Human Physiology II — Excretion and Locomotion — Practice

Question 1

Humans excrete their nitrogenous waste mainly as:
(a) urea (b) ammonia (c) uric acid (d) amino acids

Accepted Answer

(a) urea.

Humans are ureotelic: the chief nitrogenous waste is urea, less toxic than ammonia and needing moderate water. Birds and reptiles are uricotelic; bony fish are ammonotelic.

Question 2

Which group of animals is uricotelic?
(a) birds and reptiles (b) bony fish (c) mammals (d) aquatic amphibians

Accepted Answer

(a) birds and reptiles.

Uricotelic animals (birds, reptiles, insects) excrete uric acid as a semi-solid paste, conserving water — an advantage for flight and for eggs laid on land.

Question 3

Ultrafiltration of blood in the nephron occurs at the:
(a) glomerulus (b) proximal convoluted tubule (c) loop of Henle (d) collecting duct

Accepted Answer

(a) glomerulus.

Blood is filtered under pressure across the glomerular capillaries into Bowman's capsule; the filtrate resembles plasma minus proteins and cells.

Question 4

The glomerular filtration rate (GFR) in a normal adult human is about:
(a) 125 mL/min (b) 25 mL/min (c) 500 mL/min (d) 1 mL/min

Accepted Answer

(a) 125 mL/min.

GFR is roughly 125 mL/min, about 180 L per day. Around 99% is reabsorbed, so only about 1.5 L becomes urine.

Question 5

Glucose in the glomerular filtrate is normally completely reabsorbed in the:
(a) proximal convoluted tubule (b) distal convoluted tubule (c) loop of Henle (d) collecting duct

Accepted Answer

(a) proximal convoluted tubule.

Glucose is freely filtered but completely reabsorbed in the PCT, so normal urine contains no glucose. Its appearance signals blood glucose has exceeded the reabsorptive threshold.

Question 6

In the loop of Henle, the ascending limb is:
(a) impermeable to water but pumps out NaCl (b) permeable to water only (c) permeable to both water and salt (d) impermeable to both

Accepted Answer

(a) impermeable to water but pumps out NaCl.

The ascending limb actively transports NaCl out while being impermeable to water; the descending limb loses water but not salt. This asymmetry drives the counter-current multiplier that concentrates urine.

Question 7

ADH (vasopressin) increases water reabsorption chiefly in the:
(a) distal tubule and collecting duct (b) glomerulus (c) ascending loop of Henle (d) Bowman's capsule

Accepted Answer

(a) distal tubule and collecting duct.

ADH from the posterior pituitary makes the DCT and collecting duct more permeable to water, so more water is reabsorbed and a small volume of concentrated urine is formed.

Question 8

A deficiency of ADH leads to:
(a) diabetes insipidus (b) diabetes mellitus (c) glycosuria (d) uraemia

Accepted Answer

(a) diabetes insipidus.

Without ADH the kidney cannot reabsorb enough water, so large volumes of dilute urine are passed — diabetes insipidus. This is unrelated to diabetes mellitus, which involves insulin and glucose.

Question 9

The hormone that lowers blood pressure by promoting sodium loss is:
(a) ANF (b) aldosterone (c) renin (d) ADH

Accepted Answer

(a) ANF.

Atrial natriuretic factor, released by the atria of the heart when blood pressure rises, promotes sodium (and water) loss and lowers blood pressure — opposing the renin–angiotensin–aldosterone system.

Question 10

The functional contractile unit of a muscle fibre, lying between two Z-lines, is the:
(a) sarcomere (b) myofibril (c) myofilament (d) sarcoplasm

Accepted Answer

(a) sarcomere.

The sarcomere, the region between two successive Z-lines, is the repeating contractile unit of the myofibril, containing the actin and myosin filaments.

Question 11

Muscle contraction is triggered when calcium ions bind to:
(a) troponin (b) myosin (c) actin directly (d) the Z-line

Accepted Answer

(a) troponin.

Ca²⁺ released from the sarcoplasmic reticulum binds troponin, shifting tropomyosin to expose the actin binding sites so that myosin heads can attach; ATP then powers the cross-bridge cycle.

Question 12

During muscle contraction, which of the following remains unchanged in length?
(a) A-band (b) I-band (c) H-zone (d) sarcomere

Accepted Answer

(a) A-band.

The A-band (occupied by thick myosin filaments) stays constant, while the I-band and H-zone shorten as the thin filaments slide inward — the sliding-filament model.

Question 13

The total number of bones in the adult human skeleton is:
(a) 206 (b) 200 (c) 226 (d) 306

Accepted Answer

(a) 206.

The adult skeleton has 206 bones: 80 in the axial skeleton (skull, vertebral column, sternum, ribs) and 126 in the appendicular skeleton (limbs and girdles).

Question 14

The joint between the humerus and the pectoral girdle (shoulder) is a:
(a) ball-and-socket joint (b) hinge joint (c) pivot joint (d) gliding joint

Accepted Answer

(a) ball-and-socket joint.

The shoulder (and hip) is a ball-and-socket joint allowing movement in all planes including rotation. The knee and elbow are hinge joints allowing movement in one plane.

Question 15

Osteoporosis, a decrease in bone mass common in older women, is linked to a decreased level of:
(a) oestrogen (b) insulin (c) thyroxine (d) adrenaline

Accepted Answer

(a) oestrogen.

Osteoporosis (reduced bone mass and increased fracture risk) is associated with lowered oestrogen levels, especially after menopause, along with reduced calcium. Gout, by contrast, is caused by uric-acid crystals in joints.

Practice — Human Physiology II — Excretion and Locomotion

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