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Hormones: a message broadcast in the blood that only some cells can read questions
Exocrine and endocrine glands, the hypothalamus and the two lobes of the pituitary, why a peptide hormone needs a second messenger and a steroid hormone does not, adrenaline acting through cyclic AMP, negative feedback as a control principle with positive feedback contrasted, and how hormonal coordination compares with nervous coordination.
6 original questions · 22 marks · the hormones: a message broadcast in the blood that only some cells can read notes · Hormonal communication, plant responses and homeostasis
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Describe how adrenaline in the blood causes a liver cell to release glucose, naming the molecules involved in the order they act.
Mark scheme
- B1 adrenaline binds to a receptor on the outer surface of the cell surface membrane and does not enter the cell
- B1 binding changes the tertiary structure of the receptor, which activates adenylate cyclase on the inner face of the membrane
- B1 adenylate cyclase converts ATP into cyclic AMP, the second messenger
- B1 cyclic AMP activates a protein kinase, which phosphorylates and so activates the next enzyme in the chain
- A1 glycogen phosphorylase is activated and hydrolyses glycogen into glucose, which leaves the cell
Explain why a steroid hormone such as oestrogen can act directly on the genes of its target cell while a peptide hormone such as insulin needs a second messenger.
Mark scheme
- B1 a steroid hormone is lipid-soluble, so it diffuses straight through the phospholipid bilayer of the membrane
- B1 inside the cell it binds to a receptor and the hormone-receptor complex acts in the nucleus as a transcription factor, switching genes on or off
- B1 a peptide hormone is not lipid-soluble and cannot cross the bilayer, so it binds to a receptor on the outer surface of the membrane instead
- A1 the message must therefore be carried inwards by a different molecule made in the cytoplasm, and because every step of that chain is enzyme-catalysed the signal is amplified as it goes
Explain how negative feedback holds a variable such as blood glucose close to a set point, and explain why two antagonistic hormones give tighter control than one.
Mark scheme
- B1 a receptor detects a deviation of the variable from the norm
- B1 a coordinator, which may be a hormone, a nerve or both, carries the information to an effector
- B1 the effector brings about a response that moves the variable in the direction that removes the original deviation, which is what makes the feedback negative
- A1 one effector can only push the variable one way and then wait for it to drift back, whereas two antagonistic hormones correct in both directions and so correct faster
Compare nervous coordination with hormonal coordination, writing paired statements about the route the message takes, its speed, its target and how long its effect lasts.
A tumour of the anterior pituitary secretes thyroid-stimulating hormone continuously, whatever else is in the blood. Suggest why the concentration of thyroxine in this person's blood is much higher than normal, and suggest what has happened to the releasing factor secreted by their hypothalamus.
Name the hormone secreted by the adrenal medulla, and name the second messenger produced inside a liver cell when that hormone binds to its receptor.
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