Lesson 3: Stems & Roots

1. Unit 5 Plants Lesson 3: Stems & Roots

2. Functions of Stems • Economic value: wood products/lumber • Connect the vascular tissue in the leaves to the vascular tissue in the roots, allowing water and dissolved substances to be transported throughout the body

3. Function of Stems • Raise and support the leaves (maximizing photosynthesis) and reproductive organs (maximizing the likelihood of being pollinated and producing fruits and seeds)

4. Stem Structures – Herbaceous Plants • Herbaceous Plants: • plants that have stems that do not contain wood • Relatively pliable stems • Stems carry out photosynthesis • Thin epidermis

5. Anatomy of Herbaceous Stems • Vascular tissue in herbaceous plant stems are arranged in vascular bundles • Vascular bundles contain xylem and phloem • Xylem is always closer to the centre of the stem • Phloem is always closer to the outside of the stem • In monocots: • Vascular bundles found through out the ground tissue • In dicots: • Vascular bundles form a ring

6. Monocot Herbaceous Stem (ex: corn)

7. Eudicot Herbaceous Stem (ex: alfalfa)

10. Stem Structures – Woody Plants • Woody plants: • Stems that contain wood • Woody stems are relatively hard • Have bark • Usually do not carry out photosynthesis

11. Anatomy of Woody Stems • Wood stems grow thicker every year due to the presence of the vascular cambium • Vascular Cambium: the meristematic cell layer in the vascular tissue that divides to form new xylem and phloem tissue • Xylem is on the inside of the vascular cambium • Phloem is on the outside

12. Wood – Sapwood and Heartwood • Wood is many layers of xylem tissue cells • Sapwood is the younger xylem through which water and minerals are transported to the leaves • Eventually, the older xylem fills up with resin and oils and they no longer conduct water forming the heartwood which is very rigid and helps support the tree

14. https://www.youtube.com/watch?v=jrXSHLyAQeQ • https://www.youtube.com/watch?v=CdyA3I43YSA

15. Bark consists of all tissues found outside the vascular cambium • Phloem • transports sugars made in the leaves throughout the plant. • Cork cambium • meristematic tissue that produces cork • Cork • the tough, outer layer of the tree that prevents water loss from the stem

16. Growth Rings • Growth only happens in the spring and summer • In spring, vascular cambium grows rapidly, producing large xylem cells that have relatively thin walls that form a layer of lighter-coloured wood • In summer, fewer xylem cells are produced and they have thicker cells walls that form a layer of darker-coloured wood • The spring and summer wood together forms one growth ring

18. More on Xylem: Recall: • Xylem cells are thick walled and dead at maturity • Rich in lignin (a carb that makes cells stronger) • Xylem cells can be stacked to form long, continuous tubes

19. More on Xylem: 2 types of xylem cells • Two types of xylem cells: tracheids and vessel elements • Tracheids: long, cylindrical cell with tapered ends that have pits along the cell walls allowing water and solutes to pass through to neighbouring xylem cells

20. More on Xylem: 2 types of xylem cells • Two types of xylem cells: tracheids and vessel elements • Vessel Elements: shorter and wider than a tracheid and less-tapered ends. Side cells walls contain pits. End walls of have perforation plates which allow water and solutes to pass through

22. More on Phloem Recall: • Phloem cells are living at maturity • Contain cytoplasm • Phloem cells can be stacked to form long, continuous tubes

23. More on Phloem: 3 Types of phloem cells • Three types of phloem cells: sieve cells, sieve tube elements, companion cells • Sieve Cells: have narrow pores in all their cell walls and contains all necessary organelles including a nucleus

24. More on Phloem: 3 Types of phloem cells • Three types of phloem cells: sieve cells, sieve tube elements, companion cells • Sieve Tube Elements: have cytoplasm but lack many cell organelles. It has no nucleus. The end walls of these cells are called sieve plates where sugar solutions can pass to neighbouring phloem cells.

25. More on Phloem: 3 Types of phloem cells • Three types of phloem cells: sieve cells, sieve tube elements, companion cells • Companion Cells: are always associated with a sieve tube element. Companion cells have a nucleus and all other organelles that the sieve tube lacks.

28. https://www.youtube.com/watch?v=SjWbw9smEOU

29. Roots • Function of Roots: • Anchors the plant • Keeps it upright • Absorbs waters and nutrients (0ther than carbohydrates) • Store water and carbohydrates

30. Root Systems • Taproot: a root system composed of a large, thick root; can have smaller lateral roots • Fibrous: a root system made up of many small, branching roots

31. General Structure of Roots • Tip of root contains the root cap and a meristem • Root Cap: mass of cells that form a protective covering for the meristem at the root tip; allows the root to penetrate the soil with minimal damage

32. Roots • Root hairs project out of the epidermis and increase the surface area allowing for greater water and nutrient absorption • Root cortex is a region of parenchyma cells beneath the epidermis where carbohydrates can be stored and water can be transported fro the epidermis to the xylem • Endodermis: is the innermost layer of cells in the root cortex

33. Endodermis • The endodermis cell walls are wrapped with a wax-like substance forming a continuous barrier called the Casparian strip. The Casparian strip prevents substances from passing through the spaces between the endodermal cells

35. Monocot and Eudicot Roots • Vascular tissue is arranged differently in monocot roots and eudicot roots

36. Homework Questions