AP Biology - Unit 2 Quiz 2

Amphipathic

a protein having both hydrophilic and hydrophobic parts

Plasmodesmata

hole-like structures in the cell wall filled with cytosol that connects adjacent cells

Cell wall

extracellular structure (not found in animal cells); provides shape, structure, and protection as well as regulating water intake

Plasma membrane

separates internal cell environment from external environment; comprised primarily of a bilayer, cholesterol, and proteins (which forms fluid mosaic); are amphipathic

Cellulose

composes the cell wall; non-digestible for most mammals (e.g. humans) but cows have a special stomach enzyme to help break it down

Phospholipid

major component of the cell membrane (two fatty acids attached to a glycerol and phosphate); assemble as a bilayer for H2O (tails-hydrophilic, head - hydrophobic)

What is the relationship between cell size and the SA:V ratio?

SA:V ratio increases as cell size decreases (optimizes the exchange of materials at the plasma membrane); SA:V ratio decreases as cell size increases (larger the cell, the cell efficient)

What are phospholipid heads and tails made up of?

Heads (hydrophobic) - phosphate groups and glycerol

Tails (hydrophilic) - fatty acids (saturated and unsaturated)

How is cellular metabolism related to size?

Cellular metabolism is determined by size

How is the membrane composition different for organisms that live in different/colder climates?

Organisms will have a higher proportion of unsaturated fatty acids to increase fluidity and prevent the cell from becoming rigid and rupturing.

SA:V Ratio

Cells that have HIGHER SA:V ratios are MORE efficient at exchanging materials.

For storage of materials, larger cells are best. LARGER cells have LOWER SA:V ratios

FOLDS in membrane INCREASES SA:V ratio

Fluid Mosaic Model

“Fluid” - the membrane is held together by weak interactions

“Mosaic” - comprised of macro molecules

Sections of the Plasma Membrane

Integral Proteins: embedded into the lipid bilayer - aka transmembrane protiens, ampipathic

Peripheral Proteins: loosely bonded to the surface; important for cell-to-cell recognition

• Glycolipid: carbohydrates bonded to lipids

• Glycoproteins: carbohydrates bonded to proteins

SA:V Ratio Formulas

SA = 6s²

V=lwh

SA:V=SA/V

What types of molecules freely cross the membrane?

Gases: oxygen, carbon dioxide, and nitrogen are small and non polar so they can easily cross the membrane

Charged molecules: requires channels or pumps/active transport. Their charge prevents them from interacting with hydrophobic interior of the membrane

Hydrophobic molecules: hydrophobic molecules can interact with hydrophobic interior of membrane, allowing them to pass through