Help please.

[RHINO7]

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I require information on this question, please help---

Compare the visual acuity of two named mammals and relatethis to their way of life.

[jannny]

I dont recall this being in the comm syllabus, mostly it says to compare mammals to another invertebrate etc.

but anyway I'll have a go

Humans - high visual acuity due to a large presence of rods and cones (15million) in the retina. They need high visual acuity to distinguish which food is edible or not, as well as escaping from predators (before).

Dogs - low visual acuity, mostly have rods. They do not really depend much on their eyesight (someone correct me if im wrong) and mostly use their hearing on locating objects.

[Buiboi]

^^^ i think its more based on their sense of smell rather than hearing?

insects have poor visual acuity compared to humans, such that they see things as a mosaic image, whereas humans view images that are inverted, focused and altered, worms ahve the poorest visual acuity and dont really produce images.

humans consist of rods and cones for colour vision, movement detection, howver bees have a much better reaction to movement due ot he thousands of ommatidium = 1000's of lenses, worms have eyecups =ocelli which doesnt form an iamge but uses eyecup to idntify where the light is coming from (direction) and its intesnity...therefore its visual acuity is poor

[RHINO7]

not quite sure about this one, should i just discuss rods and cones?

why is it that animals that are active at night do not usually have colour vision?

[Buiboi]

Originally Posted by RHINO7

not quite sure about this one, should i just discuss rods and cones?

why is it that animals that are active at night do not usually have colour vision?

animals active at night dont rely on cones, but on rods, cones are the photorecpetors responsible for colour vision in order for cones to be triggered there needs to be light, your rods are responsible for 'night vision' hence requires very little light. so at night you use rods not cones, what colour can be seen if there is little or no light at all.

i forgot to add from last post that , humans have more photorecptors than the fly, hence have a better visual acuity...its more concentrated, because the fly compound eyes have thousands of ommatidiums compared to the millions of rods and cones in human eye.

[yoakim]

Also, it's much harder for cones to get stimulated by the light to create an electrochemical signal to the neurones. However, rods are VERY SENSITIVE TO LIGHT hence their suitability in darkness where there is little light.

A good practical example is this: During night, when you try to look at the stars directly, its hard, because in the middle of your retina is the fovea (no rod cells there). But when you look about 1 cm to the left of the star, you see it clearer because the light isnt going into your fovea but on the peripheral area where you rods are - hence rods are more suitable during night time.