C2 - Homeostasis of Organisms · 2.1 Cell structures and cell organization 2.1.1 What is a cell?...

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


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


Amoeba


Escherichia coli


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


Nerve Cell


Red Blood Cell


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.


1. 2. 3.

4. 5.


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


2.1.3 Animal cell vs plant cell

Typical Animal Cell


Typical Plant Cell


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)


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)


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.


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


Ribosomes

- Spherical.

- Two subunits complex containing RNA and

proteins.

- Attached to RER or free in the cytoplasm

- Functions:

- Sites of protein synthesis.


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.


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.


- 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.


Cytoplasm

- Jelly like place where biochemical reactions occur.


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.


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.


Flagellum (plural flagella)


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.


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.

C2 - Homeostasis of Organisms · 2.1 Cell structures and cell organization 2.1.1 What is a cell?...

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