Biology - Cells

1 1. Organelle /Cell structure Organelle Structure Function Remarks Visible under light microscope (1000x, view living specimens in natural colour) & electron microscope Chloroplast - Contains chlorophyll, starch grains, circular DNA and fluid. - Found in plant, oval shape - Trap sunlight, convert light energy to chemical during photosynthesis - Absent in root hair cell, xylem, upper and lower epidermis of leaf Cell surface membrane - Partially permeable - Contain protein & fat - Can be destroyed by heat/pH →become fully permeable - Control substances entering and leaving the cell - No osmosis or active transport if it is destroyed Cell wall - Full permeable (linked to osmosis qn) - Made of cellulose to provide structural support. - Provide turgor pressure when placed in high water potential - Maintain shape of cell - Cellulose helps to prevent constipation Cytoplasm - Jelly-like substance - A site for chemical reactions - Xylem has no protoplasm Vacuole - Plant: Large central vacuole - Animal: Many, small, temporary vacuoles - Plant: contains cell sap enclosed by tonoplast - Animal: Store water and food substance - cell sap = water + sugar, mineral salts, amino acids metabolic waste. Nucleus (singular) Nucleoli (plural) - Consists of nucleous, nucleoplasm, nuclear envelope, nuclear pore, DNA/chromatin + RNA - Largest organelle - Contains genetic information, involves cell division and protein synthesis, control cell activities. - Red blood cells do not have nucleus → short life span, cannot reproduce. Visible under electron microscope only. (200 000x, view dead specimen in black & white colour). Mitochondrion (singular) Mitochondria (plural) - Has ribosomes, fluid, circular DNA & RNA - Highly folded inner membrane to ↑SA: VR Contains enzyme that release energy through aerobic respiration using oxygen and glucose - Active transport - Found in muscle/liver Ribosome - Attached to rough endoplasmic reticulum or lies freely in cytoplasm - Protein synthesis - Active protein synthesis CELL STRUCTURE AND ORGANISATION

2 Chloroplast (Chloroplasts) Mitochondrion (Mitochondria) Converts light energy into chemical energy (glucose) Converts chemical energy (glucose) into another form of energy (ATP) Uses carbon dioxide Uses oxygen and glucose Produce glucose Produces carbon dioxide Both carry out biochemical reactions and contains DNA 2. Plant cell VS animal cell Plant cell Animal cell Presence of cell wall and centriole Absent of cell wall and centriole Presence of chloroplast (for most plant cells) Absence of chloroplast Presence of (usually one) large central vacuole, Lesser cytoplasm Presence of many, temporarily tiny vacuoles. More cytoplasm Note: - Protoplasm = living conponent of the cell, consists of cytoplasm, nucleus, cell surface membrane and nutrients. - Centriole: for cell division Plant cell Animal cell nucleous nucleoplasm DNA/chromatin nuclear envelope nucleus cell wall cell surface membrane mitochondrion chloroplast tonoplast ribosome large central vacuole (contains cell sap) cytoplasm nucleous nucleoplasm DNA/ chromatin nuclear envelope nucleus cell surface membrane mitochondria ribosome vacuole cytoplasm centriole

3 3. Specialised cell Differentiation is a process where cells change in shape and form and are adapted to accquire special features to perform its specific function. Cell Adaptation to function Red blood cell Function: - To transport oxygen around body by allowing oxygen bind reversibly with haemoglobin. Structure for adaptation: - Contains haemoglobin which bind reversibly to oxygen to form oxyhaemoglobin (bright red colour) - Circular, biconcave disc shape to ↑SA: VR for diffusion - No nucleus to pack in more haemoglobin - Elastic to form bell-shaped to squeeze through tiny blood capillaries. Root hair cell Function: - Absorb water and mineral salts into the roots, anchor plant to soil Structure for adaptation: - Long and narrow cellular extension / long and narrow protruded root hair to ↑SA: VR for diffusion and osmosis. -No chloroplast present as it is underground and does not receive sunlight. - Tonoplast prevents leakage of cell sap →low water potential in root hair cell. Muscle cell Function: - To contact and relax to cause movement in the body. Structure for adaption: - Has many mitochondria to release energy for muscle contraction. Common specialised cell and its (general) structure to function Sperm cell Mitochondria to release energy for flagellum to swim to the egg Ciliated cell Cilia to sweep dust and mucus away Neurone/ nerve cell Long axon to transmit information Intestinal villus Microvilli to ↑SA: VR for absorption of digested food. Egg cell Cytoplasm contains food reserve for zygote Guard cell Chloroplast for photosynthesis Phagocytes Lobed nucleus for the cell to move through tiny gaps. Liver cell Has a lot ribosomes & mitochondria.