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OCR A level biology > Carbohydrates > Flashcards

Carbohydrates Flashcards

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1
Q

What is the function of carbohydrates?

A

To provide energy. This can be immediately (e.g. glucose) or as stored energy (e.g. glycogen in animals and starch in plants).

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2
Q

What are the 3 broad groups carbohydrates can be split into?

A

Monosaccharides, disaccharides, and polysaccharides

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3
Q

What is the general formula for monosaccharides?

A

Cn(H2O)n

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4
Q

What properties must a substance have to be classed as a sugar?

A
  • Must dissolve in water
  • Must be crystalline
  • Must be sweet to taste
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5
Q

Are all monosaccharides classed as sugars?

A

Yes

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6
Q

What is the general name for monosaccharides containing:

a) 3 carbons
b) 5 carbons
c) 6 carbons

A

a) triose
b) pentose
c) hexose

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7
Q

Give an example of a 3 carbon sugar

A

G3P

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8
Q

How is sucrose formed?

A

A condensation reaction between alpha glucose and fructose

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9
Q

What hydrolyses sucrose?

A

Sucrase

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10
Q

Give 3 examples of disaccharides

A

Maltose, sucrose, and lactose

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11
Q

What kind of bond forms between sugars in a condensation reaction?

A

A glycosidic bond

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12
Q

How is maltose formed?

A

From a condensation reaction between two alpha glucose molecules

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13
Q

What hydrolyses maltose?

A

Maltase

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14
Q

How do two alpha glucose molecules bond to form maltose?

A

There is a reaction between the hydroxyl group of Carbon 1 of one molecule and Carbon 4 of the other molecule (be careful to specify C1 of one molecule and C4 of another)

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15
Q

Is the bond formed in the condensation reaction of alpha glucose above or below the plane of the ring?

A

Below

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16
Q

Give the two functions of polysaccharides

A

1) Energy storage
2) Structure in the form of cellulose in plant cell walls or chitin in insect wings and fungi walls

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17
Q

In what form is energy stored in:

i) plant cells
ii) animal cells

A

i) Starch
ii) Glycogen

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18
Q

Why are polysaccharides not classed as sugars? (3 reasons)

A
  • They do not taste sweet
  • They are not crystalline
  • They do not dissolve in water
19
Q

What are the three physical properties of both starch and glycogen that make them excellent storage molecules?

A
  • They are insoluble in water
  • They form very compact molecules
  • They can be easily hydrolysed to release a glucose
20
Q

(i) How does Starch and glycogen’s insolubility in water make them good storage molecules?
(ii) What would happen if they were soluble in water?

A

(i) They do not dissolve and therefore do not affect the water potential of cells
(ii) They would dissolve and change the water potential of the cell, causing water to move into the cell by osmosis and cause cell damage

21
Q

Why is the ability to form compact molecules favourable for a storage molecule?

A

A lot of the molecules can fit into a small space, meaning more efficient storage

22
Q

Why is it beneficial that starch and glucose can be easily hydrolysed?

A

Easy hydrolysis means that both starch and glycogen can provide a readily available source of glucose for respiration and so provide quick release energy.

23
Q

What reacts to form glycogen?

A

Alpha glucose

24
Q

What type of bonding occurs in glycogen? Why?

A

1,4 and 1,6 glycosidic bonding

  • This allows for branching so each molecule has many ends where glucose can be added
  • This means glycogen is a more compact molecule
  • This means more terminal glucose molecules that can be simultaneously hydrolysed
25
Q

What are the two components of starch?

A

Amylose and Amylopectin

26
Q

i) What happens to the shape of amylose once it has been formed?
ii) What shape does this give it?
iii) What causes this change in shape to occur?

A

i) It coils
ii) Giving a helical shape
iii) Hydrogen bonds form within the coil

27
Q

i) Which molecules make up amylose?
ii) What kind of bonding links these together?
iii) Therefore what kind of molecules is produced?

A

i) Alpha-glucose
ii) 1,4 glycosidic bonds
iii) Linear

28
Q

i) What molecules make up amylopectin?
ii) What kind of bonding is present in amylopectin?
iii) Therefore which molecule is amylopectin similar to?

A

i) Alpha-glucose
ii) 1,4 and 1,6 glycosidic bonds
iii) Glycogen

29
Q

i) How can the presence of starch be tested for?
ii) What is observed if starch is present?
iii) Why does this occur?

A

i) Potassium iodide solution is added
ii) The solution will go from being orange/brown to black/blue
iii) The iodine sits in the coils of the amylose component of starch, this complex appears blue/black

30
Q

Where is cellulose found?

A

In plant cell walls

31
Q

What is the monomeric unit of cellulose?

A

Beta glucose

32
Q

What is the difference between alpha and beta glucose?

A

The OH group on Carbon 1 is above the plane of the ring in beta glucose but below the plane of the ring in alpha glucose

33
Q

i) What bonding is present in cellulose?
ii) What issue arises with this bonding?
iii) Therefore what must happen to allow the bonding to occur?

A

i) 1, 4 glycosidic bonds between beta glucose molecule ii) The hydroxyl groups lie on different planes of the ring iii) Every other beta glucose must be rotated 180 degrees relative to the previous beta glucose

34
Q

What are the monomeric units of sucrose?

A

Alpha glucose and fructose

35
Q

Are all monosaccarides reducing sugars?

A

Yes

36
Q

Are all disaccharides reducing sugars?

A

No, only some are

37
Q

Give an example of a non-reducing sugar

A

Sucrose

38
Q

Give an example of a reducing sugar

A

Maltose or lactose

39
Q

Give an example of a 5 carbon sugar

A

Ribose or deoxyribose

40
Q

Give an example of a 6 carbon sugar

A

Glucose or fructose or galactose

41
Q

What type of reaction is the breakdown of maltose by maltase?

A

Hydrolysis

42
Q

What is produced by the hydrolysis of maltose?

A

Two alpha glucose molecules

43
Q

What is a reducing sugar?

A

Sugars that donate electrons resulting in the reduction of another molecule

OCR A level biology (44 decks)

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