Class 7 Science Notes Chapter 10 (Chapter 10) – Examplar Problems Book

Detailed Notes with MCQs of Chapter 10, 'Respiration in Organisms', from your Science Exemplar book. This chapter is crucial not just for your class exams but also forms a foundation for many questions in competitive government exams. Pay close attention to the details.

Chapter 10: Respiration in Organisms - Detailed Notes for Competitive Exams

1. What is Respiration?

• It's NOT just breathing. Respiration is a fundamental biological process occurring within the cells of all living organisms.
• Cellular Respiration: The process of breaking down food (primarily glucose) in the cell with or without oxygen to release energy.
  • Glucose -> Energy (ATP) + Byproducts
• This released energy is stored in molecules called ATP (Adenosine Triphosphate), the energy currency of the cell, used to fuel all life activities.
• Breathing (External Respiration): The mechanical process of taking in oxygen-rich air (inhalation) and giving out carbon dioxide-rich air (exhalation). It facilitates the supply of oxygen for cellular respiration and removal of its byproduct, carbon dioxide.

2. Why Do Organisms Respire?

• To obtain energy from food.
• This energy is essential for survival and performing various life functions like growth, movement, repair, and maintaining body temperature.

3. Types of Cellular Respiration:

• a) Aerobic Respiration:

  • Occurs in the presence of oxygen.
  • Takes place primarily inside the mitochondria of the cell.
  • Involves the complete breakdown of glucose.
  • Equation:
    Glucose (C₆H₁₂O₆) + Oxygen (O₂) → Carbon Dioxide (CO₂) + Water (H₂O) + Energy (ATP)
  • Yields a large amount of energy.
  • Most multicellular organisms (humans, animals, plants) rely mainly on aerobic respiration.

• b) Anaerobic Respiration:

  • Occurs in the absence of oxygen.
  • Takes place in the cytoplasm of the cell.
  • Involves the incomplete breakdown of glucose.
  • Yields a much smaller amount of energy compared to aerobic respiration.
  • Examples:
    • In Yeast (Fermentation): Yeast are single-celled fungi (anaerobes) that can respire without oxygen.
      • Equation:
        Glucose (C₆H₁₂O₆) → Ethanol (Alcohol) + Carbon Dioxide (CO₂) + Energy (ATP)
      • Applications: Used in baking (CO₂ makes dough rise) and brewing industries (production of alcohol).
    • In Human Muscle Cells: During strenuous physical activity (like running fast), the oxygen supply may not meet the energy demand. Muscle cells switch temporarily to anaerobic respiration.
      • Equation:
        Glucose (C₆H₁₂O₆) → Lactic Acid + Energy (ATP)
      • Effect: Accumulation of lactic acid causes muscle fatigue and cramps. Relief can be obtained through rest, massage, or a hot water bath, which improves blood circulation and oxygen supply, helping break down the lactic acid.

4. Breathing (External Respiration) in Humans:

• Mechanism: Involves the movement of the rib cage and the diaphragm (a large muscular sheet below the lungs).
  • Inhalation (Taking air in):
    • Diaphragm contracts and moves down.
    • Ribs move up and outwards.
    • Volume of the chest cavity increases.
    • Pressure inside the chest cavity decreases, and air rushes into the lungs.
  • Exhalation (Giving air out):
    • Diaphragm relaxes and moves up.
    • Ribs move down and inwards.
    • Volume of the chest cavity decreases.
    • Pressure inside the chest cavity increases, and air is forced out of the lungs.
• Breathing Rate: The number of times a person breathes in one minute.
  • Average resting rate for an adult: 15-18 breaths/minute.
  • Increases significantly during physical exercise to meet the higher demand for oxygen.

5. Human Respiratory System:

• Pathway of Air: Nostrils → Nasal Cavity (air filtered by hair, warmed, moistened) → Pharynx (common passage for food and air) → Larynx (voice box) → Trachea (windpipe; supported by C-shaped cartilage rings to prevent collapse) → Bronchi (singular: bronchus; one enters each lung) → Lungs → Bronchioles (finer branches) → Alveoli (tiny air sacs).
• Lungs: Spongy, elastic organs located in the chest cavity.
• Alveoli: Millions of tiny, thin-walled air sacs surrounded by blood capillaries. This is the site of gaseous exchange.
  • Oxygen from inhaled air diffuses across the thin walls of alveoli and capillaries into the blood.
  • Carbon dioxide from the blood diffuses into the alveoli to be exhaled.
• Diaphragm: Forms the floor of the chest cavity; its movement is crucial for breathing.

