Nucleus is the most important component of the living cell. It is round or spherical in shape and situated in the centre of the cell. Nucleus is separated from cytoplasm by a membrane called nuclear membrane. This membrane is porous and allows the movement of materials between the cytoplasm and inner side of the nucleus. There is a small and spherical body in the nucleus. It is called nucleolus. Nucleus contains thread-like structures called chromosomes. These carry genes and help in inheritance or transfer of characters from the parents to the offspring. Nucleus also acts as a control centre of the activities of the cell.

The small coloured bodies in the cytoplasm are called plastids. These are found only in plant cells but not in animal cells. Plastids are of different colours. Some of them contain green pigment called chlorophyll. The plastids having other than green colour are called chromoplast. Some plastids are colourless called leucoplast. These coloured plastids provide various colours to flowers and fruits. The chloroplasts having chlorophyll help in the formation of food by leaves through the process called photosynthesis.

Parts of the Cell: The basic components of a cell are:
(i) Cell membrane
(ii) Cytoplasm
(iii) Nucleus
(i) Cell membrane : The cytoplasm and nucleus are enclosed within the cell membrane. It is also called plasma membrane. It separates cell from another cell and from the surrounding medium. It is porous in nature and allows movement of substance or material both inward and outward.
(ii) Cytoplasm: It is the jelly like substance present in between the cell membrane and the nucleus. Various other components, or organelles of cells are present in the cytoplasm. These are mitochondria, golgi bodies, ribosomes etc. (iii)Nucleus: It is an important component of the cell. It is generally spherical and located in the centre of the cell. It is surrounded by nuclear membrane. It is porous in nature. It has a smaller spherical body called nucleolus. The nucleus contains thread like structures called chromosomes. They carry genes and help in transferring the characteristics from parents to offsprings.

Gene is a unit of inheritance in living organism. It controls the transfer of hereditary characteristics from parents to offsprings.
This means that your parents pass some of their characteristics to you. If your father has brown eyes, you may have brown eyes. However, the different combination of genes from parents results in different characteristics.

(i) Compound microscope It is needed to see cells because these are too small to be seen by naked eye.
(ii) Chloroplast Found only in plant cell, these are small-oval shaped structures.
(iii) Chlorophyll It is the green pigment present in chloroplast which allows plants to absorb energy from light.
(iv) Photosynthesis It is the process by which plant cells use water and CO₂ to produce food.
(v) Cell wall It is a non-living part of the plant cell. It gives shape and support to the cell as well as protects the cell against atmospheric variations

The size of the cells of an organism is not related to the size of organism. This can be understood with the example of an elephant and a rat.
The cells in elephant are not big in size as compared to the cells of small animal like rat. Hence, cells are not related to the size of an organism 
However, the size of a cell is related to the function that a cell performs. The nerve cells in both rat and elephant are long and branched and perform the function of transferring and receiving messages and also help in coordination of different functions of body parts 

Ans. A - Nucleus B - Chromosomes
C - Genes D - Cytoplasm
E - Mitochondria F - Cell membrane
Gene is a unit of inheritance in living organisms. It controls the transfer of hereditary characteristic from parents to offspring. This means that your parents pass some of their characteristics on to you. If your father has brown eyes, you may also have brown eyes.

(a) Cytoplasm is the transparent, jelly-like substance that makes up most of the inside of a cell. It is present between the cell membrane and nucleus.
Various structures such as the nucleus, mitochondria are present in it. These are called organelles. Salts, proteins, sugars and other substances are dissolved in this fluid.
Function Most of the chemical reactions which keep the cell alive take place in the cytoplasm.
(b) The nucleus and the cytoplasm together make up the protoplasm which is called the living substance of the cell.
The main constituent elements of protoplasm are carbon, hydrogen, oxygen and nitrogen

Brick and cell are considered one and the same.
The arrangement of cells is comparable to bricks of a building. As bricks are assembled to make a building, similarly, cells are put together to make
the body of an organism.
Just as cells are the basic structural unit of an organism, bricks are the structural unit of a building.
Also, as buildings may differ in designs, shapes and sizes but are made up of bricks. In the same way, organisms may differ from one another (e.g. a human, a dog and a plant) but all of them are made up of cells

Organelles are distinct, highly organised structures that perform specialised functions within the cell.
The organelles that are found in most cells are mitochondria, ribosomes and vacuole.
Functions of nucleus
(i) It is concerned with the transmission of hereditary traits from the parent to offspring (i.e.inheritance).
(ii) It controls all the metabolic activities of the cell (i.e. control centre of cell activities).