Cell Organelles and Their Functions
NCERT Class 9 • Science • Chapter "The Fundamental Unit of Life"
Cell Organelles and Their Functions
Inside a eukaryotic cell, specific jobs are handled by specialised structures called organelles, each enclosed in its own membrane. This division of labour lets many different chemical processes run at the same time without interfering with one another.
The Major Organelles
- The nucleus controls all cell activity and carries the chromosomes, which hold the genetic information.
- Mitochondria carry out respiration and release energy, so they are called the powerhouse of the cell; they have their own DNA.
- Ribosomes are the site of protein synthesis and are found free in the cytoplasm or attached to the endoplasmic reticulum.
- The endoplasmic reticulum is a network of membranes; the rough type carries ribosomes and makes protein, while the smooth type makes fat and detoxifies poisons.
- The Golgi apparatus modifies, packages and dispatches materials made in the cell, so it is called the dispatching unit.
- Lysosomes contain digestive enzymes that break down worn out parts and foreign material, which is why they are called suicide bags.
- Plastids are found only in plant cells; chloroplast carries out photosynthesis, chromoplast gives colour and leucoplast stores food.
Vacuole, Cytoplasm and Cell Division
- The vacuole stores water, food, waste and pigments, and in plant cells it keeps the cell turgid.
- The cytoplasm is the jelly like fluid in which all organelles are suspended and most reactions occur.
- Mitosis produces two daughter cells identical to the parent cell and is used for growth and repair.
- Meiosis produces four cells with half the chromosome number and occurs during the formation of gametes.
- Meiosis is essential for sexual reproduction because it keeps the chromosome number constant across generations.
- Cell division is also the process through which a single fertilised cell grows into a whole organism.
- Cell membrane and cell wall together decide the shape a cell takes and how much water it can hold.
- Damaged organelles are broken down and their parts reused, so the cell constantly renews itself.
| Organelle | Main Function | Nickname |
|---|---|---|
| Mitochondria | Respiration and energy release | Powerhouse of the cell |
| Ribosome | Protein synthesis | Protein factory |
| Golgi apparatus | Modifying and dispatching | Dispatching unit |
| Lysosome | Digestion of worn out parts | Suicide bag |
Lysosome — an organelle containing digestive enzymes that breaks down worn out cell parts and foreign material.
Exam me kaise aata hai
- The powerhouse of the cell is — mitochondria
- Protein synthesis takes place at the — ribosome
- Suicide bags of the cell are — lysosomes
- Photosynthesis occurs in which plastid — chloroplast
UPSC/State PSC ke liye
- Mitochondria have their own DNA and ribosomes, which supports the view that they were once free living organisms taken inside an early cell.
- Lysosomes are called suicide bags because they burst and digest the cell itself when it is damaged or aged beyond repair.
Yahan confuse hote hain
✗ Ribosomes make energy | Ribosomes make protein; mitochondria release energy | ✓
✗ All plastids carry out photosynthesis | Only chloroplast does; chromoplast gives colour and leucoplast stores food | ✓
✗ Mitosis and meiosis both halve the chromosome number | Only meiosis halves it | ✓
Ek nazar me
- Nucleus controls the cell; mitochondria release energy; ribosomes make protein.
- Endoplasmic reticulum transports; Golgi packages; lysosome digests.
- Plastids occur only in plant cells and include the chloroplast.
- Mitosis gives identical cells; meiosis halves the chromosome number for gametes.