Plant Biology Vocabulary

Plant Form - Chapter 30

Common Plant Features

• Shoot System:
  • Reproductive shoot (flower)
  • Vegetative shoot
  • Apical bud
  • Axillary bud
  • Stem
  • Node
  • Internode
  • Leaf
    • Blade
    • Petiole
• Root System:
  • Taproot
  • Lateral (branch) roots

30.1 - The Plant Body

Plant Organ Systems

• Vascular plants have 2 main organ systems:
  • Root system
  • Shoot system
    • Vegetative: Leaves and stems
    • Reproductive: Flowers & fruit

Plant Tissues

Meristematic

• Found in meristems (areas of continuous cell division and growth).
• Cells are either undifferentiated or differentiated.
• Contribute to the growth of the plant.
• 3 types:
  • Apical
  • Lateral
  • Intercalary

Permanent

• Plant cells that are no longer actively dividing and growing.

More on Meristems

Meristematic Tissue to Permanent Tissue

• Once divided and specialized, meristematic tissues become permanent tissue.

Dermal Tissue

• Covers and protects the plant.

Vascular Tissue

• Transports water, nutrients & sugar.

Ground Tissue

• Site for photosynthesis.
• Support matrix for vascular tissue.
• Storage for sugars and water.

Plant Tissues - Simple vs. Complex

Simple

• Composed of similar cell types.
  • Example: Dermal tissue

Complex

• Composed of different cell types.
  • Example: Vascular tissue
    • Xylem: composed of 3 cell types
    • Phloem: composed of 4 cell types
• Xylem and phloem are always adjacent to each other, forming the vascular bundle.

The Xylem

• Transports water & nutrients from the roots to the plant.
• Cell types:
  • Vessel elements
  • Tracheids
  • Xylem parenchyma (stores water)
• Xylem cells are dead at maturity.

Phloem

• Transports organic molecules from the site of photosynthesis to other plant tissues.
• Cell types:
  • Sieve cells: conduct photosynthesis
  • Companion cells: maintain pressure of sieve cells
  • Phloem parenchyma: store food and other substances
  • Phloem fibers: provide structural support
• Phloem cells are alive at maturity

30.2 - Stems

What is the Stem of a Plant?

• Functions: provide support, hold leaves & flowers, store food
• Vary in length and width
• Woody or herbaceous
• Branched or unbranched
• Connects roots and shoots to help transport water, nutrients & sugar
• Characterized by nodes & internodes
  • Nodes are attachment sites for leaves, roots & flowers
  • Internodes are the spaces between nodes
• Arise from ground tissue axil
• Axillary bud, Apex & apical bud

Stem Anatomy - Parenchyma Cells

• Most common plant cell
• Found in:
  • Roots
  • Leaf
  • Fruit pulp
• Mainly responsible for metabolic functions:
  • Photosynthesis
  • Wound repair
• Can store starch

Stem Anatomy - Collenchyma Cells

• Elongated
• Contain unevenly thickened cell walls
• Structural support for stems and leaves
• Alive at maturity
• Strings in a celery stalk

Stem Anatomy - Sclerenchyma Cells

• Provide structural support
• Most are dead at maturity
• Two types:
  • Fibers: long, slender
  • Sclereids: smaller (what gives pears gritty texture)
• Both have secondary cell walls with lignin
• Lignin is used to make rope & linen

Stem Anatomy - Dermal Tissue

• Mostly epidermis
  • Single layer of cells that covers and protects tissues beneath
• Leaf epidermis contains stomata
  • Site of gas exchange
  • Surrounded by 2 guard cells that open and close
• Trichomes (hair like structures)
  • Prevent water loss during transpiration
  • Help reflect some solar radiation
  • Store substances that prevent predation

Stem Anatomy - Vascular Tissue

• Xylem
• Phloem
• Transport water, nutrients, sugars throughout the plant

Stem Anatomy - Ground Tissue

• Mostly parenchyma cells but contains some sclerenchyma and collenchyma cells
• Functions as support to the stem
• Divided into 2 types
  • Pith: located towards the interior of vascular tissue
  • Cortex: located between the vascular bundles and epidermis

