Section 2:Transport across membranes

Question 1

Five points

What are the main functions of the cell membrane?

Answer 1

• Acts as a barrier
• Acts as a site for cell recognition
• It acts as for binding hormones/transmitter chemicals via protein receptor molecules
• To allow communication between cells
• Forms impermeable barrier to water soluble substances

Question 2

Describe the molecules of the cell membrane structure

Answer 2

Phosphollipid bilayer, proteins, cholesterol and carbohydrates

Question 3

Describe the structure of a triglyceride

Answer 3

Glycerol binded to three fatty acid chains by an ester bond

Question 4

What’s the difference between saturated and unsaturated fatty acids?

Answer 4

Unsaturated fatty acids have a double bond(s), this means that the carbon atoms are not bonded to all the hydrogen atoms as possible

Question 5

Why is the cell membrane described as ‘fluid mosaic’?

Answer 5

Fluid~molecules of phospholipid and proteins have a degree of mobility within the membrane
Mosaic~proteins and phospholipids ‘fit’ together to form together patchwork of molecules

Question 6

Describe the structure of a phospholipid

Answer 6

Hydrophillic polar charged head
Hydrophobic non-polar tail

Question 7

How are phospholipids arranged in the cell surface membrane?

Answer 7

Bilayer~hydrophilic phosphate head facing outwards and hydrophobic fatty acid tails facing inwards

Question 8

What type of proteins are found in the cell membrane?

Answer 8

Glycoproteins, channel proteins and carrier proteins

Question 9

What are the roles of proteins in the cell membrane?

Answer 9

Help substances ,e.g. ions,sugars and amino acids, that cannot diffuse across the membrane but are vital to a cell’s functioning

Question 10

Six points

What are the functions of the proteins?

Answer 10

• Carrier molecules
• Channels and pumps for ions and other substances
• Enzymes to speed up surface reactions
• Receptors for hormones
• Recognition sites for for identifying types of cells
• Adhesion sites to allow cells to stick together

Question 11

What is a glycoprotein?

Answer 11

A protein with a carbohydrate (polysaccharide)attached to it

Question 12

What is a glycolipid?

Answer 12

A lipid with a carbohydrate(polysaccharide) attached to it

Question 13

What is the role of glycoproteins and glycolipids?

Answer 13

Involved in cell-cell signalling and cells recognising one another

Question 14

What is the role of cholesterol in the cell membrane?

Answer 14

Important in keeping membranes stable at normal body temperature-without it,cells would burst without it

Question 15

Define passive diffusion

Answer 15

The net movement of molecules or ions from an area of higher concentration to an area of low concentration

Question 16

What factors that affect diffusion rate?

Answer 16

• Difference in concentration~faster when there is a greater difference
• Surface area~faster when larger surface area
• Thickness of cell membrane~faster when thinner
• Temperature~faster at higher temperature

Question 17

What is fick’s law ?

Answer 17

surface area x difference in concentration/thickness of substance

Question 18

Five points

How do carrier proteins work?

Answer 18

1. The molecule to be transported to binds to the carrier protein
2. Molecules must be complementary in shape to the carrier and able to bind
3. As a result, binding the carrier protein changes shape
4. The molecule to be transported is delivered to the other side of the membrane as a result
5. The carrier returns to normal shape

Question 19

Explain the difference between simple diffusion and facilitated diffusion

Answer 19

SD~is the movement of particles freely across the plasma membrane from a high conc to low conc
FD~when protein carriers or channels are used to facilitate diffusion.This is process is also passive,doesn’t require ATP

Question 20

Define osmosis

Answer 20

The passage of water molecules from an area of high water potential to an area of low water potential through a partially permeable membrane

Question 21

Why is water potential of a substance always less than 0 and what is measured in?

Answer 21

Distilled water has a water potential of 0 which is the highest possible water
Measured in kPa

Question 22

What happens to water potential as solute is added?

Answer 22

The water potential lowers

Question 23

What happens to an animal cell when placed in:
* hyponotic solution
* isotonic solution
* hypertonic solution

Answer 23

• Hyponotic~water enters,cells swells and may burst (lysis)
• Isotonic~no net movement of water,cell normal size
• Hypertonic~water leaves,cell shrinks and crenates

Question 24

What happens when a plant cell is placed in:
* Hypotonic solution
* Isotonic solution
* Hypertonic solution

Answer 24

• Hypotonic~water enters,cell swells a bit and becomes turgid
• Isotonic~not net movement of water,cell normal size and incipient plasmolysis
• Hypertonic~water leaves,cytoplasm shrinks and plasmolyses

Question 25

Describe what hypotonic,isotonic and hypertonic solutions are

Answer 25

• Hypotonic solution~lower water potential than the cell
• Isotonic solution~same water potential as the cell
• Hypertonic solution~higher water potenial than cell

Question 26

Give two ways osmosis is differs from facilitated diffusion

Answer 26

• Osmosis transports water
• No proteins or other carrier molecules are used
• Occurs through phospholipid bilayer

Question 27

Define active transport

Answer 27

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

Question 28

When might active transport be used?

Answer 28

Plants take up mineral ions which are present in very small concentrations in the soil

Question 29

Six points

How does active transport occur?

Answer 29

1. Molecule binds to carrier protein
2. ATP also binds to carrier protein
3. ATP breaks down~ADP and phosphate=releases energy
4. As a result carrier protein changes shape and transfers molecule to other side of the membrane
5. Carrier protein reverts back to its original shape
6. Phosphate recombines with ADP to form ATP during respiration

Question 30

What energy is required for diffusion,FD and osmosis to occur?

Answer 30

kinetic energy of particles

Question 31

Four points

How is the small intestine adapted for absorb digested materials?

Answer 31

• Vili=increases surface area
• Thin (one cell thick)=short diffusion pathway
• Epithelial cells have microvili=increase surface area
• Vili have good blood supply=helps to maintain a concentration gradient

Question 32

Four points

Describe the process of co-transport

Answer 32

• The sodium-potassium pump, pumps Na+ out of epithelial cell into the blood using protein carrier molecules via AT
• Maintains high con of ions in the lumen + low in epithelial cell
• Na+ diffuses into the epithelial cell via a cotransport protein molecule, the Na+ is coupled with glucose or an amino acid
• The glucose or amino acid then diffuses into the blood stream by faciliated diffusion using a different carrier