The Fundamental Unit of Life — Important Questions

Osmosis

Step 1: Osmosis is the net movement of water molecules through a selectively permeable membrane. Step 2: Water moves from an area of higher water concentration to lower water concentration. Step 3: This movement continues until equilibrium is reached on both sides of the membrane. Step 4: Osmosis is actually a special type of diffusion that involves only water molecules. Step 5: Other options are different processes - diffusion involves any substance, endocytosis is engulfing materials, plasmolysis is cell shrinkage due to water loss.

Cell wall

Step 1: The cell wall is a rigid outer covering present only in plant cells. Step 2: It is mainly composed of cellulose, which is a strong, complex carbohydrate. Step 3: The cell wall lies outside the plasma membrane and provides structural support. Step 4: It protects the cell from mechanical damage and helps maintain cell shape. Step 5: Other options have different functions - cell membrane is selectively permeable, cytoplasm contains organelles, vacuole stores materials, but only cell wall provides structural strength.

Cell swells up due to water entering

Step 1: A hypotonic solution has higher water concentration than inside the cell. Step 2: Due to osmosis, water moves from higher concentration (outside) to lower concentration (inside cell). Step 3: As water enters the cell, the cell volume increases and it swells. Step 4: In extreme cases, animal cells may burst, but plant cells are protected by cell walls. Step 5: Other options describe different scenarios - shrinking occurs in hypertonic solutions, no change in isotonic solutions, membrane permeability doesn't change with solution type.

Ribosomes

Step 1: Ribosomes are small organelles present in all active cells. Step 2: They are the sites where proteins are manufactured using genetic instructions. Step 3: Ribosomes can be free in cytoplasm or attached to endoplasmic reticulum (making it rough ER). Step 4: They read genetic code from nucleus and assemble amino acids into proteins. Step 5: Other organelles have different functions - lysosomes digest materials, vacuoles store substances, Golgi apparatus packages proteins made by ribosomes.