08 Tys Dec Hol (sci) T8 Ms

1/12/09

TYS Unit 9.1 Struct Q1 (ai) Lens ii) To refract and focus the light rays onto the retina

Sci Bio it9.1 y a d i l Dec Ho ework T8 Un m TYS Ho

iii) Cornea iv)

09

Jan 20

TYS Unit 9.1 Struct Q1 (b) A

TYS Unit 9.1 Struct 2 (a)

(ci) Iris ii) In bright light, the circular muscles of the iris contract [0.5] & the radial muscles relax [0.5]; This causes the pupil to constrict, preventing too much light from entering the eye;

TYS Unit 9.1 Struct 2 (ci) Yellow spot/ fovea of the retina; ii) Lens becomes thinner; and less convex; iii) Ciliary muscle relax, suspensory ligaments become taut; and pull on the elastic lens to become thinner and less convex;

(bi) Retina ii) The sensory neurones in the optic nerve conduct nerve impulses from the photoreceptors in the retina to the brain in this reflex action.

TYS Unit 9.1 Struct 3 (ai) A-retina

B-Blind spot

C-Iris

ii) C (bi) The lens refracts and focuses light rays onto the retina; Changes in the curvature of the lens can alter the focal length of the lens (accommodation); To enable clear images of objects at varying distances to be formed on the retina clearly; (ii) Cornea

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1/12/09

TYS Unit 9.1 Essay Qn 1

  Light rays from a distant object are almost parallel whereas light rays from a nearby object are diverging;

  The rays are refracted by the cornea and the lens to focus onto the retina. Fine focusing to form a sharp image is done by the lens;

2.8A Q2(b)

  For distant objects, the ciliary muscles relax and the suspensory ligaments are pulled taut, pulling on the edge of the lens

  The elastic lens becomes thinner & less convex;

  For nearby objects, the ciliary muscles contract, which releases the pull on the suspensory ligaments

  The elastic lens becomes thicker & more convex;

  In both cases, the image is sharply focused onto the yellow spot/fovea of the retina.

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