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AS/A-Level Biology > BM: Carbohydrates COPY > Flashcards

BM: Carbohydrates COPY Flashcards

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1
Q

Why is life based on carbon?

A

Carbon readily forms bonds with other carbons.

This allows sequences of carbon to build up, forming ‘backbones’ upon which other molecules can attach.

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2
Q

Carbon-containing molecules are known as what?

A

Organic molecules.

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3
Q

What is a monomer?

A

A small, basic molecular unit.

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4
Q

A small, basic molecular unit, is also known as what?

A

A monomer.

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5
Q

Give examples of monomers?

A

Monosaccharides, amino acids and nucleotides.

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6
Q

Monosaccharides, amino acids and nucleotides are all examples of what?

A

Monomers.

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7
Q

What do all organisms on Earth contain?

A

A few carbon-based compounds that interact in similar ways.

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8
Q

What are polymers?

A

Large, complex molecules composed of long chains of monomers joined together.

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9
Q

What elements do all carbohydrates contain?

A

C, H and O.

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10
Q

What monomers are carbohydrates composed of?

A

Monosaccharides.

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11
Q

Give general properties of monosaccharides:

A
  • Sweet- tasting
  • Soluble
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12
Q

What is the general formula of monosaccharides?

A

‘n’ can be any number from 3 to 7.

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13
Q

Give examples of monosaccharides:

A

Glucose, fructose and galactose.

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14
Q

What is glucose?

A

A hexose sugar.

A monosaccharide with six carbon atoms in each molecule.

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15
Q

What are the two types of glucose?

A

Alpha - α

Beta - β

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16
Q

What are isomers?

A

Molecules with the same molecular formula as each other, but with atoms connected in different ways.

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17
Q

α - glucose and β - glucose are examples of what?

A

Glucose isomers.

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18
Q

Draw the structure of α - glucose:

A
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19
Q

Draw the structure of β - glucose:

A
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20
Q

What is a condensation reaction?

A

When two molecules join together with the formation of a new chemical bond and the release of a water molecule.

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21
Q

What is released when a glycosidic bond is formed?

A

A molecule of water.

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22
Q

How are monosaccharides joined?

A

Through condensation reactions.

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23
Q

What type of bond joins monosaccharides?

A

A glycosidic bond.

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24
Q

Give examples of disaccharides:

A
  • Maltose
  • Sucrose
  • Lactose
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25
Q

How is the disaccharide maltose formed?

A

Two α - glucose molecules joined together via a condensation reaction.

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26
Q

How is a the disaccharide sucrose formed?

A

Via a condensation reaction between a glucose molecule and a fructose molecule.

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27
Q

How is the disaccharide lactose formed?

A

Via a condensation reaction between a glucose molecule and a galactose molecule.

28
Q

How can polymers be broken down into monomers?

A

Through hydrolysis reactions.

29
Q

What is a hydrolysis reaction?

A

A reaction that breaks the chemical bond between monomers using a water molecule.

30
Q

What is the general term for monosaccharides and disaccharides?

A

Sugars.

31
Q

How can all sugars be classified?

A

As either:

Reducing

or

Non-reducing

32
Q

Reducing sugars are what?

A

All monosaccharides and some disaccharides.

33
Q

All monosaccharides and some disaccharides are…

A

… reducing sugars.

34
Q

What is reduction?

What does this mean a reducing sugar is?

A

Reduction is a chemical reaction involving the gain of electrons or hydrogen.

A reducing sugar is therefore a sugar that can donate electrons to another chemical, eg Benedict’s reagent.

35
Q

What is the test for reducing sugars?

A

The Benedict’s test.

36
Q

Describe the Benedict’s test for reducing sugars:

A
  • Add Benedict’s reagent to the sample - ensure it is in excess.
  • Heat it in a water bath that’s been brought to the boil.
  • If the test’s positive a coloured precipitate will form:
    • Blue - green - yellow - orange - red, depending on concentration of reducing sugar.
37
Q

Draw a table of results for the reducing sugars test:

A

The higher the concentration of the reducing sugar, the further the colour change goes.

38
Q

How would you get more accurate results in the reducing sugars test?

A

Filter the solution and weigh the precipitate.

39
Q

How do you test for non-reducing sugars?

Eg, sucrose

A
  • Break them down into monosaccharides
    • Get a sample of the test solution
    • Add dilute hydrochloric acid
    • Carefully heat in a water bath that’s been brought to the boil
    • Neutralise this with sodium hydrogencarbonate.
  • Then, carry out the test for reducing sugars/Benedict’s test.
40
Q

What is a positive result in the non-reducing sugars test?

A

A coloured precipitate will form - as with the reducing sugars test.

