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AS AQA BIOLOGY > Transport across cell membranes > Flashcards

Transport across cell membranes Flashcards

1
Q

What is the cell surface membrane made up from?

A

Phospholipids

Proteins

Cholesterol

Glycolipids

Glycoproteins

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2
Q

How does a phospholipid bilayer form?

A

Hydrophilic phosphate heads
point to the outside of the cell surface membrane
Attracted to water either side

Hydrophobic fatty acid tails
point Into the centre of the cell membrane
Repealed by water either side

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3
Q

What is the function of the phospholipid bilayer?

A

Allow lipid soluble substances to move through the cell membrane

Prevent water soluble substances moving through the cell membrane

Make the membrane flexible and self sealing

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4
Q

What is the function of a protein that DOESN’T extend across the bilayer?

A

Give mechanical support to the membrane

Act as cell receptors
For cell identification
For hormones

Help cells adhere together

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5
Q

What is the function of a protein that DOES extend across the bilayer?

A

Act as channels for water soluble substances

Allow active transport across the membrane

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6
Q

Describe the properties of cholesterol

A

Occur within the phospholipid bilayer

Very hydrophobic

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7
Q

What is the function of cholesterol in the bilayer?

A

Reduce movement of phospholipids /
Make the membrane less fluid at high temperatures

By pulling the fatty acid tails together

Prevent leakage of water and dissolved ions from the cell

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8
Q

What is a glycolipid?

A

A carbohydrate covalently bonded to a lipid

Extends from the bilayer

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9
Q

What is the function of glycolipids in the bilayer?

A

Recognition sites

Maintain membrane stability

Help cells to adhere
To form tissues

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10
Q

What is a glycoprotein?

A

Carbohydrate chains attached to extrinsic proteins

On the outer cell surface of the membrane

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11
Q

What is the function of glycoproteins in the cell membrane?

A

Cell recognition sites

Hormone and neurotransmitter receptors

Help cells adhere
To form tissues

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12
Q

What is the function of membranes WITHIN a cell?

A

Control movement into and out of discrete organelles

Separate organelles from the cytoplasm
So metabolic reactions occur in the organelle

Provide an internal transport system

Isolate enzymes that may damage the cell

Provide surfaces for reactions to occur

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13
Q

What molecules CANNOT diffuse across the cell surface membrane?

A

Non lipid soluble molecules

Large molecules

Charged ions (same as the protein channel)

Polar molecules

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14
Q

Define the term fluid mosaic

A

Fluid: individual phospholipid molecules are not bonded and can move relative to one another
Giving the membrane a flexible structure constantly changing shape

Mosaic: proteins embedded in the bilayer vary in shape size and pattern
Like that of mosaic tiles

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15
Q

Define diffusion

A

The net movement of particles or ions

From a region of high concentration

To a region of lower concentration

Until even distribution is reached

Down a concentration gradient

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16
Q

Define facilitated diffusion

A 
The net movement of particles or ions
From a region of high concentration 
To a region of lower concentration
Until even distribution is reached
Down a concentration gradient

Using protein channels or carrier proteins

17
Q

Describe how a protein channel functions

A

Opens in the presence of a specific ion
Ions bind to the protein
Causing a change in shape of the protein
That causes one side to open and the other side to close
Allowing passage

18
Q

Describe how a carrier protein functions

A

Specific (large) molecules bind to the protein
Causing a change in the proteins shape
Realising the molecule into the membrane

19
Q

Name three factors affecting the rate of diffusion

A

Concentration gradient

Area over which diffusion is occurring

Thickness of exchange surface

Temperature

20
Q

Define passive

A

No ATP from respiration is used

Only the inbuilt kinetic energy of the molecules themselves

21
Q

Define osmosis

A

The net movement of water molecules

From a region of high water potential

To a region of lower water potential

Through a partially permeable membrane

22
Q

What factor lowers water potential?

A

Addition of solutes

23
Q

Describe the effects of a higher water potential outside of animal cell

A

Water enters the cell by osmosis

The cell swells and eventually bursts

Releasing the contents of the cell

By breaking the bilayer

(Haemolysed in rbc only)

24
Q

Describe the effects of a lower water potential outside of animal cell

A

Water exits the cell by osmosis

Causing the cell to shrink and shrivel

(Gives rbc a darker appearance
Due to concentrated Hb)

Making the cell plasmolysed

25
Q

Describe the effects of a lower water potential outside of plant cell

A

Water exits the cell by osmosis

Causing the protoplast to shrink

And pull away from the cell wall

Making the cell plasmolysed

26
Q

Describe the effects of a higher water potential outside of animal cell

A

Water enters the cell by osmosis

Causing the protoplast to swell

And push against the cell wall

Making the cell turgid

27
Q

Why don’t plant cells burst when surrounded by a higher water potential?

A

The cell wall keeps the protoplast from bursting

28
Q

Define active transport

A

The net movement of molecules or ions

Into or out of a cell

From a region of low concentration

To a region of higher concentration

Using ATP and carrier proteins

29
Q

How is ATP used in active transport?

A

Directly moves molecules

Individually moves molecules using a concentration gradient set up by active transport
Co-transport

30
Q

How does active transport differ from passive forms of transport?

A

ATP is needed

Substances move against the concentration gradient

Carrier protein molecules act as pumps

It’s a selective process

31
Q

Describe direct active transport

A

Molecule or ion binds to the carrier proteins receptor sites

ATP binds to the protein
Causing it to split into ADP and a phosphate
Causing the protein to change shape

Releasing the molecule in the otherwise of the membrane
Releasing the phosphate molecule
-Reverting the protein to its original shape

32
Q

Describe co-transport of sodium and potassium

A

Na+ is actively transported out of the epithelial cell into the the blood by the NaK pump

While K+ is actively transported into the epithelial cell from the blood

Maintaining a high concentration of Na+ in the lumen

Na+ ions (facilitated) diffuse from the lumen into the epithelial cell
Carrying amino acids or glucose

Glucose/Amino acids (facilitated) diffuse into the blood

AS AQA BIOLOGY (8 decks)

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