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not needed anymore > deck_5557422 > Flashcards

deck_5557422 Flashcards

1
Q

How does diffusion distance affect the rate of simple diffusion?

A

The thicker the membrane across which molecules have to diffuse, the slower the rate of diffusion

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2
Q

How does surface area affect the rate of simple diffusion?

A

More diffusion can take place across a larger surface area. Cells specialised for absorption have extensions to their cell surface membranes called microvilli, which increase surface area

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3
Q

How does the size of the diffusing molecules affect the rate of simple diffusion?

A

Smaller ions or molecules diffuse more rapidly than larger molecules

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4
Q

How does the concentration gradient affect the rate of simple diffusion?

A

The steeper the gradient, the faster the diffusion to the side where there are fewer molecules, down the gradient

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5
Q

Small molecules that have polarity such as ions that have an electrical charge, are insoluble in lipid, why?

A

Because they can’t interact with the hydrophobic tails of the lipid bilayer, meaning they diffuse through water filled protein channels (pores) embedded in the membrane

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6
Q

What is the diameter around these channels?

A

0.8nm

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7
Q

How do cholesterol molecules within membranes affect the permeability of the membranes?

A

They reduce the permeability to small water-soluble molecules

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8
Q

Can glucose molecules diffuse through the water filled protein channel in membranes?

A

No, they are too large but they can bind to a transmembrane carrier protein which then opens to allow the glucose to pass out on the other side of the membrane. There are specific carrier proteins for different types of molecules

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9
Q

How to membranes differ in different cell types?

A

Different cell types have membranes with differing proportions of transmembrane protein channels and transmembrane protein carriers. This allows cells to control the types of molecules that pass in or out

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10
Q

What are neurone plasma membranes like?

A

They have many channels specific to either sodium or potassium ions. The diffusion of these ions into and out of the neurone axon is crucial for the conduction of nerve impulses. At synapses, there are also calcium ion channels and there may be chloride ion channels

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11
Q

What are the plasma membrane of epithelial cells that line airways like?

A

They have chloride ion channels and these play a crucial role in regulating the composition of mucus to trap particles and pathogens

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12
Q

What is the definition of osmosis?

A

The passage of water molecules down their water potential gradient, across a partially permeable membrane-It is the diffusion of water molecules

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13
Q

What is the definition of water potential?

A

The measure of the tendency of water molecules to diffuse from one region to another

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14
Q

What is a solvent?

A

In a solution, the liquid in which solute molecules are disolved

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15
Q

What is the solvent in an aqueous solution?

A

Water

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16
Q

What are the conditions like inside and outside of the cell?

A

Inside the cell is cytoplasm which contains water and the external medium is also watery as its surrounded by extracellular tissue fluid

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17
Q

Why do water molecules spread out?

A

Because they have kinetic energy and move about randomly

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18
Q

What is the process of osmosis?

A

The net diffusion from a region where there are relatively more water molecules to an area where there are fewer water molecules across a partially permeable membrane

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19
Q

What happens when solute molecules are added to water?

A

The relative number of water molecules, in the resulting solution, is changed

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20
Q

What happens if the solute molecules dissociate into charged ions such as sodium chloride dissociating into sodium and chloride ions?

A

They exert more effect on the relative number of water molecules than larger, non polar molecules such as glucose, because the number of particles in the solution doubles

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21
Q

What is water potential?

A

A measure of the tendency of water molecules to diffuse from one region to another

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22
Q

What sort of water has the highest possible water potential?

A

Pure water

23
Q

What happens when solute molecules are added?

A

They lower the water potential of the solution, the more solute molecules in the solution, the lower the water potential

24
Q

What happens if two aqueous solutions are separated by a partially permeable, such as a plasma membrane or a cell organelle membrane?

A

Water molecules will move from the solution with the higher water potential to the solution with the lower water potential

25
Q

What happens when the water potential on both side of the membrane becomes equal?

A

There will be no net osmosis, though water molecules will continue to move randomly

26
Q

What is water potential measured in?

A

Kilopascals (kPa) 0kPa is highest and very low would be -500 kPa

27
Q

What is water potential like inside cells?

A

It is lower than that of pure water as there are solutes in solution, in the cytoplasm and inside the large vacuole of plant cells

28
Q

What happens when cells are placed in a solution of higher water potential?

A

Water molecules move by osmosis, down the concentration gradient, across the plasma membrane, into the cell

29
Q

What happens in animal cells if a lot of water molecules enter?

A

The cell will swell and burst as the plasma membrane breaks, this is called cytolysis

30
Q

What happens in plant cells if there is a lot of water?

A

They have rigid and strong cellulose cell walls that prevent bursting so the cell will swell up when the contents pushes against the cell wall and resist any further swelling

31
Q

What is the swollen cell described as?

