Water

Question 1

Why is a water molecule described as dipolar?

Answer 1

Oxygen atom has a partial negative charge and hydrogen atoms have partial positive charges, so molecule has both positive and negative poles

Question 2

What two features gives water it’s unusual properties?

Answer 2

• hydrogen bonds
• dipolar molecule

Question 3

How does the hydrogen bonding between the molecules occur?

Answer 3

Positive pole of one water molecule is attracted to the negative pole of another - attractive forces between opposite charges is a hydrogen bond

Question 4

Is a hydrogen bond weaker or stronger than a covalent bond?

Answer 4

Weaker (about 1/10th the strength)

Question 5

Why do molecules stick together?

Answer 5

Numerous Hydrogen bonds between molecules.

Question 6

How does the tendency for water molecules to stick together affect the specific heat capacity?

Answer 6

Means it takes more energy to separate them than would be needed if they weren’t bonded to one another - so boiling point is higher than expected.

Question 7

What state would water be in without hydrogen bonding?

Answer 7

Gas

Question 8

Does water have a high specific heat capacity?

Answer 8

Yes

Question 9

How does its specific heat capacity make aquatic environments temperature stable?

Answer 9

It’s high specific heat capacity allows it to act as a buffer against sudden temperature variations.

Question 10

Why does water also buffer organisms against sudden temperature changes? (Especially in terrestrial environments)

Answer 10

Organisms are mostly water.

Question 11

How does hydrogen bonding affect the latent heat of vaporisation?

Answer 11

It makes it very high

Question 12

How does water’s latent heat of vaporisation give effective means of cooling for the body?

Answer 12

Evaporates water via sweat from mammals and so body heat is used to evaporate this water.

Question 13

What is cohesion?

Answer 13

The tendency of molecules to stick together

Question 14

Why does water have large cohesive forces?

Answer 14

It’s hydrogen bonding.

Question 15

What does it’s cohesive forces allow in plants’ xylem vessels?

Answer 15

Allows water to be pulled up a tube as molecules stick together

Question 16

What is surface tension?

Answer 16

Where water molecules meet air they tend to be pulled back into the body of water rather than escaping it.

Question 17

Is surface tension a force?

Answer 17

Yes

Question 18

Why is water strong enough to support small organisms such as pond skaters?

Answer 18

The water surface acts like a skin and is strong.

Question 19

What does the fact that up to 98% of a jellyfish and mammals are typically 65% water demonstrate?

Answer 19

Water is the main constituent of all organisms

Question 20

What are 3 reasons water is very important?

Answer 20

1) main constituent of living organisms
2) where life on earth arose
3) environment where many species live

Question 21

What are 3 used of water in metabolism?

Answer 21

1) used to break down complex molecules in hydrolysis/ is produced by condensation reactions
2) chemical reactions take place in aqueous medium.
3) is a raw material in photosynthesis

Question 22

For what 4 things does water act as a solvent for?

Answer 22

1) gases such as Oxygen and CO2
2) wastes such as ammonia and urea
3) inorganic ions and small hydrophilic molecules (E.G. AAs, ATP…)
4) enzymes whose reactions take place in solution.

Question 23

What does water not easily able to be compressed mean?

Answer 23

Water can provide support - for example the hydrostatic skeleton of animals such as earthworm and turgor pressure of herbaceous plants

Question 24

What does water being transparent mean? (2)

Answer 24

Aquatic plants can photosynthesise
Light rays can penetrate the jelly like fluid covering that fills the eye so light can reach the retina

Question 25

Where are inorganic ions found? (4)

Answer 25

• in organisms in solution
• the cytoplasm of cells
• in body fluids
• part of larger molecules

Question 26

What is the specific function of an ion related to?

Answer 26

It’s properties.

Question 27

Where is an iron ion used?

Answer 27

They are found in haemoglobin where they associate with an oxygen molecule and transport it to respiring tissues.

Question 28

How are phosphate ions used?

Answer 28

Have a structural role in DNA molecules
Store energy in ATP molecules

Question 29

Why are hydrogen ions used?

Answer 29

They determine the pH of solutions so control the functioning of enzymes.

Question 30

What are sodium ions’ purpose?

Answer 30

Important in the transport of glucose and amino acids across plasma membranes