A-LevelBiologyThe mitotic cell cycle9700/43 · May/June 2020 · Q29 Marks

Diabetes insipidus (DI) is a condition in humans that causes a person to have an excessive thirst, which leads to increased drinking. One form of DI is caused by a tumour in the region of the hypothalamus concerned with osmoregulation. Explain how a tumour develops in the hypothalamus.

(a)(i)Diabetes insipidus (DI) is a condition in humans that causes a person to have an excessive thirst, which leads to increased drinking. One form of DI is caused by a tumour in the region of the hypothalamus concerned with osmoregulation. Explain how a tumour develops in the hypothalamus.[2]
(a)(ii)Suggest how a tumour in the hypothalamus can lead to a person producing a large volume of dilute urine.[3]
(b)The nervous and endocrine systems of a mammal co-ordinate responses to changes in the internal and external environment. Table 2.1 compares some features of the nervous and endocrine systems. Complete Table 2.1. Table 2.1 feature | nervous system | endocrine system ---|---|--- signal | impulse | method of transmission of signal | | in blood type of communication | | chemical duration of effect | |[4]

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Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

[2] any two from:
1 uncontrolled mitosis / continuous cell cycle / cell cycle checkpoints not controlled ;
2 abnormal mass of cells formed;
3 no programmed cell death / no apoptosis / cells immortal ;
4 ref. mutation;
5 ref. tumour suppressor genes / (proto)oncogenes ;
[3] any three from:
1 ref. (effect on) neurosecretory cells in hypothalamus ;
2 production / synthesis, of ADH, decreases / stops;
3 idea of less ADH secreted (into blood) by posterior pituitary ;
4 collecting duct walls less permeable to water;
5 water remains in collecting duct / most water remains in urine ;
[4] signal: hormone;
method of transmission of signal: neurone / axon;
type of communication: electrical;
duration of effect: short term ; long-lasting;

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