Chapter 4: Nutrients

Question 1

What are nutrients?

Answer 1

nutrients refer to biological molecules in food that provide energy and materials needed by the body.

Question 2

What are the 3 main functions of water?

Answer 2

1. It serves as a solvent for various substances
2. It serves as the medium for metabolic reactions to occur
3. Needed for reactions such as hydrolysis in chemical digestion

Question 3

How does water help in the transport of dissolved substances around the body? (Hint: give examples of water transporting substances)

Answer 3

1. It transports digested food products from small intestine to other parts of the body.
2. It transports waste products from cells to excretory organs.
3. It transports hormones from glands to parts of body that require them

Question 4

What are the functions of water in plants?

Answer 4

1. It is essential for photosynthesis
2. Keeps plants upright by maintaining turgor pressure
3. It transports dissolved mineral salts from the roots to all parts of the plant in xylem vessels
4. Transports water from roots to other parts of the plant in xylem vessel
5. It transports sucrose and amino acids from the leaves to other parts of the plant via the phloem

Question 5

What are examples in which water is a vital component of?

Answer 5

1. Protoplasm
2. Lubricants found in joints (Reduce friction between joints during movement)
3. Digestive juices
4. Blood
5. Tissue fluid
6. Aids in the control of body temperature through sweating.

Question 6

What is the amount of H20 needed by a person dependent on?

Answer 6

1. How active a person is. A person who plays sports or carry out physical labour needs more water.
2. The environmental conditions. People living in hot and dry climates need more water than those living in temperate climates.

Question 7

What are carbohydrates?

Answer 7

They are organic compounds made up of the elements carbon, hydrogen, and oxygen. Hydrogen and oxygen atoms are present in the ratio 2:1.

Question 8

Glucose can be converted to other organic compounds to serve various functions. What are some examples of these compounds?

Answer 8

1. Starch and glycogen, used for storage in plant cells and animal cells respectively
2. Cellulose, which is a structural polysaccharide
3. Fats, which is used for energy storage
4. Nucleic acids, which contains genetic material.

Question 9

What are examples of Monosaccharides, Disaccharides, and polysaccharides?

Answer 9

Monosaccharides: Glucose
Disaccharides: Maltose
Polysaccharides: Starch and glycogen
Structural polysaccharides: Cellulose

Question 10

Why are glycogen and starch suitable as storage material?

Answer 10

1. They are insoluble in water, so they do not change the water potential in the cells. Hence there is no water potential gradient, and thus no net movement of water molecules
2. They are large molecules which cannot diffuse through cell membranes, so they will not be lost from the cell.
3. They can be easily hydrolysed to glucose when needed
4. Their molecules have compact shapes, thus they occupy less space compared to individual glucose molecules that make up a glycogen or starch molecule.

Question 11

What are fats?

Answer 11

Fats water insoluble organic compounds made up of the elements carbon, hydrogen and oxygen. Fats contain much less oxygen in proportion to hydrogen.

Question 12

What is a condensation reaction?

Answer 12

A condensation reaction is a chemical reaction in which two simple molecules are joined together to form a larger molecule with the removal of one water molecule.

Question 13

State and describe the test used to test for reducing sugars.

Answer 13

Benedict’s test. If large amounts of reducing sugars are present, the blue solution produces a brick-red precipitate. If the blue solution produces a yellow/orange precipitate, there is a moderate amount of reducing sugar. If the blue solution produces a green precipitate, there are trace amounts of reducing sugar.

Question 14

What is a hydrolysis reaction?

Answer 14

hydrolysis reaction is a reaction in which a water molecule is needed to break up a complex molecule into smaller molecule.

Question 15

What are the function of fats?

Answer 15

1. It is a source and storage amounts of energy
2. It provides thermal insulation to reduce heat loss, and electrical insulation.
3. Serves as a solvent for fat-soluble vitamins (Vitamins A,D, E and K)
4. It is an essential part of the protoplasm

Question 16

State and describe the test for fats.

Answer 16

The test is called an Ethanol-emulsion test. If a white emulsion is present, there are fats present. If the mixture remains colourless/no white emulsion observed, fats are absent.

Question 17

What are proteins?

Answer 17

Proteins are complex organic substances made up of elements, C, H.O and N. Another element, Sulfur, may also be present.

Question 18

What are functions of proteins?

Answer 18

1. They synthesis new protoplasm for cellular growth and repair of worn-out cells
2. They synthesize enzymes and some hormones
3. Formation of antibodies to combat diseases

Question 19

What do different sequences of amino acids give rise to?

Answer 19

Different sequence of amino acids give rise to the different polypeptide and eventually protein molecules.

Question 20

What is a protein molecule made of?

Answer 20

A protein molecule is made up of 2 or more polypeptides linked and folded together, having a unique 3 dimensional functional shape. When the protein loses its 3-D shape, it becomes denatured.

Question 21

Why must proteins be broken down in the body?

Answer 21

Protein molecules are too large to pass through the living cell surface membranes of an animal cell. Thus protein molecules have to be broken down by enzymes during digestion so that they can be absorbed by body cells.

Question 22

State and describe the test to test for proteins.

