The correct option is (c) 2 and 3 only
Explanation
The transport of substances across the plasma membrane occurs primarily through two mechanisms:
active transport (requiring energy) and
passive transport (requiring no energy). Diffusion and osmosis are forms of passive transport where molecules move along a concentration gradient.
Statement-wise Analysis
- Statement 1 is Incorrect. Diffusion is the movement of substances from a region of higher concentration to a region of lower concentration. For CO2 (cellular waste) to move out of the cell, its concentration inside the cell must be higher than the concentration outside. The statement incorrectly suggests it moves out when the concentration inside is lower.
- Statement 2 is Correct. Water moves across the cell membrane through a specific type of diffusion known as osmosis. Osmosis is the movement of water molecules from a region of higher water concentration to a region of lower water concentration through a semi-permeable membrane. Therefore, water obeys the fundamental law of diffusion.
- Statement 3 is Correct. Oxygen enters the cell by the process of simple diffusion. Since the concentration of oxygen is typically higher outside the cell (from the blood or environment) than inside (where it is consumed), it moves into the cell along the concentration gradient. This is a passive process and does not require the expenditure of energy (ATP).
Key Takeaway
Passive transport involves the movement of gases (like CO
2 and O
2) and water across the cell membrane driven solely by concentration gradients, without the consumption of cellular energy.