Chapter 1

Question 1

What are hydrogen bonds?

Answer 1

A hydrogen bond is a weak bond between two molecules resulting from an electrostatic attraction between a proton in one molecule and an electronegative atom (oxygen, nitrogen, or fluorine) in the other molecule.

Question 2

Define the term dipole

Answer 2

A dipole refers to a separation of electrical charges within a molecule or a bond, where one end becomes slightly positive (δ⁺) and the other end becomes slightly negative (δ⁻) due to differences in electronegativity.

Question 3

Define the term polar molecule

Answer 3

A polar molecule is a molecule that has an uneven distribution of charge, resulting in a net dipole moment. This occurs when the individual bond dipoles do not cancel out, usually because of the molecule’s shape and differences in electronegativity between atoms.

Question 4

Why should, when testing for the presence of a non-reducing sugar, first test for reducing sugars first to ensure there is no reaction with Benedict’s solution?

Answer 4

Reducing Sugars React with Benedict’s Solution: Reducing sugars, like glucose or maltose, react directly with Benedict’s solution, producing a color change (blue to green, yellow, orange, or red, depending on concentration).

Avoiding False Positives: If reducing sugars are present and you proceed directly to the non-reducing sugar test (involving hydrolysis and subsequent testing with Benedict’s), the reducing sugars present from the beginning could give a positive result. This might incorrectly suggest the presence of non-reducing sugars.

Sequential Testing is Logical: By confirming no reducing sugars are present initially, any positive result in the second test after hydrolysis (e.g., with sucrose breaking into glucose and fructose) is confidently attributed to non-reducing sugars.

Question 5

What is covalent bonding?

Answer 5

Covalent bonding: the atoms involved in the reaction share electrons. Covalent bonds are very strong, and the molecules formed are usually neutral. In some covalent compounds, the molecules are slightly polarised (electrons are not evenly shared).

Question 6

What is water? What type of molecule is it?

Answer 6

WATER… Is a polar molecule because the electrons are held closer to the oxygen atom than to the hydrogen atoms.
The oxygen has a very small negative charge and the hydrogen atoms have very small positive charges.
The slightly negative region of one water molecule is attracted to the slightly positive region of another water molecule (hydrogen atom), and this weak electrostatic attraction is a hydrogen bond.

Question 7

Define dissociation

Answer 7

Dissociation is the process by which a compound or molecule breaks apart into smaller components, such as ions, atoms, or simpler molecules, typically when dissolved in a solvent like water.

Question 8

Define hydrogen bonds

Answer 8

Weak electrostatic intermolecular bonds formed between polar molecules containing at least one hydrogen atom.

Question 9

Why does water have a relatively high melting/boiling point?

Answer 9

There are many hydrogen bonds sticking the water molecules together -> Water has high melting and boiling points because of the energy needed to break all the hydrogen bonds.

Question 10

Define macromolecule

Answer 10

A macromolecule is a large molecule composed of many smaller subunits (monomers) bonded together. These molecules are typically complex and have high molecular weights. Examples of macromolecules include proteins, nucleic acids (DNA and RNA), and polysaccharides.

Question 11

Why is water important in life?

Answer 11

Water is important because…
1. Excellent solvent: Can dissolve covalent compounds and ionic compounds (because of its polar nature) -> Ideal solvent for chemical reactions in biological systems & excellent transport medium.
2. Very stable medium in life: Slow to absorb & release heat
3. Use in hydraulic systems: it is liquid in room temperature and can’t be compressed
4. Important in movement to xylem of plants: Water molecules are cohesive (stick together) & adhesive (stick to other substances) -> important properties for the water movement up to xylem.
5. Have high surface tension (because of the attraction between molecules—hydrogen bonds) -> form a thin ‘skin’ of surface tension -> important in plant transport systems & in life at the surface of lakes and water masses

Question 12

Why is cohesion useful in biological systems?

Answer 12

Cohesion is the main force supporting columns of water as they are pulled up the xylem in plants. The water molecules stick together as a constant column.

Question 13

Why is adhesion useful in biological systems?

Answer 13

It allows water to move against the pull of gravity up the xylem.

Question 14

Explain what carbohydrates are. Name three main functions and give some examples of which foods contain them.

Answer 14

Organic compounds:
Are biological molecules containing carbon, hydrogen, and oxygen atoms.
*
Energy source for cells
*
Store energy
* Form important part of cell wall in plants, fungi and bacteria
Best known carbohydrates->
1. SUGARS -> sucrose (white crystalline table sugar), glucose (used as fuel by cells
of our body)
2. STARCH -> is in rice and potatoes

Question 15

What do disaccharides consist of?

