1. What is meant by negative feedback ?
Answer
A change in an internal environment factor away from the norm is detected and brings about a corrective mechanism that brings the factor back to the norm.
2. The mechanism of action of glucagon and adrenaline is described using a second messenger model. Explain what this means.
Answer
They do not have a direct effect on liver cells. Instead, they bind to specific receptors on the cell surface, which triggers a series of reactions inside the cell. This leads to the activation of adenyl cyclase, an enzyme that converts ATP into cyclic AMP (cAMP). The cAMP then acts as a second messenger by activating protein kinase, which catalyses the breakdown of glycogen into glucose phosphate, ultimately increasing blood glucose concentration.
3. The ascending limb of the loop of Henle ensures that water is lost by osmosis from the filtrate in the descending limb. Explain how.
Answer
Na+ and Cl- ions are actively transported out of the ascending limb, which lowers the water potential of the medulla. As a result, water moves out of the descending limb by osmosis.
4. The figure below shows a single nephron. Name processes X, Y and Z.
Answer
X = osmosis,
5. Processes Y and Z enable Process X to occur. Explain how.
Answer
Ions are actively transported or diffuse into the medulla, lowering its water potential. Only the descending limb of the loop of Henle is permeable to water, so water moves out by osmosis into the medulla from the descending limb.
6. Proteins are not present in the urine of a healthy person. Explain why.
Answer
Too large to pass through basement membrane.
7. Explain how contraction of the muscles in the walls of arteries and arterioles increases blood pressure.
Answer
As muscles contract, the lumen of arteries and arterioles becomes smaller. The same blood volume is then forced into a smaller space.
8. Explain how stimulating sodium ion reabsorption in the kidney increases blood pressure.
Answer
Stimulating sodium ion reabsorption increases the concentration of sodium ions in the blood, which lowers its water potential. As a result, more water enters the blood by osmosis, increasing blood volume and therefore raising blood pressure.
9. Diabetes insipidus is caused by lack of antidiuretic hormone (ADH). People with this condition often feel thirsty and need to urinate frequently. What is the cause of these symptoms ?
Answer
Feeling thirsty - Too much water excreted from dct/collecting duct. Lowers water potential of blood.
Needing to urinate frequently - Less water reabsorbed from filtrate.