Chapter 7 Reading quiz

2. Chapter 7 Reading quiz What does �cell fractionation� do? What is the boundary called that ALL cells have? What is the simplest cell type? Which tiny organelles make protein? Which organelle acts as the cell�s �post office�?

3. 1. Distinguish between magnification and resolving power. Magnification How much larger an object is made to appear compared to its real size Resolving Power Minimum distance between two points that can still be distinguished as 2 separate points Limited by the wavelength of visible light ?

4. 2. Describe the advantages and limitations of the light microscope, transmission electron microscope, and the scanning electron microscope. Light � 1000X magnification, wavelength problem TEM � absorbs electrons � transmitted through by using electromagnetic lenses; can study internal cellular ultrastructure SEM � studies surface of a specimen � beam scans surface usually coated in gold & excites secondary electrons on surface produces a 3D image Disadvantages of electrons ? only dead cells (elaborate preparation needed) ?

5. 3. Describe the major steps of cell fractionation and explain why it is a useful technique (top of p. 105) Involves centrifuging disrupted cells at various speeds & durations to isolate components of different sizes, densities, and shapes Homogenize tissue Centrifuge slowly � form pellet Supernatant decanted & centrifuged again to get small stuff (faster) 3rd step repeated each time faster and faster to get smaller Once components are separated & identified, functions may be determined ?

7. 4. Distinguish between prokaryotic and eukaryotic cells. Prokaryotes Bacteria/ archaebacteria No true nucleus or envelope Genetic stuff in nucleoid region No membrane-bound organelles Eukaryotes Protista, Fungi, Plants, Animals True nucleus with nuclear envelope Cytoplasm with membrane-bound organelles ?

9. 5. Explain why there are both upper and lower limits to cell size. Lower limits � probably determined by the DNA to program metabolism (metabolic requirements) Ribosomes, enzymes & cellular components Upper limits � by surface area to volume ratio (volume does not grow proportionately to surface area) Plasma membrane � exchange oxygen, nutrients, wastes ?

10. 6. Explain why compartmentalization is important in eukaryotic cells. Compensate for small surface area to volume ratio by having internal membranes Partitions cell into compartments Unique compositions depending on functions Enzymes may be incorporated Provide localized environmental conditions necessary for specific metabolic processes ?

11. 7. Describe the structure and function of the nucleus, and briefly explain how the nucleus controls protein synthesis in the cytoplasm. Nucleus � membrane-bound cellular organelle in eukaryotes Contains most of the genes that control the entire cell mRNA transcribed in nucleus from DNA ? passes through nuclear pores to cytoplasm ? attaches to ribosomes where the genetic message is translated into primary protein structure ?

13. 8. Describe the structure and function of a eukaryotic ribosome. Cytoplasmic organelle that is the site for protein synthesis Complexes of RNA and protein Constructed in the nucleolus (no membrane) Cells with high rate of protein synthesis have lots of ribosomes bound and free (ER vs. cytoplasmic) ?

14. 9. Describe the structure and function of the ER, the Golgi apparatus, lysosomes, and vacuoles and summarize the relationships among them. Nuclear envelope � double membrane with pores ER � manufactures membranes (smooth vs. rough/ lipid vs. protein synthesis) Golgi apparatus � finishes, sorts, and ships cell products Lysosomes � bag of hydrolytic enzymes; digest all macromolecules Vacuoles � sac; come in food, contractile, and central forms ?

17. 10. Distinguish among the types of vacuoles and explain how their functions differ. Food vacuole � formed by phagocytosis ? site of intracellular digestion by some protists and macrophages Contractile vacuole � vacuole that pumps excess water from cell in some freshwater protozoa Central vacuole � large vacuole found in most mature plant cells ?

19. 11. Describe the structure of the mitochondrion and explain the importance of compartmentalization in mitochondrial function. Organelle which is the site of cellular respiration, a catabolic oxygen-requiring process that uses energy from food to produce ATP Number of mitochondria correlates with cell activity Can move, change shape, and divide 2 membranes � outer and inner Mitochondrial matrix ?

21. 12. Distinguish among amyloplast, chromoplast, and chloroplast. All are plastids Amyloplast � colorless, store starch, found in roots and tubers Chromoplast � pigments other than chlorophyll � responsible for fruit, flower, and autumn leaf colors Chloroplast � chlorophyll containing � site for photosynthesis ?

22. 13. Describe the structure of a chloroplast, and explain the importance of compartmentalization in chloroplast function. Intermembrane space � separates chloroplast from cytosol Thylakoid space � another membrane system � segregates the chloroplast into 2 compartments (thylakoid and stroma) Chlorophyll is here stacked into grana (light rxns) Stroma � (dark reactions) energy ? sugar Viscous fluid outside thylakoids ?

24. 14. Identify why peroxisomes are important in eukaryotic cells. Membrane- bound organelles that contain specialized teams of enzymes for specific metabolic pathways All contain peroxide-producing oxidases Breakdown fatty acids into smaller molecules for food Detoxification of alcohol, etc. ?

25. 15. Describe probable functions of the cytoskeleton. Gives mechanical support to the cell and helps maintain shape Enables cell to change shape in an adaptive manner Associated with motility Signal transmission from surface to interior Constructed from 3 types of fibers ?

26. 16. Describe the structure, components and functions of microtubules, microfilaments and intermediate filaments. Microtubules � straight hollow fibers - globular proteins called tubulin - used in cell support, organelle movement, separation of chromosomes during cell division Microfilaments � solid rods, globular protein monomers (actin) - cell support, muscle contraction, localized cell contraction Intermediate � diverse class of cytoskeletal elements (keratin) - bear tension, reinforce shape, fix organelle position ?

27. 17. Describe the development of plant cell walls. Young plant cell secretes a thin flexible primary cell wall Between the primary walls of adjacent cells a middle lamella made of pectins cements cells together Cell stops growing and strengthens wall ?

28. 18. Describe the structure and list some of the functions of the extracellular matrix in animal cells. Meshwork of macromolecules outside the plasma membrane of animal cells (ECM) Provides support and anchorage for cells Helps control gene activity in nucleus (mechanical stimuli) Functions in cell�s dynamic behavior (orient filaments) ?

29. 19. Describe the structure of intercellular junctions found in plant and animal cells, and relate their structure to function. Plants Plasmodesmata = channels that perforate plant cell walls � cytoplasmic strands communicate Lined by plasma membrane of adjacent cells are continuous Allows free passage of water, etc. (cytoplasmic streaming) Animals Tight junctions ? intercellular junctions that hold cells together tightly enough to block transport of substances Desmosomes ? junctions that rivet cells together into strong sheets, but still permit substances to pass freely Gap junctions ? intercellular junctions specialized for material transport between the cytoplasm of adjacent cells ?