CBSE

1. What is Cell Biology?
Branch of biology that deals with various aspects of structure, chemistry, development, genetics and functioning of cells are called cell biology.
 
2. Basic unit :
The cell is the basic unit of life as no organism can have life without being cellular because the cell is a unit of both structure and function.
 
Organisms types ( on the basis of cell types)

Unicellular or acellular (organisms made of a single cell)

Eg: chlamydomonas, acetabularia, bacteria,yeast,amoeba
   
Multicellular (organisms made of many cells)

E.G., newly born infant (2 x 1012 cells)

3. Discovery of the cell:
   
1: Zacharias Janssen (1590): built the first microscope

2: Galileo (1610): Modified Microscope

3: Robert Hooke (1635-1703): a developed new microscope with which he studied the internal structure of a number of plants. His work was famous for the study of cork cells.

Robert Hooke > took a piece of cork of Spanish oak > prepared thin slice by means of sharp pen knife > deep planoconcave lens used  for throwing light > latter observed > cork had honeycomb structure with number of box-like compartments, each having a pore and separated from others by diaphragms > named as cellular (now known as cells).

Hooke microscope and structure of cork cells

4: Leeuwenhoek (1673): first to describe and sketch a live cell. He observed protozoa, spermatozoa, red blood cells etc.

5: Malpighi (1675) & grew (1682): gave an account of the internal structure of plants.

6: Mirbel (1802): said "Plants are formed by membranous cellular tissue"

7: Dutrochet (1824): stated " all organic tissues are really globular cells of an extreme smallness which are united by cohesion"

8: Robert Brown (1831) discovered the presence of nucleus in the cells of the orchid root.

9: Dujardin (1835): living semifluid substance of cells > named sarcode

10: Schleiden (1838): found all plant cells to have a similar structure- cell wall, a clear jelly-like substance and a nucleus.

11: Schwann(1838): discovered that animal cells lacked the cell wall.

12: Purkinje and Mohl (1838): renamed sarcode or jelly-like the substance of the cells as protoplasm

Flower is the reproductive organ of a plant. A flower may be a monoecious or dioecious, depending on whether the flower has either male or female organ or both the organs respectively. The female organ is known as the Gynaecium and the male organ is known as the Androecium. The female organ consists of the carpel, style and the stigma. The male organ includes stamens and anthers. The carpel is oval shaped and  contains the ovary,which further consists of the female gametes. The style is a stalk-like structure, which helps in transporting the pollen grains landed on the stigma to reach the ovules. The stamen is again a feathery stalk-like structure which holds the anther or box-like structure. Anthers contains the pollem grains or the male gametes,inside the pollen sacs. Most flowers are bright and showy and give nectar and sweet smell to attract insects for pollination. In return of the honey,the insects spread the pollen grains. The transfer of pollen grains from the anther of a flower to the stigma of another flower is known as pollination. Pollination can be of two types:Self and Cross. Self pollination occurs either between the anther and stigma of the same flower or of a different flower on the same plant. Cross Pollination occurs between the stigma of one flower and anther of another flower on 2 different plants. Pollination can occur in insects, wind, water, and animals and can take place both by naturally and by artificial means. Natural Pollination can occur only between the plants which are genetically similar to each other. The fusion of male gametes and female gametes is known as sexual reproduction.

Constructor and Destructor

What is the need of a constructor and it can be explained with an example:

//   Turbo C compiler

#inlcude

#include

#include

class Stud

{

int Rno;

char Name[10];

public:

void Input()

{

cout<<"Enter Roll number:";

cin>>Rno;

cout<<"Enter name :";

gets(name);

 }

void Output()

{

cout<<"\nEntered Roll number:"<<Rno;

cout<<"\nEntered name :";

puts(name);

 }

};

void main()

{

Stud S;

S.Output();

}

/* When Program is compiled the output will be a garbage value and now let us see how constructor is useful in this situation.  The above will now include a constructor and destructor

*/

#inlcude

#include

#include

#include

class Stud

{

int Rno;

char Name[10];

public:

Stud() // constructor

{

Rno=5;

strcpy(Name,"Rahul");

}

void Input()

{

cout<<"Enter Roll number:";

cin>>Rno;

cout<<"Enter name :";

gets(name);

 }

void Output()

{

cout<<"\nEntered Roll number:"<<Rno;

cout<<"\nEntered name :";

puts(name);

 }

~Stud() //destructor

{cout<<"Object destructed";}

};

void main()

{  //line 1

Stud S; //line 2

S.Output();

}//last line

/* Now When program is compiled  at line 2 constructor is automaticaly called and initializes the value for its datamember we will get the output as 

Entered Roll number: 5

Entered name : Rahul

and when the program ends i.e last line  destructor will be called automatically */

/*If any doubt regarding the above code can be cleared by asking questions and in the next session I will explain all types of constructor*/

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The fall in price of tomatoes when the local harvest starts reaching the market is due to following two readons:

1. When supply is in much excess of demand , as per basic theory of economics the price of commodity, here tomatoes , falls.

2. Tomatoes are perishable. They can't be preserved for longer time by all the farmers as all of them  do not have storage facility. Hence tomato growers are compelled to sell them off so price comes down.