Exam qs

• Suggests two signs or symptoms which may result from a decrease in ADH (2)

  • thirsty/dehydration
  • increased volume of urine
  • less concentrated urine.
• Describe effect of ADH on permeability of collecting ducts (3)

  • stimulates addition of protein channels into membrane
  • more permeable to water
  • by osmosis
• Efferent arteriole out of glomerulus has a narrower lumen than the afferent arteriole. This creates hydrostatic pressure, forcing water and soluble substances out of the glomerulus.
• Describe how ultrafiltration produces glomerular filtrate. (5)

  1. Blood pressure / hydrostatic pressure;

  2. Small molecules / named example;

  3. Pass through basement membrane / basement membrane acts as filter;

  4. Protein too large to go through / large so stays behind;

  5. Presence of pores in capillaries / presence of podocytes;
• Some people who have diabetes do not secrete insulin. Explain how a lack of insulin affects reabsorption of glucose in the kidneys of a person who does not secrete insulin. (4)

  1. High concentration of glucose in blood;

  2. High concentration in tubule / in filtrate;

  3. Reabsorbed by facilitated diffusion / active transport;

  4. Requires proteins / carriers;

  5. These are working at maximum rate / are saturated;

  6. Not all glucose is reabsorbed / some is lost in urine;
• Explain the role of the loop of Henle in the absorption of water from the filtrate. (6)

  1. In the ascending limb sodium (ions) actively removed;

  2. Ascending limb impermeable to water;

  3. In descending limb sodium (ions) diffuse in;

  4. Descending limb water moves out / permeable to water;

  5. Low water potential / high concentration of ions in the medulla / tissue fluid;

  6. The longer the loop, the lower the water potential in medulla / tissue fluid;

  7. Water leaves collecting duct

  8. By osmosis / down water potential gradient;
• Explain the role of ADH in the production of concentrated urine. (4)

  1. When water potential of the blood too low;

  2. Detected by receptors in the hypothalamus;

  3. Pituitary secretes / releases (more) ADH;

  4. ADH increases the permeability / recruitment of aquaporins / opens channels for water in collecting duct;

  5. More water is reabsorbed / leaves the nephron moves into the blood;

  6. By osmosis down the water potential gradient;
• Explain how urea is concentrated in the filtrate.

  1. Reabsorption of water / by osmosis
  2. At the proximal convoluted tubule
  3. At the collecting duct
  4. Active transport of ions / glucose creates gradient (in context)
• A person with diabetes may have a plasma glucose concentration greater than the threshold value for glucose reabsorption. Explain what causes this raised plasma glucose concentration.

  decrease in insulin production / receptors not responsive to insulin / membrane less permeable to glucose
• The glomerular filtration rate is the total volume of filtrate formed per minute. Explain the effect on the glomerular filtration rate of a large loss of blood from the body. (2)

  1. blood pressure decreased
  2. (less pressure) forms less filtrate
• Describe how ultrafiltration occurs in a glomerulus (3)

  • High blood / hydrostatic pressure
  • Two named small substances pass out e.g. water, glucose, ions, urea
  • (Through small) fenestrations in (capillary) endothelium
  • (And) through (capillary) basement membrane
• Thicker medulla means a longer loop of Henle, this means an increase in sodium ion concentration (in medulla)

  • therefore, water potential gradient maintained for longer, so more water reabsorbed by osmosis from loop and collecting duct
• Some desert mammals have long loops of Henle and secrete large amounts of antidiuretic hormone (ADH). Explain how these two features are adaptations to living in desert conditions. (6)


  • More water (from filtrate) reabsorbed
  • By osmosis
  • From collecting duct
  • Due to longer loop of Henle
  • For loop of Henle
  • Sodium ions absorbed from filtrate in ascending limb
  • Gradient established in medulla
  • ADH acts on collecting duct
  • Makes cells more permeable / inserts aquaporins in plasma membranes
• Selective reabsorption from the glomerular filtrate occurs in the proximal convoluted tubule. Explain two ways in which the cells of the proximal convoluted tubule are adapted for reabsorption. (2)


  • microvilli provide large surface area
  • carrier proteins (in membrane) for active transport
  • channel proteins for facilitated diffusion
  • specific carriers for specific molecules / sodium pumps
  • (many) mitochondria for active transport
• Describe what is meant by negative feedback (1)

  where a change triggers a response which reduces the effect of a change
• Water is removed from the body via the kidneys. Give two other ways in which water is removed from the body. (2)

  • breathing
  • sweating
• Explain how ADH increases the movement of water from the lumen of the collecting duct into the blood (4)

  1. ADH causes vesicles containing aquaporins / aquaporins to be inserted into membrane
  2. water enters cell through aquaporins
  3. by osmosis / down a water potential gradient
  4. (from cell) to capillary
• How does maintaining a constant body temperature allow metabolic reactions in cells to proceed with maximum efficiency?

  • Body temp. is optimum temp for enzymes
  • excess heat denatures enzymes / alters tertiary structure / alters shape of active site / enzyme so substrate cannot bind
  • reactions stop / slowed
  • too little reduces kinetic energy of molecules
  • fewer collisions / fewer ES complexes formed
• What is homeostasis? (1)

  Maintaining a constant internal environment