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Alevel bio and chem > Chapter 5 - Plasma Membranes > Flashcards

Chapter 5 - Plasma Membranes Flashcards

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1
Q

What are the roles of membranes at the surface of cells?

A
  • partially permeable barrier between cell and its surroundings
  • allows for cell signalling
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2
Q

What are the roles of membranes within the cells?

A
  • partially permeable membranes act as barriers between organelle and cytoplasm
  • chemical reactions take place
  • vesicles can be formed
  • molecules can leave and enter (ie RNA leaving nucleus)
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3
Q

Describe how the phospholipid bilayer is arranged.

A

(1) phospholipid bilayer:

- phospholipids aligned with hydrophilic heads pointing outwards, hydrophobic tails facing inwards

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4
Q

What is the structure of cholesterol in the phospholipid bilayer, how is it binded and what is its function?

A

Cholesterol:

  • lipid like molecule
  • binds to hydrophobic tail of phospholipids
  • packs phospholipids close together and decreases fluidity and makes them rigid
  • at low temperatures, cholesterol prevents from packing closely and increases fluidity
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5
Q

What are the two types of proteins in the phospholipid bilayer?

A

intrinsic and extrinsic proteins

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6
Q

What is an intrinsic protein?

A

transmembrane (goes through both layers of phospholipid bilayer)

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7
Q

What are the two types of intrinsic proteins and how are they embedded into the membrane?

A

channel and carrier proteins

- have hydrophobic R groups on outer surface and bind to hydrophobic tails in phospholipid bilayer

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8
Q

What are two other carbohydrate based molecules in the membrane and what are their functions?

A

glycolipids:

  • cell markers/ antigens
  • recognised by immune system as self/ non self cells

glycoproteins:

  • cell adhesion
  • site where hormones can bind to
  • act as receptors for cell signalling
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9
Q

What affects membrane structure and permeability?

A

(1) increasing temperature
- phospholipids have more KE therefore vibrate
- membrane becomes more fluid, loses its structure
- increases permeability
(2) solvents
- phospholipids dissolve in alcohol
- increases permeability

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10
Q

What substances can/ cant pass through the phospholipid bilayer?

A
  • polar molecules, ions (charged molecules) cant pass straight through phospholipid bilayer (hydrophobic tails act as a barrier)
  • lipid soluble molecules can pass straight through membrane through diffusion
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11
Q

Describe the procedure (including equipment) of how you could investigate membrane permeability.

A

method:

(1) cut 5 equal pieces of beetroot
(2) wash them thoroughly
(3) place each piece in 100 ml of distilled water each increasing by 10 degrees
(4) samples taken after 5 mins of the beetroot being soaked
(5) absorbance measured with a colorimeter

equipment:

  • colorimeter (cuvettes)
  • beetroot
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12
Q

PAG:

Why are the beetroot pieces washed under water?

A

to remove any surface pigment released by damaged cells

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13
Q

PAG:

Why were samples of the water containing beetroot taken after 5 mins of soaking?

A

to allow the mixture to equilibrate

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14
Q

PAG:

Why is the experiment repeated three times?

A

to increase reliability

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15
Q

PAG:

Why was the absorbance of the samples measured using a colorimeter with a blue filter?

A

because the pigment of the beetroot is red

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16
Q

PAG:

How does the amount of pigment affect the absorbance?

A

more pigment - absorbs the light therefore less light is transmitted

17
Q

What is diffusion/ facilitated difusion?

A

The passive movement of particles from a region of high concentration to low concentration (down a concentration gradient)

18
Q

How does facilitated diffusion differ from diffusion?

A
  • facilitated diffusion requires the use of channel/ carrier proteins
  • facilitated diffusion occurs when large molecules, polar molecules/ ions need to be transported
19
Q

How are ions/ polar molecules transported through channel proteins?

A

channel proteins have a pore through which the molecules can diffuse through

20
Q

How can large molecules travel through carrier proteins?

A

molecule attaches to carrier protein, it changes shape and allows molecule to pass through

21
Q

What is active transport?

A

The active movement of particles from a low concentration to a high concentration (against concentration gradient)

22
Q

How does active transport work through a plasma membrane?

A
  • uses carrier protein
  • molecule attaches to carrier protein
  • ATP binds to protein and gets hydrolysed (breaks into ADP + P)
  • P binds to carrier protein and changes its shape making pathway for molecule to pass through
  • P released from carrier protein and binds with ADP to form ATP again
23
Q

What are the two type of bulk transport (bulk transport)?

A

endocytosis and exocytosis

24
Q

What are the two types of endocytosis and describe how it occurs?

A

phagocytosis (solids)
pinocytosis (liquids)

  • membrane starts to bend inwards when molecule comes near it, gets engulfed by plasma membrane forming a vesicle
  • vesicle is pinched off and moves into cytoplasm
25
Q

Describe how exocytosis occurs.

A
  • vesicles formed by Golgi apparatus move towards plasma membrane
  • contents of the vesicle are released
26
Q

What is osomosis?

A

The net movement of water particles through a partially permeable membrane from a region with a high water potential to a region with a low water potential

27
Q

What will happen to an animal cell when put into a hypotonic, isotonic and hypertonic solution?

A

hypotonic - cytolysis (burst)
isotonic - remain the same as water is entering + leaving the cell at the same rate
hypertonic - crenate (shrivel)

28
Q

What will happen to an plant cell when put into a hypotonic, isotonic and hypertonic solution?

A

hypotonic - turgid
isotonic - remains same as movement of water is equal rate
hypertonic - plasmolysed (shrivel)

29
Q

What are the factors affecting diffusion?

A

(1) temperature - higher temp, faster rate of diffusion as particles have more KE and moving at faster rate
(2) difference in concentration - steeper the concentration gradient, faster the rate of diffusion

30
Q

Describe the practical for investigating the factors affecting diffusion rates in modal cells.

A
  • use dialysis tubing (similar to a membrane - partially permeable, doesn’t let large molecules pass through)
  • fill it with a solution of molecules (glucose and starch)
  • place in beaker of water
  • do benedicts and iodine test

Alevel bio and chem (8 decks)

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