Page 14 - Biology_F5

Cytology

(d) They have membrane bound organelles, cytoplasm of the neighbouring cells called
such as mitochondria and plastids. plasmodesmata. Beneath the cell wall,
(e) The cell walls, if present, are there is a cell membrane, which is semi-
chemically composed of cellulose permeable. Cell membrane controls the
and/or chitin. passage of materials in and out of the cell.
The adjacent cells are usually bound to
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(f) They have large, helical DNA which one another by a thin layer called middle
is associated with histone protein to lamella.
form chromosomes.

(g) Cilia and flagella, if present, arise from The cytoplasm is a fluid content that fills the
basal bodies and contain microtubules cell giving its shape; it contains proteins and
that are arranged in a “9+2” pattern. dissolved ions used in cellular activities.
It is a place where all cell organelles
The plant cell are housed. Most of the plant cells have
Plant cells are eukaryotic and are present large organelles called chloroplasts.
in organisms of the kingdom Plantae. They Chloroplasts contain chlorophyll which is
have a true nucleus along with specialised a green pigment used for photosynthesis.
structures called organelles that carry Other vital organelles found in the plant
out different functions. Plant cells differ cells include mitochondria, endoplasmic
from the cells of other organisms in reticulum, ribosomes and Golgi vesicles.
Mitochondrion acts as a powerhouse of
that they have cell walls, chloroplasts, the cell because it produces energy used
and central vacuoles. Therefore, the for all cell activities.
distinctive features of plant cells include

the presence of cell walls containing The Endoplasmic Reticulum (ER) is a
cellulose, hemicelluloses and pectin, and large folded membrane system found in
the presence of chloroplasts capable of the cytoplasm of the cell. Some ER are
performing photosynthesis. associated with ribosomes while others
are not. The ER that are associated
Structure of the plant cell with ribosomes are known as Rough
The general structure of the plant cell Endoplasmic Reticula (RER), whereas
can be viewed by using an electron those not associated with ribosomes are
microscope (Figure 1.4). A plant cell has known as Smooth Endoplasmic Reticula
an outer layer surrounding the cell, called (SER).
a cell wall. It is composed of cellulose,
which is a stiff carbohydrate. The cell wall Ribosomes are the organelles responsible
provides protection, structural support for protein synthesis within a cell. Hence,
and mechanical strength to the cell. The the RER provides a surface area for
presence of cellulose also helps the plant protein synthesis while the SER provides
cell to maintain its regular shape. The a surface area for lipid synthesis. There
cell wall has perforations that connect are small vesicles in the cytoplasm called

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