A1.1: Water

Question 1

State where the first cells originated

Answer 1

In water

Question 2

​List reasons why water is a substance on which life depends​

Answer 2

• it is a metabolite (chemicals involved in metabolism)
• it maintains biological structures
• it is a temperature buffer (absorbs heat due to its high shc)

Question 3

Describe the structure of an atom.

Answer 3

• Protons (+vely charged) and Neutrons (no charge) within the nucleus (called Neucleons together)
• Electrons (-vely charged)
• Atoms that have a deficit or a surplus of electrons are called ions

Question 4

Outline the formation of ionic and covalent bonds between atoms.

Answer 4

Covalent bonds:
- Electrostatic attraction between shared pair of electrons between the nuclei of two atoms

Ionic bond:
- Electrostatic attraction between oppositely charged ions (+vely charged is cation, -vely charged is anion)

Question 5

Explain the sharing of electrons between atoms in a polar covalent bond.

Answer 5

• Polar covalent (share electrons unequally)
• Slight positive charge (delta +) due to fewer electrons around that nucleus. VV for delta -

Question 6

State the location of the polar covalent bond within a water molecule.

Answer 6

Can occur in amino acid R groups which impact the tertiary structure of a protein

Question 7

Explain the partial charges of the oxygen and hydrogen atoms within a water molecule.

Answer 7

As the O2 atom has more protons, it attracts the shared e- more often thus creating an unequal distribution of charge
- Delta - is Oxygen
- Delta + is Hydrogen

Question 8

Draw a water molecule, including notation to depict the partial charges of the atoms.

Answer 8

Dotted line connects H atom and O atom
- O2 has Delta - charge
- H2 has Delta + charge

Question 9

Outline the cause of the formation of hydrogen bonds between water molecules.

Answer 9

• Partially positive H atoms of one water molecule are attracted to the partially negative O2 atom of a different water molecule forming a hydrogen bond.
• Each H2O can form up to 4 Hydrogen bonds with 4 other H2O molecules

Question 10

Outline the consequences of the collective strength of hydrogen bonds between water molecules.​

Answer 10

Allows it several emergent properties:
- Adhesion
- Cohesion
- Solvency
- High specific heat capacity

Question 11

Define cohesion.

Answer 11

When water molecules stick together and form H bonds between different water molecules

Question 12

Describe how water moves through the xylem of a vascular plant.

Answer 12

• Transpiration occurs due to stomata being open to allow gas exchange for photosynthesis which causes tension
• Tension pulls water in the xylem drawing water up
• Cohesion pulls water molecules up and out of the stomata in a column due to the H bonds between water molecules

Question 13

Outline the cause of surface tension.

Answer 13

There are H bonds between the water molecules as water molecules are more attracted to one another than to air molecules

• This allows them to resist an external force thus, the cohesive nature of water allows it to have high surface tension

Question 14

State 2 benefits to living things that result from surface tension.

Answer 14

• Allows organisms like water striders to live on the surface of water
• Allows some seeds to disperse away from the parent plant

Question 15

Define adhesion.

Answer 15

• The attraction of water molecules to other polar molecules allowing plants to move water using capillary action

Question 16

Define polar.

Answer 16

Unequal sharing of electrons between atoms within the molecules

Question 17

Define ion.

Answer 17

Formed when ions have different number of electrons and protons

Question 18

Compare cation and anion.

Answer 18

Cations have positive charges as it has more protons than electrons

Question 19

Explain why water is attracted to molecules that are polar or charged.

Answer 19

Anions have negative charges as it has more electrons than protons

Question 20

Outline the cause of capillary action.

Answer 20

• Adhesion of water to the walls causes an upward force on the liquid causing
• Cohesion between Water molecules

Question 21

Describe capillary action in plant tissue.

Answer 21

• Movement of water in a tube in opposition to the external forces of gravity
• H bonds betw. water molecules and cellulose in xylem cell wall help this movement from the roots to the leaves -

Question 22

Outline the cause and effect of capillary action in soil.

Answer 22

Cause:
- Water adheres to surface of soil particles and plants absorb the water via osmosis

Effect:
- Water moves upwards through soil pores and the height water rises to is dependent on the soil type

Question 23

Identify solvent and solutes of a solution.

Answer 23

Solvent:
- Liquid in which a solute dissolves

Solute:
- Substance that dissolves in the solvent

Question 24

Define solvation.

Answer 24

The interaction of a solvent with the dissolved solute

Question 25

Explain why water is able to dissolve charged and polar molecules.

Answer 25

• Water is a solvent
• When solutes dissolve in water, each molecule gets surrounded by the water molecules
• the water forms H bonds with the solute thus, forming a hydration shell around the solute

Question 26

Outline the solvation of hydrophilic and hydrophobic substances.

Answer 26

Solvation of Hydrophilic substances:
- partially positive charge of water’s H atom is attracted to the negative charge of an anion. VV for a partially negative charge of water’s O2 atom

Solvation of Hydrophobic substances:
- Hydrophobic molecules are non-polar and don’t have charged atoms thus, they are attracted to other hydrophobic molecules and are insoluble in water

Question 27

State an example of the function of a molecule depending on its being hydrophobic and insoluble.

