Question 1
1
Mice (Mus musculus) have various defence systems against predators such as foxes (Vulpus vulpus) or stoats (Mustela erminea). The mice release specific alarm compounds when under threat that serve as danger signals for other mice. Predators also release scents that the mice can detect. In one study, mice were exposed to paper soaked in compounds taken from other mice, foxes or stoats in a test chamber. The scientists then measured the reaction of three different groups of neurons used in smelling: G1, G2 and G3, as shown in the diagram. The percentage of G1, G2 and G3 neurons responding to the mouse, fox and stoat compounds, as well as a control compound, are shown in the chart.
14 marks
Question 1(h)
1(h)
Another study was carried out on the defence systems in aphids (Myzus persicae) which feed on thale cress plants (Arabidopsis thaliana). Individual aphids release an alarm compound containing the chemical (E)- \(\beta\)-farnesene (EBF) when attacked by a predator. Other aphids are repelled and leave the thale cress plant or hide. The gene for EBF was inserted to produce transgenic (T) thale cress plants to test aphid reaction to EBF over several generations. Aphids were raised on wild type (W) thale cress and then allowed to feed for three generations on either W or T thale cress. Aphids were tested in each generation for their reaction when EBF was added to a choice chamber. The percentages of aphids attracted to or repelled by EBF and those which made no choice were recorded. Identify, with a reason, the aphids that were most strongly repelled by EBF.
Mediumstructured1 marks
Answer
the aphids that were fed on wild-type thale cress/ W as they had 80 % «or more» repelled each generation/ always had the higher \% response OR the aphids that fed on wild-type thale cress plants/W of G3 as they had «about» 85 % repelled/had the higher \% response Answer should refer to a percentage.
Question 1
1
Angora rabbits (Oryctolagus cuniculus) have soft and silky coats with fine hairs that grow about 30 mm per month. These hairs can be collected and used as wool. Hair growth in mammals depends on stem cells in the base of hair follicles called dermal papilla cells. Research was carried out to investigate the role of the WIF1 gene in hair growth. Wool was collected from 6-month-old angora rabbits. Expression of the WIF1 gene was assessed by measuring the quantity of WIF1 mRNA produced in cells taken from each rabbit. The rabbits were divided into groups according to their rate of wool production (low or high). The table shows mean wool production per rabbit in the low and high wool production groups and relative expression of the WIF1 gene. Removed for copyright reasons
structured9 marks
Question 1(d)
1(d)
Outline the effect of pcDNA-WIF1 on the expression of each of the three genes. In other species, expression of WIF1 has been found to affect rates of apoptosis (programmed cell death) and cell proliferation. These two processes were measured in the modified rabbit dermal papilla cells. The pie charts show apoptosis rates, and the graph shows cell proliferation rates. Removed for copyright reasons
Hardstructured3 marks
Answer
a. no significant effect on EGF expression OR (small) increase in (mean) EGF expression but error bars overlap/difference is not statistically significant/is not within 0.01 confidence/99\% confidence; b. SFR2 (expression) is increased/promoted (by pcDNA-WIF1); c. CCND1 (expression) is decreased/inhibited (by pcDNA-WIF1);
Question 1
1
Antiretroviral drugs are used to treat Human Immunodeficiency Virus (HIV) infections. Zidovudine (ZDV) and nevirapine (NVP) are examples of antiretroviral drugs. There are concerns that these drugs may be toxic to body cells in mitosis. In a study using Allium cepa, root tips were exposed to the drugs for 96 hours at a range of concentrations. The control treatment was a drug concentration of \(0 \mu \mathrm{~mol}\). In the graph, root lengths after the 96-hour treatment period are expressed as a percentage of the length of the control.
10 marks
Question 1(g)
1(g)
Outline the role of leptin in appetite control.
Mediumstructured1 marks
Answer
a. acts on receptors in the hypothalamus/appetite centre b. inhibits appetite Outline Accept WTTE for mpb 1 max
Question 2
2
In an experiment to determine the effect of diet on response to leptin, mice were fed a control diet or a high fructose diet for six months and then either injected with a saline (salt) solution or injected with leptin. The food intake of both groups was then monitored over a 24 hour period. Removed for copyright reasons
3 marks
Question 2(a)
2(a)
Distinguish between the effect of leptin injection on 24 hour food intake in the mice fed the control diet and in the mice fed the high fructose diet.
