B4 Transport across Cell Membrane

Question 1

Definition of cell surface membrane

Answer 1

The boundary formed between the cytoplasm and the environment

Question 2

What does the cell surface membrane do?

Answer 2

Controls the movement of substances in and out of the cell. Selectively permeable to regulate transport of substances. Involved in cell signalling/cell recognition

Question 3

What are the cells and organelles surrounded by?

Answer 3

They are surrounded by a partially permeable membrane containing a sea of phospholipids with protein molecules embedded within them

Question 4

What is the fluid mosaic model?

Answer 4

The fluid mosaic model describes the structure of the plasma membrane as a mosaic of phospholipids, cholesterol, proteins, and carbohydrates. This gives the membrane a fluid character.

Question 5

What do phospholipids form?

Answer 5

Phospholipid bilayer

Question 6

Name and describe the functions of phospholipids?

Answer 6

Allow lipid soluble substances to move through the membrane
Prevents water soluble substances to move through the membrane
Makes the membrane flexible and self sealing

Question 7

What do phospholipid bilayer contain?

Answer 7

Hydrophillic heads that point outwards and Hydrophobic tails point inwards

Question 8

What are the main components of cell surface membrane?

Answer 8

Proteins
Cholesterol
Glycolipids
Glycoproteins

Question 9

What are the functions of proteins in cell surface membrane?

Answer 9

They are integrated throughout the membrane as intrinsic proteins or on the surface as extrinsic proteins. Proteins are present to aid movement across the membrane providing mechanical support and acting in conjunction with glycolipids and receptors

Question 10

Name a intrinsic protein and what do they do?

Answer 10

Carrier proteins allow substances to cross the membrane

Question 11

What is the function of cholesterol in the cell surface membrane?

Answer 11

Its present in the membrane to make it more rigid and reduce lateral movement of the phospholipids. Prevents leakages of water and dissolved ions from the cell as it is very hydrophobic

Question 12

What are the functions of glycolipids in the cell membrane?

Answer 12

These are carbohydrates bound to lipids and they extend on the surface acting as cell receptors for certain molecules also allowing cells to adhere to another to form tissue

Question 13

What are the functions of glycoproteins in the cell membrane?

Answer 13

These are carbohydrates attached to extrinsic proteins and act as cell surface receptors and neurotransmitters. These allow cells to recognise one another as cells attach to form tissues

Question 14

What are the five main types of movement?

Answer 14

Diffusion
Facilitated diffusion
Osmosis
Active transport
Co- transport

Question 15

Definition of diffusion

Answer 15

Diffusion is the net movement of small non polar molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed down a concentration gradient

Question 16

What are the factors that affect diffusion and how do they?

Answer 16

Surface area
Shorter diffusion pathway
Steeper diffusion gradient
Temperature increase due to more ke
thinner exchange surface

Question 17

Definition of facilitated diffusion?

Answer 17

Facilitated diffusion requires a channel protein in the cell membrane to transport polar molecules, charged and water soluble molecules across the membrane from an area of higher conc to lower conc

Question 18

What are the factors that affect FD?

Answer 18

Higher concentration gradient faster the rate
Number of channel proteins

Question 19

Name an example of a protein channel in the cell surface membrane?

Answer 19

Aquaporins

Question 20

What do protein channels do?

Answer 20

Proteins turn water filled hydrophillic channels that allow specific water soluble ions to pass through pores

Question 21

What do carrier proteins do?

Answer 21

When a specific molecules binds to a carrier protein it causes the protein to change shape in a way that the molecule is released in the inside of the membrane (conformational change)

Question 22

Definition of osmosis

Answer 22

Diffusion of water molecules from an area of higher water potential to an area of lower water potential through a partially permeable membrane

Question 23

Definition of active transport

Answer 23

Movement of molecules or ions into or out of a cell from a region of lower concentration to an area of higher concentration using energy from ATP and use of carrier proteins

Question 24

Definition of co transport?

Answer 24

movement of a substance against its concentration gradient is coupled with the movement of another substance down its concentration/electrochemical gradient. Movement simultaneously

Question 25

How does Co - transport work?

Answer 25

Substances bind to complementary intrinsic proteins.
Symport - transport substances in same direction
antiport - transport substances in opposite direction e.g Na/K pump

Question 26

Explain how co - transport is involved in the absorption of glucose/amino acids in the small intestine

Answer 26

1. Na+ actively transported out of epithelial cells into bloodstream
2. Na+ concentration lower in epithelial cells than lumen of gut
3. Transport of glucose/amino acids from lumen to epithelial cells is couple to facilitated diffusion of Na+ down a electrochemical gradient

Question 27

What is water potential?

Answer 27

Pressure created by water molecules measured in kPa
More solute more negative wp

Question 28

Whats fluid about the FMM?

Answer 28

PLB in which individual phosopholipids can move so membrane has a flexible shape

Question 29

Whats mosaic about the FMM?

Answer 29

Extrinsic and intrinsic proteins of different sizes and shapes are embedded

Question 30

Explain the functions of membranes within cells

Answer 30

Provide internal transport system
Selectively permeable to regulate passage of molecules into/out of organelles
Provide reaction surface
Isolate organelles from cytoplasm or specific metabolic reactions

Question 31

How are cells adapted to maximise the rate of transport across their membranes?

Answer 31

Many carrier/channel proteins
Folded membranes increase surface area

Question 32

State Ficks law

Answer 32

surface area x difference in concentration/ diffusion distance

Question 33

How does osmosis affect plant and animal cells?

Answer 33

Osmosis into cell
Plant - protoplasts swells making cell more turgid
Animal - lysis

Osmosis out of cell
Plant - protoplast shrinks = cell flaccid
Animal crenation