you're not you
you are consist of trillons of cells each and every cell have neculas
and quatrillons of atoms which have electrone nutrones quark electromagnetic waves
every atom know how to live
every cell know how to reproduce
think we are fully functional because of millons of cells trillons of atoms function!
that's why i love science espacially phygics
Answers
Answer:
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Answer:
You have already learnt that things around us are either living or non-living. Further, you may recall that all living organisms carry out certain basic functions. Can you list these functions?
Different sets of organs perform the various functions you have listed. In this chapter, you shall learn about the basic structural unit of an organ, which is the cell. Cells may be compared to bricks. Bricks are assembled to make a building.Similarly, cells are assembled to make the body of every organism.
1. Discovery of the Cell
Robert Hooke in 1665 observed slices of cork under a simple magnifying device. Cork is a part of the bark of a tree. He took thin slices of cork and observed them under a microscope. He noticed partitioned boxes or compartments in the cork slice [Fig 8.1].
Fig 8.1: Cork cells as observed by Robert Hooke
These boxes appeared like a honey-comb.
He also noticed that one box was separated from the other by a wall or partition. Hooke coined the term 'cell' for each box. What Hooke observed as boxes or cells in the cork were actually dead cells.
Cells of living organisms could be observed only after the discovery of improved microscopes. Very little was known about the cell for the next 150 years after Robert Hooke's observations. Today, we know a lot about cell structure and its functions because of improved microscopes having high magnification.
2. The Cell
Both, bricks in a building and cells in the living organisms, are basic structural units [Fig. 8.2(a), (b)]. The buildings, though built of similar bricks, have different designs, shapes and sizes. Similarly, in the living world, organisms differ from one another but all are made up of cells. Cells in the living organisms are complex living structures unlike non-living bricks.
A hen's egg can be seen easily. Is it a cell or a group of cells?
Fig 8.2: (a) Brick wall and (b) Onion peel
The egg of a hen represents a single cell and is big enough to be seen by the unaided eye.
3. Organisms show Variety in Cell Number, Shape and Size
How do scientists observe and study the living cells? They use microscopes which magnify objects. Stains (dyes) are used to colour parts of the cell to study the detailed structure.
There are millions of living organisms. They are of different shapes and sizes. Their organs also vary in shape, size and number of cells. Let us study about some of them.
Number of Cells
Can you guess the number of cells in a tall tree or in a huge animal like the elephant? The number runs into billions and trillions. Human body has trillions of cells which vary in shapes and sizes. Different groups of cells perform a variety of functions.
A billion is a thousand million. A trillion is a thousand billion.
Organisms made of more than one cell are called multicellular ( multi : many; cellular : cell) organisms. The number of cells being less in smaller organisms does not, in any way, affect the functioning of the organisms. You will be surprised to know that an organism with billions of cells begins life as a single cell which is the fertilised egg . The fertilised egg cell multiplies and the number of cells increase as development proceeds.
Look at Fig 8.3 .Both organisms are made up of a single cell. The single-celled organisms are called unicellular ( uni : one; cellular : cell) organisms. A single-celled organism performs all the necessary functions that multicellular organisms perform
Fig. 8.3 : (a) Amoeba (b) Paramecium
A single-celled organism, like amoeba, captures and digests food, respires, excretes, grows and reproduces. Similar functions in multicellular organisms are carried out by groups of specialised cells forming different tissues. Tissues, in turn, form organs.
ACTIVITY 8.1
The teacher may show a permanent slide of Amoeba and Paramecium under a microscope. Alternatively, the teacher can collect pond water and show these organisms by preparing the slides.
Shape of Cells
Refer to Fig, 8.3 (a) . How do you define the shape of Amoeba in the figure? You may say that the shape appears irregular. Infact, Amoeba has no definite shape, unlike other organisms.It keeps on changing its shape. Observe the projections of varying lengths protruding out of its body. These are called pseudopodia ( pseudo: false; podia : feet) , as you learnt in Class VII. These projections appear and disappear as Amoeba moves or feeds.
What advantage does Amoeba derive by changing shape?
The change in shape is due to formation of pseudopodia which facilitates movement and help in capturing food.
A white blood cell (WBC) in human blood is another example of a single cell which can change its shape. But while WBC is a cell, amoeba is a full fledged organism capable of independent existence.
What shape would you