The Leaf

1. the leaf is important because it is the center of photosynthesis and a basic food source for most heterotrophs

2. typically, leaves have a network of veins that contain the vascular tissue, which is continuous with the xylem and phloem in the stem

3. each leaf is connected to the stem by a leaf stalk called a petiole

4. if the leaf is a single blade it is called a simple leaf

5. a blade divided into two or more parts is called a compound leaf

6. the leaf epidermis is covered by a cuticle and is pierced by tiny pores called stomata

7. each stoma is bounded by a pair of sausage-shaped guard cells

8. water and carbon dioxide concentration levels determine the opening and closing of the stoma

9. the guard cells contain many chloroplasts which begin the process of photosynthesis at sunrise.

10. As photosynthesis continues the carbon dioxide is used up to make sugar, causing the guard cells to open and let in more carbon dioxide

11. between the upper and lower epidermis is a photosynthetic layer called the mesophyll

12. the mesophyll consists of two types of parnechyma cells called palisade on the upper side and spongy mesophyll on the lower side of the leaf

13. palisade cells, which contain many chloroplasts, are brick shaped and are arranged neatly side by side

14. the spongy mesophyll cells, have few chloroplasts and are irregular in shape and arranged haphazardly

15. in the middle of the leaf is xylem and phloem tissue, contained in vascular bundles called veins

Transport in Plants

16. about 90% of water loss in plants occurs through stoma

17. this losses of water to the atmosphere is called transpiration

If a tree is 100 m tall, how do the leaves near the top of the tree receive water that is stored in the roots?

18. several forces are involved

a. As water is lost in a leaf it is replaced by osmosis, which continuously pulls water into the roots

b. The force of attraction of water that pulls the water up the narrow xylem tubes is called capillary action

c. The major force behind water movement in plants is the attraction of water molecules for one another. This is known as the cohesion-tension or transpiration-cohesion theory

19. In this theory it is believed that the water adheres to the sides of the xylem tubes

20. these water molecules that are >stuck= to the sides then stick or attract other water molecules

21. foods produced by photosynthesis are moved from leaf cells to other plant parts through phloem tissue called translocation

22. translocation refers to the conduction of organic compounds throughout the plant by way of phloem vessels