carbohydrates (p)

Question 1

Carbohydrates contain only the elements

Answer 1

carbon, hydrogen and oxygen

Question 2

Monosaccharides all have the formula …..Name 3 common properties.

Answer 2

(CH2O)n, where n is between 3 and 7. Soluble in waterSweet tastingAble to form crystals

Question 3

The most common & important monosaccharide is It’s formula is

Answer 3

glucose, which is a six-carbon sugar. C6H12O6

Question 4

There are many monosaccharides, with the same chemical formula (C6H12O6), but different structural formulae. Give 2 examples.

Answer 4

These include fructose and galactose.

Question 5

Disaccharides are formed when two monosaccharides are joined together by

Answer 5

a glycosidic bond e.g.two glucose molecules joining together to form the disaccharide maltose.

Question 6

Disaccharides are formed when two monosaccharides are joined together by ……………….. reaction involves the formation of what

Answer 6

a molecule of water (H2O).This kind of reaction, where water is formed, is called a condensation reaction

Question 7

Why is it is called a 1-4 glycosidic bond.

Answer 7

Because this bond is between carbon 1 of one molecule and carbon 4 of the other molecule

Question 8

When bonds are broken by the addition of water (e.g. in digestion), is called a

Answer 8

hydrolysis reaction

Question 9

polymerisation reactions are ___________ reactions whilstbreakdown reactions are ___________ reactions

Answer 9

condensationhydrolysis

Question 10

what are the three common disaccharides:

Answer 10

maltose sucrose lactose

Question 11

what is maltose

Answer 11

(or malt sugar) is glucose & glucose. It is formed on digestion of starch by amylase, because this enzyme breaks starch down into two-glucose units. Brewing beer starts with malt, which is a maltose solution made from germinated barley.

Question 12

what is sucrose

Answer 12

(or cane sugar) is glucose & fructose. It is common in plants because it is less reactive than glucose, and it is their main transport sugar. It’s the common table sugar that you put in tea.

Question 13

what is lactose

Answer 13

(or milk sugar) is galactose & glucose. It is found only in mammalian milk, and is the main source of energy for infant mammals

Question 14

Polysaccharides are long ________ of many _________ joined together by ____________

Answer 14

chains monosacharidesglycosidic bonds

Question 15

There are three important polysaccharides

Answer 15

STARCHGLYCOGENCELLULOSE

Question 16

Describe starch - 5 facts

Answer 16

is the plant storage polysaccharideinsoluble forms starch granules inside many plant cellsbeing insoluble means starch does not change the water potential of cells, so does not cause the cells to take up water by osmosis (more on osmosis later). Stored in chlorplasts and in starch grains.Starch can be broken down to glucose molecules that can be respired to release energy for ATP.

Question 17

Starch is not a pure substance but is a mixture of (2)

Answer 17

amylose and amylopectin

Question 18

Amylose is simply _________, so is a straight chain.

Answer 18

poly-(1-4) glucose In fact the chain is floppy, and it tends to coil up into a helix.

Question 19

Amylopectin is poly(1-4) glucose with about 4% ___________

Answer 19

(1-6) branches.This gives it a more open molecular structure than amylose. Because it has more ends, it can be broken more quickly than amylose by amylase enzymes.

Question 20

Both amylose and amylopectin are broken down by the enzyme __________ into __________, though at different rates.

Answer 20

amylasemaltose

Question 21

Describe glycogen (5)

Answer 21

It is made by animals as their storage polysaccharide is found mainly in muscle and liver. *Because it is so highly branched, it can be mobilised (broken down to glucose for energy) very quickly. *Glycogen is similar in structure to amylopectin. *It is poly (1-4) glucose with 9% (1-6) branches.

Question 22

Describe cellulose (5)

Answer 22

Cellulose is only found in plantswhere it is the main component of cell walls. *It is poly (1-4) glucose, but with a different isomer of glucose. *Cellulose contains beta-glucose, in which the hydroxyl group on carbon 1 sticks up. *This means that in a chain alternate glucose molecules are inverted.

Question 23

Can the beta-glycosidic bond of cellulose be broken down by amylase?

Answer 23

No. It requires a specific cellulase enzyme. The only organisms that possess a cellulase enzyme are bacteria, so herbivorous animals, like cows and termites whose diet is mainly cellulose, have mutualistic bacteria in their guts so that they can digest cellulose. Humans cannot digest cellulose, and it is referred to as fibre.

