3. Nutrients

Question 1

State the 4 uses of water in living organism.

Answer 1

1. As a solvent of chemical reactions
2. As a component of protoplasm, tissue fluid, lubricants, digestive juices and blood.
3. Controlling body temperature
4. Transporting dissolved substances.

Question 2

State the 4 uses of water in plants.

Answer 2

1. Water is necessary for the light-dependent reactions of photosynthesis.
2. Water keeps cells turgid.
3. Mineral salts dissolve in water and are transported up the xylem of plants.
4. Sucrose and amino acids are transported in water through the phloem,
   from the photosynthetic parts to all parts of the plants.

Question 3

What are carbohydrates made up of?

Answer 3

Carbon, hydrogen and oxygen

Ratio of hydrogen to oxygen is 2 to 1

Question 4

What are the three groups of carbohydrates?

Answer 4

monosaccharides, disaccharides and polysaccharides

Question 5

What are the three monosaccharides and their formula?

Answer 5

glucose, galactose and fructose

all C6H12O6

Question 6

What are the 2 functions of monosaccharides?

Answer 6

Glucose is the substrate in cellular respiration. Oxidation of glucose releases energy.
Simple sugars also function as the raw material for the synthesis of other biological molecules, such as amino acids and fatty acids.

Question 7

How are disaccharides formed?

Answer 7

Two monosaccharides can join with a glycosidic linkage to form a disaccharide in the process known as condensation. Condensation reaction is the chemical reaction in which two simple molecules are joined together to form a larger molecule with the removal of one water molecule.

Question 8

How are the three disaccharides formed?

Answer 8

Maltose is formed by joining two glucose molecules.
Sucrose is formed by joining glucose and fructose.
Lactose is formed by joining glucose and galactose.

Question 9

How does a disaccharides split?

Answer 9

A disaccharide can be split to form two monosaccharides in the process known as hydrolysis. Hydrolysis or a hydrolytic reaction is a reaction whereby a water molecule is added to split up a complex molecule into smaller molecules.

Question 10

What are polysaccharides made up of?

Answer 10

Polysaccharides are made up of hundreds to thousands of monosaccharides (commonly glucose) joined by glycosidic linkages.

Question 11

What are the storage and structural roles of polysaccharides?

Answer 11

1. Some polysaccharides serve for storage and are hydrolysed as sugars are needed. Plants store excess glucose as starch within chloroplasts. The simplest form of starch, amylose, is unbranched. Branched forms such as amylopectin are more complex. Animals that feed on plants, especially parts rich in starch, have digestive enzymes that can hydrolyse starch to glucose, making the glucose available as substrate for cellular respiration.
2. Humans store excess glucose as glycogen in muscles and liver. Glycogen is highly branched, like amylopectin.
3. Cellulose is a major component of the tough walls of plant cells. Cellulose is the most abundant organic compound on Earth.

Question 12

State 5 uses of glucose, 1 for starch and 1 for glycogen.

Answer 12

1. Glucose is the substrate for cellular respiration.
2. Glucose is needed to synthesise lubricants (e.g. mucus) and flower nectar.
3. Glucose is also needed for the formation of nucleic acids (e.g. DNA).
4. Glucose is the basic unit for the formation of cellulose cell walls in plants.
5. Glucose can convert to other organic molecules (e.g. fats, amino acids) in
   plants.
6. Starch is the storage form of carbohydrates in plants.
7. Glycogen is the storage form of carbohydrates in animals.

Question 13

What elements are fats made up of?

Answer 13

Carbon, hydrogen and oxygen

Question 14

What molecules are fats made up of?

Answer 14

In a fat molecule, three fatty acids are joined to one glycerol by an ester linkage, forming a triglyceride.

Question 15

Explain the difference between saturated fats and unsaturated fats.

Answer 15

If the fatty acid has no carbon-carbon double bonds, then the molecule is a saturated fatty acid.If the fatty acid has one or more carbon-carbon double bonds formed by the removal of hydrogen atoms from the carbon skeleton, then the molecule is an unsaturated fatty acid. A saturated fatty acid is a straight chain, but an unsaturated fatty acid has a kink wherever there is a cis double bond.Most animal fats are saturated. Saturated fats are solid at room temperature. Plant and fish fats are liquid at room temperature and are known as oils. The kinks caused by the cis double bonds prevent the
molecules from packing tightly enough to solidify at room temperature.

Question 16

State the 5 functions of fats.

