Low light

Question 1

What is the range of visible light?

Answer 1

300-800nm

Question 2

Define Luminance/Radiance

Answer 2

amount of light emitted from an object, detected by a receiver of DIRECT light only

Question 3

Define Illuminescence/irradiance

Answer 3

amount of light falling on a surface (direct + scattered light) Unit: lumens per sq mtre.

Question 4

What is light attenuation?

Answer 4

Gradual loss of intensity
Three types: 
Spherical Spreading
Scattering
Absorption

Question 5

How is bioluminescence achieved?

Answer 5

LUCIFERIN - chemical reaction mediated by Luciferase
Expensive to produce
Less intense than sun

Question 6

How is coloured vision achieved?

Answer 6

Diffrent photoreceptors absorbing different wavelengths due to different visual pigments.
Receptors with overlapping sensitivities
Coloured oil droplets in photoreceptor cells act as filters

CONE:ROD RATIO GIVES INDICATION OF IMPORTANCE OF COLOUR VISION
Animals living in poorly lit environments often MONOCHROMATIC, colour blind

Question 7

What is a dichromat?

Answer 7

Two cone cells, most mammals

Question 8

What is a trichromat?

Answer 8

three cone types - humans, old world monkeys

Question 9

What is a tetrachromat?

Answer 9

Have 4 cone types - birds, turtles, some fish, butterflies

Question 10

How is a better resolution obtained?

Answer 10

Larger eyes - image spread over more photoreceptors
tighter packing photoreceptors
increase ratio cones:rods

Question 11

How is better sensitivity obtained?

Answer 11

Larger eyes = bigger pupils

increasing ratio of rods:cones

Question 12

What is light attenuation by scattering?

Answer 12

Light changing directions by various processes.
Reflection
Refraction
Diffraction
Releigh scattering - light path changes direction as it passes between media of different densities
light diffracted by small particles is dependent on wavelengths. i.e short wavelengths (blue), are scattered more than long (red) - hence why the sky is blue
larger particles produce frequency independent scattering

Question 13

Describe compound eyes

Answer 13

Each ommatidium accepts light from narrow angle
Diffraction through small lenses constrains resolution
to increase resolution, larger and more ommatidia
3 types:
apposition - high resolution, low sensitivity
superposition - low sensitivity, high resolution
neural superposition eye - high resolution and sensitivity

Question 14

Desribe eyes in cephelapod molluscs

Answer 14

Lack of rods and cones
have optic ganglion instead of optic nerve
Microvillar photoreceptors
Pigments different to vertebrates -

Question 15

What is an apposition eye?

Answer 15

compound eye where each ommatidium sheather by pigment cells . high resolution, low sensitivity.

Question 16

What is a superposition eye?

Answer 16

Compound eye where light leaks between some ommatidia - LOWER RESOLUTION HIGH SENSITIVITY.

Question 17

What is a neural superposition eye?

Answer 17

Compound eye where each ommatidium contain 7 rhabdoms.

Question 18

what are the adaptations of the colossal squid eyes?

Answer 18

nearly 3x diameter of any other animal, football size
spherical 2 part lens
ocular photophores - photophores contains symbiotic, bioluminescent bacteria
oxidation of LUCIFERIN

Question 19

What is a pit eye?

Answer 19

Primitive eye for simple spatial vision

Question 20

What are features of cup eyes?

Answer 20

poor resolution due to lack of focusing ability

cup filled with medium of highly refractive index

Question 21

What are features of an aquatic eye?

Answer 21

Protective cornea does not focus light, as cornea has same refractive index as water.