The Cell: Structure and Functions
The Cell: Structure and Functions
Biology is the largest slice of the 40-question science paper, worth roughly 14 questions. The cell is where that block begins, and it gives 2 of them. Organelle-and-function matching is the standard format, and the plant-versus-animal comparison is the standard trap.
Discovery and the Cell Theory
- Robert Hooke discovered the cell in 1665 while examining a slice of cork.
- Anton van Leeuwenhoek first observed living cells.
- Robert Brown discovered the nucleus.
- Schleiden and Schwann proposed the cell theory: all living things are made of cells, and the cell is the basic unit of life.
- Virchow added that every cell arises from a pre-existing cell.
Hooke saw dead cell walls, not living cells — a distinction between him and Leeuwenhoek that is asked directly.
Organelles and What They Do
| Organelle | Function | Nickname |
|---|---|---|
| Nucleus | Controls all cell activity | Control centre |
| Mitochondria | Releases energy through respiration | Powerhouse |
| Ribosome | Protein synthesis | Protein factory |
| Chloroplast | Photosynthesis; found only in plants | Kitchen of the cell |
| Vacuole | Storage; large and central in plant cells | — |
| Lysosome | Digests waste and worn-out parts | Suicide bag |
| Cell membrane | Controls what enters and leaves | Selectively permeable |
The lysosome as suicide bag and the mitochondrion as powerhouse are the two nicknames asked most often, and both come with the reason attached.
Plant Cell Versus Animal Cell
| Feature | Plant cell | Animal cell |
|---|---|---|
| Cell wall | Present, made of cellulose | Absent |
| Chloroplast | Present | Absent |
| Vacuole | Large and central | Small or absent |
| Shape | Fixed and regular | Irregular |
| Centriole | Absent | Present |
Both have a cell membrane; only the plant cell has a cell wall outside it. Saying a plant cell has no membrane is a common error, since the wall is only an extra layer.
✗ A plant cell has a cell wall instead of a cell membrane | ✓ It has both — the wall lies outside the membrane
Types of Cells
A prokaryotic cell has no true nucleus and no membrane-bound organelles, as in bacteria. A eukaryotic cell has both, as in plants, animals and fungi.
- The largest cell is the ostrich egg; the largest human cell is the ovum.
- The smallest cell is a bacterium such as Mycoplasma.
- The longest cell is the nerve cell.
- The human red blood cell is unusual because the mature form has no nucleus.
- Cells vary in shape according to their function — nerve cells are long, RBCs are disc-shaped.
Unicellular organisms such as Amoeba and Paramecium carry out every life process within a single cell, while multicellular ones divide the work between tissues and organs. That division of labour is the point a teaching paper likes to test.
पादप कोशिका में कोशिका भित्ति और झिल्ली दोनों होती हैं।
TRE pointer: Biology is worth about 14 of the 40 science questions in Part-III, more than physics or chemistry alone, so this block deserves the most preparation time. The organelle nickname table is the highest-yield half-page here. Note that Hooke saw dead cork cells while Leeuwenhoek saw living ones — the pair is offered as alternatives. With five options and −1/3 for a wrong answer, the plant-and-animal comparison table is worth memorising outright.
60-Second Recap
- Hooke discovered the cell in 1665 in cork; Leeuwenhoek first saw living cells.
- Nucleus controls, mitochondria release energy, ribosomes make protein, lysosomes digest waste.
- Chloroplast and cell wall are found only in plant cells; both cell types have a membrane.
- Prokaryotes lack a true nucleus; eukaryotes have one.
- Ostrich egg is the largest cell; the nerve cell is the longest; mature RBCs have no nucleus.
- Amoeba and Paramecium are unicellular and perform all functions in one cell.
Frequently Asked Questions
Who discovered the cell and what did he actually see?
Robert Hooke, in 1665, looking at a thin slice of cork through his microscope. What he saw were the empty walls of dead cells, which he compared to small rooms and named cells. Anton van Leeuwenhoek was the first to observe living cells.
Why is the mitochondrion called the powerhouse of the cell?
Because it releases energy from food through respiration and stores it in a usable form. Cells that need a lot of energy, such as muscle cells, contain more mitochondria than others. The lysosome, by contrast, is called the suicide bag because it digests worn-out parts.
Does a plant cell have a cell membrane?
Yes. A plant cell has both a cell membrane and a cell wall, with the rigid cellulose wall lying outside the membrane. Animal cells have only the membrane. Assuming the wall replaces the membrane is one of the commonest errors in this topic.
What is the difference between prokaryotic and eukaryotic cells?
A prokaryotic cell has no true nucleus and no membrane-bound organelles, and bacteria are the standard example. A eukaryotic cell has a well-defined nucleus enclosed in a membrane, along with organelles such as mitochondria, and is found in plants, animals and fungi.