Water and its functions

Question 1

What does inorganic mean?

Answer 1

No carbon

Question 2

What is an ion?

Answer 2

A charged particle

Question 3

Why are inorganic ions important?

Answer 3

Play an important role in many essential cellular processes

Question 4

Where do inorganic ions occur?

Answer 4

In the cytoplasm and body fluids of organisms

Question 5

Define details of inorganic ions

Answer 5

• Some occur in high concentrations and some in low
• The concentration of certain ions can fluctuate and can be used in cell signalling and neuronal transmission
• Each type of inorganic ion has a specific role depending on its properties

Question 6

What are the uses of iron ions (Fe2+/Fe3+)?

Answer 6

• Haemoglobin to bind with oxygen for transport for aerobic respiration
• Transfer of electrons during respiration and photosynthesis

Question 7

What are phosphate ions used for (PO4^3-)?

Answer 7

• ATP, storing energy in bonds
• Phospholipid bilayer
• Structural role in DNA molecules (DNA and RNA)

Question 8

What are magnesium ions (Mg2+) used for?

Answer 8

• Production of chlorophyll

Question 9

What are Hydrogen ions (H+) used for?

Answer 9

• Optimal pH of enzymes and functioning of enzymes
• pH
• Bohr effect
• Active transport of sucrose in the phloem

Question 10

What are sodium ions (Na+) used for?

Answer 10

• Transport of glucose and amino acids across plasma membranes
• Transmission of nerve impulses

Question 11

What is the dipolar water molecule?

Answer 11

Although a water molecule has no overall charge, the oxygen atom has a slight negative charge, while the hydrogen atom has a slight positive one - has both positive and negative so described as dipolar

Question 12

What kind of bonding occurs between water molecules?

Answer 12

The positive pole of one water molecule will be attracted to the negative pole of another water molecule - known as hydrogen bonds

Question 13

How do hydrogen bonds help water molecules?

Answer 13

Each bond is fairly weak (1/10 strength of covalent bond) but together they form important forces that cause water molecules to stick together

Question 14

What is the advantage of the hydrogen bonds causing water molecules to stick together?

Answer 14

• More energy is required to separate them than if they were not bonded so the b.p. is higher than expected
• Takes more energy to heat a given mass of water i.e. high specific heat capacity

Question 15

Without its hydrogen bonding, what would water exist as at temperatures commonly found on earth?

Answer 15

A gas

Question 16

Because of its high specific heat capacity, what does water act as?

Answer 16

• A buffer against sudden temperature variations, making the aquatic environment a stable one
• As organisms are mostly water, it also buffers them against sudden temperature changes especially in terrestrial environments

Question 17

How does hydrogen bonding affect the latent heat of vaporisation of water?

Answer 17

The bonding means a lot of energy is required to evaporate 1 gram of water

Question 18

How is the latent heat of vaporisation of water useful in mammals?

Answer 18

• Evaporation of water such as sweat in mammals is a very effective way of cooling as body heat is used to evaporate water (so a lot of energy, which is heat, is used)
• It allows organisms to control their temperature

Question 19

What is cohesion?

Answer 19

The tendency of molecules to stick together

Question 20

How is cohesion of water useful in plants?

Answer 20

• Water has large cohesive forces (due to hydrogen bonding) and these allow it to support columns of water in tube-like transport cells of plants
• Water can be pulled up through a tube, such as a xylem vessel, in plants

Question 21

How is cohesion of water useful for water surfaces?

Answer 21

• Where water molecules meet air, they tend to be pulled back into the body of water
• This force is called surface tension and means that the water surface acts like a skin and is strong enough to support small organisms (pond skaters)

Question 22

Why is water important?

Answer 22

It is the main constituent of all organisms - mammals are typically 65% water

Question 23

What is water in terms of metabolism?

Answer 23

A metabolite

Question 24

How is water used in metabolism?

Answer 24

• Used to break down many complex molecules by hydrolysis
• Also produced in condensation reactions

Question 25

Where do chemical reactions take place?

Answer 25

In an aqueous medium

Question 26

Why is water important in photosynthesis?

Answer 26

It is a major raw material

Question 27

Why is water an important solvent?

Answer 27

It is an important solvent where metabolic reactions occur

Question 28

Which substances will water readily dissolve?

Answer 28

• Gases such as oxygen and CO2
• Wastes such as ammonia and urea
• Inorganic ions and small hydrophilic molecules (amino acids, ATP, monosacharrides)
• Enzymes, whose reactions take place in solution

Question 29

How is water useful in terms of structure?

Answer 29

Not easily compressed and so provides support (turgor structure in herbacceous plants)

Question 30

How is water useful for aquatic plants?

Answer 30

Transparent so aquatic plants can photosynthesise

Question 31

How is water useful for the eye?

Answer 31

Light rays can penetrate the jelly-like fluid that fills the eye and so reach the retina