Definitions [2]
Define the following term:
Nucleoplasm
Nucleoplasm, also known as nuclear sap or karyoplasm, is the gel-like fluid inside the nucleus of a cell. It surrounds and supports the nucleolus and chromatin, helping to maintain the shape and structure of the nucleus and enabling the movement of materials within it.
Definition: Chromatin Fibres
The nucleoplasm contains a network of dark-coloured fibres called chromatin fibres.
Key Points
Key Points: Cell Theory
- Cell theory was proposed by Matthias Schleiden (1838) and Theodor Schwann (1839), stating that all plants and animals are made up of cells.
- Rudolf Virchow (1855) further expanded the theory by stating that new cells arise from pre-existing cells (“Omnis cellula e cellula”).
- According to modern cell theory, all living organisms are composed of cells and their products.
- The cell is the basic structural and functional unit of life.
- Cells arise only from pre-existing cells through cell division.
- The theory established that cells are the fundamental building blocks of all living organisms and highlighted the importance of cell division.
- Early cell theory had limitations as it did not explain cell formation, which was later resolved by Virchow.
Key Points: Plant Cell Vs Animal Cell
| Feature | Animal Cell | Plant Cell |
|---|---|---|
| Cell Wall | Absent | Present |
| Chloroplasts | Absent | Present |
| Vacuole | Small or absent | Large central vacuole |
| Shape | Generally round and irregular | Generally rectangular and regular |
| Lysosomes | Present | Present (though less common) |
| Centrioles | Present | Generally absent in most plant cells |
| Plasmodesmata | Absent | Present |
| Microvilli | Present | Generally absent |
| Golgi Apparatus | Present | Present |
| Mitochondria | Present | Present |
| Rough Endoplasmic Reticulum | Present | Present |
| Smooth Endoplasmic Reticulum | Present | Present |
| Ribosomes | Present | Present |
| Nucleus | Present | Present |
| Nucleolus | Present | Present |
| Plasma Membrane | Present | Present |
| Peroxisome | Present | Present |
| Cytoplasm | Present | Present |
| Middle Lamella | Absent | Present |
| Microtubules | Present | Present |
Key Points: Nucleus
- The nucleus is the largest, spherical organelle located centrally in the cytoplasm, enclosed by a double-layered membrane with pores.
- It contains nucleoplasm, one or more nucleoli, and a network of chromatin fibres.
- Nucleolus produces ribosomes and assists in protein synthesis by forming and storing RNA.
- Chromatin fibres (made of DNA) condense into chromosomes during cell division and carry hereditary information.
- The nucleus controls all cell functions, and its removal leads to cell death.
