A1.1 water

Question 1

why is water necessary for life

Answer 1

water is a solvent and is the medium for metabolic reactions. it is also a transport medium, e.g plasma blood is made mostly of water

Question 2

modes of transport in the blood

Answer 2

+ glucose, dissolved in blood plasma, polar molecule (soluble)
+ amino acids, dissolved in blood plasma, polar molecules (soluble)
+ sodium chloride, dissolved in blood plasma, ionic compound (soluble)

• cholesterol and lipids, lipoprotein complexes, non-polar (insoluble)
• oxygen, attached to haemoglobin, non-polar

Question 3

water

Answer 3

oxygen atom covalently bonded to two hydrogen atoms. water is a polar covalent molecule.

Question 4

why water forms hydrogen bonds

Answer 4

uneven sharing of electrons, one oxygen atom covalently bonded to two hydrogen atoms. oxygen is more electronegative than the hydrogen atoms because oxygen has a more positive nucleus than hydrogen so it has a stronger attraction to the shared electrons of the covalent bond. This gives water a slightly negative charge and hydrogens a slightly positive one. Hydrogen bonds are weak intermolecular forces between the polar water molecules.

Question 5

properties of water

Answer 5

• adhesion
• cohesion
• buoyancy
• viscosity
• specific heat capacity
• thermal conductivity

Question 6

cohesion

Answer 6

water molecules are cohesive due to their polarity. polar water molecules are attracted to other polar water molecules. negatively charged oxygen of one polar water molecule is attracted to the positively charged hydrogens of another polar water molecule, forming hydrogen bonds between them.

Question 7

surface tension

Answer 7

due to cohesive nature of water molecules a relatively strong surface tension forms at the surface of water. the water molecules are only surrounded on some sides by other water molecules along or just below the surface which gives water its high surface tension

Question 8

adhesion

Answer 8

polar water molecules bind to other different types of polar molecules, forming hydrogen bonds

Question 9

transport in the xylem- cohesion and adhesion

Answer 9

cohesive nature of polar water molecules allows water to form a continuous column of water molecules moving up the xylem.

polar water molecules adhere to the polar molecules in the xylem wall since they are unlike molecules which allows the water molecules to flow against gravity and up the xylem

Question 10

capillary action in soil

Answer 10

the ability of water to flow against gravity in a narrow space.

soil is porous because the clay and organic matter in the soil are polar

water adheres to the polar soil particles and moves up the soil towards the root of the plant.

capillary action is greater in fine clay soils than porous sandy soil because the smaller spaces between particles can retain water against gravity more effectively

Question 11

capillary action in cells

Answer 11

water can move from cell to cell by capillary action, polar water molecules adhere to polar cellulose molecules in the cell wall. Water is transferred to the cytoplasm through the apoplast pathways in the cell wall due to adhesion. cellulose is polar.

Question 12

why do ions dissolve in water

Answer 12

ions are charged and they dissolve in water because of the polar water molecules surrounding the charged ions

Question 13

lipid molecules

Answer 13

• non-polar
• hydrophobic
• insoluble, cannot dissolve in water
• transported in blood as lipoproteins:
  + phospholipids (hydrophilic head, hydrophobic tail), cholesterol and proteins on the outside
  + lipids inside

Question 14

metabolism

Answer 14

metabolic reactions occur in aqueous solution, reactants and enzymes dissolved in water

some molecules in living organisms are hydrophobic and their functions depend on this property. these substances are not charged and do not readily dissolve in water

Question 15

buoyancy in water

Answer 15

water is denser than air, greater buoyancy for aquatic animals which allows them to conserve energy and swim/float effortlessly

Question 16

viscosity of water

Answer 16

water has a higher viscosity than air which means its more difficult for animals the move through, hence their adaptations. However for smaller aquatic animals it makes it possible for the movement of their small fins

Question 17

thermal conductivity of water

Answer 17

water has a higher thermal conductivity than air which means it is more difficult to change its temperature, aquatic animals lose more heat to the environment.

Question 18

specific heat capacity of water

Answer 18

very high SHC, a lot of energy required to break hydrogen bonds between water molecules. temperature of large bodies of water makes it a more stable environment than air. helps to maintain a constant body temperature in endotherms.

Question 19

the ringed seal adaptations

Answer 19

• buoyancy: layer of blubber that provides buoyancy and helps them to float on the surface
• viscosity: streamlines body shape which allows them to move smoothly through the water, flippers use drag to facilitate movement
• thermal conductivity: layer of insulating blubber that prevents heat loss + seals huddle on land, decreasing overall exposed surface area, less heat lost
• SHC: endotherms and adapted to maintain constant body temperature high SHC of water helps them to maintain a constant body temp

Question 20

black-throated loon

Answer 20

• buoyancy: able to adjust its density by changing the volume of air in its air sacs, allows bird to control depth when it’s swimming. hollow bones further reduces its density. increases surface area by spreading its wings which increases buoyancy.
• viscosity: streamlines body shape and webbed feet
• thermal conductivity: endotherm that maintains constant body temp. bird’s feather trap air and provide insulation, feathers are covered in a hydrophobic oil which keeps them dry
• SHC: high SHC of water helps it to regulate its body temp which is important for cold water dives

Question 21

why water was not on the earth when the planet formed

Answer 21

planets formed by clumping together of solid particles

water in ice form was not present because the temp was too high and in gaseous form was removed by solar winds

Question 22

explain how earth gained its oceans

Answer 22

water formed solid ice particles in the outer solar system as a result of low temp (far from the sun)

ice formed asteroids and comets, water arrived from carbonaceous chondrites (asteroids), similar ratios of heavy hydrogen atoms to earths water

Question 23

explain why earth did not lose its water

Answer 23

earths large mass creates enough gravity to retain liquid and gaseous water on the planet. it is the habitable zone of the solar system where water can exist in liquid form

• gravity
• low temperatures enough to condense water to liquid form

Question 24

the goldilocks zone

Answer 24

planets are in the habitable zone when their orbit around their stars allows liquid water

planet is not too hot and not too cold for liquid water to exist