Plants make their food by the process of photosynthesis, but animals cannot make their food themselves. Animals get their food from plants. Some animals eat plants directly while some animals eat plant eating animals. Thus, animals get their food from plants either directly or indirectly. This food is brokendown in an animal's body into simpler substances to obtain energy.
The process by which food is taken in by an organism and used by its body is called nutrition.
Nutrition in complex animals involves following steps:
Digestion: The process of breaking down of complex component of food into simpler substances is called digestion. The process of digestion is different in human, grass eating animals, amoeba, etc.
Absorption: The process of passing of digested food into blood vessels in the intestine is called the absorption.
Assimilation: The conversion of absorbed food in complex substances such as proteins and vitamins required by body is called assimilation. In other words, assimilation is the conversion of absorbed food (nutrients) into living tissues. Through the process of assimilation our cells are supplied with oxygen and nutrients.
Egestion: Removal of waste materials from the body is called egestion. The faecal matter is removed through the anus from time-to-time. Since the waste of food left after digestion is also called faeces, hence the process of egestion is also known as defecation.
Different Ways of ingesting Food
Different organism takes food in different ways.
- A humming bird sucks nectar of plants.
- Human beings use their hands to put food into their mouth and swallow the food after chewing.
- Infants of human and many other animals feed upon their mother’s milk by sucking them.
- A snake swallows the animals they prey upon without chewing them.
- A frog captures prey with its sticky tongue.
- An earthworm uses its muscular pharynx to swallow its food.
- Spiders weave sticky web in which small insects get stuck.
- Some aquatic animals filter tiny particles floating nearby and feed upon them.
- Amoeba, a unicellular animal, engulfs tiny particles of food by using pseudopodia. Amoeba surrounds the food by pseudopodia and then makes a food vacuole to engulf the food.
- In multicellular organisms; like hydra there are numerous tentacles around their mouth. Hydra uses tentacles to surround its prey and kill them with its stinging cells. Then the food is pushed inside the body cavity.
After taking of food, food is digested and then it is passed to the different parts of body for the growth, repair and other vital functioning of body.
The food we take is primarily in the form of complex substances. Food in such complex form is not used as such by animals. Hence, they need to be first broken down into simpler soluble forms so that they can be absorbed by the cells of the body.
Enzymes help in the breakdown of complex molecules like carbohydrates, protein, fats, etc. into simple molecules.
Digestion in unicellular animals; like Amoeba; is intracellular. The digestive enzymes are secreted in the food vacuoles.
Question 1: What is ingestion?
Answer: The intake of food is called ingestion.
Questions 2: What is digestion?
Answer: The breaking down of solid and complex food into simple and soluble forms is called digestion.
Question 3: What is absorption?
Answer: The process of passing of digested food into blood vessels in the intestine is called the absorption.
Question 4: What do you understand by assimilation?
Answer: The conversion of absorbed food in complex substances such as proteins and vitamins required by body is called assimilation.
Question 5: What do you understand by egestion?
Answer: Removal of waste materials from the body, time to time from anus is called egestion.
Questions 6: What are the steps of nutrition involved in animals?
Answer: There is five steps of nutrition involved in animals. These are Ingestion, Digestion, Absorption, Assimilation and Egestion.
Questions 7: What are Pseudopodia?
Answer: Finger-like outgrowths on amoeba are called pseudopodia.
(The word pseudopodia is the combination of pseudo and podus. Pseudo means false and podus means feet. Singular of pseudoposida is pseudopodium)
Digestion in Human
The digestive system of humans is well developed. It consists of the gut or alimentary canal, along with many associated digestive glands. The alimentary canal is divided into mouth, oesophagus, stomach, small intestine, large intestine and rectum.
Mouth: The food is ingested through the mouth. The mouth contains tongue, teeth and salivary glands. Teeth break the food into smaller particles. This process is called mastication. The chewed food is mixed with saliva. Saliva is a watery fluid secreted by the salivary glands. Saliva contains a type of enzyme called the salivary amylase, which converts starch into sugar.
