4.2.13 Microtubules - slender unbranched tubes about 20 nm in diameter & several um in length Functions: 1 act as an internal skeleton (cytoskeleton) for the cells & determine their shapes 2 aid in transport within cells by providing routes for materials to move 3 form a framework along which the cell wall is laid down 4 major component of cilia and flagella for movement 5 form centrioles of the spindle during cell division

4.2.14 Cilia and flagella - cilia are shorter & more numerous than flagella - both about 0.2 um in diameter; cilia about 10 um long, flagella about 100 um

1 To move an entire organism, Functions: 1 To move an entire organism, e.g. cilia of parameucium and flagellum of bacteria 2 To move materials within an organism, e.g. cilia within the respiratory tract, oviduct Flagellum (EM) (x92000 app.)

4.2.15 Centrioles - same basic structure as basal bodies of cilia Centrosome: a distinct region of the cytoplasm containing the two centrioles During cell division they migrate to opposite poles of the cell and make the microtubules of the spindle. * Higher plants (flowering plants) do not have centrioles, but they form spindle for cell division

4.2.16 Microfilaments - very thin strands about 6 nm in diameter - with actin & myosin proteins (similar to muscles), thus probably play a role in movement within cells/cell as a whole

e.g. kidney tubules and intestinal epithelium 4.2.17 Microvilli - finger-like projection about 0.6 um in length on the membranes of cells brush border: - actin filaments within the microvilli allow them to contract, with a larger surface area created, microvilli facilitate absorption, e.g. kidney tubules and intestinal epithelium Microvilli (EM) (x23000 app.)

Cotton plants Cellulose microfibril

4.2.18 Cellulose and cell wall -glucose  cellulose chain  micelle  microfibril  fibril embedded in polysaccharide matrix

Functions: 1 To provide support for young seedlings & herbaceous plants 2 To give mechanical strength to the plant as a whole. Strength may be increased by ligninfication. 3 Freely permeable to water, thus allow movement of water in the plant, e.g. in the cortex of roots 4 Lignin helps to keep water within the xylem; Cutin (epidermis of leaves) prevents water loss; Suberin (in root endodermis) prevents movement of water across them and controls water in by passage cells.

(a) protein synthesis - G: endoplasmic reticulum; (b) photosynthesis - B: chloroplast (c) electron transport (respiratory chain) - A: mitochondrion (or B) (d) protein/carbohydrate complex formation - H: golgi apparatus (e) generation of ATP - A: mitochondrion (or B) (f) ribosome production - F: nucleolus

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4.3 Movement in and out of cells 1 diffusion, 2 osmosis, 3 active transport, 4 phagocytosis, and 5 pinocytosis

Rate of diffusion depends upon: 4.3.1 Diffusion - the process by which a substance moves from a region of high concentration of that substance to a region of low concentration of the same substance. Rate of diffusion depends upon: 1. The concentration gradient 2. The distance over which diffusion takes place 3. The area over which diffusion takes place 4. The nature of any structure across which diffusion occurs 5. The size & nature of the diffusing molecule

Facilitated diffusion is a special form of diffusion which allows more rapid exchange. It involves channels (or carriers) within a membrane to make diffusion easier. It is passive, not involving energy.

Osmosis - the passage of water from a region of higher water potential to a region of lower water potential through a selectively permeable membrane. osmotic pressure (old term – a +ve value): pressure applied to the system to prevent osmosis to occur water potential: the difference between the chemical potential of water in the system and the chemical potential of pure water under standard temperature (25°C) and pressure (1 atmosphere).

- water potential of pure water is 0. - water will diffuse from a region of higher water potential to a region of lower water potential hypotonic solution: a dilute solution with higher water potential than the cell sap hypertonic solution: a concentrated solution with lower water potential than the cell sap

pressure potential

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4.3.4 Active transport

4.3.4 Active transport - energy is spent to drive the transport of molecules across membranes because molecules are transported against a concentration gradient, e.g. from a region of lower concentration to a region of higher concentration. - Mechanism: through proteins that span the membrane Characteristics of cells & tissues carrying active transport: 1 presence of numerous mitochondria (why?) 2 high concentration of ATP 3 high respiratory rate - any factors that affect respiratory rate will affect active transport, e.g. temperature, oxygen concentration and cyanide

4.4.3.5 Phagocytosis - the process by which the cell can obtain particles which are too large to be absorbed by diffusion or active transport cell invagination to contain particle  vacuole  lysosomes fuse with vacuole  enzymes digest particle  useful materials absorbed examples: phagocytes (WBCs) and amoeba for feeding

4.3.6 Pinocytosis - cell drinking - similar to phagocytosis but vacuoles (pinocytic or micropinocytic vesicles) are smaller - for intake of liquids endocytosis: both pinocytosis and phagocytosis are methods by which materials are taken into the cell in bulk exocytosis: materials are removed from cells in bulk

The enzymes contained within lysosomes are synthesized on rough ER and transported to the Golgi apparatus. Golgi vesicles containing the processed enzymes later bud off are called primary lysosomes.

Functions of lysosomes: 1 Digestion of material taken in by endocytosis 2 Autophagy: a process to remove unwanted structures within the cell 3 Release of enzymes outside the cell (Exocytosis), e.g. osteoclasts (remodelling of bones) 4 Autolysis: self-destruction of the cell

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