4.Transport Across Cel Membranes

Question 1

What is a plasma membrane

Answer 1

Membrane surrounding cells and their organelles

Question 2

What is cell surface membrane for

Answer 2

Plasma membrane Forms boundary between environment and cytoplasm-controls movement in and out of cell

Question 3

What do phospholipids do

Answer 3

Form bilayer
Hydrophilic phosphate heads attracted to and associate with water whereas hydrophobic tails repelled by water and form lipid soluble membrane

Question 4

What’s the function of lipid soluble membrane

Answer 4

Only allows lipid soluble substance to pass through
Water soluble substance prevented from passing through
Makes me,brand flexible and self selecting

Question 5

What are the types proteins used in the plasma membranes

Answer 5

Interspersed throughout
Embedded within the phospholipids

Intrinsic-carrier proteins and channel proteins, span across whole bilayer

Extrinsic-only in surface of bilayer, for mechanical support, form glycolipids, act as receptors

Question 6

How do carrier and channel proteins work

Answer 6

Carrier-ions bind to protein then it changes shape releasing ion or molecule to other side

Channel-Water filled so only water soluble ions diffuse across membrane

Question 7

What’s the function of membrane proteins

Answer 7

Structural support
Act as channels for transporting water soluble molecules
Active transport
Cell surface receptors for identifying cells
Help cells adhere
Receptors eg hormones

Question 8

Facts about cholesterol in membranes

Answer 8

Embedded with phospholipid bilayer
Very hydrophobic
Pulls fatty acids tails together limiting their movement

Question 9

Function of cholesterol in membranes

Answer 9

Reduces lateral movement
Adds strength
Makes membrane less fluid at high temp
Prevents leakage of water

Question 10

What is a glycolipid

Answer 10

Carb covalently bonded to lipid

Carb extended from bilayer into watery environment

Question 11

What’s the function of a glycolipid

Answer 11

Act as recognition sites
Helps cells attach to one another and form tissues
Cell surface receptors

Question 12

What’s the function of glycoproteins

Answer 12

Act as cell surface receptors specifically for hormones and neurotransmitters

Recognition sites
Help cells attach to one another eg lymphocytes recognising self material

Question 13

Why can’t most molecules freely diffuse across cell surface membrane?

Answer 13

Too large
Not lipid soluble
Get repelled if same charge as channel
If electrically charged have trouble passing through non polar hydrophobic bilayer

Question 14

Why is the cell surface membrane related to fluid Mosaic model

Answer 14

Fluid-individual phospholipid molecules can move relative to one another, giving membrane a flexible structure that’s constantly moving and changing shape

Mosaic-the proteins that are embedded into the phospholipids bilayer vary in shape, size and pattern in the same way the tiles of a mosaic are

Question 15

What is diffusion

Answer 15

The met movement of molecules or ions from a region where they are highly concentrated to a region where they are less concentrated until evenly distributed

Question 16

What is simple diffusion

Answer 16

Passive transport
Movement is due to the kinetic energy that the particles possess
Move randomly

Question 17

What’s facilitated diffusion

Answer 17

Passive process that requires a channel or carrier protein

Question 18

What is osmosis

Answer 18

Passage of water from region of high water potential to a region of low water potential through s semi permeable membrane

Question 19

Facts about water potential

Answer 19

Measured in kilopascals
Standard conditions water has w.p of 0
Addition of solutes to pure water lowers its w.p
Always -ve value
The more solute the more -ve
Water moves from less -ve to more -ve

Question 20

What is a hypertonic solution

Answer 20

Has a lower w.p than the tissue

Question 21

What’s a hypotonic solution

Answer 21

Higher w.p

Question 22

What happens when an animal cell is put in it a hypertonic solution

Answer 22

The water moves out of cell into solution and so cell shrinks

Question 23

What happens when an animal cell is put in a hypotonic solution

Answer 23

The cell undergoes lysis (bursts) as water moves from the solution into the cell

Question 24

What happens when a plant cell is placed in a hypertonic solution

Answer 24

Cell is plasmolysed as the water leaves the cell and the protoplasm pulls away from the cell wall

Question 25

What happens when plant cell is put in an isotonic solution (same water potential)

Answer 25

Cell in incipient plasmolysed

Question 26

What happens when you put a plant celll into a hypotonic solution

Answer 26

Cell swell, protoplast pushes onto cell wall, cell is turgid

Question 27

What is active transport

Answer 27

Movement of ions or molecules into or out of a cell from region of low conc to region of higher conc using ATP and carrier proteins

Question 28

What is ATP used fo

Answer 28

Directly move molecules

Individually move molecules using conc gradient that was set up by atp in (direct)

Question 29

How does direct transport work

Answer 29

Carrier protein span plasma membrane
Ion or molecule binds to receptor site
On inside atp binds to protein, causing it to hydrolyse into adp + pi
As result protein changes shape releasing to other side
Phosphate is released, protein reverts back to orig shape
During respiration phosphate recombined with adp

Question 30

How to increase rate of movement across membranes

Answer 30

1-epithelial cells lining the ileum possess micro ills finger like projections
2-provide larger surface area for insertion of proteins which allow active, facilitated and simple diffusion
3-increase no of protein carriers/channels

Question 31

What’s the role of diffusion in absorption

Answer 31

Carbs n glucose continuously digested, higher conc in ileum than blood, facilitated diffusion into blood
Cells use up carbs n glucose so it maintains the conc gradient down

Question 32

What’s the role of active transport in absorption

Answer 32

Diffusion will result in dynamic equilibrium so not all amino acids/glucose absorbed
Co transport of na+ and glucose/amino acids maintain the conc grad

Question 33

How does the na+/k+ pump work

Answer 33

• Na+ is actively transported out by the pump, into the blood by carrier proteins in epithelial cells
• maintains higher conc of na+ in ileum than epithelial
• na+ diffuse down grad into epithelial cells through carrier proteins
• na+ is actively transported along with either amino acids or glucose molecule
• pass int blood by facilitated diffusion