Carbohydrates

Question 1

What is the general formula of a monosachharide

Answer 1

(CH2O)n - where n can be any number between three and seven (3,4,5,6,7)

Question 2

What type of substance is a monosaccharide

Answer 2

A sweet tasting, soluble sugar that cannot be broken down further by hydrolysis as it is already in its simplest sugar form.

Question 3

Which two monosaccharides combine to make maltose

Answer 3

Glucose + Glucose

Question 4

What disaccharide is made of two glucose monosaccharides

Answer 4

Maltose

Question 5

Which two monosaccharides combine to form sucrose

Answer 5

Glucose + fructose

Question 6

What disaccharide is formed when glucose and fructose combine

Answer 6

Sucrose

Question 7

Which two monosaccharides combine to form lactose

Answer 7

Glucose + galactose

Question 8

What disaccharide is formed when glucose and galactose combine

Answer 8

Lactose

Question 9

What reaction breaks down a disaccharide into its constituent monosachharides

Answer 9

Hydrolysis

Question 10

What type of reaction is it when two monosaccharides combine to form a disaccharide

Answer 10

Condensation reaction

Question 11

Define monosachharide

Answer 11

A single saccharide/sugar monomer. They are not decomposable to simpler sugars by hydrolysis as they are already in their simplest form

Question 12

Define polysaccharide

Answer 12

Polymers consisting of many monosacharide monomers/subunits that are joined by glycosidic bonds formed in a condensation reaction

Question 13

What are three key properties of polysaccharides

Answer 13

1) they are insoluble
2) they are large,compact molecules
3) when hydrolysed, they break down into disaccharides or monosaccharides.

Question 14

Which organisms store glucose as starch

Answer 14

Plants

Question 15

Why can glucose not be stored as a monosaccharide

Answer 15

Glucose is extremely soluble in water. This means it affects the cells water potential. If a cell contains a high amount of dissolved glucose, this would cause water to move into the cell via osmosis and this could cause the cell to burst.

Question 16

Describe why glucose is soluble in water

Answer 16

Glucose contains a large amount of hydroxyl groups which are polar due to the small negative charge on the oxygen atom and the small positive charge on the hydrogen atom. This means that the hydroxyl groups form hydrogen bonds with water and this makes glucose extremely soluble in water.

Question 17

Describe the structure of starch

Answer 17

Starch is made up of chains of a-glucose monosaccharides.
The chains are branched and unbranched and the unbranched chains allow starch to be wound into a tight coil that’s makes the molecule very compact.
The OH groups point inwards and form the hydrogen bonds that hold the helix in place.

Question 18

Describe how the structure of starch is suited to its function

Answer 18

• It is insoluble and therefore does not affect the cells water potential.
• It is large and insoluble so it doesn’t diffuse out of cells.
• It is compact, so a lot of it can be stored in a small space.
• When hydrolysed it forms a-glucose, which is both easily transported and readily used in respiration.
• The branched chains have many ends, each of which can be acted on simultaneously by enzymes which means glucose monomers are easily released.

Question 19

Describe the structure of glycogen

Answer 19

• Glycogen is made of a-glucose monomers and is highly branched (more so than starch).
• It also forms an a-helix shape (like starch) which is held together by hydrogen bonds and this makes it compact.

Question 20

Describe how the structure of glycogen is suited to its function

Answer 20

• It is insoluble and therefore does not affect a cells water potential.
• It is large and insoluble so it does not diffuse out of cells.
• It is compact- a lot of it can be stored in a small space.
• It is highly branched so has more ends that can be acted on simultaneously by enzymes which means it is very rapidly broken down to form glucose monomers,which are used in respiration.

Question 21

Which organisms store glucose as glycogen

Answer 21

Animals

Question 22

Why is glycogen more highly branched than starch

Answer 22

Glycogen is found in animals whereas starch is found in plants. Animals have a higher metabolic rate than plants and this includes respiratory rate so more rapidly need glucose. Glucose can be released more rapidly from glycogen due to it being more highly branched meaning enzymes can work on more ends simultaneously.

Question 23

What is the main difference in structure between cellulose and starch/glycogen

Answer 23

Cellulose consists of b-glucose monomers whereas glycogen and starch are made of a-glucose monomers.

Question 24

Describe the structure of cellulose

Answer 24

Cellulose has straight, unbranched chains of b-glucose.
The chains run parallel to each other which allows hydrogen bonds to form cross-linkages between adjacent chains.
The hydrogen bonds add collective strength to the molecule.
The cellulose molecules are grouped together to form microfibrils which in turn are arranged into groups called fibres. This structure gives cellulose a high tensile strength.

Question 25

How is cellulose adapted/used in plant cell walls

Answer 25

Cellulose provides rigidity to the plant cell. It applies an inward pressure which stops the plant cell from bursting as water enters it via osmosis. Living plant cells are turgid and push against one another which makes the non-woody parts a of the cells semi-rigid.

Question 26

What is the difference between how the glucose monomers are joined in cellulose and starch

Answer 26

The cellulose, unlike starch, has adjacent molecules rotated by 180 degrees.