Topic 9 – Plant Science

1. Topic 9 – Plant Science

2. Introduction to Plants • Plants make up over 50% of the living organisms on this planet • They belong to the kingdom Plantae • There are five phylum: • Bryophyta • Filicinophyta • Coniferophyta • Angiospermophyta

3. Introduction to Plants (cont) • Angiosperms are the most dominant phylum • Angiosperms, or flowering plants, produce seeds enclosed inside fruits. • Angiosperm comes from the word • angerion – a container • sperma – a seed • phyton – a plant.

4. Introduction to Plants (cont) • Angiosperms are divided into two large groups:  • Monocotyledons (Monocots) • Dicotyledons (Dicots) • These names refer to the number of leaves contained in the embryo, called cotyledons.

5. Typical Monocot

6. Monocots vs. Dicots

7. Typical Dicot

8. Shoot Apical Meristems

9. Lateral Meristems

10. Comparison of Growth for Apical and Lateral Meristems Apical Meristems Lateral meristems • Primary growth • Allows plant to grow longer (upwards) • Forms leaves and branches • Increases photosynthetic capacity • Found in both monocots and dicots • Secondary Growth • Allows plant to grow in width • Widening of main trunk for support and depositing of vascular tissue and bark • Found only in dicots

11. Stems • Supports the leaves for photosynthesis • Transports water and nutrients from roots to leaves • Support is achieved by: • Tugor • Cellulose walls • Lignin reinforcing the xylem

12. Stems • Consist of an epidermis which surrounds the vascular tissue, composed of xylem (water transport, up the stem) and phloem (mineral and sugar transport, up and down the stem to sinks for storage) • Meristems deposit secondary xylem and phloem, which will grow outwards to become primary xylem and phloem.

13. Plan Diagram of the Stem

14. Leaf Structure • Consists of a: • Leaf Blade • Leaf stalk Leaves have a large surface area and a small space between layers Designed for photosynthesis

15. Leaf Structure (cont) • Leaves consist of: • Outer structure - Epidermis • Tough, transparent layer • Upper – waxy Cuticle • Lower – specialized cells called guard cells, that form openings in the bottom, called Stoma • Inner Structure – Specialized Cells • Mesophyll cells

16. Leaf Structure (cont) • Upper Surface – Palisade Mesophyll • Tightly packed • Contain chloroplasts • Lower Surface – Spongy Mesophyll • Loosely packed with air spaces • Vascular Bundles • Consist of xylem and phloem • Bring water to and transport sugars and minerals away and to leaves • Support the leaves along with cellulose and turgor

17. Plan Diagram of the Leaf

18. Roots • First stage of development for the seed when it germinates • Tap Roots • Lateral Roots • Roles • Absorption • Anchors • Support • Storage

19. Roots (cont) • Roots have an outer coat, called the epidermis, and the inner portion is called the cortex • In the root, there is a vascular bundle, of xylem and phloem • Branching of roots allow for a greater surface area • Root hairs off of growing roots, increase the surface area as well.

20. Diagram of Roots and tissue Plan Diagram

21. Modifications of Stems, Roots and Leaves • Roots • Prop Roots • Storage Roots • Pneumatophores • Buttress Roots

22. Examples of Root Modifications

23. Modifications of Stems, Roots and Leaves • Stems • Bulbs • Tubers • Rhizomes • Stolons

24. Examples of Stem Modifications

25. Modifications of Stems, Roots and Leaves • Leaves • Tendrils • Reproductive Leaves • Bracts or floral leaves • Spines

26. Control of Plant Growth - Phototropism • Plant growth is controlled by gravity and light • Plant grows against gravity • Plants grow towards the light • Responses to the above stimuli, called tropisms • Growth towards light called phototropism • Controlled by a hormone called auxin • Produced in the tip of the shoot

27. Control of Plant Growth - Phototropism • Steps of phototropism • Photoreceptors in the tip of the plant sense the light • Stimulate the production of auxin • Auxin will travel to the “shady side” of the plant, as detected by the phototropins • Promotes the elongation of cells in stems, by loosening the connections between the cell walls and cellulose microfibrils • Promotes the stem to grow more on the shadier side and go towards the light. • Allows the leaves on the sunny side to get more light and photosynthesize at a greater rate.

