CBSE Tutorials

Life Processes | Respiration

Respiration In Plants

Plants need energy. This energy is obtained through the process of respiration :

• Plants exchange gases through stomata by the process of diffusion.
• Exchange of gases CO₂ and O₂ in Plants :

At Night
® No Photosynthesis only Respiration ® CO₂ is given out

At Daytime
® Photosynthesis and Respiration ® O₂ is given out ® CO₂ is used up in photosynthesis.

Comparison between respiration in animals and plants

Respiration in Animals

The food material taken in during the process of nutrition is used in cells to provide energy for various life processes. Break-down of food in cells to release energy is called cellular-respiration.

Some organisms use oxygen to break-down glucose (food) in cells completely into carbon dioxide and water (aerobic respiration).

Glucose

Organisms like yeast do not use oxygen and break-down of glucose is not complete resulting in break-down of glucose into ethanol, carbon-dioxide and release of energy (anaerobic respiration).

Similarly, during vigorous exercise in our body muscles, anaerobic respiration takes place resulting in formation of lactic acid and energy.

In all cases, the first step is the breakdown of glucose, a six-carbon molecule, into a three carbon compound called Pyruvate.

This break-down takes place in cytoplasm.

The break-down of pyruvate in presence of oxygen takes place in mitochondria resulting in release of energy. Hence, mitochondria are also known as power-house of the cell.

Difference between aerobic and anaerobic respiration :

ATP : It is a nitrogenous compound. The energy released during cellular respiration is used to synthesise, a molecule called ATP (Adenosine triphosphate) which is the energy currency of living organisms.

It is commonly called energy currency of the cell.

When the terminal phosphate linkage in ATP is broken using water, the energy equivalent to 30.5 KJ / mol is released.

ATP is used in body for muscle contraction, protein synthesis conduction of nerve impulses and all other activities.

Aerobic organisms need to ensure that there is sufficient intake of oxygen.

Animals have evolved different organs for the uptake of O₂ and release of CO₂.

Aquatic animals use the O₂ dissolved in water. Since the amount of O₂ in water is fairly low as compared to the amount of O₂ in the air, the rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms.

Fishes, take in water through their mouths and force it past the gills where the dissolved O₂ is taken up by blood.

Terrestrial organisms use the O₂ in the atmosphere for respiration. This O₂ is absorbed by different organs in different animals.

Respiratory system of all organisms have following features.

1. Large, fine and delicate surface area.
2. Respiratory surface is well protected having a passage for air to reach it and having good supply of blood.
3. A mechanism for moving the air in and out of this area, where the oxygen is absorbed.

Respiration in Humans

In human beings, the air is taken into the body by nostrils the air while passing through the nostrils is filtered by fine hairs that line the passage so that the air going into the body is free of dust and other impurities. The passage is also lined with mucus which helps in this process.

From nostril, the air passes through the throat into the lungs via trachea, rings of cartilage are present in the trachea which ensures that the air-passage does not collapse.

Nasal Passage ® Pharynx ® Larynx ® Trachea ® Bronchi ® Bronchioles ® Terminal Bronchioles ® Alveoli ® Alveolar sacs ® Exchange of gases.

Human respiratory system

The passage (trachea) divides into two bronchi and bronchioles in lungs which finally terminate in balloon-like structure called alveoli. The alveoli provide a surface where exchange of gases takes place. The wall of alveoli contains an extensive network of blood vessels.

When we breathe in, our chest cavity becomes larger due to lifting of rib cage and flattening of diaphragm.

When our chest cavity becomes larger the air rushes in through nostrils (inhalation or inspiration).

Just reverse happens when we breathe out (exhalation or expiration).

During breathing cycle, when the air is taken in and let out, the lungs always contain a residual volume of air so that there is sufficient time for O₂ to be absorbed and for the CO₂ to be released.

In humans, respiratory pigment haemoglobin is present in the RBC which has very high affinity for O₂.

Solubility of CO₂ is more as compared to O₂ in water and hence is mostly transported in dissolved form in our blood.

Carbon mono-oxide when binds with haemoglobin a stable compound carboxy-haemoglobin is formed which can cause death as no haemoglobin is left for transport of O₂.

(a)    Mechanism of Breathing

Before inhalation : The diaphragm contracts and becomes straight, expanding the chest cavity. The intercostal muscles contract, ribs coming outwards. This further enlarges the chest cavity, lowering the pressure inside lungs. Therefore air rushes in.

Before exhalation : The diaphragm relaxes and coming in its normal arched position, compressing the lungs. Intercostal muscles relaxes and move inwards. This reduces the volume of chest cavity which is already full of air. This forces the air out.

Inhalation ® Lifting of Ribs + Flat Diaphragm ® Increase in Volume of Chest Cavity ® Air is sucked inside the Nostrils ® Alveoli and Vice Versa for Breathing out

(b) Exchange of Gases CO₂ and O₂ between blood and tissues

Air in Alveoli ® Blood Vessels ® Blood ® RBC ® Respiratory Pigment (Haemoglobin) ® Oxygen Links with Hb (high pressure of O₂) ® O₂ is released in tissues from Hb (Low O₂ Pressure in Tissues) High CO₂ in Tissues ® CO₂ Released into Blood Blood Vessels in Alveoli ® CO₂ Released out Through Nostrils.