Botany (the Study of Plants)

1. Botany(the Study of Plants)

2. General Plant Review • All plants are: • Eukaryotic • Autotrophic • Multicellular • Cell Walls with cellulose • Chloroplasts w/ chlorophyll a, b, and carotenoids • May have waxy cuticle to prevent water loss. • Stomata allow gas exchange. • Plants probably evolved from green algae (charophytes) • Chloroplast similarity • Biochemical similarities • Cell Wall similarities

3. Plant ReproductionAlternation of Generations – plants grow a separate, haploid organism to produce gametes; the same plant exists in two different forms during its life, although sometimes it’s hard to differentiate between the forms Multicellular Sporophyte – (2N) Mitosis Meiosis Zygote (2N) Unicellular Spores (N) fertilization Unicellular Gametes (egg & sperm) Multicellular Gametophyte (N)

4. Evolutionary Trend – early plants displayed the haploid gametophyte (n) as the dominant structure, modern plants show the diploid sporophyte (2n) as dominant form (Ex: Moss is HAPLOID, but Oak Trees are DIPLOID) zygote SPOROPHYTE (2n) GAMETOPHYTE (n) GREEN ALGA BRYOPHYTE FERN GYMNOSPERM ANGIOSPERM

5. Classifying Plants • Plants can be divided into 2 major categories based on their characteristics: • Nonvascular Plants • Do NOT have specialized tissues to transport water and nutrients • Instead, these plants transport water from cell-to-cell by osmosis • Vascular Plants • Have specialized tissues to transport water and nutrients in plants • Xylem – carries water upward from roots • Phloem – carries nutrients and carbohydrates produced by photosynthesis

6. Nonvascular Plants (Bryophytes) • Short with no specialized tissues to transport water • Major types: • Mosses • Liverworts • Hornworts

7. Nonvascular Plants/ Bryophytes • Mosses • Have rhizoids that anchor them to the ground (instead of roots) • Depend on water for fertilization • The sperm must swim to the egg • Therefore, nonvascular plants must live in MOIST environments • Gametophyte is the dominant phase of the life cycle

8. Moss/ Bryophyte Life Cycle Zygote grows, develops into a sporophyte while still attached to gametophyte. mature sporophyte zygote Diploid Stage Meiosis Fertilization Haploid Stage Spores germinate. sperm-producing structure male gametophyte egg-producing structure female gametophyte

9. Vascular Plant Divisions • Have specialized tissues to transport water and nutrients in plants called Xylem & phloem • Vascular plants (tracheophytes) can be divided into 2 categories: • Seedless vascular plants (spores) • Seed (vascular) plants

10. Seedless Vascular Plants • Ferns – A Close Up • Diploid sporophyte is the dominant stage • Have rhizomes, which are underground stems • Fronds: large “leaves” where spores develop • Develop spores in sporangia on underside of fronds • Reproduce using spores • A sorus (plural: sori) is a cluster of sporangia

11. Fern Life Cycle Sporophyte still attached to gametophyte sorus rhizome zygote Diploid Stage fertilization meiosis Haploid Stage Spores are released Spores develop egg sperm mature gametophyte Spore germinates

12. Seed (Vascular) Plants • Have true roots, leaves, and stems • Have the ability to form seeds, which are used for reproduction • Seed plants are the most dominant group of photosynthetic organisms on land • There are 2 types of seed (vascular) plants: • 1. gymnosperms (cones) • 2. angiosperms (flowers)

13. Seed (Vascular) Plants • Gymnosperms = “cone bearers” • “naked seeds” – not enclosed in ovaries • Bear seeds directly on the surfaces of cones • Cones = sporophyte structures that produce gametophytes (seeds) • Coniferous trees are the major example • Pines, junipers, spruces, etc.

14. Pine Life Cycle section through one ovule surface view of one cone scale (houses two ovules) ovule surface view of one cone scale (houses a pollen-producing sac) mature sporophyte section through a pollen-producing sac seed coat zygote seeding Diploid embryo seed fertilization meiosis pollen tube Haploid microspores form eggs sperm-producing cell megaspores form pollination female gametophyte

15. Seed (Vascular) Plants • Angiosperms = flowering plants • Seeds are enclosed by an ovary • Flowers are reproductive organs • Evolutionary advantage  attract pollinators • Flowering plants contain ovaries • Ovaries surround and protect seeds • Ovary develops into a fruit after pollination & helps with seed dispersal when eaten • Examples: • Maple trees, tulips, grass

16. sporophyte Flowering Plant Life Cycle Diploid Double fertilization Meiosis Meiosis Haploid mitosis without cytoplasmic division microspores pollination two sperm enter ovule female gametophyte

17. Evolutionary Tree for Plants Nested monophyletic groups flowering plants green algae gnetophytes zygophytes, related groups charophytes lycophytes horsetails ginkgos bryophytes ferns cycads conifers seed plants euphyllophytes embryophytes (land plants) vascular plants (closely related groups)

18. Transport in Vascular Plants

19. Transport Within Plants • Water and minerals absorbed by roots are drawn upward in the xylemto the shoots • Sugar produced by photosynthesis is exported from leaves to other organs via the phloem • Transport can be passive or active

20. Short- and Long-Distance Transport in Plants • Water and sugars move differently in plants, depending on whether they’re going a short or a long distance • Ie. – walking down the street or taking an airplane across the world

21. Short-Distance Transport 1. Simple diffusion/osmosis • substances in one cell move out of one cell, across the cell wall, and into another cell 2. Plasmodesmata • Plasmodesmata are connections between the cytoplasm of adjacent plant cells • Substances move between cells through these openings

