Try Now for FREE
- 1. Select your country from the
dropdown. - 2. Mobile : Enter just the mobile no. without any codes
- 3. Landline : Enter the
STD code followed by the phone no. Example 040-66979999.
CBSE - IX
Cell Structure
Cell Structure
The cell is the fundamental and structural unit of life.
The cell wall is composed of cellulose, and is permeable. It separates the contents of the cell from the surroundings, and gives shape and protection to the cell.
The plasma membrane is a living membrane made of lipoproteins. It allows the movement of some substances into and out of the cell.
The nucleus has a nuclear membrane, which is perforated to allow substances to enter and leave the nucleus. The nucleus plays a major role in cell division and cell development.
The nucleus contains chromosomes, which are composed of Deoxyribo Nucleic Acid, or DNA, and proteins. The functional segments of DNA are called genes.
The cytoplasm supports and protects the cell organelles that perform different metabolic functions.
Endoplasmic reticulum is an irregular network of double tubular membrane, continuous with the nuclear membrane on the inside.
Rough endoplasmic reticulum has ribosomes on it. It synthesises proteins, while smooth endoplasmic reticulum synthesises lipids and fats. Some of these proteins and lipids help in building cell membrane, and some function as enzymes and hormones.
Endoplasmic reticulum serves as a channel for the transport of proteins between various regions of the cytoplasm.
Ribosomes are naked granules with no membrane. They are found scattered in the cytoplasm or attached to the outside of the endoplasmic reticulum.
The Golgi apparatus is named after Camillo Golgi, who first described it. The Golgi apparatus consists of stacks of flattened membrane-bound sacs or vesicles. These stacks are called cisterns.
Mitochondria have their own DNA and ribosomes to synthesise respiratory enzymes. These enzymes oxidise glucose molecules to produce energy in the form of Adenosine Triphosphate or ATP.
When the cell gets damaged, the lysosome may burst and its enzymes may digest the cell itself.
Starch granules are storage droplets of starch, while lipid granules are storage droplets of fat.
Vacuoles store water, energy and waste products, and substances like amino acids, sugars and proteins. The fluid in them is called “cell sap”. A vacuole is covered by a living membrane called “tonoplast”.
Chloroplasts carry out photosynthesis, while leucoplasts store starch, oils and protein granules.
There is a difference between plant cells and animal cells. Plant cells are large, with a cell wall and a large vacuole, with fewer or no lysosomes. Animal cells are small, have no cell wall, and have small vacuoles, if present, and lysosomes.
