Cells Content Booklet (gr-8, 9, 10) Very Useful
Cells Content Booklet (gr-8, 9, 10) Very Useful
Cells Content Booklet (gr-8, 9, 10) Very Useful
Content Booklet
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INTRODUCTION:
1.All the living organisms are made up of fundamental unit of life called “cell”.
3. The scientist Robert Hooke,1665 saw a little room in the cork (the bark of a tree) resembled the structure of a
honeycomb. The use of the word “Cell” to describe these units is used till this day in Biology as” Cell Biology”
also known as cytology.
4. The Compound Microscope consist eye piece, objective lens and condenser to observe a cell after putting a
drop of Safranin (for plant cell) and methylene blue (for animal cell).
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5. The scientist Leeuwenhoek saw free living cells in the pond water for the first time. (Father of
microbiology)
7. The cell theory states that all the plants and animals are composed of cells, it was proposed by Schleiden
and Schwann.
8. The cell theory was further expanded by Virchow by suggesting that “all cells arise from the pre-existing
cells”.
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10. A single cell may constitute a whole organism as in Amoeba, Chlamydomonas, Paramecium and
Bacteria; these are called as unicellular organisms. Whereas in multi-cellular organisms (Human beings)
division of labour is seen.
11. The feature in almost every cell is same: Plasma membrane, nucleus and cytoplasm.
Osmosis: it is the passage of water from the region of high-water concentration to a region of low water
concentration through a selective permeable membrane.
a) The cell gains water, if the medium surrounding the cell has a higher water concentration (Hypotonic
solution) than the cell.
b) The cell maintains the same water concentration as the cell (Isotonic solution), water crosses the cell
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membrane in both directions.
c) The cell loses water, if the medium has lower water concentration (Hypertonic solution) than the cell.
Note - The cell drinking is endosmosis - omission of water is called ex-osmosis.
13. The cell engulfs food is called endocytosis and ejects solid is called exocytosis. Amoeba acquires food through
endocytosis and excretion of solid is called exocytosis.
14. The cell wall is a rigid outer covering composed of cellulose. It provides structural strength to plant cells.
When a living cell loses water, there is shrinkage of contents of a cell away from the cell wall. This
phenomenon is called as plasmolysis. The cell walls permit the cells of plants, fungi and bacteria to withstand
very dilute (Hypotonic) external media without bursting.
15. The Nucleus: It is a dark coloured, spherical or oval, dot-like structure near the centre of a cell called
Nucleus. The nucleus plays a central role in cellular activities/ reproduction. The chromatin material gets
organized into chromosomes. The chromosomes contain information for inheritance of features from parents to
next generations in the form of DNA (Deoxyribose Nucleic Acid) and protein molecules. The functional
segments of DNA are called genes.
16. In some organisms like Bacteria nucleus is not covered by nuclear membrane. Hence it is called
as prokaryote. (Pro= primitive; karyote = karyon = nucleus.) The organisms with cells having a nuclear
membrane are called eukaryotes.
18. Cell organelles: Every cell has fluid matrix (other than nucleus) is called cytoplasm. The nucleus and
cytoplasm are together called as protoplasm. The protoplasm term was coined by Purkinje. It has important cell
organelles: Endoplasmic Reticulum (ER), Golgi apparatus, Lysosomes, Mitochondria, Plastids, and vacuoles.
19. Endoplasmic Reticulum (ER): It is a large network of membrane –bound tubules and vesicles.
- There are two types of Endoplasmic Reticulum
- Rough Endoplasmic Reticulum (RER) (It looks rough
because Ribosomes are attached to its surface. They are the
sites of protein synthesis).
- Smooth Endoplasmic Reticulum (SER) (It looks smooth
because Ribosomes are not attached to its surface. They are
the sites of fat molecules synthesis).
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3. Proteins and fat molecules produced by ER helps in membrane biogenesis.
