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Biology > Biological Membranes 2.1.5 > Flashcards

Biological Membranes 2.1.5 Flashcards

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1
Q

What is a passive process?

A

.Some substances can pass across a membrane without using any of the cell’s metabolic energy
.These are passive processes as they use only the kinetic energy of the molecules and do not use ATP

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2
Q

State 2 passive processes

A

-diffusion
-facilitated diffusion

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3
Q

Define (simple) diffusion

A

The net movement of molecules from an area of high concentration to an area of low concentration.Down a concentration gradient. It does not involve metabolic energy (ATP)

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4
Q

Define facilitated diffusion

A

Movement of molecules from an area of high concentration of that molecule to an area of low concentration , across a partially permeable membrane via protein channels or carriers. It does not involve metabolic energy (ATP)

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5
Q

How does simple diffusion occur ?

A

-all molecules have kinetic energy
-if there is a high concentration of a certain type of molecule in an area ,the molecules will bump in to each other as they randomly move and will eventually spread further from each other
-more will move to an area where they are in lower concentration until eventually they will become evenly dispersed
-when molecules have moved down their concentration gradient they are still moving randomly but remain evenly dispersed so there is no net diffusion. They have reached equilibrium

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6
Q

What particles can diffuse by simple diffusion across the phospholipid bilayer?

A

-lipid soluble, small, uncharged molecules

E.g oxygen, carbon dioxide , steroid hormones

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7
Q

How is the concentration gradient maintained ?

A

-many molecules entering cells then pass into organelles and are used for metabolic reactions
-this maintains the concentration gradient and keeps more of the molecules entering the cell

E.g. oxygen diffuses into the cytoplasm of respiring cells , then diffuses into mitochondria and is used for aerobic respiration

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8
Q

Define osmosis

A

The net movement of water molecules from a higher water potential to a lower water potential, down a water potential gradient.Across a partially permeable membrane

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9
Q

What is water potential?

A

A measure of the concentration of water molecules that are able to diffuse

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10
Q

What has the highest water potential?

A

-pure water has the highest possible water potential(0kPa)
-when solute molecules are added , they lower the water potential of the solution(it becomes more negative)The more solute molecules the lower the water potential of the solution
-if 2 aqueous solutions are separated by a partially permeable membrane -water molecules will move from the solution with the highest water potential to the solution with the lowest water potential
-if the water potential on both sides becomes equal ,there will be no net osmosis but the water molecules will continue to move randomly

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11
Q

What is water potential measured in?

A

-kPa (kilopascals)

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12
Q

What is cytolysis?

A

In animal cells if a lot of water molecules enter , the cell will swell and burst so the plasma membrane breaks.This is cytolysis

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13
Q

What prevents plant cells from bursting ?

A

-the rigid and strong cellulose wall will prevent bursting.
-The cell will swell up to a certain size when its contents push against the cell wall
-which will resist any further swelling
-the swollen cell is described as turgid (turgidity of the plant cell has supports plants)

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14
Q

What is a HYPOtonic solution?

A

-the solution has a small amount of solute and higher water potential
-it is dilute

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15
Q

What is an ISOtonic solution?

A

-the solution the cell is in has the same amount of solute and the same water potential as the inside of the cell

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16
Q

What is a HYPERtonic solution ?

A

-the solution has a large amount of solute
-and a lower water potential
-it is concentrated

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17
Q

What happens when a cell is placed in a hypotonic solution (high water potential )?

A

-water molecules moves by osmosis , down the water potential gradient , across the plasma membrane ,into the cell
-in animal cells ,if a lot of water molecules enter the cell , it will swell and burst as the plasma membrane breaks. This is called cytolysis / haemolysis

-in plant cells the cell wall prevents the cell from bursting , instead the cell becomes turgid

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18
Q

What happen if a cell is placed in an isotonic solution?

A

-there is no net osmosis
-the cells neither shrink or swell
-they will not gain or lose any mass

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19
Q

What happens if a cell is placed in a hypertonic solution (low water potential)?

A

-water leaves the cell by osmosis across the partially permeable plasma membrane
-animal cells shrivel and are described as crenated

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

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20
Q

What happens to plant cells that are plasmolysed ?

A

-they suffer a degree of dehydration and their metabolism cannot proceed , as enzyme catalysed reactions need to be in solution

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21
Q

Define active transport

A

The movement of molecules and ions from an area of lower concentration to an area of higher concentration (against the concentration gradient) using ATP and carrier proteins.

22
Q

How are carrier proteins used in active transport?

A

-the molecule or ion to be transported attaches to a receptor site on the carrier protein, this takes place on the side of the membrane where the chemical is at a lower concentration
-a molecule of ATP binds to the carrier protein,the molecule of ATP undergoes hydrolysis producing a molecule of ADP and a phosphate (this releases energy)
-the phosphate attaches to the carrier protein and causes it to change conformation (it’s shape) with help from the energy released
-this shape change causes the carrier protein to transport the molecule or ion to the other side of the membrane where it is released
-the phosphate leaves the protein causing it to return to its previous shape

23
Q

Why are carrier proteins specific?

A

Each carrier protein will only transport one molecule or ion

24
Q

Cell membranes are …… barriers

A

partially permeable barriers

-they do not let all types of molecules pass through them
-the component molecules of the cell membrane determine its permeability

25
Q

What are the roles of membranes?

