CAIE A-Level Biology A2 14 Homeostasis Questions

Practise negative feedback, kidney function, osmoregulation, glucose and temperature control by identifying receptors, coordinators and effectors in data and mechanisms.

Covered syllabus points

14.1 Homeostasis in Mammals 14.2 Homeostasis in Plants

[Maximum number: 4]

(a)

An important function of control systems in mammals is homeostasis.
Explain what is meant by the term homeostasis.

[ 1 ]

(b)

Insulin plays a part in homeostasis. It affects muscle and liver cells to bring about a decrease in blood glucose concentration, particularly after a meal.

[ 3 ]

(i)

Describe the effects of insulin on muscle cells.

[ 3 ]

[Maximum number: 6]

There are more than 600 plant species in the genus Ipomoea. Many species are grown for their attractive flowers, and some species are used as crop plants.

(a)

Scientists investigated the response of stomata to changing carbon dioxide ( $\mathrm{CO}_{2}$ ) concentrations in the beach morning glory, I. pes-caprae.

The scientists placed I. pes-caprae plants in chambers. They measured the width of open stomata (stomatal apertures) after the plants had been exposed to different $\mathrm{CO}_{2}$ concentrations for 40 minutes. Light intensity and temperature were kept constant.

The relationship between $\mathrm{CO}_{2}$ concentration and the mean width of stomatal apertures is shown in Fig. 3.2.

Fig. 3.2

[ 6 ]

(i)

In 2016, a study measured the atmospheric $\mathrm{CO}_{2}$ concentration as $400 \mu \mathrm{~mol} \mathrm{~mol}^{-1}$ .

In the future, climate change may reduce water availability and increase atmospheric $\mathrm{CO}_{2}$ concentrations in some habitats.

Suggest how the stomatal response shown in Fig. 3.2 would allow I. pes-caprae to survive the effects of climate change.

[ 2 ]

any two from:
1 (as climate changes) increase in $\mathrm{CO}_{2}$ concentration causes, stomatal aperture to decrease / stomata to be less open ;
2 less water, lost / evaporated / transpired (though stomata) ;
3 compensates for / allows survival in, low water availability / dry conditions ;

(ii)

Under certain conditions, the closure of stomata is controlled by abscisic acid.

Describe how abscisic acid causes the closure of stomata.

[ 4 ]

any four from:
1 (abscisic acid / ABA) binds to receptor on, (guard) cell surface membrane ;
$2 \quad \mathrm{H}^{+}$ stops moving, out of cell/into cell wall ;
$3 \mathrm{Ca}^{2+}$ ions enter, cytoplasm / cell
or
$\mathrm{Ca}^{2+}$ ions act as second messenger ;
$4 \mathrm{~K}^{+}$ ions leave cell ;
5 water leaves cell, by osmosis / down water potential gradient ;
6 less turgid / flaccid, guard cell(s) close stoma(ta) ;

[Maximum number: 7]

Explain what is meant by the term homeostasis and describe the principles of homeostasis in mammals.

[Maximum number: 11]

(a)

In mammals, excess amino acids cannot be stored in the body.
Outline the formation of urea from excess amino acids by liver cells.

[ 3 ]

deamination/amine group removed;
A amino/ $\mathrm{NH}_{2}$
ammonia/ $\mathrm{NH}_{3}$ , formed ;
combined with carbon dioxide ;
urea cycle ;
A ornithine cycle

(b)

The mammalian kidney is composed of many nephrons.

Describe the process of ultrafiltration in the nephron.

[ 4 ]

(c)

Fig. 7.1 is a diagram of a nephron.

Fig. 7.1

Complete Table 7.1 by naming a part of the nephron that corresponds to each of the statements.

Table 7.1

[ 4 ]

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Covered syllabus points

Question 1

Question (a)

Question (b)

Question (i)

Question 2

Question (a)

Question (i)

Question (ii)

Question 3

Question 4

Question (a)

Question (b)

Question (c)