Test review

Question 1

1c. Describe how mutations in proto-oncogenes and tumour suppressor genes can lead to the formation of a secondary tumour. [7]

Answer 1

-proto-oncogenes - genes that code for proteins that stimulate normal cell division.
-Mutations can convert proto-oncogenes into oncogenes, leading to overexpression
-tumour suppressor genes encode proteins that inhibit cell division
-mutations in tumour suppressor genes result in no
protein being translated
-(secondary tumor) a primary tumour forms at the original mutation site

Question 2

2a. Outline the adaptations of mangrove trees that allow them to thrive in saline, anoxic and unstable soils. [3]

Answer 2

specialised glands on the leaves actively remove excess salt
-aerial roots grow upward from submerged roots to access atmospheric oxygen
- stilt roots anchor the tree and spread out widely

Question 3

2c. Discuss the structural adaptations of the nephron for excretion and osmoregulation in mammals. [8] (Strengths)

Answer 3

-LOH’s descending limb allows water to exit the filtrate passively,
-microvilli in the PCT increase surface area for reabsorption of useful substances
-ADH increasing nephron’s ability to finely tune water

Question 4

2c. Discuss the structural adaptations of the nephron for excretion and osmoregulation in mammals. [8] (weakness)

Answer 4

-ascending limb of the loop of Henle uses energy-intensive active transport to move
Na+ and Cl- ions into the medulla
-high metabolic cost due to energy demands of active transport in PCT
-unregulated passive water loss in the descending limb may reduce control over water balance in some environments

Question 5

3a. Compare and contrast the structures of cellulose, starch and glycogen. [4]

Answer 5

ALL are polysaccharides

ALL are made from glucose monomers

different: glycogen is more highly branched
different: polymers of cellulose form many hydrogen bonds with each other WHEREAS starch and glycogen do not