Biological functions of many plants and animals vary in cycles that

It is not clear what is meant by line 2-5. However I would presume (because the OA is E) that the hypothesis is: "alteration in the intensity of incident light is the stimulus that controls these biological rhythms."

Option E states the even under constant light intensity the biological rhythm follows the day-night cycle (and NOT the light intensity, if the rhythm followed light intensity the rate of photosynthesis would not change).

Following is a frequently used logic chain in GMAT:
Hypothesis: X causes Y.
Evidence: Z causes Y.
Therefore the evidence weakens / contradicts the Hypothesis.

Here,
X = alteration of light intensity
Y = biological rhythm
Z = day-night cycle

Stated Hypothesis: Intensity of Incident light has direct relation to the biological rhythms.

The answer choice that weakens the hypothesis will introduce facts that varying intensity also produces the same rhythms effect or same light intensity produces varying rhythms.

(A) Human body temperature varies throughout the day, with the maximum occurring in the late afternoon and the minimum in the morning. [ Yes, supports the hypothesis – eliminate it]

(B) While some animals, such as the robin, are more active during the day, others, such as mice, show greater activity at night [ Direct or inverse relation – no effect]

(C) When people move from one time zone to another, their biological rhythms adjust in a matter of days to the periods of sunlight and darkness in the new zone. [Irrelevant – When biological rhythms get adjusted – eliminate it]

(D) Certain single-cell plants display daily biological rhythms even when the part of the cell containing the nucleus is removed. [irrelevant – eliminate it]

(E) Even when exposed to constant light intensity around the clock, some algae display rates of photosynthesis that are much greater during daylight hours than at night. [Hold it]

Answer: E

Biological functions have a 24 hour rhythm. It means that every 24 hrs, one would expect a similar phase. For example, if a certain species sleeps in the afternoon at 3, one would expect it to sleep every day in the afternoon at 3. If it hunts at 10 in the morning, one would expect it to hunt every day at 10 in the morning (approximately, of course!)

Hypothesis - Alteration in the intensity of incident light is the stimulus that controls these daily biological rhythms
When incident light is higher, they do certain activities, when lower, they do other activities. The amount of light controls their biological functions.

What can be evidence to contradict the hypothesis?
If we find that even when the amount of light remains the same, they carry on with the 24 hour rhythm, then we can say that the hypothesis is not true. We have to show that amount of light falling does not control the biological functions.

(A) Human body temperature varies throughout the day, with the maximum occurring in the late afternoon and the minimum in the morning.

Doesn't contradict. It just gives us the daily rhythm of human body's temperature. It lights up in the morning so temperature starts rising and reaches maximum by later afternoon. Thereafter, intensity of light starts reducing so body temperature starts falling and keeps falling throughout the night and reaches minimum by morning. Then it starts rising again. Or some such explanation.

(B) While some animals, such as the robin, are more active during the day, others, such as mice, show greater activity at night.

Again, gives us the daily rhythm of robin's activity. It could be related to amount of light.

(C) When people move from one time zone to another, their biological rhythms adjust in a matter of days to the periods of sunlight and darkness in the new zone.

How the body adjusts to sudden changes in the variations in light is irrelevant.

(D) Certain single-cell plants display daily biological rhythms even when the part of the cell containing the nucleus is removed.

What role nucleus has to play, we don't know. If we were told that the nucleus is the one that senses light and the rest of the plant does not, then this would be contradicting our hypothesis. But we don't that anything about nucleus and light. Hence, not correct.

(E) Even when exposed to constant light intensity around the clock, some algae display rates of photosynthesis that are much greater during daylight hours than at night.

Correct. Here we are keeping the light intensity constant. Still we are seeing the daily rhythms. This means the daily rhythms exist not because of changing light intensity but some other reason. This contradicts our hypothesis.

Answer (E)
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Doesn't it explain that the livings actions' change is related with light therefore related with timing?

The official answer is E, yet about the logic I did not get anything. In E it explains algea is effected by sunlight so it does show many reactions in daylight than night. So if the question asks us to undermine not support the conclusion. There has to lie another logic.

In simple terms you need an option that would show that biological functions are not dependent on sun light as told in the arguememt. If you see carefully, option E states that even on giving light for 24 hours .. algae were active during the day and not at night time.. hence it shows that sunlight is not the factor. Hence answer E.

Please give kudos!

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Biological functions of many plants and animals
vary in cycles that are repeated every 24 hours. It is
tempting to suppose that alteration in the intensity
of incident light is the stimulus that controls
these daily biological rhythms. But there is much
evidence to contradict this hypothesis.

Which of the following, if known, is evidence that contradicts the hypothesis stated in lines 2-5 above?

(A) Human body temperature varies throughout the day, with the maximum occurring in the late afternoon and the minimum in the morning.

- This option talks about the temperature impact on human body and nowhere mentions the impact of the light, hence this option is irrelevant.

