A1.1 Water

Question 1

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

Answer 1

1. The first cells originated in water
2. Water is the “universal solvent”, allowing it to dissolve and transport molecules around a body
3. Water is a metabolite in condensation and hydrolisis reactions
4. Water is a temperature buffer in bodies and ecosystems

Question 2

Describe the structure of an atom.

Answer 2

Protons and neutrons make up the necleus of the atom, while electrons orbit it in a “cloud.”

The electrons in an atom are attracted to the protons in the nucleus by an electromagnetic force in which the positive charge of the proton attracts the negative charge of the electron.

Question 3

Outline the formation of ionic bonds between atoms.

Answer 3

An ionic bond is an attraction between a positively charged ion and a negatively charged ion.

Question 4

Outline the formation of
covalent bonds between
atoms.

Answer 4

In a covalent bond, two atoms share one or
more pair of electrons.

Question 5

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

Answer 5

In a polar covalent bond, the nucleus of one
atom has more pull on the shared electrons
than the other atom. As a result, it has a
bigger electron cloud surrounding it. Because
electrons have a negative charge and there
are MORE ELECTRONS around this nucleus,
there is a slight negative charge ( -) on this nucleus. Because there are LESS ELECTRONS around the second atom’s nucleus, there is a slight positive charge ( +) on this nucleus.

Question 6

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

Answer 6

There are two polar covalent bonds within a
water molecule; one between the oxygen atom
and each hydrogen atom.

Question 7

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

Answer 7

The nucleus of the oxygen atom of a water molecules has more pull on the shared electrons than the hydrogen atom. As a result, it has a bigger electron cloud surrounding it.- Because electrons have a negative charge and there are MORE ELECTRONS around the oxygen nucleus, there is a slight negative charge ( -) on this nucleus. Because there are LESS ELECTRONS around the hydrogen atom’s nucleus, there is a slight positive charge ( +) on this nucleus.

Question 8

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

Answer 8

The partially positive hydrogen atoms of one
water molecule are attracted to the partially
negative oxygen atom of a different water molecule, forming a hydrogen bond.

Question 9

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

Answer 9

Water’s ability to make hydrogen bonds with
itself and other charged molecules grants it a
number of emergent properties such as cohesion, adhesion, solvency and a high specific heat. Collectively these property make water the primary medium of life.

Question 10

Define cohesion.

Answer 10

Cohesion is the property of water in which
it makes hydrogen bonds with itself, causing
water molecules to stick together.

Question 11

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

Answer 11

1. Transpiration (evaporation) occurs through
   stomata of a leaf. As transpiration occurs, it
   creates negative pressure
2. The tension created by transpiration “pulls”
   water in the plant xylem, drawing the water
   upward
3. Cohesion pulls up water molecules in a
   chain as the top-most water is pulled up and
   out of the stomata.

Question 12

Outline the cause of surface
tension.

Answer 12

The molecules on the surface are more attracted other molecules of the liquid than to molecules in the surrounding air. The net effect is an inward force that causes water to behave as if its surface were covered with a stretched elastic membrane

Question 13

State a benefit to living
things that results from surface tension.

Answer 13

Surface tension allows organisms like water
striders to “walk on water” and provides a
stable environment for other organisms that
live on or near the surface of water. To break
through the surface of the water, enough force
must be applied to break many hydrogen
bonds simultaneously.

Question 14

Define adhesion.

Answer 14

The attraction of water to other polar or charged molecules is called adhesion.

Question 15

Define polar.

Answer 15

Polar means there is unequal sharing of electrons in a covalent bond between two atoms

Question 16

Define ion.

Answer 16

An ion is an atom with different (unequal) numbers of electrons and protons.

Question 17

Compare cation and anion.

Answer 17

A cation has a positive charge because it has
more protons than electrons (Na+)
An anion has a negative charge because it has
more electrons than protons (Cl-)

Question 18

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

Answer 18

The slight negative charge (´-) of water oxygen atom is attracted to the [slight] positive charge of molecules that are polar or charged

Question 19

Outline the cause of capillary action.

Answer 19

Capillary action is the movement of water in through a narrow space, often in opposition to external forces like gravity. Adhesion of water to the walls of a vessel will cause an upward force on the liquid.

Question 20

Describe capillary action in
plant tissue.

Answer 20

Capillary action helps bring water from the roots all the way up to the branches and leaves. Adhesion of water to the xylem walls will cause an upward force on the water.

Question 21

Outline the cause and effect
of capillary action in soil.

Answer 21

Capillary action in soil the primary force that enables the soil to retain water. In the same way that water moves upwards through a tube against the force of gravity; water moves upwards through soil pores, or the spaces between soil particles.

Question 22

Identify solvent and solutes
of a solution.

Answer 22

Solvent: the liquid in which a solute dissolves
Solute: the substance that dissolves in a solvent.

Question 23

Define solvation.

Answer 23

Solvation is the interaction of a solvent with the dissolved solute.

Question 24

Explain why water is able
to dissolve charged molecules.

Answer 24

Water is electrostatically attracted to ions.
The slight positive charge (´+) of of water hydrogen atom is attracted to the negative charge of an anion.

The slight negative charge (´-) of of water oxygen atom is attracted to the positive charge of a cation.

Question 25

Explain why water is able to
dissolve polar molecules.

