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A Level Biology: 2.1.5 Biological Membranes > 2.1.5b Diffusion > Flashcards

2.1.5b Diffusion Flashcards

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1
Q

see slide 2 for dia of outside/inside the cell membrane

A
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2
Q

5 different ways substances enter/leave cells

A
  1. Simple diffusion (passive process)
  2. Facilitated diffusion (passive)
  3. Osmosis (passive)
  4. Active transport (active, requires ATP energy)
  5. Bulk transport (endocytosis & exocytosis) (active)
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3
Q

What is a concentration gradient

A

The difference in concentration of particles between 2 areas. Either steep or shallow

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4
Q

Concentration gradient in relation to rate of diffusion

A
  • If concentration gradient is steep, rate of diffusion is faster
  • If concentration gradient is shallow, rate of diffusion is slower
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5
Q

What is simple diffusion

A

The net (overall) random movement of particles (atoms, molecules, ions) from a region of higher concent to lower concent, down a concent gradient

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6
Q

How are particles able to move in simple diffusion

A

Due to the random movement & collisions of particles (which have their own kinetic energy)

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7
Q

What type of process is simple diffusion

A

PASSIVE - meaning no ATP energy required

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8
Q

When does simple diffusion stop

A

Continues until there is a concentration equilibrium between both sides

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9
Q

Eg of simple diffusion

A

Oxygen molecules diffuse into cells by simple diffusion

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10
Q

What type of molecules can move via simple diffusion

A
  • Small, non polar molecules eg. oxygen & CO2 can diffuse easily through the cell surface membrane
  • This is bc they are very small & can pass through spaces between the phospholipids
  • Water is also small enough to fit between phospholipids, so it’s able to diffuse across plasma membranes even though it’s polar. This is called osmosis
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11
Q

What is facilitated diffusion

A

The passive movement of molecules down a concentration gradient (high to low concentration) across a membrane, & involves a special carrier & channel proteins in the membrane

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12
Q

What molecules can move in facilitated diffusion

A

Some larger polar molecules (eg. amino acids, glucose, or ions sa sodium ions & chloride ions) cannot simply diffuse directly through the phospholipid layer of the cell surface membrane

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13
Q

What is needed in facilitated diffusion

A

Substances can only cross the phospholipid bilayer w the help of certain proteins:
- Channel proteins
- Carrier proteins
They are highly specific (they only allow one type of molecule or ion to pass through)
see slide12 for dia

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14
Q

What are channel proteins

A
  • Water-filled pores. They allow charged substances (eg. ions) to diffuse through the cell membrane.
    (see slide13)
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15
Q

How do channel proteins work

A
  • The diffusion of these ions does not occur freely, most channel proteins are ‘gated’, meaning that part of the channel protein on the inside surface of the membrane can move in order to close or open the pore
  • This allows the channel proteins to control the exchange of ions
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16
Q

What are carrier proteins

A
  • Unlike channel proteins which have a fixed shape, carrier proteins can switch between two shapes
  • This causes the binding site of the carrier protein to be open to one side of the membrane first, & then open to the other side of the membrane when the carrier protein switches shape
    (see slide 14 for dia)
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17
Q

What does the direction of movement of molecules depend on

A

Direction of movement of molecules diffusing across the membrane depends on their relative concentration on each side of the membrane

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18
Q

Net diffusion of molecules or ions into or out of a cell will occur…

A

…down a concentration gradient (high to low)

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19
Q

What does facilitated diffusion depend on

A

Concentration gradient - the higher the concent gradient, the faster the rate of facilitated diffusion (up to a point). As equilibrium is reached, rate of facilitated diffusion levels off

No. of channel or carrier proteins - once all the proteins in a membrane are in use, facilitated diffusion can’t happen any faster, even if you increase the concent gradient. So the grater the no. of channel or carrier proteins in cell membrane, the faster the rate of facilitated diffusion

20
Q

Why can water diffuse directly through the membrane

A

Even though its polar, it can diffuse directly through due to its relatively small size

21
Q

see slide 17 for comparison between carrier & channel proteins

A
22
Q

Where does the energy come from in simple & facilitated diffusion

A

Kinetic energy of the molecules

23
Q

see slide 21 for comparison between simple & facilitated diffusion

A
24
Q

Factors affecting the rate of diffusion

A
  • Concentration gradient (steep/shallow)
  • Temperature
  • SA of membrane
  • Thickness of exchange surface/membrane
  • SA:V
  • Properties of molecules/ions
25
Q

Factors affecting the rate of diffusion: Concentration gradient

A
  • If there are more molecules on one side of a membrane than on the other, at any one moment more molecules will randomly move across membrane from that side than from the other.
  • Steeper the gradient, faster the rate of diffusion
26
Q

