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Biology · May / June 2022 · Paper 42 · Question 3

0610

As printed in the paper

The question as text

The eye is adapted for focusing on near and distant objects. Fig. 3.1 shows the parts of the eye involved in focusing. The eye is focused on a distant object. cornea Fig. 3.1

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  • 3(a)(i)[1]

    refraction ;

  • 3(a)(ii)[3]

    any three from:

    ciliary muscles contract ;

    tension in suspensory ligaments decreases ;

    lens becomes more convex ;

    causing more refraction ;

  • 3(b)(i)[4]

    any four from:

    rods / cones, are light receptors OR detect / respond / sensitive, to light ; rods:

    sensitive to / function in, light of low intensity OR used for night vision ; provide black and white vision ;

    cones:

    sensitive to light of high intensity ;

    ref. to three different types of cone ;

    provide colour vision ;

    AVP ;

  • 3(b)(ii)[3]

    distribution across the retina

    receptor

    peripheral retina

    blind spot

    fovea rods

    many

    none

    none / few cones

    few

    none

    many

    ; ;

  • 3(c)(i)[1]

    only males, are colour-blind / colour-blindness is more common in males / no females are colour-blind / person 1 and 2 had two male colour-blind children (but no female colour-blind children) ;

  • 3(c)(ii)[2]

    XAXa ;;

  • 3(c)(iii)[5]

    1

    correct genotype for person 3, i.e. (X)A(X)a ;

    2

    correct genotype for person 4, i.e. XAY ;

    3

    correct gametes from the parental genotypes ;

    4

    correct offspring genotypes from their gametes / parental genotypes (in any order) ;

    5

    correct offspring correct probability ;

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