Plant Structure, Growth, and Development

Chapter 35

PLANTS

developmental plasticity = ability of plant to alter form to respond to environment

Biological heirarchy

• Cell – basic unit of life

• Tissue – group of cells perform a common function

• Organ – multiple tissue types with a common function

• Organ system – multiple organs with common function

• Organism – all of above

Example

Parenchyma cells

Plant epidermis

Leaf

Shoot system

Plant

PLANTS Moss, ferns, gymnosperms, angiosperms

ORGAN SYSTEMS

1. Root System Root (organ)

Anchors plant

Absorbs minerals and water

Stores food

Root hairs

Absorption of water

and minerals

Large surface area

Renewed continually

Extension of root

epidermis

Radish seedling

Extension of epidermis

A. Taproot system

Embryonic root Taproot = main

vertical root, deep

Stores sugar, starch

So, harvest carrots before they flower

Lateral roots

deep

Radish, mustard, carrot,

B. Fibrous root system (embryonic root dies)

Begins with Adventitious roots

Roots arise from stems or leaves

Shallow mat

Maize: Prop roots are adventitious

From stem on bottom of bulb canary island date palm

Monocots and seedless vascular plants

ferns

grains, grass, lilies, onions

scallion

grass

fern

2. Shoot system

Stem (organ)

Nodes = points at which leaves are attached

– Internodes= stem segments between nodes

– Axillary bud can form a lateral shoot, or branch

– Apical bud near shoot tip for elongation

• Apical bud is dominant

– Pinch off apical bud plant grows laterally

Stem adaptations: Rhizome =modified stem (shoot below surface)

iris ginger bamboo

Storage leaves

Stem

Onion bulb is an

underground shoot

Stolons of strawberry plant

Stolon= horizontal

shoot or runner

Tubers = enlarged rhizome ends

Eye is cluster of axillary buds (can plant)

Leaves (organs) • Photosynthesis

• Blade

• Petiole

– stalk joins leaf to node of stem

• cc

Simple =single

blade

Compound - blade

has multiple leaflets

Doubly compound =

each leaftlet divided

into smaller leaflets

LEAF MORPHOLOGY (shape)

• Leaf veins = vascular tissue of leaves

• parallel veins

– ex. lily, orchid, grass (monocots)

• branching veins

– Ex. apple, maple, dandelion (eudicots)

Grape (Vitis) daylily mint

Plant tissues

1. Dermal tissue system

• Protection against:

– Water loss

– Disease

– Damage

A. Epidermis (non-woody plants)

– Waxy cuticle on leaves, stems

Specialized epidermis

Trichomes

– Hair-like

– Reduce water loss

– Reflect excess sunlight

– May secrete sticky or toxic fluids

– May sense prey (carnivorous plants)

trichomes

B. Periderm (woody plants) from epidermis

– On older stems and roots (cork, bark)

Very hairy pod

(10 trichomes/

mm2)

Slightly hairy pod

(2 trichomes/

mm2)

Bald pod

(no trichomes)

Very hairy pod:

10% damage

Slightly hairy pod:

25% damage

Bald pod:

40% damage

EXPERIMENT

RESULTS

Does soybean

trichome density

relate to beetle

damage?

Read experiment

Chapter 35

Cerotoma trifurcata, the bean leaf beetle

Dermal tissue

Ground tissue Vascular

tissue

Fig 35.8

2. vascular tissue system long-distance transport from roots to shoots

• Xylem tissue • Transports water, minerals from roots shoots

• One way transport

• Older xylem = wood

• Phloem tissue • transports sugars from leaves to where needed

(leaves, fruits)

• 2 way transport

Xylem vessels – cells not alive at maturity

Phloem – cells alive at maturity

3. ground tissue system – Storage

– Photosynthesis

– Support

• pith tissue internal to vascular tissue

• cortex tissue external

A transverse section of corn (Zea mays) internode showing ground

tissue

Plant growth

• Mature plant contains

• Embryonic cells

• Developing organs

• Mature organs

Life cycles

• Annuals complete life cycle in <year

• Germinate grow flower seed

• Biennials require two growing seasons

foxglove thistle sweet william

• Perennials live for many years

PLANT GROWTH

• Determinant growth

– Some organs grow to certain size

• Leaves

• Flowers

Indeterminate growth

• Plant grows throughout life

• Meristems = embryonic tissue

• Apical meristems for primary growth • Tips of roots, shoots, leaves

• New cells either remain as meristematic or differentiate

• Apical meristem in stem with leaf primordium

• Apical meristem in root

Primary Growth of Roots

• root cap covers root tip

– protects apical meristem as root pushes through soil

Primary Growth of Shoots

• Leaves from leaf primordia

• Note: Axillary buds

• Lateral meristems

• Secondary growth

• Roots and stems

• Increases thickness

• Woody plants

Organization of stems • Vascular bundles of tissue

Monocot bundles throughout stem

Eudicot bundles in outer ring

Same tissues different arrangement

Monocot ex. corn, grass

Eudicot example:

African violet

Organization of Leaves Stomata In epidermis

guard cells regulate stomata opening and closing

mesophyll

ground tissue of leaf

Between upper and lower epidermis

Scanning electron microscope image of leaf from a Black Walnut tree. Image shows a cross-

section of a cut leaf, its upper epidermal layer, mesophyll layer with palisade cells and vascular

bundles, and lower epidermal layer. Dartmouth College

RMS

• Monocot leaf

• Eudicot leaf

Same tissues, different arrangements