Edexcel IAL Biology 2.16 Cystic fibrosis gene mutation effects

Trace the answer from changed CFTR structure to chloride movement and water potential, then connect viscous mucus to the named airway, duct or reproductive outcome.

[Maximum number: 6]

Cystic fibrosis is an inherited disorder.

The diagrams show a cross section through a trachea from a person without cystic fibrosis and from a person with cystic fibrosis.

Figure for Question 2.16—Cystic fibrosis gene mutation effects question 1 — Edexcel A-Level Biology AS

*(ii) Explain why cystic fibrosis causes the differences shown in the diagrams.

*8(a)(ii)

Indicative content:

Descriptions of diagrams (D points)

- reduced diameter of lumen (in person with CF)

- thicker or inflamed muscle layer (in person with CF)

- more mucus (in person with CF)

Cystic fibrosis (C points)

- CF results in the production of very \{sticky / thick\} mucus (credit this point only once)

- CF is due to a \{mutation in the CFTR gene / faulty CFTR allele\}

- (resulting in) \{the CFTR protein not functioning properly / abnormal or defective CFTR protein / abnormal channel proteins / CFTR channel blocked\}

- this affects transfer of chloride ions out of cells

- ( $\mathrm{Cl}^{-}$ accumulate in cells so) \{water moves out of mucus / water remains in cytoplasm\} / mucus is dehydrated \}

Change in lumen diameter (L points)

- CF results in the production of very \{sticky / thick\} mucus (credit this point only once)

- diameter of lumen in patient with CF is reduced

- because the mucus builds up

- (because the) cilia cannot move / beat (idea of cilia normally clearing mucus)

- (because the) cilia cannot move mucus away (it is too thick) (credit this only once)

- Inflammation of muscle (narrows lumen) (credit this only once)

Inflammation (I points)

- cilia cannot move mucus away (it is too thick) (credit this only once)

- mucus (is very sticky and) traps bacteria

- bacteria have ideal growth conditions (in mucus)

- bacteria can cause (chest) infections

- CF characterised by coughing \{to remove mucus / as a result of infection\}

- \{coughing / infection\} damages \{cells / tissues\} (lining airways)

- (leading to) inflammation of muscle (credit this only once)

(6)

Level

Marks

0

No awardable content

1

1-2

Level 1: description of diagrams

1 mark: one D or one C point

2 marks: second D or C point

2

3-4

Level 2: explanation of either change in diameter of lumen or inflammation linked to CF

3 marks: three L points or 3 I points

4 marks: as 3 marks plus additional C point

3

5-6

Level 2: explanation of both change in diameter of lumen and inflammation linked to CF

5 marks: three L points and 3 I points

6 marks: as 5 marks plus additional C point

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2.16—Cystic fibrosis gene mutation effects question 1