carbohydrates and lipids

Question 1

What is a monomer? 1

Answer 1

Small identical /similar molecules which can be joined together to make LARGER molecules called POLYMERS

Question 2

What is a POLYMER? (2)

Answer 2

A large molecule made from the joining (by chemical bonds) of 3 or more similar or identical monomer molecules.

Formed by condensation reaction.

Question 3

State 3 carbohydrate monomers (Monosaccharides).

Answer 3

Glucose
Fructose
Galactose

Question 4

Name 3 Polysaccharides.

Answer 4

Cellulose
(Formed from BETA glucose monomers)

Starch
(Formed from ALPHA glucose monomers)

Glycogen
(Formed from ALPHA glucose monomers)

Question 5

State 3 biological monomers

Answer 5

Amino acids (all 20 of them)
Monosaccharides (Glucose / Fructose / Galactose)
Nucleotides (DNA or RNA)

Question 6

Name the TWO main types of biochemical reaction.

Answer 6

HYDROLYSIS: The breaking of a chemical bond, using a water molecule. Polymers to Monomers

CONDENSATION: The formation of a chemical bond, releasing a water molecule. Monomers to Polymers.

Question 7

State the elements found in all carbohydrates.

Answer 7

Carbon (C)

Hydrogen (H)

Oxygen (O)

Question 8

What is the ratio of Hydrogen to Oxygen in (Most) monosaccharides,

(True when number of Carbons range between 3 AND 6)

Answer 8

2:1

Question 9

State the chemical formula for glucose isomers.

Answer 9

C6H12O6

Question 10

What is a DIMER?

Answer 10

TWO similar/identical monomers joined together by a chemical bond by condensation reaction.

Question 11

What is a SIX carbon sugar called?

Answer 11

HEXOSE sugar

Question 12

Name the monosaccharides that make MALTOSE

Answer 12

TWO Alpha Glucose molecules

Question 13

Name the monosaccharides that make SUCROSE

Answer 13

Alpha Glucose

AND

Fructose

Question 14

Name the monosaccharides that make LACTOSE

Answer 14

Alpha Glucose

AND

Galactose

Question 15

A starch molecule has a spiral shape.

Explain why this shape is important to its function in cells. (1)

Answer 15

Compact/occupies small space/tightly packed;

Question 16

The structure of cellulose is related to its role in plant cell walls. Explain how. (4)

Answer 16

Long, straight, unbranched chains of Beta glucose;
(Joined by) many WEAK hydrogen bonds;
Form microfibrils / macrofibrils;
Provide rigidity/strength/support;

Question 17

Give one feature of starch and explain how this feature enables it to act as a storage

substance.

Answer 17

Helical / spiral So compact / tightly packed / can fit (lots) into a small space;
Insoluble So no osmotic effect / does not leave cell / does not affect water potential;
Large molecule / long chain (So) does not leave cell / contains large number of glucose units;
Branched chains (So) rapid hydrolysis to remove glucose for respiration;

Question 18

Hydrogen bonds are important in cellulose molecules. Explain why. (3)

Answer 18

Holds chains/cellulose molecules together/forms cross links between chains/cellulose molecules/forms microfibrils;
Providing strength/rigidity (to cellulose/cell wall);
Weak Hydrogen bonds provide strength in large numbers;

Question 19

Describe how the student would show that reducing sugars were present in a solution. (3)

Answer 19

1. Add Benedict’s;
2. Heat to 95°C;
3. Red/orange/yellow/green precipitate (shows reducing sugar present);

Question 20

Describe how you would test a sample of food for the presence of starch. (2)

Answer 20

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

Question 21

Describe how you would test a liquid sample for the presence of lipid and how you would recognise a positive result. (2)

Answer 21

1. (Mix / shake sample) with ethanol, then add water and shake;
2. Cloudy White / milky (emulsion);

Question 22

Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample. (6)

Answer 22

Lipid

1. Add ethanol/alcohol then add water and shake/mix OR Add ethanol/alcohol and shake/mix then pour into/add water;
2. White/milky emulsion OR emulsion test turns white/milky;

Non-reducing sugar

3. Do Benedict’s test and stays blue/negative;
4. Boil with acid then neutralise with alkali;
5. Heat with Benedict’s and becomes red/orange (precipitate);

Amylase

6. Add biuret (reagent) and becomes purple/violet/mauve/lilac;
7. Add starch, (leave for a time), test for reducing sugar/absence of starch;

Question 23

Compare and contrast the structure of starch and the structure of cellulose. (6)

Answer 23

Similarities:

1. Both polysaccharides OR Both are glucose polymers OR Both are made of glucose monomers;
2. Both contain glycosidic bonds (between monomers);
3. Both contain carbon, hydrogen and oxygen/C, H and O;

Differences:

4. Starch has α-glucose WHEREAS cellulose has β-glucose;
5. Starch (molecule) is helical/coiled HOWEVER cellulose (molecule) is straight;
6. Starch (molecule) is branched WHEREAS cellulose is not/unbranched;

7.Cellulose has (micro/macro) fibrils HOWEVER starch does not;

8. Starch has 1–6 glycosidic bonds AND cellulose does not

OR Starch is amylose AND amylopectin and cellulose is one type of molecule;

Question 24

Describe how lactose is formed. (3)

Answer 24

Glucose and galactose
Joined by condensation
Joined by glycosidic bond

Question 25

Omega-3 fatty acids are unsaturated. What is an unsaturated fatty acid? (2)

Answer 25

Double bond(s); (Bonds) between carbon atoms within the hydrocarbon chain;

Question 26

Describe how an ester bond is formed in a phospholipid molecule. (2)

Answer 26

1. Condensation (reaction) OR Loss of water; 2. Between OH of glycerol and COOH of fatty acid;

Question 27

Some seeds contain lipids. Describe how you could use the emulsion test to show that a seed contains lipids. (4)

Answer 27

1. Crush/grind; 2. With ethanol/ alcohol, to dissolve the lipid; 3. Then add water then shake; 4. Forms a white cloudy emulsion;

Question 28

What are the differences between a triglyceride and a phospholipid? (2)

Answer 28

1. Fatty acid removed; 2. Replaced with a phosphate group;

Question 29

Compare and contrast the structure and properties of triglycerides and phospholipids (5)

Answer 29

Both contain ester bonds Both contain glycerol Fatty acids on both may be saturated or unsaturated Both are insoluble in water Both contain C, H and O but phospholipids are also contain P Triglyceride has three fatty acids and phospholipids have two fatty acids plus phosphate group Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region Phospholipids form monolayer/micelle/bilayer but triglycerides don’t.

Question 30

A student carried out the Benedict’s test. Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution. (2)

Answer 30

1. Filter and dry (the precipitate); 2. Find mass/weight;

Question 31

Compare and contrast the structure and properties of triglycerides and phospholipids. (5)

Answer 31

Both contain ester bonds Both contain glycerol Fatty acids on both may be saturated or unsaturated Both are insoluble in water Both contain C, H and O but phospholipids are also contain P Triglyceride has three fatty acids and phospholipids have two fatty acids plus phosphate group Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region Phospholipids form monolayer/micelle/bilayer but triglycerides don’t.