1A - Chemistry of Life

Question 1

polar molecule

Answer 1

a molecule containing a dipole

Question 2

dipole

Answer 2

the sepration of charge in a molecule when the electrons in covalent bonds are not evenly shared

Question 3

dissociation

Answer 3

splitting of a molecule into smaller molecules, atoms or ions, especially by a reversible process

Question 4

hydrogen bonds

Answer 4

weak electrostatic intermolecular bonds formed between polar molecules containing at least one hydrogen bond

Question 5

nitrate ions (NO3-)

Answer 5

(plants) make DNA, amino acids, and proteins from the products of photosynthesis

Question 6

phosphate ions (PO4^3-)

Answer 6

(all) make ATP, ADP, DNA and RNA

Question 7

chloride ions (Cl-)

Answer 7

(animals) needed in nerve impulses, sweating and secretory systems

Question 8

hydrogencarbonate ions (HCO3-)

Answer 8

(animal) buffer blood pH to prevent it becoming too acidic

Question 9

sodium ions (Na+)

Answer 9

(animals) needed in nerve impulses, sweating and secretory systems

Question 10

calcium ions (Ca2+)

Answer 10

(plants) for formation of calcium pectate for the middle lamella between two cell walls
(animals) for bone formation and muscle contration

Question 11

hydrogen ions (H+)

Answer 11

for cellular respiration and photosynthesis, and in numerous pumps and systems as well as pH balance

Question 12

magnesium ions (Mg2+)

Answer 12

(plants) needed for production of chlorophyll

Question 13

why is water a polar molecule?

Answer 13

electrons are held closer to the oxygen atom than to the hydrogen atom

Question 14

how are hydrogen bonds formed between water molecules?

Answer 14

the slightly negative oxygen atom of one water molecule will attract the slightly positive hydrogen atoms of another water molecule => hydrogen bond

Question 15

Simplified reasons to the importance of water

Answer 15

• ionic substances can dissolve in it
• it’s an excellent transport medium
• ice is less dense than water and floats => forming an insulating layer
• has a high specific heat capacity
• incompressible
• water molecules are cohesive
• water molecules are adhesive
• high surface tension

Question 16

how does water allow ionic substances to dissolve in it

Answer 16

because water is a polar molecule, many ionic substances like sodium chloride dissolve in it
- many covalently bonded substances are polar and will dissolve in water, but often do not dissolve in other covalently bonded solvents

Question 17

why is water an excellent transport medium?

Answer 17

because the dipole nature of water enables many different substances to to dissolve in it

Question 18

how is ice less dense than water and why is this a good thing for living organisms?

Answer 18

• max density of water is at 4C
• further cooling = molecules become more widely spaced = ice less dense and floats
• ice forms an insulating layer and prevents water underneath from freezing
• melts quickly since its exposed to sun
• so temperature of large bodies of water doesn’t change much => good habitats for living organisms

Question 19

importance of water being incompressible?

Answer 19

its important in many hydraulic mechanisms in living organisms

Question 20

importance of water being cohesive?

Answer 20

• (cohesive = forces between the molecules mean they stick together)
• important for the movement of water from the roots to the leaves of plants (transpiration pull)

Question 21

importance of water being adhesive?

Answer 21

• (adhesive = attracted to other different molecules)
• important in plant transport systems and in surface tension

Question 22

why does water have a surface tension?

Answer 22

• the attraction between the water molecules (including hydrogen bonds) is greater than attraction between water molecules and air
• so, water molecules hold together forming a thin ‘skin’ of surface tension

Question 23

importance of water having high surface tension?

Answer 23

• important in plant transport system
• affects life at the surface of ponds, lakes and other water masses