Saturday, April 15, 2006

How Do Plants And Water Break Rocks?

You have probably seen people use big hammers to break rocks (in movies) or bulldozers to knock down large buildings. Did you know that plants too can break rocks? Have you seen tiny plants come out of cracks in the road or a concrete sidewalk? It is amazing to see a tiny plant break apart a big rock as it grows in a crack in the rock.

Plants exert a large amount of force on everything around them. All this hidden strength in plants and seeds come from the process of imbibition. Imbibition simply means taking up or absorbing water. This process can be understood by knowing what plants are made of.

Plants are made up of millions of little cells. Cells are the building blocks of living organisms. In plants, the cells are close together but are still set apart by a large number of pores, empty spaces between cells in plants.

Each cell in a plant has a flexible outer covering called cell wall. When the plants or seeds are near water, they absorb the water into their pores and also into the cells. Since the cell wall is flexible, it allows the cell to expand in size and yet not break.

The expansion of all cells is what causes a seed to enlarge so much or wood to swell. Did you know that long, long ago (several thousand years ago) the people who built pyramids in Egypt and temples in India used the power of the swelling in wood to break large rocks?

They used to place wooden wedges in cracks of large rocks, pour some water, and wait. In a few days the wood would swell up and slowly crack the rock open. Then the broken rocks were used to build pyramids and stones. The ancients even used the swelling to wood to lift the rocks, but that story is difficult to explain here!

Other fun experiments on plants are at: It is going to be spring time so growing plants is the fun thing to do! For information on pyramids and temples visit: and

Little Lion Experiment:

The great strength of wood-based materials when they expand due to water absorption can be easily shown at home. Seeds and beans (whole dry beans) are similar to woody matter and swell if soaked in water over a few hours. The interesting thing with soaking beans or seeds in water is that you will end up getting sprouted beans after a couple of days.

This experiment can be set up in few minutes, but will show results only after few hours, so some patience will be needed. You will need these materials:

  • dry beans (green mung beans, or red kidney beans or garbanzo beans - you have to use dry beans)
  • a small plastic container with a lid (yogurt containers with clear lids work best)
  • water
  • a large plastic bowl or plate


  1. Fill the container with dry beans leaving small amount of room at the top.
  2. Set this container into the large bowl or plate.
  3. Add water slowly to the beans until you see water reach the top.
  4. Place the lid on the small container and close it firmly. If you use plastic wrap, you can clasp it tightly to cover the top and then put a rubber band around the container wall.
  5. Write down the time, and check the container at intervals of 1 hour.