CAIE A-Level Biology A2 14.1 Homeostasis in Mammals Questions

Practise mammalian homeostasis by interpreting kidney and nephron diagrams, tracing urine and ADH responses, and explaining insulin or glucagon control of blood glucose.

Exam points

Explain homeostasis using narrow limits for body temperature, blood glucose and water potential.
Trace receptors, coordination and effectors in negative feedback that restores a set point.
Explain liver deamination of excess amino acids and urea formation for excretion.
Label the kidney cortex, medulla, pelvis, ureter and renal blood-vessel branches in sections.
Identify nephron structures and associated vessels in diagrams or micrographs.
Explain glomerular ultrafiltration and selective reabsorption in the proximal convoluted tubule.
Relate Bowman’s capsule filtration barriers and proximal-tubule adaptations to their functions.
Trace falling blood water potential through hypothalamus, pituitary, ADH and collecting-duct aquaporins.
Trace glucagon signalling from its receptor through G protein, cAMP and PKA to glycogen breakdown.
Interpret blood-glucose curves to explain insulin or glucagon feedback restoring the set point.
Compare test-strip colour from glucose oxidase/peroxidase with biosensor current for glucose concentration.

Covered syllabus points

14.1.1—Homeostasis definition and importance 14.1.2—Homeostasis control principles 14.1.3—Urea production 14.1.4—Kidney gross structure 14.1.5—Nephron structure 14.1.6—Urine formation 14.1.7—Nephron structure and function 14.1.8—Osmoregulation with ADH 14.1.9—Glucagon cell signalling 14.1.10—Negative feedback control of blood glucose 14.1.11—Glucose test strips and biosensors

[Maximum number: 6]

Explain what is meant by homeostasis in a mammal and explain why it is important to maintain body temperature, blood glucose concentration and the water potential of blood.

any six from:
1 maintain / keep / regulate, internal, environment / conditions ;
2 within, narrow / set, limits or around, optimum value / set point / norm ;
3 low (body) temperature and consequence ;
4 high (body) temperature and consequence ;
5 low blood glucose (concentration) and consequence ;
6 high blood glucose concentration and consequence ;
7 low, (blood) water potential / $\psi$ , and consequence ;
8 high, (blood) water potential / $\psi$ , and consequence ;

[Maximum number: 5]

Glucagon-like peptide-1 (GLP-1) is a hormone consisting of 31 amino acids. It is secreted by specialised intestinal epithelial cells known as L cells.

Fig. 6.1 outlines the secretion of GLP-1 and its effects on the pancreas, brain and stomach.

(a)

GLP-1 inhibits the secretion of glucagon by $\alpha$ cells in the pancreas.

Describe two processes in the liver that are stimulated by glucagon.

[ 2 ]

(b)

GLP-1 inhibits the emptying of the stomach. This is an example of negative feedback.

Explain what is meant by negative feedback.

[ 3 ]

[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 2

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Question (b)

Question 3

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Question (c)