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Alevel Biology OCR > 2.1.5 - Biological Membranes > Flashcards

2.1.5 - Biological Membranes Flashcards

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1
Q

What are the roles of a cell surface membrane?

A
  • acts as a partially permeable barrier (between cell and environment)
  • controls what enters/leaves the cell
  • cell communication (cell signalling)
  • allow recognition with other cells
  • some chemical reactions
  • sites of chemical reactions
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2
Q

What are the roles of a membrane within a cell?

A
  • comparementisation (divides cell and keeps cell organelles separate)
  • partially permeable barrier (between organelles and cytoplasm and within organelles)
  • can form vesicles
  • control what enters/leaves organelles
  • sites of chemical reactions
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3
Q

What is cell signalling?

A

communication between cells

-one cell releases a molecule, which attaches to another cell’s receptor so that it is detected by the cell

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4
Q

What is the fluid mosaic model?

A

a model which shows the arrangement of molecules (eg. phospholipids, proteins, etc) in a cell membrane

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5
Q

What is the role of phospholipids within the fluid mosaic model of a cell membrane?

A
  • acts as a barrier to large polar (dissolved) substances -water soluble substances can’t dissolve through as hydrophobic centre to bilayer don’t let them through
  • fat soluble and small molecules can pass straight through
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6
Q

Describe the structure of phospholipids in the fluid mosaic model of a cell membrane

A
  • form a bilayer
  • hydrophilic phosphate heads on outside
  • hydrophobic fatty acid chains on inside
  • about 7nm thick
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7
Q

What is the role of cholesterol within the fluid mosaic model of a cell membrane?

A
  • makes membrane less fluid and more rigid
  • reduces permeability to charged particles
  • interacts with phospholipids (hydrophobic end interacts with heads + hydrophilic ends interact with tails -pulls them together for stability)
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8
Q

What is the role of glycolipids within the fluid mosaic model of a cell membrane?

A
  • act as antigens (cell markers)

- stabilise membrane by forming hydrogen bonds with surrounding water molecules

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9
Q

What is the role of glycoproteins within the fluid mosaic model of a cell membrane?

A
  • stabilise membrane by forming hydrogen bonds with surrounding water molecules
  • act as antigens (cell markers)
  • act as receptors (for cell signalling)
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10
Q

What is the role of proteins within the fluid mosaic model of a cell membrane?

A

-control what enters/leaves cells

different types: channel proteins, carrier proteins, etc

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11
Q

What factors affect membrane structure and

permeability?

A
  • temperature

- solvent

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12
Q

Why is it important that cell membranes are fluid?

A
  • diffusion of substances across membrane
  • fusing of membranes
  • movement and shape change of cells
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13
Q

How does an increase of temperature affect the permeability of a membrane?

A
  • increases permeability
  • increased kinetic energy of phospholipids
  • creates gaps between bilayer (disrupts it)
  • molecules can pass through gaps
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14
Q

What is the structure and permeability of a membrane like below 0°C?

A
  • phospholipids don’t have much energy so can’t move much (are packed closely together) so membrane is rigid
  • channel and carrier proteins in membrane deform so permeability increases
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15
Q

What is the structure and permeability of a membrane like around 0-45°C?

A
  • phospholipids can move and aren’t so packed together
  • membrane is partially permeable
  • as temp increases, permeability increases (more energy to move so more fluid)
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16
Q

What is the structure and permeability of a membrane like above 45°C?

A
  • phospholipid bilayer begins to melt
  • membrane becomes more permeable
  • water inside cells puts pressure on membrane
  • channel and carrier proteins denature
17
Q

How do solvents affect the permeability of a membrane?

A
  • solvents increase a membrane’s permeability

- solvents dissolve lipids in membrane so membrane looses it structure

18
Q

How do molecules move across membranes?

A
  • diffusion
  • facilitated diffusion
  • active transport
  • endocytosis
  • exocytosis
19
Q

What is diffusion?

A
  • net movement of particles down a concentration gradient (from a region of high concentration to a region of low concentration)
  • passive transport
20
Q

What is simple diffusion across a membrane?

A

small, non-polar molecules in high concentration on one side can easily diffuse directly across the phospholipid bilayer

21
Q

What is facilitated diffusion across a membrane?

A

diffusion of larger or polar molecules/ions across a membrane through protein channels or carrier proteins

22
Q

How do molecules move across a membrane through carrier proteins?

A
  • large molecule attaches to a carrier protein in membrane
  • protein changes shape
  • molecule is released on opposite side of membrane
23
Q

How do molecules move across a membrane through channel proteins?

A
  • channel proteins have pores which charged particles diffuse through
  • different channel proteins facilitate the diffusion of different charged particles
24
Q

What is active transport across a membrane?

A

movement against a concentration gradient (from low to high concentration) using carrier proteins and ATP

25
Q

How do molecules move across a membrane via active transport?

A
  • molecule/ion binds to receptors in carrier protein’s channel
  • on inside of cell, ATP binds to carrier protein and is hydrolysed into ADP and a phosphate
  • binding of phosphate to protein causes protein to change shape (opening up way into inside of cell)
  • molecule is released into inside of cell
  • phosphate molecule is released and rejoins ADP to make ATP
  • carrier protein goes back to original shape
26
Q

What is endocytosis?

A

the bulk transport of material into a cell

27
Q

What is exocytosis?

A

the bulk transport of materials out of a cell

28
Q

What is osmosis?

A

movement of water across a partially-permeable membrane down a water potential gradient (from a more dilute solution to a more concentrated one)

29
Q

What is an isotonic solution?

A

solution with the same water potential as the cell

30
Q

What is a hypotonic solution?

A

solution with higher water potential than cell

31
Q

What is a hypertonic solution?

A

solution with lower water potential than cell

32
Q

What happens to an animal cell in an isotonic solution?

A
  • water potential is equal inside and outside the cell
  • water enters and leaves cell at equal rate
  • equilibrium
  • cell doesn’t change
33
Q

What happens to an animal cell in a hypotonic solution?

A
  • higher water potential outside cell
  • water enters cell
  • cell swells and bursts
  • lysis
34
Q

What happens to an animal cell in a hypertonic solution?

A
  • lower water potential outside cell
  • water leaves cell
  • cell shrinks
  • crenation
35
Q

What happens to a plant cell in an isotonic solution?

A
  • water potential is equal inside and outside the cell
  • water enters and leaves cell at equal rate
  • equilibrium
  • cell doesn’t change
36
Q

What happens to a plant cell in a hypotonic solution?

A
  • higher water potential outside cell
  • water enters cell
  • cell swells and becomes turgid (increased turgor pressure against cell walls)
37
Q

What happens to a plant cell in a hypertonic solution?

A
  • lower water potential outside cell
  • water leaves cell
  • cell becomes flaccid
  • cytoplasm pulls away from cell wall (plasmolysis)
  • contents of cell shrink

Alevel Biology OCR (26 decks)

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