Answer 27

Phospholipids have hydrophobic tails made of fatty acids which form bilayers in water with the tails being tucked away from water

Question 28

State an example of the function of a molecule depending on it being hydrophilic and soluble.

Answer 28

Dissolved substances in the cytosol are required for metabolic processes to keep the cell alive

Question 29

Outline the role of water as a medium for metabolism.

Answer 29

Water is needed for cellular metabolism as it:
- dissolves the reactants and enzymes for reactions
- catabolic reactions break down larger molecules into smaller molecules
- anabolic reactions build larger molecules from smaller molecules

Question 30

Describe the role of water as a medium for transport in vascular plants.

Answer 30

• Dissolved minerals are transported in the xylem from the roots to the leaves
• Dissolved sugars produced in photosynthesis are transported in the phloem from the source to sink

Question 31

Describe the role of water as a medium for transport in animal blood.

Answer 31

Water dissolves substances in solution around the body of an organism:
- Proteins like antibodies
- Glucose which is used in cellular respiration
- Waste products of metabolism like urea which is removed from the blood at the kidney

As lipids are hydrophobic, they can’t be transported in solution
- In order to be transported in blood, fat droplets are coated in proteins and phospholipids forming Lipoproteins

Question 32

Define physical property.

Answer 32

A measurable behaviour of matter that exists without the matter interacting with other things

Question 33

List physical properties of water that are consequential for animals in aquatic habitats.

Answer 33

• Buoyancy
• Viscosity
• Thermal Conductivity
• highest specific heat capacity of any liquid

Question 34

Outline the cause and effect of buoyancy.

Answer 34

Cause:
- Upward force applied to an object that is immersed in a fluid

Effect:
- Depends on the density of the object and not mass; If the density of the object is lower than the density of the fluid, the buoyant force will be greater than the force due to gravity and the object will float. VV

Question 35

Outline the cause and effect of viscosity.

Answer 35

Cause:
- Due to the amount fo friction the molecules of a liquid experience as they flow over each other. A thick fluid is more viscous and a thin fluid is less viscous

Effect:
- Water is more viscous than some other substances as it can form H bonds with itself that increase the friction and reduce water’s tendency to flow.

Question 36

Compare the viscosity of air to water to blood.

Answer 36

• Blood is more viscous than pure watermas cells and dissolved solutes increase viscosity however, blood is more viscous than air

Question 37

Define thermal conductivity.

Answer 37

A measure of a material’s ability to move heat across a temperature gradient determined by how easily energy transfers through the material

Question 38

Compare less conductive to more conductive materials.

Answer 38

Less conductive materials (styrofoam, air):
- Heat slowly moves through the material
- Better at insulation and preventing heat loss

More conductive materials (fat, water):
- Heat rapidly moves through the material
- Better for absorbing and transferring heat

Question 39

Outline a consequence to the life of the thermal conductivity of air and water.

Answer 39

Water:
- Thick later of fat provides insulation from cold ocean temperatures in marine mammals

Air:
- A person will more quickly become hypothermic in cold water than in cold air as the water rapidly conducts body heat away from the body

Question 40

Define specific heat capacity.

Answer 40

The quantity of heat needed to raise the temperature of a chemical per unit mass (water heats up very slowly)

Question 41

Describe why water has the highest specific heat capacity of any liquid

Answer 41

• Caused by its numerous H bonds where each bond is weak but there are so many of them that collectively, a lot of energy must be required to break them all

Question 42

State two benefits to life of the high specific heat capacity of water.

Answer 42

• Helps body temperature rise and fall slowly when eternal temperatures become very hot or cold
• Temperature of aquatic habitats rise and fall slowly when surrounding air temperatures become very hot or cold

Question 43

Compare the physical properties of water to those of air.

Answer 43

The physical properties of water are much higher than air

Question 44

Describe how the black-throated loon (Gavia arctica) interacts with the physical properties of water in their habitat.

Answer 44

Black-Throated Loon:
- Buoyancy allows the seal to stay afloat without expending lots of energy
- Water’s viscosity allows the seal to swim streamlined
- Water’’s great thermal conductivity allows the seal to insulate itself with blabber to maintain body temperature
- Water’s high SHC allows habitat stability for the seal

Question 45

Explain the hypothesis that asteroids are responsible for the origin of water on Earth.

Answer 45

Extraplanetary objects like asteroids contain large amounts of water and plummeted into the earth

Question 46

State two reasons why water was retained on early Earth.​

Answer 46

1. The distance of the Earth from the Sun maintains a temperature on Earth to stay in liquid form as a result of the cohesion of water molecules via H bonds
2. Earth’s gravity keeps water from escaping the planet

Question 47

Explain why the presence of water is considered fundamental to the search for extraterrestrial life.

Answer 47

The presence of water is precedent to the search for extraterrestrial life

Question 48

Define “Goldilocks zone” in relation to the search for extraterrestrial life.

Answer 48

Just the right distance from a star for water to remain at least periodically in liquid form on the surface