Respiration in Organisms 7th CBSE Notes

Class 7 Science (Biology)- Respiration

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➥ Respiration is the process of releasing energy from food.

➥ Glucose is the best source of energy in this process.

➥ Respiration has two phases:-

1. Breathing (External Respiration)
2. Repiration (Internal Respiration) or Cellular respiration

Respiration vs. Breathing:

Respiration	Breathing
It is the process of breaking down glucose to produce energy.	It is the process of inhaling and exchanging air in and out of the lungs.
It takes place inside the cells.	It takes place in the lungs.
It is a chemical process and involuntary.	It is a physical process and voluntary.
Energy is released in the form of ATP molecules.	No energy is produced during breathing.
It is an intracellular process.	It is an external process.

1. Breathing (Ventilation):

➥ This is the physical process of taking air into the lungs and expelling it out.

➥ Breathing Rate refers to the number of breaths a person takes per minute.

Normal Breathing Rate in Humans:

Children: Typically higher, around 20-30 breaths per minute.

Adults: 12-20 breaths per minute.

➥ It consists of two phases:

1. Inhalation (Inspiration):
   • The diaphragm contracts and moves downward.
   • The intercostal muscles (muscles between the ribs) contract, expanding the chest cavity.
   • The volume of the chest cavity increases, creating a low-pressure area in the lungs.
   • Air rushes into the lungs to equalize the pressure, filling the alveoli with fresh oxygen.
2. Exhalation (Expiration):
   • The diaphragm relaxes and moves upward.
   • The intercostal muscles relax, reducing the chest cavity's size.
   • The pressure in the lungs increases, forcing air out of the lungs.
   • Carbon dioxide is expelled from the body.

2. Internal respiration or Cellular Respiration:

➥ Inside cells, oxygen is used to break down glucose and produce energy in the form of ATP (Adenosine Triphosphate).

• 1. Aerobic Respiration:

  ➥ This process occurs in the presence of oxygen and produces a large amount of energy. The general equation for aerobic respiration is:

  Glucose + Oxygen → Carbon Dioxide + Water + Energy (ATP)
  C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP)

  ➥ In aerobic respiration, glucose is completely broken down into carbon dioxide and water, releasing a large amount of ATP.

• 2. Anaerobic Respiration:

  ➥ This process happens in the absence of oxygen and produces less energy. The general equation for anaerobic respiration (in muscle cells during vigorous exercise) is:

  Glucose → Lactic Acid + Energy (ATP)
  C₆H₁₂O₆ → 2C₃H₆O₃ + Energy (ATP)

  ➥ In anaerobic respiration, glucose is partially broken down into lactic acid, releasing a small amount of ATP.

Types of Respiration:

Aerobic Respiration	Anaerobic Respiration
Respiration occurs in the presence of oxygen.	Respiration occurs without oxygen.
Produces a large amount of energy.	Produces much less energy.
Energy is stored in ATP molecules.	Energy is stored in ATP molecules, but in smaller amounts.
Example: Humans	Example: Yeast, Bacteria

Human Respiratory System:

➥ The human respiratory system consists of a pair of lungs connected to a series of tubes that open outside through the nostrils.

Main Structures of the Human Respiratory System:

1. Nostrils: Two nostrils form a nasal passage. The inner lining has hairs to filter dust from inhaled air.
2. Pharynx: A tube-like structure that continues after the nasal passage.
3. Larynx (Voice Box): Located after the pharynx, helps in sound production.
4. Trachea (Windpipe): Composed of cartilaginous rings to prevent collapse in the absence of air.
5. Bronchi: The trachea divides into two bronchi, each entering one lung.
6. Bronchioles: The bronchi further divide into smaller bronchioles inside the lungs.
7. Alveoli: The bronchioles end in small air sacs called alveoli. Here, oxygen mixes with the blood and carbon dioxide is expelled.

Respiration in Plants

➥ Plants break down glucose (sugar) to get energy. This process is called respiration. They take in oxygen and give out carbon dioxide at night.

Glucose + Oxygen → Carbon Dioxide + Water + Energy (ATP)
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP)

Gaseous Exchange in Unicellular Plants:

➥ In tiny plants like algae, gases are exchanged directly through their surface.

1. Gaseous Exchange through Leaves:

➥ Leaves have tiny openings called stomata. These allow plants to take in carbon dioxide and release oxygen during the day. At night, they take in oxygen and release carbon dioxide.

2. Gaseous Exchange through Roots:

➥ Roots take in oxygen from the air in the soil. Carbon dioxide is released into the soil.

3. Gaseous Exchange through Stems:

➥ In green stems, gases are exchanged through the surface. In woody stems, small openings called lenticels allow gas exchange.

Transpiration in Plants

➥ Transpiration is the process by which plants lose water vapor through the stomata on their leaves. It helps cool the plant and pull water up from the roots.

• Water vapor leaves the plant through stomata.
• This helps bring water and nutrients from the roots to the leaves.
• Transpiration also helps keep the plant cool.

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