Ch 3 The cellular level of organization

Question 1

Describe the phospholipid structure

Answer 1

A phospholipid molecule consists of:
-a polar phosphate “head”, which is hydrophilic
- a non-polar lipid “tail”which is hydrophobic

Unsaturated fatty acids result in kinks in the hydrophobic tails

Question 2

Describe the phospholipid bilayer

Answer 2

-consists of two adjacent sheets of phospholipids, arranged tail to tail

-hydrophobic tails associated with one another, forming the interior of the membrane

-the polar heads contact the fluid inside the outside of the cell

Question 3

Describe the cell membrane

Answer 3

-a phospholipid bilayer containing many different molecular components, including proteins and cholesterol, some with carbohydrate groups attached

-two types of transport across the cell membrane: PASSIVE AND ACTIVE TRANSPORT

Question 4

Describe diffusion across the cell (plasma) membrane

Answer 4

The structure of the lipid bilayer allows only small, non-polar substances such as oxygen and carbon dioxide to pass through the cell membrane, down their concentration gradient, by simple diffusion

Question 5

Describe facilitated diffusion

Answer 5

A-takes place with the help of proteins such as channel proteins and carrier proteins

A-channel proteins are less selective than carrier proteins, and usually mildly discriminate between their cargo based on size and charge

B-Carrier proteins are more selective, often only allowing one particular type of molecule to cross

Question 6

Describe osmosis

Answer 6

-osmosis is the diffusion of water through a semipermeable membrane down its concentration gradient

-if a membrane is permeable to water, though not to a solute, water will equalize its own concentration by diffusing to the side of lower water concentration (and thus the side of higher solute concentration)

-in the beaker on the left, the solution on the right side of the membrane is hypertonic

Question 7

What are the 3 types on concentration solution

Answer 7

HYPERTONIC SOLUTION
-solute concentration higher than another solution

ISOTONIC SOLUTION
-solute concentration equal to another solution

HYPOTONIC SOLUTION
-solute concentration lower than another solution

Question 8

Describe the sodium-potassium pump

Answer 8

-found in many cell (plasma) membranes

-powered by ATP, the pump moves sodium and potassium ions in opposite directions, each agains its concentration gradient

-In a single cycle of the pump, 3 sodium ions are extruded from and two potassium ions are imported into the cell

-active transport

Question 9

What is endocytosis and what are the 3 forms

Answer 9

Endocytosis is a form of active transport in which a cell envelopes extracellular materials using its cell membrane

PHAGOCYTOSIS
-relatively nonselective
-cell takes in a large particle

PINOCYTOSIS
-cell takes in small particles in fluid

RECEPTOR-MEDIATED
-quite selective
-when external receptors bind a specific ligand, the cell responds by endocytosing the ligand