IB Biology HL D3.3 Homeostasis Questions

Practise IB Biology HL D3.3 by tracing glucose and temperature feedback, comparing diabetes evidence and explaining nephron filtration and ADH control.

Exam points

Define homeostasis from regulated variables such as blood pH, water balance and glucose.
Trace insulin/glucagon responses to blood-glucose changes and interpret glucose or turnover data.
Compare type I beta-cell destruction with type II insulin resistance, risk and treatment evidence.
Trace temperature feedback and predict vasomotor, sweating, shivering or heat responses.
Explain glomerular ultrafiltration, PCT reabsorption and urine formation from blood filtrate.
Relate loop-of-Henle salt transport and water permeability to the medullary gradient.
Trace osmoreceptor–ADH feedback, aquaporins and water reabsorption in collecting ducts.
Interpret exercise-related blood-flow changes as vasoconstriction or vasodilation to tissues.

Covered syllabus points

D3.3.1—Homeostasis definition D3.3.2—Negative feedback loops D3.3.3—Blood glucose regulation D3.3.4—Diabetes D3.3.5—Thermoregulation D3.3.6—Thermoregulation mechanisms D3.3.7 (HL)—Kidney role D3.3.8 (HL)—Glomerulus, Bowman's capsule, PCT D3.3.9 (HL)—Loop of Henle D3.3.10 (HL)—Osmoregulation by collecting ducts D3.3.11 (HL)—Blood supply changes

[Maximum number: 1]

The dimensions of four structures were measured in the hearts of eleven patients with anorexia and in the same number of control subjects.
(a) Discuss the support provided by the data for the claim that anorexia leads to the breakdown of heart tissue.
(b) In control subjects, blood potassium levels are maintained, through homeostasis, between 3.5 and 4.5 mmol litre ${ }^{-1}$ . In patients with anorexia, blood potassium can fall below this level. This is known as hypokalemia. In patients with kidney failure, levels can rise above this range, causing hyperkalemia. The traces show the electrocardiograms (ECGs) of a patient with hypokalemia, a normal subject and a patient with hyperkalemia.

Sometimes hyperkalemia occurs as a body tries to respond to low blood pH . State the normal range of blood pH in the human body.

[Maximum number: 7]

Living organisms have mechanisms for preventing or reducing change.

Describe the mechanisms used to keep blood glucose levels within narrow limits in humans.

[Maximum number: 1]

Which condition is associated with type II diabetes?

A lack of beta cells in the pancreas

Excess glucagon in the blood

Obesity

Early onset

[Maximum number: 8]

Explain the control of body temperature in humans.

normal body core temperature constant/ 36.5 to $37.5^{\circ} \mathrm{C}$ ;
(accept single values within this range);
regulated by negative feedback/homeostatic mechanisms;
hypothalamus is the centre of thermoregulation;
hypothalamus sends impulses to the body to increase/decrease temperatures;
release of sweat (by sweat glands in the skin) if skin temperature rises;
evaporation of water cools the body;
(concept of evaporation must be mentioned)
heat is transferred by blood;
transfer of heat from body core in blood to surface;
if temperature rises, increased flow of blood/heat to the skin/vasodilation of skin blood vessels/arterioles;
(do not accept veins, arteries or capillaries)
if temperature drops, decreased flow of blood/heat to the skin/vasoconstriction of skin blood vessels/arterioles;
(eg reducing activity (to lower body temperature) / reducing exposed surfaces (to reduce heat loss)

[Maximum number: 1]

Average human internal (core) body temperature is $36.4^{\circ} \mathrm{C}$ , with slight variations between day and night. The average surface temperature of the Earth in the 20th century was $13.9^{\circ} \mathrm{C}$ . It has now risen to $14.8^{\circ} \mathrm{C}$ .

Outline one change that happens in the human body in response to a rise in body temperature above $36.4^{\circ} \mathrm{C}$ .

[Maximum number: 1]

What is normally found in the urine of a healthy individual?

Glucose

Red blood cells

Proteins

Sodium ions

[Maximum number: 1]

Where is the greatest quantity of water reabsorbed from the nephron?

Bowman's capsule

Proximal convoluted tubule

Loop of Henle

Collecting duct

[Maximum number: 1]

What is the function of the loop of Henle?

To reabsorb salt

To maintain a hypertonic solution in the medulla

To transport liquid from the collecting ducts to the convoluted tubules

To reabsorb glucose

[Maximum number: 4]

Feedback mechanisms are used in living organisms both to promote and respond to change.

Outline the role of ADH in osmoregulation.

[Maximum number: 1]

What is a reason for the changes in blood flow during exercise?

Increased blood flow to the kidneys removes waste products from exercise.

Blood flow to the brain decreases so that blood is diverted to the kidneys.

Increased blood flow to the skin removes heat.

Increased blood flow to the digestive system provides more glucose to muscles.

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Covered syllabus points

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