrograph image

Answer 9

• measure the length of the image in mm
•  convert this length to μm (×1000)
•  calculate the actual size of the image by dividing the length of image in μm by the magnification.

Question 10

To calculate the magnification of an electron micrograph image using a scale bar, you need to:

Answer 10

•  measure the length of the scale bar in mm
•  convert the length into μm
•  Work out the magnification by dividing the measured length of the scale bar by the number written on the scale bar.

Question 11

working out sizes

Answer 11

actual size = length of image in um/ magnification

Question 12

polygenic inheritance.

Answer 12

1. idea of more than one gene for a single characteristic ;
2. at different loci / eq ;
3. idea of giving rise to continuous variation

Question 13

Suggest an explanation for the changes in mean height of these two groups of adult males.

Answer 13

. idea of change in diet or differences in diets between Northern and Southern Europeans ;

2. difference in diet described, eg more protein ;
3. idea of improved health care or better sanitation ;
4. less effects of disease on growth / eq ;
5. differences due to migration / eq ;
6. idea of changes to gene pool as a result of migration

Question 14

Describe three structural differences between prokaryotic and eukaryotic cells.

Answer 14

presence of { membrane bound / named membrane bound } organelle in eukaryotic cells / eq ;
presence of { plasmids / slime capsule / pili / eq} in prokaryotic cells ;
size of ribosomes i.e. larger in eukaryotic cells / 70S prokaryotes and 80S in eukaryotes / eq ;
in
DNA in a nucleus in eukaryotic cells /eq ;
{ DNA / chromosome } linear in eukaryotic cells and circular in prokaryotic cells / eq ;
relevant comment regarding cell walls e.g. cell walls always present in prokaryotic cells, only in some eukaryotic cells;

Question 15

xplain what is meant by the term molecular phylogeny.

Answer 15

1. idea of molecular { differences / similarities } ;
2. in { DNA / RNA } ;
3. in proteins / proteomics ;
4. idea of (evolutionary) relationships between organisms ;

Question 16

Explain the role of mitosis

Answer 16

idea of increasing cell number ;
1. ACCEPT ‘production of new cells’ and cells divide multiply or replicate
2. idea of replacing {damaged / dead } cells OR
idea of repairing (damaged) tissue ; 3. to produce genetically identical cells

Question 17

) Describe one safety precaution that should be taken when carrying out this procedure.root tip stain

Answer 17

1. { safety goggles / safety glasses / gloves } when handling { acid / stain }
2. care (with scalpel) when cutting root tip 3. care with slide when squashing root tip ;

Question 18

Explain how cells differentiate to become specialised tissues.

Answer 18

1. idea of chemical stimulus e.g. signal protein, growth substance ;
2. ACCEPT hormone
3. idea of some genes {active / inactive / eq} ;
4. ACCEPT genes switched on / off
5. idea of transcription of active genes ;
6. ACCEPT mRNA synthesised
7. mRNA translated / { polypeptide / protein } made / eq ;
8. idea of cell {structure / function} determined / cell modified e.g. lignin synthesised ;

Question 19

Name a process that may be observed in cells undergoing meiosis but not mitosis.

Answer 19

pairing of homologous chromosomes, chiasmata

Question 20

Suggest how the scientist could have ensured that this investigation was valid. plant minerals

Answer 20

1. idea of using genetically similar plants e.g. raised from seeds from same plant, clones ;
2. idea of repeats {at each level of nitrate fertiliser / used to produce mean data / to identify outliers or anomalies} ;
3. environmental variable related to soil controlled e.g. soil pH, concentration of other mineral ions ;
4. ACCEPT same area, location
5. another environmental variable controlled e.g. temperature, light (intensity), water ;
6. idea of control described, e.g. no nitrate/ soil with no extra nitrate ;
7. idea of same method of extraction of oil used ;

Question 21

Suggest why stem cells can be used to reverse this paralysis.

Answer 21

stem cells are totipotent
can specialise or differentiate / can give rise to
{differentiated / specialised} cells ;
3. idea that these can replace damaged cells (in spinal cord of Dachshund) / new nervous tissue can be formed / eq ;
3. ACCEPT new nerve cells
4. capable of continuous division / no Hayflick limit ;

Question 22

Suggest how this strategy of transferring individuals from one population to another could help the species survive.

Answer 22

1. idea that this increases the gene pool ;
2. ACCEPT introduction of genetically different individuals, { new / different } alleles introduced into population
3. idea that this increases potential for the species to { adapt / survive } ;
4. ACCEPT population but not individuals
5. description of how this will increase survival e.g. better hunters, disease resistance ;

Question 23

Suggest how natural selection has led to the evolution of this species of wolf, adapted for life in the mountains of Ethiopia.

