Transport Over Membranes

Question 1

Explain the phospholipid bilayer in the fluid mosaic model

Answer 1

Phospholipids form a bilayer with hydrophilic heads pointing out (attracted to the water) and hydrophobic tails point inwards (repelled by water)

Question 2

What are the functions of the phospholipids in the membrane

Answer 2

Allow lipid soluble substances to enter/leave but prevent water soluble substances. Make the membrane flexible and self sealing
1. Form water impermeable barrier to water soluble substances/ allows non polar molecules to pass through
2. Able to fuse with other membranes/ form vesicles

Question 3

Describe a phospholipid

Answer 3

ONE phosphate head, TWO fatty acid tails, also glycerol

Question 4

Functions of proteins in the membrane

Answer 4

Structural support, channels to transport water soluble molecules, allow active transport through carrier proteins, form cell surface receptors, help cells adhere together

Question 5

Functions of cholesterol in the membrane

Answer 5

Add strength to the membranes, they are hydrophobic so prevent water loss and dissolved ions leaving the cell, they pull fatty acid tails of phospholipids (limiting their movements without making membrane rigid

Question 6

What makes up the mosaic model membrane

Answer 6

Phospholipids, cholesterol, glycolipids, glycoproteins, proteins

Question 7

Why is the fluid mosaic called that

Answer 7

Fluid as the phospholipids can move (gives membrane flexible structure so can change shape), mosaic because proteins are imbedded in the bilayer

Question 8

Diffusion definition

Answer 8

The net movement of molecules or ions from a region where they a more highly concentrated to one where their concentration is lower until they are evenly distributed

Question 9

What kind of molecules can diffuse across a membrane

Answer 9

Small, non polar (like oxygen or carbon dioxide), lipid soluble

Question 10

What are factors affecting diffusion

Answer 10

Temperature (increasing in kinetic energy makes membrane more permeable) molecular size, concentration gradient steepness

Question 11

What is facilitated diffusion

Answer 11

Protein specific to substance, and binds to a carrier/channel protein, moves down a concentration gradient

Question 12

Describe how protein channels work

Answer 12

They form water filled hydrophilic channels across the membrane. They allow water soluble ions to pass through. The channels are selective (control over entry and exit) the ions bind with the protein causing it to change shape (closes and opens both sides of membrane)

Question 13

What are affecting factors of facilitated diffusion

Answer 13

Temperature, conc gradient steepness, number of channels available in membrane

Question 14

Osmosis definition

Answer 14

Passage of water from a region where it has a higher water potential to a region where it has a lower water potential , through a selectively permeable membrane

Question 15

What is a solute

Answer 15

A substance dissolved in a solvent

Question 16

What is water potential presented by and what is it measured in

Answer 16

Psi and measured in kPa (kilopascals)

Question 17

What water potential does pure water have

Answer 17

0

Question 18

What will lower water potential

Answer 18

Addition of solute

Question 19

What does a more negative value mean in terms of water potential

Answer 19

Lower water potential

Question 20

When will osmosis continue until

Answer 20

Dynamic equilibrium is reached (no net movement of water)

Question 21

What does isotonic mean

Answer 21

Water potential is the same on internal and external

Question 22

The effect of solution with a higher water potential on a red blood cell

Answer 22

The water enters the cell through osmosis and the cell swells and bursts meaning it’s contents (haemoglobin) are released

Question 23

The effect of an external solution having lower water potential than a red blood cell

Answer 23

Water potential of solution is lower so water leaves the cell through osmosis making it shrink

Question 24

The effect of a solution with higher water potential on a plant cell

Answer 24

Water enters cell through osmosis , protoplast swells and the cell becomes turgid

Question 25

What is the state of a plant cell in isotonic solution

Answer 25

Incipient plasmolysis

Question 26

The effect of a solution with lower water potential on a plant cell

Answer 26

Water leaves cell through osmosis , protoplast shrinks and cell is plasmolysed

Question 27

Active transport definition

Answer 27

The movement of molecules into/out of a cell from a region of lower concentration to higher concentration using ATP and carrier proteins

Question 28

How does active transport differ from other transport methods

Answer 28

Metabolic energy in the form of atp is needed, substances are moved against a concentration gradient (low to high), carrier proteins act as pumps, selective process

Question 29

Describe the active transport of a single molecule

Answer 29

1 Carrier proteins bind to the molecule, (molecule binds to receptor sites on proteins) 2. On inside of cell, ATP binds to protein, causing it to split into ADP + phosphate molecule Which cause protein molecule to change shape and open at opposite side of membrane and molecule released 3. Release causes protein to revert and phosphate recombined to form ATP

Question 30

Differences between active transport and facilitated diffusion

Answer 30

Facilitated is passive, active is requires energy. Active occurs against a conc gradient but facilitated goes down conc gradient

Question 31

Similarities between active transport and facilitated diffusion

Answer 31

Both involve carrier proteins

Question 32

Which cells posses micro villi and what does it do

Answer 32

Epithelial cells lining the ileum, microvilli provide more surface area for insertion of carrier proteins so diffusion, facilitated diffusion and active transport can take place

Question 33

What’s are methods to increase rate transport across membranes

Answer 33

Increase number of protein channels&carrier proteins and increase the surface are via microvilli for insertion of protein channels/carrier proteins

Question 34

Describe co transport

Answer 34

1. Na+ ions are actively transported OUT of epithelial cells via sodium potassium pump into the blood 2. This maintains a higher conc of Na+ ions in the lumen of intestine than in epithelial cells 3. Na+ diffuse into the epithelial cells via facilitated diffusion down this conc gradient through a protein carrier but as they diffuse in, they carry either an AA or glucose molecule with them, AGAINST their conc gradient

Question 35

What powers the glucose into the cell during co transport

Answer 35

The sodium ion concentration gradient, rather than ATP, making it an indirect form of active transport

Question 36

What are the functions of extrinsic proteins in the CSM

Answer 36

Act as cell recognition sites/ for cell recognition, binding to hormones, identification of cell