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Biology OCR A - A-level > Biological Membranes > Flashcards

Biological Membranes Flashcards

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1
Q

Where are plasma membranes located?

A

The surface of cells

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2
Q

What is a plasma membrane?

A

A barrier between the cell and its environment that controls which substances enter and leave

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3
Q

What is a membrane within a cell?

A

A barrier between the organelle and the cytoplasm

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4
Q

What can membranes inside a cell form?

A

Vesicles

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5
Q

What term is used to describe the structure of a membrane?

A

Fluid mosaic

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6
Q

What part of the phospholipid is hydrophilic? What does that mean?

A

The phospholipid head - it attracts water

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7
Q

What part of the phospholipid is hydrophobic? What does that mean?

A

The fatty acid tails - it repels water

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8
Q

What do phospholipids do in a membrane?

A

Act as a barrier to dissolved substances because of its hydrophobic bilayer

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9
Q

What does cholesterol do in membranes?

A

Makes the membrane less fluid and more rigid

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10
Q

What happens to cholesterol and membranes at lower temperatures?

A

Cholesterol prevents the phospholipids from packing close together, increasing fluidity

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11
Q

What do channel proteins do?

A

Allow small or charged particles through

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12
Q

What do carrier proteins do?

A

Transport molecule and ions across the membrane by active transport and facilitated diffusion

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13
Q

How do glycoproteins and glycolipids stabilise the membrane?

A

By forming hydrogen bonds with surrounding water molecules

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14
Q

How do cells communicate with each other?

A

1) Cell releases messenger molecule (hormone)
2) Molecule travels to another cell
3) Messenger detected by cell as it binds to receptor on the cells membrane

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15
Q

What proteins on the cell membrane act as receptors?

A

Membrane bound receptors

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16
Q

What do temperatures above 45°c do to a membrane?

A

Phospholipid bilayer breaks down and proteins denature, making the membrane more permeable.

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17
Q

What do temperatures between 0-45°c do to a membrane?

A

Phospholipids can move around and the membrane is partially permeable

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18
Q

What do temperatures below 0°c do to a membrane?

A

Phospholipids have little energy so cannot move and are packed closely together, making the membrane rigid. Proteins denature, increasing the permeability of the membrane.

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19
Q

What is a solvent?

A

A substance (molecule) with the ability to dissolve other substances (solutes) to form a solution

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20
Q

What do solvents (ethanol) do to a membrane?

A

Increase the permeability because it dissolves the lipids and the membrane loses its structure

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21
Q

What is diffusion?

A

The net movement of particles from an area of high concentration to low concentration

22
Q

What is the concentration gradient? Which way do particles diffuse?

A

Path from an area of high concentration to an area of low concentration. Particles diffuse down the gradient.

23
Q

Why is diffusion a passive process?

A

No energy is needed for it to happen

24
Q

What molecules diffuse through the membrane?

A

Small non-polar molecules like O and CO2

25
Q

What polar molecule can diffuse through plasma membranes and why?

A

Water because it is small enough to diffuse through via osmosis

26
Q

What effect does the concentration gradient have on the rate of diffusion?

A

The higher it is, the faster the rate of diffusion

27
Q

What effect does the thickness of the exchange surface have on the rate of diffusion?

A

The thinner the surface the faster the rate of diffusion

28
Q

What effect does the surface area have on the rate of diffusion?

A

The larger the surface area the faster the rate of diffusion

29
Q

What effect does the temperature have on the rate of diffusion?

A

The warmer it is the faster the rate of diffusion (particles more kinetic energy)

30
Q

What colour is phenolphthalein in alkaline soloutions?

A

Pink

31
Q

What colour is phenolphthalein in acidic soloutions?

A

Pink

32
Q

What are channel proteins?

A

Proteins that form pores (channels) for charged particles to diffuse through via facilitated diffusion

33
Q

What are carrier proteins?

A

Proteins that move large molecules into or out of the cell via active transport

34
Q

What is active transport?

A

Moving molecules and ions across plasma membranes against a concentration gradient using energy (ATP)

35
Q

What are the steps of a carrier protein moving a large molecule?

A

1) Large molecule attaches to carrier protein
2) The protein changes shape
3) The molecule is released on the opposite side of the membrane

36
Q

What is endocytosis?

A

If a molecule is too large for proteins a cell will surround a molecule with a section of its membrane and form a vesicle

37
Q

Does endocytosis use energy?

A

Yes, ATP

38
Q

What is exocytosis?

A

Vesicles containing substances leave the golgi apparatus and fuse with the plasma membrane to release their contents outside the cell

39
Q

Does exocytosis use energy?

A

Yes, ATP

40
Q

What is osmosis?

A

The diffusion of water molecules across a partially permeable membrane down a water potential gradient

41
Q

What is water potential?

A

The likelihood of water molecules to diffuse into or out of a solution

42
Q

What has the highest water potential?

A

Pure water

43
Q

What happens when an animal cell is in a solution with a higher water potential?

A

The cell will bust because net moment of water is into the cell

44
Q

What happens when an animal cell is in a solution with a lower water potential?

A

The cell will shrink because the net movement of water is out of the cell

45
Q

What is a hypotonic solution?

A

A solution with a higher water potential than the cell

46
Q

What is a hypertonic solution?

A

A solution with a lower water potential than the cell

47
Q

What is an isotonic solution?

A

A solution with the same water potential as the cell

48
Q

What happens when an animal cell is in a hypotonic solution?

A

The vacuole swells as net movement of water is into the cell. The cell becomes turgid.

49
Q

What happens when an animal cell is in a hypertonic solution?

A

The cell becomes flaccid as net movement of water is out of the cell. The cell is flaccid. Plasmolysis also occurs.

50
Q

What is plasmolysis?

A

When a plant cell is in a hypertonic solution, the cytoplasm and the membrane pull away from the cell wall.

Biology OCR A - A-level (24 decks)

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