Compound microscope
Microscopes in which more than one lens is used are
called compound microscopes.
Why is a mirror fixed in a microscope?
The mirror is fixed to focus light on the objects to be
observed.
Why do we use a slide made of glass to place the material
to be observed?
A transparent surface is required to pass light through
the material to be observed. So glass slide is used to place it.
Discovering the cell
Who discovered cells?
Robert Hook
What is cell biology?
The study of the cells is known as cell biology.
Who discovered the centre of the cell(nucleus)?
Robert Brown
Who discovered that body of a plant is made up of cells?
M J Schleiden
Who discovered that body of an animal is made up of
cells?
Theodore Schwann
Who proposed that new cells arise from the existing
cells?
Rudolf Virchow
Functions of cells
Synthesise biomolecules
Release energy from nutrients
Resist foreign particles
Protoplasm
All substances inside the cell membrane constitute the
protoplasm.
Cytoplasm
Cytoplasm is the part of the protoplasm excluding the
nucleus. All factors required for life activities are present in the cytoplasm.
Cell organelles
Cell organelles are the specific parts seen in the cytoplasm to perform physiological functions.
A compound microscope can
magnify an object upto a maximum _________ times its size.
Ans: 2000
An electron microscope can
magnify an object upto _________ times its size.
Ans: million times
Nucleus – the regulatory
centre of the cell
The various proteins produced in the cell play
a major role in regulating various activities in the cell. The synthesis of
proteins is under the control of genes in the chromatin reticulum in the
nucleus. Hence the nucleus is considered as the regulatory centre of the cell.
Plastids
Plastids
are the cell organelles that are exclusively found in plant cells. They are of
three kinds namely chromoplast, chloroplast and leucoplast.
Functions
of Plastids
Photosynthesis
is performed by chloroplast. Chromoplasts impart colour to flowers and fruits.
Xanthophyll (yellow), carotene (yellowish orange), anthocyanin (red, purple)
etc., are certain pigments in the chromoplasts. Various ranges of these
pigments impart different colours to various parts of the plant. Leucoplasts
are plastids having no specific colour. Leucoplasts are seen in plenty in the
cells where food materials are stored. As fruits ripen, chloroplasts change to
chromoplasts. Starch is converted to sugar. This is the secret behind the change
in the colour and taste of fruits.
Various cell organelles in
the animal cell
Lysosome
Lysosome contains the digestive enzymes that are required for the destruction of foreign substances entering the cell. It is seen in animal cells.
Centrosome
Centrosome is the cell organelle that is found
only in animal cells. The centrioles that play a major role in cell division
are seen in the centrosome.
Ans:
i)A – chloroplast
B –
Mitochondrion
C – Endoplasmic
reticulum
D – Vacuole
E – Nucleus
ii) A – Performs
photosynthesis.
B – Helps in
the production and storage of energy.
C – Conduction
of materials inside the cell and provides firmness
and shape to cells.
iii) Genes are seen in the chromatin reticulum in the
nucleus.
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