Responding to the Responding to the external environmentexternal environment

Responding to the Responding to the external environmentexternal environment

Animals and plantsAnimals and plants(light)(light)

The eye• http://www.99mai

n.com/~charlief/Blindness.htm

Location and protection

• Located in the orbits.

• Protection – bony ridges of the orbit and eye lids

• Lachrymal gland.• Conjunctiva.

retina

Rods and cones• Transducers and are

sensitive to different light stimuli.

• Rods - _____ light intensity.

Pigment - rhodopsin• Cones - ___, ___, &

_____ light.Pigment – iodopsin.

Rods• Evenly distribution.• Rhodopsin is found

in the outer segment – the lamellea.

• Mitochondria is needed for the resynthesis of rhodopsin.

Rhodopsin

• Made from opsin (a protein) and retinal (derived from Vit A).

• Retinal – cis and trans form. In light it changes to the trans form.

• A generator potential forms – hyperpolarisation.• Na is pumped and the membrane becomes less

permeable so Na can’t re-enter (-ve charge).

• Rhodopsin breaks down quickly, but time some time to resynthesis. The cells are bleached.

Cones - colour• Fewer vesicles.• Contain iodopsin (3 forms) –

trichromatic theory.• Higher concentration around

fovea.• Different synapse structure.

synapses

Detecting light in plants

• Phytochrome pigment