1. Aseel Samaro Understanding the importance of plants

4.  A huge variety of plants grow on land and in water.  Throughout the world humans plant, cut down and replant trees.  They also cultivate many types of plant. Why do we grow plants? Why are plants so important to us? Introduction

5. 1.Plants allow us to survive. We use plants every day for food.  All food is either a plant or comes from an animal that has eaten plants. 2.Some plants give us raw materials for fabrics, building and fuel; others are used in medicine. 3.We even use plants as decoration in our gardens, homes and parks. 2.Plants also : remove carbon dioxide from the atmosphere release oxygen into the atmosphere. Useful plants

6. How do we use these plants?

7. List the ways that we use plants. Describe the ways that we use plants. Give at least one example for each use. Explain why plants are essential to the survival of life on our planet.

8. List the ways that we use plants. for food; building; textiles; medicine; oils; dyes; rubber; biofuels etc Describe the ways that we use plants. Give at least one example for each use. Wood from trees is used to build boats, houses and furniture. Palm leaves are woven into baskets, hats and mats. Explain why plants are essential to the survival of life on our planet. Plants absorb (remove) carbon dioxide from the atmosphere and release oxygen; which animals use to respire

9.  Small seeds grow over many years into very large trees.  Up until the 1600s, most scientists thought that plants grew by taking in solid materials from the soil.  The Belgian scientist Jan Baptist van Helmont (1580–1644) devised a plan to test this idea.  He did an experiment that involved growing a willow tree in a large pot of soil. Plants and soil

10.  Before the experiment, van Helmont measured the mass of the soil and the tree.  He covered the soil with a transparent lid, but watered the plant regularly.  After five years he again measured the mass of the soil and the tree. The results he obtained were similar to those in the following figure.

11. Van Helmont’s experiment

12. List five variables that might affect this experiment. What was the change in the mass of the tree? What was the change in the mass of the soil? Explain how this experiment suggested that plants did not grow by taking in solid materials from the soil. What other explanations could there be for the results van Helmont found? How could van Helmont’s experiment be improved?

13. List five variables that might affect this experiment. temperature; humidity; light intensity; disease; amount of water; amount of minerals What was the change in the mass of the tree? 80 – 2 = 78 kg What was the change in the mass of the soil? 100 − 99 = 1 kg Explain how this experiment suggested that plants did not grow by taking in solid materials from the soil. the soil lost only 1 kg; but the tree gained 78 kg What other explanations could there be for the results van Helmont found? the tree used other materials to grow – e.g. water and carbon dioxide How could van Helmont’s experiment be improved? set up repeats; use a control with no plant; use different types of plants

14.  J.B. van Helmont concluded that all of the wood, bark and roots that had grown during the experiment must have come by the plant using only water.  We now know much more about how plants grow.  Look at the plants shown in the following figure, the water hyacinth. Its roots are not anchored in soil but are free-floating Special Plants

15. Water hyacinths grow in fresh water.

16. What conclusions can you draw from this information? Is this sufficient information to support van Helmont’s conclusion that plants do not use soil to grow? Why did van Helmont cover the pot with a lid?

17. What conclusions can you draw from this information? Many plants grow naturally without soil. Is this sufficient information to support van Helmont’s conclusion that plants do not use soil to grow? no; van Helmont did not measure the amount of water he added, so he could not know if water caused the growth Why did van Helmont cover the pot with a lid? to prevent: the evaporation of water; materials being added to or taken from the soil

18.  ‘Hydroponics’ is a method of growing plants in water using mineral nutrient solutions.  The roots are not kept in soil. Did you know…?

19. Thank you