Answer 16

1. Storage of energy. A gram of fat stores more than twice as much energy as a gram of a polysaccharide. Plants use oils when dispersal and compact storage are important, such as in seeds. Animals carry energy stores with them, so they benefit from having a more compact fuel reservoir of fat. Humans and other mammals store fats as long-term energy reserves in adipose cells that swell and shrink as fat is deposited and withdrawn from storage.
2. Adipose tissue also functions to cushion vital organs, such as thekidneys
3. A layer of fat can function as insulation. This subcutaneous layer is especially thick in whales and most other marine mammals.
4. Phospholipids are major components of cell membranes.
5. Steroids include cholesterol and certain sex hormones.

Question 17

What elements are proteins made up of?

Answer 17

Carbon, hydrogen, oxygen, nitrogen and sometimes sulfur.

Question 18

What are proteins made up of?

Answer 18

The basic unit of protein is an amino acid. There are 20 naturally occurring amino acids. Short-chain proteins are known as polypeptides. Amino acids are joined together by peptide bonds.

Question 19

State the 7 functions of proteins.

Answer 19

1. Synthesis of new protoplasm, for growth and repair of worn out parts of
   the body
2. Synthesis of enzymes and some hormones
3. Formation of haemoglobin that binds oxygen
4. Formation of antibodies, to defend against foreign substances
5. Formation of support structures – e.g. silk fibres, spider webs, collagen, keratin of hair
6. Formation of storage structures – e.g. ovalbumin in egg, casein in milk
7. Membrane proteins that move molecules across the phospholipid bilayer

Question 20

What elements are nucleic acids made up of?

Answer 20

Carbon, hydrogen, oxygen, nitrogen and phosphorus

Question 21

State 2 features of nucleic acids.

Answer 21

Nucleic acids are the genetic materials on which the genetic information of all living organisms are encoded.
Nucleic acids belong to a class of biological molecules. Other classes include proteins, lipids and carbohydrates.

Question 22

What does nucleotides consist of?

Answer 22

Pentose sugar, nitrogenous base and phosphate group

Question 23

What are the two types of nucleic acids?

Answer 23

Deoxyribonucleic acid and ribonucleic acid

Question 24

State the procedure and results for iodine test.

Answer 24

1. Place 1 cm3 of the crushed/chopped food pieces on a white tile.
2. Place two drops of iodine solution (or potassium iodide solution) onto the chopped food pieces.
3. Observe and record changes in the colour of the iodine solution.
4. Observations are recorded as follows:
   (+) “solution turned from brown to blue black / specimen was stained blue-black”
   (–) “solution remained brown / specimen was stained brown”

Question 25

State the procedure and results for Benedict’s test.

Answer 25

1. Place 1 cm3 of the crushed/chopped food pieces into a clean test tube and label the tube appropriately.
2. Add 2 cm3 of water to the tube to dissolve the reducing sugar in the sample. Decant
3. Add in 2 cm3 of Benedict’s Solution to the solution containing the nutrient. Shake thoroughly to mix.
4. Place tube in boiling water bath for 2–3 minutes.
5. After 2–3 minutes, remove tubes from the water bath.
6. Observe and record changes in the colour of the mixture, if any.
7. Observations are recorded as follows:
   (+) “solution turned from blue to green / yellow/ orange / brick-red with precipitate (with precipitate compulsory for orange and red)”
   (–) “solution remained blue”

Question 26

For sucrose, how can it be tested positive in Benedict’s test?

Answer 26

1. Heat 2 cm3 of the sample solution with dilute hydrochloric acid for a few minutes to hydrolyse the glycosidic bonds.
2. Neutralise with sodium hydrogen carbonate.
3. Perform the Benedict’s Test for Reducing Sugar.

Question 27

State the procedure and result of biuret test.

Answer 27

1. Place 1 cm3 of the crushed/chopped food pieces into a clean test tube and label the tube appropriately.
2. Add 2 cm3 of water to the tube to the chopped sample. Shake thoroughly to mix. Decant.
3. Add in equal volume sodium hydroxide solution to the solution containing the nutrient. Shake thoroughly to mix.
4. Add in 1% copper sulfate solution drop by drop. Shake the test-tube after adding each drop.
5. Observe and record any colour changes, if any.
6. Observations are recorded as follows:
   (+) “solution turned from blue to violet”
   (–) “solution remained blue”

Question 28

State the procedure and result for ethanol emulsion test.

Answer 28

1. Place 1 cm3 of chopped food pieces into a clean and dry test tube and label the tube appropriately.
2. Add 3 cm3 of ethanol into the chopped food mixture.
3. Shake thoroughly to mix.
4. Record changes in the solution.
5. Decant 1 cm3 of the mixture into another test tube.
6. Add the equal volume of water to the liquid portion. Observe and record formation of white emulsion, if any.