Form 4 Biology Bab 2: Cell Biology and Organisation
2.1 Cell Structure and Function
Cells are the basic units of all living things. (p.22)
Wet mount slide of onion epidermis: stain with iodine using the irrigation technique (filter paper draws stain under the cover slip); remove air bubbles by tapping the cover slip. (p.22)
Cheek cells are stained with methylene blue solution using the same technique. (p.23)
Plasma membrane: proteins and phospholipids, thin, elastic, partially permeable; separates cell contents from the environment and controls movement of substances. (p.24)
Mitochondrion: rod-shaped or spherical, smooth outer membrane and folded inner membrane; site of glucose oxidation in cellular respiration, releasing energy as ATP. (p.24)
Centriole: small cylindrical pairs of microtubules in animal cells only; forms spindle fibres during cell division. (p.24)
Golgi apparatus: stack of flattened sacs; processes, modifies, packs and transports proteins, carbohydrates and glycoproteins. (p.24)
Nucleus: largest component, enclosed in a porous nuclear membrane; controls all cell activities; chromosomes contain DNA. (p.25)
Endoplasmic reticulum: rough ER has ribosomes and transports proteins; smooth ER has no ribosomes and synthesises and transports glycerol and lipids and detoxifies drugs. (p.25)
Ribosome: small granules of protein and RNA on rough ER or free in cytoplasm; site of protein synthesis. (p.25)
Lysosome: small sac with a single membrane containing hydrolytic enzymes; hydrolyses complex organic molecules and breaks down bacteria and damaged cell components. (p.25)
Cell wall: strong rigid outer layer of cellulose, fully permeable; maintains shape and gives mechanical support to plant cells. (p.26)
Cytoplasm: jelly-like medium; the medium for biochemical reactions in cells. (p.26)
Chloroplast: oval, two membranes, chlorophyll in the grana; absorbs sunlight and converts it to chemical energy in photosynthesis. (p.26)
Vacuole: fluid-filled sac of cell sap surrounded by the tonoplast; young plant cells have many small vacuoles, mature cells one large vacuole; in unicellular animals the vacuole contracts during osmoregulation. (p.26)
Plant cells: fixed shape, cell wall, chloroplasts, large vacuole, store starch, no centriole. (p.27)
Animal cells: no fixed shape, no cell wall, no chloroplasts, no or small vacuole, store glycogen, have centrioles. (p.27)
Both have nucleus, cytoplasm, plasma membrane, Golgi apparatus, mitochondrion, endoplasmic reticulum and ribosomes. (p.27)
2.2 Living Processes in Unicellular Organisms
Unicellular organisms (e.g. Amoeba sp. and Paramecium sp.) carry out respiration, movement, nutrition, response to stimuli, reproduction, growth and excretion. (p.28)
Movement: Amoeba sp. extends pseudopodia followed by cytoplasm flow; Paramecium sp. moves by rhythmic cilia beats. (p.28)
Response: both move away from stimuli such as chemicals, touch or bright light. (p.28)
Respiration: gases exchanged through the plasma membrane by simple diffusion. (p.28)
Growth: by synthesising new cytoplasm. (p.28)
Nutrition in Amoeba sp.: pseudopodia trap food by phagocytosis; food vacuole fuses with lysosome; nutrients absorbed; undigested food discharged. (p.28)
Paramecium sp.: cilia move food into the oral groove; undigested food leaves through the anus. (p.28)
Excretion and osmoregulation: water enters the contractile vacuole by osmosis in freshwater; it contracts to expel water; waste such as CO2 and ammonia leaves by diffusion. (p.29)
Reproduction: binary fission through mitosis in favourable conditions; Amoeba sp. forms spores in unfavourable conditions; Paramecium sp. reproduces by conjugation. (p.29)
2.3 Living Processes in Multicellular Organisms
Specialised human cells: muscle cell (multinuclear striated fibres), sperm cell (long tail), nerve cell (long and thin), white blood cell (changes shape), epithelial cell (thin and flat), red blood cell (no nucleus, biconcave disc). (p.30)
Nerve tissue is made of neurones (cell body, dendrite, axon) and sends nerve impulses. (p.33)
Connective tissue: tendons connect bone to muscle, ligaments connect bone to bone; adipose tissue stores fat; bone forms the frame; cartilage encloses bone tips; blood transports, regulates and protects. (p.34)
Plant tissues: meristem (apical and lateral), dermal, vascular (xylem and phloem), ground (parenchyma, collenchyma, sclerenchyma). (p.35)
Collenchyma supports young non-woody stems; parenchyma stores starch, protein and water and can photosynthesise; sclerenchyma gives mechanical strength to mature parts. (p.35)
Xylem transports water and mineral salts; phloem transports organic matter such as sucrose from leaves. (p.36)
Sperm cell, muscle cell and plant meristem cell have many mitochondria (high energy requirement). (p.36)
Palisade and spongy mesophyll cells have many chloroplasts to absorb sunlight. (p.36)
Pancreatic cells have abundant rough ER and Golgi apparatus to synthesise and secrete digestive enzymes; goblet cells produce mucus; liver cells metabolise carbohydrates and detoxify drugs and poisons. (p.36)
Failure of mitochondria can cause stunted growth, weak muscles, hearing and vision problems; Tay-Sachs disease results from failure of lysosomal enzyme production. (p.37)
2.4 Levels of Organisation in Multicellular Organisms
Organs are formed from different tissues; the heart contains epithelial, cardiac muscle, connective and nerve tissue. (p.37)
Sequence: cell → tissue → organ → system → multicellular organism. (p.39)
Human body has 11 main organ systems. (p.38)
Respiratory: trachea, nose, lungs, diaphragm; gas exchange. Muscular: contracts and relaxes to produce movement. Endocrine: glands secreting hormones. Lymphatic: spleen, lymph nodes, lymph vessels. (p.38)