Rhizobium is used as a biofertilizer primarily for: MCQ with Answer and Explanation

Explanation:
The cell membrane (plasma membrane) is selectively permeable, meaning it allows certain substances to pass through while restricting others, maintaining cellular homeostasis. The nucleus is the control center of the eukaryotic cell, housing the DNA and directing cellular activities like growth, metabolism, and reproduction. The cell wall is a rigid outer layer present in plant cells, fungi, and bacteria, but it is completely absent in animal cells, which only have a flexible cell membrane. Thus, statements 1 and 3 are correct.

Explanation:
Enzymes speed up reactions by lowering activation energy and are not consumed; they remain unchanged after the reaction. Thus, statement 2 is false. 1 and 3 are correct.

Explanation:
Carbon dioxide (CO₂) is the primary greenhouse gas, along with methane (CH₄), nitrous oxide (N₂O), water vapor, and CFCs. These trap heat in the atmosphere, leading to global warming and climate change. CO₂ levels have risen due to fossil fuel burning and deforestation. The greenhouse effect is natural and essential, but enhanced levels cause global temperature rise.