AQA A2 (Module 6) Human Biology

ANSWERS TO IN-CHAPTER QUESTIONS

Unit 8: Growth & Development to maturity

COMPARE YOUR ANSWER WITH THE SUGGESTED RESPONSE GIVEN BELOW: RETURN YOUR MARKED SCRIPT TO YOUR TUTOR

IF YOU ARE UNCLEAR OR UNCERTAIN ABOUT ANY ASPECT OFTHIS CHAPTER IT IS ESSENTIAL THAT YOU ARRANGE FOR EXTRA TUTOR HELP AND GUIDANCE

Q1. ‘Growth’ is defined as ‘an increase in dry body mass’, thus ‘putting on weight’ is growth just as much as an increase in height (which stops at 16ish for girls and 21ish for boys, hence men are taller than women by an average of 8 inches, since they grow for 5 more years). To work out your child’s expected height take the average height of the two parents and add 4 inches for a boy and subtract 4 inches for a girl. 90% of children will be within 1 inch of that predicted height.

The answer to the question is thus ambiguous, since some people continue to gain weight throughout much of their lives. Women always gain weight when pregnant, too (and usually fail to lose it all after the birth!). The answer that is expected is ‘all except the last two’, but that would be wrong!

Q2. Because how much you have drunk/eaten will affect your weight for some time afterwards. It is easiest to do this first thing in the morning after a visit to the WC, since you have not eaten or drunk anything, are in the bathroom and nude!

Q3. Longitudinal. Because they show the change over time.

Q4. Because it stimulates metabolism and so speeds up all the body’s normal processes, including growth (below adulthood).

Q5. Chromosomes have ‘waste’ DNA on their ends known as telomeres. Each time the cell divides, some of this DNA is lost until it has all gone. At that point, that cell loses the ability to divide further. Cloning therefore, by taking ‘middle-aged’ cells, means that the clone is born with ‘middle-aged’ cells and so is susceptible to the diseases of old age (arthritis, deafness, muscle wasting) much earlier – as Dolly the sheep has demonstrated. In contrast, cancer cells never lose this DNA and so can live and divide forever. In theory, it should be possible to genetically engineer this characteristic into normal cells and so allow effective cloning, but the dangers of copying cancer genes are self-evident.

In old age, the ability of many cells in the body to regenerate has been lost and so the recovery process takes longer. Drugs are now available to help to speed this process up – oestrogen is one such, so you can appreciate that a cancer developing during pregnancy will be particularly aggressive.

UV light damages DNA and collagen in the skin, so people from sunny climates often have badly wrinkled faces in late middle age – just look around you next time you are on holiday in Greece, Spain etc at the faces of the old women. Maybe the Victorians women, who covered up and kept out of the sun, were not such fools after all. Smoking makes this effect worse, and some people are born with genes which make them ‘fresh-faced’; they age much more slowly than the rest of us!

Q6. Stored fat (= adipose) cells have a very low metabolic rate and so the more of these you have the lower your overall BMR – which naturally lowers with age anyway (hence ‘middle-aged spread’. And why do women worry about their hips and not about their bums as they get older? A man’s beer-belly is caused by the same problem.) Counteracting this, however, is the fact that, with so much extra weight to carry around, you will need to work the rest of your cells harder just to keep going – at least, with a decent amount of exercise you will.

Q7. Collagen and elastin will be exposed more to UV light with outside exercise, so more wrinkles. Losing a lot of weight would also mean less of you inside the same sized skin, hence more wrinkles too – look at Granny’s triceps region (inside her upper arms).

Regular moderate exercise is good, but over-exercising results in longer to recover and more visits to A&E at the hospital and more admissions to the cardiac wards – not good!

With regular exercise, your BMR rises and stays higher, so reducing the onset of the dreaded ‘middle-aged spread’. Much the same effect occurs if you turn the heating down and wear less clothes – thus saving money into the bargain!

Exercise increases the heart rate and so maintains cardiac output for longer. Much of this decline is due to older people becoming more sedentary – so get Granny a dog and she’ll live forever!

Nerves decline with age, but the effect is minimal and of little interest unless you are a pilot or about to have a car accident. Brain exercises (e.g. crosswords, bridge etc.) do maintain the efficiency of synaptic transmission in the brain, though, so buy Granny a Scrabble set too!

Q8. Rises, then steadies, instead of following a monthly cycle. This is because FSH secretion is inhibited by oestrogen, so, with no oestrogen being produced, FSH secretion will rise. Hormone Replacement Therapy (HRT) reduces or stops the effects on a woman’s body that follow the decline in female hormones after the menopause. Thinning hair, moustache growth and osteoporosis (‘widow’s stoop’) are all preventable with this treatment, which is also supposed to do wonders for their libido!

Q9. Oxidised DNA would, presumably, be incapable of dividing or functioning normally, so the mitochondria containing them would be less effective. This in turn would lead to the cell being less active and the individual having less energy for activity.