Chapter 2- Water, Carbohydrates and lipids

Question 1

Abundance of carbon

Answer 1

In a carbon atom, the four electrons in its outer shell repel each other and thus push away to shape the atom into a tetrahedron.
Carbon’s four such bond sites form covalent bonds that are stable and strong enough larger molecules.

Question 2

Carbohydrates

Answer 2

Also known as saccharides or sugars.
Acts as an energy source and store.
Contains carbon, hydrogen and oxygen.
Appears in the ratio, Cx(H2O)x
A single unit is called monosaccharide. Ex: glucose, fructose and ribose.
When two monosaccharides join, they form disaccharide. Ex: lactose, sucrose
When two or more monosaccharides are linked they form a polymer, polysaccharide. Ex: Glycogen, cellulose and starch. These are large carbs.

Question 3

What is Glucose? What is Alpha and beta?

Answer 3

The biochemical energy in its bonds are released during cellular respiration.
Is a monosaccharide and has a hexose structure (has six carbons)
Other hexose monosaccharides include fructose and galactose.
Has a formula of C6H12O6
In diagrams, the carbons are numbered clockwise beginning with the carbon to the right of the oxygen atom within the ring.
Two types- alpha and beta
The position of OH differs in these structures.
Alpha and beta glucose molecules are isomers.

Question 4

Is glucose soluble in water?

Answer 4

Glucose molecules are polar and soluble in water
The lone pair of oxygen in the water molecule and the OH in the glucose molecule form hydrogen intermolecular interactions.
Due to this the glucose is dissolved in the cytosol of the cell.
It is the main respiratory substrate resulting in energy being released
Can be broken down into smaller and simpler molecules such as CO2 and H2O.

Question 5

What happens in a condensation reaction between alpha glucose molecules?

Answer 5

Two hydroxyl groups interact with each other when two alpha molecules are side by side.
When this happens, bonds are broken and new bonds reforms in different places producing a 1-4 glycosidic bond and a water molecule.
It is called 1-4 glycosidic bond because carbon-1 from one glucose and carbon-4 from another glucose molecule bond.
Most organisms can only break down polymers of alpha glucose, they do not have the necessary enzymes to break down polymers of beta glucose.

Question 6

Polarity of a water molecule

Answer 6

In a water molecule, the oxygen atoms are bigger and also more electronegative than hydrogen atoms.
It attracts the electrons in the outmost shells of the adjacent hydrogen atoms. This is why it has a higher share of electrons than hydrogen atoms. It leaves some regions positive, and others negative. (See appendix)

Question 7

Hydrogen bonds in a water molecule

Answer 7

Hydrogen bonds are relatively weak intermolecular interactions which break and reform between constantly moving water.
When a water molecule forms bonds, the negative and positive regions interact with each other.

Question 8

Boiling point of water

Answer 8

Has an unusually high boiling point due to hydrogen bonds in a water molecule
Water is a liquid at room temperature
Requires a lot of energy to increase the temperature of water and convert its state to a gas.

Question 9

Density of water

Answer 9

At solid state, its density is lower.

This is because the hydrogen bonds form slightly further apart

Question 10

What is the opposite of condensation reaction?

Answer 10

Opposite of condensation reaction is hydrolysis.
Hydrolysis breaks down all Non-reducing sugars to reducing sugars.
Non- Reducing sugars include disaccharides (except maltose)and polysaccharides.
Reducing sugars are monosaccharides- ex: glucose, fructose, ribose etc
Two ways we can carry out a hydrolysis reaction, is by boiling a reducing sugar along with dilute acid and also by using enzymes.
It is an enzyme controlled reaction.

Question 11

Examples of monosaccharides (hexose and pentose)

Answer 11

Glucose is a hexose
Source of energy as easily hydrolysed; transported in the blood of animals.
Fructose is a hexose too
Isomerase converts fructose to glucose and back.
Ribose and deoxyribose are pentose
Ribose are part of all types of RNA molecules and ATP molecules, so it is an important part of protein synthesis.
Deoxyribose is a part of DNA for inherited information
Both of these are important in forming nucleic acids (acids formed by nucleotides)
Triose sugars are important for respiration and photosynthesis.
Only monosaccharides can provide energy

Question 12

Examples of disaccharides

Answer 12

These are small and soluble
Maltose-> glucose + glucose
This is formed when amylase breaks down starch by a hydrolysis reaction.
Sucrose-> glucose + fructose
Lactose-> glucose + galactose
Fructose is sweeter than glucose and this is sweeter than galactose

Question 13

Examples of polysaccharides

Answer 13

These are large, complex, insoluble and stable molecules
Starch- this form of saccharide is found in plants
Glycogen- this form of saccharide is found in animals
Cellulose- structural and strong molecule which forms the cell wall in plants and algae

Question 14

Starch and glycogen

Answer 14

Many alpha glucose molecules can be joined by glycosidic bonds to form two slightly different polysaccharides, collectively known as starch.
Glucose is formed through photosynthesis and is stored as starch in amyloplasts ( a type of plastid) in plant organs.
In animals, glucose that is not needed immediately, is stored as glycogen in muscle and liver cells.