6. Respiration in Other Animals:

• Insects (e.g., Cockroach, Grasshopper):
  • Have a network of air tubes called tracheae.
  • Air enters through small openings on the sides of the body called spiracles.
  • Tracheae branch into finer tubes (tracheoles) that reach all body tissues directly, supplying oxygen without the involvement of blood.
• Earthworm:
  • Breathes through its moist skin (Cutaneous respiration). Gases exchange directly through the thin, moist skin surface into the blood capillaries underneath.
• Fish:
  • Breathe through gills (Branchial respiration).
  • Gills are richly supplied with blood vessels.
  • Water containing dissolved oxygen enters through the mouth, flows over the gills, oxygen is absorbed by the blood, and carbon dioxide is released into the water which exits through gill slits. Fish often breathe faster than land animals because the concentration of dissolved oxygen in water is much lower than in air.
• Frogs:
  • Can breathe through their moist skin when in water and through lungs when on land (possess both cutaneous and pulmonary respiration).

7. Respiration in Plants:

• Plants also respire to get energy from glucose (produced during photosynthesis).
• They exchange gases (O₂ and CO₂) through:
  • Stomata: Tiny pores, mainly on the surface of leaves. Each stoma is surrounded by guard cells that control its opening and closing.
  • Lenticels: Small openings in the bark of older stems and roots for gas exchange.
  • Root Hairs: Extensions of root epidermal cells absorb air (oxygen) from the spaces between soil particles. This is why waterlogged soil is harmful to plants – it cuts off the oxygen supply to the roots.
• Key Points:
  • All parts of a plant (roots, stem, leaves) respire individually.
  • Plant respiration occurs continuously, day and night.
  • Photosynthesis (using CO₂, releasing O₂) occurs only during the day in the presence of sunlight, primarily in leaves.
  • During the day, photosynthesis rate is usually higher than respiration, so the net effect is O₂ release and CO₂ uptake. At night, only respiration occurs (O₂ uptake, CO₂ release).

Multiple Choice Questions (MCQs) for Practice:

1. Cellular respiration, the process of breaking down food to release energy, primarily occurs in the:
   (a) Lungs
   (b) Alveoli
   (c) Mitochondria
   (d) Trachea

2. During heavy physical exercise, muscle cramps occur due to the anaerobic breakdown of glucose into:
   (a) Ethanol and Carbon dioxide
   (b) Carbon dioxide and Water
   (c) Lactic acid
   (d) Ethanol only

3. Which organism performs anaerobic respiration that is utilized in the baking and brewing industries?
   (a) Earthworm
   (b) Yeast
   (c) Fish
   (d) Human muscle cells

4. During the process of exhalation in humans, the diaphragm:
   (a) Contracts and moves down
   (b) Relaxes and moves up
   (c) Contracts and moves up
   (d) Relaxes and moves down

5. Insects like cockroaches exchange respiratory gases through a network of tubes called:
   (a) Gills
   (b) Lungs
   (c) Moist skin
   (d) Tracheae

6. Gas exchange in the leaves of plants primarily takes place through:
   (a) Lenticels
   (b) Stomata
   (c) Root hairs
   (d) Bark

7. The end products of aerobic respiration in organisms are:
   (a) Ethanol, Carbon dioxide, and Energy
   (b) Lactic acid and Energy
   (c) Carbon dioxide, Water, and Energy
   (d) Carbon dioxide and Energy only

8. Which of the following correctly describes the movement of the rib cage during inhalation?
   (a) Ribs move down and inwards
   (b) Ribs move up and inwards
   (c) Ribs move down and outwards
   (d) Ribs move up and outwards

9. Earthworms carry out respiration through their:
   (a) Spiracles
   (b) Gills
   (c) Lungs
   (d) Moist skin

10. Which statement is TRUE about respiration in plants?
    (a) Respiration occurs only during the night.
    (b) Only leaves respire in plants.
    (c) Respiration occurs in all plant parts, 24 hours a day.
    (d) Plants do not require oxygen for respiration.

Answer Key for MCQs:

1. (c) Mitochondria
2. (c) Lactic acid
3. (b) Yeast
4. (b) Relaxes and moves up
5. (d) Tracheae
6. (b) Stomata
7. (c) Carbon dioxide, Water, and Energy
8. (d) Ribs move up and outwards
9. (d) Moist skin
10. (c) Respiration occurs in all plant parts, 24 hours a day.

Make sure you understand the difference between breathing and cellular respiration, the types of respiration and their products, and the diverse mechanisms organisms use for gas exchange. Revise these notes thoroughly. Good luck with your preparation!