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1. The main structural component of the cell membrane is the phospholipid.
2. Archaea prokaryotes tend to live in environments of extreme pH, salinity, and heat. This is a remnant of their ancient ancestry because the first cells to evolve on Earth had to survive in the extreme conditions present on the planet 3.5 billion years ago.
3. A. phospholipid, B. protein, C. hydrophilic phosphate group, D. hydrophobic tails, E. phospholipid bilayer
4. Transmembrane proteins span the entire width of the membrane (from the outside of the cell all the way to the inside of the cell), thus providing a tunnel through which things can move.
5. If a cell suddenly was exposed to much colder temperatures, the cell membrane would become too stiff. In order to counteract the stiffness, it would increase the percentage of unsaturated phospholipids. Unsaturated phospholipids have double bonds in the tails of the fatty acid chains, which make them unable to pack tightly together. Because they can’t pack tightly, this increases the fluidity (and helps to counteract the stiffness caused by cold temperatures).
6. Prokaryotic cells (bacteria) are the smaller and simpler cell types that lack organelles.
7. Characteristics of life: a. made of cells, b. reproduces and creates progeny, c. has a heritable genetic code (DNA), d. uses materials and undergoes metabolic processes, e. requires energy to survive, f. strives to maintain constant internal conditions (homeostasis), g. responds to its environment, h. evolves
8. A single phospholipid is amphipathic, meaning the phosphate head group portion of the molecule is polar and loves water, whereas the two fatty acid chains are nonpolar and hate water.
9. If a cell lived in very hot conditions (such as a volcanic deep-sea vent), its phospholipids would be composed of more saturated fatty acids in order to prevent the cell membrane from becoming too fluid. This is because saturated fatty acids form straight chains (without kinks and bends) and can pack tightly together. If the phospholipids of the phospholipid bilayer can pack tightly together, that makes the cell membrane more solid (which is good in really hot conditions).
10. List three possible roles for cell membrane proteins, and provide a brief description of each:
1. Transmembrane proteins can be used for transport, providing a pathway from the outside of the cell into the interior of the cell. Aquaporin is a specific example, and it provides a pathway for water molecules, increasing their movement into cells.
2. Proteins embedded in or on the cell membrane can be enzymes and play important roles in cell metabolism.
3. Some proteins are receptors and can latch onto a chemical signal on the outside of the cell. Once bound, it “transmits” the signal into the cell (this is called the process of signal transduction).
11.
a. Cell membrane Y
b. Nucleus N
c. Flagella Y
d. DNA Y
e. Cell wall Y
f. Ribosomes Y
g. Mitochondrion (an organelle) N
h. Nucleoid Y
12. An advantage to prokaryotic cells’ simplicity is it enables them to reproduce very quickly. Furthermore, their quick reproduction helps them to evolve quicker!
13.
a. An atom
b. A molecule
c. A virus 
Nope, not alive (because a virus is not made of a cell!)
d. An amoeba A single-celled amoeba is definitely alive!
e. A tree
14. The cell membrane is how a cell can create internal conditions different from its surroundings. The semipermeability of the membrane helps to keep certain things in the cell (and keep other things out of the cell).