Nutrition and digestion in animals Biology Science notes

Nutrition and digestion in animals
Complete circle foodchain

All animals require
food for obtaining energy, growth, repair of damaged parts and functioning of
the body. The process of taking food by an animal and its
utilisation in the body is called animal nutrition.

the previous chapter we learned that plants can prepare their own food by photosynthesis but
animals cannot.

  • Animals get their food from
    plants, either directly by eating plants or indirectly by eating animals
    that eat plants. So animals exhibit heterotopic mode of nutrition.
  • Again from previous chapter it
    is clear that all living organisms (both plants and animals) need certain
    nutrients to stay alive and grow and these nutrients are obtained from
  • Since this Chapter is about
    nutrition in animals so in this chapter we will learn about the process of
    intake and utilization of food in animals.
  • All the animals can be divided
    into three groups on the basis of their food habits. These are:
  • We take food through our mouth,
    digest and utilise it.
  • Figure given here shows the
    human digestive system.
  • Human digestive system consists
    of alimentary canal and its associated human digestive system glands.
  • Various organs of human
    digestive system in sequence are
  • The glands which are associated
    with human digestive system are
  • We take food through our mouth
    and the process of taking food into the body is called ingestion.
  • The mouth or buccal
     contains teeth, tongue and salivary glands.
  • Digestion begins in the mouth
    when we chew the food with the help of our teeth.
  • The teeth cut the food into
    smaller pieces, chew and grind it.
  • Teeth are used for cutting,
    grinding and tearing the food before you swallow it.
  • You have different types of
    teeth to do the job.
  • Milk teeth:- A child has only 20 teeth, 10 in each jaw. These
    are known as milk teeth. They begin to fall at the age between 6 to 8 and
    then new set of teeth grows.
  • Permanent teeth:- This set contains 32 teeth, 16 in each jaw. There are 4
    incisors, 2 canines, 4 premolars and 6 molars in each jaw.

  • The salivary glands secrete
    watery liquid called saliva. Saliva is a digestive juice that
    helps to partially digest the starch present in the food.
  • The tongue helps in mixing
    saliva with the food.
  • Tongue is a muscular organ that helps you eat the food.
    It mixes saliva with the food during chewing and helps in swallowing it.
  • We also taste food with our
    tongue as it has taste buds that detect different tastes of food.
  • The swallowed food passes into
    the food pipe or oesophagus 
  • the movement of food in food
    pipe which runs along the neck and chest.
  • So, the oesophagus leads from
    your mouth to the stomach. It is made up of the muscles.
  • Food is pushed down by movement
    of the wall of food pipe.
  • Stomach is the thick walled bag present on the left side
    of the abdomen.
  • It is the widest part of the
    alimentary canal. Oesophagus brings slightly digested food from mouth into
    the stomach.
  • The stomach walls contains
    three tubular glands in its walls which secrete gastric juice.
  • The gastric juice contains
    three substances: Hydrochloric acid, the enzyme pepsin and mucus.
  • The hydrochloric acid creates
    an acidic medium which facilitates the action of the enzyme pepsin that is
    the digestion of protein into simple substances.
  • The acid kills many bacteria
    that enter along with the food.
  • The mucus helps to protect the
    stomach wall from its own secretions of hydrochloric acid.
  • The partially digested food
    then goes from the stomach into the small intestine.
  • Small intestine is highly
    coiled and is about 7.5 m long.
  • After leaving stomach food
    enters small intestine and last steps of digestion takes place in small
  • It receives secretions from
    liver and pancreas and wall of small intestine also secretes juices.
  • Liver:- Liver is the largest gland in the body and is
    situated in the upper part of the abdomen on the right side. It secrets
    bile juice that is stored in gall bladder.
  • Pancreas:- It is the large cream coloured gland located just below
    the stomach. The pancreatic juice acts on carbohydrates, fats and proteins
    and converts them into simple form.
  • The partially digested food now
    reaches the lower part of the small intestine.
  • The walls of the small
    intestine contain glands which secretes 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.
  • The small intestine is the main
    region for the absorption of digested food.
  • The inner surface of the small
    intestine has numerous finger-like projections called villi which increase
    the surface area for rapid absorption of digested food.
  • The digested food which is
    absorbed through the walls of the small intestine goes into our blood.
  • The blood carries these useful
    substances to each and every part of the body. The body uses these
    substances for its growth and maintenance. The absorption of digested food
    and its utilization by the body is known as assimilation.
  • Glucose, which is the final
    product of carbohydrate digestion, is broken down with the help of oxygen
    into carbon dioxide and water to release energy. Amino acids are used for
    growth and repair of worn out cells.
  • Fatty acid and glycerol Store
    below the skin as energy reserves.

