Definitions [2]
Define the following term:
Aster
The centrosome (in animal cell) splits into two along with the simultaneous duplication of the centrioles contained in it. The daughter centrioles move apart and occupy opposite "poles" of the cell. Each centriole is surrounded by radiating rays and is termed an aster (aster : star).
Define cell division.
Cell division is one of the most fundamental characteristics of life. This is the method which enables life to perpetuate generation after generation.
Key Points
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: Vacuoles & Granules
- Vacuoles are clear spaces containing water or dissolved substances, enclosed by a membrane called the tonoplast.
- Plant cells have fewer but larger vacuoles, while animal cells have smaller ones.
- Vacuoles store water, food, pigments, and waste, and help maintain cell turgidity.
- Some vacuoles contain pigments like anthocyanins (violet-blue).
- Granules are non-living particles (starch, glycogen, fats) that serve as food reserves for the cell.
Key Points: Cell Division
- Cell division is a vital process for growth, repair, and the formation of new organisms, helping maintain life in all living beings.
- It occurs in two forms: mitosis (in somatic and stem cells) for producing diploid identical cells, and meiosis (in germ cells) for forming haploid gametes.
- Mitosis supports body growth and tissue repair, while meiosis ensures genetic variation and maintains chromosome number in reproduction.
- Before division, the cell’s chromosome number doubles (e.g., from 2n to 4n) to ensure accurate distribution during mitosis or meiosis.
