chapter 4.2 and 4.3

Question 1

What are the methods of movement across a membrane

Answer 1

 Passive transport (diffusion and facilitated diffusion)
 Active transport
 Osmosis

Question 2

Active and passive what’s are difference due to

Answer 2

• If substances require energy to move them it is called active transport.
• If substances do not require energy to move them it it called passive transport. Diffusion is an example of passive transport.

Question 3

Diffusion is defined as

Answer 3

the net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed.

Question 4

Net movement

Answer 4

all particles move at random in diffusion, it’s just that more move in one direction than in the other. This is due to concentration difference. So therefore the net movement would be toward the area where there is higher concentration, as diffusion moves from high to low concentration.

Question 5

Examples of substances that can diffuse freely across the bilayer

Answer 5

• Small like oxygen and carbon dioxide can diffuse around the cell membrane. .
• hydrophobic substances
• soluble in lipids so can pass through the phospholipid bilayer
• non-polar molecules like oxygen and carbon dioxide
• however, small, polar molecules like water and urea also diffuse across, but much more slowly

Question 6

Examples of substances that cannot diffuse across the bilayer

Answer 6

Charged particles are unlikely to diffuse across a membrane, even if they are very small.

Question 7

Molecules that diffuse through membrane with the assistance of transport protein

Answer 7

• Hydrophilic substances like water molecules
• large molecules
• polar molecules diffuse through membrane due tot the hydrophobic nature of the fatty acid tails

Question 8

Is facilitated diffusion a passive process

Answer 8

Yes

Question 9

Two types of protein molecules are involved

Answer 9

protein channel and carrier protein

Question 10

What job do protein channels do

Answer 10

• These proteins form water-filled hydrophilic channels across the membrane.
• They allow specific water and water-soluble ions to pass through, such water and ions.

Question 11

Are protein channels selective

Answer 11

yes each opening in the presence of a specific ion, or in response to a specific messenger or a change in voltage across the membrane. If the particle ion is not present, the channel remains closed

Question 12

Why are protein channels selective

Answer 12

So there is control over the entry and exit of ions. The ions bind with the protein causing it to change shape in a way that closes to one side of the membrane and opens it to the other side.

Question 13

How do protein channels and carrier proteins bind with their specific ion and transport it across the membrane

Answer 13

The specific molecules temporarily binds with the protein it causes it to change shape. This causes it to change shape in such a way that it closes to one side of the membrane releasing it to the inside of the membrane and closes to the other of the membrane.

Question 14

Can carrier proteins move molecules in either direction

Answer 14

yes

Question 15

Is a carrier protein a passive form of transport

Answer 15

Yes it requires no external extra energy except only on the inbuilt motion of kinetic energy of the diffusing molecules

Question 16

Why are all protein channels and carrier proteins only specific to one type of molecule

Answer 16

All protein channels and carrier proteins have specific tertiary structures, this means one particular type of ion or molecule can pass through or bind with them, as they have to be complementary to the shape of the tertiary structure.

Question 17

what does Fick’s law show

Answer 17

It describes the relationship between the rate of diffusion (how fast diffusion is) and three factors that effect surface area, concentration gradient and thickness of membrane. It states that rate of diffusion is proportional (as one factor goes up the other factor goes up) to surface area and concentration difference and is inversely proportional (as one factor goes up the other goes down) to the thickness of the membrane

Question 18

What is Fick’s law

Answer 18

that rate of diffusion is proportional to:
Surface area x difference in concentration
————————————————————-
length diffusion path (membrane thickness)

Question 19

Increasing thickness of the cell membrane will

Answer 19

• I decrease the rate of diffusion.
• Increasing the surface area across of the cell membrane will increase the rate of diffusion
• The rate of diffusion is directly proportional to the surface area and difference in concentration but indirectly proportional to the length of diffusion path.

Question 20

Increase surface area across the cell membrane will

Answer 20

increase the rate of diffusion

Question 21

1. The rate of diffusion directly proportional to?
2. The rate of diffusion indirectly proportional to?
3. What does proportional mean?
4. What does indirectly?

Answer 21

1. increase surface area and difference in concentration difference
2. length of diffusion path (thickness)
3. As one factor goes up the other factor will go up
4. As one factor goes up the other factor goes down

Question 22

Is diffusion rapid in gases and can it occur in solids

Answer 22

yes diffusion is very rapid in gases and it can occur in solids but just not as fast

Question 23

what is used to mimic the cell membranes

Answer 23

Visking tubing is used in the lab to mimic the cells membrane.

Question 24

What is the definition of osmosis

Answer 24

the passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a selectively permeable membrane.

