Assertion A: A population growing logistically stops increasing when its density reaches K. Reason R: At N = K, the factor (K − N)/K becomes zero, so dN/dt is zero. Choose the correct answer.

Both A and R are correct and R is the correct explanation of A

Both A and R are correct but R is not the correct explanation of A

A is not correct but R is correct

A is correct but R is not correct

Organisms and Populations

17 NEET-UG practice questions on Organisms and Populations, part of Botany. The first 17 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
Assertion A: A population growing logistically stops increasing when its density reaches K. Reason R: At N = K, the factor (K − N)/K becomes zero, so dN/dt is zero. Choose the correct answer.
1. ABoth A and R are correct and R is the correct explanation of A
2. BBoth A and R are correct but R is not the correct explanation of A
3. CA is not correct but R is correct
4. DA is correct but R is not correct
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Answer: A · Both A and R are correct and R is the correct explanation of A
Substituting N = K makes the factor zero, so dN/dt is zero and the curve levels off at the asymptote. R therefore explains A.
- B: R is the direct mathematical cause of A.
- C: A is the correct behaviour at K.
- D: R is a correct result of the equation.
Remember this
At carrying capacity, dN/dt = 0 and the sigmoid curve levels off.
Question 2 · Easy
Growth slows as a population nears the limit its habitat can support. Which equation expresses this model of Verhulst and Pearl?
1. AdN/dt = rN((K − N)/K)
2. BdN/dt = rN((N − K)/K)
3. CdN/dt = rN
4. DdN/dt = rK((K − N)/N)
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Answer: A · dN/dt = rN((K − N)/K)
Logistic growth reduces exponential growth by the factor (K − N)/K, which falls to zero as N approaches K.
- B: This reverses the term and gives negative growth below K.
- C: This is the exponential equation.
- D: This puts K and N in the wrong places.
Remember this
Exponential dN/dt = rN gives a J curve; logistic rN((K − N)/K) gives a sigmoid curve.
Question 3 · Medium
Match List-I with List-II. List-I (symbol in growth equations) A. r B. K C. N₀ D. e List-II (meaning) I. Base of natural logarithms II. Population density at time zero III. Carrying capacity IV. Intrinsic rate of natural increase
1. AA-IV, B-II, C-III, D-I
2. BA-III, B-IV, C-II, D-I
3. CA-IV, B-III, C-I, D-II
4. DA-IV, B-III, C-II, D-I
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Answer: D · A-IV, B-III, C-II, D-I
In Nₜ = N₀eʳᵗ, r is the intrinsic rate of natural increase, N₀ is the density at time zero and e is the base of natural logarithms. K in the logistic equation is the carrying capacity.
- A: This swaps K and N₀.
- B: This swaps r and K.
- C: This swaps N₀ and e.
Remember this
r is intrinsic rate, K carrying capacity, N₀ starting density, e the base of natural logarithms.
Question 4 · Medium
Which of these statements about predation are correct? A. Predators help to keep prey populations under control. B. Prickly pear in Australia was controlled after a cactus-feeding moth was introduced from its natural habitat. C. Predators lower species diversity by intensifying competition among prey. D. Nicotine and quinine are made by herbivorous animals to deter plants.
1. AC and D only
2. BA, B and C only
3. CA, B and D only
4. DA and B only
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Answer: D · A and B only
A and B are correct. C is reversed, since predators maintain diversity by reducing competition among prey. D is wrong, since plants make these chemicals as defence against herbivores.
- A: These are the two false statements.
- B: This includes C, which reverses the predator's effect.
- C: This includes D, though plants make these chemicals.
Remember this
Plant chemicals such as nicotine, caffeine and quinine defend against herbivores; predators sustain prey diversity.
Question 5 · Hard
Which of these statements about parasitism are correct? A. Cuscuta has functional leaves and makes its own food by photosynthesis. B. The human liver fluke uses a snail and a fish as intermediate hosts. C. The cuckoo lays its eggs in the nest of a crow. D. Copepods live as ectoparasites on many marine fishes.
1. AA, C and D only
2. BB and C only
3. CB, C and D only
4. DA, B and C only
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Answer: C · B, C and D only
B, C and D are correct. A is wrong: Cuscuta has lost its chlorophyll and leaves and takes nutrition from its host.
- A: This includes A and omits B.
- B: This omits D, which is correct.
- D: This includes A and omits D.
Remember this
Parasitic adaptations include loss of unnecessary organs, as in Cuscuta, and complex life cycles, as in the liver fluke.
Question 6 · Medium
Match List-I with List-II. List-I (pair) A. Ophrys and a bee B. Cattle egret and grazing cattle C. Abingdon tortoise and goats D. Cuckoo and crow List-II (interaction) I. Competition II. Brood parasitism III. Mutualism with sexual deceit IV. Commensalism
1. AA-III, B-IV, C-II, D-I
2. BA-III, B-IV, C-I, D-II
3. CA-III, B-I, C-IV, D-II
4. DA-IV, B-III, C-I, D-II
Answer and explanation in LearnFree account
Question 7 · Easy
Barnacles grow on the back of a whale. What kind of interaction is this?
1. AParasitism
2. BCommensalism
3. CAmensalism
4. DMutualism
Answer and explanation in LearnFree account
Question 8 · Easy
Which attribute belongs to a population and not to an individual organism?
1. AMetabolic rate
2. BSex ratio
3. CLifespan
4. DBody weight
Answer and explanation in LearnFree account
Question 9 · Hard
A population follows logistic growth with r = 0.5 per year and K = 1000. At what rate, in individuals per year, does it grow when N = 200?
1. A500
2. B20
3. C80
4. D100
Answer and explanation in LearnFree account
Question 10 · Medium
Given below are two statements: Statement I: Logistic growth produces a J-shaped curve when resources become limiting. Statement II: Exponential growth produces a J-shaped curve when resources are unlimited. Choose the correct answer.
1. ABoth Statement I and Statement II are correct
2. BStatement I is incorrect but Statement II is correct
3. CBoth Statement I and Statement II are incorrect
4. DStatement I is correct but Statement II is incorrect
Answer and explanation in LearnFree account
Question 11 · Hard
In a field experiment, all the starfish Pisaster were removed from an enclosed rocky intertidal area of the American Pacific Coast. What was found within a year, and why?
1. AInvertebrate species stayed the same, as predators do not affect diversity
2. BOver ten invertebrate species became extinct there, due to increased interspecific competition
3. CInvertebrate diversity rose, as all species were freed from predation
4. DOver ten invertebrate species became extinct there, due to increased parasitism
Answer and explanation in LearnFree account
Question 12 · Medium
A pond holds 80 water lily plants. In one year, 20 new plants arise by reproduction and 8 plants die. What is the birth rate?
1. A0.20 per plant per year
2. B0.10 per plant per year
3. C0.25 per plant per year
4. D0.15 per plant per year
Answer and explanation in LearnFree account
Question 13 · Hard
Given below are two statements: Statement I: On the rocky coasts of Scotland, the barnacle Balanus excludes the smaller barnacle Chthamalus from the intertidal zone. Statement II: Five closely related warbler species could not live on the same tree, as MacArthur showed. Choose the correct answer.
1. ABoth Statement I and Statement II are correct
2. BStatement I is correct but Statement II is incorrect
3. CStatement I is incorrect but Statement II is correct
4. DBoth Statement I and Statement II are incorrect
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Question 14 · Medium
A plot contains one huge banyan tree and 200 Parthenium plants. Which measure best shows the relative importance of the two species?
1. ABirth rate
2. BPercent cover or biomass
3. CNumber of individuals
4. DSex ratio
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Question 15 · Easy
What does an urn-shaped age pyramid show about a population?
1. AIt is expanding
2. BIt has reached zero birth rate
3. CIt is stable
4. DIt is declining
Answer and explanation in LearnFree account
Question 16 · Medium
A population follows the Verhulst-Pearl logistic model, dN/dt = rN(K − N)/K. Which graph correctly shows how dN/dt changes with population size N?
Figure: MedExams
1. AGraph C
2. BGraph A
3. CGraph B
4. DGraph D
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Question 17 · Medium
Given below are two statements: Statement I: Population X in the figure is an expanding population. Statement II: Population Z in the figure is a declining population. Choose the correct answer.
Figure: MedExams
1. AStatement I is correct but Statement II is incorrect
2. BBoth Statement I and Statement II are correct
3. CBoth Statement I and Statement II are incorrect
4. DStatement I is incorrect but Statement II is correct
Answer and explanation in LearnFree account

