BIO( Cell its structure and functions)

           Cell its structure and functions

 Typical Cell:

All the organelles shown in the typical

plant or animal cell will not exist in every cell.

For example, chloroplasts are always   

shown in the typical plant cell, yet all the

plant cells do not have chloroplasts. They

are mostly found in the cells of green

leaves, tender stems etc. The organelles

that feature in most of the cells are included

in this model. The typical cell provides a

way to study cells.

 In plant cell there is

another layer present over the cell                       

membrane known as the cell wall. With the

help of the given activity you will be able

to see a cell membrane.

Observing the cell membrane..(act-1)

Take Rheo leaf, tear the leaf in a single

stroke. Observe it against the light. Take a

small piece of leaf peel with light coloured

transparent portion. Put it on slide and put

a drop of water on it. Cover it with cover

slip and observe the Lighter portion of leaf

under the microscope.

                                          Cell membrane

Cell wall:

This is a unique feature seen in plant

cells. While the cell membrane acts as the

outer layer in an animal cell, in a plant cell

there is an extra layer (mainly of cellulose)

outside the cell membrane which is known

as the cell wall. This is considered to be

one of the major difference between a plant

and an animal cells.

The cell wall is a tough but flexible

porous layer that lends a definite shape and

gives protection to the cell. Earlier it was

believed to be inactive, but now it is

considered to be one of the most

significant parts of the cell that

continuously exchanges information with

other cells during growth and development.

What are the functions of the cell wall

in plant cells?

It exerts an inward wall pressure to

resist the outward pressure exerted by the

cell sap. Hence, the plant cells can

withstand much greater changes of

surrounding medium than the animal cells.

Nucleus:

Aim: To observe the nucleus in cheek

cells.

Material required: A tooth pick or

ice-cream spoon or spatula, glass slide,

coverslip, watch glass, needle, blotting

paper, 1% methylene blue, normal saline,

glycerine, microscope, etc.

Procedure:

1. Wash your mouth and scrape a little

of the internal lining of your cheek

inside your mouth with a clean

tooth pick or spatula or ice-cream

spoon.

2. Place the scraped material in a

watch glass containing a very small

quantity of normal saline.

3. Then place the material on a glass

slide.

4. Put a drop of methylene blue and

wait for a couple of minutes.

5. Put a drop of glycerine over it.

6. Place a coverslip. Tap the coverslip

with the blunt end of needle so as

to spread the cells.

7. Wipe off the extra stain with a fine

cloth or blotting paper.

 

Precautions:

1. Do not scrape the cheek too hard

as it may injure your buccal

mucosa.

2. Scraped material should be spread

uniformly on the slide.

3. Excess stains should be drained off.

4. There should be no air-bubbles

under the cover slip.

This is one

of the most

important organelles of the cell. This is also

known as the cell’s control room. The

nucleus is the largest and the most distinct

of all cell organelles. Schleiden, who was

one of the proponents of cell theory,

thought that new cells were created from

the nucleus and he called it as cytoblast.

Barring a few exceptions, almost all

eukaryotic cells have a nucleus. Red blood

cells in mammals and phloem sieve tube in

plants are examples of cells that do not have

a nucleus. Even these cells do have nuclei

in the beginning, but it is later thrown out

of the cells and destroyed.

The nucleus regulates and controls all

the functions of a cell and determines the

characteristics of the organism. It consists

of all genetic information. The nucleus is

also closely involved in the process of cell division.

                                               Nucleus

Nuclear Membrane:

The membrane that encloses the nucleus and separates it from contents of cytoplasm is known as the nuclear membrane. Almost the entire genetic material of the cells is found in the nucleus.

Prokaryotic Cells the above

description was primarily about eukaryotic

cells that contained a membrane bound

nucleus. Cells that do not have a nuclear

membrane bound nuclear material are

called prokaryotic cells. We have

mentioned earlier that the bacterium is a

prokaryotic cell. Cyanobacteria (bluegreen algae) also belong to this category.

Cytoplasm:

When we look at the temporary mounts

of onion peel, we can see a large region of

each cell enclosed by the cell membrane.

