Chapter 4

Question 1

Basic Characteristic of Life

Answer 1

Regulation

Response to Environment

Question 2

Cellular Membranes

Answer 2

All cells enclosed by a membrane

Composed of phospholipids
Amphipathic molecule

Hydrophilic heads point outward
Towards water

Hydrophobic tails point inward
Away from water

Question 3

Fluid Mosaic Model of Membranes

Answer 3

NOT rigid

Proteins associated with membrane
Float and bob in lipid bilayer

Question 4

Evidence of Membrane Fluidity

Answer 4

Obtained experimentally
Two cells were fused with different marked proteins
After fusion, surface proteins were mixed

Question 5

Membrane Proteins

Answer 5

Two types of membrane proteins

Integral proteins are embedded in the membrane

Peripheral proteins are loosely associated with one side of the membrane

Question 6

Two Membrane Proteins

Answer 6

Integral

Peripheral

Question 7

Membrane Permeability

Answer 7

Molecules need to cross cell membrane
Semi-permeable

Diffusion (passive transport)

Active Transport

Question 8

Diffusion (Passive Transport)

Answer 8

Osmosis
Facilitated Diffusion (Transport Proteins)

Net movement of particles from an area of greater concentration to an area of lower concentration

No energy is required for this process

Question 9

Active Transport

Answer 9

Requires energy and transport proteins

Sometimes a cell needs to actively uptake something
Needs higher levels of a molecule than naturally present

Works against natural diffusion gradient

Five main steps

Question 10

Osmosis

Answer 10

Refers to the passive movement of water across a semi-permeable membrane

Question 11

Cellular Water Levels (No Cell Wall)

Answer 11

Cells need to maintain a certain level of water

Ideal levels - Isotonic environment

Too much water in the cell - Hypotonic environment
Cell lysis (bursts)

Not enough water in the cell - Hypertonic environment
Cell shrivels

Question 12

Cellular Water Levels (Cell Water)

Answer 12

Some cells have a cell wall which can protect them in hypotonic environment (burst)

Cell walls exert Turgor Pressure preventing lysis

Does not protect against Hypertonic environments (plasmolyzed / shrivel up)

Question 13

Facilitated Diffusion

Answer 13

Proteins can help get things through the membrane

Assist polar compounds and ions through the membrane

Channel Proteins
Carrier Proteins

Question 14

Channel Proteins

Answer 14

Provide a pathway through the membrane

Question 15

Carrier Proteins

Answer 15

Physically carries a molecule through the membrane

Question 16

Five Steps of Active Transport

Sodium/Potassium Pump

Answer 16

1. Na+ inside the cell binds to pump
   Shape stimulates Na+ binding
2. Na+ binding causes phosphorylation by ATP
   Results in change of shape
3. Na+ bound to the pump protein is released outside the cell
4. New shape likes to bind K+
   Ion is bound from outside the cell
   Causes loss of phosphate group
5. Loss of phosphate restores original shape
6. K+ is released inside the cell and the cycle repeats

Question 17

Electrochemical Gradients

Answer 17

Cells have voltages across their membranes
Cells are negatively charged

Due to increased levels of negative ions inside relative to outside

Question 18

Co-transport

Answer 18

Diffusion across the membrane can do work
Generate energy
Transport another molecule

Question 19

Endocytosis

Answer 19

Cells can take in molecules and compounds by surrounding them with their membrane (endocytosis)

Three main types of endocytosis

Question 20

Three Main Types of Endocytosis

Answer 20

1. Phagocytosis
   Cellular “eating”
   Uptake of extracellular fluids
2. Pinocytosis
   Cellular “drinking”
   Uptake of extracellular fluids
3. Receptor-Mediated Endocytosis
   Uptake of bulk quantities of a specific substance
   Identified by receptors on the outer membrane

Question 21

Exocytosis

Answer 21

Cell can release particles/molecules into their surroundings

Intracellular vesicles fuse with the outer membrane
Release contents