Answer 25

Polar molecules can form hydrogen bonds
with water. The slight positive charge (´+) of a water hydrogen atom is attracted to the negatively charged region of the solute.

The slight negative charge (´-) of a water oxygen atom is attracted to the positively charged region of the solute.

Question 26

Outline the solvation of hydrophilic and hydrophobic
substances.

Answer 26

Hydrophobic means water fearing. Because they are not polar or charged, hydrophobic molecules will not dissolve in water. They are insoluble.

Hydrophilic means water loving. Because they are polar or charged, hydrophilic molecules will dissolve in water. They are soluble.

Question 27

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

Answer 27

Because they have hydrophillic amino acids, enzymes can dissolve in cytoplasm where they are used to catalyze chemical reactions in the cell.

Question 28

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

Answer 28

Because of their hydrophobic tail, phospholipids will form bilayers in water, with the tails not exposed to water.

Question 29

Outline the role of water as a
medium for metabolism.

Answer 29

Cytosol is the liquid part of the cytoplasm, a structure common to all cells. It is composed of about 80 percent water and also contains dissolved salts, fatty acids, sugars, amino acids, and proteins such as enzymes. These substances must be dissolved in water in order to carry out the metabolic processes required to keep the cell alive.

Question 30

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

Answer 30

Water is used to transport molecules through
the body of vascular plants.
Dissolved mineral ions are transported in the
xylem from roots to leaves

Question 31

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

Answer 31

Water is used to transport molecules through
the body within the blood of animals. Blood plasma transports
Salt ions
Amino acids
Proteins
Glucose
Waste products of metabolism
A small amount of dissolved gasses

Question 32

Define physical property.

Answer 32

A physical property is a measurable behavior
or characteristic of matter that exists without
the matter reacting or 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
Specific heat capacity

Question 34

Outline the cause and effect
of buoyancy.

Answer 34

Cause:
an upward force applied to an object that is immersed in a fluid.

Effect:
If the buoyant force of the fluid is greater than the object’s weight, the object will float.

Question 35

Outline the cause and effect
of viscosity.

Answer 35

Cause:
Viscosity is due to the amount of friction the molecules of a liquid experience as they flow over each other.

Effect:
A thick fluid is more viscous and a thin fluid is less viscous.

Question 36

Compare viscosity of air to
water to blood.

Answer 36

Air < Water < Blood

Molecules in air have little friction as they flowover each other, so air is not viscous.

Molecules in water can form hydrogen bonds with each other, increasing the friction and
viscosity.

Cells and dissolved solutes in blood cause even more friction as the blood flows, increasing viscosity.

Question 37

Define thermal conductivity.

Answer 37

Thermal conductivity is a measure of a material’s ability to move heat across a temperature gradient.

Question 38

Compare less conductive to
more conductive materials.

Answer 38

Less Conductive
Heat slowly moves through the material.
Better at insulation and preventing heat loss.

More Conductive
Heat rapidly moves through the material.
Better for absorbing and transferring heat.

Question 39

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

Answer 39

Marine mammals are exposed to both air and water. The animal will lose more body heat
to the environment when in water than in air because water rapidly absorbs and removes
heat from the body. As a result, these animals have large layers of blubber which insulate their body heat sources (muscles) from the environmental. Fat is less conductive of thermal
energy than water, so the animal is able to retain more body heat than it would be able to
without the blubber.

Question 40

Define specific heat capacity.

Answer 40

Specific heat capacity is the quantity of heat needed to raise the temperature of a chemical per unit mass.

Question 41

Describe why water has a
high specific heat capacity.

Answer 41

Water’s high heat capacity is caused by its numerous hydrogen bonds. Each individual “bond” is weak, but there are so many of them that collectively a lot of energy must be added to break them all.

Question 42

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

Answer 42

As a result of its high specific heat capacity, water heats up or cools down very slowly. This
provides for a stable internal environment and habitat of living things.

Question 43

Outline a benefit to life of
water’s high specific heat
capacity.

Answer 43

Because living body’s contain a lot of water, body temperature is slow to fluctuate when
environmental temperatures change. Water’s high specific heat capacity helps body temperature rise and fall slowly when external temperatures becomes very hot or cold.

Question 44

Compare the physical properties of water to those of
air.

Answer 44

Water
greater buoyant force
greater viscosity
greater thermal conduction
greater specific heat capacity

Air
lower buoyant force
lower viscosity
lower thermal conduction
lower specific heat capacity

Question 45

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

Answer 45

Buoyancy in water allows the bird to stay afloat without expending a lot of energy, however when flying through air the bird must expend
energy to stay aloft. Air is not viscous, so the loon can easily move through it when flying.
The loon doesn’t lose as much body heat to the air because air has low thermal conductivity. However, because the air has a low specific heat, its temperature changes as rapidly.

Question 46

Describe how the ringed
seal (Pusa hispida) interacts
with the physical properties
of water in their habitat.

Answer 46

Buoyancy in water allows the seal to stay afloat without expending a lot of energy.
However, the water is viscous, so the seal has adaptations for streamlining as it swims
through it. Water has a greater thermal conductivity than air, so the seal needs to insulate itself with blubber to maintain body temperatures. However, because the water has a high
specific heat, the temperature of the water does not change as rapidly as the air around
it, providing habitat stability for the seal.