Hey students! As we already know that
 
there are two modes of nutrition
 
autotrophic mode of nutrition and
 
heterotrophic mode of nutrition. In
 
autotrophic mode of nutrition, organisms
 
synthesize their own food,
 
while in heterotrophic mode of nutrition
 
organisms depend on other organisms for
 
their food supply as they cannot
 
synthesize their own food,
 
so in this lesson we'll mainly focus on
 
heterotrophic mode of nutrition. The word
 
heterotroph is made up of two words
 
hetero and troph. Hetero means
 
another and troph means nutrition, so the
 
word heterotroph means depending on
 
others for nutrition. Animals and fungi
 
are the examples of heterotrophic
 
organisms.The kind of food taken differs
 
from organism to organism and so
 
there are differences between the
 
digestive apparatus of all the organisms,
 
but still there are some basic steps
 
which are followed by all the organisms
 
which are digestion, absorption and
 
excretion of food. In some organisms food
 
is digested outside the body that is the
 
organisms break down the food outside
 
their body and then they absorb it.
 
This type of nutrition is found in fungi
 
like bread mould, yeast and mushrooms
 
while in some other animals like deer,
 
lion, elephant or even in us, food is
 
digested inside our body, but since the
 
kind of food taken and the way the food
 
is taken differs among all the organisms
 
so there are differences within the
 
digestive systems of all the organisms
 
and so to study these different
 
digestive systems all the organisms are
 
classified into two main classes
 
unicellular organisms and
 
multicellular organisms. Unicellular
 
organisms are the organisms that have
 
only one cell in their body to perform
 
all their body functions. For example
 
Amoeba, Paramecium, Euglena, etc. On the
 
other hand multicellular organisms are
 
the organisms that have more than one
 
cell or many cells to perform their body
 
functions. For example Lizard, Reptiles
 
Birds and even us. So, in this lesson we'll
 
mainly focus on heterotrophic mode of
 
nutrition in unicellular organisms like
 
Amoeba, Paramacieum, etc. So amoeba, it is
 
filled with jelly like substance called
 
cytoplasm, these finger-like
 
projections around the cell are called
 
pseudopods. These pseudopods help amoeba
 
in their locomotion.
 
These pseudopods also help amoeba to
 
capture its prey.
 
Whenever amoeba finds its prey like
 
bacteria, algae or dead plants or animals
 
it extends its pseudopodia around them.
 
These pseudopodia extensions then fuse
 
around the fluid particle and make food
 
vacuoles. These food vacuoles are the
 
structures in which the food is stored
 
inside amoeba, the food is then
 
digested or broken down into smaller
 
particles inside these food vacuoles so
 
that it can then travel from these
 
vacuoles outside into the cytoplasm. The
 
remaining undigested food is taken to
 
the surface of the cell and is thrown
 
out. So, we have just seen that how amoeba
 
captures its food with the help of
 
pseudopodia stores it in food vacuole
 
and throws it out of the surface of the
 
cell. Now we'll see one more example of
 
unicellular organisms.
 
How about Paramecium? Let's have a look
 
on a paramecium cell.
 
All these tiny structures around the cell
 
are called Cilia. Cilia helps in moving
 
the food particles inside the paramecium
 
cell to a specific spot. The food
 
particles then get stored in the food
 
vacuoles and in food vacuole the
 
digestion of the food particles start
 
and then the waste products are thrown out
 
of the paramecium body. So, we saw how
 
unicellular organisms obtain their food.
 
Let's have a quick recap. In the
 
beginning we studied that some organisms
 
digest the food outside their body, like
 
some fungi, like mushrooms, red moles
 
yeast. While there are some other
 
organisms that digest the food
 
inside their body like animals, elephant
 
lion, fishes and us.
 
Next we studied that organisms are
 
classified into two classes unicellular
 
organisms and multicellular organisms. In
 
unicellular organisms there is only one
 
cell to perform all the body functions
 
while in multicellular organisms there
 
are many cells that perform all the body
 
functions. At last we saw the process of
 
nutrition in Amoeba and Paramecium