Organisms and Populations

Assertion A: A population growing logistically stops increasing when its density reaches K. Reason R: At N = K, the factor (K − N)/K becomes zero, so dN/dt is zero. Choose the correct answer.

Growth slows as a population nears the limit its habitat can support. Which equation expresses this model of Verhulst and Pearl?

Match List-I with List-II. List-I (symbol in growth equations) A. r B. K C. N₀ D. e List-II (meaning) I. Base of natural logarithms II. Population density at time zero III. Carrying capacity IV. Intrinsic rate of natural increase

Match List-I with List-II. List-I (pair) A. Ophrys and a bee B. Cattle egret and grazing cattle C. Abingdon tortoise and goats D. Cuckoo and crow List-II (interaction) I. Competition II. Brood parasitism III. Mutualism with sexual deceit IV. Commensalism

Barnacles grow on the back of a whale. What kind of interaction is this?

Which attribute belongs to a population and not to an individual organism?

A population follows logistic growth with r = 0.5 per year and K = 1000. At what rate, in individuals per year, does it grow when N = 200?

Given below are two statements: Statement I: Logistic growth produces a J-shaped curve when resources become limiting. Statement II: Exponential growth produces a J-shaped curve when resources are unlimited. Choose the correct answer.

In a field experiment, all the starfish Pisaster were removed from an enclosed rocky intertidal area of the American Pacific Coast. What was found within a year, and why?

A pond holds 80 water lily plants. In one year, 20 new plants arise by reproduction and 8 plants die. What is the birth rate?

Given below are two statements: Statement I: On the rocky coasts of Scotland, the barnacle Balanus excludes the smaller barnacle Chthamalus from the intertidal zone. Statement II: Five closely related warbler species could not live on the same tree, as MacArthur showed. Choose the correct answer.

A plot contains one huge banyan tree and 200 Parthenium plants. Which measure best shows the relative importance of the two species?

What does an urn-shaped age pyramid show about a population?

A population follows the Verhulst-Pearl logistic model, dN/dt = rN(K − N)/K. Which graph correctly shows how dN/dt changes with population size N?

Given below are two statements: Statement I: Population X in the figure is an expanding population. Statement II: Population Z in the figure is a declining population. Choose the correct answer.