(B) While some animals, such as the robin, are more active during the day, others, such as mice, show greater activity at night

- Once again, this option talk about day and night but we cannot conclude that light is playing a role in this behaviour. Hence, B is irrelevant too.


(C) When people move from one time zone to another, their biological rhythms adjust in a matter of days to the periods of sunlight and darkness in the new zone.
- Time zones is completely out of Scope.


(D) Certain single-cell plants display daily biological rhythms even when the part of the cell containing the nucleus is removed.
- Talks about biological rhythms but does not mention anything about light, once again out.


(E) Even when exposed to constant light intensity around the clock, some algae display rates of photosynthesis that are much greater during daylight hours than at night.

- This option is clearly taking into consideration the impact of light. It definitely weakens the argument.

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Read the second part of the question carefully, "alteration" in the intensity...reason for the change in biological rhythms.
so we are concerned with the change in light intensity, be it any light.

option E clearly states that, even after providing "constant light intensity" exposure to algae, rates of photosynthesis (biological rhythms)...greater during daylight hours( we are speaking only of hours, the light intensity is still constant) than at NIGHT( whoa!! there is a variation in biological rhythms!!...who the hell did it, definitely not light intensity coz that was kept constant throughout!)
whoa!! again hypothesis overruled

hope you understood it.

please give a kudos if you understood!!:)

GMATNinja could you give an explanation for option B?
Is it because B doesn't say anything about the intensity of the light, rather just talks about the light in the day and night? The intensity could vary or might remain the same, is that a good reason to reject B?

(B) While some animals, such as the robin, are more active during the day, others, such as mice, show greater activity at night.


I initially chose B but couldn't find any good explanations for not choosing B under this problem.

Here is what I think: yes, B talks about varied intensity of light (morning and night). However, the different activity levels on robin and mice might be due to other reasons which is not talked about in this problem. Therefore, B is not a strong answer.

If we have to make this answer fit the best answer choice, we could change the stimulus to a specific animal such as mice which experience different intensity of light. And B would be mice show greater activity at night. Then B would probably work because it is talking about a specific animal (conditions are the same, only the results are different, and this would offer a counterexample. If the conditions are not even the same, it is not comparable)
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Biological functions of many plants and animals vary in cycles that are repeated every 24 hours. It is tempting to suppose that alteration in the intensity of incident light is the stimulus that controls these daily biological rhythms. But there is much evidence to contradict this hypothesis.

Which of the following, if known, is evidence that contradicts the hypothesis stated in lines 2-5 above? (Bolded)

Premise: biological functions vary in cycles
Conclusion: change in the intensity of light --> change in biological rhythms
Possible weaken choice: change in intensity of light doesn't change biological rhythms


(A) Human body temperature varies throughout the day, with the maximum occurring in the late afternoon and the minimum in the morning.

the conclusion talks about light. A has nothing to do with light.
If someone has to say that afternoon and morning have different intensity of light, some people like me have no idea how to compare the intensity of light between afternoon and morning! (If you do, try not to bring your knowledge into the problems because that might affect your judgement / make assumptions)

(B) While some animals, such as the robin, are more active during the day, others, such as mice, show greater activity at night.

I initially chose B but couldn't find any good explanations for not choosing B under this problem.

Here is what I think: yes, B talks about varied intensity of light (morning and night). However, the different activity levels on robin and mice might be due to other reasons which is not talked about in this problem. Therefore, B is not a strong answer.

If we have to make this answer fit the best answer choice, we could change the stimulus to a specific animal such as mice which experience different intensity of light. And B would be mice show greater activity at night. Then B would probably work because it is talking about a specific animal (conditions are the same, only the results are different, and this would offer a counterexample. If the conditions are not even the same, it is not comparable)

(C) When people move from one time zone to another, their biological rhythms adjust in a matter of days to the periods of sunlight and darkness in the new zone.

This choice is saying: the rhythms will self-adjust to sunlight/darkness (different intensities). It doesn't necessarily means that intensity causes the changes in rhythms. However, if someone insists that causal relationship, it can only strengthen the conclusion.

(D) Certain single-cell plants display daily biological rhythms even when the part of the cell containing the nucleus is removed.

Does removed nucleus have anything to do with light? Nope.

(E) Even when exposed to constant light intensity around the clock, some algae display rates of photosynthesis that are much greater during daylight hours than at night

"constant" is key here. Under constant intensity, photosynthesis still have patterns --> different conditions (conclusion: different intensity, choice: same intensity) same results (rhythms exist) lead to a correct answer.
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The hypothesis is that alteration in the intensity of incident light is the stimulus that controls these daily biological rhythms.

If the hypothesis were true, we'd expect cyclical biological functions in plants and animals to be controlled by alternation in the intensity of natural light in their environment.

First off, it's not clear to me from your post whether you are trying to eliminate (B) because it supports the hypothesis or you are trying to eliminate (B) because it contradicts the hypothesis. So just to be clear, the correct answer choice should present evidence that contradicts this hypothesis. We are eliminating any choice that supports this hypothesis.

