This free quiz has 10 real AQA A-level Biology exam questions on the kidney and osmoregulation (24 marks, about 30 minutes). It marks itself: the tick-box and table questions are marked for you, and for written answers you check your work against the real AQA mark scheme.
What the quiz covers (AQA 3.6.4.3)
how glucose and water are reabsorbed in the proximal convoluted tubule
matching statements to the glomerulus, convoluted tubules and collecting duct
how ultrafiltration happens in the glomerulus
why protein is not normally found in urine
features of tubule cells that allow rapid reabsorption of glucose
where ADH is released and how it affects the collecting ducts
why glucose appears in the urine in untreated diabetes, and how a drug that blocks ion absorption increases urine volume
explaining how the thickness of the medulla affects urine concentration
How to use it
Write each written answer in full before you open the mark scheme, then tick only the points you really made. Give full names, such as proximal convoluted tubule and posterior pituitary, because abbreviations and half-names lose marks. Whenever water moves, say which way it goes and that it moves by osmosis.
Where students lose marks (from AQA examiners’ reports and mark schemes)
Each point below is followed by wording that gained marks.
Through gaps, not cells. Some students had small molecules crossing the cells of the capillary wall, or gave the cells or the basement membrane holes. Less successful answers wrote “small molecules” without naming any, and many described the afferent and efferent arterioles, which are not part of the glomerulus.
✔ Gains credit: named small substances, such as water, glucose, ions and urea, pass out through gaps (pores or fenestrations) in the capillary endothelium and then through the basement membrane.
The basement membrane. Answers that just said “membrane”, capillary, endothelium or glomerulus missed the mark, and some thought there are no proteins in the blood, only amino acids. A common wrong idea was that protein in urine comes from proteins not being reabsorbed.
✔ Gains credit: plasma proteins are too large to pass through the basement membrane, so if the basement membrane is damaged, proteins can pass into the filtrate.
Features of the cells. The weakest answers described the tubule rather than its cells, e.g. “one cell thick” or “good blood supply”, and some confused microvilli with villi. Only the better answers said that “many” proteins or organelles are present, and leaving it out was penalised.
✔ Gains credit: microvilli (or a folded cell-surface membrane) give a large surface area, and the cells have many of each feature, such as many ribosomes to make carrier and channel proteins.
Glucose in urine. Fewer than 3% of students gained all three marks. Many wrote a “high amount” or “high level” of glucose instead of a high concentration, said “no glucose” is reabsorbed, or said carriers are “used up”.
✔ Gains credit: a high concentration of glucose in the blood or filtrate means not all of it is reabsorbed, because the carrier or co-transport proteins are saturated (working at their maximum rate).
Loop of Henle and medulla. Most students didn't link a thicker medulla to a longer loop of Henle, and some wrote about a long diffusion pathway. Many wrote “ions” rather than sodium ions, had water moving into the loop instead of out, or left out osmosis.
✔ Gains credit: a thicker medulla means a longer loop of Henle, so more sodium ions are moved out into the medulla; the water potential gradient is maintained, so more water is reabsorbed out of the filtrate by osmosis.
Posterior pituitary. Only 30% of students named the right gland. The two most common errors were leaving out “posterior” or naming the hypothalamus.
✔ Gains credit: ADH is released into the blood by the posterior pituitary.
ADH and aquaporins. Many students had water moving in the wrong direction, into the filtrate, mentioned aquaporins without saying they go into the membrane, or didn't mention osmosis. Only 23% gained full marks.
✔ Gains credit: ADH stimulates the addition of channel proteins (aquaporins) to the cell-surface membrane, increasing permeability so more water leaves the filtrate and enters the blood by osmosis.
Keep practising
The other AQA 3.6 self-marking quizzes: Stimuli and receptors · Nervous coordination · Muscle contraction · Blood glucose
Next, topic 3.7: the inheritance quiz
The AQA topic index
weekly AQA group classes: Year 12 on Tuesdays at 5.15pm, Year 13 on Wednesdays or Thursdays at 6.30pm
Questions © AQA, from past A-level and AS Biology papers, with their mark schemes and examiners’ reports.