7+HS+BIO+Basic+Chemistry+Lesson+5

(video tape yourself freezing a bottle of water).

(Get alkaseltzer & water)

(Water & wax paper experiment)

Water



Organisms (plants, animals, insects) are made up of about 70 percent water. The cells in your body have between 70 and 95 percent water content.





Water has many unique properties.

The unique properties of water molecules give water the following characteristics.



Water has the ability to hold heat. As water heats, water molecules begin to break down, causing it to heat up quick. As water cools, the water molecules begin to re-bond.



Water moderates temperature by releasing heat in cold environments and absorbing heat in warm environments.



Where on Earth do you think the water is warmest? Why?

Water moderating temperature helps to control the temperature of human bodies. When a person perspires, water evaporates from the surface of the skin. Perspiration draws heat from the skin to maintain a cooler body temperature by releasing heat in cold environments and absorbing heat in warm environments.



Water molecules stick together. They do this by holding on tight to each other and pull inward. When it falls on on a flat slick surface, it stays together rather than spreading out.

Water expands as it freezes. As it cools, the molecules in water move farther apart from each other and form ice. When it cools it becomes denser.



Ice floats in its liquid form as it is less dense than its liquid form due to the molecules not being bunched together.



Water is an excellent solvent. Water dissolves most biological substances.

(go over experiments)

Review:

1) Approximately how much of our body is made up of water?

a) 100% b) 50% c) 70% d) 1%

2) How does our body keep cool?

a) sweating b) digesting food c) thinking

True of false, Ice is less dense than water.

4) What do most things do in water?

a) float b) fly c) dissolve

3) What happens when water freezes?

a) it blows up b) it cracks c) it catches on fire d) it expands