This region takes up very little stain. It is

called the cytoplasm. The cytoplasm is the

fluid content bounded by the plasma

membrane. It also contains many

specialised cell organelles. Each of these

organelles performs specific function for

the cell.

Cell organelles are enclosed by membranes. In prokaryotes, beside the absence of a defined membrane bound nucleus (or nuclear region), the membrane bound cell organelles are also absent. Except membrane less Ribosomes.

Endoplasmic reticulum (ER)

When the cell was observed under the

electron microscope, a network of

membranes was observed throughout the

cytoplasm. This network creates passages

within the cytoplasm for the transport of 

substances from one part of the cell to

another. This network of membranes is

known as the endoplasmic reticulum.

Thus, one function of the ER is to serve

as channels for the transport of materials

(especially proteins) between various

regions of the cytoplasm or between the

cytoplasm and the nucleus. It also functions

as a cytoplasmic framework providing a

surface for some of the biochemical

activities of the cell. In vertebrate liver cells

SER plays a crucial role in detoxifying many poisons and drugs.

Golgi body or Golgi complex:

Although Camillo Golgi had observed this organelle in the year 1898 using a compound microscope, its finer structure could be observed only under an electron microscope. This organelle is also made up of several membranes. These membranes create sac-like structures around which many fluid-filled vesicles abound. The proteins and other substances produced in the ribosome reaches the golgi body through these vesicles.

The number of golgi bodies varies from cell to cell. Their number is particularly large in those cells that secrete hormones and enzymes.

Lysosome:

One of the facts that troubled the scientists for a long time was that, certain enzymes present in the cell have the ability  to destroy almost all the structures in the cell but didn’t damage it. This puzzle was solved when lysosomes were discovered as tiny particles visible in the cytoplasm. It was found that they contained the destructive enzymes. These enzymes normally do not come in contact with the rest of the cell. The materials that need to be destroyed are transported to the lysosomes. Then the lysosomes get them digested at times, the lysosomes burst and the enzymes are released to digest the cell. Hence, lysosomes are also known as the suicidal bags of the cell.

Mitochondria..(act-2):

Mitochondria are small, spherical or

cylindrical organelles. Generally a

mitochondrion is 2-8 micron long and

about 0.5 micron wide. It is about 150 times

smaller than the nucleus. There are about

100-150 mitochondria in each cell. When

seen under the compound microscope, the

mitochondria appear as oval or cylindrical

dots in the cell. The diagram of

mitochondria shown in typical cell is

hypothetical. Electron microscope reveals

their unique internal structure in great

detail.

Information derived from the electron

microscope tells us that the mitochondria

are made up of a double-membrane wall.

The inner membrane of the wall protrudes

into the interior in folds and forms

structures called cristae; the space between

cristae is known as the matrix.

Mitochondria are responsible for

cellular respiration, a process through

which the cell derives its energy to do work.

Because of this, mitochondria are also

known as the powerhouses of the cell.

Ribosomes:

There are small granule like structures

in the cytoplasm of the cell. They are called

ribosomes. They are formed of RNA

proteins. They are two types. Free

ribosomes are scattered in cytoplasm.

Attached ribosomes are on the surface of

rough endoplasmic reticulum. Ribosomes

are the sites for protein synthesis.

Plastids..(act-3):

Observing chloroplast in algae

Collect some algae from pond and

separate out thin filaments of them. Place

a few filaments on a slide. Observe it under

the microscope. Take the help of given

figure and draw the picture of chloroplast

that you have observed under the

microscope.

Chloroplast is a type of plastids in

green colour. Plastids are present only in

plant cells. Plastids are mainly of three

types: (i) chromoplasts (coloured)

(ii) leucoplasts (colourless) and (iii) chloroplasts (green coloured).

   Chloroplasts are of different shapes i.e. 

disc, oval etc,. In algae, these can be found

as ladders or star or spirally coiled or

reticulate structures. The diameter of

chloroplasts in higher plants can vary

between 4 to 10 micron. The primary

function of chloroplasts is to trap the

energy from sunlight and transform it to

chemical energy, thus helping to carry out

photosynthesis.