Module 1 - Carbohydrates

Question 1

What is a carbohydrate

Answer 1

A carbohydrate is an organic molecule made of hydrogen, oxygen and carbon

Question 2

What is a monosaccharide

Answer 2

A monosaccharide is an organic monomer that cannot be hydrolysed to a simpler sugar

Question 3

What is a polysaccharide. Give 3 examples

Answer 3

A polysaccharide is a large chain of monosaccharides chemically bonded together joined by glyosidic bonds.
Cellulose, starch and glycogen

Question 4

Give examples of hexose monosaccharides

Answer 4

Glucose, fructose and galactose

Question 5

Give 4 ways in which glucose is important

Answer 5

For respiration, building larger carbohydrates, it is small so easily transported through cells and soluble so easily transported around organisms.

Question 6

What are the 2 isomers of glucose

Answer 6

Alpha and beta glucose

Question 7

What is a ribose and define the structure

Answer 7

Ribose is a pentose sugar made of 5 carbons and is founds in RNA and ATP which provides energy.

Question 8

What is a disaccharide

Answer 8

A disaccharide is 2 monosaccharides chemically joined together in a condensation reaction in the presence of water

Question 9

Give 3 disaccharides and how they are formed.

Answer 9

Alpha glucose + alpha glucose = Maltose
Alpha glucose + fructose = sucrose
Alpha glucose + galactose = Lactose

Question 10

What is a glyosidic bond

Answer 10

A covalent bond formed between 2 monosaccharides by a condensation reaction.

Question 11

How does alpha - glucose differ from beta - glucose

Answer 11

Alpha - glucose has a H (top) and OH (bottom) atom branching from carbon 1. In Beta - glucose, the H and OH atoms are switched at carbon 1.

Question 12

What 4 properties do polysaccharides of alpha-glucose have.

Answer 12

They are compact so can be stored in a small space. They are insoluble so do not affect the water potential of a cell. Easily hydrolysed (readily accessible energy) and they are a large molecule so cannot diffuse out of a cell.

Question 13

Where is starch found

Answer 13

Starch is found in photosynthesising cells in leaves and storage cells.

Question 14

What are the 2 different polysaccharides starch contains

Answer 14

Amylose and amylopectin

Question 15

Define the structure of both polysaccharides in starch

Answer 15

Amylose - a long chain of alpha-glucose molecules joined by 1,4 glycosidic bonds which coils up into a helix shape making them compact.
Amylopectin - a chain of alpha-glucose with 1,4 and occasional 1,6 glycosidic bonds.

Question 16

Between Amylose and Amylopectin, which is quicker to break down? why?

Answer 16

Amylopectin because it has more than 2 accessible ends for enzymes to attach to and break down. This means that it is quicker for hydrolysis to occur.

Question 17

Describe the structure of glycogen and where it is found

Answer 17

Glycogen has a similar structure to the polysaccharide Amylopectin however the 1,6 glycosidic bonds are more frequent. They are found in animal cells with high metabolic rate

Question 18

How and where is glycogen stored

Answer 18

Glycogen is stored as small granules in the liver and muscle

Question 19

Describe an important property that glycogen has

Answer 19

Glycogen is less dense and more soluble than starch. This allows it to break down more rapidly thus indicating the high metabolic requirements needed in animals compared to plants.

Question 20

What is cellulose and how is it different from the other 2 polysaccharides

Answer 20

Cellulose is another polysaccharide useful for the overall structure of a plant. This is different from starch and glycogen as they are more important for being energy stores. Also consists of beta-glucose molecules.

Question 21

What does turgidity means and how is this significant in plants

Answer 21

Turgidity means when enough strength is being provide to each cell in order for the structure of the plant to remain upright. In cells walls there is cellulose which supports cells with helping plants maintain their shape.

Question 22

What is cellulose made from

Answer 22

Cellulose is made form thousands of beta-glucose molecules held together by 1,4 glycosidic bonds. To be able to form these 1,4 glycosidic bonds, each molecule must be inverted 180 degress from the previous molecule

Question 23

How does each beta-glucose molecule being inverted 180 degrees from the previous molecule support the structure of cellulose.

Answer 23

It allows the chains of beta-glucose molecules to be straight and not coil up. This therefore allows chains to be parallel meaning hydroxyl groups will be in close proximity forming hydrogen bonds.

Question 24

What is the significance of hydroxyl groups forming hydrogen bonds between each cellulose chain?

Answer 24

It allows cellulose to be very strong.

Question 25

What do many cellulose chains form and what do these do to make plants very strong?

Answer 25

Many cellulose chains come together forming Microfibrils and then these wrap around plant cells in multiple layers at different angles making it strong

Question 26

Why can animals not digest Cellulose

Answer 26

Animals do not contain the cellulose enzyme - cellulase - in order to hydrolyse the very strong cellulose.

Question 27

Describe the reducing sugars benedict’s test. Say the possible results that could be concluded.

Answer 27

Reducing sugars are monosaccharides and some disaccharides.
First add a food solution to a test tube and add the same volume of benedict’s solution to the test tube. Then place it on a warm bath for 5 minutes and record results. Blue is negative, Green is very low concentration, yellow is low, orange is high and brick-red is very high.

Question 28

Benedict’s solution is chemically known as copper (ii) sulphate solution. What happens to the copper ions that creates an orange-red precipitate.

Answer 28

The copper 2+ ions reduce to form copper+ ions.

Question 29

Describe the non-reducing sugar test

Answer 29

If the reducing sugar test was negative, then a blue precipitate will form. So we add a clean food solution sample to a clean test tube and add hydrochloric acid to hydrolyse the disaccharide then place on a warm bath for 3 - 5 minutes. Then add some sodium hydrogen carbonate to neutralise the solution and place in hot bath for 5 minutes again. Repeat benedict’s test and if colour changes then a non-reducing sugar is present.

Question 30

What are reducing sugars and give examples:

Answer 30

Reducing sugars can donate electrons. Examples include glucose, fructose and maltose.

Question 31

What are non-reducing sugars and give examples:

Answer 31

Cannot donate electrons therefore cannot be oxidised

Examples include: sucrose.