Answer 22

Biuret Test.
1. If the blue solution turns violet. proteins are present
2. If the blue solution produces a pink coloration, polypeptides are present
3. If the blue solutions remains blue, proteins are absent

Question 23

What are catalysts?

Answer 23

A catalyst is a substance which can alter or speed up a chemical reaction, without itself being chemically changed at the end of the reaction

Question 24

What are enzymes?

Answer 24

Enzymes are proteins that function as biological catalysts. They can alter or speed up chemical reactions. they remain chemically unchanged at the end of the reaction.

Question 25

How do enzymes speed up reactions?

Answer 25

Enzymes speed up the rate of reactions by lowering the activation energy needed for the reaction to start the reaction.

Question 26

Why are enzymes only required in minute amounts?

Answer 26

Since enzymes remain chemically unchanged in the reactions they catalyse, the same enzyme molecules reused to bind with another substrate molecule

Question 27

How are enzymes specific in action?

Answer 27

Each metabolic reaction in a cell requires unique set of enzymes. Each type of enzyme has a specific functional 3d conformation, called the active site, which determines the type of substrate it can bind to. Thus, enzymes are substrate-specific molecules.

Question 28

What are anabolic reactions and catabolic reactions?

Answer 28

Both are types of enzyme-catalysed reactions.

Anabolic reactions are the synthesis of complex molecules from simple molecules (e.g. synthesis of starch from glucose molecules)

Catabolic reactions are hydrolysis of complex molecules into simple molecules (e.g. the chemical breakdown of fats into 3 fatty acids and glycerol)

Question 29

What is an active site?
What is the name of the substance that is made from the binding of enzyme and substrate?

Answer 29

The active site refers to a depression on the enzymes surface that has a specific shape, complementary that of its substrate.

An enzyme-substrate complex

Question 30

Using 4 steps, describe how substrate molecules are converted into product molecules. (lock and key)

Answer 30

1. An enzyme has a specific 3 dimensional shape. It has a depression called the active site. the substance on which the enzyme acts on is called the substrate.
2. Only the substrate with a 3D shape complementary to that of the active site will fit into the enzyme. This results in the formation of an enzyme-substrate complex.
3. While the substrate is attached to the active site, chemical reactions occurs. The substrate is converted to the products.
4. Later, the products leave the active site. The enzyme remains unchanged and its active site is now available to bind to another substrate (Biological catalyst)

Question 31

What is denaturation? What is it caused by

Answer 31

Denaturation is the change in three-dimensional structure of the active site of enzyme or any other soluble protein caused by heat or chemicals such as acids or alkali. For enzymes, high temperatures and extreme pH levels beyond optimum levels results in denaturation.

Question 32

Big essay Qn: Describe the changes to enzyme activity when temperature is increased. (From very low to very high)

Answer 32

1. At low temperatures, enzymes activity is low as enzymes are inactive.
2. As temperature increases, this increases the kinetic energy and molecular movement of enzymes and substrate molecules, increasing the rate of collusion between enzyme and substrate molecules.
3. This increases the rate of enzyme-substrate complex formation and conversion of substrate product. Thus increasing the rate of reaction until optimum temperature is reached.
   4.Beyond optimum temperature, weak bonds within the enzyme molecules are broken
4. The enzymes loses its functional 3-D shape and its active site.
5. Enzymes are hence unable to bind to its substrate, and is said to have denatured.
6. Therefore, substrate is unable to fit into the active site of the enzyme, decreasing rate of substrate-complexes formed, and thus decreasing the rate of reaction

Question 33

State the procedure to test for fats

Answer 33

For solid food sample
1. Prepare 1.0g of small chopped food samples into a test tube
2. Add about 5.0cm3 of ethanol
3. Decant and pour out about 2.0com3 of the clear solution into another clean test tube
4. Add an equal volume of distilled water
5. As a control experiment, add 2.0com3 of ethanol to 2.0cm3 of distilled water, instead of food sample
6. Shake both test tubes well and record your observations in a suitable table format
For liquid food sample
1. Add about 2.0cm3 of ethanol to an equal volume of liquid food sample in a test tube.
2. Decant out clear portion of the mixture into another clean test tube.
3. Add about 2.0cm3 of distilled water into the test tube
4. As a control experiment, repeat step 3 using 2cm3 of distilled water, instead of food sample
5. Shake both test tubes well and record your observation sin a suitable table format

Question 34

State the procedure to test for proteins

Answer 34

1. Add about 2.0cm3 of food sample solution ito an equal volume of sodium hydroxide in a test tube
2. As a control to the experiment, repeat step 1 using 2cm3 of distilled water, instead of food sample
3. Shake both test tubes well
4. Add copper(II) sulfate solution dropwise, gently shaking after each drop
5. Record your observations in an appropriate table

Question 35

State the procedure to test for reducing sugars

Answer 35

1. Prepare a boiling water bath using a half-filled 250cm3 beaker.
2. Using a syringe, transfer 2.0cm3 of foo sample solution into a boiling tube
3. Add an equal volume of Benedict’s solution into the tube
4. Turn off the Bunsen burner after water has started to boil
5. Shake the mixture and place the boiling tube in the boiling water bath for 5 minutes
6. Observe for any colour changes and record the observations an appropriate table.