diffusion Flashcards

1
Q

what are the two types of diffusion

A

-simple diffusion
-facilitated diffusion

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2
Q

definition for diffusion

A

-the net movement of particles from a region of higher concentration to region of lower concentration

net movement of particles down a concentration gradient

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3
Q

describe why diffusion is a passive transportation process

A

diffusion moves molecules/ions down a concentration gradient

-diffusion does not require a metabolic source of energy such as ATP to transport molecules across the membrane

it instead relies on the energy from the natural, random movement of particles

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4
Q

explain why simple diffusion occurs and when it stops

A

-the particles of gas/liquid have kinetic energy
-their movement is random
-This creates an unequal distribution of particles between two areas
-This establishes a concentration gradient as substances diffuse from a region of higher concentration to a region of lower concentration

-Diffusion stops when an equilibrium is established, meaning that there is an equal distribution of particles between the two areas

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5
Q

what does an equilibrium being reached mean in terms of the movement of particles

A

particles are still constantly moving, however they now move equally in both directions

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6
Q

what factors affect the rate of diffusion

A

-steepness of concentration gradient
-surface area
-thickness of membrane
-temperature
-properties of molecules

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7
Q

what is the rate of uptake dependent on for simple diffusion

A
  • the concentration
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8
Q

explain what is meant by the steepness of the concentration gradient

A

-firstly concentration gradient means the difference in the concentration of a substance between the two areas

-steepness-refers to the degree of a difference, the larger the difference between concentrations ,the steeper the concentration gradient

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9
Q

how does the steepness of the concentration gradient affect the rate of diffusion.
Explain your answer

A

The bigger the difference in the concentration of a substance , between the two areas ,the higher the rate of diffusion will be.

This is because the overall movement of particles from a region of higher concentration to a region of lower concentration will be larger.

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10
Q

explain how temperature effects the rate of diffusion

A

-as temperature increases, molecules have more kinetic energy thus move faster, this results in higher rate of diffusion

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11
Q

how does the thickness of a membrane affect the rate of diffusion. Explain

A

-the thicker the membrane, the longer the diffusion distance will be ,meaning that particles will collide more ,decreasing the rate of diffusion

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12
Q

describe how the surface area has an affect on the rate of diffusion

A

-the larger the surface area, the higher the number of molecules that can diffuse through at once, increasing the rate of dission

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13
Q

how can we increase the surface area

A

-the folding of a membrane increases the SA.

-like cristae in mitochondria

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14
Q

how does the SA:V ratio affect the rate of diffusion

A

-as the size of a cell increase, its SA:V ratio decreases.

This increases the diffusion distance of molecules and thus slows down the rate of diffusion

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15
Q

why is the rate of diffusion faster over short distances and slower over long distances

A

-particles move at high speed and are constantly colliding

-over short distances particles collide less thus rate of diffusion is faster

-over longer distances ,particles collide more thus the rate of diffusion is slower

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16
Q

what type of molecules are transported by facilitated diffusion and what by simple diffusion

A

-small, non-polar molecules such as oxygen are transported down a concentration gradient and across the membrane by simple diffusion

-larger and polar molecules like glucose are transported down a concentration gradient and across the membrane using carrier/channel proteins via facilitated diffusion

17
Q

definition of facilitated diffusion

A

diffusion across a membrane using channel/carrier proteins

18
Q

what are the two types of proteins involved in facilitated diffusion

A

-carrier proteins
-channel proteins

19
Q

why are channel ad carrier proteins said to be specific

A

they are specific to and thus only transport one type of ion/molecule

20
Q

difference between channel and carrier proteins

A

channel proteins do not change shape to transport substances across the membrane, whereas carrier proteins do

21
Q

how do channel proteins control the exchange of charged/polar molecules

A

-they are ‘‘gated’’, meaning that a part of them moves to open and close the pore as the substance is being transported across the membrane

22
Q

how do carrier proteins transport a polar molecule across the membrane

A

-the binding site of the carrier protein opens
-a molecules attaches to the binding site of the carrier protein which is embedded within the membrane

-this causes the carrier protein to change shape and release the molecule on the opposite end of the membrane

-the molecules are moved down a concentration gradient

23
Q

is facilitated diffusion passive

A

yes

24
Q

what other factors also affects the rate of facilitated diffusion

A

-the number of carrier/channel protein embedded in the cell membrane,

the higher the number of carrier/channel protein, the more molecules can be transported across at once, thus increasing the rate of diffusion

25
Q

when does facilitated diffusion stop?