Second, note that the hypothesis doesn't say HOW exactly these cycles correlate to the intensity of incident light. The hypothesis ONLY states that if the intensity of light is altered, then we can expect a corresponding change in daily rhythms.


This evidence SUPPORTS the hypothesis because it links the Robin's activity to more intensity of light and links the activity of mice to less intensity of light. That is exactly what we'd expect to see if alterations in the intensity of incident light (whether those alterations increase or decrease the intensity) control daily rhythms in biological functions.

Because (B) is evidence that supports the hypothesis, we can eliminate this choice and move on.

I hope this helps!
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A) Human body temperature varies throughout the day, with the maximum occurring in the late afternoon and the minimum in the morning.
Human body is too genralised- incorrect
(B) While some animals, such as the robin, are more active during the day, others, such as mice, show greater activity at night.
its about same animal biological rythm
(C) When people move from one time zone to another, their biological rhythms adjust in a matter of days to the periods of sunlight and darkness in the new zone.
TIme ZOne - Incorrect
(D) Certain single-cell plants display daily biological rhythms even when the part of the cell containing the nucleus is removed.
Nucleus is removed -irrelevant
(E) Even when exposed to constant light intensity around the clock, some algae display rates of photosynthesis that are much greater during daylight hours than at night.
COrrect- contradicts the statement in lines

IMO-E
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GMATNinja KarishmaB

I was confused btw B and E -
(B) While some animals, such as the robin, are more active during the day, others, such as mice, show greater activity at night.
(E) Even when exposed to constant light intensity around the clock, some algae display rates of photosynthesis that are much greater during daylight hours than at night.

In B, change in intensity of light resulted in different biological cycle. The change in intensity is measured by day and night. In E, although it is mentioned that light intensity is constant, the daylight and night changes the intensity.

I am not able to understand why daylight and night are not considered as change in intensity of light in E.

The question asks us which answer choice contradicts the hypothesis in the passage. That hypothesis states that "alteration in the intensity of incident light is the stimulus that controls these daily biological rhythms."

So, we're looking to eliminate options that support (or don't impact) the link between the intensity of light and biological rhythms. We'll keep the option that weakens that link.

With that in mind, look at (B):

(B) tells us that some animals are more active during the day, when presumably there's more light, and other animals are more active at night, when there's presumably less light.

What this doesn't tell us is WHY the animals behave this way. Are robins waking up in the morning because of the increasing intensity of light? Or is there something else driving that behavior?

Similarly, what causes the mice to become more active at night? Do they sense the decrease in light, or is there something else that wakes them up at that time?

(B) simply doesn't tell us why the animals behave the way they do -- it could be because of the changes in light, or it could be something else. So, we can't say that (B) contradicts the hypothesis that the animals are reacting to changes in light.

Eliminate (B).

Here's (E):

(E) tells us that algae are exposed to "constant light intensity around the clock" -- perhaps they are located indoors, or their environment is altered in some other way to keep the light constant. So, while day and night are still occurring on a 24 hour rhythm, the algae are NOT exposed to the changes in light that go along with the shift from day to night.

Despite the light staying the same, the algae continue to adhere to "daily biological rhythms." Specifically, their rates of photosynthesis change in accordance to daylight hours, even when the intensity of light to which the algae are exposed is kept completely constant.

This breaks the link between behavior and intensity of light. Some other factor (an internal clock? changes in temperature? who knows), must be causing the change in the algae's behavior.

(E) contradicts the hypothesis that the intensity of light controls daily biological rhythms, so (B) is the correct answer.

I hope that helps!
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We need to identify the option that contradicts this hypothesis.

Option (A) states that human body temperature varies throughout the day, with the maximum occurring in the late afternoon and the minimum in the morning. While this provides information about human body temperature, it doesn't directly contradict the hypothesis about light intensity as the stimulus for daily biological rhythms.

Option (B) mentions that different animals show varying activity patterns, with some being more active during the day and others more active at night. Although this statement provides information about animal activity, it doesn't specifically contradict the hypothesis regarding light intensity as the controlling stimulus for biological rhythms.

Option (C) discusses how people's biological rhythms adjust to periods of sunlight and darkness when they move from one time zone to another. While this statement highlights the adaptability of biological rhythms, it doesn't directly contradict the hypothesis about light intensity as the controlling factor.

Option (D) describes certain single-cell plants displaying daily biological rhythms even when the nucleus is removed. This statement suggests that the presence or absence of the nucleus doesn't affect the biological rhythms, but it doesn't directly challenge the hypothesis about light intensity.

Option (E), the correct answer, states that some algae display significantly higher rates of photosynthesis during daylight hours compared to nighttime, even when exposed to constant light intensity. This evidence contradicts the hypothesis that variation in light intensity is the stimulus controlling daily biological rhythms since the algae's photosynthesis rates are not solely determined by light intensity.

In conclusion, option (E) is the statement that contradicts the hypothesis by presenting evidence that some algae display different rates of photosynthesis during daylight and nighttime, even under constant light intensity.