Another Biology Question!!?

Question

Which of the following cell organelles is made mostly of fats and proteins and controls substances moving in and out of the cell?

Chloroplast
Cell Membrane
Cell Wall
None of the above

Answer 1

Cell membrane is correct

Chloroplast: found in photosynthetic cells (plants, algae). Contains chlorophyll as a means to trap light energy. This is where photosynthesis occurs.

Cell Wall: a rigid outer structure found in plants. It prevents against dessication, which is a constant threat for plants, since they don't have the option of moving around to find water. Plant cells communicate with other plant cells through tight junctions between the cell walls.

Cell membrane: a phospholipid bilayer (the fatty section). The proteins provide ways that cells can communicate with each other and the outside environment. Often, proteins provide channels for molecules and hormones - think of the sodium/potassium pump. The protein changes conformation in order to allow specific substrates through. Realize that the membrane is not a rigid structure; rather, it's liquidy (more so when there are more unsaturated fatty acids, as the kinks in their tails prevents crowding of the heads) and the molecules/proteins are often moving around.

Answer 2

The cell membrane also known as the plasma membrane is the best choice because made of phospholipids.
For those of you who are not aware, phospholipids are fatty groups that are conjoined to phosphorous atoms, resulting in one side that is hydrophillic (that is one side that is attracted to water) and another side that is hydrophobic ( or repelled by water- similar to a phobia).
The Plasma membrane also controls what enters or leaves the cell through a selectively permeable membrane that filters proteins, large carbohydrates, and enzymes. Note the plasma membrane doesn't filter steroids (including cholesterol) and certain gases (ie. oxygen, and carbon dioxide.)

Answer 3

cell membrane; but don't know if it's appropriate to call it an organelle as it itself borders the cell & is not "in" the cytoplasm.

Answer 4

cell membrane