28. Control of Plant Growth - Phototropism

29. Transport in Angiosperms • Root System • Transpiration • Water uptake • Factors affecting Transpiration • Translocation

30. Transport in Angiosperms • Roots – Absorption and uptake • Provide large surface area for uptake of water and minerals • Water is absorbed by osmosis • Amount of water absorbed is increased by root hairs, on ends of growing roots • Minerals absorbed by active transport

31. Water uptake • Occurs by osmosis • Flows through epidermis, into cortex by mass flow, as the cells are interconnected • Three possible routes for uptake of water: • Apoplast Pathway (Mass Flow) • Symplast Pathway • Vacuolar Pathway

32. Water uptake • Apoplast Pathway (Mass Flow) • Most common way for water to move (faster) • Water does not enter the cell • Moves through the cell walls until it reached the endodermis • Cells of the endodermis have a Casparian Strip around them that is impermeable to water • The water is diverted to the spaces of dead cells, eventually to the xylem

33. Water uptake • Symplast Pathway • Water enters the cytoplasm but not the vacuole • It passes from cell to cell via connections between cellular cytoplasm of adjacent cells, called plasmodesmata • The organelles are packed together in cells, and as a result, block significant progress of water • It is not the major pathway for water. Minerals mainly move through this pathway.

34. Water uptake • Vacuolar Pathway • Water enters the cell and move into the vacuole • It can be stored in the cells • It can also travel through the cytoplasm and the cell wall to the next cell, to move into cortex Once in the endodermis, water can move into the xylem and pulled via transpiration forces.

35. Pathways for water uptake

36. Uptake of Minerals • Minerals are important to build cells walls, carbohydrate storage and protein synthesis • Processes for mineral uptake: • Active transport • Mass flow (in water) • Fungal hyphae

38. Transpiration • Transpiration • the loss of water vapour from the leaves and stems of plants. • Like perspiration • As water is lost, the amount of water in the plant decreases. A pull is created in the plant to “pull” water up the plant. This is similar to maintaining homeostasis.

39. Transpiration (cont) • Water moves from root to leaf by transpiration pull • Water moves up the stem to leaves in the xylem • Dead material • Made of tracheids and xylem vessels

40. Xylem Tissue

41. Mechanism of Movement of Water – Transpiration Pull • Controlled by stomata • Stomata open and close depending on the amount of water in the plant • If there is a lot of water – high turgor pressure in guard cells and stomata are open • If there is a deficiency of water – low turgor pressure in guard cells and stomata close • If water drops, abscisic acid is released, overriding all variables and stomata close

42. Mechanism of Movement of Water – Transpiration Pull • When stomata are open, water vapour is lost to the external environment • Concentration gradient is created • The lost water needs to be replaced • Water moves from the high concentration (roots) to lower concentration (leaves) and moves up the plant • Cohesive forces of water allow water to move in a continuous flow

43. Transpiration

44. Factors that affect Transpiration • Biotic Factors • Size of the plant • The thickness of the cuticle • How widely spaced the stomata are • Whether the stomata are open or closed

45. Factors that affect Transpiration • Abiotic Factors • Temperature • Humidity • Wind • Light • All of these can be over ridden by abscisic acid

46. Translocation • Movement of manufactured food (sugars and amino acids). • Occurs in the phloem tissues of the vascular bundles. • Moves sugars from source to sink (leaves to storage) and from source to areas of new growth, like ends of shoots and new leaves. • Phloem tissue allows movement up and down the stem of the plant

47. Translocation • Phloem Tissue, is living tissue, and consists of: • Sieve tubes • Flow of sugars and minerals • Companion cells • Control flow / Active transport • Theory of Translocation is by mass flow, from source to sink • Source and sink can change, depending on use and season

48. Translocation

49. Transpiration and Adaptations of Xerophytes • Small, thick leaves • Reducing the number of stomata • Stomata located in crypts or pits on the leaf surface • Thickened, waxy cuticle • Hair-like cells on the surface to trap water vapour • Become dormant in the dry months • Store water in the fleshy stems and restore the water in the rainy season • Using alternative photosynthetic processes called CAM photosynthesis (Crassulacean acid metabolism) and C4 photosynthesis

50. Reproduction in Flowering Plants • Parts of the flower • Pollination • Fertilization • Seed formation and dispersal • Seed germination • Control of flowering - Photoperiodism