Life Processes

Step 1: Flaccid guard cells can close stomata. Step 2: Closed stomata reduce carbon dioxide entry. Step 3: Low carbon dioxide reduces food formation.

Step 1: Photosynthesis needs raw materials along with light. Step 2: Carbon dioxide is needed to form glucose. Step 3: Without glucose starch will not be formed.

Step 1: A leaf may already contain stored starch. Step 2: In darkness the plant uses up that starch. Step 3: Then the test shows newly formed starch.

Step 1: Light is necessary for photosynthesis. Step 2: Only the part receiving light can make food. Step 3: Therefore starch will be seen clearly in that part with iodine.

Step 1: Water vapour leaves when stomata remain open. Step 2: During high water loss the plant may close stomata. Step 3: This reduces carbon dioxide entry and photosynthesis.

Step 1: Salivary enzyme acts on starch in the mouth. Step 2: The stomach has an acidic medium. Step 3: This medium can stop the action of salivary enzyme.

Step 1: The stomach contains strong acid and digestive enzymes. Step 2: Mucus protects the inner wall from them. Step 3: Without mucus the wall may be damaged.

Step 1: Bile divides large fat droplets into smaller droplets. Step 2: This increases surface area. Step 3: Pancreatic enzymes can then act better on fat.

Step 1: Fat exists as large droplets. Step 2: Bile breaks it into smaller droplets and increases surface area. Step 3: Without bile enzymes act less effectively on fat.

Step 1: Villi increase surface area of the small intestine. Step 2: Digested nutrients enter blood through villi. Step 3: Blood vessels carry them to body cells.

Step 1: Digestion converts food into simple substances. Step 2: For energy these substances must reach cells through blood. Step 3: Damaged villi reduce absorption.

Step 1: Muscles in the food pipe wall contract and relax. Step 2: This wave like movement pushes food forward. Step 3: Thus food reaches the stomach even when body position changes.

Step 1: The large intestine absorbs water from remaining material. Step 2: If too much water is removed the material becomes dry. Step 3: This can make faeces harder.

Step 1: Oxygen is available in aerobic respiration. Step 2: This allows more complete breakdown of glucose. Step 3: Therefore more energy is released.

Step 1: During hard exercise oxygen demand increases greatly. Step 2: If oxygen is insufficient muscles perform anaerobic respiration. Step 3: Lactic acid formation can cause pain and cramps.

Step 1: Both processes are related to low or no oxygen condition. Step 2: Yeast forms ethanol and carbon dioxide. Step 3: Muscles can form lactic acid.

Step 1: Gas exchange occurs in alveoli. Step 2: Thick walls and low surface area slow oxygen entry. Step 3: Less oxygen reduces aerobic respiration and energy production.

Step 1: Lungs bring oxygen into blood. Step 2: Haemoglobin in blood binds and carries oxygen. Step 3: Low haemoglobin reduces oxygen delivery to cells.

Step 1: Respiration in cells releases energy. Step 2: Carbon dioxide is formed as a waste in this process. Step 3: Lungs remove it so it is also linked with waste removal.

Step 1: Humans need more energy for an active body. Step 2: Cells need good oxygen supply for energy. Step 3: A four chambered heart helps by keeping blood separate.

Step 1: Arteries carry blood from the heart under high pressure. Step 2: Veins have lower pressure and return blood to the heart. Step 3: Thus arteries need elastic walls and veins need valves.

Step 1: Blood from legs must return to the heart against gravity. Step 2: Pressure in veins is low. Step 3: If valves fail blood can flow backward and pool.

Step 1: Capillary walls are very thin. Step 2: They are close to body cells. Step 3: This allows exchange of oxygen nutrients and wastes.

Step 1: Blood comes out when injury occurs. Step 2: Platelets help form a clot. Step 3: The clot reduces blood loss and protects the body.

Step 1: Xylem carries water to leaves. Step 2: Water is a raw material for photosynthesis. Step 3: Water availability is also linked with loss of water vapour from leaves.