Question 15

What is a plastid

Answer 15

Specialised membrane-bound organelles found in plant cells, for example chloroplasts and amyloplasts.
These store starch grains.

Question 16

Amylose

Answer 16

Is made by alpha glucose molecules joined only by 1-4 glycosidic bonds.
This long of glucose twists to form a helix due to the angle of the bond. This is reinforced by hydrogen bonding within the molecule.
This makes it less soluble.

Question 17

Amylopectin

Answer 17

Consists of 1-4 glycosidic bond along with 1-6 glycosidic bond
It is a long branched chain with short side arms of glucose units attached to the main chain of 1-4 glycosidic bonds. These short arms are the 1-6 glycosidic bonds.
This is makes it more compact than amylose.

Question 18

Amylose and the iodine test

Answer 18

Iodine gets trapped in the coiled structure of amylose resulting in the solution becoming blue-black.

Question 19

Why is the structure of starch ideal for storage

Answer 19

Compact and stable due to coiling and folding
Individual bonds are weak but multiple are stable
Is insoluble; therefore does not affect water potential and osmotic properties.
Can be easily broken down by enzymes into glucose when needed.

Question 20

Cellulose

Answer 20

Formed by beta glucose molecules
In a beta molecule, the hydroxyl group of carbon-4 is at the bottom while the hydroxyl group of carbon-1 is at the top.
These groups cannot react since they are too far.
The only way that beta glucose molecules can join together and form a polymer is if the hydroxyl group in the second beta glucose molecule is turned upside down.
When a polysaccharide is formed from glucose in this way it is unable to coil or form branches
Which is why it only forms straight chain molecules

Question 21

How is a fibre made?

Answer 21

Cellulose chains have many OH groups on the outside which allows hydrogen bonds to form between the cellulose chains. This form microfibrils. There are cross links between cellulose chain in a microfibril.
These microfibrils join together through hydrogen bonds forming macro fibrils
These then form fibres by hydrogen bond cross links.
Fibres are strong and insoluble. These are used to make cell walls.
It is hard to break down the monomers that form the ‘fibre’ or ‘roughage’ necessary for a healthy digestive system.

Question 22

Differences between Glycogen and Amylopectin

Answer 22

They both are branched chains due to the 1-6 glycosidic bonds joining the main chain of 1-4 glycosidic bonds
However, the glycogen chain tend to be shorter and so the molecules are very compact.
There are 1-6 glycosidic bonds every 24 to 30 1-4 glycosidic bonds in an amylopectin
There are 1-6 glycosidic bonds every 8 to 12 1-4 glycosidic bond in a glycogen.
Glycogen is stored as granules in muscle and liver cells.

Question 23

How quickly is energy available in reducing and non-reducing sugars

Answer 23

reducing sugars release energy easily

Polysaccharides need to be broken down in order to release energy

Question 24

Other examples of polysaccharides

Answer 24

Chitin- the cell wall of fungi

Peptidoglycan or meurein- the cell wall of prokaryotic cells

Question 25

Structure of water

Answer 25

The hydrogen atoms are slightly further apart from the oxygen atom. This produces a giant, rigid but open structure.
Every oxygen atom is at the centre of tetrahedral structure of hydrogen atoms. This makes it less dense and therefore float.
This also gives water its cohesive properties.

Question 26

Cohesion and adhesion of water

Answer 26

The molecules are attracted to each other and therefore move together as one mass.
This is why water can be drawn in through the roots of a plant and also why we can drink water through a straw.

Water molecules are attracted to other materials as well.
Ex: after washing hands, the water does not just run off your hands; it lingers on your hands.

Question 27

Surface tension

Answer 27

Water molecules are more cohesive to each other than they are to air. This is why they have a ‘skin’ of surface tension

Question 28

Solvent properties of water

Answer 28

In an organism, you can dissolve many solutes in water. Water can be used as a solvent because it is a polar molecule. Its polar nature attracts other molecules or compounds which are pulled apart due to the opposite charges in the water molecule.

The cytosol of prokaryotic (bacterial) and eukaryotic cells is mainly water. The solutes include nucleic acids, amino acids, sugars and proteins. These are all polar molecules.

Carbon containing molecules with charged ionised groups such as carboxyl groups (-COO) and amino groups (-NH3) easily dissolve by forming hydrogen bonds with the water hydroxyl groups (-OH).

