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2. Absorption & Secretion Of Materials
- 1. Absorption & Secretionof Materials Higher Biology Unit 1
- 2. Why do cellsneed to transport?
- 3. What are thedifferent mechanisms of transport?
- 4. Key Terms Finddefinitions for: Absorption Secretion Diffusion Osmosis Active transport
- 5. Cell Boundaries Whatsurrounds cells? Make notes on the plant cell wall. What is its structure? What role does it play in the movement of substances in and out of plant cells? Describe how the chemical nature of cell membranes has been investigated. What were the conclusions of this work?
- 6. Structure of plasmamembrane
- 7. Structure of plasmamembrane Cell membranes have a structure involving phospholipids, proteins and carbohydrates. The model of this structure is described as the fluid mosaic model. Why? Sketch a 2-D diagram showing the fluid mosaic structure of the cell membrane.
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- 9. Phospholipids The phospholipidsspontaneously form a bilayer due to their hydrophilic phosphate heads and hydrophobic fatty acid tails. The interaction between the phospholipids provide the membrane with stability. The structure of phospholipids also provide the membrane with selective permeability. What molecules will be able to pass through the phospholipid bilayer?
- 10. Proteins Protein revisionWhat are the monomers? What are the bonds between the monomers? Proteins are said to be specific, what does this mean? What gives them this specificity? How can their function be altered?
- 11. Proteins Transport Intrinsicproteins span the membrane and are used by the cell in the transport of specific, small, water-soluble substances such as glucose: carrier proteins. Specific proteins called channel proteins allow ions to pass through the membrane. Channel proteins are specific and can open & close and are therefore described as gated.
- 12. Proteins Enzymes Membraneproteins may also act as enzymes. E.g. microvilli on epithelial cells lining some parts of the gut contain digestive enzymes in their cell surface membranes. Another example of a membrane enzyme is ATPase link to photosynthesis & respiration.
- 13. Proteins Receptors Proteinshave very specific shapes. What gives them this shape? What type of bonds hold it together? This makes them ideal as receptor molecules for chemical signalling between cells. Can you think of some examples of this?
- 14. Proteins Antigens Antigensact as cell identity markers. These antigens are glycoproteins. What are glycoproteins? There are numerous possible shapes to the glycoprotein. Describe how this feature allows glycoproteins to act as antigens. What advantage does this ‘name-tagging’ convey to the organism?
- 15. Glycolipids What areglycolipids? Glycolipids are also involved in cell-cell recognition. With glycoproteins, they are also involved in sticking cells together in tissues.
- 16. Diffusion What isdiffusion? Can you define it? Diffusion is due to the kinetic energy of molecules and occurs because particles of liquids and gases undergo continuous random movements. Diffusion occurs across cell membranes through the phospholipid bilayer where concentration differences arise provided the molecules are small or non-polar.
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- 18. Diffusion But howcan polar molecules diffuse across membranes? Facilitated Diffusion Transport proteins have many of the properties of enzymes: they are specialised for the solute they transport they can become saturated they can become inhibited Unlike enzymes, they do not catalyse chemical reactions. Instead they catalyse the physical process of transporting molecules across the membrane.
- 19. Facilitated Diffusion Thereare two models for the mechanisms of facilitated diffusion. Carrier proteins bind to the molecule to be transported and a change in the shape of the protein results in the molecule being transported across the membrane.
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- 21. Facilitated Diffusion Channelproteins simply provide selective corridors allowing ions to cross the membrane, some of which are gated.
- 22. Facilitated Diffusion Facilitateddiffusion occurs because of the kinetic energy of the molecules involved. Energy from metabolism is not required. The rate of diffusion is affected by: gradient surface area distance temperature molecule size & polarity
- 23. Active Transport Some transport proteins can move solutes against their concentration gradients. To move a molecule across a membrane against its gradient the cell must expend its own metabolic energy. ATP supplies the energy for active transport.
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- 25. Osmosis Osmosis isa special case of diffusion across a selectively permeable membrane. What do you remember about osmosis from SG?
- 26. Osmosis Consider twocells separated by a partially permeable membrane: In which direction will the net movement of water be?
- 27. Osmosis Effect oncells Use the information on p9-11 to explain what happens to plant cells and animal cells when they are placed in each of the following solutions: Isotonic to the cell cytoplasm Hypertonic to the cell cytoplasm Hypotonic to the cell cytoplasm
- 28. Bulk Transport Howare large molecules transported across the membrane? Use p15 to draw diagrams and make notes on Endocytosis & Exocytosis . Answer the testing your knowledge questions for chapter 2.