gneet notes for NEET

Topic Digestion and Absorption

Biology Notes Index


• Food provides energy and organic materials for growth and repair of tissues. Biomacromolecules in food cannot be utilized by our body in their original form. They have to be broken down and converted into simple substances in the digestive system. This process of conversion of complex food substances to simple absorbable forms is called digestion and is carried out by our digestive system by mechanical and biochemical methods
• Digestion can be categoresd as
(1) Interacellular digestion: It is a form of digestion which takes place within the cytoplasm of organism. Intracellular digestion takes place in animals without digestive tract, in which food items are brought into cell for digestion.
(2) Extracellular digestion: Extracellular digestion is a process in which animals feed by secreting enzymes through the cell membrane onto the food. The enzymes break the food into molecules small enough to be taken pass through the cell membrane into the cell.
• The process of digestion in humans include five activities
(1) Ingestion: Entry of food into alimentary canal through the mouth and swallowing of food.
(2) Digestion: Process of conversion of complex food substances to simple absorbable form.
(3) Absorption: Process of conversion of complex food substances to simple absorbable form.
(4) Assimilation: The process by which chemicals from food are taken into the cell of body after digestion and absorption. The food is absorbed by blood vessels.
(5) Egestion: Process of removing the undigested food material from body through the anus

Nutrition is a process by which animals obtain essential and nonessential substances called nutrients and utilize these produce to energy required for various life process such as growth, repair, development, reproduction and other activities from the surrounding as food.
Autotrophic nutrition • Preparation of organic food from the inorganic materials is called autotrophic nutrition.
• It is of two types : Photoautotrophic and chemoautotrophic.
a) Photoautotrophic nutrition
• All green plants, certain Protists ( Euglena viridis) and some bacterial ( green sulphur bacterium, chlorobium) take carbon dioxide and water from the environment and transform these into glucose and oxygen with the help of Sun’s energy trapped by chlorophyll.
photosynthesis equation
b) Chemoautotrophic nutrition
• Some bacteria utilize light as source of energy during the synthesis of food, utilize the energy obtained in the form of A.T.P
• Examples of chemoautotrophic bacteria
i) Sulphur bacteria – Beggiatoa, thiothrix and Thiobacillus thiooxidans
ii) Iron bacteria
iii) Nitrifying bacteria – Nitrosomonas, Nitrosococcus, Nitrobacter and Nitrocystis
Heterotrophic nutrition
• Animals, fungi etc. cannot manufacture their food. They depends upon autotrophs directly or indirectly.
i) Holotrophic ( Holozoic) nutrition
• Most vertebrates and invertebrates take solid or liquid food through their mouth is called holozoic nutrition.
ii) Saprozoic nutrition
• It consists of obtaining food from dead and decaying organic food by first pouring digestive juices over the same and then sucking the digested food. Example – Spider, housefly
iii) Parasitic nutrition
• In this type of nutrition, food is obtained in liquid form from the body of another killing him
• Example – Plasmodium, Trypanosoma, Taenia, Ascaris



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