1. Digestion-
ü Carbohydrate, protein and fat are complex components that we gain from food.
ü The above complex components are simplified so that our body can utilize them.
ü The process of conversion of complex components like carbohydrates into simpler components like glucose so that living body can utilize it is called as digestion.
Figure - Complex to simpler component
2. Digestion In Humans-
ü The food passes through a continuous canal which begins at the buccal cavity and ends at the anus.
ü The canal can be divided into various compartments- the buccal cavity, foodpipe or oesophagus, stomach, small intestine, large intestine ending in the rectum and the anus.
ü These parts together form the alimentary canal (digestive tract).
ü The food components gradually get digested as food travels through the various compartments.
ü The inner walls of the stomach and the small intestine, and the various glands associated with the canal such as salivary glands, the liver and the pancreas secrete digestive juices.
ü The digestive juices convert complex substances of food into simpler ones.
ü The digestive tract and the associated glands together constitute the digestive system.
3. Buccal Cavity-
ü The buccal cavity is more commonly known as the mouth, and it is the beginning of the digestive system for humans.
ü It consists of the tongue and teeth.
ü Teeth: Helps in chewing food and breaking down food into smaller particles.
ü Tongue: Fleshy muscular organ attached at the back to the floor of the buccal cavity.
ü Saliva is secreted in the mouth and helps in the break down of food.
(a) Saliva and Salivary Gland-
ü Three pairs of salivary glands are present around the mouth and they pour their secretion, saliva, into the mouth by salivary ducts.
ü Saliva has mucous and salivary amylase.
ü Mucous helps in easy passage of food through the food pipe.
ü Salivary amylase is an enzyme responsible for breaking of starch content of food into simpler sugars.
(b) Tongue-
ü It is a muscular organ, fleshy in nature attached to the back of the base of the buccal cavity.
ü It helps in mixing saliva with food while chewing and aids in swallowing.
ü The tongue possesses tastes buds that help us recognize different tastes.
Figure - Regions of tongue
(c) Tooth Decay-
ü Bacteria present in mouth break down the sugars present from the leftover food and release acid.
ü These acids gradually damage the teeth and results in tooth decay.
4. Oesophagus or Food pipe-
ü The food that is swallowed, passes into the oesophagus.
ü It is a muscular tube, about 25 cm long, with a sphincter (valve/opening) at each end.
ü Its function is to transport food and fluid, after being swallowed, from the mouth to the stomach.
ü Food is propelled down by as there in movement through the walls of the food pipe.
5. Stomach-
ü It is a thick-walled bag-like structure.
ü It obtains food from the food pipe and opens into the small intestine towards the other opening.
ü The inner lining of the stomach produces mucus, hydrochloric acid (HCl)and other digestive juices.
ü Food is churned into semi-solid mass in the stomach.
ü Enzymes present in the gastric juice disintegrate the food.
ü Hydrochloric acid helps in partial digestion of proteins and also kills harmful bacteria.
Figure - Stomach
6. Small Intestine-
ü This is a highly coiled organ of 7.5 meters length.
ü It receives secretion from the liver and pancreas.
ü Complete digestion and absorption of food take place in the small intestine.
ü The inner walls of the intestine have finger-like outgrowth called villi.
ü Villi increase the surface area for absorption of food.
ü Each villus has a small network of blood vessels.
ü Absorbed food by villi is transferred to the body via blood vessels.
(a) Gall Bladder-
ü The gallbladder is a small pear-shaped organ present under the liver, on the right side of the body.
ü It stores bile juice secreted by the liver.
ü Bile plays an important role in the digestion of fats.
7. Large Intestine-
ü It is wider and shorter than the small intestine.
ü It is 1.5m in length.
ü Absorption of water and salt from undigested food occurs in the large intestine.
ü Remaining waste matter is passed out through the rectum.
ü Time to time, faecal matter is removed through the anus (egestion).
8. Anus-
ü The anus is the opening at the end of the human digestive tract.
ü The removal of faecal matter from the large intestine occurs through the anus and this process is called egestion.
9. Human Teeth-
ü The first set of teeth grows during infancy and they fall off at the age between six to eight years. These are termed milk teeth.
ü The second set that replaces them are the permanent teeth. The permanent teeth may last throughout life or fall off during old age or due to some dental disease.
ü Incisors – The four front teeth in both the upper and lower jaws are called incisors. Their primary function is to cut food. The two incisors on either side of the midline are known as central incisors. The two adjacent teeth to the central incisors are known as the lateral incisors. Incisors have a single root and a sharp incisal edge.
ü Canines – There are four canines in the oral cavity. Two in the maxillary arch and two in the mandibular area. They are behind and adjacent to the lateral incisors. Their main function is to tear food. They have a single, pointed cusp and a single root. They have the longest root of any tooth. They also serve to form the corners of the mouth.
ü Premolars (Bicuspids) – These teeth are located behind and adjacent to the canines and are designed to crush food. There are eight premolars in the oral cavity. There are two in each quadrant of the mouth. The one closest to the midline is the first premolar and the one farthest from the midline is the second premolar. These teeth can have 3-4 cusps. The maxillary first premolar has two roots, and the remaining premolars have a single root. There are no premolars in the primary dentition.
ü Molars – The most posterior teeth in the mouth are the molars. They have broader and flatter surfaces with 4-5 cusps. They are designed to grind food. Mandibular molars typically have 2 roots. Maxillary molars, which are located behind the second premolars, typically have 3 roots. There are 12 molars in the permanent dentition with three in each quadrant of the mouth. They are named starting with closest to the midline as first molars, second molars and third molars. Although, some people do not fully develop the third molars. Third molars are often referred to as wisdom teeth. The primary dentition only contains eight molars.
