Biological Membranes

Question 1

What do membranes allow at the surface of cells

Answer 1

Recognition by other cells, cell signaling, diffusion, osmosis and active transport

Question 2

What is in the fluid mosaic model

Answer 2

Phospholipid bilayer, cholesterol, proteins (channel, intrinsic, extrinsic, carrier), some have glycoproteins or glycolipids (carbohydrate chain)

Question 3

What happens at membranes within cells

Answer 3

• Divide the cell into compartments acting as a barrier between the organelle and the cytoplasm
• Can form vesicles
• Control what enters and exits the cell (partially permeable)
• Site of chemical reactions

Question 4

Phospholipid head is…

Answer 4

Hydrophilic (attracts water)

Question 5

Fatty acid tail is…

Answer 5

Hydrophobic (repels water)

Question 6

What does the bilayer not allow in

Answer 6

Water soluble substance such as ions

Question 7

What does the bilayer allow through

Answer 7

Fat-soluble substances

Question 8

What is cholesterol

Answer 8

A type of lipid present in all cell membranes except bacteria

Question 9

Where id cholesterol in cells and how does it act

Answer 9

They fit between the phospholipids and bind to the hydrophobic tails causing them to pack more closely together making the membrane less fluid and more rigid. At low temperatures membrane fluidity is increased

Question 10

What do proteins do in the membrane

Answer 10

• Form channels in the membrane
• Transport molecules and ions across the membrane
• Act as receptors in cell signaling

Question 11

What do glycoproteins and glycolipids do

Answer 11

• Act as receptors for messenger molecules by stabilizing the membrane and forming hydrogen bonds with surrounding water molecules.
• Sites where drugs hormones and antibodies bind
• Antigens as involved in immune response

Question 12

What is cell signaling

Answer 12

Cells communicating with each other to control processes inside the body to respond to changes in the environment

Question 13

How do cells communicate with each other

Answer 13

1) One cell releases a messenger molecule
2) This molecule travels to another cell
3) This is detected by the cell because it binds to a receptor on its cell membrane

Question 14

How are receptors used in cell signaling

Answer 14

• Proteins act as receptors for messenger molecules called membrane-bound receptors
• They have specific shapes that can bind to
• Different cells have different types of receptors and respond to different messenger molecules
• A cell that respond to a particular messenger molecule is called a target cell

Question 15

How to investigate permeability of membranes

Answer 15

1) Cut five equal sized pieces of beetroot and rinse to remove any pigment
2) Place the five pieces in five different test tubes with 5cm of water
3) Place each test tube in a water bath at different temperatures (10,20,30,….)
4) Remove the pieces of beetroot from the tubes, leaving just the colored liquid
5) Use a calirometer to see how much light is absorbed

Question 16

Best temperature for phospholipids

Answer 16

0-45 degrees celcius

Question 17

What does changing the solvent do to membrane permeability

Answer 17

Surrounding it in a solvent increases the permeability of cell membranes as they dissolve the lipids in a cell membrane so it loses its structure. Increasing concentration also = increased permeability

Question 18

Diffusion is …

Answer 18

The net movement of particles from an area of high concentration to low concentration going down the concentration gradient. This is a passive process

Question 19

What type of molecules diffuse through the cell membrane

Answer 19

Small, non-polar molecules eg oxygen and carbon dioxide

Question 20

Rate of diffusion factors

Answer 20

Concentration gradient, thickness of exchange surface, surface area, temperature

Question 21

Facilitated diffusion is…

Answer 21

Diffusion through carrier or channel proteins in the cell membrane down the concentration gradient. It is a passive process

Question 22

How do carrier proteins work in facilitated diffusion

Answer 22

• They move large molecules down the concentration gradient
  1) First a large molecule attaches to a carrier protein in the membrane
  2) Then the protein changes shape
  3) This releases the molecule on the opposite side of the membrane

Question 23

How do channel proteins work in facilitated diffusion

Answer 23

They form pores in the membrane for charged particles to diffuse through. Different channel proteins facilitate the diffusion of different charged particles

Question 24

Active transport…

Answer 24

Uses energy to move molecules and ions across plasma membranes against a concentration gradient involving carrier proteins

Question 25

The stages of active transport

Answer 25

1) A molecule attaches to the carrier protein
2) The protein changes shape
3) Molecule is moved across the membrane and released on the other side

Question 26

What is bulk transport

Answer 26

When molecules are too large for carrier proteins such as proteins and lips so a vesicle forms and pinches off the substance

Question 27

What is endocytosis

Answer 27

When the vesicle of the substance is ingested into the cell

Question 28

What is exocytosis

Answer 28

Vesicles containing substances pick off from the Golgi apparatus in sacs and fuse with the plasma membrane before being released outside the cell

Question 29

What is osmosis

Answer 29

The diffusion of water molecules across a partially permeable membrane down a water gradient.

Question 30

What is water potential

Answer 30

Liklihood of water molecules to diffuse out of or into a solution

Question 31

What has the highest water potential, and of what

Answer 31

Pure water of 0

Question 32

What happens when a animal cell is placed in a hypotonic solution (water potential higher than the cell)

Answer 32

Net movement of water molecules is into the cell and so the cell bursts

Question 33

What happens when a animal cell is placed in a isotonic solution (water potential the same as the cell)

Answer 33

Water molecules pass into and out of the cell in equal amount. The cell stays the same

Question 34

What happens when a animal cell is placed in a hypertonic solution (water potential lower than the cell)

Answer 34

Net movement of water molecules is out of the cell and so the cell shrinks

Question 35

What happens when a plant cell is placed in a hypertonic solution (water potential lower than the cell)

Answer 35

Net movement of water is out of the cell. The cell becomes flaccid and the cytoplasm and membrane pull away from the cell wall. Called plasmolysis

Question 36

What happens when a plant cell is placed in a isotonic solution (water potential the same as the cell)

Answer 36

Water molecules pass into and out of the cell in equal amount. The cell stays the same

Question 37

What happens when a plant cell is placed in a hypotonic solution (water potential higher than the cell)

Answer 37

Net movement of water is into the cell. The vacuole swells and it with the cytoplasm push against the cell wall and it becomes turgid.