Class IX, BIOLOGY, "Organelles in Cytoplasm"

Mitochondria

They re oval or rod like in shape. Their membrane is doubled. Outer membrane is smooth while inner membrane has enfolding in the mitochondrial matrix. These enfolding are called cristae. The cristae bear small rounded bodies which are called particles.
There are about one million elementary particles in one mitochondrian. They are involved in oxidative phosphorylation. They also have many respiratory enzymes.

Number of Mitochondria

Their number is different in different cells of different animals. In more active cells, their number is more than 1000 e.g. liver cell.s The cells of ear lobes have a few number of mitochondria.

Function

Mitochondria re very important organelles of Eukaryotic cell.s Many oxidation-reduction reaction occur in the mitochondria. As a result energy is produced. This energy is used by cell in various functions. This the reason that mitochondria are also called “Power house of cell”.

Golgi Bodies

They were discovered by Camillo Golgi. They consist of set of smooth, flattened sacs which are called cristernae. The cristemae are stacked over each other. Golgi bodies are in the form of network in some cells or meshwork or filamentous in other cells.

Function

Golgi bodies store the secretions, convert them into finished products and pack them at their margins into small rounded sacs called Golgi vesicles, which transport secretions outside the cell.

Endoplasmic Reticulum

It is a network of tubules and cristemae extending throughout the cytoplasm from nuclear membrane to cell membrane.

Types of Endoplasmic Reticulum

Following are the two types of Endoplasmic Reticulum:

Smooth Endoplasmic Reticulum
It is also called non-granular endoplasmic reticulum because ribosomes are not attached on it.

Rough Endoplasmic Reticulum
It is also called granular endoplasmic reticulum because ribosomes are attached on it.

Functions

1. Smooth endoplasmic Reticulum plays a role in synthesis of lipids.
2. Rough endoplasmic reticulum plays an important role in synthesis of proteins. It also transports materials from one part of cell to other.
3. Endoplasmic reticulum provides support to the cell.

Ribosomes

These are tiny granular structures. These re not bounded by any membrane. These are formed in the nucleolus nd re freely dispersed in cytoplasm or attached with endoplasmic reticulum.

Functions

Ribosome is involved in protein synthesis. It is the only organelle which is also found in Prokaryotic cell.

Plastids

These are pigment containing organelles. These are found in plant cells. Many plastids have one or more than one pigments.

Types of Plastids

Plastids are of three types which are as follows:

Chloroplasts
These are mot important plastids. These re green in colour and found in green parts of plant. These contain chlorophyll which helps in photosynthesis. The study of ultra structure reveals that it is bounded by a double membrane.
Inside the chloroplast there is present a semifluid matrix called called stroma, which is made up of proteins and other chemicals. The inner membrane forms stacked membrane system which becomes suspended in the stroma. Each membrane stack is called granum (plural grana. The membranes of grana are the sites where photosynthesis occurs in the presence of sun light.

Functions
In chloroplasts, photosynthesis takes place and food is prepared for plant.

Chromoplasts
These are second type of plastids. These are of various colours other than green. In plants, colours other than green are due to chromoplasts. These are present in the petals of the flowers and in the ripened fruit.

Functions
These help the plants in pollination. These impart various colours to petals and fruits.

Leucoplasts
These are third type of plastids. These are colourless plastids. These are triangular tubular or of any other shape. These are found in food storage prts of the plant especially the roots and tubers.

Centriole

In animal cells, two centrioles are present near the nucleus. There are hollow and cylindrical. Each centriole consists of nine triplets of microtubules.

Function

Centrioles help in spindle formation during division of animal cell. Spindle is composed of protein fibers which help the chromosomes to move. Centrioles are absent in cells of higher plants. In some cells, centrioles help in the formation of flagella or cillia.

Vacuole

It is a fluid filled small sac which is bounded by a single membrane. In animal cells, these are comparatively smaller in size but many in number while in plant cells; there is a large central vacuole which is filled with water and salts.

Functions

In small organisms, extra water and wastes are excreted through contractile vacuoles, while food is digested in food vacuole. Increase in size of vacuole results in an increase in size of cell.