Cell and Tissues
Cell and tissues asks for structure–function links: which organelle does what, and which tissue performs which job.
Cell structure
The plasma membrane is selectively permeable; the cell wall (plants, fungi, bacteria) is made of cellulose and gives rigidity. The nucleus holds the chromosomes and controls activity. Cytoplasm is where the organelles sit: mitochondria (respiration, ATP, 'powerhouse'), plastids (chloroplast for photosynthesis), endoplasmic reticulum (rough with ribosomes for protein synthesis, smooth for lipids), Golgi apparatus (packaging and secretion), lysosomes (intracellular digestion, 'suicide bags'), vacuoles (storage; the large plant vacuole maintains turgidity). Prokaryotes lack a true nucleus; eukaryotes have one.
Plant and animal tissues
Meristematic tissue (apical, lateral) divides and produces growth; permanent tissues are parenchyma (storage), collenchyma (flexibility), sclerenchyma (strength), and the conducting tissues xylem (water and minerals upward) and phloem (food, in both directions). Animal tissues: epithelial (covering and lining), connective (bone, cartilage, blood), muscular (striated, smooth, cardiac) and nervous (neuron).
Cell division
Mitosis produces two identical diploid cells for growth and repair; meiosis produces four haploid cells (gametes) and generates variation.
Worked example
A plant cell placed in pure water does not burst. Water enters by osmosis, but the cellulose wall resists the pressure and the cell becomes turgid. An animal cell without a wall would swell and lyse.
Traps
Drawing the cell wall inside the membrane; claiming mitochondria are present in mature mammalian RBCs (they lack a nucleus and most organelles); confusing meiosis with growth.