A1.1 Water (SL)

Question 1

Define “Cohesion”

Answer 1

Water is attracted to other water molecules

- each individual water molecule is connected with another water molecule thru weak hydrogen bonds

Question 2

Explain the solvent properties of water

Answer 2

water is a good solvent because it is a polar molecule → will dissolve polar solutes easily

polar attractions cause water molecules to surround and isolate the solute molecules

ionic solids dissociate in water (break into their ions)

water cage (surrounded by water) / clathrate / colloid

solvation

Question 3

Explain what is a solute, a solvent and a solution

Answer 3

a solute is the substance that dissolves (NaCl)

a solvent is the liquid used for dissolving (water)

a solution is the dissolved product

Question 4

Explain the thermal properties of water

Answer 4

• high specific heat capacity: takes a lot of energy for the temperature of water to change by 1°C
• so many H-bonds (hydrogen bonds between water molecules)
• temperature of water remains relatively stable

Question 5

Why is water a good coolant?

Answer 5

it takes a lot of energy to make water evaporate

(evaporating water removes a lot of heat energy from the organism)

Question 6

Explain the property of water: water is a coolant

Answer 6

• high temps damage tissues and denature proteins → causing enzymes to cease to work
• when water evaporates, it removes a lot of energy from the system (e.g. sweating)

Question 6

Explain high latent eat of vaporisation

Answer 6

• getting to boiling point then vaporising → water has a much higher boiling point
• relatively high energy input is necessary to vaporise water
• e.g. excess heat energy is removed from the body

Question 6

Explain why water is a transport medium

Answer 6

• Water is a solvent → dissolves nutrients, gases and waste products
• circulatory system + thru xylem & phloem in vascular plants
• thru water in soil / aquatic habitats
• water can transport molecule across membranes in diffusion + within the cell/intersititial (between-cell) fluid
• water is dense → it can support the mass of large and small organisms — they can float or swim in water
• aquatic systems are rarely still: they have flows and currents that can carry planktonic organisms, spores, seedsand nutrients over a large area

Question 6

Explain why water is a medium for metabolic reactions

Answer 6

Water as a medium for metabolic reactions

• dissolved particles can move around and diffuse
• moving particles → likely to collide with one another, leading to a reaction
• all metabolic reactions (reactions in living things) occur in solution — the reactants are dissolved
• membranes and biological surface are wet

Question 7

State the advantages of water as a habitat and explain each advantage

Answer 7

• stable temp: less extreme changes
• thermal properties: ice floats, life on top, life below
• surface tension: insects live on surface
• density: larger organisms float than could live on land
• currents: transport organisms, nutrients, seeds, spawn, minerals and heat
• transparent: allows light through, so photosynthesis occurs in water
• solvent: dissolves nutrients and oxygen
• solvent: removes waste, e.g. urea
• expansive: covers most of the surface of earth