water

Question 1

describe the structure of a water molecule

Answer 1

a water molecule contains one oxygen atom and two hydrogen atoms. the two hydrogens are bonded to the oxygen with a covalent bond. the oxygen pulls electrons closer to it as they are shared unequally so oxygen becomes slightly negative and hydrogens become slightly positive.

Question 2

name the bond that can link two water molecules together

Answer 2

hydrogen bond

Question 3

explain what a hydrogen bond is.

Answer 3

hydrogen bonds are weak bonds which form between two slightly oppositely charged ions/atoms. in biology they occur between any two polar regions, for example in water, proteins etc.

Question 4

define the term polar

Answer 4

when one area or atom of a molecule has a slight charge.

Question 5

explain why water is polar.

Answer 5

water is a polar molecule because the oxygen pulls electrons closer to it, away from the hydrogen atoms.

Question 6

define the term electronegativity

Answer 6

the pull an atom has on electrons, for example oxygen has a greater electornegativity than hydrogen.

Question 7

define the term dipole

Answer 7

a molecule with two areas of slight, different charge.

Question 8

list five roles water plays in life.

Answer 8

• useful in transport systems
• habitat for aquatic organisms
• used as a cooling system in some organisms
• transparent so plants can photosynthesise under water
• helps organisms maintain a constant body temperature

Question 9

explain how the polar nature of water allows it to act as a solvent

Answer 9

many biological substances in the body are charged ions, meaning that the polar regions of water can surround these, form hydrogen bonds with them and dissolve them.

Question 10

explain how the polar nature of water allows it to act as a transport medium.

Answer 10

forms flexible hydrogen bonds which allows it to be flexible and flow through organisms. it also acts as a useful solvent.

Question 11

explain how the polar nature of water allows it to act as a coolant

Answer 11

water forms lots of hydrogen bonds due to it’s polar regions. these bonds are individually weak but en mass it takes a lot of energy to break them - meaning that water has a high latent heat of vaporisation. so sweating transfers a lot of energy off the organism.

Question 12

explain how the polar nature of water allows it to act as a reactant

Answer 12

being polar makes water very reactive

Question 13

explain how the polar nature of water allows it to act as a habitat.

Answer 13

being polar makes water very adhesive and cohesive as molecules tend to stick together. this makes a surface tension which some organisms run/skip across.

Question 14

define the term hydrophillic

Answer 14

water loving - substances which will dissolve in water

Question 15

define the term hydrophobic

Answer 15

water hating - substances which will not dissolve

Question 16

define the term cohesion

Answer 16

the attraction between molecules of a similar substance

Question 17

define the term adhesion

Answer 17

the attraction between molecules of different substances

Question 18

describe two features (not related to it’s polar nature) water has that makes it useful for life.

Answer 18

• high specific heat capacity which means organisms maintain a constant temp more easily
• ice becomes less dense when it freezes so it floats up and insulates the water below.

Question 19

list ten examples of how water is used in life

Answer 19

• provides a liquid environment inside cells
• transport medium in plants and animals
• pond skaters use surface tension as a habitat
• aquatic life is insulated by floating ice
• plant roots benefit from low viscosity and capillarity
• heat can be lost through sweating in mammals
• cell contents are slow to freeze
• plants can photosynthesize under water
• hydrostatic skeleton in worms
• takes part in digestive reactions
• can act as a lubricant such as mucous.