c2 - homeostasis of organisms · 2.1 cell structures and cell organization 2.1.1 what is a cell?...
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C2 - HOMEOSTASIS OF ORGANISMS
2.1 Cell structures and cell organization
2.1.1 What is a cell?
Cell is the fundamental, structural and
functional unit of all living organisms
Robert Hooke (1665) – an English scientist
who observed honeycomb like dead cells
and coined the term CELL
All living organisms are composed of cells
and product of cells
All cells arise from preexisting cells
through the process of cell division
The body of living organisms is made up of one or more cells
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2.1.2 Cell number, size and shape
2.1.2.1 Number
Unicellular organisms – Organisms with single cell, capable of
independent existence and carries all functions like digestion,
excretion, respiration, growth & reproduction (acellular).
Examples: Amoeba, E. coli
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C2 - HOMEOSTASIS OF ORGANISMS
Amoeba
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Escherichia coli
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Multicellular organisms – Organisms with more than one cell. Cells
in multicellular organisms vary in size and shape depending on
function.
Examples: nerve cell, blood cell
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C2 - HOMEOSTASIS OF ORGANISMS
Nerve Cell
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C2 - HOMEOSTASIS OF ORGANISMS
Red Blood Cell
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2.1.2.2 Shape
Parenchyma (1) - Polyhedral cells performs storage.
Sclerenchyma (2) - spindle shaped cells & provides mechanical support.
Nerve cells (3) - long and branched cells conducting nerve impulses.
Red blood cells (4) - Biconcave & helps in carrying oxygen.
Muscle cells (5) - cylindrical or spindle shaped concerned with the
movement of body parts.
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1. 2. 3.
4. 5.
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2.1.2.3 Size
Varies from few microns (1mm=1000 µm) to few
centimeters.
Smallest living cell is PPLO ( Pleuro Pneumonia
Like Organism) - 0.1µm
Largest living cell is the egg of an Ostrich - 170 to
180 mm in diameter.
Bacteria – 0.1 to 0.5 µm
Sclerenchyma fiber - up to 60cms in length
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2.1.3 Animal cell vs plant cell
Typical Animal Cell
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Typical Plant Cell
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2.1.4 Components and functions
2.1.4.1 Present in animal and plants cells
Nucleus
- Spherical
- Consists of nuclear membrane,
nucleoplasm, nucleolus and chromatin
- DNA (genetic material), RNA and
proteins carried in the chromatin
- Functions:
Controls all the activities of the cell.
Nucleolus is involved in the synthesis of ribosomes and ribonucleic
acid (RNA)
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Mitochondrion (plural mitochondria)
(Power house of the cell)
- Cylindrical or oval shape
- Two layers of membranes where
inner membrane is folded to form
cristae
- Functions:
Sites of cellular respiration
Enzymes involved in cellular
respiration helping to oxidize glucose to release energy in the form of
ATP (adenosine triphosphate)
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Endoplasmic reticulum (ER)
- Extensive flattened membrane folded repeatedly to form a large network
of interconnected tubes and sacs.
- Continuation of the nuclear membrane.
- Two types of ER:
Rough ER (RER), with ribosomes on its
surface
Smooth ER (SER), with no ribosomes
- Functions:
- RER – Transport of proteins synthesized by ribosomes
- SER – Synthesis of lipids and is the center for detoxification of drugs.
- Transport of its products by pinching off a vesicle.
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Golgi apparatus (Golgi complex)
- Consists of a stack of membrane-bound sacs
with building vesicles around it.
- Functions:
- Centre for processing, packing and transporting
macromolecules.
- Mainly modifies proteins prepared by RER.
- Produces Enzymes.
- Creates lysosomes.
- Involved in the transport of lipids.
- Stores products of the ER
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Ribosomes
- Spherical.
- Two subunits complex containing RNA and
proteins.
- Attached to RER or free in the cytoplasm
- Functions:
- Sites of protein synthesis.
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Lysosomes
(Suicidal bags)
- Spherical
- Produced from Golgi complex.
- Bounded by single membrane.
- Functions:
- Contains vesicles housing digestive
enzymes (to break apart macromolecules
such as proteins, lipids, etc.)
The cell’s digestive system
- Recycling by breaking down defective organelles and membrane sections.
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Vacuoles
- Usually present in plant cells.
In animal cells, if vacuoles are
present, they are small)
- Spherical or oval shaped sacs
filled with fluid.
- Fluid is known as cell sap
which contains sugars, salts,
amino acids and waste
substances.
- Bounded by a semi-permeable
membrane called tonoplast.
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- Functions:
- Store food substances to be
digested.
- Site for waste products.
- Regulate water balance in cells.
- Turgidity of cells gives support to
plants.
- Contractile vacuoles help to
regulate amount of water in
microorganisms.
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Cytoplasm
- Jelly like place where biochemical reactions occur.
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Plasma membrane
- Thin, semi-permeable membrane.
- Composed of phospholipids and proteins.
- Functions:
- Isolates the cells contents from the external
environment.
- Regulates the flow of materials into and
out of the cell, thanks to its semi-permeable
characteristic.
-Allows for interaction with other cells and
the extracellular environment.
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2.1.4.2 Only present in animal cells
Centrosome with centriole
- Centrosomes are composed of two
centrioles arranged at right-angles to each
other
- Centrioles are small cylindrical
structures.
- Functions:
- Forming spindles fibers during cell
division.
- Synthesize cilia and flagella of small organisms.
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Flagellum (plural flagella)
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2.1.4.3 Only present in plant cells
Cell wall
- Rigid outer layer of plant cell which is made up of cellulose fiber.
- Permeable
- Functions:
- Maintains the shape of the plant.
- Protects the cell from bursting.
- Gives support to cells.
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Chloroplasts
- (In green plants only)
- Disc-shaped organelle bounded by 2 membranes.
- Has orderly stacks of grana
in the stroma.
- Grana contain chlorophyll.
- Functions:
- Site for photosynthesis.
- Chlorophyll in the granum
traps light energy for photosynthesis.