Ionic substances such as sodium chloride (NaCl) release positively charged ions (cations) or negatively charged ions (anions) such as Na+ and Cl-, by forming clusters of water around the ions.

Question 29

Medium of transport and capillary action

Answer 29

Helps transport dissolved compounds into and out of cells.

Due to its cohesive nature, water molecules stick together when water is transported through the body.
Adhesion occurs too between water molecules and other polar molecules as well as surfaces.
The effect of this along with cohesion result in water demonstrating capillary action.
This is when water can rise up a narrow tube against the force of gravity.

Question 30

Coolant

Answer 30

Water helps lessen the temperature change during chemical reactions as plenty of energy is required to overcome hydrogen bonding.

Since enzymes work in a narrow temperature range, it is very important to maintain a constant temperature in cellular environment.

Question 31

Habitat

Answer 31

It is stable since it does not change temperature or become a gas easily. This provides a constant environment.

The ice floats on the surface of the ponds (as ice is less dense than water) and lakes rather than form the bottom.
This provides an insulating layer above the water.
This helps some aquatic organisms to survive.
Some organisms also live at the surface of water.
Surface tension is strong enough to support small insects such as pond skaters.

Question 32

Viscosity

Answer 32

Since water is a solvent and acts as a transport medium, it needs low resistance so it can flow easily and quickly.

Question 33

Specific Heat Capacity

Answer 33

Due to the large number of hydrogen bonds between the water molecules, these are able to absorb a lot of heat without a significant rise in the temperature.

Question 34

Transpiration and translocation

Answer 34

Due to water’s cohesive properties, it can be drawn in through the roots and be carried up the vascular bundle as well as be lost from the surface of the leaf.

Question 35

Maximum density

Answer 35

Water has a maximum density of 1g/cm^3 at 4 degrees celsius.

Below 4 degrees celsius, the density of water decreases which makes ice float

Question 36

Metabollite

Answer 36

Metabolism is a collective term for all the chemical reactions that take place within a cell. The chemicals involved are called metabolites.
Water is a metabolite in the photosynthesis.
At the first stage of photosynthesis, water splits into hydrogen and oxygen atoms.

Question 37

Digestion and absorption

Answer 37

Water is absorbed primarily in the small intestine which is then added to the blood stream to help maintain blood volume and therefore stabilise blood pressure.

Water and other liquids help break down food so that your body can absorb the nutrients.

Question 38

Medium for enzyme activity

Answer 38

Enzymes require a certain level of water in their structures in order to maintain their natural shape, allowing them to deliver their full functionality.

Question 39

Turgor and plasmolysis

Answer 39

Plasmolysis- the cell sap escapes the protoplast and causes shrinkage of the cell. This happens whenever water moves out of the cell.

Turgor pressure- when water flows into the cell sap causing the excess cell sap to push against the cell wall.

Question 40

Colour of water

Answer 40

The red, yellow, green wavelengths of sunlight are absorbed by water molecules in the ocean. When sunlight hits the ocean, some of the light is reflected back directly, but most of it penetrates the ocean surface and interacts with the water molecules that it encounters.

Question 41

Hydrostatic skeleton

Answer 41

This is a skeleton supported by fluid (including water) pressure.
Common among invertebrate organisms.

Question 42

Definition of plastid

Answer 42

plastids are doubled membraned ‘sac-like’ organelles, generally involved in either the manufacture or storage of food.

Question 43

Role of lipids

Answer 43

They have a high energy yield and therefore act as an important energy source, which can be respired.
Plants store lipids as lipid droplets; animals store lipids as fats in adipose tissue.
Act as an insulating layer, forming thermal insulation under the skin of mammals and an electrical insulator around some of the nerve cells in vertebrates and some invertebrates.
Biological membranes made of lipids and so are the group of hormones called steroids.
Also a waxy layer of leaves

Question 44

What are triglycerides

Answer 44

Fats and oils which are formed from a condensation reaction between two groups of molecules: fatty acids and glycerol.
A glycerol and three fatty acids linked by three ester bonds.
They form an ester bond or ester link.
Glycerol is an alcohol and this never changes in triglycerides. However, the fatty acids do, depending on the fat or oil formed.

Question 45

How does a glycerol look like

Answer 45

There are three carbons at the centre of the chain. Each are linked to a hydroxyl group on one end and an hydrogen atom on the other. The carbons at each corner of this chain have another hydrogen atom each sticking out.

Question 46

What are fatty acids

Answer 46

Large molecules consisting of a hydrocarbon chain with a carboxyl group (COOH) at one end.
However, these acids can vary considerably in the length of the hydrocarbon chain.
The number of carbons in the hydrocarbon chain depends on what type of fatty acid it is. But this is usually between 14 to 22 carbon atoms long.
It may contain a methyl group (CH3) at the other end depending on the acid.

