A1.1 Water

Question 1

Why water is essential for living things (5)

Answer 1

• Many reactions in living organisms require water.
• Water helps organisms regulate their temperature.
• Water is a habitat for a lot of living organisms.
• Water is a solvent so things dissolve in it.
• Because it is a solvent, it can transport substances.

Question 2

Define water

Answer 2

Substance in which cells first developed and life processes still occur.

Question 3

Chemical structure of water

Answer 3

Electrons are not evenly shared between O and H; O is more electronegative because it has more protons.

Question 4

Define Electronegativity

Answer 4

Ability of an atom to attract a shared pair of electrons which is affected by number of protons and number of outer shells.

Question 5

Hydrogen bonds

Answer 5

Formed when a slightly negatively charged part of a molecule comes close to a slightly positively charged hydrogen molecule.

Question 6

Define Cohesion

Answer 6

A property of water in which water molecules are attracted to each other by hydrogen bonding; allowing the molecules to move together.

Question 7

Define Adhesion

Answer 7

A property of water in which water molecules are attracted to polar substances such as walls of the cells, vessels or tubes.

Question 8

Define Tension

Answer 8

A force that tends to stretch something.

Question 9

Define Hydrophobic

Answer 9

Molecules usually nonpolar and cannot dissolve in water; no charge.

Question 10

Define Hydrophilic

Answer 10

Molecules usually polar and soluble in water; has charge

Question 11

Water as a solvent (4)

Answer 11

• Makes up cytoplasm.
• Makes up fluid inside all organelles.
• Permits transport of substances in and out of cells.
• Essential component of blood and other bodily fluids.

Question 12

Define Specific Heat Capacity

Answer 12

Amount of energy needed to heat 1kg of a liquid by 1 degree Celsius. For water it is 4.186J/°C, which is relatively high and therefore good for organisms because water can withstand large swings in temperature, keeping things relatively constant. Especially important to support the chemical reactions that happen in the body to ensure stable internal temperature is maintained.

Question 13

Define Buoyancy

Answer 13

Force that counteracts gravity on a partially/fully submerged object. Relied on density: if density of an object is greater than density of water, this force will break and object will sink. Density of water is 997kg/m3.
Example: Green algae can float as it produces oxygen from photosynthesis, and oxygen gets trapped between algae’s filaments making it lighter and float. They also have gas vacuoles that increase its buoyancy.

Question 14

Define Viscosity

Answer 14

Resistance to flow and is related to how much energy is needed to change the shape of a liquid. Viscosity of water is very low (1-5 cps).

Question 15

Define Thermal Conductivity

Answer 15

Ability to transfer heat during a difference in temperature. Water’s thermal conductivity is 0.6, relatively high which means heat is more easily moved. Our body is mainly composed of water, so heat is easily transferred in body. Example: Fennec fox which live in dessert conditions have large ears with many blood vessels, helping it dissipate heat from blood to exterior environment, allowing it to cool down.

Question 16

Describe the Origin of Water

Answer 16

When Earth was first formed 4.5 billion years ago, it was too hot to have liquid water on surface. Water was delivered by water-rich asteroids. Earth began to cool, water condensed and gravity helped retain water on the surface.

Question 17

What is the Goldilocks Zone concept

Answer 17

Range of orbital distances around a star in which liquid water may exist on a planet.

Question 18

Contrast between how physical properties of water and air have consequences for animals that live in these two habitats

Answer 18

Specific heat: Water - 4.186J/°C; Air -1.005J/°C
Thermal conductivity: Water - 0.6; Air - 0.024
Density: Water - 997kg/m3; Air - 1.225kg/m3

Question 19

How does moderate temperature and gravity help retain water on surface of Earth.

Answer 19

Earth started to cool, so water became liquid and force of gravity allowed water to be retained on surface of earth.

Question 20

Properties of water that affect the Ringed Seal compared to properties of air that affect the Black-Throated Loon

Answer 20

Water is more viscous than air so ringed seal uses more energy moving throughout the water, and fighting against buoyancy forces than the Loon does flying in the air. Water has a higher heat conductivity than air so more heat is pulled faster from the seal than the Loon. Adaptation of seal is thick coat of fur to help retain and regulate body heat, and streamlined shape to reduce drag against viscosity.