A

-partially permeable barriers between the cell and its environment as well as between organelles and the cytoplasm and within organelles
-sites of chemical reactions
-sites of cell communication (cell signalling)

26
Q

What is the thickness of a membrane ?

A

7-9nm

27
Q

What are membrane bound receptors ?

A

Sites where hormones and drugs can bind

28
Q

Define endocytosis

A

Bulk transport of molecules too large to pass through a cell membrane even via channel or carrier proteins into a cell
Requires ATP

29
Q

Define Exocytosis

A

Bulk transport of molecules too large to pass through a cell membrane even via channel or carrier proteins out of a cell
Requires ATP

30
Q

What is phagocytosis ?

A

-means eating by cells
-refers to the intake of solid matter by cells
-a type of endocytosis

31
Q

What is Pinocytosis ?

A

Cells ingesting liquid
Type of endocytosis

32
Q

Halophytes are plants that have the ability to live in soils with a very low water potential. In the UK these plants form part of the salt marsh communities. Suggest and explain how the root hairs of the halophytes are able to absorb water by osmosis from the soil of the salt marsh.
(2marks)

A

-there is lower water potential inside root hair
-root hair cells contain ions ,salts and solutes
(As they actively transport ions, salts and solutes into root hair cells )

33
Q

What is the role of extrinsic proteins in the phospholipid belayer?

A

-provide mechanical support
- used to make glycoproteins and glycolipids

34
Q

What is the role of glycolipids and glycoproteins?

A

-cell recognition, they act as receptors

35
Q

What is the function of intrinsic proteins in the phospholipid bilayer?

A

-communication across membrane

36
Q

What is the difference between protein channels and carrier proteins?

A

-protein channels form tubes that fill with water to enable water-soluble ions to diffuse
-whereas carrier proteins will bind with other ions and larger molecules ,such as glucose and amino acids, and change shape to transport them to the other side of the membrane

37
Q

What factors affect the structure and permeability of a membrane?

A

-temperature
-solvents

38
Q

What happens to the membrane structure when temperature drops?

A

-saturated fatty acids become compressed
-the many unsaturated fatty acids in the cell membrane phospholipid bilayer -as they compress the kinks in their tails push adjacent phospholipid molecules away. This maintains membrane fluidity
-cholesterol prevents a reduction in the membranes fluidity by preventing the phospholipid molecules from packing together too closely

39
Q

What is the effect on the membrane structure and permeability of increasing the temperature ?

A

-high temperatures increase the kinetic energy of the phospholipids so that they move around more
-this increases fluidity of the membrane, increasing the permeability making it easier for particles to cross membrane-the presence of cholesterol buffers the effect of increasing heat by reducing the increase in membrane fluidity
-high temperatures can denature carrier and channel proteins in the membrane

40
Q

What is the effect of solvents on the cell membrane?

A

-organic solvents like alcohol, dissolve the phospholipid bilayer in membranes
-this damage causes the fluidity of the membrane to increase and become more permeable

41
Q

Membranes contain a variety of proteins. Some of these proteins are combined with carbohydrates to form glycoproteins.
Describe the functions of glycoproteins in the cell surface membrane
5 marks

A

-they act as antigens
-in the recognition of cells as self
-they are used in cell signalling which is communication between cells
-they act as a receptor for hormones and chemical signals
-they attach to water molecules to stabilise membrane

42
Q

How do small non-polar substances enter cell?

A

-they diffuse through membrane

43
Q

How do large substances enter a cell?

A

-through endocytosis -the bulk entry of molecules into a cell using ATP

44
Q

How do polar substances enter cell?

A

-using carrier proteins that use ATP

45
Q

Glucose can be moved into cells by facilitated diffusion using proteins called GLUT proteins.These proteins expose a single binding site on one side of the membrane. This change moves the glucose across the membrane and releases it on the other side.

Explain why facilitated diffusion via GLUT proteins requires no metabolic energy
(2 marks)

A

-particles have their own kinetic energy
-particles move down concentration gradient

46
Q

Explain why glucose cannot pass through a cell membrane by simple diffusion
(2 marks)

A

-phospholipids act as a barrier
-glucose molecules too large

47
Q

The rough endoplasmic reticulum is where translation of some proteins take place in a eukaryotic cell. Explain the role of the membrane in the rough endoplasmic reticulum
(2 marks)

A

-compartmentalisation/ maintains different conditions from cell cytoplasm
-separating proteins (synthesised) from cell cytoplasm

48
Q

What 2 substances are required to break the glycosidic bond in lactose?
(2 marks)

A

-water
-lactase

49
Q

Suggest and explain why a low pH might cause the red pigment to leak out of the beetroot cells
(2 marks)

A

-low pH denatures/ changes tertiary structure of (membrane) proteins
-therefore membrane permeability (to pigment) is increased

50
Q

Explain why progesterone can move across membranes
(2 marks)

A

-progesterone is hydrophobic/ lipid (fat) soluble
-so diffuses through the phospholipid bilayer

51
Q

The fluid mosaic model describes plasma membranes of all living organisms. How does the fluid mosaic model describe the structure of plasma membranes?
(2 marks)

A

-phospholipid bilayer
-hydrophilic/phosphate heads facing outwards/towards external environment and hydrophobic tails facing inwards/ away from external environment

(Proteins free to move in membrane, proteins scatttered /randomly arranged throughout )

Biology (13 decks)

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