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๐ฌ Think about it
Think of a busy kitchen. One person cooks, one washes, one packs. Each has a job, and together they run the kitchen. A cell is like that — a tiny factory where every part does one special job. Let us look inside.
What are the three basic parts of most cells?
- A selectively permeable membrane (plasma membrane).
- A semi-fluid, jelly-like cytoplasm.
- A prominent nucleus.
| Basic part | What it is |
|---|---|
| Plasma membrane | The selectively permeable outer boundary. |
| Cytoplasm | A semi-fluid, jelly-like substance inside. |
| Nucleus | A prominent control centre of the cell. |
What are organelles?
- The cytoplasm holds tiny sub-cellular parts called organelles.
- Each organelle does a specific job.
- Most are visible only under an electron microscope.
Example:
A cell is like a tiny factory, with each part doing a specific job.
In this Activity, we will study diagrams of a bacterial cell, a plant cell and an animal cell, and record which structures each one has.
Materials needed
Diagrams of a bacterial cell, a plant cell and an animal cell (Fig. 2.10 a, b and c).
Procedure
1. Study the given diagrams of a bacterial cell, a plant cell and an animal cell.
2. Observe the different structures present in each of them.
3. Record your observations in Table 2.1.
2. Observe the different structures present in each of them.
3. Record your observations in Table 2.1.
Table 2.1 — Comparison of different kinds of cells based on their structure
| S. No. | Cell structures | Bacterial cell | Plant cell | Animal cell |
|---|---|---|---|---|
| 1. | Cell membrane | Present | Present | Present |
| 2. | Cell wall | Present | Present | Absent |
| 3. | Cytoplasm | Present | Present | Present |
| 4. | Well-defined nucleus (genetic material enclosed by a membrane) | Absent | Present | Present |
| 5. | Primitive nucleus (nucleoid) (genetic material without membrane around it) | Present | Absent | Absent |
| 6. | Membrane-bound organelles | Absent | Present | Present |
Observation
A bacterial cell lacks a well-defined nucleus and membrane-bound organelles. Plant and animal cells have a well-defined nucleus and several membrane-bound organelles.
Explanation
Cells without a well-defined nucleus are called prokaryotic cells. Cells with a well-defined nucleus and membrane-bound organelles are called eukaryotic cells. So the bacterial cell is prokaryotic, while plant and animal cells are eukaryotic.
โ Summary
- Compare three cells.
- Bacteria: no true nucleus.
- Plant, animal: true nucleus.
- So prokaryotic vs eukaryotic.
What are prokaryotic cells?
- They lack a well-defined nucleus.
- They lack membrane-bound organelles.
- Most activities happen directly in the cytoplasm.
- "Pro" means primitive and "karyon" means nucleus.
Example:
A bacterial cell is a prokaryotic cell.
What are eukaryotic cells?
- They have a well-defined nucleus.
- They have several membrane-bound organelles.
- "Eu" means true and "karyon" means nucleus.
Prokaryotic cell
Eukaryotic cell
Primitive nucleus present.
Primitive nucleus absent.
Diameter 1 to 10 µm.
Diameter 10 to 100 µm.
Usually unicellular.
Can be unicellular or multicellular.
Membrane-bound organelles absent.
Membrane-bound organelles present.
Membrane-bound nucleus absent.
Membrane-bound nucleus present.
Important Points
- Most cells have three basic parts: membrane, cytoplasm and nucleus.
- Organelles are tiny parts inside the cytoplasm, each with a job.
- Bacterial cells are prokaryotic; plant and animal cells are eukaryotic.
๐ก Ready to Go Beyond
- Viruses, viroids and prions are acellular (no cells).
- They are too small to see under a light microscope.
- Viruses have genetic material with a protein coat.
- Viroids lack a protein coat; prions are misfolded proteins.
๐ก Ready to Go Beyond
- A network of fine fibres forms the cytoskeleton.
- It gives support, shape and helps internal transport.
- It is seen only under an electron microscope.
- Stored starch, calcium oxalate or silica are called cell inclusions.
โ Test Yourself
-
Name the three basic parts of most cells.
View Answer
The plasma membrane, the cytoplasm and the nucleus. -
What does "prokaryotic" literally mean?
View Answer
"Pro" means primitive and "karyon" means nucleus. -
Which cell type has membrane-bound organelles?
View Answer
The eukaryotic cell. -
Is a bacterial cell prokaryotic or eukaryotic?
View Answer
Prokaryotic — it has no well-defined nucleus. -
Are viruses made of cells?
View Answer
No, they are acellular — they have no cells.
Important Definitions
- Cytoplasm — the semi-fluid, jelly-like substance filling the cell.
- Organelles — tiny sub-cellular parts in the cytoplasm, each with a special job.
- Prokaryotic cell — a cell with no well-defined nucleus or membrane-bound organelles.
- Eukaryotic cell — a cell with a well-defined nucleus and membrane-bound organelles.
๐ NCERT Question 9 — Indicate the presence or
Indicate the presence or absence of given structures in bacterial and animal cells.
View Answer →