If the test’s negative, the solution will stay blue, which means the sample does not contain any sugar (either reducing or non-reducing).

41
Q

What type of data does the Benedict’s test produce?

A

Semi-quantitative, so an approximate estimate of reducing sugar in the sample can be made.

42
Q

Name three polysaccharides:

A

Starch, glycogen and cellulose.

43
Q

What is starch?

A

A polysaccharide.

It is the main storage material in plants.

44
Q

Where do plants get their energy from?

When they have excess of this, what do they do?

A

Get energy from glucose.

They store excess glucose as starch, which can be broken down when needed.

45
Q

What is starch a made of?

A

Two polysaccharides of alpha-glucose.

Amylose and amylopectin.

46
Q

What is amylose?

A

A long, unbranched chain of alpha-glucose.

47
Q

Describe the shape of amylose and explain how this relates to its function:

A
  • Coiled structure (due to the angles of the glycosidic bond).
  • This makes it compact, so it is great for storage because you can fit a lot of it in a tight space.
48
Q

What is amylopectin?

A

A long, branched chain of alpha-glucose.

49
Q

Describe the shape of amylopectin and explain how this relates to its function:

A
  • It has lots of side branches.
  • These many side branches can all be acted on by enzymes simultaneously, meaning starch can be broken down for quick energy release.
50
Q

Describe how the structure of starch makes it adapted to its function:

A
  • Insoluble in water, so does not affect the water potential or cause cells to swell via osmosis.
  • Large and insoluble so doesn’t diffuse out of cells.
  • Compact (amylose) so lots can be stored in one place.
  • When hydrolysed it forms alpha glucose, which is easily transported and readily used in respiration to make energy
  • The branched form means it has many ends, which can be acted on enzymes simultaneously meaning glucose monomers are released rapidly
51
Q

What is glycogen?

A

The main energy storage material in animals.

52
Q

What is the test for starch?

A

Iodine test.

53
Q

Describe how you would perform the iodine test for starch:

A
  • Add iodine dissolved in potassium iodide solution to the test sample.
  • Shake or stir.
54
Q

What would a positive result be in the iodine test for starch?

A

When starch is present, the sample changes colour from browny-orange to a dark, blue-black colour.

55
Q

Describe the structure of glycogen:

A

Alpha-glucose molecules joined by glycosidic bonds.

Very similar to amylopectin, however it is even more highly branched .

56
Q

Where do animals get their energy from?

How do they store this when they have excess?

A

They get their energy from glucose.

When they have excess, they store it as glycogen.

57
Q

Draw starch:

A
58
Q

Draw glycogen:

A
59
Q

How does the structure of glycogen mean it is adapted to its function?

A
  • More highly branched than starch and has more ends that can be simultaneously acted on by enzymes
    • So more rapidly broken down to form glucose monomers, that can be used in respiration.
    • Important for animals which have higher metabolic and respiratory rates than plants, because they are more active.
  • Insoluble and so tends not to draw water into cells by osmosis.
  • Does not diffuse out of cells, and so is ideal for storage, as it is insoluble.
  • Compact, so a lot can be stored in a small place.
60
Q

What is cellulose?

A

The major component of cell walls in plants.

61
Q

What is cellulose made of?

A

Long, unbranched chains of beta-glucose.

62
Q

What forms when beta-glucose molecules bond?

A

Straight cellulose chains.

These run parallel to each other, allowing hydrogen bonds to form cross-linkages between adjacent chains.

These are known as microfibrils.

63
Q

What are microfibrils?

A

Parallel chains of beta-glucose, joind via hydrogen bonds.

They group together to form fibres.

64
Q

Draw cellulose:

A
65
Q

What is the function of glycogen?

A

It is the stored version of glucose, which is used in animals to facilitate respiration.

66
Q

What is the role of cellulose?

A
  • Cellulose adds structure and rigidity to plants.
  • Prevents plants cells from bursting as water enters via osmosis.
    • It does this by exerting an inward pressure that stops any more water from entering
    • So, living plant cells are turgid and push against each other
    • This is important in making stems and leaves turgid, so that they provide the maximum surface area for photosynthesis.
  • It can only be broken down by enzymes produced by certain bacteria or fungi
    • So, only certain animals, like termites or cows (which harbour this bacteria in their gastrointestinal tracts) can digest and utilize cellulose as an energy source.
67
Q

How does the structure of celluose relate to its function?

A
  • Made of β-glucose so form long, straight, unbranched chains
  • Chains run parallel to each other and are cross-linked by hydrogen bonds which add collective strength
  • Molecules are grouped to form microfibrils, which are then grouped to form fibres, which provide even more strength.

AS/A-Level Biology (190 decks)

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