o Types of respiration- (i) Aerobic respiration (ii) Anaerobic respiration 

1.  Respiration- The process by which digested food is broken down with the help of Oxygen to release energy.
   

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Difference Between Aerobic and Anaerobic Respiration

o Some common features of Respiratory organs-
(i) Large surface area- for greater rate of diffusion of respiratory gases.
(ii) Thin permeable walls – to ensure easy diffusion & exchange of gases.
(iii) Extensive blood supply- Respiratory organs are richly supplied with blood vessels for quick transport of gases.
o Gaseous exchange in plants-

•   Process – Diffusion
•   Direction of diffusion depends on- (i) Environmental conditions (ii) Requirement of the plant.
•   Day time- Carbon dioxide given out during respiration is used for photosynthesis. Therefore only Oxygen is released, which is a major activity during the day.
•   Night time – Only respiration takes place. Therefore only Carbon dioxide is released, which is a major activity during the night.

o Gaseous exchange in animals-
 Terrestrial animals- take Oxygen from the atmosphere.
 Aquatic animals- take Oxygen dissolved in water. (Oxygen content is low in water,
therefore they breathe faster. o Human Respiratory system-
External nostrils → Nasal cavity → Trachea→ Bronchi → Bronchioles →Alveoli

•   Rings of cartilage present in the throat ensure that the trachea (air passage) does not
  collapse when there is less air in it.
•   Lungs – (i) Present in the thoracic cavity.
  (ii) They are spongy, elastic bags consisting of Bronchi, Bronchioles and Alveoli
  
• o Respiration occurs in two phases-
• o (i) External-Breathing, which is a mechanical process.
  (ii) Internal - Cellular respiration
  o Mechanism of breathing – It includes : (i)Inhalation (ii) Exhalation o Exchange of gases-
   Unicellular organisms- By Diffusion
   Animals- (i) As the body size is large, diffusion alone is not enough.
  (ii) Respiratory pigments also required.
  (iii) Respiratory pigment in human beings is Haemoglobin,
  which is present in red blood corpuscles.
  (iv) It has very high affinity for Oxygen.
  (iv) Carbon dioxide is more soluble in water than Oxygen, so it
  Gets dissolves in blood and is thus transported.