Biology O Levels/IP Notes (Sec3-4) Compilation

Topic 1: Cell Structure and Organisation Cell Structure: Cell Organelle: Appearance: Functions: Cytoplasm - Aqueous ground substance - Acts as site for chemical reactions in cell - Contains organelles Nucleus - Largest organelle - Double layered nuclear membrane - Controls and directs activities e.g. cell growth, reproduction, repairing of cells Cell Membrane - Selectively permeable membrane - Controls substances entering or leaving cell - Acts as receptor sites for recognising external stimuli and chemicals Mitochondria - Bound by double membrane - Mostly spherical, rod-shaped - Releases energy in the form of ATP during cellular respiration for activities such as growth, cell division, active transport Vacuole - Fluid filled - Large and central (plant) - Smaller, numerous, less permanent (animal) - Provides support for plants when filled with water by maintaining turgidity of cell - Temporarily stores waste products, food reserves (dissolved in) Chloroplast - Bounded by - Stores starch grains converted from

double membrane excess glucose made during photosynthesis (other starch found in cytoplasm) - Contains pigment chlorophyll to t rap sunlight during photosynthesis producing glucose Cell Wall - Made of cellulose - Inelastic, inflexible, fully permeable - Provides mechanical support - Protects cell from overexpansion Ribosomes - Found in cytoplasm, some attached to Rough ER - Synthesises proteins Rough ER - Covered with ribosomes - Granular appearance - Sheet-like - Numerous in enzyme secreting organs e.g. pancreas - Transports secretory proteins manufactured by ribosomes on ER surface Smooth ER - Lacks ribosomes - More tubular - Numerous in liver, skin oil glands - Synthesises fats, steroids (sex hormones) - Detoxification of harmful substances into harmless materials - Give rise to golgi body

Golgi Apparatus - Compact stack - Has convex face, concave face - Normally 1 in animal cell, many in plant cell - Chemically modifies substances made by ER - Stores, packages substances in vesicles for secretion out of cell e.g. Carbohydrates added to protein to form glycoproteins (mucus) Cell Differentiation: - Definition: Process whereby a cell becomes specialised for a specific function Advantages: Disadvantages - A specialised cell is able to carry out its tasks more efficiently - As a specialised cell normally loses its ability to carry out other functions, it is less able to change its function if an unusual need arises Examples: Root hair cell: Long and narrow to increase surface area to volume ratio for absorption of water