Plant Structure and Growth

1. Plant Structure and Growth Chapter 35

2. Objectives • List the differences between dicotyledons and monocotyledons • Describe the basic structure of all plants • Describe how the structure of plants is an adaption to the basic function of plants in terrestrial environments • Name the six types of cells and three types of tissue systems found in plants and describe their distinguishing characteristics

3. Differentiate between primary and secondary growth, and describe where and how each kind of growth occurs

4. Introduction • Angiosperms are largest group of plants • make up 90% of world’s plant species • two major groups of angiosperms • monocotyledons • include orchids, bamboos, palms, lillies and grasses • distinguishing characteristics include • single seed leaf; cotyledon • leaves usually parallel-veined • scattered vascular bundles in stems • floral parts in multiples of three • fibrous root system

5. dicotyledons • includes most angiosperms including most shrubs and trees (except conifers) and many herbaceous plants • distinguishing characteristics include • two cotyledons • net-veined leaves • vascular bundles in ring in stems • floral parts in multiples of four or five • taproot system

6. Plant Structure • Plant body consists of roots and shoots • allows plants to function in terrestrial environment • take up water and minerals from soil • absorb light • take in CO2 from air • create plant bodies from molecules assembled from these raw materials and products of photosynthesis

7. root system • anchors plant • absorbs and transports minerals, water and stores food • ultimate site of absorption is root hair • outgrowth of epidermal cells • increases absorptive surface area

8. shoot system • consists of supporting stems, photosynthetic leaves and reproductive structures • composed of • nodes-point where leaves, flowers and other stems attached • internodes-stem between nodes • leaves composed of photosynthetic blades and short stalks (petioles) that join blades to nodes

9. buds • undeveloped shoots • contain potential nodes, internodes and leaves • two types • terminal bud at plant apex; source of growth in height • axillary bud in angle of petiole and stem; usually dormant but can produce new branches

10. apical dominance • results from release of hormones from terminal buds • inhibits growth of axillary buds • removal of terminal bud stimulates development of axillary buds • basis for pruning

11. Many plants have modified roots and shoots • modified tap roots of some dicots used for food storage • stored as starch • examples-root crops • stems can be modified for several purposes • asexual reproduction • runners-strawberries • food storage • rhizomes-irises • tubers-potatoes

12. leaves can be modified • food storage • leaf bases of celery • grasping and climbing • tendrils of cucumbers • protection • spines of cactus

13. Plant cells and tissues diverse in structure and function • cells have unique features • photosynthetic and contain chloroplasts • often have large central vacuole; maintain turgor • bounded by cell wall composed of cellulose • many cells have additional secondary wall hardened with lignin • plasmodesmata provide continuous cytoplasmic link between adjacent cells

14. six types of plant cell; based on wall morphology and chemistry, shape and function • parenchyma • abundant and unspecialized; primary cell walls • food storage, photosynthesis and aerobic respiration • collenchyma • similar to parenchyma but have thicker primary wall • provide support for young growing parts of plant

15. sclerenchyma • have rigid cell walls hardened with lignin • provide support and protection • seed coats • gritty texture of pear

16. vessel elements and tracheids • found in xylem • elongated and secondary wall thickening; dead and open ended when functioning as water conducting cells • connected end-to-end • tracheids • tapered ends • covered with open pits • vessel elements • wider and shorter; completely open ends

17. sieve-tube members • found in phloem • relatively thin primary walls, no secondary wall; alive but lack nucleus and ribosomes when functioning • contain numerous pits with plasmodesmata • associated with at least one companion cell • provides nucleus functions for sieve-tube member

18. Three tissues make up plant body • epidermis • composed of single, surrounding layer of cells • first defense against infection and damage • vascular tissue • composed of xylem and phloem • conducts water and nutrients through plant

19. ground tissue • fills space between epidermis and vascular tissue • composed mainly of parenchyma • functions include photosynthesis, storage and support • each system continuous from organ to organ

20. roots • surrounded by epidermal cells with root hairs; no cuticle • ground tissue (cortex) conducts material from root surface to central vascular tissue • inner layer of cortex (endodermis) forms selective barrier; regulates flow into vascular tissue

21. stems • epidermal cells covered by waxy layer-cuticle • dicots-vascular tissue bundles in outer ring of ground tissue cortex surrounding parenchyma pith • monocots-vascular tissue bundles scattered in uniform ground tissue

22. leaves • also have cuticle • lower epidermis includes pores (stomata) surrounded by guard cells-gas exchange • ground tissue arranged in two mesophyll layers • lower loose layer (spongy mesophyll) for gas exchange • upper compact layer (pallisade mesophyll) for photosynthesis • branches of vascular tissue enter leaf and provide transport to and from photosynthetic cells

23. Plant Growth • Primary growth lengthens roots and shoots • indeterminate growth-grow during entire life • three seasonal growth patterns • annuals-complete life cycle in one year • biennials-complete life cycle in two years • perennials-live and reproduce for many years

24. indeterminate growth results from presence of meristems • unspecialized cells that continue to divide • apical meristems at root and shoot tips and in axillary buds • differentiation controlled by master control genes (homeotic genes)

25. apical meristem in root tip divides cells downwards • root cap protects meristem; abraided by soil • other cells grow upward, forming three rings of tissue-become epidermis, cortex and vascular cylinder • above meristem cells elongate; force root tip down • above this region, cells differentiate

26. apical meristem of shoot forms three downward-forming cylinders of embryonic tissue • contains zones of elongation and differentiation • some meristem cells remain in lateral position • form meristem of axillary buds

27. Secondary growth increases girth of woody plants • involves meristems that grow laterally in stems • most evident in trees, shrubs and vines

28. vascular cambium-cylindrical meristem • develops from parenchyma cells between xylem and phloem of shoots • cells dividing inwards form new secondary xylem outside primary xylem • cells dividing outwards add secondary phloem inside primary phloem • secondary xylem cells larger during favorable growth periods and smaller at other times • annual growth rings

29. new layers of phloem do not accumulate • sloughed off in bark at same rate produced • in secondary phloem, meristematic cells (cork cambium) produce cork cells • dead when mature • thick, waxy walls-protect stem surface

30. wood divided into two layers • heartwood-nonfunctioning xylem, plugged with resin • acts as endoskeleton; strong, rigid but flexible core • sapwood-functioning secondary xylem • wood rays are collections of parenchyma cells forming connections between heartwood and sapwood