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Biology questions help

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Rozalin:
Q1)
Explain why large animals cannot take in all the substances they need from outside the body through their skin?
Q2)
Red blood cells are unusual in not having a nucleus. Explain how this is an adaptation for their role in carrying oxygen and why they have a limited life??
Q3)
Why are valves important in veins but necessary in arteries?

Thaaaaaaaaanks in advance!  :)

@d!_†oX!©:
here you go,

1)Although these animals are large, they still are made up of millions of very small cells...these cells on their skin are mostly smaller than the substances that they have to intake, and so they have to take them through the mouth and then digest it to smaller compounds for them to be assimilated....in short, the substances are mostly big enough to not being able to pass through the skin cells by diffusion or even active transport....

2) Red blood cells not having a nucleus gives them more space for haemoglobin and thus their efficiency in carrying large amount of oxygen increases...so in this way it is an adaptation for their role in carrying more and more oxygen....now about having a short life...it is simply because of the fact that they do not have a nucleus..

3)In arteries, the blood is constantly flowing at a fast rate due to the pressure from the heart, and thus there is no problem of blood flowing backwards....But in veins, the blood flows from the body parts towards the heart, and there is no pressure so the blood moves very slowly and there is a chance of it back-flowing....thus to prevent back-flowing of blood there are valves present in veins....


hope you get the answers..if you need more explanation.....do write in and i'll provide as much help as possible from my side....

nid404:
Thanks adi.. :)

vanibharutham:
Im not quite sure the cells are smaller that substances needed for question1 ?


Surface area to volume ratio plays a vital part. In smaller organisms such as eukaryotes, the surface are to volume ratio is extremely large this allowing a large amount of area from which substances can diffuse into the cells. However, in large organisms, the surface area to volume ratio decreases. Diffusion would still take place but not at a rate fast enough to maintain the high metabolic needs of the organism.

Also, the skin is impermeable from outside due to keratin isnt it?

@d!_†oX!©:

--- Quote from: vanibharutham on December 10, 2009, 03:46:31 pm ---Im not quite sure the cells are smaller that substances needed for question1 ?


Surface area to volume ratio plays a vital part. In smaller organisms such as eukaryotes, the surface are to volume ratio is extremely large this allowing a large amount of area from which substances can diffuse into the cells. However, in large organisms, the surface area to volume ratio decreases. Diffusion would still take place but not at a rate fast enough to maintain the high metabolic needs of the organism.

Also, the skin is impermeable from outside due to keratin isnt it?

--- End quote ---
1) I am not sure if the bolded point you've made is correct or not....i dont think it happens that ways....diffusion cannot take place at all....
2) The keratin point is invalid in my opinion cuz acc. to my knowledge keratin is only part of our nails and hair, and not our skin....

Please correct me if i am wrong

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