Biology holiday homework

BIOLOGY

HOLIDAY

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WORKTHE FUNDAMENTAL

UNIT OF LIFE

In 1665 Robert Hooke examined the slice of

cork by self designed microscope .

Cork is a substance which comes from bark of

tree.

By microscope cork resembled the structure

of a honey comb consisting of many little

compartments.

This was very important invention in the history

of science that living things appear to consist

of separate small units.

The word cell use to describe this unit in

biology .

HISTORY

In1839 Purkinje discovered some fluid

substance in the cell termed protoplasm.

In 1940 with the discovery of electron

microscope complex structure of cell and

various organelles could understand.

CELL All organisms around us are made up of cells.

Some organisms are made up of single cell called

unicellular organism .e.g. Amoeba.

Many cells grouped together in a single body and

perform various functions called multicellular

organisms .

Some organisms have different kinds of cells with

different shape and size.

Each living cell has a capacity to perform certain

basic function . That are characteristics of all living

forms .

All living cell perform this basic function.

As we know there is a division of labour in

multicellular organism such as human being ,

means different part of our body perform different

part of our body perform different functions .

A single cell also perform different functions with

the help of its component which is known as cell

organelles .

These organelles together constitute the basic unit

called the cell.

STRUCTURE OF A CELLA cell have 3 features –

Plasma membrane

Nucleus

Cytoplasm

Plasma membraneCell membrane is the outer most covering of the cell

that separate the content of the from its external

environment .Structure The plasma membrane is flexible made up of

organic molecules –

Lipid

Protein

We can observe the structure of plasma only

through an electron microscope .

The flexibility of cell membrane also enable the cell

to engulf the food and other material from its

external environment . This process is known as

endocytosis. Ex :- Amoeba enquires its food through

this process.

Cell wall In plants cells addition to the plasma membrane

another rigid outer covering called the cell wall.

Structure

This is made up of complex substance cellulose .

It provide strength to plant.

Functions Cell walls permit the cell of plant , fungi and

bacteria to with stand very dilute external media

without bursting .

It take water by osmosis.

Function of plasma membrane Separation of content of cell.

Permit the entry and exit of material .

Prevent movement of some other material called

selectively permeable membrane .

Some substance like carbon dioxide , oxygen can

move across the cell membrane by a process

called diffusion. In diffusion substance move from a

region of high concentration to low concentration.

Use of diffusion – waste product can excrete out by

the cell like carbon dioxide , Respiration.

Movement of water through semi permeable

membrane is called osmosis.

Use of osmosis –

Transportation of water

Transportation of dissolve substance

Transportation of nutritious substance

Transportation/excretion of waste product

Examples of osmosis – unicellular fresh water organism

and most plant cell absorb water by plant root.

Use of diffusion – waste product can excrete out by

the cell like carbon dioxide , Respiration.

Movement of water through semi permeable

membrane is called osmosis.

Use of osmosis –

Transportation of water

Transportation of dissolve substance

Transportation of nutritious substance

Transportation/excretion of waste product

Examples of osmosis – unicellular fresh water organism

and most plant cell absorb water by plant root.

NUCLEUSNucleus is a darkly coloured spherical or oval

dot like structure near the Centre of each cell.

StructureDouble layer covering of nucleus – Nuclear

membrane.

Functions of nuclear membrane – porous and

transfer the material from nucleus to cytoplasm.

Chromosomes are rod shapely structure.

Parts of chromosomes – DNA and protein.

DNA – genes and chromatin .

Function of Nucleus – cellular reproduction

Types of nucleus –

Organisms with poorly defined nuclear membrane

is known as prokaryotes .

Organisms with well defined nuclear membrane is

known as eukaryotes.

NUCLEUS

Nucleus

chromosome

DNA

Genes Chromatin

Protein

Nuclear Membrane

CYTOPLASM The cytoplasm is the fluid content inside the plasma

membrane. It contains many specialized cell organelles .

CELL ORGNELLES Large and complex cells of multicellular organism

need a lot of chemical activities to support their complicated structure and functions.

To perform these activities membrane bounded little structures are present called organelles, this is the feature of eukaryotic cell

These organelles are visible only with electron microscope.

TYPES OF CELL

PROKARYOTIC CELL

Size:generally small

Nuclear region :poorly defined, nuclear membrane is absent.

Chromosome : single

Membrane-bounded cell organelles absent .

EUKARYOTIC CELL

Size:generally large

Nuclear region :well defined , nuclear membrane is present.

Chromosomes : more than one.

Membrane-bounded cell organelles present.

These organelles are :

1. Endoplasmic reticulum

2. Golgi apparatus

3. Lysosomes

4. Mitochondria

5. Plastids

6. Vacuoles

ENDOPLASMIC RETICULUM (ER) It is a large network of membrane bound tubes and

sheets.

Structure Long tubules and round or oval vesicles.

Type Rough Endoplasmic Reticulum (RER)

Looking rough under microscope because it contains

particles called ribosomes attached to its surface.

Ribosomes : sight of protein manufacturer

depending on need.

Smooth Endoplasmic Reticulum (SER)

Size of SER – Varies in size

Smooth in different cells and forms network system.

Functions Of Endoplasmic Reticulum Transport of material like protein within the cell

organs .

Providing a surface framework for some

biochemical activities of cell.

Detoxifying many poison and drugs .

GOLGI APPARATUS It was discovered by Camilo Golgi by his name is

called Golgi Apparatus .

Structure Membrane bounded vesicles arrange

approximately parallel to each other called cistern.

It is also connected with the membrane of ER so its

also complex cellular membrane system.

Functions Storage

Modifications

Packaging of products in vesicles

Formation of lysosomes

LYSOSOMES It is known as waste disposal system of the cell .

Helps to keep the cell clean by digesting any

foreign material like bacteria or food.

It contains powerful digestive enzymes which help

to digest foreign materials .

It is also known as suicide bags of a cell.

Structure Membrane bound sacs, filled with objective

enzymes.

MITOCHONDRIA Mitochondria are known as power house of the

cell.

It release energy for various chemical activities.

Structure It have 2 membrane covering outer membrane

is very porous while inner one is deeply folded .

These folds create a large surface area for

formation of ATP.

Functions ATP is Adenosine triphosphate .

It produce energy so it is known as the energy

currency of the cell.

It is a organelle of sense because it produce DNA

PLASTIDS Plastids are present only in plant cells.

Types Chromoplast – coloured plastids–green , yellow etc.

Leucoplast – white or colourless plastids .

Structure The internal organization of the plastids consist of

numerous membrane layers embedded in a

material called the stroma.

Functions It contains pigment chlorophyll known as

chromoplast and leucoplast .

Chloroplast contain pigment chlorophyll used for

photosynthesis , it is found in the chromoplast.

Leucoplast is used for storage.

Plastids work like mitochondria because its own

DNA and Ribosomes

VACUOLES Vacuoles are storage sac for solid or liquid

contents.

In plant cells there is very large central

vacuole , providing rigidity to cell.

CONCLUSION Cells have a basic structural organization with the

help of membrane and organelles.

Cells perform functions like respiration, obtaining

nutrition, forming new proteins and cleaning of

waste materials etc.

Thus cell is the fundamental structural and

functional unit of life.

PRESENTED BY –

Paridhi Gouri Patel

CLASS – 9th