Teeth: Our teeth cut, tear and grind the food before we swallow it. There are four types of teeth in our mouth.
- Incisors: These are flat and chisel-shaped teeth. They lie in the front of the mouth. There are eight incisor teeth; four in the upper jaw and four in the lower jaw. The incisor teeth are well adapted for cutting and biting of food items.
- Canines: These are round shaped, sharp and pointed teeth. Canines are well adapted to hold and tear the food. There are four canine teeth found in human.
- Premolars: There are two premolars on each side of each jaw. Premolars help in crushing and grinding the food. There are 8 premolar teeth in an adult human.
- Molars: There are two molars on both sides in both the jaws. They have almost a flat surface with small projections. These teeth are meant for fine grinding of food.
There are 12 molar teeth including the wisdom teeth in an adult human. The 4 molar teeth are also called wisdom teeth. Wisdom teeth usually grow between the ages of 18 to 21.
The tooth is covered with a white substance called enamel. It is the hardest substance in the human body.
Milk teeth and Permanent teeth
Humans get two sets of teeth in their lifetime. The first set comes out when we are babies, are called milk teeth. Milk teeth last until we are about 8 years old. Milk teeth are replaced by the second set of teeth which are called permanent teeth.
An adult human has 32 teeth in all; 16 in each jaw.
Question 1: How many types of teeth are found in human beings?
Answer: There are four types of teeth in human beings. These are called incisors, canines, premolars and molars.
Question 2: How many incisors are found in an adult human?
Answer: There are 8 incisors, 4 in lower and 4 in upper jaw, found in an adult human.
Question 3: What is the function of incisors?
Answer: Incisors are used to cut and bite the food.
Question 4: How many canines are found in an adult human?
Answer: There are four canine found in an adult human.
Questions 5: What is the function of Canines?
Answer: Canines are the type of teeth, which help to hold and tear the food.
Question 6: How many premolars are found in an adult human?
Answer: There are 8 premolars found in an adult human.
Question 7: What is the function of premolars?
Answer: Premolars help in crushing and grinding the food.
Question 8: How many molars are found in an adult human?
Answer: There are 12 molars are found in an adult human.
Question 9: What is wisdom tooth?
Answer: Wisdom teeth are molar teeth that grow usually between the ages of 18 to 21 in an human. These are the last teeth to grow in human beings.
Question 10: How many teeth does a human adult have?
Answer: A human adult has 32 teeth in all; 16 teeth in each jaw.
Question 11: What do you understand by milk and permanent teeth?
Answer: Human has two sets of teeth. These are called milk teeth and permanent teeth. Milk teeth start growing at the baby stage and are replaced gradually by permanent teeth from the age of 8 year.
Question 12: What is Enamel?
Answer: The white substance that covers our teeth is called enamel. It is the hardest substance in the human body.
Tongue: The tongue is a muscular organ. Tongue helps to mix saliva in the food. It also helps to push the food down the food-pipe or oesophagus. Taste receptors are present on tongue and give us the sense of taste.
Oesophagus: It is a tube-like structure connecting the mouth and the stomach. It is about 30 cm. long. Oesophagus has powerful muscles which gently push the food down to the stomach. The oseophagus contracts and relaxes in a rhythmic fashion to facilitate the forward movement of food. This movement happens in other parts of the alimentary canal as well and is called peristalsis. No digestion takes place in oesophagus.
Stomach: It is a muscular J- shaped thick walled bag. Stomach is the widest part of alimentary canal. It receives food at one end from food pipe and opens into the small intestine on the other end.
Stomach churns the food to mix digestive juices. The food in the stomach is churned into semi solid. The churned semi-solid food is called chime. Gastric juice is secreted from the wall of stomach and mixed with food. Gastric juice contains some enzymes and hydrochloric acid. The enzymes present in the gastric juices break down protein from food. The hydrochloric acid kills the harmful bacteria (if any) present in the food and helps the gastric enzymes to work.
Small intestine: The food leaves the stomach at certain intervals of time and enters into the small intestine.
