1. World of Plants Making Food G Davidson

2. Food Webs and Plants Animals get their food by eating other living things. They either eat plants, or eat animals which have eaten plants. Plants have to make their own food. When energy in the form of food passes from a plant to an animal and then on to another animal, it forms a food chain. When we link up all the food chains in an environment we form a food web, e.g.

3. Woodland web HAWK FOX BLACKBIRDS BLUETIT INSECTS FRUITS & SEEDSGRASSTREE BARKROOTS RABBITS SQUIRREL WOODLICE BEETLES If some of the plants in this web were to disappear it would have a major effect on other organisms.

4. Plants and Light Plants manufacture their own food in a process called PHOTOSYNTHESIS. When a plant carries out photosynthesis it combines simple substances to make more complex substances like glucose and starch. Photosynthesis is carried out in the leaves of a plant. PHOTOSYNTHESIS (Light) (To build)

5. Photosynthesis Carbon Dioxide +WaterGlucose+Oxygen CO 2 H2OH2OC 6 H 12 O 6 O2O2 Light energy Raw MaterialsProducts

6. Photosynthesis Photosynthesis CANNOT work without: Carbon dioxide Water Chlorophyll sunlight If any of the above are in short supply they are said to be “Limiting Factors”.

7. Photosynthesis We can check for evidence of photosynthesis by testing a leaf for starch. 1. Boil the leaf in water (kills cells) 2. Boil the leaf in alcohol (removes chlorophyll) 3. Dip leaf in hot water (softens the leaf) 4. Put leaf in iodine solution (test for starch)

8. Photosynthesis So what happens to the sugar made in the leaves? It can be used in a number of ways Sugar Used as building Material (e.g. cellulose in cell walls Used immediately For energy Stored as starch And Converted back when Sugar is needed by Plant.

9. Photosynthesis If a plant is converting carbon dioxide and water to carbohydrate, then it’s weight should increase. If a plant is dried out and weighed, it’s weight increases during a day. This is done by taking discs from a leaf at different times of the day, drying them and weighing them.

10. Leaf Surfaces Leaves take in carbon dioxide from the air. In exchange they give out oxygen produced during photosynthesis. These gases must be able to get in and out of a leaf. Leaves have special structures which allow gas exchange. STOMATA These structures are called STOMATA.

11. Stomata Tiny pores on the surface of a leaf which allow gases in and out. They also allow water to escape. Each pore is a STOMA and is surrounded by 2 GUARD CELLS.

12. Stomata

13. Leaf Surfaces A leaf is very thin and flat. We know it has stomata on it’s surface. Since it’s job is photosynthesis, there must be reasons for it’s design. Inside the leaf there are a number of layers, all with different jobs. However, they all help to make photosynthesis as quick and efficient as possible.

14. Leaf Surface

16. Water Transport in Plants The transport system of a plant does 2 jobs. One is to carry materials needed for photosynthesis. The other is to carry materials produced by photosynthesis.

17. Water Transport in Plants Water and minerals have to be carried from the roots to the leaves. In the leaves water is used in photosynthesis. Tubes, in the stem, called XYLEM vessels carry the water and minerals. If a plant is cut and placed in red dye, it is easy to see where the xylem vessels are.

18. Transport in Plants The other job of the plant’s transport system is to carry food from the leaves to every part of the plant. Tubes called the PHLOEM carry the food. The xylem and phloem are usually found close together in bundles called VASCULAR BUNDLES. The position of the vascular bundles in roots and stems is not the same. In most plants the xylem and phloem are found in the centre of the root, whereas in a stem they are found round the outside.

19. Transport in Plants Epidermis Cortex Xylem Phloem Root – Cross Section

20. Transport in Plants Stem – Cross section Phloem Xylem Epidermis

21. Structure of the Xylem Xylem cells are dead and have no cell contents. The end walls have disintegrated LIGNIN The side walls have become inlaid with a tough waterproof substance called LIGNIN Lignin is arranged in the side walls usually as rings or spirals. A number of these cells laid end to end forms a rigid pipe. This adds considerable support to the plant

22. Structure of Xylem In this case the lignin is spiral

23. Structure of the Phloem Phloem contains 2 types of cell Sieve tubes Companion cells In sieve tubes the end walls are perforated (sieve plates) Strands of cytoplasm pass through the pores and allow contact with the next cell. The companion cells lie next to the sieve tubes.

24. Structure of the Phloem

25. Elodea Bubbler When green plants photosynthesise they produce oxygen. In aquatic plants, this oxygen is given off as bubbles which are easily seen. The Canadian pondweed, Elodea, has large spaces in its stem. When the stem is cut, and the plant is placed in strong light, bubbles of oxygen can be seen coming from the cut end. The number of bubbles produced every minute, i.e. the rate, gives us an idea of how fast the plant is photosynthesising.

26. Elodea bubbler

27. Elodea Bubbler Light IntensityNo. of Bubbles / 3 minutes 100 206 3015 4026 5035 6038 7038 Typical Set of Results

28. Elodea Bubbler

29. Limiting Factors Photosynthesis does not just depend on light, carbon dioxide and a suitable temperature, but also the amounts of each available. If they are in short supply, they cut down or LIMIT the rate of photosynthesis. “Limiting Factors”. Light, water, carbon dioxide and temperature can act as “Limiting Factors”.