N21 H2 P3 answers for uploading updated 2023

Section A 1 (a) Suggest and explain three different hypotheses, other than those related to diet, that could account for any of the trends shown in Table 1.1. At least one of the hypotheses must refer to TB and at least one must refer to CVD. [6] Hypotheses about [quote data] tuberculosis death rate decreasing gradually over the years from 1900 to 2015, from 195 to 1 per 100 people per year respectively: 1. Development of antibiotics to treat infected TB patients since TB is caused by Mycobacterium tuberculosis bacterial infections which can be treated with bacteriocidal and/or bacteriostatic antibiotics; 2. Vaccination programme so that US citizens have herd immunity to prevent the spread of TB, reducing the number of deaths; 3. Vaccination programme to produce memory B cells in individuals so that there is a faster, larger secondary immune response which reduce the death rate; 4. Increased awareness about the need to isolate infected patients as preventative measures so that the Mycobacterium tuberculosis bacterial infections which are transmitted by airborne means are limited in spread; Hypotheses about [quote data] CVD death rate first increasing from 1900 to 1950, from 250 to 450 per 100 people per year respectively, and then decreasing from 1950 to 2015, from 450 to 220 per 100 people per year respectively: 5. Increase in stress due to work as US economy became more industrialised from 1990 to 1950, and an improvement in emergency healthcare or drugs from 1950 to 2015; 6. Lack of awareness about CVD being caused by a sedentary lifestyle from 1990 to 1950, and a greater awareness of active lifestyle from 1950 to 2015; At least 1 from points 1-3 and 1 from points 5-6. (b) (i) Draw a line of best fit on Fig. 1.1. [1]

(ii) Explain what is shown by the slope of the line of best fit you have drawn on Fig. 1.1. [1] 1. An increase in percentage of energy intake in the diet that comes from saturated fatty acids is correlated to (Reject: cause) a proportional increase in concentration of cholesterol in the blood; 2. [Quote Data] E.g. An increase from 6.6% to 20.2% of energy intake in diet that comes from saturated fatty acids is seen to correspond to an increase in 1.8 mg cm- 3 to 2.6 mg cm-3 of cholesterol in blood; (iii) Distinguish between a triglyceride and a fatty acid. [2] 1. A triglyceride is hydrophobic due to the absence of carboxylic acid groups, while a fatty acid is hydrophilic due to the presence of carboxylic acid groups; 2. A triglyceride has a glycerol joined to three fatty acids by three ester linkages, while a fatty acid does not have any ester linkage and no glycerol; (iv) State two roles of cholesterol in cells. [2] 1. Cholesterol provides mechanical stability as it forms weak hydrophobic interactions with neighbouring hydrocarbon chains of phospholipids; 2. Cholesterol regulates membrane fluidity* by preventing the membrane from being overly fluid at warmer temperatures as cholesterol’s rigidity restricts phospholipids’ lateral movement; (Points 3 and 4 are further elaborations of point 2) 3. The membrane is prevented from being overly firm at lower temperatures as cholesterol prevents close packing of phospholipids and hence prevents its solidification/ crystallization; 4. Permeability increases when the membrane is overly fluid; (c) Complete Table 1.2 to show for each set of results:  which of the causal links of the Diet-Heart Hypothesis represented by the arrows in Fig. 1.2 was investigated (write A, B or C)  whether the results support the causal link shown by this arrow (write yes or no). Table 1.2 results causal link investigated do the results support the causal link? Fig. 1.3 C No Fig. 1.4 C No Fig. 1.5 B Yes Fig. 1.6 A Yes [4] (d) (i) Dietary fats, proteins and carbohydrates are digested by enzymes in the gut before being absorbed into the blood. These enzymes hydrolyse bonds in the food molecules that originally formed by condensation reactions. List three types of covalent bonds broken by these digestive enzymes in the gut. [3] 1. Glycosidic bond 2. Peptide bond 3. Ester bond

(ii) State the main roles in the body of the products of digestion of proteins and carbohydrates. [3] 1. Protein is digested to amino acids* while carbohydrates such as starch is digested to glucose*; 2. Amino acids are needed for synthesis of enzyme, proteins embedded in cell membrane such as receptors or transport proteins, for synthesis of signal molecules such as insulin; 3. Glucose is main respiratory substrate that upon oxidation by respiration produces ATP/ releases energy; (iii) Name the membrane system or organelle within the gut epithelial cells where each of these events may take place: [2] formation of triglyceride droplets smooth endoplasmic reticulum formation of exocytotic vesicles Golgi apparatus (iv) Suggest and explain why lipoprotein spheres are used to transport triglycerides in the blood. [2] 1. Triglycerides have long non-polar hydrocarbon chains and are hydrophobic* and insoluble* in water of the blood plasma; 2. Lipoprotein sphere has phosphate head of phospholipid which is charged and hydrophilic* as well as the hydrophilic regions of embedded proteins facing outwards that can interact with water molecules; 3. Triglycerides need to be packaged within the lipoprotein spheres in order to be transported in the blood as blood plasma is a hydrophilic environment; (e) Use this information and the data in Table 1.3 to discuss whether the dietary changes triggered by the Diet-Heart Hypothesis improved the health of people in the USA. [4] 1. Percentage prevalence of type 2 diabetes increases slightly by 1.5 % over a period of 40 years from 1925 to 1975 but increases significantly by 5.1% over a shorter period of 50 years from 1975 to 2015; 2. There is an gradual increase in obesity of 11% from 1900 to 1975 and a steep increase of 22% from 1975 to 2015/ increase in obesity percentage from 1975 to 2015 is twice that of increase from 1900 to 1975; 3. Dietary change from fats to carbohydrate based on Diet-Heart Hypothesis did not improve health as percentage of people suffering from type 2 diabetes and obesity increases more; 4. However the data did not provide sufficient information such as the number of people involved, age and sex and whether their daily diets were monitored/ other factors such as regularity of exercise and adequacy of sleep were not taken into consideration; [Total: 30]

2 (a) Explain what can be learnt by comparing genomes of different species of fish such as seahorses and zebrafish. [3] 1. Evaluating molecular homologies based on DNA of cytochrome c gene (any example) can determine degree of nucleotide similarity; 2. The more related they are, the greater similarity there is in the sequence of their homologous gene/DNA allowing the determination of ancestor-descendant relationships; 3. Understand the link between genotype and phenotype; 4. Reveal structure of genetic variation between different populations of the individual species; (b) Complete Table 2.1 by inserting the letters P, Q or R to show which type of genetic change is most likely to have occurred during the evolution of the seahorse from a zebrafish-like ancestor, for each of the phenotypic features listed. [2] phenotypic feature zebrafish seahorse type of genetic change number of fin locations 5 3 R male has pouch for development of embryos absent present Q number of teeth 22 0 P (c) Scientists carried out PCR (polymerase chain reaction) on the DNA of seahorses and zebrafish using a set of primers for a particular zebrafish gene. The scientists suspected that this gene was missing from seahorses. • Outline how the scientists could analyse the co