Nutrition in Animals Class 7 Science Notes - Chapter 2

 Different Ways of Taking Food

Each species or type of organism has their own way of taking in food.

Bees and humming birds suck plant-nectars, infant of humans and some animals feed on mother’s milk, Snakes such as python consume the animals upon which they prey.

Aquatic animals filter small food particles floating close by and feed on them.

Digestion in Humans

The digestive tract and the associated glands together constitute the digestive system in humans.

This constitutes the whole path along which, food moves through the body, starting from the mouth and ending at the anus.

Digestive tract includes the oesophagus, stomach, small intestine and large intestine.Salivary glands, liver and pancreas are the major digestive glands.

Buccal Cavity

The buccal cavity is more commonly known as the mouth, and it is the beginning of the digestive system for humans.It consists of the tongue and teeth.Teeth: Helps in chewing food and breaking down food into smaller particles.

Tongue: Fleshy muscular organ attached at the back to the floor of the buccal cavity.Saliva is secreted in the mouth and helps in the break down of food.TongueIt is a muscular organ, fleshy in nature attached to the back of the base of the buccal cavity.It helps in mixing saliva with food while chewing and aids in swallowing.The tongue possesses tastes buds that help us recognise different tastes.

Tooth Decay

Bacteria present in mouth break down the sugars present from the leftover food and release acid.These acids gradually damage the teeth and results in tooth decay.

Oesophagus or food pipeThe food that is swallowed, passes into the oesophagus.It is a muscular tube, about 25 cm long, with a sphincter (valve/opening) at each end.Its function is to transport food and fluid, after being swallowed, from the mouth to the stomach.Food is propelled down by as there in movement through the walls of the food pipe.StomachIt is a thick-walled bag-like structure.It obtains food from the food pipe and opens into the small intestine towards the other opening.The inner lining of the stomach produces mucus, hydrochloric acid(HCl)and other digestive juices.Food is churned into semi-solid mass in the stomach.

Enzymes present in the gastric juice disintegrate the food.Hydrochloric acid helps in partial digestion of proteins and also kills harmful bacteria.

Small Intestine

This is a highly coiled organ of 7.5 metres length.It receives secretion from the liver and pancreas.Complete digestion and absorption of food take place in the small intestine.The inner walls of the intestine have finger-like outgrowth called villi.Villi increase the surface area for absorption of food.Each villus has a small network of blood vessels.Absorbed food by villi is transferred to the body via blood vessels.

Large Intestine

It is wider and shorter than the small intestine.It is 1.5m in length.Absorption of water and salt from undigested food occurs in the large intestine.Remaining waste matter is passed out through the rectum.Time to time, faecal matter is removed through the anus (egestion).

Anus

The anus is the opening at the end of the human digestive tract.The removal of faecal matter from the large intestine occurs through the anus and this process is called egestion.Saliva and Salivary glands

Three pairs of salivary glands are present around the mouth and they pour their secretion, saliva, into the mouth by salivary ducts.Saliva has mucous and salivary amylase.

Mucous helps in easy passage of food through the food pipe.Salivary amylase is an enzyme responsible for breaking of starch content of food into simpler sugars.

Gall Bladder

The gallbladder is a small pear-shaped organ present under the liver, on the right side of the body.It stores bile juice secreted by the liver.

Bile plays an important role in the digestion of fats.Ingestion

The process of taking food into the body is called ingestion

Digestion

The breakdown of complex components of food into simpler substances is called digestion.

Partial digestion takes place in the stomach and complete digestion takes place in the intestine.Absorption & Assimilation in Small IntestineThe digested food is taken up by the blood vessels lining the small intestine’s walls. This phenomenon is referred to as absorption.The inner walls of the small intestine have many finger-like outgrowths called villi.The substances that are absorbed are transported through blood vessels to various organs of the body where it

Absorption & Assimilation in Small Intestine

The digested food is taken up by the blood vessels lining the small intestine’s walls. This phenomenon is referred to as absorption.The inner walls of the small intestine have many finger-like outgrowths called villi.The substances that are absorbed are transported through blood vessels to various organs of the body where it is utilized to build complex substances like proteins essential for the body. This is called assimilation. 

Digestion in Grass Eating Animals

Digestive system in grass eating animals is different from that of humans.These animals are chewing continuously even when they are not eating.They swallow the grass very fast and store it in a chamber called Rumen.In the rumen, the bacteria partially digest the food and now it is called as cud.Later, cud reverts to the mouth and animal chews it again slowly.This phenomenon is referred to as rumination and the animals are called as ruminants.They also have very long small intestine which helps in complete digestion of cellulose, the main component of grass.CudPartially digested food, returned from rumen into the mouth, for further chewing is called as cud.

Rumination 

Rumination is the process by which the cattle regurgitates previously consumed feed and masticates it a second time.

Feeding and Digestion in Amoeba

AmoebaAmoeba is single-celled organism, microscopic in nature found in pond water.Amoeba regularly changes its shape and position.Process of Digestion in AmoebaAmoeba captures the food particles with the help of pseudopodia. The process is called as phagocytosis.A food vacuole is thus created with the food material inside.

Digestive juices are produced into the food vacuole when it is moving through the cytoplasm.They act on the food and disintegrate it down into simpler substances and the digested food is then absorbed.Finally, the food vacuole opens to the outside and undigested food is released into surrounding water.