Question 74: Describe the alimentary canal of man.
Answer: The human alimentary canal has following main parts:
Question 75: Explain the process of breathing in man.
Answer: Breathing Mechanism: The breathing mechanism of lungs is controlled by the diaphragm and the intercostalis muscles. Diaphragm is a membrane which separates the thoracic chamber from the abdominal cavity. When diaphragm moves down, the lungs expand and air is inhaled. When diaphragm moves up, the lungs contract and air is exhaled.
Question 76: Explain the importance of soil for plant growth.
Answer: Soil is important for plant growth. Soil provides the base on which all the terrestrial plants and even some aquatic plants grow. Soil is the reservoir of water which is essential for all metabolic activities of a plant. Moreover, soil is also the reservoir of essential minerals required by plants.
Question 77: How do carbohydrates, proteins and fats get digested in human beings?
Answer: Digestion of carbohydrates: Starch is digested in the mouth by salivary amylase. Other forms of carbohydrates are digested in the small intestine.
Starch + Salivary Amylase → Sucrose
Maltose + Maltase → Glucose
Lactose + Lactase → Glucose + Galactose
Digestion of Proteins: Partial digestion of protein takes place in the stomach by gastric enzyme pepsin. Further digestion of protein happens in the small intestine.
Protein + Pepsin → Peptone + Proteose
(Protein + Peptone + Proteose) + (trypsin + chymotrypsin) → Dipeptides
Digestion of Fat: Fat is at first emulsified by bile and then its digestion happens in the small intestine.
Fat + Lipase → Fatty acids + Glycerol
Question 78: Explain the mechanism of photosynthesis.
Answer: Photosynthesis: The process by which green plants prepare food is called photosynthesis. The whole process of photosynthesis can be shown by following equation:
6CO2 + 6H2O + Sunlight + Chlorophyll → C6H12O6 + 6O2
Steps of Photosynthesis:
Question 79: Explain the three pathways of breakdown in living organisms.
Answer: Fate of Pyruvic Acid: The breakdown of pyruvic acid takes place in mitochondria and the molecules formed depend on the type of respiration in a particular organism. Respiration is of two types, viz. aerobic respiration and anaerobic respiration.
Anaerobic Respiration: This type of respiration happens in the presence of oxygen. Pyruvic acid is converted into carbon dioxide. Energy is released and water molecule is also formed at the end of this process.
Aerobic Respiration: This type of respiration happens in the absence of oxygen. Pyruvic acid is either converted into ethyl alcohol or lactic acid. Ethyl alcohol is usually formed in case of anaerobic respiration in microbes; like yeast or bacteria. Lactic acid is formed in some microbes as well as in the muscle cells.
Glucose (3-carbon molecule)(In cytoplasm) → Pyruvate (3-carbon molecule) + Energy
Pyruvate (In yeast, absence of oxygen) → Ethyl alcohol + Carbon dioxide + Energy
Pyruvate (In muscles, absence of oxygen) → Lactic acid + Energy
Pyruvate (In mitochondria, presence of oxygen) → Carbon dioxide + Water + Energy
Question 80: Describe the flow of blood through the heart of human beings.
Answer: The following flow chart shows the circulation of blood through the heart:
Systemic Vein → Sinus Venosus → Right Auricle → Right Ventricle → Pulmonary Artery → Lungs → Pulmonary Vein → Left Auricle → Left Ventricle → Trunchus Arteriosus → Systemic Circulation
The blood from the systemic circulation comes to the right auricle. From the right auricle, the blood is pumped into the right ventricle. The right ventricle pumps the blood to lungs; through pulmonary artery. Oxygenation of blood takes place in alveoli in lungs. The oxygenated blood; from the lungs; comes to the left auricle through pulmonary vein. From left auricle, the blood is pumped into the left ventricle. Finally, the left ventricle pumps the blood into the systemic circulation.
Question 81: Describe the process of urine formation in kidneys.
Answer: Urine formation in kidneys: Filtration happens because of very high pressure inside the glomerulus. The lumen of efferent arteriole is smaller than that of afferent arteriole. Due to this, the blood entering the glomerulus experiences very high pressure and due to this, the waste products are filtered out through the thin membrane of capillaries in the glomerulus. The filtered blood is sent to the systemic circulation through efferent arteriole and the filtrate goes to the Bowman’s capsule. That is how urine is formed inside the kidneys. Reabsorption of water and some other filtrates takes place in the tubular part of the nephron. This increases the concentration of urine. The human urine is mainly composed of water and urea.
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