A

Turgid. Turgidity of plant cells helps support plants, especially those that are not woody

32
Q

What happens when cells are placed in a solution of lower water potential?

A

Water leaves the cells by osmosis across a partially permeable plasma membrane, Animal cells shrivel and are described as crenated

33
Q

What happens in plant cells when there is lower water potential surrounding them?

A

The cytoplasm of plant cells shrinks and the membrane pulls away from the cellulose cell wall, the cells are described as plasmolysed. Plant tissue with plasmolysed cells is described as flaccid

34
Q

What happens to cells that are plasmolysed?

A

They suffer a degree of dehydration and their metabolism cant carry on, as enzyme catalysed reactions need to be in solution

35
Q

What is the definition of active transport?

A

The movement of substances against their concentration gradient across a cell membrane using ATP and protein carriers

36
Q

What is the definition of endocytosis?

A

Bulk transport of molecules, too large to pass through a cell membrane, even via channel proteins, into a cell

37
Q

what is the definition of exocytosis?

A

Bulk transport of molecules too large to pass through a cell membrane even via channel proteins, out of a cell

38
Q

How do cells get the energy to move substances against the concentration gradient, as kinetic isn’t enough

A

They hydrolysis of ATP which is often described as the universal energy currency as all cells make use of it to supply their energy needs

39
Q

How do cells or organelles accumulate more of a particular ion if they need to?

A

By simple of facilitated diffusion eg root hair cells use active transport to absorb ions from soil

40
Q

How do carrier proteins work?

A

They have specific regions or sites that combine reversibly with only certain solute molecules or ions. They also have a region that binds to and allows the hydrolysis of ATP to release energy, in this way they act as enzymes

41
Q

What does the ATP energy help carrier proteins change?

A

It’s conformation (shape) so it carried the ion form one side of the cell membrane to the other

42
Q

What is an example of this?

A

In guard cells, ATP made by chloroplasts provide energy to actively transport potassium ions from surrounding cells into guard cells. The influx of ions lowers the water potential in the cells so that water enters from surrounding cells by osmosis. As the guard cells swell, their tips bulge and this opens the stoma between them

43
Q

Why is bulk transport needed?

A

Some cells need to transport large molecules and particles that are too large to pass through the plasma membrane in or out, the process requires energy from ATP

44
Q

What is endocytosis?

A

How large particles may be brought into a cell, they don’t pass through the plasma membrane and instead a segment of the plasma membrane surrounds and encloses the particle, and brings it into the cell, enclosed in a vesicle

45
Q

What is phagocytosis?

A

It means ‘eating by cells’ and refers to the type of intake of solid matter

46
Q

What is pino(endo)cytosis?

A

If cells ingest liquids by endocytosis

47
Q

What is exocytosis?

A

How large molecules may be exported out of cells, they don’t pass through the plasma membrane, a vesicle containing them is moved towards and then fuses with the plasma membrane

48
Q

Where can this be seen?

A

At synapses, where chemicals in vesicles are moved, by motor proteins moving along cytoskeleton threads, to the presynaptic membrane. Here, the vesicle membranes and plasma membranes fuse and the neurotransmitter chemicals are released into the synaptic cleft

49
Q

In all cases, what is needed to fuse the membranes together as well as for moving the vesicles?

A

ATP. A molecule of ATP is hydrolysed for every step that a motor proteins takes along the cytoskeleton thread as it drags the vesicle

50
Q

What happens to fatty acids when temperature drops?

A

Saturated fatty acids become compressed however there are many unsaturated fatty acid making up the cell membrane phospholipid bilayer, as they become compressed, the kinks in their tails push the phospholipid molecules away, maintaining the membrane fluidity

51
Q

What does this mean?

A

The proportions of unsaturated and saturated fatty acids within a cell membrane determines the membranes fluidity at cold temperatures

52
Q

What does cholesterol do in relation to temperature?

A

It buffers the effect of lowered temperature to prevent a reduction in the membranes fluidity, by preventing the phospholipid molecules from packing together too closely because cholesterol molecules are in between groups of phospholipid molecules

53
Q

How do some organisms deal with temperature change?

A

They change the composition of the fatty acids in their cell membranes in response to lowered temperatures

54
Q

What happens when temperature increases?

A

Phospholipids gain more kinetic energy and move around more, increasing membrane fluidity. Permeability increases. Membrane embedded proteins are positioned differently and function differently so some enzymes catalyse at different rates. Increase in fluidity may affect infolding of the plasma membrane during phagocytosis and may also change ability of cells to signal other cells by releasing chemicals by exocytosis. The presence of cholesterol molecules buffers to reduce effects and reduce increase in membrane fluidity

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