O-LevelBiologyCoordination & Response5090/21 · Oct/Nov 2023 · Q410 Marks

A sneeze can be triggered by dust irritating receptor cells in the lining of the nose or throat. During a sneeze, air is exhaled from the lungs with some force and the eyelids close. [Figure 4.1]

(a)(i)Suggest how the closure of the eyelids during a sneeze is coordinated.[4]
(a)(ii)Suggest how sneezing can result in disease transmission.[2]
(b)(i)A sudden increase in light intensity can trigger sneezing in some people. This is called photic sneezing. It is estimated that 18–35% of the human population can be triggered to sneeze by an increase in light intensity. The genetic basis for photic sneezing is not fully understood but it is thought that a dominant allele is involved. Give the name of this type of variation in a population and explain your answer. type of variation explanation[2]
(b)(ii)Describe what is meant by the term dominant allele.[2]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2023). The mark or mark type is shown in brackets.

[4] 4(a)(i) any four from: impulse in sensory neurone ; passes to CNS / brain; relay neurone ; motor neurone to effector/ muscle ; contraction of muscle closes eyelid ;
[2] 4(a)(ii) expelled air contains pathogen / bacteria / viruses ; breathed in by another person/lands on another person / taken in from contaminated surfaces;
[2] 4(b)(i) discontinuous ; only two phenotypes / sneeze or don't sneeze / no intermediates / caused by genes only ;
[2] 4(b)(ii) dominant: always expressed AW ; allele: alternative form of a gene / variation of a gene AW ;

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