Exercises

1. Complete the journey of food through the alimentary canal: Food → Mouth → Oesophagus → Stomach → Small Intestine → Large Intestine → Rectum → Anus.

2. Sahil (chapati), Neha (chewed chapati), and Santushti (mashed potato) add iodine. Observations:

• Sahil (Test tube A - Chapati): Turns blue-black. Reason: Starch is present.
• Neha (Test tube B - Chewed chapati): No color change (or light). Reason: Saliva broke down starch into sugars.
• Santushti (Test tube C - Mashed potato): Turns blue-black. Reason: Potato is rich in starch.

3. What is the role of the diaphragm in breathing?

• (iii) To help in inhalation and exhalation.
• Explanation: Its downward movement allows air into the lungs, and upward movement pushes it out.

4. Match the following:

• (i) Nostrils → (a) fresh air from outside enters
• (ii) Nasal passages → (d) tiny hair and mucus trap dust
• (iii) Windpipe → (e) air reaches our lungs through this part
• (iv) Alveoli → (b) exchange of gases occurs
• (v) Ribcage → (c) protects lungs

5. Anil claims respiration and breathing are the same. Questions to ask:

1. Is breathing a physical or a chemical process?
2. Where does the release of energy from food occur—in the lungs or inside the cells?
3. Do we produce water and CO2 from glucose while just inhaling air?

6. Which statement is correct and why?

• Tanu: We inhale air rich in oxygen.
• Why: We don't inhale pure oxygen; we inhale atmospheric air which contains 21% oxygen.

7. Why do we sneeze when we inhale dust-laden air?

• Dust particles irritate the sensitive inner lining of the nasal passage. Sneezing is a reflex action to expel these foreign particles and clear the passage.

8. Why was Anusha breathing faster than Paridhi after running?

1. Anusha might have run faster or more intensely, requiring more energy.
2. To meet the high energy demand, her body needed more oxygen to break down glucose rapidly, leading to an increased breathing rate.

9. Yadu’s experiment with saliva and rice flour:

• He wants to test: The action of saliva on starch (rice flour).
• Result: Test tube B (with saliva) will not turn blue-black because starch is digested.

10. Rakshita’s experiment with lime water:

• Investigation: Comparing the CO2 content in inhaled air (A) vs. exhaled air (B).
• Confirmation: Test tube B will turn milky quickly, proving that exhaled air contains significantly more CO2.