These DAV Class 7 Science Notes and DAV Class 7 Science Chapter 2 Notes – Nutrition in Living Organisms: Animals and Man act as excellent revision resources, particularly in preparation for board exams.
Nutrition in Living Organisms: Animals and Man Class 7 DAV Notes
→ Three main steps in Animal Nutrition: Food requirement/food habit, mode of intake of food and utilisation in the body.
→ Food Habits of Animals:
→ Herbivores: Animals which eat only plant materials are called herbivores, e.g. cow and deer.
→ Carnivores: Animals which eat other animals are called carnivores, e.g. lion and tiger.
→ Omnivores: Animals which eat both animal flesh and plant materials are called omnivores, e.g. bear and man.
→ Saprotrophic Nutrition: The mode of nutrition in which a living being feeds on dead remains of plants and animals is called saprotrophic nutrition. In this case, the digestion of food takes place before ingestion. Examples; mushroom, bread mould and some bacteria.
→ Parasitic Nutrition: The mode of nutrition in which a living being feeds on a live living being; either by living on or inside the body of the host; is called parasitic nutrition. Example: Dodder, Cuscuta, etc. .
→ Holozoic Nutrition: The mode of nutrition in which an animal ingests its food and digestion happens inside the body of the organism is called holozoic nutrition. Examples: Amoeba, man, etc.
→ Nutrition in Humans:
→ Nutrition in human happens in following steps:
- Ingestion: The act of getting and eating food is called ingestion. Human beings take food through mouth.
- Digestion: The breakdown of complex molecules into simple soluble molecules is called digestion. Digestion of food takes place with the help of certain chemicals which are called enzymes.
- Absorption: The digested food is absorbed by the wall of the small intestine. The absorbed food enters the blood supply and is sent to different parts of the body.
- Assimilation: The utilization of absorbed food; for growth and repair is called assimilation.
- Egestion: Elimination of undigested food from alimentary canal is called egestion.
→ Alimentary Canal: It is a hollow tube which begins from the mouth and ends in the anus. Digestion of food takes place in the alimentary canal. The alimentary canal consists of following parts:
→ Mouth and buccal cavity: Mouth leads to the buccal cavity. Buccal cavity contains teeth and tongue; in humans. Salivary glands are also present; which secrete saliva.
→ Teeth are rooted in the sockets of jaw bones. The part of a tooth which remains under the gums is called the root. The exposed part of a tooth is called crown. Crown is covered with a white protective material; called crown.
→ Human beings get two sets of teeth in their lifetime. The first set of teeth begins to come when a child is about 6 months old. These are called milk teeth. The second set of teeth begins to come at about 7 years of age and are called permanent teeth. An adult has 32 teeth; 16 in each jaw.
- Incisors: These teeth are used for cutting the food.
- Canines: These teeth are used for tearing the food.
- Premolars: These teeth are used for grinding the food.
- Molars: These teeth are also used for grinding the food.
→ Tongue is a muscular organ which is attached to the floor of the buccal cavity. Tongue is free at front and can move in all directions. Taste buds are present on tongue and help us in getting the sensation of test. Tongue also helps in mixing the saliva with food.
→ Food pipe or Oesophagus: It is a long, narrow and muscular tube which connects the buccal cavity to the stomach. The muscles in the walls of oesophagus move to facilitate forward movement of food.
→ Stomach: It is a bag-like organ and is the widest part of the alimentary canal. The stomach wall is highly muscular and thick. The inner lining of the stomach secretes gastric juice which contains, mucus, hydrochloric acid and digestive juices.
→ Mucus protects the inner lining of stomach.
→ Hydrochloric acid kills bacteria which may enter with food. Hydrochloric acid makes the medium inside stomach acidic; which is necessary for gastric enzymes to work.
→ Digestive enzymes of stomach carry out partial digestion of protein.
→ Small Intestine: it is a highly coiled, tube-like structure. The stomach opens into small intestine. Major part of digestion takes place in small intestine and digestion is completed here.
→ Small intestine receives bile from liver. Bile plays an important role in digestion of fat.
→ Small intestine also receives pancreatic juice; which comes from pancreas. The enzymes in the pancreatic juice act on carbohydrates, proteins and fats.
→ Small intestine also secretes certain enzymes which digest carbohydrate, protein and fat.
→ Absorption of food: The inner wall of the small intestine has large number of finger-like projections; called villi. Villi increase the surface area for absorption of digested food. The digested food passes into blood vessels which are present in the villi.
→ Large Intestine: The large intestine is wider but shorter than small intestine. Undigested and unabsorbed food reaches large intestine. Some minerals and excess water are absorbed in the large intestine. The remaining waste then goes to the rectum; where it is stored in the form of semi-solid faeces. The faeces are eliminated through anus; from time to time.
→ Nutrition in cub chewing herbivore animals:
Grass eating animals are called ruminants. There are four chambers in their stomach. The first chamber is the largest and is called rumen. Some microorganisms live in the rumen and help in digestion of cellulose. Grass eating animals quickly swallow the food and store it in rumen. After partial digestion in the rumen; the food comes back to mouth; in the form of small lumps. This food is called cud. The animal then chews the cud properly and hence is called cud-chewing or ruminating animals. It is important to note that without the help of certain microorganisms, these animals cannot digest cellulose.
→ Nutrition in Amoeba: Amoeba is a unicellular organism which shows holozoic nutrition. Pseudopodia keep on forming and disappearing on the body of an amoeba. Amoeba surrounds the food particle with its pseudopodia and makes a food vacuole around the food particle. The food; along with water; is thus taken inside the food vacuole. Digestion and absorption takes place in the food vacuole. After that, the food vacuole expels undigested food.
→ Milk teeth: Set of temporary teeth in humans.
→ Permanent teeth: Set of teeth which replace the milk teeth.
→ Crown: The exposed part of a tooth.
→ Enamel: The white layer on the crown of a tooth.
→ Saliva: The juice secreted by salivary glands.
→ Enzymes: Special chemicals which break down complex molecules into simple soluble substances.
→ Assimilation: Utilisation of digested food for growth and repair in the body.
→ Rumen: The first chamber in the stomach of grass-eating animals.
→ Cud: Partially digested food in rumen.
→ Ruminating: The act of chewing the cud.
→ Pseudopodia: False feet of amoeba which are utilized for trapping food and for locomotion.
→ Villi: Finger-like structures inside small intestine which help in absorption of food.
→ Alimentary canal: The long muscular tube in human body through which food passes after ingestion.