Life Processes — Important Questions

Answers

• Filtration: Blood enters the glomerulus under high pressure, and small molecules like water, glucose, amino acids, salts, and urea are filtered from the blood into Bowman's capsule, forming the glomerular filtrate.
• Reabsorption: As the filtrate passes through the renal tubule, useful substances like glucose, amino acids, most of the water, and some salts are selectively reabsorbed back into the blood.
• Secretion: Some waste products and excess ions are secreted from the blood into the tubule.
• Urine Formation: The remaining fluid, now concentrated urine, passes into the collecting duct. [5 marks]
  4. Digestion of carbohydrates begins in the mouth with salivary amylase breaking down starch into simpler sugars. In the small intestine, pancreatic amylase and enzymes from the intestinal wall further break down carbohydrates into glucose.
  Digestion of proteins begins in the stomach with pepsin breaking down proteins into smaller peptides. In the small intestine, trypsin and other peptidases break down peptides into amino acids.
  Digestion of fats primarily occurs in the small intestine. Bile salts emulsify fats into smaller globules, and then lipase enzymes break them down into fatty acids and glycerol. [5 marks]
  5. The circulatory system in human beings is responsible for transporting essential substances throughout the body and removing waste products.
• Heart: A muscular organ that acts as a pump, continuously pumping blood.
• Blood Vessels: Arteries carry oxygenated blood away from the heart, veins carry deoxygenated blood towards the heart, and capillaries are tiny vessels where exchange of materials occurs between blood and tissues.
• Blood: A fluid connective tissue that transports oxygen, nutrients, hormones, and waste products. Red blood cells carry oxygen, white blood cells fight infection, platelets help in blood clotting, and plasma carries dissolved substances. [5 marks]
  6. Aerobic respiration is the breakdown of glucose in the presence of oxygen to produce carbon dioxide, water, and a large amount of energy (ATP). This occurs mainly in the mitochondria.
  Anaerobic respiration is the breakdown of glucose in the absence of oxygen to produce ethanol and carbon dioxide (in yeast) or lactic acid (in muscle cells), and a small amount of energy (ATP). This occurs in the cytoplasm.
  Differences: Aerobic respiration yields much more energy than anaerobic respiration and requires oxygen, while anaerobic respiration occurs without oxygen. [3 marks]
  7. Breathing in human beings is a two-step process:
• Inhalation: The diaphragm contracts and moves downwards, and the external intercostal muscles contract, lifting the ribs up and outwards. This increases the volume of the thoracic cavity, decreasing the pressure inside the lungs, causing air to rush in.
• Exhalation: The diaphragm relaxes and moves upwards, and the external intercostal muscles relax, causing the ribs to move down and inwards. This decreases the volume of the thoracic cavity, increasing the pressure inside the lungs, forcing air out. [3 marks]
  8. Food, primarily in the form of sugars like sucrose, is transported from the leaves (where it is synthesized during photosynthesis) to other parts of the plant (roots, stems, fruits, seeds, etc.) through the phloem tissue. This process is called translocation. It is an energy-dependent process. [3 marks]
  9. Transpiration is the process of loss of water in the form of vapour from the aerial parts of the plant, mainly through stomata.
  Its roles:
• Absorption and Transport: It creates a transpiration pull, a suction force that pulls water and dissolved minerals from the roots up to the leaves through the xylem.
• Temperature Regulation: Transpiration helps in cooling the plant surface by evaporating water. [3 marks]
  10. Plants excrete waste products through various methods:
• Transpiration: Excess water is removed as vapour.
• Storage in Vacuoles: Waste products like oxygen (a byproduct of photosynthesis) and carbon dioxide (a byproduct of respiration) are exchanged through stomata. Other waste products can be stored in cell vacuoles.
• Shedding of Leaves: Waste products are stored in leaves which are later shed.
• Deposition in old tissues: Waste products can be deposited as gums and resins in old xylem tissues.
• Excretion into soil: Some waste products are released into the surrounding soil. [3 marks]
  11. Assertion (A): The rate of breathing increases during strenuous exercise. Reason (R): Increased physical activity requires more energy, which is produced by the breakdown of glucose using oxygen. [1 mark]
  12. Dialysis is a process used to remove waste products and excess fluid from the blood when the kidneys are not functioning properly. The principle behind an artificial kidney is diffusion. The patient's blood is passed through a machine containing a semi-permeable membrane. This membrane separates the blood from a dialysing fluid. Waste products like urea, which are present in higher concentration in the blood, diffuse across the membrane into the dialysing fluid, which has a lower concentration of these wastes. Excess salts and water also move into the dialysing fluid. The purified blood is then returned to the patient. [3 marks]
  13. (a) I: Guard cells, II: Chloroplast
  (b) Guard cells regulate the opening and closing of stomata. When guard cells are turgid (swollen with water), they curve outwards, causing the stomatal pore to open, allowing for gas exchange (CO2 intake and O2 release) for photosynthesis and transpiration. When guard cells lose water and become flaccid, they become straight, and the stomatal pore closes, reducing water loss. [3 marks]
  14. The part labelled 'X' is the small intestine. Its primary function is the completion of digestion of carbohydrates, proteins, and fats, and the absorption of these digested nutrients into the bloodstream. [3 marks]
  15. Photosynthesis is crucial for plants as it is the process by which they produce their own food (glucose), which provides them with energy for growth and other metabolic activities. It also releases oxygen, which is essential for the survival of most living organisms. The pigment that traps light energy is chlorophyll. [2 marks]
  16. The walls of the left ventricle are thicker than the walls of the right ventricle because the left ventricle has to pump oxygenated blood to the entire body at a much higher pressure than the right ventricle, which only pumps deoxygenated blood to the lungs. [2 marks]
  17. Respiratory pigments like haemoglobin have a very high affinity for oxygen. They are present in red blood corpuscles and bind with oxygen in the lungs. They then transport this oxygen to tissues that are deficient in oxygen, where it is released. This ensures efficient transport of oxygen to all parts of the body, meeting the high energy demands of aerobic respiration. [2 marks]
  18. Villi are finger-like projections lining the inner wall of the small intestine. They greatly increase the surface area available for the absorption of digested food. This increased surface area allows for more efficient and rapid absorption of nutrients into the bloodstream. [1 mark]
  19. The process by which plants release excess water into the atmosphere is called transpiration. [1 mark]
  20. (a) Carbon dioxide ($C{O}_2$) is the gas present in exhaled air responsible for turning lime water milky.
  (b) This gas is produced during cellular respiration as a waste product. In aerobic respiration, it is formed in the mitochondria. [2 marks]