Life Processes

Anaerobic respiration

Step 1: During sudden vigorous exercise, muscles need a lot of energy very quickly. Step 2: The supply of oxygen to muscle cells becomes insufficient at that moment. Step 3: In the absence of sufficient oxygen, muscle cells switch to anaerobic respiration. Step 4: In this process, pyruvate is converted to lactic acid (instead of CO₂ and water). Step 5: The build-up of lactic acid in muscles causes the painful cramps we feel after exercise. Note: Fermentation also involves anaerobic respiration but happens in yeast and produces ethanol, not lactic acid.

Haemoglobin

Step 1: Oxygen absorbed in the lungs needs to be transported to all cells of the body through blood. Step 2: Simple diffusion cannot carry enough oxygen for the entire body, so a special pigment is needed. Step 3: This respiratory pigment is called haemoglobin and is found in the red blood corpuscles (RBCs). Step 4: Haemoglobin has a very high affinity (attraction) for oxygen, allowing it to carry large amounts efficiently. Step 5: Chlorophyll is a pigment in plants for photosynthesis; plasma is the liquid part of blood; insulin is a hormone — none of these carry oxygen.

Liver

Step 1: When food from the stomach enters the small intestine, it needs to be processed further. Step 2: Fats in the food exist as large globules that are difficult for enzymes to work on. Step 3: Bile juice, produced by the liver, is secreted into the small intestine to help with fat digestion. Step 4: Bile salts break large fat globules into smaller ones — this is called emulsification, similar to how soap removes oily dirt. Step 5: The pancreas produces pancreatic juice (not bile); the stomach produces gastric juice; the small intestine produces intestinal juice.

Alveoli

Step 1: Air enters the lungs through the nostrils, throat, and windpipe (trachea). Step 2: Inside the lungs, the passage divides into smaller and smaller tubes. Step 3: These tubes finally end in tiny balloon-like structures called alveoli (singular: alveolus). Step 4: The walls of alveoli are very thin and surrounded by blood capillaries, making them ideal for gas exchange — oxygen enters blood and carbon dioxide leaves. Step 5: Nephrons are filtration units in kidneys; villi are in the small intestine for food absorption; stomata are pores in plant leaves — all are wrong for lung gas exchang