Outline – Plant structure Next few lectures are on plant form and function Today: Plant Structure I. Plant Cells – structure & different types Exam II is on F March 31 II. Types of meristems Apical meristems: primary growth Lateral meristems: secondary growth

III. Tissues in cross sections IV. Leaves: regulation of gas exchange and water loss

Plant Cells: Distinguishing features Plant Cell Walls Chain of glucose molecules (Ch. 4 – refresher) • Neighboring cells are glued together: middle lamella • Chloroplasts - photosynthesis • Vacuoles - sacs of liquid • Primary cell wall - • Cellulose cell wall cellulose as the cell grows Animal Cell

• Secondary cell wall – Fig 35.6 cellulose impregnated with lignin or suberin:

Secondary Plant Cell Walls

Cell Walls • Plasmodesmata: thin spots where strands of cytoplasm pass through the cell walls Some cells produce a thick • Allows direct communication between neighboring secondary wall. Contains: cytoplasms. • Lignin - is hard and woody. Fig 35.7

•Or suberin, which is corky and plasmodesmata waterproof.

1 Plant Cell Walls Common Plant Cell Types • Pits - interruptions of the secondary wall for There’s several types of plant cells – each plasmodesmata with different structures and functions

1. Parenchyma 2. Collenchyma 3. Sclerenchyma

4. Xylem (tissues) 5. Phloem

Fig 35.8

Common Plant Cell Types Common Plant Cell Types (1) Parenchyma cells have thin cellulose walls with Parenchyma no secondary wall. • Photosynthetic • Green cells - photosynthesis in leaves. • Storage (starch or lipids.) • Function when alive •Some bulk/structure

Common Plant Cell Types Common Plant Cell Types Chollenchyma •“Flexible support”, e.g., leaf stalks, (2) Chollenchyma cells: non-woody stems have primary walls with thick corners (no • Support for young growing organs secondary wall). E.g., Celery “strings” • Usually long and narrow. • Function when alive

2 Common Plant Cell Types Common Plant Cell Types Sclerenchyma • Strengthen tissues that have ceased growing. (3) Sclerenchyma cells: •Two kinds: have thick, often lignified secondary walls. • Greek skleros = “hard” ‹ Fibers- long thin, e.g., flax or hemp fiber, bark • Usually dead at maturity when functioning • Rigid support

‹ Sclereids- shorter, may be branched, e.g., shells of nuts, peach pit, grit in pears

Plant Cells Plant Cells Vascular plants have specialized conducting (4) Xylem for water transport tissues: • Move water roots Æ aboveground (4) Xylem for water transport • Function when dead

(5) Phloem for sugar and nutrient transport 2 kinds: • Tracheids and vessel elements

Plant Cells Plant Cells Tracheids and vessel elements - Vessel elements: lignified secondary walls. • stack to form long open tubes • Tracheids connected with pits • A bubble will ruin the whole tube ‹ found in all vascular plants Tracheids: • pits block even the smallest • Vessel elements have big holes. bubble

‹ restricted to angiosperms. • damage is localized to only one cell.

3 Plant Cells Plant Cells (5) Phloem for moving sugars (5) Phloem around. • Sieve tubes stack end to end • Transport carbohydrates and forming a long tube. nutrients • Companion cells regulate it: • Function when living: Linked by plasmodermata Retain organelles

Sieve tube elements

Review of Plant Cells Review of Plant Cells • Which cells function when dead? Which of the following is most correct? • Which cells provide flexible support?

a. Only the primary cell walls are made of cellulose •Parenchyma b. Only the secondary cell walls are made of cellulose c. Only the primary cell walls contain lignin or suberin •Chollenchyma d. Only the secondary cell walls contain lignin or suberin •Sclerenchyma

Plant Tissues and Tissue Systems Plant Tissues and Tissue Systems • Vascular tissue: conducts water, minerals, Fig 35.12 3 tissue systems in plants: and the products of • vascular tissue photosynthesis. • dermal tissue •Dermal tissue: • ground tissue protects the body surface.

• Ground tissue: produces and stores food

4 Forming the Plant Body Forming the Plant Body

• Root and shoot apical Plants grow from localized meristems give rise to regions: meristems the entire plant body of where cells divide. herbaceous plants.

• apical meristems Growth of the primary plant • Woody plants show body secondary growth. Secondary ‘body’ is wood • lateral meristems and bark Growth of the secondary plant body

Apical meristems Apical meristems

• Plants grow only vertically from these Give rise to: growing tips: • Roots ‹ Hammer a nail 5 feet from the ground •Shoots into a 10 ft. sequoia sapling. • Plant organs

‹ In a thousand years when the tree is 300 ft., how high will the nail be?

Roots •The cortex – food storage Roots • Endodermis – waterproof layer keeps water from moving inside without passing • Root cap through the cytoplasm. Fig 35.17 • Root hairs • Xylem and phloem • Epidermis

• Mycorrhizae are associated with epidermis and root hairs

5 Roots – Water uptake Casparian strip –Suberin Shoots • Makes waterproof ring

• Water cannot go between cells The shoot apical meristem • Osmotic Regulation gives rise to leaf primordia: • Leaves and • buds

Fig 36.5

Shoots Shoots Eudicot Monocot

Vascular tissue: Roots - the center

Young stems – bundles in a ring or scattered.

Vascular tissue is in bundles in a ring or scattered. (Fig 35.18)

Phloem Shoots Eudicot Monocot Shoots

Vascular Cambium

Xylem

Rest is parenchyma with some strengthening • Vascular bundle of a young eudicot stem collenchyma around the outside. storage • Primary growth: growth from apical meristems • Epidermis secretes a waxy cuticle

6 Lateral Meristems Æ secondary Secondary growth of stems growth of stems

•Thicken to wood and bark

•This is secondary growth resulting from the two lateral meristems: vascular and cork cambium. • Vascular cambium in the vascular bundles becomes a continuous cylinder • secondary xylem to the inside • secondary phloem to the outside

Secondary growth of stems Secondary growth of stems

• Secondary xylem: mostly vessel elements, Annual rings: fibers and parenchyma Plants growing in seasonal WOOD environments often produce • Secondary phloem: • wide, thin-walled vessels mostly sieve tubes or tracheids in the spring members, companion •and narrower, thick- cells, fibers and walled cells in the parenchyma summer. part of BARK

Secondary growth of stems Leaves

Lenticels • Where photosynthesis occurs

• Bring together the precursors: H2O, CO2.

• Export the products: Bark sugar, O2. • Tissues outside the phloem •The cork cambium produces new protective tissue: Cork – suberized

7 Leaves Leaves Conflicting needs: 1. Avoid desiccation. Mesophyll – 2. Obtain CO2. Green parenchyma where photosynthesis occurs.

Open - easy access for CO . Fig 35.23 2 • Epidermis – Flat cells covered by a waxy cuticle. Good at 1. but not 2. Fig 35.23

• Stomata – Regulated pores that let CO2 in

Review of Structure

Which meristem causes elongation? Which meristem causes thickening?

How to leaves balance the conflicting need for CO2 and the negative effects of desiccation?

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