Chapter 5: Life Processes
Nutrition
Autotrophic nutrition: green plants make food by photosynthesis: 6CO2 + 6H2O โ C6H12O6 + 6O2 (in the presence of chlorophyll and sunlight). Gas exchange happens through stomata. Heterotrophic nutrition: animals take in ready-made food.
Digestion in humans: mouth (saliva, amylase) โ oesophagus โ stomach (HCl, pepsin) โ small intestine (bile, pancreatic juice, absorption by villi) โ large intestine (absorbs water).
Respiration
Breakdown of glucose first forms pyruvate in the cytoplasm. Aerobic respiration (in mitochondria) gives CO2 + water + energy (ATP). Anaerobic respiration: ethanol + CO2 in yeast, lactic acid in muscles (cramps). Path of air in humans: nostrils โ pharynx โ larynx โ trachea โ bronchi โ alveoli. Haemoglobin carries oxygen.
Transportation
The heart is four-chambered and humans have double circulation. Blood vessels are arteries, veins and capillaries. Blood has plasma, RBC, WBC and platelets. In plants: xylem carries water and minerals (by transpiration pull), phloem carries food (translocation).
Excretion
In humans, the kidneys filter blood to form urine. The nephron is the unit: filtration happens in the glomerulus, then useful substances are reabsorbed and the rest forms urine. When kidneys fail, dialysis is used. Plants remove wastes as gums, resins and falling leaves.
Important questions
Q1. What are life processes?
The basic functions that keep an organism alive, such as nutrition, respiration, transport and excretion.
Q2. Differentiate between autotrophic and heterotrophic nutrition.
Autotrophs (like green plants) make their own food. Heterotrophs (like animals) depend on others for food.
Q3. Write the overall reaction of photosynthesis.
6CO2 + 6H2O โ C6H12O6 + 6O2, in the presence of sunlight and chlorophyll.
Q4. What is the function of stomata?
Exchange of gases (CO2 in, O2 out) and loss of water in transpiration. Guard cells open and close them.
Q5. Why is the small intestine long?
For complete digestion and absorption of carbohydrates, proteins and fats. Villi increase the surface area for absorption.
Q6. What is the role of saliva?
Saliva contains salivary amylase, which breaks down starch into sugar.
Q7. What is the role of hydrochloric acid in the stomach?
It creates an acidic medium so that the enzyme pepsin can work, and it kills bacteria that come in with food.
Q8. What is the role of bile?
Bile made in the liver breaks fats into small droplets (emulsification) and makes the food alkaline so that pancreatic enzymes can act.
Q9. Where is digested food absorbed?
In the small intestine, through the villi.
Q10. What are aerobic and anaerobic respiration?
Aerobic respiration needs oxygen and gives CO2, water and energy. Anaerobic respiration occurs without oxygen, giving ethanol + CO2 in yeast and lactic acid in muscles.
Q11. What is ATP?
The energy currency of the cell, in which energy is stored and used when needed.
Q12. Why do muscles cramp after heavy exercise?
Lactic acid builds up in the muscles from anaerobic respiration.
Q13. What carries oxygen in the blood?
Haemoglobin in the red blood cells.
Q14. Write the path of air in humans in order.
Nostrils โ pharynx โ larynx โ trachea โ bronchi โ alveoli.
Q15. Why are alveoli well suited for gas exchange?
They have a very large surface area, thin walls and a rich network of blood vessels around them.
Q16. Why is the human heart four-chambered?
So that oxygenated and deoxygenated blood do not mix, which allows efficient supply of oxygen to a body with high energy needs.
Q17. Differentiate between arteries and veins.
Arteries carry blood away from the heart and have thick, elastic walls. Veins carry blood towards the heart, have thin walls and contain valves.
Q18. Name the components of blood.
Plasma, red blood cells (RBC), white blood cells (WBC) and platelets.
Q19. What do xylem and phloem carry?
Xylem carries water and minerals, while phloem carries the food (sugars) made in the leaves to all parts of the plant.
Q20. Name the unit of the kidney and state its function.
The unit of the kidney is the nephron, which filters blood to form urine.
Quiz
1. Which organisms make their own food?
Green plants are autotrophs.
2. Where does the digestion of starch begin?
Salivary amylase begins digesting starch in the mouth.
3. Which pigment carries oxygen in the blood?
Haemoglobin carries oxygen.
4. What is the functional unit of the kidney?
The nephron filters blood to form urine.
5. What does xylem transport?
Xylem transports water and minerals.