Describe the role of the hormone glucagon in the control of blood sugar concentration. (6)
Binds to (specific) receptor;
On muscle / liver cell;
Activation of enzymes (in liver);
Hydrolysis of glycogen; Glycogenolysis:
(Facilitated) diffusion of glucose out of (liver cells) cells;
Increases blood glucose levels;
A diabetic person and a non-diabetic person each ate the same amount of glucose.
One hour later, the glucose concentration in the blood of the diabetic person was higher than that of the non-diabetic person. Explain why. (3)
1 Lack of insulin / reduced sensitivity of cells to insulin;
2 Reduced uptake of glucose by cells / liver / muscles; Penalise zero/no
3 Reduced conversion of glucose to glycogen;
Reabsorption of glucose takes place in the proximal tubule. Explain how the cells of the proximal tubule are adapted for this function. (2)
(Many) mitochondria provide ATP/energy for active transport; (Many) carrier proteins for active transport/channel proteins for facilitated
diffusion; Microvilli/brush border provide large surface area (for absorption);
In some forms of kidney disease, proteins from the blood plasma are found in the
urine. Which part of the nephron would have been damaged by the disease to cause proteins from blood plasma to be present in the urine? Explain your answer.
1 Glomerulus / Bowman’s capsule / renal capsule;
2 Basement membrane;
3 Proteins are large (molecules)/ proteins cannot normally pass through filter / proteins
can only pass through if filter damaged;
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
Explain the role of the loop of Henle in the absorption of water from the filtrate. (6)
- In the ascending limb sodium(ions) actively removed;
- Ascending limb impermeable to water;
- In descending limb sodium(ions) diffuse in;
- Descending limb water moves out/permeable to water;
- Low water potential/high concentration of ions in the medulla/tissue
fluid; - The longer the loop/the deeper into medulla, the lower the water
potential in medulla/tissue fluid; - Water leaves collecting duct/DCT;
- By osmosis/down water potential gradient;
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. (5)
- More water (from filtrate) reabsorbed / returned to blood / less lost in urine;
- By osmosis;
- From collecting duct / from end of second convoluted tubule;
- Due to longer loop of Henle;
For loop of Henle, maximum 2 marks: - Sodium / chloride ions absorbed from filtrate in ascending limb;
- Gradient established in medulla / concentration of ions increases down medulla;
For ADH, maximum 2 marks: - Acts on collecting duct / distal convoluted tubule / second convoluted tubule;
- Makes cells more permeable / inserts aquaporins in plasma membranes
Explain how the loop of Henle maintains the gradient of ions which allows water to be reabsorbed from filtrate in the collecting duct (5)
(epithelial cell) of tubule cells carry out active transport;
transport chloride / sodium ions out (of filtrate);
against concentration gradient;
into surrounding tissue / tissue fluid;
creates / maintains water potential gradient for water reabsorption;
countercurrent multiplier;
Explain how ADH is involved in the control of the volume of urine produced. (4)
if water potential of blood falls, detected by receptors in hypothalamus;
leads to more ADH released from pituitary gland. ADH makes cells of collecting duct / distal convoluted tubule more permeable to water;
(accept DCT)
water leaves filtrate by osmosis;
smaller volume of urine produced
