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H/Ws 1 to 4. Types Cells Structure Response Q: Why are cells important? A: Basic unit of Life: reproduce, metabolize, respond to stimuli, grow, and die. Q: what are the two main types of cells? A: Prokaryote and Eukaryote. Prokaryote DNA material DNA in nucleoid No organelles Have cytoplasm 0.1 – 10micrometers in size All reactions in one compartment Eukaryote DNA material DNA in nucleus Have organelles Have cytoplasm 10 – 100micrometers in size Different reactions in different compartments Q: Why is Surface Area to Volume ratio important? A: Need to have fast exchange of materials between cell and external environment. Therefore need high surface area to volume ratio. That is why as an organism increases in size it increases the number of cells NOT size of the individual cells Fig. 6.7. Q: What are the two types of Eukaryote cells? A: Plant and animal cells. Plant Cell Nucleus and other organelles Cytoskeleton Plasma membrane Chloroplast Cell wall Central vacuole Tonoplast Plasmodesmata Animal Cell Nucleus and other organelles Cytoskeleton Plasma membrane N/A N/A N/A N/A N/A Lysosomes Flagellum Fig. 6.9. Q: What are lysosomes and their function? A: Sac of hydrolytic enzymes (hydrolysis). -Carry out intracellular digestion. -Recycle the cell’s own organic material ( autophagy). -Fig. 6.14 phagocytosis and autophagy (breakdown of damaged organelles). Q: What are vacuoles? A: Similar to lysosomes but have other functions: - Food vacuole =formed by phagocytosis. - Contractile vacuole = pumps out excess water Ex. in fresh water protists. - Central vacuole (plants) = holds food reserves (proteins, inorganic ions). - Disposal of metabolic byproducts. - Contain pigments. - Protect against predators (poisons). - Gets larger as cell grow so little cytoplasm. Cytosol therefore a small proportion of cell and ratio of membrane surface area to cytosolic volume is great, even for a large plant. Q: What is the fluid mosaic model? A: A membrane and various proteins embedded or attached to the double phospholipids layer. Q: Why a bilayer? A: This arrangement allows for a stable boundary between two aqueous compartments (water inside and outside of the cell). Q: Where do the proteins fit in the membrane? A: The difference in adherence of the cell membrane (CM), to water is due to the hydrophilic proteins in the membrane. Only the hydrophilic region exposed to water. Hydrophobic region in the membrane. Q: Why is it important to maintain the fluidity of the CM? A: Needs to be permeable and activity of enzymes in membrane affected. Q: How is the CM kept from solidifying? A: Cholesterol is the “temperature buffer.” As temperature goes down close packing of phospholipids prevented by the cholesterol and so lowers the temperature required for solidification. The type of lipid determines the fluidity of the membrane. Saturated pack closer together than unsaturated lipids. Usually membranes are as fluid as salad oil. Fig. 7.5. Hydrophobic interactions which are weaker than covalent. Fig. 7.7 and 7.9. Structure and functions. Q: What is a key function of any biological membrane? A: A key function of a biological membrane is regulation of transport of molecules into and out of the cell. Example of form fitting function. Q: How is a membrane selectively permeable? A: - Non-polar molecules ( hydrocarbons, O2, CO2), dissolve in the lipid bilayer and cross. - Ions and polar molecules (glucose, water, Na+ etc), need transport proteins. a) Channel proteins that have a hydrophilic channel (like a tunnel). Water goes through aquaporins (nobel prize 2003 – Dr. Agre). b) Carrier proteins actually hold molecule and change shape so that molecule is moved across membrane. - Concentration gradient. Molecules diffuse down a concentration gradient form high to low. Requires no energy even if facilitated by membrane proteins. - Active transport is against the concentration gradient and requires energy (ATP). Review Questions: 1. Why is a high surface area to volume ration so important to a cell? 2. What are the two main types of cells? What are the differences and similarities? 3. How does the central vacuole help a plant keep a high SA: Vol ratio as it grows? 4. Draw a phospholipids bilayer and explain how form fits function. 5. What determines the fluidity of a bilayer membrane? 6. What is the role of cholesterol in membrane structure? 7. Go over fig. 7.7 and be able to identify and describe functions of all the components. Review Questions: 1. Why is a high surface area to volume ration so important to a cell? 2. What are the two main types of cells? What are the differences and similarities? 3. How does the central vacuole help a plant keep a high SA: Vol ratio as it grows? 4. Draw a phospholipids bilayer and explain how form fits function. 5. What determines the fluidity of a bilayer membrane? 6. What is the role of cholesterol in membrane structure? 7. Go over fig. 7.7 and be able to identify and describe functions of all the components.