More Practice CELLS UNIT Questions! ANSWER KEY

More practice CELLS UNIT questions! ANSWER KEY

1. For a class project, Tom made two electron micrographs of mouse cells, two of bean leaf cells, and two of E. coli bacteria. Unfortunately, he forgot to label the pictures and they became mixed up. The micrographs are close-ups, so only the structures listed below are visible. Which pictures can you positively identify? Is it possible to sort out the others? How? Identify as many as you can.

Electron Micrograph Type of Cell Reason Picture A: chloroplast, ribosomes, Bean leaf cell Must be eukaryotic (has nucleus nucleus); must be plant cell (has chloroplast) Picture B: cell wall, plasma E. coli cell Could be prokaryotic or plant membrane cell; process of elimination rules out other choices Picture C: mitochondrion, cell Bean leaf cell Must be eukaryotic (has wall, plasma membrane mitochondrion); must be plant cell (has cell wall) Picture D: microtubules, golgi Mouse cell Must be eukaryotic (has golgi) apparatus Picture E: plasma membrane, E. coli cell Could be either prokaryotic or ribosomes eukaryotic; process of elimination rules out other choices Picture F: nucleus, rough ER Mouse cell Must be eukaryotic (has organelles)

2. Mrs. Stewart gets annoyed when she is buying vegetables at the grocery store and the sprayers come on to spray the vegetables. Grocery stores do this to keep the vegetables plump and delicious looking, rather than wilted and unappetizing. Using your knowledge of osmosis, explain why spraying the outside of vegetables keeps them plump.

Spraying the vegetables with fresh water keeps the plant cells turgid in the grocery store. Water sprayed onto the surface of the vegetables diffuses into the plant cells as they have a higher solute concentration than the fresh water. This prevents the plant cells of the vegetables from becoming flaccid and making the produce look wilted.

3. Glucose is absorbed through protein channels in the plasma membrane of epithelium cells in the small intestine. Which characteristics of glucose prevent its diffusion through the phospholipid bilayer? (This Q is from last spring’s IB Bio exam.)

a. It is non-polar and therefore hydrophobic. b. Its hydrogen bonds link with amino acids in the protein channel. c. It is polar and therefore hydrophilic. d. Its covalent bonds interact with the phospholipids. As a polar molecule, glucose is “repelled” by the hydrophobic interior of the lipid bilayer. It must travel through a carrier protein in order to enter the cell. This is an example of facilitated diffusion. 4. Which process and cause are responsible for water uptake by plant roots? (This Q is from last spring’s IB Bio exam.)

Process Cause

Simple diffusion Solute concentration in the root is lower than in the soil.

Osmosis Solute concentration in the root is greater than in the soil.

Osmosis Solute concentration in the root is lower than in the soil.

Cohesion Solute concentration in the root is greater than in the soil.

Osmosis is the diffusion of water. Water always diffuses to an area of higher solute concentration. If the root cells maintain a greater solute concentration than the soil around them, then water will naturally diffuse into the root cells without an expenditure of energy by the cells. Water can also enter via aquaporins embedded in the cell membrane of the root cells. This is still an example of osmosis as it is still diffusion (facilitated diffusion).