Transport across membranes

Question 1

Define the terms “simple diffusion”

Answer 1

Diffusion is the net movement of particles from an area of high conc to an area of low conc down the concentration gradient

Question 2

Define the terms “facilitated diffusion”

Answer 2

The diffusion of particles through carrier proteins or channel proteins in the plasma membrane

Question 3

Define the terms “osmosis”

Answer 3

The diffusion of water through a partially permeable membrane down a water potential gradient. A passive process.

Question 4

Define the terms “passive transport”

Answer 4

Passive transport is a movement of substances across cell membranes without need of energy input.

Question 5

Define the terms “active transport”

Answer 5

Active transport is the movement of particles across the plasma membrane against a concentration gradient. Requires energy

Question 6

Define the terms “endocytosis”

Answer 6

The bulk movement of materials into cells via invagination of the cell-surface membrane forming a vesicle.
The process by which a cell surrounds substances with a section of its plasma membrane and takes them into the cell.

Question 7

Define the terms “exocytosis”

Answer 7

The bulk transport of materials out of cells. Vesicles containing the material fuse with the cell-surface membrane and the contents are released to the out side of the cell.

Question 8

Define the terms “pinocytosis”

Answer 8

Is the endocytosis of liquid materials

Question 9

Define the terms “phagocytosis”

Answer 9

The process by which white blood cells called phagocytes recognise non-self cells, engulf them, digest them within a vesicle called a phagolysosome

Question 10

Explain the difference between a channel protein and a carrier protein and link this to their functions.

Answer 10

1. Channel proteins are only involved in passive They provide a hydrophilic channel for polar molecules and ion.
2. Carrier proteins are involved in both active and passive transportation. it often involves the shape of the protein changing.

Question 11

State 1 particular example of a carrier proteins

Answer 11

Carrier Protein- GLUT1 is found in almost all animal cells and specifically helps to transport glucose across the plasma membrane

Question 12

Explain the importance of the structure of ATP in active transport.

Answer 12

1. Small- moves easily in and out of and within cells
2. Water soluble- Energy-requiring processes happen in aqueous environments
3. Contain bonds between phosphates with immediate energy; large enough to be useful for cellular reactions but not so large that energy is wasted as heat
4. Releases energy in small quantities- quantities are suitable to most cellular needs so that energy is not wasted as heat
5. easily regenerated- can be recharged with energy

Question 13

List the factors affecting the rate of diffusion of a molecule.

Answer 13

1. Temperature- higher temp the higher the rate of diffusion- particles have more kinetic energy etc.
2. Concentration difference- greater the difference faster the rate of diffusion because the overall movement from the higher concentration to lower concentration will be larger.
3. Surface area- larger SA higher rate of diffusion
4. Thickness of membrane- thinner the higher the rate of diffusion.

Question 14

Explain, in a paragraph and how substances can move across a membrane by simple diffusion.

Answer 14

1. Diffusion happens because gas or liquid particles have kinetic energy.
2. The movement is random and an unequal distribution of particles will eventually become an equal distribution.
3. It is a passive process and it will continue until there is a concentration equilibrium between the two areas.

Question 15

State which types of molecule can move across a membrane by simple diffusion.

Answer 15

1. Non-polar molecules like oxygen diffuse through freely down a concentration gradient.
2. The hydrophobic interior of the membrane repels ions so they can’t pass through easily.
3. Polar molecules like water can diffuse through membranes but only at a very slow rate. Small polar ones pass through easier

Question 16

Explain, in a paragraph and with a diagram, how substances can move across a membrane by facilitated diffusion

Answer 16

1. Membranes contain channel proteins through which polar molecules and ions can pass.
2. Membranes with protein channels are selectively permeable as most protein channels are specific to one molecule or ion.
3. It can also involve carrier proteins which change shape when a specific molecule binds to it.
4. Doesn’t require energy and is down the concentration gradient
5. Has same factors affecting it as simple diffusion. but also affected by the number of channel proteins present.

Question 17

Explain, in a paragraph and with a diagram, how substances can move across a membrane by active transport

Answer 17

1. Active transport is the movement of molecules or ions into or out of a cell from a region of low concentration to high concentration.
2. It requires energy and carrier proteins. Metabollic energy is supplied by ATP
3. A molecule attaches to a carrier protein the protein changes shape and this moves the molecule across the membrane, releasing it on the other side.

