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 and minerals . Human RBC: Biconcave shape to increase surface area to volume ratio and increase the rate of oxygen absorption and release. Contains red pigment haemoglobin which binds to oxygen, and lacks a nucleus to allow more haemoglobin (not oxygen) to be packed in. Muscle cell: Elongated and cylindrical in shape, contains many mitochondria to release energy during cellular respiration for contraction , contains contractile protein fibres that contract and relax to bring about movement.

Different Levels of Organisation: - Most organisms are made of many cells, said to be multicellular Levels of Organisation: Description: Tissue - A group of cells of the same structure and origin which come together to perform a particular function . - Classified into simple tissue (e.g. epidermis)/complex tissue (e.g. blood) Organ - Different tissues being grouped together to perform a function (e.g. Stomach = Epithelium tissue(skin) + Glandular tissue(enzymes) + Muscular tissue(churning) + Nervous tissue(nerves) + Connective tissue (to connect all tissues) Organ System - A group of different organs working together for a particular function (e.g. Digestive System) Organism - Various organ systems together make up the entire living organism Cell ⇒ Tissue ⇒ Organ ⇒ Organ System ⇒ Organism Topic 2: Movement of Substances Cell Membrane: - Current model accepted is fluid (movable phospholipids) mosaic (immobile proteins embedded) model - Model contains phospholipid bilayer arranged with hydrophobic tails facing inwards - Phospholipids move within bilayer (fluid)

- Mosaic of immobile proteins embedded or attached to bilayer of phospholipids (mosaic) Functions: - Selectively permeable , controls movement of substances moving in and out of the cell - Forms boundary between contents of cell and external environment, ensuring constant internal environment within cell is maintained for more efficient chemical reactions - Responsible for cell-to-cell communication : equipped with receptor proteins that receive chemical messenger molecules from other cells. Membrane Proteins: - Two types: - Integral proteins: embedded within bilayer - Peripheral proteins: loosely attached to surface of membrane Functions: - Transport proteins move specific molecules across the membrane by acting as channel or carrier proteins - Some proteins are enzymes with active sites exposed to substances on either side of membrane - Act as receptors to receive chemical messenger from other cells(e.g. hormone), relays message to inside of cell - Determine if other cells encountered are alike or different from itself (e.g. WBC recognising bacteria/viruses) - Attaches to protein on adjacent cells to hold together Diffusion, Facilitated Diffusion, Osmosis (energy not required): Process: Definition: Feature: Diffusion - Net movement of particles from a region of higher concentration to a region of lower concentration, - Passive process - Slow process

down a concentration gradient Facilitated Diffusion - Substance aided across a membrane by transport proteins (channel/carrier proteins) - For charged particles (e.g. ions), relatively large polar molecules (e.g. amino acids, sugars, fatty acids, glycerol) - Channel proteins provide hydrophilic passage for polar molecules by shielding from hydrophobic bilayer - Carrier proteins binds to ion/molecule, causing change in shape of protein forming hydrophilic channel Osmosis - Net movement of water molecules from a solution of higher water potential to a solution of lower water potential, down a water potential gradient through a selectively permeable membrane - Passive process Plant cell in solution with higher water potential: - Cell sap has a lower water potential than its surrounding solution - Water enters cell by osmosis through selectively permeable cell membrane - Large central vacuole increases in size - Cytoplasm gets pushed against cell wall, resulting in turgor pressure - Cell is turgid

Turgor/turgidity in plant cells help to: - Keep stems upright - Keep leaves flat so they can better absorb sunlight Animal cell in solution with higher water potential: - Cell has a lower water potential than its surrounding solution - Water enters cell by osmosis through selectively permeable