chapter 3 p1

Question 1

Molecules are built from

Answer 1

atoms.

Question 2

atoms are built from

Answer 2

smaller components including protons, neutrons, and electrons

Question 3

Elements:

Answer 3

Different types of atoms
are distinguished by the number of protons in their atomic nuclei.
There are over a hundred known elements in the universe but only a small percentage of these are present in the living world.

Question 4

all living things are made primarily from four key elements:

Answer 4

carbon (C), hydrogen (H), oxygen (0) and nitrogen (N).
In addition, phosphorus (P) and sulfur (S) also have important roles in the biochemistry of cells.
These six elements are the most abundant elements present in biological molecules.
Other elements, including sodium (Na), potassium (K), calcium (Ca), and iron (Fe), also have important roles in biochemistry.

Question 5

Answer 5

Question 6

Bonding:

Answer 6

Atoms connect with each other by forming bonds.
Atoms can bond to other atoms of the same element, or atoms of different elements, provided this follows the ‘bonding rules’
When two or more atoms bond together the complex is called a molecule.
A covalent bond occurs when two atoms share a pair of electrons.
The electrons used to form bonds are unpaired and present in the outer orbitals of the atoms.
Life on this planet is often referred to as being ‘carbon-based’ because carbon, which can form four bonds, forms the backbone of most biological molecules.

Question 7

Bonding follows some simple rules, determined by the number of unpaired electrons present in the outer orbitals of different elements:

Answer 7

Carbon atoms can form four bonds with other atoms.
Nitrogen atoms can form three bonds with other atoms.
Oxygen atoms can form two bonds with other atoms.
Hydrogen atoms can only form one bond with another atom.

Question 8

Answer 8

Question 9

Ions:

Answer 9

An atom or molecule in which the total number of electrons is not equal to the total number of protons

Question 10

cation.

Answer 10

If an atom or molecule loses one or more electrons it has a net positive charge

Question 11

anion

Answer 11

If an atom or molecule gains electrons, it has a net negative charge

Question 12

In ionic bonds

Answer 12

one atom in the pair donates an electron and the other receives it.
This forms positive and negative ions that are held together by the attraction of the opposite charges.

Question 13

electrolytes:

Answer 13

Ions in solution are called

Question 14

following tables list some of the important roles of ions in living organisms: cations

Answer 14

Question 15

following tables list some of the important roles of ions in living organisms: anions

Answer 15

Question 16

Carbohydrates elements

Answer 16

carbon, hydrogen, and oxygen, usually in the ratio Cx(H20)x

Question 17

Lipids elements

Answer 17

carbon, hydrogen, and oxygen.

Question 18

Proteins elements

Answer 18

carbon, hydrogen, oxygen, nitrogen, and sulfur.

Question 19

Nucleic acids

Answer 19

carbon, hydrogen, oxygen, nitrogen, and phosphorus.

Question 20

Polymers:

Answer 20

Biological molecules are often polymers.
Polymers are long-chain molecules made up by the linking of multiple individual molecules (called monomers) in a repeating pattern.
In carbohydrates the monomers are sugars (saccharides) and in proteins the monomers are amino acids.

Question 21

Water
The bonds of life:
p1

Answer 21

• Atoms join together to form molecules by making bonds with each other.
• In ionic bonds, atoms give or receive electrons.
• They form negative or positive ions that are held together by the attraction of the opposite charges.
• Covalent bonds occur when atoms share electrons.
• However, the negative electrons are not always shared equally by the atoms of different elements.
• In many covalent bonds, the electrons will spend more time closer to one of the atoms than to the other.
• The atom with the greater share of negative electrons will be slightly negative compared with the other atom in the bond, which will therefore be slightly positive (Figure 1).

Question 22

Water
The bonds of life:
p2

Answer 22

• Molecules in which this happens are said to be polar - they have regions of negativity and regions of positivity.
• Oxygen and hydrogen are examples of elements that do not share electrons equally in a covalent bond.
• Oxygen always has a much greater share of the electrons in an 0—H bond.
• Many organic molecules contain oxygen and hydrogen bonded together in what are called hydroxyl (OH) groups and so they are slightly polar.
• Water (H2O) is an example of such a molecule, in fact, water contains two of these hydroxyl groups (Figure 2).

