CH15 DETECTING THE ENVIRONMENT

Eye

Sclera: white, tough

Conjunctiva

Cornea

Choroid

Iris

Pupil : light enter eye

Retina

Lens: refracts and focuses light on retina

Ciliary body: change lens thickness by constrict/relax ciliary muscles

Suspension ligament: connects lens to ciliary body

Aqueous humour: supplies oxygen and nutrients to conjunctiva, lens and cornea, reflects light and maintains shape of eyeball

Vitreous humour: reflects light and maintains shape

Seeing

Process

image formed on retina --> light-sensitive cells stimulaed by light, send nerve impulses along optic nerve to visual centre
Brain interprets upright image of object

amount of light

Bright: circular muscles contract, radial muscles relax, pupil contricts
Dim: circular muscles relax, radial muscles contracts, pupil dilates

Eye accommodation

Near objects: Circular ciliary muscles contract, suspensory ligaments becomes slackened, lens become more convex
Distant objects: circular ciliary muscles relax, suspensory ligaments are pulled, lens become less convex

Ear

Outer ear

Pinna: connects sound wavecs of sound vibrations
auditory canal: directs sound waves to the eardrum
eardrum: converts sound waves to sound vibrations

Middle ear

Ear bones: amplify and transmit vibrationsfrom eardrum to the oval window
Oval window:trnasmits vibrations from ear bones to inner ear
Eustachian tube: equalizes pressure between the middle ear and atmosphere

Inner ear

Semicircular canals: detect direction of head movement
Cochlea

Light detection by plants

Phototropism

Unilateral light
shoots grow towards light - positively phototropic: leaves obtain max amt of light
roots grow away from light - negatively phototropic: better anchorage