Question

Give reasons for the following:
(i) Alveoli in lungs are richly supplied with blood capillaries.
(ii) Respiratory pigment in the blood takes up oxygen and not carbon dioxide.
(iii) During anaerobic respiration, a 3-carbon molecule is formed as an end product instead of CO₂ in human beings.
OR
(i) Name the movements that occur all along the gut in human digestive system. How do they help in digestion?
(ii) Where is bile juice stored in human body? List two roles of bile juice.

Answer 1

(a)• (i) Alveoli in lungs are richly supplied with blood capillaries: The dense network of blood capillaries in the alveoli ensures efficient exchange of gases (oxygen and carbon dioxide) by maintaining a large surface area and proximity to the bloodstream.
• (ii) Respiratory pigment in the blood takes up oxygen and not carbon dioxide: Hemoglobin, the respiratory pigment, has a higher affinity for oxygen than carbon dioxide, enabling effective oxygen transport from the lungs to tissues.
• (iii) During anaerobic respiration, a 3-carbon molecule is formed as an end product instead of CO2 in human beings: In humans, during anaerobic respiration, glucose is partially broken down into lactic acid (a 3-carbon molecule) due to insufficient oxygen supply. This avoids complete oxidation to CO2.

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(b). • Movements in the Digestive System: The rhythmic contractions of the digestive tract are called peristalsis. These contractions push food forward and mix it with digestive juices for effective digestion.
• Storage of Bile Juice: Bile juice is stored in the gallbladder.
• Roles of Bile Juice:
– Emulsification of Fats: Bile breaks down large fat globules into smaller droplets, increasing the surface area for enzyme action.
– Neutralization of Stomach Acid: Bile neutralizes the acidic chyme from the stomach, creating an alkaline environment suitable for enzymes in the small intestine.