2.4 - Water and its functions + inorganic ions

Question 1

Why do water molecules have unusual properties

Answer 1

• its diploid nature
• and the subsequent hydrogen bonding this allows

Question 2

What three atoms are water molecules created from

Answer 2

• 2 atoms of hydrogen
• 1 atom of oxygen

Question 3

Why is a water molecule described as dipolar

Answer 3

• the oxygen atom has a slight negative charge
• while the hydrogen atoms have a slight positive charge
  —> the water molecule has both positive and negative poles = therefore described as dipolar

Question 4

Explain the water and hydrogen bonding

Answer 4

• opposite charges attract: therefore positive poles of one molecule is attracted to the negative poles of the other
• the attractive force between these charges is called: a hydrogen bond
• each bond is fairly weak, but all together = form important forces allowing the water molecules to stick together
  —> giving the water its unusual properties

Question 5

Describe the specific heat capacity of water

Answer 5

• because water molecules stick together = takes more energy (heat) to separate them than would be needed if they didn’t bond to one another
• for this reason: boiling point is higher than expected
• without its hydrogen bonding = it would be a gas at room temp
  ——> water therefore has a high specific heat capacity
  —> water therefore act as a buffer against sudden temp variations, making the aquatic environment a temp-stable one
  —> because organisms are mostly water = it also buffers them against sudden temp changes (especially in terrestrial environments

Question 6

Describe the Latent heat of vaporisation of water

Answer 6

• hydrogen bonding between water molecules means that it requires a lot of energy to evaporate 1g of water
• this energy is called the ‘latent heat of vaporisation’
• evaporation of water such as sweat in mammals is therefore a very effective means of cooling because body heat is used to evaporate the water

Question 7

Describe the cohesion and surface tension in water

Answer 7

• the tendency of molecules to stick together = known as cohesion
• with its hydrogen bonding, water has large cohesive forces and these allow it to be pulled up through a tube (such as a xylem vessel in plants.)
• in the same way, where water molecules meet air they tend to be pulled back into the body of water rather than escaping it.
  —> this force is called surface tension
  —> it means that the water surface acts like a skin, and is strong enough to support small organisms such as pond skaters

Question 8

Describe the importance of water in metabolism to living organisms

Answer 8

• water is used to break down many complex molecules by hydrolysis, e.g. proteins —> amino acids
• water is also produced in condensation reactions
• chemical reactions take place in an aqueous medium
• water is a major raw material in photosynthesis

Question 9

Describe the importance of water as a solvent in organisms

Answer 9

Water readily dissolves other substances
- gases such as oxygen and carbon dioxide
- wastes such as ammonia and urea
- inorganic ions and small hydrophilic molecules such as amino acids, monosaccharides and ATP
- enzymes, whose reactions take place in solution

Question 10

What are the other important features of water in an organism

Answer 10

• its evaporation cools organisms and allows them to control their temp
• not easily compressed, therefore provides support, e.g. the hydrostatic skeleton of animals such as the earthworm and turgor pressure in herbaceous plants
• It is transparent and therefore aquatic plants can photosynthesise and also light rays can penetrate the jelly-like fluid that fills the eye and so reach the retina

Question 11

Describe the importance of water in inorganic ions

Answer 11

• inorganic ions are found in organisms where they occur in solution in the cytoplasm of cells and bodily fluids and apart of larger molecules. Found in varying concentrations
• inorganic ions perform a range of functions. The specific function of a particular ion performs is related to its properties
• e.g. iron ions are found in haemoglobin where they play a role in transporting oxygen

Question 12

what is an electron

Answer 12

A stable subatomic particle with a charge of negative electricity

Question 13

what is an ionic bond

Answer 13

A type of linkage formed from the electrostatic attraction between oppositely charged ions in a chemical compound

Question 14

what is an Anion

Answer 14

A negatively charged ion (has gained 1 or more electrons)

Question 15

what is a Cation

Answer 15

A positively charged ion (has lost 1 or more electrons)

Question 16

what is the formula + use/importance of: hydrogen

Answer 16

• H+
• important in acid base chemistry (important for pH balance)
• establish trans-membrane electrochemical gradients (important for nerve impulses and generating ATP)

Question 17

what is the formula + use/importance of: Iron

Answer 17

• Fe 3+ / Fe2+
• iron binding proteins are involved in redox reactions, electron transport, and in the transport of oxygen (important for respiration)

Question 18

what is the formula + use/importance of: Sodium

Answer 18

• Na+
• transmission of nerve impulses and in fluid and electrolyte balance in plants. Involved in maintaining cell turgor and opening/closing the stomata (important for osmosis and water balance

Question 19

what is the formula + use/importance of: Phosphate

Answer 19

• PO4 3-
• Component of phospholipids, nucleotides and ATP. Combines with calcium as calcium phosphate in bones/teeth (important for cell membranes, DNA + RNA)

Question 20

Definition of adhesion

Answer 20

attraction between molecules of different types

Question 21

Definition of cohesion

Answer 21

attraction between molecules of the same type (important in movement of water up a plant)

Question 22

what is the definition of Latent heat of vaporisation

Answer 22

heat taken in by a liquid in order to transform it into vapor

Question 23

what is the definition of a polar molecule

Answer 23

a molecule with an uneven distribution of charge as a result of electrons being more or less attracted to different atoms within the molecule

Question 24

what is the definition of specific heat capacity

Answer 24

The amount of heat per unit mass required to raise the temp by 1’C

Question 25

how does water stick to the xylem wall

Answer 25

using adhesion and cohesion

Question 26

what is the bond between the water molecules

Answer 26

hydrogen bonds
- the hydrogen of one molecule forms a bond with the oxygen of another (cohesion)
- due to attraction between positive hydrogen and negative oxygen atoms

Question 27

what is the bond between the hydrogen and oxygen in water molecules

Answer 27

covalent bonds

Question 28

does water become more or less dense when frozen

Answer 28

it expands = less dense = hence why ice floats

Question 29

electrons are in orbit more around oxygen, what’s the effect

Answer 29

• dipolar molecule

Question 30

describe the charges of o and h

Answer 30

• o = -
• h = +

Question 31

what does surface tension demonstrate

Answer 31

cohesion
- all water molecules are attracted and form bonds between each other forming cohesion, giving it surface tension

Question 32

how does water support life (10)

Answer 32

• transparency
  –> so plants and phytoplankton can photosynthesis –> oxygen
• Low viscosity
  –> allows blood to be pumped around the body easier
• High surface tension because of cohesion
  –> gives certain organisms a habitat (pond skater)
• Adhesion (forming bonds with another surface)
  –> xylem (uses both cohesion and adhesion)
• Photosynthesis
  –> its in the formula
• High specific heat capacity
  –> 4.184 joules to raise the temp of one gram of water by 1’C
  –> so organisms have a constant environment (they wouldn’t be able to adapt quick enough to the extreme fluctuations)
  –> buffers against sudden temperature variations
• High latent heat of vaporisation
  –> it requires a lot of energy to evaporate 1 gram of water (effective for cooling down organisms)
• Insulating
  –> expands as it freezes and floats on the surface, insulating the water and organisms below
• universal solvent
  –> many polar substances dissolve in water
  –> most chemical reactions take place in an aqueous solution (e.g. cytoplasm)
• condensation reactions and hydrolysis reactions
  –> require water either being released or added

Question 33

how do water molecules form adhesion

Answer 33

forming hydrogen bonds to other molecules that are charged and polar