3.1.4 Transport into and out of Cells Flashcards Preview

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Flashcards in 3.1.4 Transport into and out of Cells Deck (88)
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1

What is a cell-surface membrane?

(Partially permeable) barrier between cell and its environment, controlling which substances enter and leave the cell

2

What is the functions of membranes around organelles?

  • Act as barriers between organelle and cytoplasm
  • Also control what comes in and out + partially permeable

3

Describe the phospholipids arrangement in a plasma membrane

  1. Bilayer
  2. Hydrophobic tails to inside
  3. Hydrophilic heads to outside

4

Describe how the plasma membrane acts as a barrier to water-souble substances

Centre of bilayer is hydrophobic ∴ membrane doesn't allow water-souble substances (like ions) through it

5

Name 3 functions of phospholipids in plasma membranes

  • Allow lipid-soluble substances to enter & leave the cell
  • Prevent water-soluble substances entering and leaving the cell
  • Makes membrane flexible 

6

Cholesterol is present in all cell membranes expect _____ ____ ________

bacterial cell membranes

7

Where are cholesterol molecules found in cell membranes?

Between phospholipids

8

What is the role of cholesterol in cell membranes?

Controls the fluidity of the membrane

(provides stability e.g. helps to maintain shape of animal cells)

9

Describe how cholesterol gives cell membranes stability

  • Cholesterol molecules bind to hydrophobic tails of phospholipids = causes them to pack more closely together
  • Restricts movement of phospholipids
  • Makes membrane less fluid and more rigid

10

What model is used to describe the arrangement of molecules in membrane?

Fluid mosaic model

11

Why is the bilayer is 'fluid'?

∵ phospholipids are constantly moving

12

How are proteins arranged in the cell membrane?

They're scattered through bilayer (like tiles in mosaic)

13

What are extrinsic proteins?

Proteins are partly embedded in bilayer (occur either on surface of it)

14

What are intrinsic proteins?

Proteins that span entire bilayer from one side to the other

15

What do channel proteins and carrier proteins allow?

Allow large molecules and ions to pass through membrane

16

What do receptor proteins on the cell-surface membrane do?

Detect chemicals released from other cells

(chemicals signal to cell to respond in some way)

17

Some proteins can ___ _______ through bilayer & others are _____ __ _____ 

Some proteins can move sideways through bilayer & others are fixed in position

18

What are glycoproteins?

Proteins that have a polysaccharide chain attached

19

What are glycolipids?

Lipids that have a polysaccharide chain attached

20

Increasing the temperature ____ membrane permeability

INCREASES

21

Temperatures below 0°C: Describe and explain the membrane permeability

  • Phospholipids don't have much energy = can't move much
    • Packed closely together & membrane is rigid
  • BUT channel proteins and carrier proteins deform = increasing permeability of membrane
  • Ice crystals may form and pierce the membrane = makes highly permeable when it thaws

22

Temperatures between 0 and 45°C: Describe and explain the membrane permeability

  • Phospholipids can move around & aren't packed as tightly together = membrane is partially permeable
  • As temperature increases = phospholipids move more ∵ have more energy = increases permeability of membrane

23

Describe the effect of high temperature on cell membranes

  • Phospholipids have more kinetic energy
  • Movement makes membranes more fluid and leaky
  • Increases no. of gaps between phospholipids
  • Glycoproteins/channel & carrier proteins denature

All increases permeability of membrane as substances can enter and leave that wouldn’t normally

24

Sketch a graph showing how increasing the temperature affects membrane permeability

25

Surrounding cells in an increasing concentration of solvent (e.g. acetone) will _______ membrane permeability

INCREASE

26

Why does surrounding cells in an increasing concentration of solvent (e.g. acetone) increase membrane permeability?

∵ the solvent dissolves lipids in the cell membrane, causing it to lose its structure

27

What could you use to investigate how different conditions (e.g. temperature and solvent concentration) affects membrane permeability?

Beetroot → higher permeability of membrane = more pigment leaks out of cell

28

Define diffusion

Net movement of particles from an area of higher concentration to area of lower concentration

29

Diffusion is a ____ process

passive

30

Particles diffuse ___ a concentration gradient

DOWN

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