22. Long-Distance Transport • Over long distances, these 3 processes (simple diffusion, apoplast,& symplast) take too long • Water and solutes move through xylem and phloem by bulk flow, the movement of a fluid driven by pressure

23. Transpiration • Transpiration is the evaporation of water from leaves and other parts of the plant; it causes a pull that brings more water up through the xylem • An average maple tree loses more than 200L of water per hour during the summer! • Unless this water is replaced by water absorbed by the roots, leaves will wilt and die

24. (Cohesion-Tension Theory) • Transpiration works through a combination of evaporation, water potential, adhesion, and cohesion to pull water up the xylem

26. The Photosynthesis-Transpiration Compromise • Exposing leaves to the sun and opening stomata (cellular “holes” in the underside of the leaf) to allow for gas exchange helps photosynthesis, but causes transpiration to occur at a faster rate. Plants balance the loss by controlling when stomata are open.

27. Mechanism for Stomatal Opening & Closing • Guard cells open and close stomata by changing shape using ion and hormone signals based on plant stress.

28. Plant Structure, Growth, & Development

29. The Diversity of Angiosperms • Angiosperms (flowering plants) can be divided into 2 major categories: • Monocots – • have one seed leaf (cotyledon) • Dicots – • have 2 seed leaves (cotyledons)

30. Monocots • Monocots have only 1 cotyledon (seed leaf) • Parallel veins • Examples of monocots: • Corn, wheat, lilies, orchids, palms

31. Dicots • Dicots have 2 cotyledons (seed leaves) • Branching veins • Examples of dicots: • Roses, clover, tomatoes, oaks, daisies

32. Woody vs. Herbaceous Plants • Angiosperms can also be subdivided into woody (produce wood) and herbaceous (do not produce wood) plants • Woody plants are made of cells with thick cell walls that support the cell body • Examples: trees, shrubs, vines • Herbaceous plants do not produce wood as they grow, and instead have smooth stems • Examples: dandelions, sunflowers

33. Plant Life Spans • The lifespan of plants, however, is genetically determined • Annuals – complete their life cycle in 1 year • Examples: marigolds, cucumbers (lots of garden plants) • Biennials - complete their life cycle in 2 years • Year 1: germinate & grow roots • Year 2: grow stems & leaves, produce flowers & seeds • Examples: evening primrose, celery • Perennials – live for more than 2 years • Examples: Maple trees, grasses, palm trees

34. Plant Structure • Plants are made up of a root system and a shoot system

35. The Root System • What do roots do? • Anchor the plant in the soil • Absorb minerals and water • Store food • Types of root systems • Fibrous root system • Found mostly in monocots • Taproot system • Found mostly in dicots

36. How do roots grow? • Roots grow down from the tip in a region called the apical meristem, where the cells are dividing quickly

37. The Shoot System • The shoot system consists of: • vegetative shoots (which bear leaves) • floral shoots (which bear flowers) • Stems have 3 important functions: • Producing leaves, flowers (reproduction), branches • Holding leaves up to the sunlight for photosynthesis • Transporting substances between roots and leaves

38. How do stems grow? • Primary growth • Increase in length • Occurs by cell divisions in apical meristem (at top of shoot) • Secondary growth • Increase in width • Occurs by cell divisions in the lateral meristems (outward growth)

39. The Shoot System: Leaves • Leaves are the primary photosynthetic organs of most vascular plants • Most leaves have a flattened blade and a petiole, which is the stalk that attaches the leaf to the stem

40. Tissues in Plants • All 3 plant organs (root/stem/leaf) have dermal, vascular, and ground tissue systems • Dermal Tissue System • Outer protective covering, similar to our skin  • Protects the plant from water loss and disease • The cuticle is a waxy coating that helps to prevent water loss

41. Tissue Systems in Plants • Vascular Tissue System • Carries out long-distance transport of materials within the plant • Xylem and phloem are examples of vascular tissues • Ground Tissue System • Pith (inside vascular tissue) and cortex (outside vascular tissue) are examples of ground tissue • Inner cells specialized forstorage, photosynthesis, and support

42. Flower Structure • Flowers are the reproductive structure of angiosperms • Sepals: • Enclose the bud before it opens • Protect flower while it’s developing • Petals: • Usually brightly colored to attract pollinators

43. Flower Structure • Stamens: • The male portion of a flower • Made up of an anther and a filament • The anther produces haploid pollen grains by meiosis • Most flowers have multiple stamens

44. Flower Structure • Carpels/Pistils: • The female portion of a flower • Stigma: • Sticky – to trap pollen • Style: • Hollow tube which connects stigma and ovary • Ovary: • Produces female gametes (ovules) • Fruit grows from an expanded ovary

45. Seed Dormancy • Seed dormancy means that a seed will not germinate, even if sown in a favorable place, until a specific environmental cue causes them to break dormancy • Seed dormancy increases the chances that germination will occur at a time and place most advantageous to the seedling

46. Stages of Seed Germination • The seed absorbs water, causing it to expand and rupture its seed coat • The embryo resumes growth, digesting the storage materials of the endosperm • The radicle (embryonic root) emerges from the germinating seed • The shoot tip breaks through the soil surface

47. Stages of Seed Germination

48. Plant Asexual Reproduction • When plant species clone themselves by asexual reproduction, it’s known as vegetative reproduction

49. Asexual Reproduction • Fragmentation is the separation of a parent plant into parts that re-form whole plants • This type of asexual reproduction is used to produce clones from cuttings (common with houseplants)

50. Plant Responses to Internal & External Signals