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Name: ___________________________________ Cells and Transport VCE Biology- Unit 3 1. What is the ‘Cell Theory’? The cell theory states that all living organisms consist of organized structures called cells or the products of cells. 2. Make a list of the advances in technology that have allowed scientists to extend their knowledge of cells and their structures. Technological advances: hand-held lens, light microscope, phase contrast microscopes, fluorescence microscopes, transmission and scanning electron microscopes, sectioning equipment and improved staining techniques. 3. Compare eukaryotic cells and prokaryotic cells, listing the major structural differences between them. Eukaryotic cells Relatively large Unicellular or parts of complex multicellular organisms Distinct nucleus Separate membrane-bound organelles Prokaryotic cells Small and lack specification Unicellular or very simple multicellular organisms Nuclear material not membrane-bound Little ‘compartmentalisation’ No membrane- bound organelles 4. Describe the major structural differences between plant and animal cells, paying attention to cell organelles unique to each cell type. Cell wall: plant cells have a thick cellulose wall and cell membrane. Animal cells only have a cell membrane. Vacuole: large permanent vacuoles are characteristic of plant cells but not animal cells. Plastids: pigment-filled organelles such as chloroplasts are found in plant cells but not animal cells. 5. Why are cells usually microscopic in size? Discuss in terms of surface area to volume ratio and movement of materials into and out of cells. Cells are microscopic in size to increase their surface area to volume ratio. It is through the surface of a cell that materials enter and leave. An increase in cell volume means a decrease in surface area to volume ratio and so the rate of exchange of materials (requirements and wastes) between a cell and its surroundings is decreased. Surface area can be increased to a certain extent by shape. Remember the ‘biconcave disc’ shape of red blood cells. This increases surface area to volume ratio of red blood cells and thus the ability for oxygen to diffuse in and out at a rapid rate. 6. How are functions of the ribosomes, endoplasmic reticulum, golgi apparatus, and vesicles related? Ribosomes are the site of protein synthesis (production). Ribosomes are attached to the endoplasmic reticulum, which contains a membrane system that provides channels for movement of materials. It is also the site where the protein is folded and carbohydrates added. Proteins produced in the cell are packaged at the golgi apparatus (packaging) and moved to the cell membrane in vesicles (export). Protein markers on the vesicles determine which membranes the vesicles can fuse with. If the vesicle fuses with the cell membrane, the contents are secreted. The endoplasmic reticulum, the golgi apparatus and the vesicles are membranous organelles whose function can be summarized as transport, packaging and export. 7. Describe the fluid mosaic model for the structure of the cell membrane. The fluid mosaic model proposes that cell membranes consist of a bi-layer of phospholipids with embedded proteins. Fat-soluble materials can pass through the lipid part of the membrane. Other materials can pass through protein channels. Name: ___________________________________ VCE Biology- Unit 3 8. How is the structure and function of cell walls different to that of cell membranes? Cellulose cell walls are found in plant cells and have a support function rather than forming an envelope for a cell’s living contents. The cell membrane provides little support. Its major role is in determining what passes in and out of cells. It is described as semipermeable. The cell membrane is made of a double layer of phospholipid molecules and embedded with lumps of proteins. The proteins form channels that allow larger molecules to move in and out of the cell. 9. Define and compare the processes: diffusion, osmosis, facilitated diffusion, active transport and vesicle mediated transport. Definition Diffusion Process where molecules of a substance move from a region of high concentration to a region of lower concentration resulting in an even spread of molecules. Can occur in gases or liquids. Comparison No external energy is required. Movement is due to random movement of all molecules. Note, however, that the rate of diffusion increases with temperature. Movement of molecules is down the concentration gradient. A special case of diffusion- refers to the movement of water molecules from solutions of differing concentrations that are separated by a permeable membrane. Net movement of water will be to the side with higher concentration of dissolved materials (solutes). As above, but note that the movement of molecules refers to water only. Facilitated diffusion Case of diffusion where movement of materials is aided (facilitated) by special protein carrier molecules. Increases rate of movement of materials across membranes when the materials concerned do not dissolve readily in the lipid bilayer of membranes. Active transport Protein carrier molecules involved in moving materials across membranes against a concentration gradient – that is, material moved to a region where it is higher in concentration. Energy is required. This process can only occur in living cells that are respiring and so producing ATP. Process is very important in plant root hairs where ions are actively absorbed from the soil and in the mammalian digestive system. Vesiclemediated transport The cell membrane and vesicles are involved in the movement of large molecules into or out of the cell. Energy is required. Involves the movement of very large molecules and vesicles fusing with the cell membrane. Osmosis Water molecules are moving down their concentration gradient.