vascular plants, test 2

meristem

site of cell division, contains undifferentiated cells

apical meristems

at tips of all shoots and roots

• RAM

• SAM

• AM → protoderm (becomes epidermis), ground meristem (ground tissue), and procambium (becomes vascular tissue) = (all primary meristems)

initials

completely undifferentiated cells that remain so and are source of all other cells

• derivative: an initial that divides more and becomes part of one of the primary meristems depending on position

primary meristems

responsible for primary growth

• elongation of shoots (taller, more branches, buds, leaves)

• elongation of roots (branching)

3 types of development

1. growth (getting bigger): cell division and enlargement

2. morphogenesis: formation of plant shape, leaves, and stem

3. differentiation: cells differentiate based on their final position in primary meristem

ground tissue (simple tissue- aggregations of one cell type)

• stems of dicots: pith (interior) or cortex (between vascular bundles and epidermis)

• leaves: mesophyll

3 cell types

1- parenchyma: mostly undifferentiated (totipotent), variable function, depending on location (pith= storing starch, in mesophyll = photo., transfer cells= move solutes through glands, nectaries, vascular tissue)

2- collenchyma: support for newly formed organs/tissue growing, pedicols + pedioles, thick cell walls that are not lignified

3- sclerenchyma: structural support for full grown plants, lignified with two cell walls, fiber cells (fibrous, elongated) and sclerid cells (star shaped, ultra hard, protective structures)

vascular tissue (2) (complex- multiple cell layers)

1) xylem: conducts water and minerals, structural support, some food supply

• tracheid’s: elongated, 2 cell walls, 2nd cell wall is pitted with larger pits at ends, dead at maturity but cell wall remains intact

• vessel elements: in angiosperms only, elongated, 2 cell walls, dead at maturity, cells joined together end to end at perforation plate, perforation plate has larger openings (perforations) in cell wall-allows H20 to flow more freely

• these two make up the tracheary elements

2) phloem: food conducting tissue (sugar), amino acids, proteins, hormones, RNA for signaling, lipids, floral stimulants

• sieve cells: in all vascular plants

• sieve areas: cell wall on end, separates 2 cells, joined end to end, uniform in size and spacing of openings

• sieve tube element: cells separated by sieve plate, some large perforations (angiosperms only, lots of p-protein that helps seal wounds) at maturity: no nucleus, no ribosomes, no golgi, no central vacuole

• all make up sieve elements

additional phloem support cells

• albuminous (parenchyma): extra mitochondria and ribosomes, support metabolite functions of a sieve cell

• companion cells: parenchyma with extra mitochondria and ribosomes that are the life support

dermal tissue (primary)

covers exterior of plant body (above and underground)

• protection

• epidermal cells: lack chloroplasts, aerial side (coated with waxy cuticle (forms waterproof barrier, prevents H2O loss)

• stomata: pores bordered by guard cells (enable gas exchange, guard cells open pore when hydrated (relax/ placid when dehydrated)

• O2, CO2, H20 moves thru stomata

• trichomeres: cells with extremely variable structures and function (ex: root hairs: increase surface area of roots to maximize absorption, ex: leaves: glandular: secrete sticky substances to capture prey, and that can be toxic to plant like salt, lots of leaves reflect solar radiation to regulate leaf temp)

root functions

anchorage, absorption, storage, conduction

types of root systems

• fibrous root systems (monocot): no main root, many roots originating from stem at soil surface, roots can branch some to increase surface area (roots don’t specifically branch, no nodes)

• taproot (dicots and other seed plants): have one main central root from which lateral roots branch, deeper than fibrous

• tree root system: tap root, more lateral roots (horizontal), 90% of are in top 2ft of soil where nutrients are, spread 4-7 times lateral spread of crown (leaves), sinker roots stem down from lateral roots,

structure of a root

1- root cap: mass of living cells (parenchyma cells), enclosing RAM, protects RAM from mechanical damage, border cells are shed into soil and remain alive for several weeks (secrete mucilage to lubricate root and prevent infection, stop desiccation, attract good bacteria, chemically mobilize elements for uptake

2- root growth: RAM (site of cell division), region of elongation (cells grow and elongate, tissues form), region of maturation (root hairs form, and tissue systems differentiate, no more inc. in length)

epidermis

in contact with soil

• no cuticle

• root hairs, numerous, dramatically increase surface area in contact with soil, infection with mycorrhizal fungi (mutually beneficial) = increases plant’s potential H2o absorption

ground tissue = cortex

• parenchyma cells: no chlorophyll, but have plastids that store starch

• more interstitial space to improve gas exchange in cells (exaggerated in water logged soil)

• endodermis: tightly packed cells enclosing vascular cylinder (space between cell sis covered/filled with casparian strips = restricts flow of water and minerals to plasmodesmata)

vascular cylinder

rings of cells called pericycle- later roots originate here, site of secondary growth, solid cylinder of xylem and phloem

secondary growth in vascular cambium

Formation of vascular cambium (secondary vascular tissue meristem) A → B

• pericycle and undifferentiated procambium turn into vascular cambium and then secondary vascular meristem

Growth of secondary vascular tissue (divides in both directions) C → D

secondary growth in roots: cork cambium

between epidermis and secondary phloem

• forms ring around secondary phloem and divides in both directions (inner layer = ring, phelloderm and outer layer = cork)