Answer 23

1. genetic variation in population / variation due to mutation / eq ;
2. description of selection pressure ;
3. ACCEPT small prey
4. idea that some individuals possessed { advantageous / beneficial / eq } characteristics ;
5. (therefore) survived to adulthood / survived to breed ;
6. passing on {advantageous alleles / eq} (to offspring) / eq ;
7. change in allele frequency (over generations) / eq ;
8. idea of {geographical / reproductive} isolation ;

Question 24

Explain how use of the Hardy-Weinberg equation allows scientists to determine whether evolution has occurred.

Answer 24

Identify changes in the allele frequency over time (1)
• if allele frequency stays the same, no evolution / if allele
frequency changes, evolution (1)

Question 25

The roots of this sunflower plant were put into a solution containing a metabolic poison. A metabolic poison prevents the production of ATP.
Explain how this would affect the transport of substances in these tissues.

Answer 25

• translocation inhibited but transpiration stream not
inhibited (1)
• phloem contains cytoplasm but xylem does not (1)
• cytoplasm has organelles/mitochondria involved in
metabolism (1)

Question 26

Describe the differences between the structure of starch and cellulose.

Answer 26

starch has α-glucose and cellulose has β-glucose (1)
• starch has α 1-4 glycosidic bonds and cellulose has β 1-4
glycosidic bonds (1)
• starch has branched chains and cellulose has straight
chains (1)
• starch has no hydrogen bonds between chains and cellulose
has hydrogen bonds between chains (1)

Question 27

Describe the differences between what is meant by the terms species richness and genetic diversity

Answer 27

species richness is the number of species in a habitat (1)
• whereas genetic diversity is the number of alleles in one
species (1)

Question 28

) It is thought that this difference may cause epigenetic changes.
Explain how these changes might affect the functioning of the genome.

Answer 28

methylation of DNA base, therefore the expression of the
gene is changed (1)
• if histones are modified, this may affect binding of other
proteins to DNA because DNA is wrapped around
histones (1)
• therefore genes may become activated or repressed (1)

Question 29

Explain the temperature that should be used to incubate the Petri dishes.

Answer 29

• 25 °C to prevent growth of human pathogens / 37
°C would encourage growth of human pathogens
(1)
• lower temperatures would inhibit growth / make
results difficult to obtain (1)
• very high temperatures would kill bacteria / no
results would be obtained (1)

Question 30

Stem cells extracted from bone marrow are pluripotent. State what is meant by the term pluripotent.

Answer 30

pluripotent stem cells can differentiate and give rise to
many cell types (1)
• because genes in pluripotent stem cells are inactivated
and therefore they cannot differentiate into all cell
types (1)

Question 31

There are many products that may increase the ability of sperm to swim. One of these products contains zinc sulphate.
Devise an investigation to obtain valid data to show whether taking zinc sulphate tablets affects the ability of sperm to swim.

Answer 31

• sample size of {several / lots / many} males
• sample selection of males of {same age / same mass / same health / same pre-treatment / same diet}
• males given tablets and males given placebo
• reference to time delay before measuring sperm motility
• use of microscope to see sperm
• sperm motility measured as distance moved / speed / μms-1
• reference to control of temperature (as it affects motility)
• reference to clinical trials before testing on humans

Question 32

Explain how this investigation could be improved.

effect of copper on growth

Answer 32

• increase the validity by ensuring repeats and controlling
variables (1)
Plus any two from the following:
• variables controlled in order to ensure that the effect is
only due to copper ions (1)
• use more concentrations of copper ions particularly
between 10-25 ppm (1)
• increase time period of experiment to find out more of
the effects of copper on root growth (1)
• measure shoot growth to see whether effect is only on
roots (1)

Question 33

Some grass plants possess an allele for copper tolerance. This allele allows them to grow in areas where there is a high concentration of copper ions in the soil.
Describe how natural selection has brought about different allele frequencies in the grass plants growing in these sites.

Answer 33

• mutation has given rise to allele for copper tolerance,
which allows survival in soil with greater concentration of
copper ions (1)
• selection pressure in that there is a greater concentration
of copper ions in one area (1)
• plants without the allele do not survive (1)
• therefore there are fewer plants and reduced competition
for resources (1)
• plants that survive pass on the allele for copper tolerance
to next generation, therefore the frequency of allele for
copper tolerance is higher in areas of high copper ion
concentration (1)