CELL WALL

• Cell wall is absent in animals.
• Plant cells, in addition to the plasma membrane, have another rigid outer covering called the cell wall. The cell wall lies outside the plasma membrane.
• The plant cell wall is mainly composed of cellulose. Cellulose is a complex substance and provides structural strength to plants. 

PLASMOLYSIS

• When a living plant cell loses water through osmosis there is shrinkage or contraction of the contents of the cell away from the cell wall. This phenomenon is known as Plasmolysis.
• Only living cells, and not dead cells, are able to absorb water by osmosis. Cell walls permit the cells of plants, Fungi and Bacteria to withstand very dilute external media without shrinkage.
• Cell wall also prevents the bursting of cells when the cells are surrounded by a hypertonic medium (medium of high concentration).
• Because of their walls, plant cells can withstand much greater changes in the surrounding medium than animal cells.

CYTOPLASM

• It is the jelly-like substance present between the cell membrane and the nucleus.
• The cytoplasm is the fluid content inside the plasma membrane.
• It also contains many specialized cell organelles [Mitochondria, Golgi Bodies, Ribosomes, Etc.
• Each of these organelles performs a specific function for the cell.
• Cell organelles are enclosed by membranes.
• The significance of membranes can be illustrated with the example of viruses.
• Viruses lack any membranes and hence do not show characteristics of life until they enter a living body and use its cell machinery to multiply.

NUCLEUS

• It is an important component of the living cell.
• It is generally spherical and located in the center of the cell.
• It can be stained and seen easily with the help of a microscope.
• Nucleus is separated from the cytoplasm by a double layered membrane called the nuclear membrane.
• This membrane is also porous and allows the movement of materials between the cytoplasm and the inside of the nucleus [diffusion].
• With a microscope of higher magnification, we can see a smaller spherical body in the nucleus. It is called the NUCLEOLUS.
• In addition, nucleus contains thread-like structures called chromosomes. These carry genes and help in inheritance or transfer of characters from the parents to the offspring. The CHROMOSOMES can be seen only when the cell divides.
• GENE is a unit of inheritance in living organisms. It controls the transfer of a hereditary characteristic from parents to offspring. This means that your parents pass some of their characteristics on to you.
• Nucleus, in addition to its role in inheritance, acts as control center of the activities of the cell.
• The entire content of a living cell is known as PROTOPLASM [cytoplasm + nucleus]. It includes the cytoplasm and the nucleus. Protoplasm is called the living substance of the cell.
• The nucleus of the bacterial cell is not well organized like the cells of multicellular organisms. There is no nuclear membrane.
• Large and complex cells, including cells from multicellular organisms, need a lot of chemical activities to support their complicated structure and function.

CHROMOSOMES

• The nucleus contains chromosomes, which are visible as rod-shaped structures only when the cell is about to divide.
• Chromosomes contain information for inheritance of features from parents to next generation in the form of DNA (deoxyribo nucleic acid)
• Chromosomes are composed of DNA and Protein.
• DNA molecules contain the information necessary for constructing and organizing cells. Functional segments of DNA are called genes.
• In a cell which is not dividing, this DNA is present as part of chromatin material. Chromatin material is visible as entangled mass of thread like structures. Whenever the cell is about to divide, the chromatin material gets organised into chromosomes.
• It also plays a crucial part, along with the environment, in determining the way the cell will develop and what form it will exhibit at maturity, by directing the chemical activities of the cell.