Answer 15

Disaccharides
Consists of two monosaccharides joined together in condensation
reaction -> form a disaccharide & a molecule of water is released

Question 16

What should you know about monosaccharides?

Answer 16

Monosaccharides:
Simple sugars
One oxygen atom & two hydrogen atoms for each carbon atom
Triose sugar: Sugar with 3 carbon atoms
Pentose sugar: Sugar with 5 carbon atoms
Hexose sugars: Sugar with 6 carbon atoms (ribose)
(Glucose, Fructose, Galactose)
Monomers of polymers
Contain mainly carbon, oxygen, and hydrogen.

Question 17

What type of reaction happens when two monosaccharides are linked together?

Answer 17

When two monosaccharides are linked together, a condensation reaction (also called a dehydration synthesis) occurs. During this process:

A water molecule is removed as the monosaccharides are joined.
A glycosidic bond is formed between the two monosaccharides.

Question 18

Define glycosidic bond

Answer 18

Glycosidic Bond
The glycosidic bond is a covalent bond that connects the anomeric carbon (the carbon that was part of the carbonyl group in the monosaccharide) of one monosaccharide to the hydroxyl group (-OH) of another monosaccharide.

For example, when glucose and fructose combine to form sucrose, a glycosidic bond links the two sugars, and a molecule of water is released.

Question 19

Define ribose

Answer 19

Ribose is a five-carbon sugar (pentose sugar) that is a crucial component of nucleotides in RNA. It has a hydroxyl group (-OH) attached to each of its carbon atoms except at the second position.

Question 20

Define Deoxyribose

Answer 20

Deoxyribose is also a five-carbon sugar but differs from ribose by having one less oxygen atom. Specifically, it lacks a hydroxyl group (-OH) at the second carbon, replaced by just a hydrogen atom (–H). It is a key component of nucleotides in DNA.

Question 21

What is the opposite process of a condensation reaction, and explain briefly what happens?

Answer 21

The opposite process of a condensation reaction is a hydrolysis reaction.

Hydrolysis Reaction
In a hydrolysis reaction, a water molecule is added to break a bond between two molecules. This process effectively splits the larger molecule into smaller components.

For example, when a disaccharide like sucrose undergoes hydrolysis, the glycosidic bond between the two monosaccharides (glucose and fructose) is broken, and water is added, resulting in the separation of the two monosaccharides.

Summary:
Condensation: Water is removed, and a bond is formed (e.g., monosaccharides join to form a disaccharide).
Hydrolysis: Water is added, and a bond is broken (e.g., disaccharide breaks into monosaccharides).

Question 22

Difference between Ribose and Deoxyribose

Answer 22

Ribose has a hydroxyl group (-OH) at the second carbon (C2).
Deoxyribose has a hydrogen atom (–H) at the second carbon instead of the hydroxyl group.
This small difference is significant because it contributes to the structural differences between RNA (which contains ribose) and DNA (which contains deoxyribose), and ultimately influences their functions.

Question 23

Justify why monosaccharides and disaccharides are both good sources of instant energy and an unfavourable energy storage.

Answer 23

Monosaccharides/Disaccharides & Energy:
Glucose -> Can be absorbed & used directly in your cells
Other monosaccharides and disaccharides are easily absorbed in body and
rapidly converted to glucose.
Good source of relatively instant energy
BUT…They can’t be used to store energy because:
1. Are chemically active
2. Are very soluble in water -> affect the water balance of cells

Question 24

Justify why polysaccharides are great storages of energy.

Answer 24

Polysaccharides & Energy:
Ideal as an energy storage molecule within a cell because:
1. Can form compact molecules -> take up little space
2. Physically & Chemically inactive -> Don’t interfere with other functions of
cell
3. Not soluble in water-> No effect on water potential within a cell & cause no
osmotic water movements

Question 25

What is starch? In which kingdom of life is starch found, and what is it important for?

Answer 25

STARCH
Starch is a polysaccharide (a carbohydrate made up of many sugar molecules) composed of glucose units linked together. It’s insoluble, compact and
can be broken down rapidly to release glucose (cellular respiration). It serves as a storage form of energy in plants. Starch is made up of two components:

Amylose – A long, unbranched chain of glucose molecules.
Amylopectin – A branched chain of glucose molecules.
Starch is found in many plant-based foods, such as potatoes, rice, and wheat. When consumed, it is broken down into glucose by enzymes in the digestive system, providing energy for the body.

Question 26

Amylopectin has two types of polymers.
Name the two types.

Answer 26

Two Types of Polymers in Amylopectin:
Linear Polymer (α-1,4-glycosidic bonds):
This is a chain of glucose molecules linked by α-1,4-glycosidic bonds. These bonds connect the hydroxyl group of one glucose molecule at carbon 1 to the hydroxyl group of another glucose molecule at carbon 4.

