A2 Level

AS Level

Unit 3

Unit 4

Unit 5

A2 Human Biology Unit 9

Text questions

P183/Q1

Faeces = undigested food. Faeces are not products of biochemical reactions in the body.

P184/Q2

Enzymes have an active site of a specific shape. Enzymes are specific, i.e. they act on specific
chemical bonds which are present in the molecule of a substrate. Some kinds of amylase will catalyse
the hydrolysis of 1,4 glycosidic bonds (→amylose), other kinds of amylase will catalyse the hydrolysis
of 1,6 glycosidic bonds (→amylopectin).

P185/Q3

	Lactobacillus
Lactose (milk)	~~~~~~~~~~~~>	Lactic acid (yoghurt)
	(anaerobic res.)	CH₃CHOHCOOH

The molecule of lactic acid is small and can be easily absorbed into the bloodstream.

P187/Q4

	lactase
Lactose	~~~~~~~~~~~~>	b glucose + galactose
(less sweat)		(more sweet)

P187/Q5

Each time a long polypeptide chain is hydrolysed/cut into two shorter polypeptide chains, the number of free ends of the chains will double (2 → 4 → 8 → 16 → �) In this way the previously long polypeptide chain is prepared for rapid digestion by exopeptidases.

P188/Q6

1 + 3 = 4

1 + 2 = 3

P189/Q7

Very long, small lumen, villi & microvilli.

P190/Q8

Salivary glands, gastric glands, pancreas, wall of small intestines (equivalent of a gland).

P191/Q9

No, because the amounts of glucose which will pass through co-transport proteins is limited. Hence, at certain glucose concentration no more glucose molecules will pass through co-transport proteins → these molecules will stay in the lumen → WP of the contents of the lumen will be more negative → water will not be reabsorbed.

P192/Q10

No HCl in the stomach → pepsinogen not converted to pepsin → protein not digested in the stomach. No trypsin produced by pancreas → proteins not digested in the small intestine. If proteins are not digested, then antibodies (proteins) will not be digested, either. Consequently, antibodies will be absorbed.

P192/Q11

Proteins (enzymes), HCl, bile salts

P193/Q12

Nervous system

Endocrine system

P196/Q13

Units of energy per 100 ml of milk is a standard rate presenting data for all kinds of foodstuffs. It enables quick comparisons between foodstuffs to be made.

P196/Q14

20cm� x 30�C = 600 calories (cal)

Proportion:
1 cal = 4.2 J
600 cal = ?

Solution:
? = (600 x 4.2) / 1 = 2520 J = 2.52 kJ

kJ g^-1 of pasta = kJ / g of pasta

Weigh "pasta shape" before [#1] and after [#2] burning it

Calculate drop in mass:
[#1] - [#2] = [#3] grams

Proportion:
[#3]g - 2.52 kJ
1g - ? kJ

Solution:
? kJ = (1 x 2.52) / [#3] = ...

P198/Q15

Essential amino acids must be present in the diet because they can not be produced by transamination in the liver. Non-essential amino acids do not have to be present in the diet because they can be produced by transamination.

Both essential and non-essential amino acids have essential functions in the body because they are needed for protein synthesis.

P199/Q16

Blood loss as a result of menstruation

P201/Q17

Pregnancy → increased BMR (increased MR of the heart, lungs, kidneys, breast, uterus, placenta, foetus)

P202/Q18

From table 9.7, p.202: PAR � 6.9
Hence, the total energy requirement: 6.9 x 260 kJ/hour x [# hours playing tennis] = ...

P204/Q19

Table 9.8, p.203;
Estimated average protein requirements (female, 13, 40kg):
0.76g/day/kg x 40kg = 30.4g/day

Animal sources:
1(Correction Fact.) x 30.4 = 30.4g/day

Cereal & vegetables:
1.2 (CF) x 30.4 = 36.5g/day

P205/Q20

Mean → median → mode P205/Q21 Heavy blood loss after IUDs have been fitted → increased risk of anaemia (especially when diet low in iron).

P206/Q22

Watercress

Source of Ca	Amount of Ca/mg/100g	Rate of absorption/%	Amount of Ca absorbed/mg/100g
Watercress	222	27	0.27 x 222 = 59.9
Skimmed milk	122	46	0.46 x 122 = 56.1

Assignment

P209/Q1

Other sources of N in the diet (e.g. DNA, RNA, ATP) ignored;

The amount of N in protein differs depending on its primary structure;

P209/Q2

Your graph;

The amount of crude protein/g/day:

Is larger when two lambs in the litter (more protein needed for growth of two lambs)
Decreases over the period of lactation from week 2 to week 10 (lambs start to produce proteases & other digestive enzymes to digest other foodstuffs than milk; less/no antibodies in the milk).