Digestion in grass eating

  • Plant
    eating animals such as cows, deer, goats, buffaloes, camels and yaks
    quickly swallow their food after chewing it once.
  • The
    swallowed food goes to a chamber called rumen. They bring back the food
    later into the mouth and chew it again. These animals are called ruminants
    and the process is called rumination.
  • The
    stomach of ruminants consists of four compartments: rumen, reticulum,
    omasum and abomasum.
  • The
    swallowed food first enters the rumen, where the microorganism begins the
    digestion of the food (cellulose- a complex carbohydrate).
  • In
    the first two chambers, the rumen and the reticulum, the food is mixed
    with saliva and separated into layers of solid and liquid material
  • Solid
    clump together to form the cud     
  • The
    cud is brought back from the rumen to the mouth, where it is chewed slowly
    by completely mixing it with saliva and is further broken down. When the
    cud is chewed and swallowed again, it enters the omasum where the food is
    broken down further into simple compounds that enter in the abomasum.
  • Hydrochloric
    acid and digestive juices (gastric juices) are secreted in these chambers
    and the food is now fully digested.
  • It
    is then sent to the small intestine for absorption and the leftover
    undigested food is passed on to the large intestine from where it is
  • Grass
    is rich in cellulose and we humans cannot digest it.

simple soluble substances.

4. Assimilation: The digested food absorbed by the cytoplasm is stored or
utilized for its growth, development, multiplication and release of


1.     Herbivores: Those
animals which eat only plants are called herbivores. Examples are Goat, Cow,
and Deer etc.
2.     Carnivores: Those
animals which eat only other animals as food are called carnivores. Examples
are Lion, Tiger, and Lizard etc.
3.     Omnivores: Those animals
which eat both, plants and animals are called omnivores. Examples are Man, Dog
and Crow etc.
Feeding habits of animals
Chewing: Animals such as cow, buffalo, deer, giraffe, goat, sheep, etc
chew the cud. That means first they bite the plants and swallow them. Later
they bring the swallowed food back into mouth for chewing it again.
Swallowing: Some animals such as snakes, lizards, birds swallow their food.
Digestion in humans
1.     Mouth (Buccal
2.     Oesophagus
(food Pipe)
3.     Liver
4.      gall bladder
5.     Stomach
6.     pancreas
7.     Small intestine
8.     Large intestine
9.     Rectum
10. Anus.

1.     Salivary glands– Located in
mouth or Buccal Cavity
2.     Liver– It is the
largest gland situated in the upper part of abdomen on the right side.
3.     Pancreas– located just
below the stomach
The mouth and buccal cavity

1.     Your front
teeth are incisors. They are used for biting and cutting.
2.     Next to
incisors are canines. These are pointed and are used for piercing
and tearing pieces of food.
3.     Teeth at the
back of your mouth are broad with almost flat surface. These teeth crush and
grind food and are called the premolars and molars. Molars are
larger then premolars
4.     White substance
that covers your teeth is called enamel.


Small intestine



Large intestine

We take in food through the mouth, digest and
utilise it. The unused parts of the food are defecated. Have you ever
wondered what happens to the food inside the body? The food passes through a
continuous canal which begins at the buccal cavity and ends at the anus. 
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
Digestion in amoeba

is a microscopic, single-celled organism. It is found in ponds, pools
and ditches. It doesn’t have a fixed shape. It constantly changes its
shape by pushing out one or more finger-like projections
called pseudopodia or false feet meant for locomotion and capturing
of food. All the processes of nutrition are performed by the single cell
of an Amoeba. 
Ingestion: Amoeba eats tiny
microscopic plants and animals as food, which floats on water in
which it lives. When an Amoeba, encounters a suitable organism, it
pushes out two pseudopodia around the organism. Gradually, the tips
of the pseudopodia fuse with each other. As a result, the food is
engulfed with a little surrounding water to form a food vacuole inside it.
Digestion: The enzymes from the surrounding cytoplasm enter the
food vacuole and break down the food into
Absorption: The digested food present in the food vacuole is absorbed
directly into the cytoplasm.
5. Egestion: The undigested
food gets stored inside the vacuole. The cell membrane of the amoeba
suddenly ruptures at any place and the undigested food is thrown
outside the body by the vacuole.