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KATRIN_1 [288]
3 years ago
8

Which describes oxygen content as Earth evolved over time? Oxygen levels sharply declined about 400 million years ago. Oxygen le

vels stay above 15 percent starting 200 million years ago Oxygen levels remain below 5 percent starting 1000 million years ago. Oxygen levels raise significantly between 1000 and 700 million years ago.
Biology
2 answers:
lora16 [44]3 years ago
5 0

Answer:

b

Explanation:

tankabanditka [31]3 years ago
4 0

the correct answer is b. i just took the quiz

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In which case would facilitated diffusion be needed?
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Answer:

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Carrier proteins - exist in two conformations, altered by high affinity binding of the transported molecule. Moves material in either direction, down concentration gradient (facilitated diffusion). EXAMPLE: GluT1 erythrocyte glucose transporter.

Channel proteins - primarily for ion transport. Form an aqueous pore through the lipid bilayer. May be gated. Moves material in either direction, down concentration gradient (facilitated diffusion). EXAMPLES: Voltage-gated sodium channel, erytrhocyte bicarbonate exchange protein.

This might be helpful... because I don't know anything about facilitated diffusion.

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