Question 25

Is the surface membrane and plasma membrane selectively permeable or permeable?
What does it mean?

Answer 25

it is selectively permeable this means it lets a some molecules through whilst blocking others

Question 26

what is a solute

Answer 26

A solute e.g. sugar is any substance that is dissolved in a solvent, for example, water. The solute and the solvent together form a solution.

Question 27

What is a solvent

Answer 27

Any substance that dissolves a solute e.g. water

Question 28

What’s a solution

Answer 28

When the solute dissolves in the solvent it forms a solution, remember if the solutes is not dissolves in the solvent it is not a solution, the solute must dissolve in the solvent for it to be a solution

Question 29

What is water potential

Answer 29

Water potential is the tendency of water molecules in a system to move. It is detonated by the Greek letter psi (Ψ), and is measured in units of pressure, usually kilopascals’ (kPa). Water potential is the pressure created by water molecules.

Question 30

What is pure water is said to have a water potential of

Answer 30

Under standard conditions of temperature and pressure (25 degrees Celsius and 100kPa), pure water is said to have a water potential of zero.

Question 31

What does the addition of a solute do to pure water

Answer 31

the addition of solute to pure water will lower its water potential

Question 32

What happens when more solute is added to water

Answer 32

the more solute that is added (i.e., the more concentrated a solution), the lower (more negative) its water potential

Question 33

What direction does water move in osmosis

Answer 33

water will move by osmosis from a region of higher (less negative) water potential (e.g. -20kPa) to one of lower (more negative) water potential (e.g. -30kPa).

Question 34

Write an explanation of osmosis

Answer 34

• The solution on the left has a low concentration of the solute molecules while the solution on the right has a high concentration of solute molecules.
• Both the solute and water molecules are in random motion due to their kinetic energy
• The selectively permeable plasma membrane, however, only allows water molecules across it and not soluble molecules
• The water molecules diffuses from the left-hand side, which has the higher water potential to the right-hand side which has the lower water potential, that is, down a water potential gradient
• At the point where the water potentials on either side of the plasma membrane are equal, a dynamic equilibrium is established and there is no net movement of water.

Question 35

What is the highest number in water potential

Answer 35

The highest value of water potential, that of pure water, is zero, and all other values are negative.

Question 36

What does it mean when the water potential number gets lower

Answer 36

The more negative the value, the lower the water potential.

Question 37

What happens when red blood cells are placed in pure water?

Answer 37

Animal cells, such as red blood cells, contain a variety of solutes dissolved in their watery cytoplasm, therefore making it have a has a lower water potential than pure water. If a red blood cell is placed in pure water it will absorb water by osmosis because it has a lower water potential. Cell surface membranes are very thin (7nm) and, although they are flexible, they cannot stretch to any great extent. The cell-surface membrane will therefore break, bursting the cell and releasing its contents (in red blood cells this is called haemolysis).

Question 38

How do they prevent red blood cells from bursting inside the body?

Answer 38

To prevent this happening, animal cells normally live in a liquid which has the same water potential as the cells. In our example, the liquid is the blood plasma. This and red blood cells have the same water potential.

Question 39

What happens when a red blood cell is placed in a solution of a lower water potential than its own

Answer 39

If a red blood cell is paced in a solution with a water potential lower than its own, water leaves by osmosis and the cell shrinks and becomes shrivelled. Also, the haemoglobin will be more concentrated so will be a more darker appearance

Question 40

How do solutes effect a waters water potential?

Answer 40

The water potential of a solution is affected by the amount of solute it contains. The greater the amount of solute, the lower the water potential. This is because water molecules bind to the solute molecules, reducing the number of water molecules that are free to diffuse. The contribution that solutes make to the water potential of a solution is the solution potential (Ψ), and is a negative value.

Question 41

What happens when solutes are added to water?

Answer 41

The contribution that solutes make to the water potential of a solution is the solution potential (Ψ) as it becomes a more negative value, check this

Question 42

If the water potential (ψ) of external solution compared to cell solution is higher

1. Net movement of water will
2. Protoplast
3. Condition of cell

Answer 42

1. Enters cell
2. Swells
3. Turgid

Question 43

Water potential (ψ) of external solution compared to cell solution is the same

1. Net movement of water
2. Protoplast
3. Condition of cell

Answer 43

1. Neither enters nor leaves
2. No change
3. Incipient plasmolysis

Question 44

Water potential (ψ) of external solution compared to cell solution is lower (more negative)

1. Net movement of water
2. Protoplast
3. Condition of cell

Answer 44

1. Leaves cell
2. Shrinks
3. Plasmolysed

Question 45

What does the central vacuole do in plants

Answer 45

It contains a solution of salts, sugars and organic acids in water. Its jobs is structural support for the plant and be a storage for waste disposal and food

Question 46

What does the protoplast do in plants

Answer 46

consisting of the outer cell-surface membrane, nucleus, cytoplasm and the inner vacuole membrane

Question 47

what is the cellulose cell wall

Answer 47

a tough, inelastic covering that is permeable to even large molecules

Question 48

How is a plant cell environment different to a animal cells?

