Lycolysis; Alcoholic fermentation; energy flow through a marine ecosystem; genetics; mutation

Question 1 :

In 1857, Louis Pasteur discovered that yeast is a living organism. The activity of yeast causes fermentation a bakeras yeast, Saccharomyces cerevisiae, has been used for centuries in the production of bread, beer and wine. In the absence of oxygen, yeast is able to derive energy from nutrient carbohydrates by switching from aerobic to anaerobic respiration. In the first step of anaerobic respiration, known as glycolysis, monosaccharides such as glucose or fructose are oxidised to form pyruvate, with the net release of energy in the form of ATP (Book 5, Figure 6.13, page 122):

Step 1 Glycolysis

glucose + ADP + NAD a  pyruvate + NAD.2H + ATP
In the second step (alcoholic fermentation) the pyruvate is reduced to form ethanol and carbon dioxide:

Step 2 Alcoholic fermentation

pyruvate + NAD.2H a  ethanol + NAD + CO2
After reading Chapters 5 and 6 of Book 5, an enterprising OU student decided to investigate the anaerobic respiration of yeast in the presence of different sources of carbohydrate. The student had a job as a laboratory technician in a school and so was able to set up the apparatus shown in Figure 1 and carry out the investigation using each of the mixtures described in Table 2 in turn. Each experiment was carried out at room temperature (20 A°C).

Table 2 The contents of the reaction mixture in each of the five experiments. You can assume that the starting concentrations of the carbohydrate solutions were the same (i.e. same mol dma 3).
(ill put printsceet shot about this one below)
Experiment A B C D E
Reaction mixture 5 cm3 yeast suspension + 1 cm3 distilled water 5 cm3 yeast suspension + 1 cm3 glucose solution 5 cm3 yeast suspension + 1 cm3 sucrose solution 5 cm3 yeast suspension + 1 cm3 starch solution
5 cm3 yeast suspension + 1 cm3 starch solution containing amylase

At the start of each experiment the measuring cylinder was filled with water and quickly inverted in the trough of water and placed on the beehive shelf (a platform with holes that allows free movement of water in or out of the measuring cylinder). The reaction mixture was made up in the bottle and the stopper quickly replaced so that any gas given off by the yeast mixture travels through the tube and is collected in the inverted measuring cylinder, the gas pushing down the water as shown in Figure 1. The volume of gas produced was measured at 5-minute intervals for 30 minutes. A graph showing the results of these five experiments is shown in Figure 2.


Figure 2 The volume of carbon dioxide collected in the measuring cylinder for each of the experiments A to E over a 30 minute period at 20 A°C.

i.Explain why the student set up experiment A with no carbohydrate in the bottle.
ii.For each of experiments A to E, briefly describe the results represented graphically in Figure 2. Explain why differences in the volume of gas collected over the 30-minute period occurred, taking into consideration the type of carbohydrate (glucose, sucrose or starch) used in each experiment. (Guideline: up to 320 words in total for parts (i) and (ii).)
b.The experiment could be extended to see how temperature affects the way the yeast respires. Predict the effect on the results of experiment B (5 cm3 yeast suspension + 1 cm3 glucose solution) if it was repeated (i) at 4 A°C and (ii) at 60 A°C and give a brief explanation for each of your predictions.

Question 2

This question addresses the energy flow through a marine ecosystem.

The amount of solar energy falling on the surface of the sea in the English Channel is 1.2 A 106 kJ ma? 2 ya? 1. Photosynthetic phytoplankton in the water assimilate energy from sunlight to generate a gross primary production (GPP) of 6.3 A 103 kJ ma? 2 ya? 1 and a net primary production (NPP) of 5.0 A 103 kJ ma? 2 ya? 1. Herbivorous zooplankton consume 4.0 A 103 kJ ma? 2 ya? 1 of phytoplankton biomass and the rest of the phytoplankton die and sink to the bottom, so that 1.0 A 103 kJ ma? 2 ya? 1 passes to detritivores and decomposers, mainly bacteria. Zooplankton convert 7.1 A 102 kJ ma? 2 ya? 1 of the phytoplankton they consume to biomass, which then passes to numerous predators that feed on the zooplankton. The waste products of the zooplankton, 4.9 A 102 kJ ma? 2 ya? 1, sink to the bottom and are consumed by detritivores and decomposers.

Note: kJ ma? 2 ya? 1 is a different (but equally valid) unit to that used in Book 5, Chapter 7, and can be used without conversion in this question.

a.Name the primary consumers in this food chain.
b.Which members of the food chain are autotrophs? Explain your answer. (Guideline: A single sentence.)
c.Gross primary production of energy is much lower than the amount of solar energy falling on the phytoplankton and water surface. Briefly discuss why the remainder of the solar energy was not assimilated by the photosynthetic phytoplankton, and suggest where this energy will have gone instead. (Guideline: two or three sentences.)
d.Calculate the percentage of the solar energy falling on the surface of the water that is lost and does not pass into the food chain of this ecosystem. Show how you worked through your calculation and give your final answer to two significant figures.
e.Calculate how much energy is lost from this ecosystem through zooplankton respiration. Show how you worked through your calculation making explicit use of the equations that describe the relationships between respiration, biomass consumption, energy assimilation and energy lost as waste products. Give your final answer to two significant figures.

Question 3

human males and females can be distinguished by a particular pair of chromosomes called the sex chromosomes. Males have one X and one Y chromosome while females have two X chromosomes. The X chromosome is considerably larger than the Y chromosome and carries a number of genes in addition to those involved in sex determination, for example colour vision, which is controlled by a single X-linked gene, with two alleles. The allele associated with colour vision deficiency is recessive to the allele associated with normal colour vision.

Figure 3 represents a family tree showing the pattern of inheritance of colour vision deficiency. Individuals shown in the family tree either have normal colour vision (shown with circles for eyes) or have colour vision deficiency (shown with crosses for eyes). Adult females (a) are represented with long hair, adult males (a ) with short hair and babies with a single curled hair.

question 4

a.Sickle-cell disease is a condition caused by a small mutation in the DNA sequence that codes for haemoglobin, the protein responsible for transporting oxygen in red blood cells. In this case, a thymine base is inserted instead of an adenine at a specific point in the DNA sequence. After transcription, the mRNA sequence differs from mRNA transcribed from normal DNA as follows:
Section of normal mRNA sequence: a¦CAC CUG ACU CCU GAG GAG AAG UCU GCCa¦

Section of mutant mRNA sequence: a¦CAC CUG ACU CCU GUG GAG AAG UCU GCCa¦

i.State the amino acid sequence resulting from each of these sections of mRNA, and identify any alterations this mutation will make to the sequence of amino acids present in the final protein.
ii.Explain why a change in the amino acid sequence of a protein can be damaging to its function. (Guideline: up to 100 words.)
iii.Explain why a mutation that causes the deletion of a base in the DNA coding for a protein is usually more damaging than one that causes the substitution of one base for another. (Guideline: up to 120 words.)
In sickle-cell disease abnormal haemoglobin is produced, which causes red blood cells to become distorted into a sickle (or crescent) shape, interfering with blood flow and the transport of oxygen throughout the body. Sickle-cell disease follows a pattern of autosomal recessive inheritance. The DNA mutation that causes the disease is found on chromosome 11, and in some West African countries 15a 30% of the population are thought to be hetero