The small intestine is the longest part of the digestive system. It is about 20 feet or seven meters long in an adult human. Small intestine is a highly coiled tube. It consists of three parts: duodenum, jejunum and Ileum.
In the duodenum, the liver and pancreas pour their secretions. Liver secretes bile juice and pancreas secretes the pancreatic juice. The bile juice contains the bile which carries out emulsification of fat. In this process, the fat is broken into tiny droplets. The pancreatic juice contains several enzymes. The enzymes of the pancreatic juice break down starch into simple sugars and proteins into amino acids.
Minerals and vitamins do not need to be changed because cells are able to absorb them easily.
From duodenum the food goes to the lower part of the intestine. There are numerous finger-like projections on the wall of the small intestine. These projections are called villi. They have fine blood capillaries to absorb the food. After absorption; food mixes in the blood stream and is carried to all the cells of the body. The cells utilize this food to release energy.
Large intestine: The digested food enters into large intestine after small intestine. The large intestine is wider and shorter than small intestine. It is about 1.5 metre in length.
In large intestine; excess of water from the materials is absorbed. The semi solid residue is stored in the last part of the large intestine called rectum and finally throw out of the body through the anus from time to time. The throwing out of waste of digested food from rectum is called egestion. Egestion is also known as defecation.
Digestion in Grass Eating Animals
Ruminants: None of the animal can digest cellulose which is a major component of the food eaten by herbivores. The plant eating animals digest their food in two steps. Their stomach is divided into four chamber, viz. rumen, reticulum, omasum and abomasum.
First of all, half chewed food is swallowed and it then goes from mouth to the rumen, the first chamber of the stomach. Here, it is acted upon by bacteria. These microorganisms digest the cellulose. This half digested food goes to the second muscular chamber; the reticulum. From the reticulum the food is sent back to the mouth; as cud; to be chewed again. Chewing of the cud is called rumination and such animals are called ruminating animals or ruminants. Cow, goat, buffaloes, sheep, bison, etc. are good example of ruminating animals. The re-chewed food is swallowed for the second time. After passing the first two chambers it enters the third chamber; the omasum. Here the food is further broken down into smaller pieces and finally enters the fourth chamber, the abomasum. Here, all enzymes act upon the food and the digestion is completed.
After digestion and absorption, nutrients from food are taken to the cells in all parts of the body. The cells oxidize the food to release energy.
Very short answer type question:
Question 1: What is a carnivorous animal? Give two examples.
Answer: Animals, which eat the flesh of other animals, are called carnivorous, e.g. lion, tiger.
Question 2: What is the function of the digestive juice secreted by the liver?
Answer: The digestive juice from the liver breaks up fat into tiny particle.
Question 3: Name the organs that make up the alimentary canal.
Answer: Mouth, oesophagus, stomach, small intestine, large intestine and rectum compose the alimentary canal.
Question 4: Name the four types of teeth.
Answer: The four types of teeth are: Incisors, Canines, Premolars and Molars.
Question 5: Name the four compartments in a ruminant’s stomach.
Answer: Four compartments in a ruminant’s stomach are: Rumen, reticulum, omasum and abomasum.
Questions 1: Movement of food through alimentary canal is called by which of these terms?
Answer: (b) Peristalsis
Question 2: The liver produces which of these enzymes?
(d) None of these
Answer: (d) None of these.
Question 3: Which of these is not a part of nutrition?
Answer: (b) Excretion.
Question 4: Digestive juice is not secreted by which of these organs?
(a) Small intestine
Answer: (b) liver
Question 5: The walls of the large intestine absorb which of these?
(b) Digested food
Answer: (d) Water.
Question 6: Which of the following is not a part of ruminant stomach?
Answer: (b) Anus
Question 7: Bile is produced by which organ?