Question 18

Explain, in a paragraph and with a diagram, how substances can move into a cell by endocytosis

Answer 18

1. Some molecules are way too large (proteins, lipids, some carbs and some white blood cells like phagocytes ) to be taken into a cell by carrier proteins.
2. Instead a cell can surround a substance with a section of its plasma membrane. the membrane pinches off to form a vesicle inside the cell containing the ingested substance.
3. This uses ATP as energy

Question 19

Explain, in a paragraph and with a diagram, how substances can move into a cell by exocytosis

Answer 19

1. Some substances produced by the cell (hormones or digestive enzymes or lipids) need to be released from the cell.
2. Vesicles containing these substances pinch off from the sacs of the Golgi apparatus and move towards the plasma membrane.
3. The vesicles fuse with the plasma membrane and release their contents outside the cell.
   Uses ATP as energy

Question 20

Identify which transport mechanisms require an input of energy from ATP.

Answer 20

Active transport
Endocytosis
Exocytosis

Question 21

Explain why it is easier for an oxygen molecule to diffuse across a membrane than a water molecule.

Answer 21

Because and oxygen molecule is non-polar so doesn’t get repelled by the hydrophobic interior of the membrane.

Question 22

Explain why steroid hormones can easily cross a membrane by simple diffusion.

Answer 22

They are lipid derived hormones

Question 23

Explain why ions are only able to cross a membrane through a protein channel.

Answer 23

Because they are repelled by the hydrophobic interior of the membrane. So need to be transported in a protein channel.

Question 24

Describe how to carry out an investigation to investigate how the rate of diffusion is affected by surface area.

Answer 24

Cut different sizes of agar jelly with phenolphthalein indicator in.
Put into a beaker of NaOH and time how long it takes for the agar to turn pink.

Question 25

Describe and explain the results you would expect to see in an investigation into how the rate of diffusion is affected by surface area.

Answer 25

The higher the surface area to volume ratio is the faster diffusion will occur.

Question 26

18. Describe how to carry out an experiment to investigate how the rate of diffusion is affected by temperature.

Answer 26

1. Prepare agar jelly and cut into equal sized cubes.
   then prepare several different boiling tubes containing the same concentration of HCl and put them in separate water baths of different temperatures.
2. When the HCl has reached desired temp put agar jelly in and time how long it takes the cube to go colourless.

Question 27

Describe and explain the results you would expect to see in an investigation into how the rate of diffusion is affected by temperature.

Answer 27

The higher the temp the faster the rate of diffusion.

Question 28

Define the terms “solvent”

Answer 28

A liquid in which substances or solutes are dissolved forming a solution

Question 29

Define the terms “solute”

Answer 29

A substance dissolved in a solvent to form a solution

Question 30

Define the terms “solution”.

Answer 30

A substance formed from a solute dissolved in a solvent

Question 31

Define the term “water potential”, state the symbol for water potential, state the water potential of pure water and explain why water potential cannot have a positive value. (F)

Answer 31

1. It is the measure of the quantity of water compared to solutes measured as the pressure created by water molecules (kPa)
2. The likelihood of water molecules to diffuse into or out of a solution.
3. Symbol- weird trident thing
4. Water potential of pure water- 0
5. You can’t have a positive water potential as the highest water potential is water and that’s 0 so nothing can be more than that.

Question 32

Define the terms “net movement of water”.

Answer 32

Overall movement of water from one area to another.

Question 33

Draw a table to compare the effects of external solutions, with different water potentials in comparison to the water potential in an animal cell.

Answer 33

Water Potential of external solution compared to cell solution:
Higher (hypotonic) - water enters the cell- swells and bursts (cytolysis)
Equal (isotonic)- no net movement of water- no change
Lower (hypertonic) - water leaves the cell- shrinks (Crenated)

Question 34

Draw a table to compare the effects of external solutions, with different water potentials in comparison to the water potential in a plant cell.

