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biological membranes Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What are all cell & organelle membranes composed of?

A

Phospholipid bilayer

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2
Q

What are the 3 main functions of a cell membrane?

A
  • provide a partially permeable membrane
  • site of chemical reactions
  • role in cell communication
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3
Q

Why is the fluid-mosaic model described as a ‘mosaic’?

A

There is a mixture of phospholipids, proteins, glycoproteins, and glycolipids that the membrane is made of

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4
Q

Why is the fluid-mosaic model described to be ‘fluid’?

A

The phospholipids align as a bilayer due to the hydrophilic heads being attracted to water and the hydrophobic tails being repelled by water, the fluidity is maintained by cholesterol

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5
Q

What are the 2 types of proteins in the cell surface membrane?

A

Extrinsic & intrinsic

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6
Q

What are the functions of extrinsic proteins?

A
  • provide mechanical support
  • make glycoproteins or glycolipids
  • cell recognition, as receptors
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7
Q

What are intrinsic proteins?

A

Protein carriers or channel proteins which are involved in the transport of molecules across the membrane

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8
Q

What are protein channels?

A

Proteins that form tubes that fill with water to enable water-soluble ions to diffuse through the membrane

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9
Q

What are carrier proteins?

A

Proteins that 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

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10
Q

What is the function of cholesterol?

A

maintains the fluidity of the membrane

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11
Q

How does temperature affect the structure & permeability of the membrane?

A

High temperature increases the kinetic energy of the phospholipids so that they move even more, this increases the fluidity of the membrane, therefore increasing the permeability which means that the structure can start to break, which makes it easier for particles to move across the membrane. If the temperature is too high, it can denature the carrier & channel proteins in the membrane

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12
Q

How can solvents affect membrane structure & permeability?

A

Organic solvents e.g. alcohol, dissolve the phospholipid bilayer in membranes, this damage causes the fluidity of the membrane to increase and they become more permeable

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13
Q

What are the 6 key modes of transport into and out of cells?

A
  • simple diffusion
  • facilitated diffusion
  • osmosis
  • active transport
  • endocytosis
  • exocytosis
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14
Q

What is simple diffusion?

A

The net movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached - this process does not require ATP, for molecules to diffuse across the membrane they must be lipid soluble & small

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15
Q

What is facilitated diffusion?

A

A passive process, down the concentration gradient, through proteins. The movement of ions & polar molecules, which cannot simply diffuse, can be transported across membranes by facilitated diffusion using protein channels & carrier proteins

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16
Q

What is osmosis?

A

The movement of water from an area of higher water potential to an area of lower water potential across a partially permeable membrane

17
Q

What is an isotonic solution?

A

When the water potential of the solution is the same as inside the the cell - there is no water potential gradient

18
Q

What is a hypotonic solution?

A

When the water potential of a solution is higher than inside the cell

19
Q

What happens to the movement of water in a hypotonic solution?

A

The water moves into the cell

20
Q

What is a hypertonic solution?

A

When the water potential of a solution is lower than inside the cell

21
Q

What happens to the movement of water in a hypertonic solution?

A

The water moves out of the cell - this causes the cell to become plasmolysed (plant cells) or crenated (animal cells)

22
Q

what happens to animal cells in a hypotonic solution?

A

it becomes cytolysed

23
Q

what happens to plant cells in a hypotonic solution?

A

they become turgid

24
Q

what happens to animal cells in a hypertonic solution?

A

they become crenated

25
Q

what happens to plant cells in a hypertonic solution?

A

they become plasmolysed

26
Q

what is 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 & carrier proteins

27
Q

why is active transport described to be a selective process?

A

only certain molecules can bind to the receptor site of carrier proteins, and ATP will bind to the protein on the inside of the membrane and is hydrolysed into ADP and Pi

28
Q

what is endocytosis?

A

a type of active transport, it is the bulk transport of molecules into a cell

29
Q

how does endocytosis work?

A
  • the cell surface membrane bends inwards around the molecules, surrounding it to form a vesicle
  • the vesicle pinches off and moves within the cytoplasm
30
Q

what are the 2 types of endocytosis?

A

phagocytosis & pinocytosis

31
Q

what is phagocytosis?

A

when a solid particle is being taken in the vesicle

32
Q

what is pinocytosis?

A

when a liquid is being taken in the vesicle

33
Q

why does endocytosis require energy from ATP?

A

for the cell to engulf and change shape around the material

34
Q

what is exocytosis

A

the bulk transport of molecules out of a cell

35
Q

how does exocytosis work?

A

vesicles move towards the cell-surface membrane, fuse with the membrane, and the content of the vesicle is released outside of the cell

36
Q

why does exoctytosis require energy?

A

ATP is needed to move the vesicle along the cytoskeleton, towards the cell-surface membrane

37
Q

how does cholesterol maintain the fluidity of the membrane?

A

Restricts the movement of other molecules in the membrane, this ensures that the membrane is less fluid at high temperatures and prevents water and dissolved ions from leaking out of the cell

biology (12 decks)

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