(b) Gall bladder
Answer: (c ) Liver
Match the following
|Column A||Column B|
|(1) Villi||(A) Large intestine|
|(2) Hydrochloric acid||(B) Liver|
|(3) Bile||(C) Mouth|
|(4) Absorption of water||(D) Stomach|
|(5) Mastication||(E) Small intestine|
Answer: 1-E, 2-D, 3- B, 4- A, 5- C
Fill in the blanks
1: Most of the enzymes in the small intestine come from ______
2: The __________ present on our tongue help us to taste food.
3: Saliva is secreted in the mouth by _______________
4: Living organisms that cannot make their own food are called__________
Answer: 1 → Pancreas, 2 → taste receptor, 3 → salivary gland, 4 → heterotrophs
Write true and false
1: Absorption and assimilation are similar processes.
2: Some plants are heterotrophic and depend on others for food.
3: Hydrochloric acid is present in the stomach.
4: Pitcher plant is an example of insectivorous plant.
5: Saprophytes are green in colour.
6: Ruminants have a three-chambered stomach.
7: An adult human has 32 teeth in all – 16 in each jaw.
8: Tongue gives the sense of smell.
Answer: 1 → F, 2 → T, 3 → T, 4 → T, 5 → F, 6 → F, 7 → T, 8 → F
Question 1: Fill in the blanks.
a. The main steps of digestion in humans are _____ ____ _____ _____ ______
b. The largest gland in 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 structure called _______.
e. Amoeba digest its food in the ________
Answer: a → ingestion, digestion, absorption, assimilation and egestion, b → liver, c → digestive juices, d → villi, e → food vacuole
Question 2: Mark T if the statement is true and F if it is false
a. Digestion of starch starts in the stomach.
b. The tongue helps in mixing food with saliva.
c. The gall bladder temporarily stores bile.
d. The ruminants bring back swallowed grass into their mouth and chew it for some time.
Answer : a → F, b → T, c → T, d → T
Question 3: Tick (√) mark the correct answer in each of the following.
a. Fat is completely digested in the
(c) Small intestine
(d) Large intestine
Answer: (c) Small intestine
b. Water from the undigested food is absorbed mainly in the
(b) food pipe
(c) Small intestine
(d) Large intestine
Answer: (d )Large intestine
Question 4: Match the column
|Column A||Column B|
|(1) Food components||(a) Products of digestion|
|(2) Carbohydrates||(b) Fatty acid and glycerol|
|(3) Proteins||(c) Sugar|
|(4) Fats||(d) Amino acids|
Answer: 1 → a, 2 → c, 3 → d, 4 → b
Question 5: What are villi? What is their location and function?
Answer: Villi is the finger like projections. These are found in the inner walls of small intestine. It helps in absorption of the digested food.
Question 6: Where is the bile produced? Which component of the food does it digest?
Answer: Bile is produced in the liver. Bile helps in digestion of fats.
Question 7: Name the type of carbohydrate that can be digested by ruminants but not by humans. Give the reason also.
Answer: Cellulose is the type of carbohydrates which is digested in ruminants but not in humans. Ruminants have a large sac –like structure between the small intestine and large intestine, in which cellulose of the food is digested by the action of certain bacteria. Such structure is not present in human. Hence human cannot digest cellulose while ruminants can.
Question 8: Why do we get instant energy from glucose?
Answer: Glucose is simple sugar so there is no need of digestion. It directly reaches the cells where it gives energy after respiration.
Question 9: Which part of the digestive canal is involved in:
(a) Absorption of food ________
(b) Chewing of food ________
(c) Killing of bacteria ________
(d) Complete digestion of food _______
(e) Formation of faeces _________
Answer: a → small intestine, b → mouth, c → stomach, d → small intestine, e → large intestine.
Question 10: Match the following column
|Column I||Column II|
|(A) Salivary gland||(1) Bile juice|
|(B) Stomach||(2) Absorption of water|
|(C) Liver||(3) Saliva secretion|
|(D) Rectum||(4) Acid release|
|(E) Small intestine||(5) Release of faeces|
|(F) Large intestine||(6) Storage of undigested food|
Answer: A -3, B - 4, C- 1, D- 5, E - 2, F- 6
Question 11: Label the diagram of the digestive system.