Biology Cells

Four basic features shared by all living cells

Plasma membrane, cytoplasm (cytosol), genetic material (DNA), and ribosomes.

Cell type lacking a nucleus and membrane-bound organelles

Prokaryotic cells (prokaryotes).

Cellular structures present in plant cells and prokaryotes but absent in animal cells

Cell walls (prokaryotes and plant cells both possess a rigid cell wall, which animal cells lack).

Organelle pathway for synthesized secretory proteins

Ribosome $\rightarrow$ Rough endoplasmic reticulum $\rightarrow$ Transport vesicle $\rightarrow$ Golgi apparatus $\rightarrow$ Secretory vesicle $\rightarrow$ Plasma membrane.

Functional significance of microvilli in epithelial cells

They dramatically expand the plasma membrane's surface area to maximize the absorption of nutrients and fluids.

Chemical property of phospholipid bilayer phosphate heads

Hydrophilic (polar and water-loving), oriented outward toward aqueous intracellular and extracellular fluids.

Membrane permeability of the nonpolar lipid bilayer core

Small, nonpolar molecules (such as $O<em>2$ and $CO</em>2$) pass freely, whereas ions, large molecules, and polar substances are blocked.

Functions of cholesterol and carbohydrate chains in the cell membrane

Cholesterol buffers membrane fluidity across varying temperatures, while membrane carbohydrates serve as cell-recognition and identification markers.

Mechanism by which nonpolar detergents disrupt cell membranes

Their nonpolar components intercalate with and dissolve the hydrophobic fatty acid tails, breaking apart the lipid bilayer structure.

Molecular activity at dynamic equilibrium across a membrane

Molecules continue to cross the membrane in both directions at equal rates, resulting in zero net concentration change.

Concentration gradient direction in passive transport

Down (with) the concentration gradient, moving from regions of higher concentration to lower concentration without energy input.

Energy requirement of active cellular transport

Requires metabolic energy, typically supplied by ATP, to move molecules against their concentration gradient.

Passive transport mechanism specific to water molecules

Osmosis (diffusion of water across a selectively permeable membrane).

Distinction between simple diffusion and facilitated diffusion

Simple diffusion allows nonpolar solutes to cross directly through the phospholipid bilayer, whereas facilitated diffusion relies on channel or carrier transport proteins to move polar or charged solutes.

Vesicle-mediated bulk transport mechanisms

Endocytosis (engulfing extracellular substances into vesicles) and exocytosis (fusing intracellular vesicles with the membrane to release materials).

Transport classification for moving ions via molecular pumps

Active transport, because molecular pumps expend ATP to drive ions against their electrochemical gradients.

Type of solution causing a cell to lose water and shrivel

Hypertonic solution (possesses a higher solute concentration than the cell's interior, drawing water out by osmosis).

Response of a plant cell placed in a hypotonic solution

Water enters by osmosis causing the cell to become turgid; the rigid cell wall exerts counter wall pressure and prevents cell lysis.

Environmental tonicity when cell mass increases from $12.0\,\text{g}$ to $14.1\,\text{g}$

Hypotonic solution (water entered the cell via osmosis because the surrounding fluid had a lower solute concentration than the intracellular environment).

Surface-area-to-volume ratio advantage of smaller cells

Smaller cells maintain a larger surface-area-to-volume ratio, facilitating faster and more efficient transport of nutrients and wastes across the membrane.

Surface-area-to-volume optimization in root hairs and mitochondrial cristae

Both structures possess specialized elongations or extensive foldings that vastly increase functional surface area without increasing overall volume, enhancing absorption and ATP synthesis rates respectively.