Properties of water

What are the 2 thermal properties of water?

• High specific heat- Water absorbs a lot of heat before its temperature rises, helping regulate the Earth’s climate and your body temperature.

• High latent heat- It takes a lot of energy to turn liquid water into steam, which is why sweating is such an effective cooling mechanism.

 

What are the 3 physical properties of water?

• Density anomaly- Water is one of the few substances that becomes less dense when it freezes. This is why ice floats, allowing marine life to survive under frozen lake surfaces.

• Cohesion- Water sticks to itself creating high surface tension (allowing bugs to walk on water).

• Adhesion- Water sticks to other surfaces (adhesion), which helps it to climb up tree roots via capillary action.

What are the 2 chemical properties of water?

• Universal solvent- Because it is polar, water can dissolve more substances (like salts and sugars) than any other liquid.

• Neutral pH- Pure water has a pH of 7, making it neither acidic or alkaline.

Why does water have the properties that it does?

• Many properties of water are due to its ability to form hydrogen bonds.

• The slight negative charge on the oxygen atom makes it attract the slightly positive hydrogen atom of another water molecule.

• The numerous hydrogen bonds in water makes it a very stable structure.

What is transpiration? Where does it occur?

Transpiration is the loss of water from the leaves of a plant. Most of this occurs from the underside of a leaf, where there are many stomata in the epidermis.

How do plants control transpiration?

Most plants control their water intake by opening and closing their stomata when water levels change in the guard cells around each stoma.

Give 3 pieces of evidence for Cohesion-Tension theory.

1. Changes in tree diamter- At high transpiration rates (during the day), diameter decreases due to the tension. At night, during low transpiration rate the diamter increases.

2. Cut flowers- Often they draw in air rather than leaking water out, as water continues to move up the cut stem.

3. Broken xylems- Broken or cut xylems stops drawing up water as the air drawn in breaks the transpiration stream- cohesion between water molecules.

What is root pressure?

• Water is drawn up a plant by the tension resulting from transpiration and cohesion between water molecules.

• If there was 100% humidity a plant would be unable to transpire. Instead, water can be transported by positive pressure from below (roots).

• Solutes are actively transported into the roots of the plant, causing water to enter by osmosis.

• This increases the hydrostatic pressure in the root, forcing water up the stem.

What happens to the stomata when the cell is turgid?

Water moves into the vacuoles by osmosis. The outer wall is more flexible than the inner wall because it’s thinner so the cell bends, opening the stomata.

What happens to the stomata when the cell is flaccid?

Water moves out of the vacuoles by osmosis. The outer wall is more flexible than the inner wall because it’s thinner so the cell bends back, closing the stomata.