Cell Structure and Function Exam Study Guide Part I

Cell Structure and Function Exam Study Guide Part I

1. Which image best depicts the hot water, which the cold? 2. What is the relationship between temperature and the speed of molecular motion? 3. If a drop of red dye was added to both, which would be pushed around and spread throughout the water faster due to molecular motion? 4. What is responsible for diffusion?

The image on the right is hot (longer arrows imply faster molecular motion). As temp. increases, so does molecular motion. Therefore, a drop of dye placed in the hot water will be pushed around more and thus spread out (diffuse) faster. The kinetic energy (random molecular motion due to heat) is responsible for the process of diffusion.

5. For the situation shown, assuming dye molecules can pass through the membrane, explain what the situation will look like after dynamic equilibrium. 6. Explain the change in terms of diffusion and concentration gradients. 7. Once dynamic equilibrium has occurred, will the dye molecules continue to cross the membrane? Explain:

The dye would diffuse down its concentration gradient from an area of higher towards lower concentration. At dynamic equilibrium, an equal number of dye molecules would be on each side of the membrane. At this point, dye molecules do continue to cross back and forth, but equally such that on average there is an equal number of molecules on each side.

Epithelial cells are the cells that line our small intestine. 8. What is the function of the small intestine? 9. Describe a specific structural feature of the epithelial cell (shown above) that relates to the cell s function. 10. Describe the glucose gradient from the epithelial cell layer (lining of the small intestine) to the blood. Which direction does glucose move and why?

Epithelial cells are the cells that line our small intestine. The function of the small intestine is nutrient absorption (nutrients removed from food and enter blood stream). The microvilli (finger-like projections) on the epithelial cell vastly increases the surface area for nutrient absorption. The glucose gradient from the epithelial cell to the blood is [high] to [low]. Thus, glucose diffuses from the epithelial cell into the blood.

The lungs are composed of branching structure (bronchioles) that end in grape-like clusters called the alveoli. The alveoli are enveloped by capillaries. 11. What is the function of the alveoli? 12. What does surface area have to do with the structure of the lungs? 13. Discuss where the labels CO 2 and O 2 should be added to the diagram. 14. Gas-exchange occurs due to diffusion. Explain the direction of gas-exchange (use the concept of concentration gradient in your explanation).

The lungs are composed of branching structure (bronchioles) that end in grape-like clusters called the alveoli. The alveoli are enveloped by capillaries. The alveoli s function is gas exchange between the atmosphere and the blood. The air-sacs called alveoli vastly increase the surface area for the diffusion of the gases. Oxygen diffused from an area of high [ ] in the alveolus to an area of low [ ], in the blood. Carbon dioxide diffuses down its concentration gradient in the opposite direction.

15. Discuss where the labels CO 2 and O 2 should be added to the diagram. 16. Gas-exchange, between red blood cells and the cells of the body, occurs due to passive diffusion. Explain the direction of gas-exchange (use the concept of concentration gradient in your explanation).

Oxygen will diffuse from an area of higher concentration, the blood, to an area of lower concentration, body cells (such as active brain cells). Carbon dioxide will also diffuse from an area of higher (body cells) to an area of lower concentration (blood).

17. Which cells have cell membranes? 18. Describe two functions of the cell membrane:

All cells have cell membranes. The membrane separates the inside environment of the cell from the outside. The membrane is also selectively permeable, and through chemical discrimination, controls traffic into and out of the cell. As a result, the environment inside a cell can be very different from one outside the cell.

2 1 19. Which part of the lipid molecule is hydrophobic? 20. Which part is hydrophilic? 21. Why do lipids form a bilayer (double-layer)? 22. Which materials can pass easily through the bilayer?

2 1 The part of the phospholipid labeled 2 is hydrophobic, while the part labeled 1 is hydrophyllic. Lipids form a bilayer because the hydrophyllic heads will orient outwards towards the watery environments, while the hydrophobic tails point inward, shielded against the water. Small nonpolar molecules can easily pass through the bilayer. Larger molecules (glucose) and polar molecules (water) use protein channels.

23. Water is a polar molecule, and thus its passage through the nonpolar hydrophobic part of the lipid bilayer would be slow. Explain how osmosis through the lipid bilayer is sped up. 24. How easily would glucose cross the lipid bilayer? Explain: How does glucose cross the bilayer?

Protein channels, such as the aquaporin shown above, span the cell membrane and provide a passageway for polar molecules such as water. As a result, large amounts of water can rapidly diffuse across the membrane. Glucose would not easily cross the membrane due to two problems: it is large and it is polar. Both would make getting through the lipid layer difficult.

25. Identify the oxygen and hydrogen atoms of the water molecules. 26. Which partial charge does the oxygen have? 27. Which partial charge does the hydrogen have? 28. Is the ion (large circle) a positively or negatively charged ion?

The oxygen is the larger atom and the two hydrogens are the smaller ones (of the Mickey-mouse ears). Oxygen has a partial negative and hydrogen atoms a partial positive charge. Since all of the oxygen atoms are pointed towards the unknown ion, we can infer that the ion is positively charged.

29. Describe what is occurring between the water molecules and the glucose molecule: 30. Explain why this interaction occurs: 31. Does glucose dissolve in water? Explain:

Hydrogen bonds have formed between the polar water molecules and polar glucose molecule. This occurs due to the electrostatic attraction of opposite partial charges. Glucose dissolves in water as a result of these interactions.

32. How many water molecules (Mikey-mouse molecules) are on each side of the membrane? 33. How many glucose molecules (large circle molecules) are on each side of the membrane? 34. Describe how the water-molecules are behaving with the glucose. 35. Compare the [free water] on both sides of the membrane and predict the net direction of water movement.

There are 24 free-water molecules on the left and only four on the right. There are five glucose molecules on the right, that are attracting most of the water molecules. As a result, there is a lower concentration of free water on the right. Therefore, water will move from the left (an area of higher) towards the right (an area of lower) free-water concentration.

B A C Shown above are cells soaked in three solutions of differing [sucrose]. Sucrose molecules are represented by the small circles. 36. For each situation (A C) describe how the [free water] inside the cell compares to that of the solution. 37. Predict the net direction of diffusion in each situation (A C) 38. Which situation was most similar to when we exposed red onion to salt?

B A C Shown above are cells soaked in three solutions of differing [sucrose]. Sucrose molecules are represented by the small circles. In A, there is a higher [free-water] outside the cell than inside so water would diffuse into the cell. In B, there is an equal [free-water] outside and inside the cell so there would be no net movement of water. In C, there is a higher [freewater] inside than outside the cell, so water would diffuse out of the cell. Situation C was most similar to exposing the red onion cells to salt water.

A B C 39. Describe the net direction of water movement in A C above. 40. Predict what the effect of each situation would be for the plant cell. 41. Match the following solution descriptions with A C above: saline solution (mild salt solution), pure water, sea-water

A B C In A, the cell is soaked in pure water, and water is diffusing into the cell, the cell swells but does not burst. In B, the cell is soaked in a saline (mildly salty) solution, there is no net water movement, the cell is dehydrated. In C, the cell is soaked in saltwater, the next direction of water movement is out of the cell, the membrane has separated from the cell wall, the cell is dying.