In angiosperms, the functional megaspore undergoes mitotic divisions to form the embryo sac, which typically contains: MCQ with Answer and Explanation

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In angiosperms, the functional megaspore undergoes mitotic divisions to form the embryo sac, which typically contains:

A. 7 cells, 7 nuclei

B. 7 cells, 8 nuclei

C. 8 cells, 8 nuclei

D. 4 cells, 4 nuclei

Answer: Option B

Solution (By JKExamLibrary)

The female gametophyte (embryo sac) in angiosperms is typically monosporic (develops from one functional megaspore). The megaspore undergoes three successive mitotic divisions to form an 8-nucleate, 7-celled structure. This includes 3 antipodal cells, 2 synergids, 1 egg cell, and 1 central cell containing 2 polar nuclei. Exam tip: Remember '8 nuclei, 7 cells' because the central cell has 2 nuclei but is 1 cell.

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Which of the following statements about the ozone layer is correct?

A. It is located in the troposphere.

B. Ozone is composed of three oxygen atoms and is harmless at ground level.

C. It absorbs harmful UV radiation.

D. It is depleted by increased CO₂ levels.

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Correct Answer: Option C

Explanation:
The ozone layer in the stratosphere absorbs most of the Sun's harmful UV radiation. CFCs, not CO₂, cause its depletion. Ozone at ground level is a pollutant. So B is correct.

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The type of joint found in the shoulder and hip is:

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B. Gliding joint

C. Pivot joint

D. Hinge joint

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Correct Answer: Option A

Explanation:
The ball and socket joint (e.g., glenohumeral, hip) allows movement in multiple axes (flexion, extension, abduction, adduction, rotation). The rounded head of one bone fits into the cup-shaped socket of another. Hinge (elbow, knee) allows movement in one plane, pivot (neck) allows rotation, gliding (wrist) allows sliding.

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Question #3

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The marine algae that form the basis of many aquatic food chains and produce much of Earth's oxygen are:

A. Phytoplankton

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Correct Answer: Option A

Explanation:
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