Simply CBSE

Respiration in Plants and Animals — Class 7 Science

Quick revision notes for exam preparation.

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📌 Key Points

  • Respiration is the process of breaking down glucose in cells to release energy. It occurs in every living cell, 24 hours a day.
  • Breathing (physical, in lungs) is NOT the same as respiration (chemical, in cells).
  • Aerobic respiration requires oxygen and produces CO2, water, and large amount of energy (38 ATP). Occurs in mitochondria.
  • Anaerobic respiration occurs without oxygen. In yeast: produces alcohol + CO2. In muscles: produces lactic acid.
  • Anaerobic respiration produces MUCH LESS energy (only 2 ATP) compared to aerobic respiration (38 ATP).
  • Muscle cramps during exercise are caused by accumulation of lactic acid from anaerobic respiration.
  • Human respiratory system: Nostrils → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli.
  • During inhalation: diaphragm contracts (moves down), ribs move up and out, chest expands, air rushes in.
  • During exhalation: diaphragm relaxes (moves up), ribs move down and in, chest contracts, air is pushed out.
  • Gas exchange occurs in alveoli - thin-walled air sacs surrounded by blood capillaries.
  • Haemoglobin in RBCs binds with oxygen and transports it to all body cells.
  • Plants respire through stomata (leaves), lenticels (stems), and root hair (roots) - day and night.
  • Fish use gills, earthworms use moist skin, insects use spiracles and tracheae, frogs use lungs and skin.
  • Fermentation by yeast is used in bread making (CO2 makes dough rise) and alcohol production.
  • Normal breathing rate: 15-18 times/minute at rest. Increases during exercise.

📘 Important Definitions

Respiration
The process by which food (glucose) is broken down in cells to release energy for life processes. It occurs in every living cell continuously.
Breathing
The physical process of taking in air (inhalation) and giving out air (exhalation) through the respiratory organs. It is NOT the same as respiration.
Aerobic Respiration
Respiration that occurs in the presence of oxygen, completely breaking down glucose into CO2, water, and a large amount of energy. Takes place in mitochondria.
Anaerobic Respiration
Respiration that occurs without oxygen, incompletely breaking down glucose into alcohol/lactic acid and a small amount of energy.
Fermentation
Anaerobic respiration carried out by yeast, converting glucose into alcohol and carbon dioxide with release of energy.
Alveoli
Tiny, thin-walled air sacs in the lungs where gaseous exchange (O2 and CO2) between air and blood takes place.
Diaphragm
A dome-shaped muscular sheet below the lungs that contracts during inhalation (moves down) and relaxes during exhalation (moves up).
Stomata
Tiny pores on the surface of leaves surrounded by guard cells, through which plants exchange gases for respiration and photosynthesis.

🔢 Formulas & Laws

Aerobic Respiration

Glucose + Oxygen → Carbon dioxide + Water + Energy

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (38 ATP)

Anaerobic Respiration (Yeast)

Glucose → Alcohol + Carbon dioxide + Energy

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + Energy (2 ATP). This is fermentation.

Anaerobic Respiration (Muscles)

Glucose → Lactic acid + Energy

Occurs during vigorous exercise when oxygen supply is insufficient. Causes cramps.

⚠️ Common Mistakes

✗ Wrong: Thinking breathing and respiration are the same process.

✓ Correct: Breathing is a physical process (inhaling/exhaling air in lungs). Respiration is a chemical process (breaking down glucose in cells to release energy). They are related but different.

✗ Wrong: Believing plants only respire at night.

✓ Correct: Plants respire ALL THE TIME (day and night). During the day, photosynthesis is faster than respiration, so the net effect appears as O2 release.

✗ Wrong: Thinking plants take in CO2 for respiration.

✓ Correct: Plants take in OXYGEN for respiration (just like animals). CO2 is used in photosynthesis, which is a completely different process.

✗ Wrong: Confusing the products of anaerobic respiration in yeast and muscles.

✓ Correct: Yeast produces ALCOHOL + CO2 (fermentation). Human muscles produce LACTIC ACID (no CO2). Different organisms, different products.

✗ Wrong: Saying the diaphragm moves down during exhalation.

✓ Correct: During INHALATION: diaphragm contracts and moves DOWN. During EXHALATION: diaphragm relaxes and moves UP.

📝 Exam Focus

These questions are frequently asked in CBSE exams:

Differentiate between breathing and respiration (at least 4 points).
3m★★★
Compare aerobic and anaerobic respiration with equations.
5m★★★
Why do we get muscle cramps during heavy exercise?
2m★★★
Describe the mechanism of breathing (inhalation and exhalation).
3m★★★
Name the respiratory organs of fish, earthworm, insects, and frog.
2m★★★
Why are alveoli suited for gas exchange? Give four reasons.
3m★★
Write the equation for aerobic respiration and explain where it occurs.
2m★★
Explain how plants respire. Do they respire at night?
3m★★
What is fermentation? How is yeast used in bread making?
3m★★

🎯 Last-Minute Recall

Close your eyes and try to recall: Key definitions, formulas, and 3 common mistakes. If you can recall 80% without looking, you're exam-ready!