Bio Unit 2

On a % change in mass vs. solute concentration graph, how do you find the osmolarity of the tissue?

The x-intercept (where % change = 0)

Where % change in mass = 0, there's no net water movement, meaning the outside solution's concentration equals the tissue's internal solute concentration — that x-value is the osmolarity.

Which best explains osmosis?

Osmosis is the passive diffusion of water across a selectively permeable membrane, moving toward the side with more solute (lower water potential).

A cell placed in a hypertonic solution will most likely:

Shrink as water leaves the cell

Hypertonic = more solute outside the cell, so water leaves the cell by osmosis, causing it to shrink (crenation in animal cells, plasmolysis in plant cells).

Why does a high surface area-to-volume ratio matter for a cell?

It allows more efficient exchange of nutrients and wastes

A higher SA:V ratio means more membrane area relative to the cell's volume, allowing faster/more efficient exchange of materials — this is why cells stay small.

What forms the 'tails' of a phospholipid, and how do they orient in a bilayer?

Hydrophobic fatty acid chains; they face inward, away from water

The fatty acid tails are hydrophobic (nonpolar), so in water they orient inward, away from the aqueous environment, while the hydrophilic heads face the water on both sides.

Which is a key visual clue that a transport process is ACTIVE rather than passive?

ATP being converted to ADP + phosphate

Active transport requires energy, so a diagram showing ATP → ADP + P (or a pump changing shape using energy) signals active transport.

Which organelle modifies, sorts, and packages proteins for secretion?

Golgi apparatus

The Golgi apparatus receives proteins from the ER, modifies them further, and packages them into vesicles for secretion or delivery elsewhere in the cell.

Which piece of evidence supports the endosymbiotic theory?

Mitochondria and chloroplasts have their own circular DNA and 70S ribosomes

Mitochondria and chloroplasts have their own circular DNA and bacteria-like (70S) ribosomes, replicate independently via a process like binary fission, and have a double membrane — all evidence they were once free-living prokaryotes.

Why is compartmentalization important in eukaryotic cells?

It lets incompatible reactions occur at the same time in different organelles

By separating functions into membrane-bound organelles, cells can run incompatible or dangerous reactions (like digestion in lysosomes) without disrupting the rest of the cytoplasm, and can increase reaction efficiency and surface area.

Which structure is found in ALL viruses, regardless of type?

A protein capsid surrounding genetic material

Every virus has a protein capsid protecting its genetic material (DNA or RNA). Envelopes are only found in some viruses, and viruses lack ribosomes and mitochondria of their own.

Which is a defining difference between prokaryotic and eukaryotic cells?

Only eukaryotic cells have a membrane-bound nucleus

Eukaryotic cells have a true, membrane-bound nucleus; prokaryotic cells have their DNA in a nucleoid region without a surrounding membrane. Both have DNA, ribosomes, and a plasma membrane.