Class Notes
Class: X Subject: Biology
Topic: Ch- 6 Life processes – II ( Nutrition in Prepared by: Bharati Mandal.
Human beings)
Nutrition in Human Beings:
Human beings are omnivore animals, which have a complex digestive system.
Human Digestive System:
The human digestive system comprises of the alimentary canal and associated
digestive glands.
Alimentary Canal: It comprises of mouth, oesophagus, stomach, small intestine
and large intestine.
Associated Glands: Main associated glands are
Salivary glands
Gastric Glands
Liver
Pancreas
Intestinal glands
(Draw the following diagram in the notebook)
The various steps of nutrition in human beings are as follows:
Ingestion:
In human beings, food is ingested through the mouth. The food is put into the mouth
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with the help of hands.
Digestion:
The digestion of food commences in the mouth itself.
The teeth help in grinding the ingested food into small pieces. This process is called
mastication(Physical digestion).
The tongue helps in rolling of food and mixing of saliva in the food while mastication.
The salivary glands in our mouth produce saliva (watery liquid) which contains an
enzyme salivary amylase which digests the starch (carbohydrate) present in the food
into Maltose, a simple sugar (Chemical digestion).
The digestion of food remains incomplete in the mouth. The semi solid form of food in
the mouth is called Bolus.
Oesophagus:
The slightly digested food in the mouth is swallowed by the tongue and goes down the
food pipe called oesophagus.
When the food enters the oesophagus, its walls start rhythemic contraction and
expansion called as a peristaltic movement.This peristaltic movement of food pipe
pushes the slightly digested into the stomach.
Stomach:
The stomach is a J-shaped organ present on the left side of the abdomen.
The stomach walls contain s three tubular glands in it walls which secrete gastric juice.
The gastric juice contains three substances: Hydrochloric acid, the enzyme pepsin,
and mucus.
The hydrochloric creates an acidic medium which activates the enzyme Rennin and
Pepsin. They help in the digestion of proteins. It also kills the bacteria which enters
along with the food.
The mucus helps to protect the stomach wall from its own secretions of hydrochloric
acid.
The partially digested and semi liquid form of food (chyme)then goes from the stomach
into the small intestine.
Small intestine:
From the stomach, the partially digested food enters the small intestine.
The small intestine is the largest part (about 6.5 m) of the alimentary canal which can be
divided into three parts- Duodenum the first part, Jejunum the middle part and Ileum the
last part.
The small intestine is arranged in the form of a coil in the abdominal cavity.
The small intestine in human beings is the site of complete digestion of food (like
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carbohydrates, proteins, and fats)
The small intestine receives the secretion of two glands: Liver and Pancreas.
The liver secretes bile (greenish yellow liquid made in the liver and stored in the
gallbladder).
Bile performs two functions:
1. Makes the acidic food coming from the stomach alkaline so that pancreatic enzymes
can act on it.
2. Bile salts break the larger fats present in the food into small globules making it easy for
the enzymes to act and digest them. This process is called Emulsification of fat.
3.
The pancreas secretes pancreatic juice which contains the enzymes pancreatic
amylase for breaking down starch, trypsin for digesting proteins and lipase for
breaking down emulsified fats.
The walls of the small intestine contain glands which produce intestinal juice. The
enzymes present in it finally convert the proteins into amino acids, complex
carbohydrates into glucose and fats into fatty acids and glycerol.
In this way, the process of digestion converts the sizably voluminous and insoluble
aliment molecules into small water-soluble molecules.
The actions of various digestive enzymes are given in the following chart-
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