Answer 34

Water Potential of external solution compared to cell solution:
Higher (hypotonic) - water enters the cell- turgid
Equal (isotonic)- no net movement of water- no change
Lower (hypertonic) - water leaves the cell- shrinks (flaccid)- plasmolysed

Question 35

Define the terms “plasmolysis”

Answer 35

The pulling away of the cytoplasm and plasma membrane from the cell wall due to lack of water

Question 36

Define the terms “protoplast”

Answer 36

The whole cell excluding the cell wall

Question 37

Define the term “crenation”

Answer 37

Cells shrink by osmosis as water leaves the cells- animal cells

Question 38

Define the term “turgid”,

Answer 38

A cell which is swollen by water

Question 39

Define the term “cytolysis”

Answer 39

The bursting of an animal cell caused by increasing hydrostatic pressure as water enters by osmosis

Question 40

Define the term “haemolysis”.

Answer 40

The rupture or disruption of red blood cells

Question 41

Describe how to carry out an experiment to investigate the effects of solutions of different water potential on plant and animal cells.

Answer 41

1. Make up NaCl solutions of different concentrations e.g 0.2, 0.4 etc and pour an equal volume into separate beakers
2. Take de-shelled eggs and carefully pat them with absorbent paper to remove excess moisture.
3. Use a mass balance to weigh each egg, record mass in a table
4. place each egg in a different beaker and leave for same amount of time.
5. remove eggs, dry them and weigh again and use results to calculate percentage change in mass- plot graph
   Repeat- with potato cylinders of equal size in sucrose solutions

Question 42

Describe and explain the results you would expect to see from an experiment to investigate the effects of solutions of different water potential on plant and animal cells.

Answer 42

Animal cell- lower concentration means bigger percentage mass gain
Plant cell- cylinders will gain water in solutions with a higher water potential.

Question 43

Describe the meaning of the symbols:

< < ~ ∝

Answer 43

< < much less
~ approximately equal to
∝ proportional

Question 44

Explain why plant cells don’t burst by osmosis by referring to solute potential and pressure potential.

Answer 44

1. They have strong cellulose walls, when water enters by osmosis the increased hydrostatic pressure pushes the membrane against the rigid cell wall- turgor.
2. As the pressure increases it resists the entry of further water and the cell is turgid.

Question 45

Write an equation to link the water potential of a cell with its pressure potential and its solute potential.

Answer 45

water potential= pressure potential+ solute potential

kPa

Question 46

Define the terms “absolute uncertainty” and “relative uncertainty or percentage error”.

Answer 46

Absolute uncertainty- the extent by which the measurement could be out
relative uncertainty- the ratio of the absolute uncertainty to the original value multiplied by 100

Question 47

Explain how to calculate the percentage error of a measurement (and when data are combined e.g. to obtain data on the change of a particular value over time).

Answer 47

1. Have the absolute uncertainty (e.g +- 0.5)
2. divide it by the amount measured (e.g 100)
3. multiply by 100
4. if measuring the change in something or have two measurements you add the uncertainties together.

Question 48

Explain the significance of where a line of best fit crosses the x-axis in a graph showing how external concentration affects mass change in plant tissues.

Answer 48

1. Because the point where the line crosses the x axis is the point where there was no osmosis.
2. So that means that it has the same water potential in and out of the cell- tells you concentration inside the cell.

Question 49

Define the term “anomaly”

Answer 49

Is a value in a set of results that is judged not to be part of the inherent variation

Question 50

Define the terms “precision”

Answer 50

1. Is the closeness of agreement between independent measurements obtained under the same conditions.
2. It depends only on the distribution of random errors and does not relate to the true value.

Question 51

Define the terms “accuracy”,

Answer 51

Is the measure of the closeness of agreement between an individual test result and the true value. If a test result is accurate, it is in close agreement with the true value.

Question 52

Define the terms “repeatability”

Answer 52

Is the precision obtained when measurement results are produced over a short timescale by one person using the same equipment in the same place

Question 53

Define the terms “reproducibility”

Answer 53

Is the precision obtained when measurement results are produced over a wider timescale by different people using equivalent equipment in different but equivalent places.

Question 54

Define the terms “resolution”

Answer 54

is the smallest change in quantity being measured that can be detected by an instrument.

Question 55

Define the terms “validity”

Answer 55

A measurement is valid id it measures what it is supposed to be measuring. an investigation procedure is valid if it is suitable to answer the question being asked.