3.1.7/8 Water and Other ions

Question 1

Give a property of Water

Answer 1

Polar
Solvent
Reactive

Question 2

Why is it useful to living organisms that water is polar?

Answer 2

Acts as a universal solvent

Question 3

Why is it useful to living cells that water is a solvent?

Answer 3

Reactions occur faster in solution

Question 4

Why is it useful to living cells that water is reactive?

Answer 4

Takes place in hydrolysis and condensation reactions

Question 5

Name an important ion

Answer 5

Hydrogen
Sodium
Iron
Phosphate

Question 6

How do water and ions enter cells?

Answer 6

They can move down a concentration gradient
Both move through channel proteins
Ions can move against a concentration gradient by active transport

Question 7

3 properties of water that are important in biology

Answer 7

Is a metabolite
Is a solvent
Has a relatively high specific heat capacity
Has relatively large latent heat of vaporisation
Has cohesion / hydrogen bonds between molecules

Question 8

Why is water having a high specific heat capacity good?

Answer 8

It takes a lot of energy (in or out) to change the temperature of water

When we heat water, the heat energy goes towards weakening or breaking the hydrogen bonds rather than increasing the kinetic energy of the water molecules. Because of this, water acts as a buffer against rapid temperature changes.

This allows water to act as a habitat for aquatic organisms.

Question 9

Density of water

Answer 9

Ice is less dense than liquid water
This means that ice floats
Ice is a habitat for a number of organisms

Ice also insulates the water below and prevents it from freezing. This means that organisms can continue to live in the water under the ice.

Question 10

Why is water having a high latent heat of vaporisation good?

Answer 10

It takes a large amount of heat energy to evaporate water.
This allows organisms o cool themselves without losing a great deal of water.
e.g. sweating

During sweating, heat energy is used to evaporate water from the surface of the skin and this transfer of heat energy allows the organism to cool down

Question 11

Why is water acting as a good solvent good?

Answer 11

Lots of substances can dissolve in water.

Both eukaryotic and prokaryotic cells contain a large amount of dissolved substances. e.g. the chemicals involved in metabolic reactions such as respiration as well as the enzymes needed to carry out these reactions.

Bodies of water such as ponds and rivers contain dissolved oxygen which is used to carry out respiration. This makes water an excellent habitat for these organisms.

It can also be used to transport substances. E.g. blood plasms. Blood plasma is the liquid part of blood and this contains a large number of dissolved substances e. CO2, Na+, glucose and amino acids etc.

Water is also used to transport substances in the xylem vessel of plants. Water in the xylem contains dissolved mineral ions such as the magnesium ion. Magnsesium ions pass into the plant roots from the soil.They are transported in the xylem from the roots to the leaves. Once in the leaves, the magnesium ions are used to make chlorophyll for photosynthesis.

Question 12

Cohesion

Answer 12

Cohesion allows long columns of water to travel in the xylem tubes.
This makes water ideal as a transport medium in plants

Cohesion also causes surface tension where water meets air.

Question 13

Water in metabolic reactions

Answer 13

Water is a reactant in many different reactions e.g. hydrolysis and in photosynthesis.

Water is also produced in certain metabolic reactions e.g. condensation reactions and aerobic respiration