Question 24

What is the basic general formula for any carbohydrate?

Answer 24

(CH2O)n

Question 25

Name 3 properties of monosaccharides

Answer 25

*sweet *polar*crystallisable

Question 26

Give an example of a triose i.e. 3 C's

Answer 26

Glyceraldehyde

Question 27

Give an example of a pentose i.e 5 C's

Answer 27

Ribose or deoxyribose

Question 28

What is the test for a reducing sugar?

Answer 28

Benedicts solution and heat turning the solution brick red

Question 29

What is the test for a non-reducing sugar?

Answer 29

*Don't react with Benedicts solution. Negative. No colour change. So make sure there are no reducing sugars, then boil with HCl

Question 30

What are carbohydrates important for (3) ?

Answer 30

StorageStructureRespiration

Question 31

Why is starch well adapted to its function? (4)

Answer 31

*compact*insoluble*has no osmotic effect*easily hydrolysed

Question 32

Describe how you would test a sample of food for the presence of starch.

Answer 32

1. Add iodine/potassium iodide solution to the food sample;2. Blue/black/purple indicates starch is present;

Question 33

The concentration of glucose in the blood rises after eating a meal containing carbohydrates.The rise is slower if the carbohydrate is starch rather than sucrose. Explain why.

Answer 33

1. Starch digested to maltose/by amylase2. Maltose digested to glucose/by maltase3. Digestion of sucrose is a single step/only one enzyme/sucrase

Question 34

Sucrose is a disaccharide formed by

Answer 34

condensation of glucose and fructose.

Question 35

Lactose is a disaccharide formed by

Answer 35

condensation of glucose and galactose.

Question 36

Glucose has two forms- chain and ring.There is also alpha glucose and beta glucose. What's the difference?

Answer 36

The only difference with alpha and beta glucose are the positions of the OH group and the H on Carbon 1.(alpha has the OH above and the H below, beta has the H above and the OH below)

Question 37

name 3 monosaccharides 3 disaccharides and 3 polysaccharides

Answer 37

Monosaccharides: fructose, glucose, galactose. Disaccharides: maltose, sucrose, lactose. Polysacchardies: starch, glycogen, cellulose

Question 38

During a condensation reaction between two monosaccharides, what happens?

Answer 38

A molecule of water is released and a glycosidic bond forms between the two monosaccharides.

Question 39

What are maltose sucrose and lactose hydrolysed into?

Answer 39

maltose (glucose and glucose), sucrose (glucose and fructose), lactose ( alpha glucose and galactose)

Question 40

People who are lactose intolerant are not able to produce the enzyme lactase. Explain why these people get diarrhoea when they drink milk containing lactose.

Answer 40

Low / decreased water potential (in gut);Water enters gut / lumen / leaves cells by osmosis;

Question 41

Describe how you could use the Biuret test to distinguish a solution of the enzyme, lactase from a solution of lactose

Answer 41

Add Biuret reagent to both solutionsLactase (an enzyme) will give purple / lilac / mauvebecause it is a proteinLactose ( a reducing sugar) will not give purple / lilac / mauve / will remain blue;

Question 42

Name the monosaccharides of which the following disaccharides are composed. 1. Sucrosemonosaccharides ...................................... and ......................................

Answer 42

Glucose and fructose

Question 43

2. Lactose monosaccharides ...................................... and ......................................

Answer 43

Glucose and galactose

Question 44

Describe how a student would show that reducing sugars were present in a solution.

Answer 44

1. Add Benedict’s2. Heat3. Red/orange/yellow/green (shows reducing sugar present)

Question 45

Sucrose is made of which 2monosaccharides ...................................... and ......................................

Answer 45

Glucose and fructose

Question 46

Lactose is made of which 2 monosaccharides ...................................... and ......................................

Answer 46

Glucose and galactose

Question 47

Name the type of reaction that joins monosaccharides together

Answer 47

Condensation

Question 48

Describe how you would test a sample of food for the presence of starch.

Answer 48

1. Add iodine/potassium iodide solution to the food sample2. Blue/black/purple indicates starch is present

Question 49

The concentration of glucose in the blood rises after eating a meal containing carbohydrates.The rise is slower if the carbohydrate is starch rather than sucrose. Explain why.

Answer 49

Starch digested to maltose/by amylase2. Maltose digested to glucose/by maltase3. Digestion of sucrose is a single step/only one enzyme/sucrase