Branched Polymer (α-1,6-glycosidic bonds):
In addition to the α-1,4-glycosidic bonds, amylopectin has branching points where glucose chains are linked through α-1,6-glycosidic bonds. These bonds connect the glucose molecules at carbon 1 to carbon 6 of another glucose molecule, creating a branching structure.

Question 27

Justify if amylopectin releases energy quickly or slowly.

Answer 27

Amylopectin releases energy relatively quickly due to its branched structure. The branching provides multiple ends where enzymes can break the molecule down into glucose units. This facilitates faster digestion and quicker release of energy compared to amylose, which is unbranched.

Question 28

What is the test for starch?

Answer 28

If you add a few drops of reddish-brown iodine solution to a sample
containing starch (whether it is a solid sample or a sample in
solution), the iodine solution will turn blue-black (see fig C).

Question 29

What is glycogen? Which kingdom of life can it be found?

Answer 29

Glycogen is a polysaccharide made up of glucose units, similar to starch, but it is more highly branched. It serves as the primary storage form of glucose in animals and fungi.

Structure: Glycogen consists of chains of glucose molecules linked by α-1,4-glycosidic bonds, with branching points formed by α-1,6-glycosidic bonds. The high degree of branching allows for rapid release of glucose when needed, which is important for quick energy mobilization.
Kingdoms of Life:
Animals: Glycogen is primarily found in animals, stored mainly in the liver and muscles. It can be broken down into glucose when the body needs energy.
Fungi: Some fungi also store glycogen as a form of energy reserve.

Question 30

What is the test for glucose?

Answer 30

PRACTICAL SKILLS: CP1 – Testing for Sugars
Benedict’s solution, a blue reagent with copper(II) ions, tests for reducing sugars. When heated, reducing sugars react, reducing copper (II) to copper (I), forming a precipitate and changing colour from blue to orange. Reducing sugars include all monosaccharides and some disaccharides (not sucrose).

Non-reducing sugars, like sucrose, do not react directly. To test them, heat with hydrochloric acid, cool, neutralize with sodium hydrogen carbonate, and hydrolyze the glycosidic bonds. This releases monosaccharides, which give a positive Benedict’s test.

Question 31

Explain what are lipids? Provide examples

Answer 31

Lipids:
1. Lipids are organic compounds that are insoluble in water but soluble in organic solvents like alcohol or acetone.
2. Made up of carbon, hydrogen, and oxygen atoms, but in different proportions than carbohydrates.
3. Lipids are hydrophobic (water-repelling) and include fats, oils, phospholipids, and steroids.

Types of Lipids:
Triglycerides – Made of one glycerol molecule and three fatty acids. They are used primarily for energy storage.
Phospholipids – Important components of cell membranes.
Steroids – Including hormones like estrogen and testosterone.
Contain carbon-hydrogen bond

Question 32

Justify that lipids are good storagers of substantial amounts of energy compared to carbohydrates.

Answer 32

Energy Storage:
Lipids store a large amount of energy compared to carbohydrates. When broken down, lipids release about 9 calories per gram, more than double the energy provided by carbohydrates or proteins (which provide about 4 calories per gram). This makes lipids an efficient way for organisms to store energy, especially for long-term reserves.

Summary:
Lipids are found in all kingdoms of life.
They store lots of energy for respiration, making them an efficient form of energy storage.

Question 33

What elements do lipids contain?
How are they formed?

Answer 33

Elements Contained in Lipids:
Carbon (C)
Hydrogen (H)
Oxygen (O)
Some lipids (like phospholipids and glycolipids) may also contain phosphorus (P) or nitrogen (N).
Formation of Lipids:

Triglycerides (Fats and Oils):
Formation: A triglyceride is formed by the condensation of one glycerol molecule and three fatty acid molecules. Three water molecules are released as ester bonds are formed between the glycerol and fatty acids.
Reaction:
Glycerol + 3 Fatty Acids → Triglyceride + 3 H₂O

Question 34

What are their physical appearance characteristics?

Answer 34

Physical appearance characteristics of lipids:

General Characteristics:
Lipids are hydrophobic (do not dissolve in water) and lipophilic (soluble in nonpolar solvents like alcohol or acetone).
They appear colourless to pale yellow, but oils may have different colours depending on their source.
Triglycerides (Fats and Oils):

Fats (from animals) are solid at room temperature and have a waxy or greasy texture.
Oils (from plants) are liquid at room temperature and have a slippery or oily texture.

Fatty Acids:
Saturated fatty acids (no double bonds) are solid at room temperature.
Unsaturated fatty acids (with one or more double bonds) are liquid at room temperature.