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BIOLOGY OCR > Biological membranes > Flashcards

Biological membranes Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What are the roles of the cell membrane?

A
  1. To act as partially (and sometimes selectively) permeable membranes between:
    a) A cell and its environment
    b) An organelle and the cytoplasm which surrounds it
    c) Within organelles (e.g. mitochondria/chloroplasts)
  2. Sites of chemical reactions — e.g. respiratory enzymes on the inner mitochondrial
    membrane
  3. Sites of cell communication and signalling
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2
Q

Define diffusion

A

The passive, net movement of particles from an area of high concentration to low concentration (down a concentration gradient)

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3
Q

What type of molecules diffuse through cell membranes?

A

Small non-polar molecules e.g. O2 and CO2. Also water as it is small enough to fit between phospholipids despite it being polar

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4
Q

What factors affect the rate of diffusion?

A
  1. Concentration gradient - higher = fast rate of diffusion
  2. Thickness of exchange surface - Thinner = short distance for particles to travel = faster rate of diffusion
  3. Surface area - large S.A = fast rate of diffusion
  4. Temperature - warmer = particles have more kinetic energy = they move faster = fast rate of diffusion
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5
Q

What is facilitated diffusion?

A

The passive net movement of larger molecules down a concentration gradient through carrier or channel proteins.

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6
Q

How do carrier proteins work?

A
  1. Large molecule attaches to a carrier protein in the membrane
  2. Protein changes shape
  3. Releases molecule on the opposite side of the membrane
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7
Q

How do channel proteins work?

A

They form pores in the membrane for charged particles to diffuse through - down the concentration gradient

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8
Q

Define active transport

A

The active movement of particles against a concentration gradient (from low to high concentration) It involves carrier proteins. Requires ATP

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9
Q

Define osmosis

A

The passive net movement of water molecules across a partially permeable membrane down a water potential gradient.

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10
Q

What molecule has the highest water potential?

A

Water

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11
Q

What is a hypotonic solution?

A

A solution with a higher water potential than the cell

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12
Q

What is an isotonic solution?

A

A solution with the same water potential as the cell

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13
Q

What is a hypertonic solution?

A

A solution with a lower water potential than the cell

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14
Q

What happens to animal cells when placed in a hypotonic solution?

A

The water potential is higher outside the cell, so water molecules move in the cell causing it to fill up and burst

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15
Q

What happens to a plant cell when placed in a hypotonic solution?

A

The water potential is higher outside the cell, so water moves in the cell causing the vacuole and cytoplasm to push against the cell wall - the cell becomes turgid

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16
Q

What happens to an animal cell when placed in an isotonic solution?

A

The water potential is equal both in and outside the cell - the cell stays the same

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17
Q

What happens to a plant cell when placed in an isotonic solution?

A

The water potential is equal both in and outside the cell - the cell stays the same

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18
Q

What happens when an animal cell is placed inside a hypertonic solution?

A

Water potential is lower outside the cell, so water moves out of the cell causing it to shrink - crenation

19
Q

What happens when a plant cell is placed in a hypertonic solution?

A

Water potential is lower outside the cell, so water moves out of the cell, it becomes flaccid, the cytoplasm and membrane pull away from the cell wall - plasmolysis

20
Q

Why does endocytosis take place?

A

Because some molecules are too large to be taken in by carrier proteins

21
Q

How does endocytosis work?

A
  1. The cell surrounds the substance with part of its membrane
  2. membrane pinches off to form a vesicle in the cell containing the ingested substance
22
Q

Why do we need exocytosis?

A

Some substances produced by the cell need to be released

23
Q

How does exocytosis work?

A
  1. Vesicles containing the substance pinch off from sacs from the golgi apparatus
  2. this moves towards the membrane
  3. vesicles fuse with the plasma membrane and release the contents outside the cell
24
Q

Which processes are examples of bulk transport?

A

exocytosis

endocytosis

25
Q

Which processes are passive?

A

Diffusion
Facilitated diffusion
osmosis

26
Q

Which processes are active?

A

Active transport

endocytosis and exocytosis (bulk transport)

27
Q

What is cell signalling?

A

Communication between cells

28
Q

How does cell signalling work?

A
  1. A cell releases a messenger molecule
  2. The molecule travels (e.g in blood) to another cell
  3. The messenger molecule is detected by the cell because it binds to a receptor on the cell membrane
29
Q

Give an example of a messenger molecule

A

Hormones

30
Q

What is the structure of a phospholipid?

A

It has a hydrophillic head - attracts water,

and a hydrophobic tail - repels water

31
Q

What is the role of phospholipids in cell membranes?

A

They form a barrier to dissolved substance
They arrange themselves into a bilayer (heads face out, tails face in). Because the centre is hydrophobic it doesn’t let water soluble substances through it

32
Q

What is cholesterol?

A

A type of lipid which fits between phospholipids in the cell membrane

33
Q

What is the role of cholesterol?

A

They bind to tails of phospholipids making them pack more closely together, making the membrane less fluid and more rigid. Gives stability to the membrane

34
Q

How do glycoproteins and glycolipids stabilise the membrane?

A

They form hydrogen bonds with surrounding water molecules.

35
Q

What is the role of glycolipids and glycoproteins?

A
  1. Site where drugs, hormones and antigens bind
  2. Act as receptors for cell signalling
  3. They are antigens - involved in the immune response
36
Q

What happens to membrane permeability below 0°C?

A

Phospholipids have little energy so they can’t move around much. They’re packed closely together and the membrane is rigid. But channel and carrier proteins deform, increasing permeability. Ice crystals may form and pierce the membrane making it highly permeable.

37
Q

What happens to membrane permeability between 0 and 45°C?

A

Phospholipids can move around and aren’t packed as tightly together, the membrane is partially permeable. As temperature increases, phospholipids move more as they have more energy, which increases membrane permeability

38
Q

What happens to membrane permeability above 45°C?

A

Bilayer starts to melt/break down and membrane becomes more permeable. Water inside the cell expands putting pressure on the membrane. Channel and carrier proteins deform so they can’t control what enters and leaves the cell, increasing permeability.

39
Q

How does changing the solvent increase permeability?

A

Surrounding cells in a solvent increases permeability because solvents dissolve lipids in the cell membrane, causing it to lose its structure

40
Q

Give examples of solvents that affect membrane permeability

A

Ethanol

Methanol

41
Q

What is the role of protein in the cell membrane

A

Proteins, which are involved in more complex functions such as carrying out chemical reactions or regulating cross-membrane transport.

42
Q

Why are cell membranes described as a fluid mosaic structure/model?

A

mosaic of components - including phospholipids, cholesterol, proteins, and carbohydrate The ‘Fluid’ part represents how some parts of the membrane can move around freely, if they are not attached to other parts of the cell.

43
Q

What is the endocytosis of liquids called?

A

pinocytosis

44
Q

Give 3 examples of active transport in cells

A

Movement of hydrogen ions out of companion cells
Movement pf salt into root hair cells
Uptake of glucose in the intestines

BIOLOGY OCR (12 decks)

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