a1.1.3 - cohesion

Question 1

define cohesion.

Answer 1

the force by which individual molecules of the same type attract and stick together
- water molecules stick together due to hydrogen bonding

Question 2

describe how water moves through the xylem of a vascular plant.

Answer 2

1. transpiration (evaporation) occurs through stomata of a leaf. as transpiration occurs, it creates negative pressure
2. the tension created by transpiration “pulls” water in the plant xylem, drawing the water upward
3. cohesion pulls up water molecules in a chain as the top-most water is pulled up and out of the stomata.

Question 3

outline the cause of surface tension

Answer 3

the molecules on the surface are more attracted other molecules of the liquid than to molecules in the surrounding air. the net effect is an inward force that causes water to behave as if its surface were covered with a stretched elastic membrane.

Question 4

state a benefit to living things that results from surface tension.

Answer 4

surface tension allows organisms like water striders to “walk on water” and provides a stable environment for other organisms that live on or near the surface of water. to break through the surface of the water, enough force must be applied to break many hydrogen bonds simultaneously.