1. Responding to the external environment Animals and plants (light)

2. The eye http://www.99main.com/~charlief/Blin dness.htmhttp://www.99main.com/~charlief/Blin dness.htm

4. Location and protection Located in the orbits. Protection – bony ridges of the orbit and eye lids Lachrymal gland. Conjunctiva.

5. retina

6. Rods and cones Transducers and are sensitive to different light stimuli. Rods - _____ light intensity. Pigment - rhodopsin Cones - ___, ___, & _____ light. Pigment – iodopsin.

7. Rods Evenly distribution. Rhodopsin is found in the outer segment – the lamellea. Mitochondria is needed for the resynthesis of rhodopsin.

8. 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.

9. Cones - colour Fewer vesicles. Contain iodopsin (3 forms) – trichromatic theory. Higher concentration around fovea. Different synapse structure.

10. synapses

11. Detecting light in plants Phytochrome pigment