Cell Biology and Cell Division
What this domain tests
Kerala SSLC questions here check cell theory, the structure–function link of each organelle, prokaryotic versus eukaryotic organisation, osmosis and plasmolysis, and the exact sequence and outcome of mitosis and meiosis. Expect one-line definitions, reasoning about labelled structures, and chromosome-number arithmetic.
Core rules
- Cell theory: all living things are made of cells, the cell is the functional unit of life, and every cell arises from a pre-existing cell.
- Prokaryotes have no nuclear envelope and no membrane-bound organelles; DNA is circular and naked; ribosomes are 70S. Eukaryotes have a true nucleus, linear DNA with histones, and 80S ribosomes.
- Mitochondrion: aerobic respiration (matrix and inner membrane cristae). Chloroplast: photosynthesis. Both are semi-autonomous and carry their own DNA.
- Ribosome makes protein; ER transports; Golgi modifies, packages and secretes; lysosome holds hydrolytic enzymes; vacuole maintains turgidity.
- Plant-cell extras: cellulose wall (fully permeable, not selectively), large vacuole, plastids, and no centriole in most higher plant cells.
- Mitosis: one cell gives two genetically identical diploid cells; stages prophase, metaphase, anaphase, telophase; function is growth, repair and asexual reproduction.
- Meiosis: two divisions, four haploid cells, crossing over in prophase I producing variation.
Worked example
Onion root-tip cells have 2n = 16. How many chromosomes are present in one cell at anaphase of mitosis? At anaphase the sister chromatids have separated but cytokinesis is not over, so the single cell temporarily holds both sets: 16 + 16 = 32 chromosomes, while each future daughter cell will get 16.
Traps that cost marks
Saying meiosis gives two daughter cells; placing crossing over in anaphase instead of prophase I; calling the cell wall selectively permeable; claiming all plant cells lack centrioles; writing that mitosis halves the chromosome number.