Carbohydrates

Question 1

What three elements are in carbohydrates

Answer 1

Carbon, hydrogen and oxygen

Question 2

What are sugars with six carbon atoms called

Answer 2

Hexose sugars

Question 3

Aqa simple glucose molecule

Answer 3

Could be asked to draw it

Question 4

What are monosaccharides

Answer 4

Single sugar molecule

Question 5

Three examples of monosaccharides

Answer 5

Glucose, galactose and fructose

Question 6

Key feature of monosaccharides

Answer 6

Soluble in water- large number of OH groups- hydroxyls groups which can form hydrogen bonds with water molecules- another name for this is hydrophilic- dissolve in water.

Question 7

Molecules with 5 carbon atoms

Answer 7

Pentose monosaccharides

Question 8

Free science lessons structure of ribose

Answer 8

Go on video scroll to end

Question 9

What are isomers

Answer 9

The two forms of glucose

Question 10

What do the numbers represent

Answer 10

Carbon atoms

Question 11

The difference between the glucose isomers

Answer 11

The position of the hydroxyl (OH) group on carbon 1

Question 12

Difference between alpha and beta glucose

Answer 12

-If carbon 1 hydroxyl points below below the ring then we call this isomer alpha glucose.

• If the carbon 1 hydroxyl group points above the ring then we call this isomer beta glucose.

Question 13

How are disaccharides formed

Answer 13

They are formed when two monosaccharides chemically react together

Question 14

What is the disaccharide called when two alpha glucose molecules react

Answer 14

Maltose

Question 15

When we make a disaccharide what do we also produce

Answer 15

A molecule of water- the water molecule is formed from a hydrogen atom from one of the monosaccharides and a hydroxyl group from the other - condensation reaction.

Question 16

What is the bond between monosaccharide molecules when forming a disaccharide

Answer 16

Glycosidic bond - formed between carbon 1 on one alpha glucose and carbon 4 on another= 1,4 glycosidic bond.

Question 17

Free science lessons maltose

Answer 17

Need to know structure

Question 18

What happens if we add water to a disaccharide

Answer 18

Breaks the glycosidic bond- converts the disaccharide back into its monosaccharides- hydrolysis reaction -in cells this reaction is normally carried out by enzymes.

Question 19

The three disaccharides you need to know

Answer 19

maltose= glucose+glucose
Sucrose=glucose+fructose
Lactose=glucose+galactose

Question 20

Is glucose soluble or insoluble in water

Answer 20

Soluble- contains a large number of hydroxyl groups- hydroxyls groups are polar due to the small negative charge on the oxygen atom and the small positive charge on the hydrogen atom- can form hydrogen bonds with water molecules.

Question 21

Problem with glucose being soluble

Answer 21

If a cell contains a large amount of dissolved glucose then this can cause water to move into the cell by osmosis - to solve this problem plant cells store glucose as starch

Question 22

What is starch

Answer 22

A storage form of glucose- find it in starch grains

Question 23

What are the two molecules starch consist of

Answer 23

Amylose and amylopectin

Question 24

Structure of amylose

Answer 24

Polymer of alpha glucose molecules- also joined by 1,4 glycosidic bonds- each bond forms in a condensation reaction, producing a molecule of water. The amylose molecule then twists into a compact helix with hydrogen bonds forming between glucose molecules along the chain -holding it in place.

Question 25

How do cells convert starch back to glucose

Answer 25

When the cell needs glucose, water is used to break the glycosidic bonds- hydrolysis reaction.

Question 26

Why does starch have a helical shape

Answer 26

Makes starch a very compact molecule

Question 27

Structure of amylopectin

Answer 27

Polymer of alpha glucose joined by 1,4 glycosidic bonds. The chains have a branch every 25-30 glucose molecules. The branch is simply another chain of alpha glucose molecules joined by 1,4 glycosidic bonds. Joining the branches is a glycosidic bond between carbon 6 and carbon 1- coil up compact.

Question 28

Is starch soluble or insoluble in water

Answer 28

Insoluble- means starch doesn’t cause water to enter cell by osmosis

Question 29

How is starch broken down

Answer 29

Enzymes used to break down the glycosidic bonds in starch- hydrolysis reaction- requires water- enzymes act at end of molecules- amylopectin has lots of branches- has lots of ends- rapid breakdown.

Question 30

What is the animal glucose storage molecule

Answer 30

Glycogen- found in liver and muscle cells- polymer of alpha glucose- most alpha glucose molecules joined by 1,4 glycosidic bonds, glycogen also contains branches, at the branch points are 1,6 glycosidic bonds. The main difference is that glycogen is more branched than amylopectin- makes it more compact- lots of free ends- rapid breakdown.

Question 31

Why does the breakdown of glycogen need to be quick

Answer 31

Animals have high rate of respiration- energy needs of animals can change rapidly- may have to move quickly to escape from predator.

Question 32

Structure of cellulose

Answer 32

-polymer of BETA glucose, glucose molecules need to be flipped every other to bond between OH.
-Unbranched- also form water
- straight chain with no branches- cellulose molecules can get close to each other.- hydrogen bonds form between neighbouring chains - lots of hydrogen bonds form- makes cellulose extremely strong.

Question 33

What is it called when cellulose chains join together

Answer 33

A microfibril- they then group together to form larger structures called macrofibrils- they then join together to form a cellulose fibre. These cellulose fibres form the plant cell wall-

Question 34

Key feature of cellulose

Answer 34

It’s strength- allows cellulose cell wall to carry out its function
-The cellulose cell wall is also permeable to molecules like water