Question 47

Ester bondS in triglycerides

Answer 47

There are three OH groups in a glycerol molecule. This is why 3 fatty acids are needed to form a triglyceride. The OH of the carboxyl groups of the fatty acids reacts with the OH of the glycerol, thus forming 3 water molecules and 3 ester bonds.

When triglycerides are broken down, three water molecules need to be supplied to reverse the reaction.

Question 48

Why are triglycerides hydrophobic

Answer 48

Unlike water, which is a polar molecule due to having negatively and positively charged regions, the hydrocarbon chain in a triglyceride have an even charge. This is why it will not form any electrostatic bonds with water, and thus not dissolve.
The molecules that dissolve in water are either polar or ionic.

Question 49

Qualities of triglycerides

Answer 49

Efficient energy stores; energy rich
Insoluble and therefore does not affect the water potential of the cell
Excellent insulator
Aids buoyancy- helps aquatic animals
Used for protection around many vital organs

Question 50

What happens when triglyceride is oxidised

Answer 50

When oxidised during respiration, triglycerides release hydrogen molecules which combine with the oxygen to form metabolic water. Many desert animals rely on metabolic water to survive.

Question 51

Emulsion test

Answer 51

Add ethanol to oil (lipid) and mix it, to ensure that the oil is dissolved.
Then add water to this.
The mixture should turn cloudy white as soon as water is added.
Milk would be different because it will already with cloudy white.

Question 52

Saturated and unsaturated fats

Answer 52

Saturated- single bonds only between the carbon atoms; maximum number of bonds with hydrogen atoms
When saturated fatty acids are combined with glycerol, it forms a saturated fat.
Ex: animal fatty acids- stearic acid and butyric acid

Unsaturated fat- hydrocarbon chain has at least one double bond.
This forms mono-unsaturated fatty acid
The double bond is between two carbons; fewer hydrogens
These are healthier
Many double bonds- a poly-unsaturated fat.
Ex: plants- oleic acid

The double bond changes the shape of an unsaturated fat; this bond kinks the hydrocarbon chain.
It does not lie straight, but instead it pushes apart, making the acids less solid and more fluid.

Question 53

Phospholipids

Answer 53

Has only two fatty acid chains attached to the glycerol.
The third OH group is attached to a phosphate group, through condensation reaction.
In most phospholipids, the phosphate group generally contains a nitrogen-containing, water soluble group such as choline.
Therefore, it has a hydrophilic head (phosphate group with choline) and two hydrophobic fatty acid molecules which act as ‘tails’.

The phosphate group (PO43-) are found in the cytoplasm of every cell. These are negatively charged, making them soluble in water.

Question 54

Phospholipids as membranes

Answer 54

These hydrophobic tails form a hydrophobic core facing away from the water- based cytoplasm and external fluid while the hydrophilic head will be submerged in the fluid. Because of this, they are called surface active agents or surfactants.

In a bilayer membrane, there are two layers of phospholipids lined on top of each other. The heads face outwards while the tails are inwards.

Question 55

Differences between phospholipids and triglycerides

Answer 55

Function of triglyceride:
Insulation layer
Under the skin or around nerves and a protective layer around organs
A waxy layer on plant leaves

Function of phospholipids:
Barrier to many ions and molecules
Basis of cell membranes when carb chains are attached
Forms glycolipids used in cell signalling

Question 56

Cholestrol

Answer 56

Has hydrophobic and hydrophilic regions
Important part of cell membrane; is positioned between the phospholipids with the hydroxyl group at the periphery of the membrane. This adds stability to cell membranes and regulates their fluidity by keeping membranes fluid at low temperatures and stopping them from becoming too fluid at high temperatures
In vertebrates, it is made in the liver and intestines; is transported to all over the body through blood
It is also used to make steroid-based hormones such as testosterone, oestrogen and progesterone; vitamin D and bile

Question 57

Lipids- polar or non-polar?

Answer 57

They are non-polar because the electrons in the outer orbitals that form the bonds are more evenly distributed than in polar molecule.
Therefore no positive or negative regions within the molecule.
Due to this lipids are not soluble in water.

Question 58

What are lipid molecules known as?

Answer 58

They are known as macromolecules

Question 59

Sterols

Answer 59

Also known as steroid alcohols
Another type of lipid found in cell
Complex alcohol molecules, based on a four carbon ring structure with a hydroxyl (OH) group at one end.
Have hydrophobic/hydrophilic characteristics
The hydroxyl group is polar and therefore hydrophilic; the rest of the molecule is hydrophobic

Question 60

Chaning health advice

Answer 60

Nutrients do not work in isolation but as part of the combined effect of a whole range of nutrients; this is called food synergy