A

when the carrier/channel protein become saturated

26
Q

describe a practical used to investigate the effect SA:V ratio has on the rate of diffusion

A

-cut the agar into required dimension, decresing the SA:V ratio with each agar cube
-the cubes contain an indicator which makes them pink
-place each agar cube into a test tube,containing equal volume of sodium hydroxide
-allow them to sit for 10 minutes
-Within that time the sodium hydroxide will diffuse into the agar cube turning the indicator colourless
-Remove the agar cubes
-Measure the distances travelled by the sodium hydroxide using a ruler

-Calculate the rate of diffusion

27
Q

what are the two formulas for calculating the rate of diffusion

A

-distance travelled/time

-volume filled/time

28
Q

which is affected by surface area and which is not

A

the volume filled is affected by the surface area, whereas the distance travelled is not

29
Q

What should the results of the investigation be

A

-we should find that with the increase of size of the agar cube and thus decrease of the SA:V ratio ,the rate of diffusion will decrease

30
Q

describe how to investigate what substances can diffuse across partially permeable membrane

A

-use something known as dialysis tubing-its used as a substitute membrane
-fill a section of the dialysis tubing with a mixture of glucose and a mixture of starch solution
-dialysis tubing has pores which prevent the passage of large molecules like starch and allow smaller molecules like glucose to diffuse across
-suspend the tubing in a beaker of water and place a lid on top so it doesn’t evaporate

-test the water outside the dialysis tubing for starch and glucose ,using a benedict test for glucose ad iodine test for starch

Results should indicate that only glucose has diffused across

31
Q

describe how you would use dialysis tubing to investigate how temperature affects the rate of diffusion

A

-use dialysis tubing, fill it with a set concentration of glucose solution
- submerge in a beaker with a set volume of water
-put the beaker in water bath set at different temperatures, e .g 20,30,40,50

-allow the beaker to sit in the water bath for the same amount of time, enough for the glucose to diffuse across and into the water

-remove the dialysis tubing from the beaker

-carry out a benedict test on the remaining solution, the bigger the colour change, the higher the concentration of glucose present and thus the faster the rate of diffusion

32
Q

how to investigate how concentration affects the rate of diffusion

A

use dialysis tubing, fill it with a set concentration of glucose solution

-fill each dialysis tube with an increasing concentration of glucose

-can create standard solutions of known concentration of glucose by carrying out serial dilutions of an existing stock solution

  • submerge in a beaker with a set volume of water ,set at the same temperature each time

-allow the beaker to sit in the water bath for the same amount of time, enough for the glucose to diffuse across and into the water

-remove the dialysis tubing from the beaker

-carry out a benedict test on the remaining solution, the bigger the colour change, the higher the concentration of glucose present and thus the faster the rate of diffusion

33
Q

explain why oxygen and carbon dioxide can move freely through cell membrane via simple diffusion

A

-small and non-polar meaning that they can easily diffuse through the spaces between the phospholipids

-water molecules can diffuse across the cell membrane despite being polar as they are small enough to fit between the phospholipids

34
Q

describe relationship between concentration and rate of diffusion

A

as a concentration of a substance increases,the rate of diffusion also increases

,this is because the concentration gradient is higher/increased

35
Q

describe how astudent can carry out an experiment investigating how concentration gradient affects the rate of diffusion in model cells

A

-can prepare equal sized agar cubes ,each containing a ph indicator

-then prepare test tubes with an increasing concentration of sodium hydroxide

-submurge the agar cubes into the test tubes and time how long it takes for the the agar cube to turn colourless

-the faster it turns colourless the higher the rate of diffusion

36
Q

which is the dependent and independent variable in the experiment

A

the dependent variable is the time taken for the agar cube to turn colourless,

the independent variable is the concentration of sodium hydroxide

37
Q

how can the student make the results precise

A

can carry out 3 repeats at each concentration and calculate a mean time taken for the cube to turn colourless