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) Gas Exchange in Lungs:
• (i) Dense capillary network around alveoli: The extensive capillary supply to the alveoli maximizes the surface area for efficient oxygen and carbon dioxide exchange.
• (ii) Hemoglobin's oxygen affinity: Hemoglobin preferentially binds oxygen over carbon dioxide, facilitating oxygen transport.
• (iii) Anaerobic respiration end product in humans: In humans, anaerobic respiration yields lactic acid (a 3-carbon molecule) instead of CO2 when oxygen is limited, preventing complete glucose oxidation.

---

(b). Digestive System Processes:
• Peristalsis: Rhythmic muscular contractions of the digestive tract propelling food and mixing it with digestive enzymes.
• Bile storage: Bile is stored in the gallbladder.
• Bile functions:
– Fat emulsification: Bile reduces large fat globules into smaller droplets, enhancing enzymatic digestion.
– Acidity neutralization: Bile counteracts stomach acid, establishing an alkaline environment for intestinal enzymes.