Figure - Human teeth
10. Digestion In Ruminants-
ü Like other vertebrates, ruminant Artiodactyla (including cattle, deer, and their relatives) are unable to digest plant material directly, because they lack enzymes to break down cellulose in the cell walls.
ü Digestion in ruminants occurs sequentially in a four-chambered stomach.
ü Plant material is initially taken into the Rumen, where it is processed mechanically and exposed to bacteria than can break down cellulose (foregut fermentation).
ü The Reticulum allows the animal to regurgitate & reprocess particulate matter ("chew its cud"). More finely-divided food is then passed to the Omasum, for further mechanical processing.
ü The mass is finally passed to the true stomach, the Abomassum, where the digestive enzyme lysozyme breaks down the bacteria so as to release nutrients.
ü Use of plant material is thus indirect, with primary processing by the bacterial flora maintained in the stomach.
ü The Perissodactyla (including horses, rhinoceroses, and tapirs) have evolved a less efficient form of ruminant digestion.
ü Bacterial fermentation occurs primarily in the intestine (hindgut fermentation), such that extraction of nutrients from plant material is less complete.
ü Although all mammals have lysozyme, the enzymatic properties of ruminant lysozyme have evolved to be especially efficient. In a superb example of convergent evolution, some leaf-eating monkeys have evolved a lysozyme with similar enzymatic properties, due to selection on independent mutations to produce identical amino acids at key active sites.
Figure - Digestion in ruminants
11. Amoeba-
ü Amoeba is single-celled organism, microscopic in nature found in pond water.
ü Amoeba regularly changes its shape and position.
ü Amoeba captures the food particles with the help of pseudopodia. The process is called as phagocytosis.
ü A food vacuole is thus created with the food material inside.
ü Digestive juices are produced into the food vacuole when it is moving through the cytoplasm.
ü They act on the food and disintegrate it down into simpler substances and the digested food is then absorbed.
ü Finally, the food vacuole opens to the outside and undigested food is released into surrounding water.
Figure - Digestion in amoeba
NCERT PRACTICE QUESTIONS
1. Fill in the blanks:
(a) The main steps of nutrition in humans are _________, __________, __________, _________ and __________.
(b) The largest gland in the human body is __________.
(c) The stomach releases hydrochloric acid and ___________ juices which act on food.
(d) The inner wall of the small intestine has many finger-like outgrowths called _________.
(e) Amoeba digests its food in the ____________ .
Solution:
Ans.- (a) ingestion, digestion, absorption, assimilation and egestion. (b) Liver. (c) digestive (d) villi. (e) food vacuole.
2.Mark ‘T’ if the statement is true and ‘F’ if it is false:
(a) Digestion of starch starts in the stomach. (False)
(b) The tongue helps in mixing food with saliva. (True)
(c) The gall bladder temporarily stores bile. (True)
(d) The ruminants bring back swallowed grass into their mouth and chew it for some time. (True)
3. Tick () mark the correct answer in each of the following:
(a) Fat is completely digested in the
(i) stomach (ii) mouth (iii) small intestine (iv) large intestine
(b) Water from the undigested food is absorbed mainly in the
(i) stomach (ii) foodpipe (iii) small intestine (iv) large intestine
Ans.- a) (iii) small intestine b) (iv) large intestine
4. Match the items of Column I with those given in Column II:
Ans.
Column- I | Column- II |
Food components | Product(s) of digestion |
Carbohydrates | Sugar |
Proteins | Amino acids |
Fats | Fatty acids and glycerol |
5. What are villi? What is their location and function?
Ans.- Villi are the finger-like projections or outgrowth present in the small intestine of our digestive system.
6. Where is the bile produced? Which component of the food does it help to digest?
Ans.- Bile juice is produced in the liver, they are stored in gall bladder and bile helps in the digestion of fats by breaking large fat globule into smaller ones.
7. Name the type of carbohydrate that can be digested by ruminants but not by humans. Give the reason also.
Ans.- Cellulose is the carbohydrate that can be digested by ruminants but not by humans because humans lack cellulase enzyme required to digest the cellulose.
8. Why do we get instant energy from glucose?
Ans.- Glucose is a simple sugar which is easily absorbed by the blood and hence, glucose gives instant energy.
9. Which part of the digestive canal is involved in:
(i) absorption of food ________________.
(ii) chewing of food ________________.
(iii) killing of bacteria ________________.
(iv) complete digestion of food ________________.
(v) formation of faeces ________________.
Ans.- i) Small intestine ii) Buccal cavity iii)Stomach iv) Small intestine v) Large Intestine
10. Write one similarity and one difference between nutrition in amoeba and human beings.
Ans.- Similarity - Both amoeba and human beings follow the holozoic type of nutrition. Difference- Humans intake food through buccal cavity. In amoeba food is ingested through pseudopodia.
11. Match the items of Column I with suitable items in Column II
Ans.-
Column-I | Column-II |
a) Salivary gland | (iii) Saliva secretion |
b) Stomach | (iv) Acid release |
c) Liver | (i) Bile juice secretion |
d) Rectum | (ii) Storage of undigested food |
e) Small intestine | (v) Digestion is completed |
f) Large intestine | (vi) Absorption of water |
|
|
12. Label of the digestive system.
13. Can we survive only on raw, leafy vegetables/grass? Discuss.
Ans.- No, we cannot survive only on raw, leafy vegetables because they mainly consist of Cellulose which cannot be digested by us due to lack of cellulase enzyme.
Junior Science Topic - Nutrition In Animals. Chapter notes, video lectures, power point presentation and NCERT exercise solution. (Class 7, CBSE syllabus, chapter 02)
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