Membrane And Transport

Question 1

Describe the structure of the cell membrane

Answer 1

The cell membrane is in a bilayer shape formed by phospholipids , which have phosphate hydrophilic heads immersed in the water pointing to the outside of the cell membrane, and fatty acid hydrophobic tails pointed to the inside away from water. In addition, there are protein scattered along the membrane of different types, including peripheral proteins, glycoproteins and gated channel. Lastly, there are cholesterol molecules in the cell membrane usually between the phospholipids, this cause the bilayer shape of the cell membrane

Question 2

Explain what is meant by fluid mosaic model

Answer 2

Fluidity of the cell memrbane due to thw ability of the phospholipids in the membrane to move, and it also refers to the fact that there are scattered proteins along the cell membrane

Question 3

Factor affecting membrane structure

Answer 3

Temperature
As increase temperature
kinetic energy - increase of phospholipid
(Vibrate more -> hydrogen bond break)

• > break H bond between tail
• more permeable

Denatures protein

Channels/carriers
- effect permeability

Question 4

Solvent factor affecting membrane structure

Answer 4

(Lipid soluble substance)
Non polar solvent sit between tails
-> ethanol will denature membrane protein by replacing hydrogen bind between amino acid with new bond between ethanol & amino acid
- break H bond -> disrupt bilayer

• dissolve the phospholipid
• increase permeability +more fluid

(I.e alcohol -ethanol)

Question 5

Phospholipid

Answer 5

Made of a glycerol molecules two fatty acid chains and a phosphate group (attached to the glycerol)
Via two condensation reactions resulting in two ester bonds

Question 6

Properties of phospholipids

Answer 6

Hydrophilic head of a phospholipid can attract with water as it is charged

Due to the phosphate being charged it repels other fats

The fatty acid chain is not charged
It is known as the hydrophobic tail and it repels water, but will mix with fats

Question 7

Cholesterol

Answer 7

Parts of a family of lipids called sterols

The hydroxyl group is hydrophilic however the rest of the molecule is hydrophobic

Cholesterol can insert into the cell membrane

The hydrophilic hydroxyl group on the cholesterol molecule can interact with head group of phospholipid

While the rest of the cholesterol molecule can interact with the hydrophobic fatty acid

Cholesterol actually plays a key role in controlling the fluidty of cell membrane

Cholesterol & phospholipid
It increases strength of the cell surface membrane -> more stable

Cholesterol reduces the sideway movement of phospholipid
-regulate (control) fluidity

Help reduce the movement of water -soluble chemicals across the cell surface membrane

Question 8

Intrinsic proteins

Answer 8

Fully embedded in the membrane from one side to the other

Question 9

Protein channel ( intrinsic proteins)

Answer 9

Selective ( some have gated channel) (this allows the channel proteins to control the exchange of ions)

• channel lined with hydrophilic amino acids & filled with water molecule
• > allow water soluble molecules & ions to diffuse through

Facilitated diffusion

Question 10

Carrier protein (selective) cell membrane

Answer 10

Move large molecules into or out of the cell down their concentration gradient

Protein undergo a confronational change

This release the molecule on the opposite side of the membrane
—> facilitated diffusion & active transport

Question 11

Extrinsic protein

Answer 11

Structural role

Act as enzyme

Cell receptors

Question 12

Glycoproteins

Answer 12

Protein attached to a carbohydrates

Carbodrates part help them hold lots of water - harder for protease to break them down
—> muscus & synovial fluid are glycoprotein

Question 13

Define diffusion

Answer 13

Net movement of particels from a region of higher concentration to a region of lower concentration down the concentration gradient
—> No ATP
—> passive process

Question 14

Define facilitated diffusion

Answer 14

Not all substances diffusion at the same rate due to the centre of cell membrane is hydrophobic
- due to the fatty acid tails of teh phospholipid molecule

Steroid molecule can diffuse rapidly across the memrbane

Hydrophilic substance ions/polar molecules cant diffuse across the membrane

Question 15

Molecules

Answer 15

Small uncharged
I.e. - CO2, O2
Passive diffusion

Charged / ions
Facilitated diffusion

Small dipole
osmosis
I.e water

Question 16

Define endocytosis

Answer 16

The movement of large molecule into cells through vesicle formation

Question 17

Define exocytosis

Answer 17

The movement of large molecule out of cell by the fusing of a vesicle containing the molecule with the surface cell membrane, the process requires ATP

Question 18

Define isotonic

Answer 18

When the solite conc is balanced woth the concentration inside the cell

Water movement still mores between the solution

Question 19

Define hypotonic

Answer 19

Solute concentration is lower than concentration inside the cell
- water moves in the cell and cause the cell to swell; cell that dont have cell wall (animal cell) burst

Question 20

Define hypertonic

Answer 20

Solute concentration is higher than concentration inside the cell

-water move out of the cell & cause the cell to shrivel

Question 21

Why do red blood cells burst when placed in water

Answer 21

First of all water molecules will move into the cell from high water potential to low water potential through a partially permeable membrane by osmosis. This cause pressure on the cell membrane of the red blood cell causing it burst

Question 22

What happens to a red blood cell when it is placed in a salt solution

Answer 22

Water will move out of the cell and into the solvent from high water potential to low water potential by osmosis through a partially permeable membrane , in order to equalize the salt concentration. This cause the cell to shrivel and become flaccid

Question 23

What happens to a plant cell when it is placed in water

Answer 23

Water will move into the cell from high water potential to low water potential by osmosis through a partially permeable membrane , bit not indefinietly , vacuole will he too full and will start to cause hydrostatic pressure on the cell membrane. The cell wall will then reply with potential pressure until no more water can enter the cell, and the plant will be in state called turgor where it is rigid

Question 24

What happen to a plant cell when it is placed in a salt solution

Answer 24

Water will move out of the cell from hgih water potential to low water potential by osmosis through a partially permeable membrane, causing the vacuole and the cell membrane to shrink in a state called incipient plasmolysis however, the cell wall is not affected

Question 25

Endocytosis process

Answer 25

Some molecule ae way too large to be taken into a cell by carrier proteins eg proteins, lipids and some carbohydrates

2) instead a cell can surround a substance with a section of its cell membrane
3) the membrane then pinches off to form a vesicle inside the cell containing the ingested substance - endocytosis
4) some cells also take in much larger object by endocytosis

Ex. White blood cell (called phagocytes) use endocytosis to take in things like microorganism and dead cells so that they can destroy them

5) like active trasnport, this process also use ATP for energy

Question 26

Exocytosis process

Answer 26

1) some substance sproduced by the cell (eg digetsive enzyme, hormones , lipid) need to be released the cell - exocytosis
2) vesicles containing these substances pinches off from the sacs of the golgi apparatus and move towards the cell membrane
3) the vesticles fuse with cell membrane and release their content outside the cell
4) some substance arent released outside the cell - instead they are inserted straight into the cell membrane
5) exocytosis use ATP as an energy source