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Organisation of an organism (Chapter- 2) - Coggle Diagram
Organisation of an organism (Chapter- 2)
Microscopes and Magnification:
Tiny structures such as cells can be observed through a microscope and a photograph too.
These photographs are also called as photo micro- graphs.
They are studied by taking thin slices of a particular part. These are called as sections. E.g.
Transverse and longitudinal section.
Light microscope- (magnification upto x 1500) ---> Magnification power
Electron microscope (Magnification upto x 10 million).
Hand lens: x 10
The way we cut specimens can be either a longitudinal section or a transverse section.
The sections are often
treated with dyes, called stains
in order to make the structures inside the cells show up more clearly. Sometimes, the tissues can be squashed or smeared on a microscope slide or treated with chemicals to separate the cells before studying them.
Magnification= Observed size of the image (or drawing)/ Actual size of the specimen
Organisation of a cell:
Cell organelles that both plant and animal cells have:
Cytoplasm
: Is a
thick liquid
which
contains all the organelles
. The particles may be
food reserves
like oil droplets or granules of starch. In the cytoplasm
a large number of reactions take place
, which keep the cell alive by providing energy and making substance that the cell needs. The liquid part of the cytoplasm is about
90% water
, with salts and sugars dissolved in it. Fats and proteins may be used to build up the cell structures, like the membranes.
Cell membrane
: A
thin layer of cytoplasm
around the outside of the cell. I
t stops the contents of the cell from escaping and controls which substances can enter and leave the cell
. Generally, oxygen, food and water are allowed to enter; waste products are allowed to leave; and harmful substances are kept out. Cell membrane
maintains the structure and the chemical reactions
of the cytoplasm.
Nucleus
: Most cells
contain more than one nucleus
. The function of the nucleus is to
control the type and quantity of enzymes produced by the cytoplasm
. It
regulates the chemical changes
that take place in a cell. It controls what the cell will be like.
Decides on the characteristics
, division and reactions. A cell without a nucleus cannot reproduce. Inside the nucleus, there are thread like structures called as chromosomes.
Special cell organelles in plant cells:
Cell wall:
Cell wall is
present outside the cell membrane
. It
contains cellulose and other compounds
. It is
non living
and
allows water and dissolved substances to pass through it.
It is
not selective
like cell membrane. It prevents cells from bursting.
Vacuole
:
Fluid- filled spaces
. The vacuole contains
cell sap
, a watery solution of sugars, salts and sometimes pigments. This large vacuole pushes the cytoplasm outwards, so that it forms just a thin lining inside the cell wall. It's this outward pressure that
makes plant cells
and their tissues firm. Animal cells may sometimes have small vacuoles, but they are usually produced to do some special job and are not permanent.
Plastids
: Are organelles which
contain chlorophyll or starch.
Chloroplasts
: Chloroplasts are
organelles that contain
green pigment/ substance known as
chlorophyll
. They trap sunlight for photosynthesis.
Other organelles:
Ribosomes:
They may be held in the membrane but can be also found free in the cytoplasm. They
build up cell's proteins
/ protein synthesis.
Mitochondria
: May appear slipper- shaped, circular or oval, when viewed in section. They have an inner and outer membrane. These are the most frequent regions of rapid chemical activity. They are
responsible for releasing energy from food substances through a process of aerobic respiration
. Note that prokaryote (bacteria) do not posses mitochondria in their cytoplasm.