Question 23

Answer 23

Question 24

formation of hydrogen bonds

Answer 24

• Polar molecules, including water, interact with each other as the positive and negative regions of the molecule attract each other and form bonds, called hydrogen bonds.
• Hydrogen bonds are relatively weak interactions, which break and reform between the constantly moving water molecules.
• Although hydrogen bonds are only weak interactions, they occur in high numbers.
• Hydrogen bonding gives water its unique characteristics, which are essential for life on this planet.

Question 25

Characteristics of water:

Answer 25

Water has an unusually high boiling point

When water freezes it turns to ice.

Water therefore has cohesive properties.

Question 26

Water has an unusually high boiling point

Answer 26

Water is a small molecule, much lighter than the gases carbon dioxide or oxygen, yet unlike oxygen and carbon dioxide, water is a liquid at room temperature.
This is due to the hydrogen bonding between water molecules.
It takes a lot of energy to increase the temperature of water and cause water to become gaseous (evaporate).

Question 27

When water freezes it turns to ice.

Answer 27

• Most substances are more dense in their solid state than in their liquid state, but when water turns to ice it becomes less dense.
• This is because of the hydrogen bonds formed.
• As water is cooled below 4°C the hydrogen bonds fix the positions of the polar molecules slightly further apart than the average distance in the liquid state.
• This produces a giant, rigid but open structure, with every oxygen atom at the centre of a tetrahedral arrangement of hydrogen atoms, resulting in a solid that is less dense than liquid water.
• For this reason, ice floats.

Question 28

Water therefore has cohesive properties.

Answer 28

It moves as one mass because the molecules are attracted to each other (cohesion).
It is in this way that plants are able to draw water up their roots and how you are able to drink water through a straw.
Water also has adhesive properties - this is where water molecules are attracted to other materials.
For example, when you wash your hands your hands become wet, the water doesn’t run straight off.
Water molecules are more strongly cohesive to each other than they are to air, this results in water having a ‘skin’ of surface tension.

Question 29

Some of the ways in which water is vital for life:

Answer 29

Because it is a polar molecule, water acts as a solvent in which many of the solutes in an organism can be dissolved.

Water makes a very efficient transport medium within living things.

Water acts as a coolant, helping to buffer temperature changes during chemical reactions

Question 30

Because it is a polar molecule, water acts as a solvent in which many of the solutes in an organism can be dissolved.

Answer 30

The cytosol of prokaryotes (bacterial) and eukaryotes is mainly water.
Many solutes are also polar molecules, amino acids, proteins and nucleic acids
Water acts as a medium for chemical reactions and also helps transport dissolved compounds into and out of cells.

Question 31

Water makes a very efficient transport medium within living things.

Answer 31

Cohesion between water molecules means that when water is transported though the body, molecules will stick together.
Adhesion occurs between water molecules and other polar molecules and surfaces.
The effects of adhesion and cohesion result in water exhibiting capillary action.
This is the process by which water can rise up a narrow tube against the force of gravity.

Question 32

Water acts as a coolant, helping to buffer temperature changes during chemical reactions …

Answer 32

in prokaryotic and eukaryotic cells because of the large amounts of energy required to overcome hydrogen bonding.
Maintaining constant temperatures in cellular environments is important as enzymes are often only active in a narrow temperature range.
Many organisms, such as fish, live in water and cannot survive out of it.
Water is stable - it does not change temperature or become a gas casily, therefore providing a constant environment.
Because ice floats, it forms on the surface of ponds and lakes, rather than from the bottom up.
This forms an insulating layer above the water below.
Aquatic organisms would not be able to survive freezing temperatures if their entire habitat froze solid.
Some organisms also inhabit the surface of water. Surface tension is strong enough to support small insects such as pond skaters.