Class 7 Science Chapter 6 Notes Respiration in Organisms
→ Aerobic respiration : When breakdown of glucose takes place with the use of oxygen, it is called aerobic respiration.
→ Anaerobic respiration : The breakdown of food without using oxygen is called anaerobic respiration.
→ Breathing rate : The number of times a person breathes in a minute is called breathing rate.
→ Cellular respiration : The breakdown of food in the cells with the release of energy is called cellular respiration.
→ Diaphragm : A muscular partition separating the abdominal and thoracic activities is called diaphragm.
→ Exhalation : The breathing out of air rich in carbon dioxide is called exhalation.
→ Gills : Gills are the respiratory organs of aquatic animals that breathe oxygen dissolved in water.
→Lungs : Lungs are sac like respiratory organs in the chest of vertebrates. It’s serve to remove carbon dioxide and provide oxygen to the blood.
→ Inhalation : The breathing in of air rich in oxygen is called inhalation.
→ Spiracles : Spiracles are small openings on the body of cockroaches and insects for breathing.
→ Tracheae :Tracheae are the air tubules forming the respiratory organ of most of the insects.
→ Ribs : The twelve pairs of curved arches of bones extending from the spine towards the sternum in human are called ribs.
→ Respiration involves two main processes; Breathing and cellular respiration.
→ Breathing is also called as external respiration. It involves inhalation and exhalation.
→ Cellular Respiration is also called internal respiration. It takes place inside the body cells.
→ During cellular respiration, a glucose molecule reacts with oxygen and is broken down into carbon dioxide and water. It is represented as : C6H12O6 +6O2 → 6CO2 + 6H2O Energy
→ This reaction is similar to the reaction that occur during burning or combustion.
→ Lime water is a solution of calcium hydroxide, Ca(OH)2. Carbon dioxide dissolves in water to form carbonic acid (H2CO3). H2CO3 and Ca(OH)2 react to form calcium carbonate (CaCO3) and H2O. Calcium carbonate is insoluble and forms a precipitate. This precipitate, causes the lime water to turn milky. If carbon dioxide is continued to be passed, more carbonic acid forms, which then reacts with calcium carbonate to form calcium hydrogencarbonate, which is soluble, so the precipitate dissolves.
Different animals have different ways in which exchange of gases takes place.
- In unicellular organisms like Amoeba, and Paramaecium, exchange of gases takes place by the process of diffusion through the cell membrane.
- In lower organisms like hydra and earthworm, exchange of gases occur through their moist outer surface (skin) by the process of diffusion. This type of respiration is called cutaneous respiration.
- Fish use gills for respiration. Gills are made up of large number of filaments which are richly supplied with thin blood vessels called capillaries.
→ Whales and dolphins do not have gills. They have openings called blowholes at the top of their heads. Blowholes act as a passageway to the trachea, through which the air passes and reaches the lungs. They need to come up to the surface of water to inhale and exhale air through their blowholes.
→ In human, respiratory system consists of nostrils, tracheae (windpipe), bronchi and lungs.
→ Mucous is secreted by the inner lining of the nose, which moistens the air passing through the nostrils. Hair and mucous present inside our nose prevent foreign particles such as dirt, dust, etc. to enter into the respiratory system.
→ The inhaled air becomes warm by the circulating blood in the nose.
→ The windpipe branches into two smaller tubes called bronchi (singular bronchus). Inside the lungs, the bronchus branches out into smaller tubes called bronchioles.
→ At the ends of each bronchiole, tiny air sacs are present called alveoli. Each lung contains about 300 million alveoli.
→ The actual gaseous exchange takes place in the alveoli of the lungs.
→ Blood contains a substance called haemoglobin. It binds with oxygen and forms
oxyhaemoglobin. Oxyhaemoglobin is carried by the blood to different tissues in our body.
→ Inside the tissues, oxygen is released from the oxyhaemoglobin and diffuses into the cells for cellular respiration.
→ Like yeasts, some bacteria can also live without oxygen. These bacteria are called anaerobic bacteria. Fermentation is the chemical breakdown of glucose by some microorganisms, such as bacteria and yeast, in the absence of oxygen which produces carbon dioxide and alcohol.
→ Plants do not have any organs of breathing like animals.
- Exchange of oxygen and carbon dioxide takes place through small pores called stomata.
- It forms an apparatus called stomatal apparatus with the guard cells surrounding it.
- The gaseous exchange takes place when the guard cells expand and contract.
- Opening and closing of the stomata depend on the contraction and expansion of guard cells due to external factors such as moisture, light, etc.
- Rate of exchange of gases is slower in plants than in animals.
→ Roots, too, need oxygen for generating energy in their cells.
- They get this oxygen from the air trapped between soil particles.
- Potted plants should not be overwatered as it replaces the air in the soil and, hence, the roots cannot breathe.
- However, plants like mangrove can grow in waterlogged areas as .they have aerial roots to take in air.
→ During respiration, plants take in oxygen and give out carbon dioxide. Although respiration takes place all the time, the rate of photosynthesis during the day is much greater than the rate of respiration. Thus, the oxygen released by plants during photo synthesis is much more than the oxygen consumed during respiration. During the night, photosynthesis does not take place due to the absence of sunlight. Only respiration takes place during the night. Plants, therefore, take in oxygen, and release only carbon dioxide at night. That is why, it is advised not to sleep under the tree at night.
→ It is not just the cells of the root and leaves which respire, but all parts of plants, including seeds, respire. In fact, dry seeds are dormant stages of living plants, as they contain a baby plant. The baby plant grows only when the seeds are provided with the right conditions which include water, air, and warmth of the sunlight. The germinating seeds have high rate of respiration. The seeds use this energy released during respiration to develop the roots and stem.
→ Lenticels are the pores present in the stems of woody plants which allow’ exchange of gases between A the atmosphere and internal tissues.