6. Life Processes | Class 10 CBSE | Web Notes | Part 3 | Respiration



It is the oxidation of the food material in cells to release energy for various life processes.

Some organisms use oxygen to breakdown glucose into CO2 and water. Some do not use oxygen.

Experiment to prove release of CO2 during respiration in human

  • Take some freshly prepared lime water in 2 test tubes.
  • In one, blow air through lime water. It immediately turns lime water milky.
  • In other test tube, pass air using a syringe or pichkari. It takes much time to turn the lime water milky.
  • It shows that the breath-out air contains more CO2 as compared to atmospheric air.

Experiment to prove release of CO2 during respiration in Yeast

  • Add some yeast to fruit juice or sugar solution. Take this mixture in a test tube fitted with a one-holed cork.
  • Fit the cork with a bent glass tube. Dip its free end into a test tube containing freshly prepared lime water.
  • Air taken out through the tube makes lime water milky. It is due to the production of CO2 in the mixture of yeast & sugar solution. Here, fermentation occurs.
In all types of respiration, the first step is the breakdown of glucose (6-carbon) into pyruvate (3-carbon). It takes place in the cytoplasm.

Anaerobic respiration: It is the respiration in the absence of air (oxygen). It releases less energy. E.g.
  • In yeast, the pyruvate is converted into ethanol & CO2. It occurs during fermentation.
  • Sometimes, when there is no oxygen in our muscle cells, the pyruvate breaks down into lactic acid (3-carbon). This build-up of lactic acid in muscles during sudden activity causes cramps.
Aerobic respiration: It is the respiration in presence of air (oxygen). It releases much energy. Here, pyruvate breaks down using oxygen in the mitochondria giving three CO2 molecules & water.
Energy released during cellular respiration is used immediately to synthesise ATP molecules (energy currency) from ADP & inorganic phosphate [℗].

ATP is used to fuel all other cellular activities. When the terminal phosphate linkage in ATP is broken using water, energy (30.5 kJ/mol) is released. It drives the endothermic reactions in the cell.

A battery is used to obtain mechanical energy, light energy, electrical energy etc. Similarly, ATP can be used for muscle contraction, protein synthesis, conduction of nervous impulses etc.

Gas exchange in plants:

It occurs through stomata. Here, CO2 & oxygen are exchanged by diffusion. The large intercellular spaces in leaves help the cells in contact with air.

During day, CO2 formed by respiration is used for photosynthesis. So, CO2 is not released but oxygen is released. At night, photosynthesis does not occur. So, CO2 is released out but oxygen is not released.

Gas exchange in animals:

Aquatic animals breathe dissolved oxygen in water.

In fishes, the respiratory organ is gills with gill slits behind their eyes. They may be covered by operculum.

During breathing, fishes open and close mouth & gill slits (or operculum) in a coordinated manner and timing. They take in water through mouth and pumps over the gills. From the gills, dissolved O2 is taken up by blood.

The amount of dissolved O2 is lower than that in the air. So, the rate of breathing in aquatic organisms is faster than that in terrestrial organisms.

In terrestrial animals, there are different types of organs to breathe atmospheric oxygen. They increase surface area which is in contact with the atmosphere.

Surface of respiratory organs is very fine and delicate for easy gas exchange. To protect this surface, it is placed within the body. So, some passages are necessary to carry air in and out of respiratory organ.

Human respiratory system

It involves lungs & air passage.

Air passage starts from nostrils through which air is taken into the body. Air passage is lined with fine hairs & mucus to filter the air.

Conduction of air through the passage is as follows:

Nostrils → nasal passage → pharynx → larynx → trachea → bronchi → bronchioles → lungs.

Rings of cartilage in the throat and trachea prevent collapsing of air-passage.

Within the lungs, the passage divides into smaller tubes (bronchi & bronchioles).

Bronchioles terminate in balloon-like structures called alveoli (sing. alveolus).

Gas exchange occurs in the surface alveoli.

Alveolar walls contain a network of blood vessels.

When we breathe in, ribs are lifted and the diaphragm gets flattened. As a result, the chest cavity becomes larger and air enters the lung alveoli.

The blood brings CO2 from the rest of the body to release into the alveoli. Oxygen in the alveoli is taken up by blood in the alveolar blood vessels and is transported to all body parts.
Tobacco or tobacco products affect tongue, lungs, heart and liver. Smokeless tobacco also causes heart attacks, strokes, pulmonary diseases & cancers.
Oral cancer is highly reported in India due to tobacco chewing in the form of gutkha.
Smoking destroys cilia on the upper respiratory tract. As a result, germs, dust, smoke etc. enter lungs and cause infection, cough & lung cancer (common cause of death).
During the breathing cycle, the lungs always contain a residual volume of air so that there is sufficient time to absorb oxygen and release CO2.

In large-sized animals, diffusion pressure is not sufficient to deliver O2 to all body parts. So, respiratory pigments take up oxygen from the lungs and carry it to tissues.

In humans, the respiratory pigment is haemoglobin on red blood corpuscles (RBC). It has high affinity for O2.

CO2 is more soluble in water than oxygen and hence is mostly transported in the dissolved form in our blood.

- If the alveolar surface were spread out, it would cover about 80 m2. The surface area of human body is about 1.9 m2.

- If diffusion were to move oxygen in our body, it would take 3 years for an oxygen molecule to get to toes from our lungs. Haemoglobin helps in faster gas transport.

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