Chapter 3: Biological Molecules

Question 1

What are carbohydrates?

Answer 1

They are organic moelcules made up of the elements carbon, hydrogen, oxygen.

Question 2

How can carbs be classified as?

Answer 2

Simple sugars, double sugars or complex carbohydrates.

Question 2

What are simple sugars?

Answer 2

They are the basic unit of a carbohydrate.

Question 2

What can simple sugars do in cells?

Answer 2

They can pass through the cell membrane and can be absorbed into the cells.

Question 3

What are the 2 common single sugars?

Answer 3

Glucose and fructose.

Question 4

How is a double sugar formed?

Answer 4

When 2 single sugars are joined together.

Question 5

What are the 2 common double sugars?

Answer 5

Maltose and sucrose.

Question 6

How can a double sugar be split into 2 single sugars?

Answer 6

By an enzyme.

Question 7

What are reducing sugars?

Answer 7

Glucose, fructose and maltose

Question 7

How do we test for reducing sugars?

Answer 7

Reducing sugars will form a red precipitate when boiled with Benedict’s solution.

Question 8

What is a complex carbohydrate?

Answer 8

It is made up of many similar molecules of a single sugar joined together to form a large molecule.

Question 9

What are examples of complex carbohydrates that are made up of numerous glucose molecules?

Answer 9

Starch, glycogen, cellulose.

Question 10

What is the structure of a starch molecule?

Answer 10

A starch molecule is made up of several thousand glucose molecules joined together.

Question 11

What are the roles of starch?

Answer 11

1. It is a store of carbohydrates in plants.
2. When needed, it can be digested to glucose to provide energy for cell activities.

Question 12

Where can starch be found in?

Answer 12

In storage organs of plants.

Question 13

What is the structure of a cellulose molecule?

Answer 13

It is made up of many glucose molecules joined together.

Question 14

What are the roles of cellulose?

Answer 14

1. The cellulose cell wall protects the cell wall from bursting or damage
2. Cellulose cannot be digested in our intestines.
3. They serve as dietary fibre that prevents constipation.

Question 15

Where can cellulose be found in?

Answer 15

Cell walls of plants.

Question 16

What is the structure of glycogen?

Answer 16

It is a branched molecule and is made up of many glucose molecules joined together

Question 17

What are the roles of glycogen?

Answer 17

1. It is the main store of carbohydrates in mammals
2. When needed, it is digested to glucose to provide energy for cell activities.

Question 18

Where can glycogen be found in?

Answer 18

In the liver and muscles of mammals.

Question 19

How do plants store glucose?

Answer 19

They store glucose in the form of starch

Question 20

Animals cannot ________starch in their bodies.

Answer 20

make or store

Question 21

Where do animals get most of their carbohydrates from and in what form?

Answer 21

From plants in the form of starch

Question 22

Tell me the relationship between starch, glucose and glycogen.

Answer 22

Starch is consumed and digested by animals, forming glucose, which is then stored in animals as glycogen

Question 23

Why are glycogen and starch suitable as stores in cells?

Answer 23

1. They are insoluble in water, so they do not change the water potential in the cell. 2. They are large molecules that cannot diffuse through cell membranes, so they will not be lost from the cell. 3. They can be easily broken down into glucose when needed. 4. Their molecules have compact shapes, so they occupy less space than all the individual glucose molecules that make up a glycogen or starch molecule.

Question 24

What happens when starch is digested?

Answer 24

1. The bonds within the polysaccharide are broken and the glucose molecules are released. 2. Amylase cannot break down maltose into glucose. 3. Maltose is hydrolysed to glucose by maltase. 4. Complete digestion of starch gives glucose molecules.

Question 25

What are the functions of carbohydrates?

Answer 25

1. They are needed as a substrate for respiration and to provide energy for all cell activites. 2. To form supporting structures 3. To be converted into other organic compounds. 4. For the formation of nucleic acids 5. To synthesise lubricants. 6. To synthesise the nectar in some flower

Question 26

How can we test for starch?

Answer 26

Iodine - any substance containing starch will produce a blue-black colour

Question 27

What are fats?

Answer 27

They are a type of lipid and are organic molecules made up of the elements carbon, hydrogen and oxygen.

Question 28

What is the difference between the elements used to make up carbs and fats?

Answer 28

Though they both are made up of the same elements, fats have much less oxygen in comparison to carbs.

Question 29

What are fats commonly used as?

Answer 29

A store of energy.

Question 30

What can fats be broken down into?

Answer 30

Fatty acids and glycerol

Question 30

What are the functions of fats?

Answer 30

1. It is a source and long-term storage of energy 2. It is an insulating material that prevent excessive heat loss. 3. It is a solvent for fat-soluble vitamins and many other vital substances 4. It is an essential part of cells, especially in the cell membrane 5. It is a way to reduce water loss from the skin surface.

Question 31

Why are fats a suitable long term-storage material?

Answer 31

Fats have a higher energy value compared to carbohydrates.

Question 32

How do fats reduce water loss from the skin surface?

Answer 32

Glands in the skin secrete an oily substance. This oily substance forms a thin layer over the skin surface, reducing the rate of evaporation of water.

Question 33

What other function does the oily substance secreted from your skin have?

Answer 33

It helps to reduce heat loss from the skin.

Question 34

How can we test for fats?

Answer 34

Ethanol emulsion test - a white emulsion is formed when ethanol and water are added to fats.

Question 35

What are proteins?

Answer 35

They are organic molecules made up of the elements carbon, hydrogen, oxygen and nitrogen.

Question 36

What is special about proteins?

Answer 36

They are present in all cells and are the largest and most complex food substance.

Question 36

What are the functions of proteins?

Answer 36

1. They are used in the synthesis of new cytoplasm, for growth and repair of worn-out body cells. 2. They are used in the synthesis of enzymes and some hormones. 3. They are used in the formation of antibodies to combat disease.

Question 36

How are protein molecules formed?

Answer 36

Many amino acids are joined in a linear manner to form a polypeptide, which then forms protein when polypeptides are linked together.

Question 37

How do we test for proteins?

Answer 37

Biuret test - the biuret solution will turn violet in the presence of proteins.

Question 38

How can we find out what nutrients are in our food?

Answer 38

We can carry out food tests.