Mediumstructured1 marks
Answer
no effect with fructose diet but «statistically significant» reduction in control
Question 2(b)
2(b)
Discuss the implications of these results for recommending leptin injections as an appetite suppressant for humans.
Hardstructured2 marks
Answer
a. effectiveness/effect of leptin depends on diet b. «if obese people have a» high fructose diet, then it will not suppress appetite c. «for obese people with a» control/low fructose diet, then it will suppress appetite d. results for mice may not be the same for humans OWTTE OWTTE 2 max
Question 2(c)
2(c)
Leptin is a hormone. Hormones are chemicals produced in one part of the body that have an effect in another part of the body. State the
0 marks
Question 2(c)(i)
2(c)(i)
tissue that produces leptin in humans.
Easystructured1 marks
Answer
adipose/fat tissue
Question 2(c)(ii)
2(c)(ii)
target that leptin normally acts on.
Easystructured1 marks
Answer
ii hypothalamus
Question 3
3
8 marks
Question 3(a)
3(a)
Blood transports molecules throughout the body. State where the blood absorbs
2 marks
Question 3(a)(i)
3(a)(i)
hormones.
Mediumshort_answer1 marks
Answer
endocrine glands / named endocrine gland (e.g. pancreas/hypothalamus/ pituitary/ovary/testes)
Question 2
2
Vibrio fischeri is a bioluminescent (light-producing) bacterium in the Pacific Ocean. V. fischeri grown in the laboratory often has less luminescence. An investigation was carried out to look at the effect of the external osmolarity (in mOsmol) on the bacterium's luminescence, at different densities of bacteria. V. fischeri cultures were grown in three different concentrations of artificial seawater. Relative luminescence is the total luminescence divided by the density of bacteria. Key: osmolarity - 1300 mOsmol - 810 mOsmol - 570 mOsmol
structured0 marks
Question 2(b)
2(b)
Comment on the effects of osmolarity on the luminescence of the bacterium V. fischeri.
Mediumstructured2 marks
Answer
a. higher luminescence at higher (external) osmolarities; b. (at all osmolarities) relative luminescence increases with bacterial density between 0 to 1 arbitrary units; c. (at the two highest osmolarities) relative luminescence remains relatively stable with bacterial density from 1 to 5 (arbitrary units); d. at low osmolarity, relative luminescence decreases after 1 (arbitrary unit); e. lack of error bars does not allow for valid comparisons; 2 max
Question 2
2
Testosterone and epinephrine (adrenaline) are two of the many hormones used for cell-to-cell communication in the human body.
structured0 marks
Question 2(a)
2(a)
State one effect on the body of each of these hormones. Testosterone: Epinephrine:
Easystructured2 marks
Answer
a. Testosterone: stimulates development of male genitalia/sperm production/male sex drive/male secondary sexual characteristics / examples of male secondary sexual characteristics; b. Epinephrine: increases the heart rate/or any other specific effect on the body;
Question 2
2
The electron micrograph shows part of a pancreas cell that secretes digestive enzymes.
structured0 marks
Question 2(e)
2(e)
The pancreas secretes other chemicals as well as enzymes. State an example of a chemical and the type of pancreatic cell that secretes it.
Mediumstructured1 marks
Answer
insulin from the beta/ \(\beta\)-cells OR glucagon from the alpha/α-cells;
Question 4
4
The pavement ant (Tetramorium caespitum) eats organic matter found within its territory. Individual ants leave their nest to forage for food. When they find a suitable source of food they return and communicate to other ants in the colony where the food can be found. The diagram shows the path of one ant when foraging for food and returning to the nest after finding food.
0 marks
Question 4(d)
4(d)
0 marks
Question 4(d)(ii)
4(d)(ii)
Suggest how the other ants in the colony were able to quickly find the same source of food.
Mediumshort_answer1 marks
Answer
retrieved a (chemical) trail/scent/ communicate with touch/smell Accept other valid suggestion.
Question 4
4
Honey bees (Apis mellifera) live in colonies where some workers exhibit scouting behaviour. The scouts communicate information on new food sources to the non-scouting workers of the colony.
9 marks
Question 4(d)
4(d)
The biologists then fed non-scout bees various substances to see if they would promote scouting behaviour. The graph shows the effect of these substances. Calculate the increase in the probability of scouting behaviour of non-scouts fed with GLT (glutamate) and OA (octopamine). GLT: OA:
Mediumdata_response2 marks
Answer
G L T:(0.13-0.08=) 0.05; O A:(0.10-0.08=) 0.02;