Page 66 - Understanding NCERT Science 09

Q uestion prokaryotic and 5.2.5 (i) ENDOPLASMIC RETICULUM (ER)

The endoplasmic reticulum (ER) is a large
1. Fill in the gaps in the following
network of membrane-bound tubes and
table illustrating differences
sheets. It looks like long tubules or round or
between
oblong bags (vesicles). The ER membrane is
eukaryotic cells.
similar in structure to the plasma membrane.
There are two types of ER– rough endoplasmic
reticulum (RER) and smooth endoplasmic
Prokaryotic Cell Eukaryotic Cell
reticulum (SER). RER looks rough under a
1. Size : generally 1. Size: generally microscope because it has particles called
small ( 1-10 µm) large ( 5-100 µm) ribosomes attached to its surface. The
1 µm = 10 m ribosomes, which are present in all active
–6
cells, are the sites of protein manufacture.
2. Nuclear region: 2. Nuclear region: The manufactured proteins are then sent to
_______________ well defined and various places in the cell depending on need,
_______________ surrounded by a using the ER. The SER helps in the
and known as__ nuclear membrane manufacture of fat molecules, or lipids,
important for cell function. Some of these
3. Chromosome: 3. More than one proteins and lipids help in building the cell
single chromosome membrane. This process is known as
membrane biogenesis. Some other proteins
4. Membrane-bound 4. _______________ and lipids function as enzymes and
cell organelles _______________ hormones. Although the ER varies greatly in
absent _______________ appearance in different cells, it always forms a
network system.

5.2.5 CELL ORGANELLES

Every cell has a membrane around it to keep
its own contents separate from the external
environment. Large and complex cells,
including cells from multicellular organisms,
need a lot of chemical activities to support
their complicated structure and function. To
keep these activities of different kinds
separate from each other, these cells use
membrane-bound little structures (or
‘organelles’) within themselves. This is one of
the features of the eukaryotic cells that
distinguish them from prokaryotic cells. Some
of these organelles are visible only with an
electron microscope. Fig. 5.5: Animal cell
We have talked about the nucleus in a
previous section. Some important examples Thus, one function of the ER is to serve as
of cell organelles which we will discuss now channels for the transport of materials
are: endoplasmic reticulum, Golgi apparatus, (especially proteins) between various regions
lysosomes, mitochondria and plastids. They of the cytoplasm or between the cytoplasm
are important because they carry out some and the nucleus. The ER also functions as a
very crucial functions in cells. cytoplasmic framework providing a surface

THE FUNDAMENTAL UNIT OF LIFE 55

Rationalised 2023-24