Ozone layer depletion in the stratosphere is primarily caused by:
A. Sulfur dioxide
B. Carbon dioxide
C. Chlorofluorocarbons (CFCs)
D. Methane
Answer: Option C
Solution (By JKSSB Mock Tests)
The ozone layer in the stratosphere protects Earth from harmful ultraviolet (UV) radiation. Its depletion is primarily caused by Chlorofluorocarbons (CFCs), which were widely used in refrigerants, aerosols, and solvents. UV radiation breaks down CFCs, releasing chlorine atoms that catalytically destroy ozone molecules. The Montreal Protocol (1987) was an international treaty to phase out the production of CFCs.
Explanation:
The potato is a modified underground stem known as a tuber. It stores food (starch) and has 'eyes' which are actually axillary buds capable of growing into new plants. This distinguishes it from modified roots like sweet potatoes, which do not possess nodes, internodes, or buds.
Consider statements about cell biology: 1. The cell membrane is selectively permeable. 2. The nucleus contains genetic material. 3. Mitochondria are the site of photosynthesis. Which are correct?
Explanation:
The cell membrane (plasma membrane) is selectively permeable, regulating the passage of substances in and out of the cell to maintain internal homeostasis. The nucleus is the membrane-bound organelle that houses the cell's genetic material (DNA) organized into chromosomes, directing cellular activities. Mitochondria are the site of aerobic cellular respiration and ATP production; chloroplasts are the organelles where photosynthesis occurs in plant cells. Thus, statements 1 and 2 are correct.
Explanation:
Double fertilization involves one male gamete fusing with the egg cell to form a diploid zygote, and the second male gamete fusing with the two polar nuclei (central cell) to form a triploid primary endosperm nucleus. The endosperm provides nutrition to the developing embryo. This unique feature ensures efficient nutrient supply and is typical of angiosperms.
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