Working+cell+essays

Essays 1. Describe the kind of molecules that cannot easily diffuse through cell membranes. How do proteins facilitate diffusion of these substances?

2. Make a sketch showing why an enzyme acts only a specific substrate.

3. Most enzyme-catalyzed chemical reactions in humans occur most readily around body temperature, 37 degrees Celsius. Why do these reactions slow down at lower temperatures? Why do they slow down at higher temperatures?

4. Which contains more potential energy, a large, complex molecule like a protein, or the smaller amino acid subunits of which it is composed? Is the joining of amino acids to form a protein an exergonic or endergonic reaction? Why must this be the case? Where does the cell obtain energy to carry out such reactions?

5. Describe the circumstances under which plant and animal cells gain and lose water by osmosis. Which of the following is the least serious problem: water gain by a plant cell, water loss by a plant cell, water gain by an animal cell or water loss by an animal cell? Why?

6. The burning of glucose molecules in paper is an exergonic reaction, which releases heat and light. If this reaction is exergonic, why doesn’t the book in your hands spontaneously burst into flame? You could start the reaction if you touched this page with a burning match. What is the role of the energy supplied by the match?

7. Seawater is hypertonic in comparison to body tissues. Explain what would happen to his stomach cells if a shipwrecked sailor drank seawater.

8. The laws of thermodynamics have imaginatively been described as the house rules of a cosmic energy card game: “You can’t win, you can’t break even and (if you want to stay alive) you can’t get out of the game.” State the law that says living things can’t win the energy game. State the law that says they can’t break even.

9. A farm worker accidentally was splashed with a powerful insecticide. A few minutes later he went into convulsions, stopped breathing, and died. The insecticide acted as a competitive inhibitor of an enzyme important in the function of the nervous system. Describe the structural relationship between the enzyme, its substrate and the insecticide.

10. Lecithin is a substance used in foods such as mayonnaise as an emulsifier, which means that it helps oil and water mix. Lecithin is a phospholipid; a lecithin molecule has a polar (hydrophilic) “head” and a nonpolar (hydrophobic) “tail”. How might the structure of lecithin allow water to surround fat droplets? Sketch a microscopic view of some fat droplets in mayonnaise and show how you think the fat, surrounding water, and lecithin molecules might be arranged.