Extra proteins needed for:

Growth of placenta
Growth/development of the mammary glands

P209/Q3

RDP digested by the bacterial flora living in the rumen & used by bacteria to built their own cells.

P209/Q4

3000g/365days = 8.2g/day

Proportion:

1g/day (protein in food)	-	0.54g/day (protein absorbed → keratin)
?	-	8.2g/day

Solution:
? = (8.2 x 1) / 0.54 = 15.2 g/day

From the question we know, that:

Keratin: 120 g/kg of S-containing amino acids (S-a/a)
Plant protein: 30 g/kg (S-a/a)

(1) If all plant protein (p/p) is digested & all a/a are absorbed, then:

Proportion:

1 kg (p/p)	-	30 g (S-a/a)
?	-	120 g (S-a/a)

Solution:
? = (120 x 1) / 30 = 4 kg
(4 kg of plant protein to be provided in the diet to produce 1 kg of keratin)

(2) However, only 54% of plant protein is absorbed (A-p/p), therefore more of p/p will have
to be provided in the diet (D p/p);

Proportion:

1 kg (D-p/p)	-	0.54 kg (A-p/p)
?	-	4 kg (A-p/p)

Solution:
? = (4 x 1) /0.54 = 7.4kg (D-p/p)
(7.4 kg of plant protein to be provided in the diet in order to grow 1 kg of keratin)

(The sequence of answers has been changed below)

P210/Q5

Restriction nuclease is an enzyme used to cut a gene out of its DNA chain.

Ligase is an enzyme which will ensure that "sticky" ends of the cut plasmid DNA
will join together with the foreign gene.

P210/Q6

S-rich protein made in leaf cells → leaves eaten by sheep → S-rich proteins made available to sheep for digestion and later for the synthesis of keratin;

If S-rich proteins are digested/absorbed by bacteria of rumen, then less S-containing amino acids will be available to the sheep (for keratin synthesis).

Examinations

P210/Q1

At least one double (C=C) bond present in unsaturated fatty acid (f/a). No (C=C) bonds in saturated f/a.

(i) Ester bond between glycerol & f/a broken by hydrolysis (→addition of H₂O molecules).

(ii) Bile: bile salts → reduction of surface tension between water molecules → triglycerides form emulsion with water/micelles → large surface area of triglycerides avilable for the formation of ES complexes with lipases → higher rate of hydrolysis/digestion.

P211/Q2

(i) Alveoli - tiny milk sacs, the basic functional units of the memory glands. Milk secreted by the cells lining the alveoli is drained via ducts to the nipple;

(ii) Enzyme complex {EC} (conjugated protein & enzyme) is capable of catalysing a certain process only if the two components of the complex are present.

(i) Biuret test : equal amounts of Biuret reagent & the sample mixed & heated up (→lilac = positive)

(ii)

(1) Caseins: essential a/a, association with Ca²⁺ (→micelles) → transport of Ca²⁺ from mother to baby;

(2) a-lactalbumin + transferase (enzyme) → Lactose Synthetase enzyme complex; then:
b-glucose + galactose ~~~~~~~> lactose by LS

(3) Antibodies/immunoglobins absorbed by the newborn → higher immunity to diseases

(i) Essential a/a must be present in the diet because they can not be synthesised by transamination in the liver. Shortage of essential a/a will affect protein synthesis in which they are monomers...

(ii) Protein clot is a semi-solid, hence it will stay in the stomach for the process of digestion to follow;

Lactose makes WP in the lumen of mammary alveoli more negative than WP of blood plasma → water is drawn in by osmosis.

Diarrhoea is usually caused by certain groups of bacteria, which multiply in the alimentary canal. Antibodies delivered with the mother's milk help to fight off the bacteria.

P212/Q3

(i) Exopeptidases hydrolyse the extreme peptide bond in the polypeptide chain.

(ii) Epithelial cells have enzymes in their plasma membranes & cytoplasm.
These enzymes hydrolyse dipeptides to a/a;

In people suffering from anaemia the limiting factor which reduces synthesis of haem group is shortage of iron. If this happens, protoporphyrin accumulates in the bone marrow (where RBC are made) and, consequently, protoporphyrin can be found in higher amounts in the RBC.

(i) IUD → increased blood loss during menstruation → anaemia

(ii) Group B: IUD → progesterone. Bleeding during menstruation is caused by dilation of the spiral blood vessels in the endometrium. Progesterone reduces this vasodilation → bleeding is reduced.

Proportion:

100ml	-	12.5g haemoglobin
(C): 41ml	-	?

Solution:
? = (41 x 12.5) / 1000 = 5.1 g haemoglobin
5.1g x 0.003 = 0.015g (15 mg) Fe