Answer 48

1. Unlike animal cells, however, they are unable to control the composition of the fluid around their cells, as it is not a constant medium as water is constantly coming up through the roots at uncontrollable rates e.g. sometimes there may a heavy rainfall followed by a light shower.
2. Indeed, plant cells are normally permanently bathed in almost pure water, which is constantly absorbed from the plant’s roots, as plants will almost normally then always have a lower water potential. This is good as it allows the plant cells to become turgid giving turgid pressure allowing the plant to stand upright., therefore the more leaves will be exposed to sunlight rain, dew, air

Question 49

How does the plant cell become turgid?

Answer 49

Water entering a plant cell by osmosis causes the protoplast (consisting of the outer cell-surface membrane, nucleus, cytoplasm and the inner vacuole membrane) to swell and press on the cell wall. Because the cell wall is capable of only limited expansion, a pressure builds up on it that resists the entry of further water. In this situation, the protoplast of the cell is kept pushed against the cell wall and the cell is said to be turgid.

Question 50

What will happen if the plant cell is placed in a solution with a lower water potential than its own?

Answer 50

If the same plant cell is placed in a solution with a lower water potential than its own, water leaves by osmosis. So the volume of the cell decreases. With no water entering the cell means the protoplast can no longer swell up and press on the cellulose cell wall. At this point the cell is said to be at incipient plasmolysis. Further loss of water will cause the cell contents to shrink further and the protoplast to pull away from the cell wall. In this condition the cell is said to be plasmolysed. The cell will then start to wilt.

Question 51

What is the positives of plant leaves wilting

Answer 51

reduce surface area so there is less spaces for water to be lost from the leaves so less water will be lost. Also, by wilting it creates a more humid environment around the leaf reducing the concentration gradient difference therefore therefore less water will lost from the leaf

Question 52

What is plasmolysis?

Answer 52

if a plant cell is placed in a solution with a lower water potential, it will lose water, via osmosis. The living part of the cell or protoplast (a cell with its cell wall partially or completely removed) will decrease in size and pull away from away from the cell wall. At this point the pressure potential is zero and so the water potential of the cell is equal so its solute potential. If water enters the cell the pressure potential increases. This process is called plasmolysis and the cell is said to be plasmolysed. The point at which the protoplast (cell without a cell wall) is just about to pull away from the cell wall is called incipient plasmolysis.

Question 53

whats turgor pressure

Answer 53

Turgor pressure also called hydrostatic pressure. It causes the cell wall to expand during growth and change its rigidity and size. A lower pressure results in a wilted cell or plant structure

Question 54

what is an isotonic solution?

Answer 54

An isotonic solution refers to two solutions having the same osmotic pressure (pressure that would be required to stop water from diffusing through a barrier by osmosis) across a semipermeable membrane. By having balanced pressure, it allows for the free movement of water across the membrane without changing the concentration of each sides solutes. The plant cell will become flaccid. Flaccid is when the protocylast will begin to pull away from the cell wall.

Question 55

what is a hypotonic solution?

Answer 55

A hypotonic solution is a solution that has a lower osmotic pressure than another solution. This generally refers to a solution that has less solute and more water. A hypotonic solution isn’t good for cells as it will fill with water and burst/lyse.

Question 56

What is a hypertonic solution?

Answer 56

A hypertonic solution is one in which the concentration of solutes is greater inside the cell than outside of it. A hypertonic solution will do just the opposite, the water will rush out of the cell, and it will shrivel up. When this happens to a plant cell, it is called a plasmolysed cell.

Question 57

Is the cellulose cell wall fully permeable

Answer 57

yes, the cellulose cell wall is fully permeable

Question 58

is it true that solutes stick to the water molecules? what does this meai

Answer 58

yes, water solutes get stuck to the solute and the water can’t move easily

Question 59

What happens to you cells when you eat too much sugar

Answer 59

problem when eat too much sugar because the water diffuses out of the cell and the cell becomes plasmolysis.

Question 60

What happens a visking tube with a high concentration starch solution is placed in an iodine solution

Answer 60

If iodine was outside a cell membrane model and starch inside it, the iodine will diffuse through the visking tubing, down the concentration gradient. The starch molecules are too large to diffuse out of the semi-permeable membrane.