AP BIOLOGY

BIOCHEMISTRY

PROPERTIES OF WATER

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
Some insects can stand on the surface of calm water. Their feet push the surface of the water down slightly, but they do not break the surface. Why?
A
The insects are light enough so they do not break the hydrogen bonds holding the water molecules together
B
The insects actually use their wings to hover slightly above the water’s surface and they only skim it with their feet.
C
The insect’s feet are non-polar, so they are repelled by the polar water molecules and are pushed away from the water’s surface.
D
The insects are small enough to see the individual water molecules, so they are able to step carefully from one molecule to the next
Explanation: 

Detailed explanation-1: -Insects can walk on water because of a phenomenon called surface tension. This is essentially a property of water (or any liquid) which allows it to resist an external force.

Detailed explanation-2: -Water striders are small insects that are adapted for life on top of still water, using surface tension to their advantage so they can “walk on water.”

Detailed explanation-3: -Water striders are able to walk on top of water due to a combination of several factors. Water striders use the high surface tension of water and long, hydrophobic legs to help them stay above water. Water striders use this surface tension to their advantage through their highly adapted legs and distributed weight.

Detailed explanation-4: -Hydrogen bonds create the ‘stickiness’ of water, causing the property of cohesion. These bonds are even stronger at the surface of water because there are fewer molecules to bond with, and this creates the surface tension that allows insects to walk on water.

Detailed explanation-5: -Because of hydrogen bonding, water can actually support objects that are more dense than it is. Water molecules stick to one another on the surface, which prevents the objects resting on the surface from sinking. This is why water striders and other insects can “walk” on water!

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