Carbohydrates

Question 1

What are carbohydrates?

Answer 1

Polymers

Question 2

What are the monomers of carbohydrates called and give some examples?

Answer 2

Monosaccharides.
e.g. typically sugars :
glucose, fructose, galactose

Question 3

How is glucose useful?

Answer 3

Used in cellular respiration to make ATP ; using oxygen alongside.

Question 4

What happens when you combine two monosaccharides give some examples.

Answer 4

You make a disaccharide.
e.g. sucrose, maltose, lactose

Question 5

What is the name for many monosaccharides?

Answer 5

A polysaccharide

Question 6

How are disaccharides formed?

Answer 6

They are formed from two monosaccharides joined together by a glycosidic bond formed by a condensation bond.

Question 7

What are the equations for the 3 known disaccharides?

Answer 7

glucose + glucose —> maltose + water
glucose + galactose —> lactose + water
glucose + fructose —-> sucrose + water

Question 8

What type of glycosidic bonds are disaccharides formed from?

Answer 8

1-4 glycosidic bond ( bond between carbon 1 and carbon 4)

Question 9

What catalyses hydrolysis in the body?

Answer 9

Enzymes

Question 10

During which process are carbohydrates hydrolysed into the body as monomers?

Answer 10

Glycogenolysis - store of glycogen hydrolysed back into glycogen when blood sugar levels drop.
Digestion - when starch is hydrolysed into glucose

Question 11

How are carbohydrates important to an organism, the structure, and function of its cells?

Answer 11

To make cells through cellulose, fungi use it to make cell walls through chitin.

Question 12

What is starch?

Answer 12

Starch is used as an energy store in plant cells. It is a polysaccharide of a - glucose.
Structure : Amylase - 1,4 glycosidic bonds —> unbranched
Amylopectin - 1,4 and 1,6 glycosidic bonds —–> branched.

Question 13

What is glycogen?

Answer 13

Glycogen is used as an energy store in animal cells. It is a polysaccharide made of a-glucose. It has 1,4 and 1,6 - glycosidic bonds —-> branched.

Question 14

How does the structure of starch ( amylase) relate to its function?

Answer 14

Starch ( amylase ) has a helical structure, making it compact for cell storage.
It is a large, insoluble polysaccharide molecule, can’t leave the cell / cross-cell membrane
Insoluble in water, the cell’s water potential is not affected ( no osmotic effect ).

Question 15

How does the structure of glycogen ( and starch amylopectin ) relate to its function?

Answer 15

It is branched, making it compact/ to fit more molecules in a small area.
Branched, more ends for faster hydrolysis - release glucose for respiration to make ATP for energy release.
Large, insoluble polysaccharide molecules, cant leave cell / cross-cell membranes.
Insoluble in water, water potential of cell not affected ( no osmotic effect ).

Question 16

What is cellulose?

Answer 16

Provides strength and structural support to plant/algae cell walls.
It is a polysaccharide of beta-glucose.
1,4 glycosidic bond —> straight, unbranched chains.
Chains are linked in parallel by hydrogen bonds forming microfibrils.

Question 17

How does the structure of cellulose relate to its function?

Answer 17

• Every other beta-glucose molecule is inverted in a long, straight, unbranched chain.
• Many hydrogen bonds link parallel strands ( crosslinks ) to form microfibrils ( strong fibrils).
• Hydrogen bonds are strong in high numbers.
• So provides strength to plant cell walls.

Question 18

Describe the test for reducing sugars.

Answer 18

Reducing sugars = monosaccharides, maltose, lactose
1. Add Benedict solution ( blue ) to the sample.
2. Heat in a boiling water bath.
3. Positive result = green/yellow/orange/red precipitate.

Question 19

Describe the test for non-reducing sugars.

Answer 19

Non-reducing sugars = sucrose.
1. Do Benedict’s test and stays blue/negative.
2. Heat in a boiling water bath with acid ( to hydrolysed into reducing sugars ).
3. Neutralise with alkali ( e.g. sodium bicarbonate ).
4. Heat in a boiling water bath with Benedict’s solution.
5. Positive result =green/yellow/orange/red precipitate.

Question 20

Suggest a method to measure the quantity of sugar in a solution.

Answer 20

• Carry out the Benedict’s test as above, then filter and dry precipiate.
• Find mass/weight.

Question 21

Describe the biochemical test for starch.

Answer 21

Add iodine dissolved in potassium iodide (orange/brown) and shake/stir
Positive result = blue/black.