[2]▶️ Answer/Explanation
- I: Glomerulus
- II: Descending limb of the Loop of Henle
- This part of the nephron (most likely Proximal Convoluted Tubule) is responsible for selective reabsorption. It reabsorbs useful substances like glucose, amino acids, minerals, and some water from the filtrate.
- These substances are absorbed back into the blood mostly by active transport, which requires energy (ATP).
| Plasma proteins / mg 100 ml⁻¹ | Glucose / mg 100 ml⁻¹ | Urea / mg 100 ml⁻¹ | |
|---|---|---|---|
| Blood plasma in renal artery | 740 | 90 | 30 |
| Glomerular filtrate | 0 | 90 | 30 |
| Urine | 0 | 0 | 1800 |
- The medulla of the kidney has a high salt concentration, which helps pull water out of the filtrate through osmosis.
- The collecting duct has special water channels called aquaporins that allow water to pass through.
- A hormone called ADH (anti-diuretic hormone) controls how much water is reabsorbed here.
- If ADH is present → more water is reabsorbed → urine becomes concentrated.
- If ADH is low → less water is reabsorbed → urine is more diluted.
I: glomerulus; ✔
II: (descending limb of) loop of Henle; ✔
(both needed)
selective re-absorption of glucose/minerals/amino acids/water/ useful substances; ✔
absorption by active transport/using ATP of glucose/minerals/ amino acids/useful substances; ✔
Award [1] for each correct row. ✔
collecting duct has water channels/aquaporins/is permeable to water; ✔
high solute concentration of medulla / medulla is hypertonic; ✔
reabsorption of water allows excretion of concentrated urine (antidiuresis); ✔
secretion of ADH/vasopressin increases permeability of collecting duct to water / vice versa; ✔
▶️ Answer/Explanation
- Homeostasis is the process of maintaining a stable internal environment in the body.
- It keeps internal conditions within a narrow, healthy range, even when external conditions change.
- Examples of factors regulated include body temperature, blood glucose, pH, CO₂ levels, and water content.
- It is controlled by nervous and hormonal systems using negative feedback where any change is detected and corrected back to normal.
- The normal body temperature is around 36.7–37°C (or 98.6°F).
- Blood helps in spreading heat throughout the body.
- The hypothalamus in the brain contains thermoreceptors that monitor body temperature.
- If it’s too hot, skin arterioles dilate (vasodilation) to release heat, and sweat glands produce sweat cooling by evaporation.
- If it’s too cold, vasoconstriction reduces heat loss, and shivering increases heat production.
- Other changes like hairs standing up or moving to shade/sun help with behavioural thermoregulation.
- Osmoregulation is the control of water balance in the body.
- The loop of Henle in the nephron makes the medulla highly concentrated (hypertonic), helping draw water out later.
- When filtrate reaches the collecting duct, water is reabsorbed based on the body’s needs.
- The hypothalamus senses how diluted or concentrated the blood is.
- If the blood is too concentrated (less water), it tells the pituitary gland to release ADH (antidiuretic hormone).
- ADH increases water permeability in the collecting duct by adding aquaporins (water channels).
- This causes more water to be reabsorbed, so less water is lost in urine → urine becomes concentrated.
- If blood is too diluted, no ADH is released → more water is lost in urine → urine is dilute.
maintaining (stable) internal environment/conditions; ✔
within (narrow) limits; ✔
example (e.g. body temperature / blood pH / blood glucose / water / CO2 concentration); ✔
levels of these variables are monitored (internally); ✔
negative feedback mechanisms / OWTTE; (reject if positive feedback included) ✔
involves hormonal / nervous control; ✔
maintained close to 36.7/37°C/98.6°F; ✔
heat is transferred/distributed in body by blood; ✔
hypothalamus contains thermoreceptors; ✔
hypothalamus monitors temperature/sends message to effectors/causes response; ✔
(vaso) dilation of skin arterioles warms skin/cools body; ✔
(vaso) constriction of skin arterioles retains body heat; ✔
skin/sweat glands produce sweat to cool the body when overheated; ✔
removal of heat through evaporation of sweat; ✔
shivering generates heat / increased metabolism / hair erection to retain heat; ✔
example of behavioural change to warm/cool the body to thermoregulate; ✔
osmoregulation is maintenance of water balance of blood/tissues; ✔
loop of Henle creates hypertonic conditions in the medulla; ✔
water reabsorbed as filtrate passes through collecting duct; ✔
hypothalamus monitors/controls water balance/content of blood; ✔
controls secretion of ADH by (posterior) pituitary gland; ✔
ADH is released when blood too concentrated/too little water/hypertonic; ✔
ADH makes the collecting duct more permeable to water; ✔
due to more aquaporins; ✔
more water reabsorbed (in response to ADH); ✔
less water in urine/urine more concentrated/urine hypertonic; ✔
no/less ADH when blood too dilute/too much water/hypotonic; ✔
collecting duct less permeable/less water reabsorption/more water in urine; ✔