CBSE Class 7 Science Chapter 10: Respiration in Organisms NCERT Solutions

During a race, an athlete's muscles perform intense physical activity, which requires a significant amount of energy. To meet this increased energy demand, the body needs more oxygen to break down food molecules (like glucose) more rapidly. This process, called cellular respiration, releases energy. Consequently, the athlete breathes faster and deeper to take in more oxygen and expel carbon dioxide more efficiently, ensuring that the muscles receive the necessary oxygen supply to produce energy and recover.

Similarities:

• Both aerobic and anaerobic respiration involve the breakdown of food (like glucose) to release energy.
• Both processes occur within the cells of living organisms.

Differences:

Our nasal passages are lined with fine hairs and mucus that trap dust particles and other foreign substances. When a significant amount of dust enters the nostrils, it irritates the lining. This irritation sends a signal to the brain, which then triggers a forceful expulsion of air from the lungs through the nose and mouth. This sudden, forceful exhalation is called sneezing, and its purpose is to eject the irritants (like dust) from the nasal cavity, thus protecting the respiratory system. Sneezing is a protective reflex action.

Test-tube A will have the highest concentration of CO₂. Here's why:

• Test-tube A (Snail only): The snail is a living organism and respires. Respiration releases carbon dioxide. Since there is no plant to consume CO₂, its concentration will increase over time due to the snail's respiration.
• Test-tube B (Water plant only): The water plant performs photosynthesis during the day, which consumes carbon dioxide and releases oxygen. It also respires, releasing CO₂, but the rate of photosynthesis is generally higher, leading to a net decrease or stable level of CO₂ if light is available.
• Test-tube C (Snail and plant): In this test-tube, the snail respires and releases CO₂. However, the water plant uses this CO₂ for photosynthesis. The plant's consumption of CO₂ will keep its concentration lower than in test-tube A.

Therefore, test-tube A, containing only the respiring snail, will accumulate the highest concentration of carbon dioxide.

1. In cockroaches, air enters the body through (iii) spiracles. These are small pores on the sides of the body that connect to the tracheal system for gas exchange.
2. During heavy exercise, when oxygen supply is insufficient, muscle cells perform anaerobic respiration, leading to the accumulation of (ii) lactic acid. This accumulation causes muscle cramps.
3. The normal range of breathing rate per minute in an average adult person at rest is (ii) 15–18 breaths.
4. During exhalation, the diaphragm relaxes and moves upwards, and the rib cage moves downwards and inwards. Therefore, during exhalation, the ribs (ii) move downwards (and inwards).

Here is the correct matching of items from Column I to Column II:

1. Yeast matches with (vi) Alcohol. Yeast undergoes anaerobic respiration, producing alcohol.
2. Diaphragm matches with (iii) Lungs. The diaphragm is a muscle that aids in breathing by working with the lungs.
3. Skin matches with (v) Body surface. Earthworms and some amphibians breathe through their moist skin.
4. Leaves match with (iv) Stomata. Plants exchange gases through small pores on their leaves called stomata.
5. Fish matches with (ii) Gills. Fish extract dissolved oxygen from water using their gills.
6. Frog matches with (iii) Lungs (and also skin). Frogs can breathe using lungs when on land and through their moist skin when in water or on land.

Note: The original source had some discrepancies in the matching options provided. The solution above uses the most appropriate matches based on biological functions. For instance, Tracheae (i) are used by insects, not listed as a primary option for the given Column I items.