Factors affecting the rate of diffusion: Temperature

A
  • Molecules & ions have more kinetic energy at higher temps
  • They move faster, resulting in more collisions, therefore resulting in higher rates of diffusion
27
Q

Factors affecting the rate of diffusion: SA of membrane

A
  • The greater the SA across which diffusion is taking place, the greater the no. of molecules or ions that can cross it at any one moment, therefore the faster diffusion occurs
  • SA of membranes can be increased by folding (eg. microvilli in the intestine or cristae in mitochondria)
28
Q

Factors affecting the rate of diffusion: SA:V

A
  • As a cell increases in size, the SA:V decreases which slows the rate of diffusion through a cell as the distance required becomes too great
29
Q

Factors affecting the rate of diffusion: Properties of molecules/ions

A
  • Large molecules diffuse more slowly than smaller ones as they require more energy to move
  • Uncharged & non-polar molecules diffuse directly across the phospholipid bilayer
  • Non-polar molecules diffuse more quickly than polar ones as they are soluble in the non-polar phospholipid bilayer
30
Q

How does SA:V affect diffusion

A
  • As the size of a cell increases, so does the SA & volume
  • BUT the volume of cell increases faster than the SA (bc vol is cubed, whereas SA is squared)
  • When volume is too large relative to the SA of cell, diffusion cannot occur at a high enough rate to supply raw materials to the entire volume of the cell
31
Q

What is surface area

A

Refers to the outside are of an object
unit: cm^2

32
Q

What is volume

A

Refers to the amount of space inside the object
unit: cm^3

33
Q

What is the Agar Jelly diffusion experiment

A

The agar jelly cubes are used to represent the cells.
- Pink agar jelly cubes are placed into a dilute hydrochloric acid at 3 differing sizes (side lengths: 0.5cm, 1cm, 2cm)
- As the hydrochloric acid diffuses into the agar cube, the colour of the indicator changes (in this case it goes colourless)

34
Q

Conclusions of the Agar Jelly diffusion experiment

A

The larger agar cubes (small SA:V) took longer to turn colourless than the smaller cubes (high SA:V)
Therefore, the greater the SA:V, the greater the rate of diffusion

35
Q

What is rate

A

A measure of how much smth is changing over time

36
Q

How to calculate rate on a linear diffusion graph

A

Gradient = change in y/change in x

37
Q

How to calculate rate on a curved (non-linear) diffusion graph

A

Draw a tangent
Find gradient of the line

38
Q

do SA:V questions on slide 40

A
39
Q

How are organs specialised to ensure diffusion is efficient

A
  • Have a large SA
  • Membrane is thin - shot diffusion pathway
  • Efficient blood supply surrounding exchange surface
  • Large SA:V ratio - there is more SA relative to the volume inside
40
Q

Adaptations of the intestines

A
  • The inside of the small intestine is covered in millions & millions of these tiny little projections called villi
  • They increase the SA so that digested food is absorbed much more quickly into blood
  • They also have:
    - a single layer of surface cells
    - a very good blood supply to assist quick absorption
    (see slide 46 for dia)
41
Q

Adaptations of the alveoli (lungs)

A
  • They are very thin - walls are only one cell thick
  • There is a very efficient blood supply network of capillaries around the alveoli
  • The lungs & alveoli have a large combined SA
  • The walls are moist, encouraging gas molecules to easily dissolve
    (see slide 47 for dia)
42
Q

Adaptations for gas exchange in fish

A
  • Fish have gills which are made up of many gill filaments - large SA
  • The gills are covered in tiny structures called lamellae - increases SA
  • Lamellae are surrounded by lots of blood capillaries
  • Countercurrent exchange system
  • Thin surface layer of cells - short diffusion pathway
    (see slide 48-51)
43
Q

Adaptations of roots of a plant

A
  • Plant roots anchor the plant into the soil & absorb water & mineral ions from the soil
  • Have extensions called root hair cells - increases SA to absorb MORE water/mineral ions
  • Root hair cells are thin - short diffusion pathway for water/mineral ions to travel into root
    (see slide 52)
44
Q

Gas exchange at the leaf

A

Leaves absorb CO2 from the atmosphere & release oxygen & water vapour in the process of photosynthesis

45
Q

Adaptations of leaves

A
  • Very thin - short diffusion pathway
  • Broad & flat - gives larger SA so more gases can diffuse into/out of leaf
  • Have tiny pores called stomata - this is where gases are exchanged
46
Q

What is a synapse

A

A junction between two neurones across which electrical signals must pass
(see slide 54 for dia)

47
Q

Diffusion across the synapse of nerve cells

A

Neurotransmitter molecules diffuse from vesicles towards the neurotransmitter receptors moving from an area of high to low concentration

A Level Biology: 2.1.5 Biological Membranes (2 decks)

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