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AQA A Level Biology > ✅4 - Transport Across Cell Membranes > Flashcards

✅4 - Transport Across Cell Membranes Flashcards

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1
Q

What are plasma membranes?

A

All membranes around and within all cells, with the same basic structure

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2
Q

The cell surface membrane…

A

…surrounds cells and forms the boundary between the cytoplasm and the environment

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3
Q

What do phospholipids form?

A

A bilayer

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4
Q

The heads of phospholipids are…

A

…hydrophilic

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5
Q

The tails of phospholipids are…

A

…hydrophobic

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6
Q

Which way do the phospholipids in the cell membrane point?

A

The heads to the outside, attracted by water and he tails to the inside, repelled by water

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7
Q

What are the functions of the phospholipids in the membrane?

A
  • allow lipid soluble substances to enter and leave the cell
  • prevent water soluble substances entering and leaving the cell
  • make the membrane flexible and self sealing
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8
Q

Where are proteins found in the cell membrane?

A

Interspersed within it

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9
Q

What is the function of proteins which don’t completely extend across the membrane?

A

To give mechanical support to the membrane or, in conjunction with glycolipids, as cell receptors for molecules such as hormones

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10
Q

What is the function of proteins which extend completely across the bilayer?

A

Protein channels - form water filled tubes to allow water soluble ions to diffuse across the membrane.
Carrier proteins - that bind to ions or molecules like glucose and amino acids then change shape to move them across

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11
Q

What are the functions of proteins in the cell membrane?

A
  • provide structural support
  • act as channels transporting water soluble substances
  • allow active transport through carrier proteins
  • form cell surface receptors for identifying cells
  • help cells adhere together
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12
Q

Where is cholesterol found in the cell membrane?

A

In the phospholipid bilayer

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13
Q

What does cholesterol do in the cell membrane?

A

Adds strength, and are very hydrophobic so play an important role in preventing the loss of water and dissolved ions

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14
Q

What are the functions of cholesterol?

A
  • reduce lateral movement of other molecules including phospholipids
  • make membranes less fluid at high temperatures
  • prevent leakage of water and dissolved ions
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15
Q

What are glycolipids made up of?

A

A carbohydrate covalently bonded with a lipid

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16
Q

Where are glycolipids found in the cell membrane?

A

From the phospholipid bilayer extending into the watery environment outside the cell

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17
Q

What are the functions of glycolipids?

A
  • act as recognition sites
  • help maintain the stability of the membrane
  • help cells to attach to one another and so form tissues
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18
Q

What are glycoproteins?

A

Carbohydrate chains attached to many extrinsic proteins on the outer surface of the cell surface membrane

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19
Q

What are the functions of glycoproteins?

A
  • act as recognition sites
  • help cells to attach to one another and so form tissues
  • allows cells to recognise one another, for example lymphocytes can recognise an organism’s own cells
20
Q

What are the functions of membranes within cells regarding entry and exits?

A

They control the entry and exit of materials in discrete organelles such as mitochondria

21
Q

What are the functions of membranes within cells regarding organelles?

A

They separate organelles from cytoplasm so that specific metabolic reactions can take place within them

22
Q

What are the functions of membranes within cells regarding transport?

A

They provide an internal transport system, such as in the endoplasmic reticulum

23
Q

What are the functions of membranes within cells regarding enzymes?

A

They isolate enzymes that might damage the cell, such as lysozymes

24
Q

What are the functions of membranes within cells regarding reactions?

A

They provide surfaces on which reactions can occur eg. protein synthesis using ribosomes on rough endoplasmic reticulum

25
Q

Why would a molecule not be able to move freely across a cell surface membrane?

A
  • if it was not soluble in lipids
  • if it was too large to pass through the channels
  • if it had the same charge as the protein channels and was repelled
  • if it was electrically charged (polar) so couldn’t pass through the non polar hydrophobic tails
26
Q

Why is the fluid mosaic model ‘fluid’?

A

Because the individual phospholipid molecules can move relative to one another. This gives the membrane a flexible structure that is constantly changing shape

27
Q

Why is the fluid mosaic model ‘mosaic’?

A

Because the proteins that are embedded in the phospholipid bilayer vary in shape, size and pattern

28
Q

Why are all particles constantly in motion?

A

Because of the chemical energy that they possess

29
Q

Is there a set pattern by which particles move around?

A

No, it is random

30
Q

Particles are constantly…

A

…bouncing off one another as well as off other objects for example the sides of the vessel in which they are contained

31
Q

What is diffusion?

A

The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed

32
Q

Is simple diffusion passive?

A

Yes, because the energy comes from the natural, inbuilt motion of particles rather than ATP

33
Q

What type of molecules can diffuse through the membrane?

A

Small, non-polar molecules such as oxygen and carbon dioxide

34
Q

Why do charged ions and polar molecules not diffuse easily?

A

Because of the hydrophobic nature of the fatty acid tailed of the phospholipids in the membrane

35
Q

What is osmosis?

A

The passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a selectively permeable membrane

36
Q

Which membranes are selectively permeable?

A

Cell surface membranes and other plasma membranes such as those around organelles. They are selectively permeable because the allow small mol flutes through, but not larger ones

37
Q

The addition of a solute to pure water will…

A

… lower it’s water potential

38
Q

The water potential of a solution must always be…

A

… less than zero

39
Q

The more solute is added, the…

A

…lower the water potential

40
Q

Water will move by osmosis from a region of higher water potential to one of…

A

…lower water potential

41
Q

How can you find the water potential of cells or tissues?

A

Place them in a series of solutions of different water potentials and where there is no net loss or gain of water from the cells or tissues, the water potential inside must be the same as outside

42
Q

What is active transport?

A

The movement of molecules and ions into or out of a cell fro a region of lower concentration to a region of higher concentration using ATP and carrier proteins

43
Q

What is ATP used for in active transport?

A
  • directory moving molecules
  • to individually move molecules using a concentration gradient which has already been set up by active transport, known as co transport.
44
Q

How does active transport differ from passive forms of transport?

A
  • metabolic energy in the form of ATP
  • substrates are moved against a concentration gradient
  • carrier protein molecules which act as ‘pumps’ are involved
  • the process is very selective
45
Q

What is the role of diffusion in absorption?

A

As carbohydrates and proteins are being digested continuously, there is normally a greater concentration of glucose and amino acids in the ileum than the blood, so glucose moves by facilitated diffusion from the ileum to the blood

46
Q

What is the role of active transport in absorption?

A

Glucose and amino acids are drawn into the cell along with sodium ions that have been actively transported by the sodium potassium pump

47
Q

Describe the process of co-transport:

A
  • Na+ actively transported out of epithelial cells by sodium potassium pump into blood.
  • Maintains a much higher concentration of Na+ in intestine than inside epithelial cells
  • Na+ diffuse into epithelial cells down the gradient, and carry glucose and amino acids with them
  • The glucose/amino acids diffuse into the blood by facilitated diffusion

AQA A Level Biology (22 decks)

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