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Arlecino [84]
2 years ago
15

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
1 answer:
denis-greek [22]2 years ago
7 0

Answer:

Oxygen levels stay above 15 percent starting 200 million years ago

Explanation:

Atmospheric oxygen levels are related to the evolution on Earth and changes in geochemical cycles that involve climate variations.

The presence of O 2 and evolution of oxygen gave new opportunities to the life on Earth. Oxygen levels in atmosphere have fluctuated between 15% and 35% of atmospheric volume, since the start of the Cambrian period.

So, form the starting 200 million years ago, oxygen level stay above 15 percent and the correct option is "B".

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When a muscle cell receives a signal from a motor neuron, every sarcomere within that muscle cell is activated. The signal moves from the motor neuron to the muscle cell by crossing the synapse. When acetylcholine binds the sodium enters the T tubules and this causes calcium to be released from the sarcoplamic reticulum. Calcium binds to tropomyosin, which allows actin to bind to myosin and each sarcomere contracts. There is nothing and no way to separate individual sarcomeres. They are all activated together.  
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3 years ago
Blood tests can be used to check a person’s blood glucose and hormone levels. The tabular column given below shows the result of
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Answer:

See the answer below

Explanation:

a) From the table, the glucose level of person 1 (5.4) was less than the glucose level of person 2 (5.6) after 12 hours of fasting. The glucose level of person 1  falls within the normal fasting blood sugar range (3.9 to 5.6 mmol/L) while that of person 2 was borderline higher than normal.  

b) Also from the table, the glucose level of person 3 (12.1) was greater than that of person 1 (6.4) when the glucose levels were measured 2 hours after drinking 75 g glucose. Normal after-meal sugar level ranges between 6 and 10.9 mmol/L. Hence, person 3 appears to be diabetic while person 1 seems normal.

c) The hormone that person 3 cannot produce is insulin.

<em>Insulin helps lower blood sugar levels when necessary by signalling the liver to convert the excess sugar to glycogen which is then stored in the body. When the blood sugar falls below the normal range, another enzyme, glucagon, signals the liver to convert the glycogen back to sugar to compensate for the decrease. </em>

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3 years ago
.Specific processes must take place within the cell for protein synthesis to occur. The processes that take place within a cell
natta225 [31]

Answer:

An mRNA template is used to create an amino acid chain.

Explanation:

Transcription is the first step in the protein synthesis process. Translation is the second.

Overall, the central dogma of biology is DNA->RNA->protein.

Transcription is that first step, DNA to RNA, and translation is RNA to protein: think of it like nucleic acids can just be transcribed, but nucleic acid to protein is like a whole different language, so it has to be translated. So the correct answer here is that mRNA is used to make amino acid chain (aka protein), which happens only in translation.

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Why does dna need to replication short answer please
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5 0
2 years ago
Which of the following is an example of diffraction?
makkiz [27]

<u>Answer:</u>

You try to pick up a shell in the water but it isn't where it appears to be is an example of diffraction

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Diffraction refers to the light bending that happens as the light passes about the edge of some object. How much bending takes place is found by the size of wavelength of light relative to that of opening. If the opening is larger than the wavelength of light, then bending will not be noticeable.

Since, light gets diffracted due to water hence the shell kept inside the water appears to be at a different position than where it actually is

8 0
3 years ago
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