24. Vacuoles: Storage sacs for solid or liquid contents. They are small in size in animals while plants have
large, may occupy 50-90 % of the cell volume. Helps to provide turgidity and rigidity to the cell. Many
substances like amino acids, sugars, organic acids and proteins are stored in vacuoles. In Amoeba food vacuole
is specialized to play an important role. 25. Cell: It is the fundamental structural unit of living organisms, helps
in respiration, obtaining nutrition and clearing waste material or forming a new protein.
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Differences between Plant cell and Animal Cell
Plasma membrane is the outer layer Cell wall is the outer layer which gives
which provides turgidity to the cell rigidity and turgidity to the cell
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HEIRARCHY OF CELL:
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What is a stem cell?
An illustration showing a stem cell giving rise to more stem cells or specialised cells.
Image credit: Genome Research Limited
Embryonic stem cells supply new cells for an embryo? as it grows and develops into a baby.
These stem cells are said to be pluripotent, which means they can change into any cell in the body.
Adult stem cells supply new cells as an organism grows and to replace cells that get damaged.
Adult stem cells are said to be multipotent, which means they can only change into some cells in the
body, not any cell, for example:
o Blood (or ‘haematopoietic’) stem cells can only replace the various types of cells in the blood.
o Skin (or ‘epithelial’) stem cells provide the different types of cells that make up our skin and
hair.
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An illustration showing different types of stem cell in the body.
Image credit: Genome Research Limited
Induced pluripotent stem cells, or ‘iPS cells’, are stem cells that scientists make in the laboratory.
‘Induced’ means that they are made in the lab by taking normal adult cells, like skin or blood cells, and
reprogramming them to become stem cells.
Just like embryonic stem cells, they are pluripotent so they can develop into any cell type.
Research is looking to better understand the properties of stem cells so that we can:
o understand how our bodies grow and develop
o find ways of using stem cells to replace cells or tissues that have been damaged or lost.
We can use stem cells to study how cells become specialized for specific functions in the body, and
what happens when this process goes wrong in disease.
If we understand stem cell development, we may be able to replicate this process to create new cells,
tissues and organs.
We can grow tissue and organ structures from stem cells, which can then be studied to find out how
they function and how they are affected by different drugs.
Cells, tissues and organs can sometimes be permanently damaged or lost by disease, injury and genetic
conditions.
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Stem cells may be one way of generating new cells that can then be transplanted into the body to
replace those that are damaged or lost.
Adult stem cells are currently used to treat some conditions, for example:
o Blood stem cells are used to provide a source of healthy blood cells for people with some
blood conditions, such as thalassemia, and cancer patients who have lost their own blood stem
cells during treatment.
o Skin stem cells can be used to generate new skin for people with severe burns.
Age-related macular degeneration (AMD) is an example of a disease where stem cells could be used as
a new form of treatment in the future:
o Some people with age-related macular degeneration lose their sight because cells in the retina?
of the eye called retinal pigment epithelium (RPE) cells stop working.
o Scientists are using induced pluripotent stem cells to produce new RPE cells in the lab that
can then be put into a patient’s eye to replace the damaged cells.
An illustration showing how stem cells can be used to produce retinal pigment epithelium (RPE) cells that can
be used to treat patients with age-related macular degeneration (AMD).
Image credit: Genome Research Limited
Stem cells could be used to generate new organs for use in transplants:
o Currently, damaged organs can be replaced by obtaining healthy organs from a donor,
however donated organs may be ‘rejected’ by the body as the immune system sees it as
something that is foreign.
o Induced pluripotent stem cells generated from the patient themselves could be used to grow
new organs that would have a lower risk of being rejected.
Signals in the body tell a cell what type of specialized cell it should be by switching some genes on and
some genes off.
To generate induced pluripotent stem cells, scientists re-introduce the signals that normally tell stem
cells to stay as stem cells in the early embryo. These switch off any genes that tell the cell to be
specialized, and switch on genes that tell the cell to be a stem cell.
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