Growth in Stems

Primary Growth

• Increase in length
• Roots & shoots

Secondary Growth

• Increase in girth
• Woody plants

Indeterminate vs Determinate Growth

Primary Growth

• Result of cell division at the apical meristem
• Enables plants to continuously seek water, nutrients & sunlight
• Apical dominance
  • Diminishes growth of axillary buds
• Pruning disrupts apical dominance

Secondary Growth

• Increase in stem thickness as a result of lateral meristem cell division (lacking in herbaceous plants)
• Formation of secondary vascular tissue
• Thick bark like tissue protects plant

Annual Rings

• Result of alternating conditions of secondary vascular tissue within the plant
• Gives information about environmental conditions during growing seasons

Stem Modifications

• Rhizome: grows horizontally underground, shoots may appear above ground
• Corm: similar to rhizomes but more round and fleshy, able to survive harsh winters
• Stolon: stems that run parallel to the ground just below the surface
• Runner: type of stolon that runs above the ground
• Tubers: stems that store starch, arise as swollen ends of stolons
• Bulbs: functions as an underground storage unit
• Tendrils: small, slender strands that enable plants to climb and hold on to vertical structures
• Thorns: modified branches for protection against herbivory

30.3 - Roots

Functions of Roots

• Anchor plants in the ground
• Absorbing water and nutrients > transporting them upward
• Storing products of photosynthesis

Types of Root Systems

• Taproot system:
  • Dicots
  • Main root with small lateral roots
  • Goes deep in the soil
• Fibrous root system:
  • Monocots
  • Dense network of roots
  • Close to the soil surface
  • Prevent soil erosion

Root Growth & Anatomy

• Root growth begins at seed germination (radical)
• Root cap: protects the elongating root tip, continuously replaced
• Root tip zones:
  • Zone of cell division
    • Actively dividing cells
  • Zone of elongation
    • Newly formed cells lengthen
  • Zone of maturation
    • Cells differentiate

Root Growth & Anatomy

• Epidermis
  • Protects root tissue
  • Aids in absorption
• Root hairs
  • Extensions of epidermis
  • Increase surface area

Root Growth & Anatomy

• Inside the root
  • Pith (very little)
  • Cortex (a lot)
• Stele: inner portion with vascular tissue
• Endodermis: separates stele from ground tissue
  • Exclusive to roots
  • Check point for materials entering vascular system, store products of photosynthesis

Root Growth & Anatomy

• Casparian Strip
  • Contains serubin
  • Forces water & molecules to flow endodermal plasma membranes
• Pericycle
  • Outermost layer of root vascular tissue
  • Gives rise to lateral roots

Root Modifications

• Bulbous roots: store starch
• Aerial roots: provide support
• Modified taproots: food storage (carrots)
• Epiphytic roots: enables a plant to grow on another

30.4 - Leaves

Leaves are the main site for photosynthesis!

CO2 + H2O \rightarrow C6H{12}O6 + O2

Structure of a Typical Leaf

• Lamina: leaf blade, widest part of the leaf
• Petiole: attach some leaves to stem
  • Leaves attached directly to the stem are called sessile leaves
• Midrib & veins of vascular tissue
  • Monocots vs. dicots

Leaf Arrangement - Phyllotaxy (leaves are classified as):

• Alternate: one leaf per node, alternate on each side of the stem
• Spiral: leaves arranged in a spiral around the stem
• Opposite: 2 leaves arise opposite each other at the same point on the stem
• Whorled: 3 or more leaves connected at a point

Leaf Form

Simple

• Leaf is completely undivided
• Some lobes but they do not meet the midrib

Compound

• Leaf blade is completely divided creating leaflets
  • Each leaf may have its own stalk but is connected at the same point known as the stalk

Compound Leaves

Palmately Compound

• Leaflets radiate from one point
• Resembles a palm

Pinnately Compound

• Leaflets arranged along the midrib

Leaf Structure & Function - external

• Epidermis: outermost layer, present on top and bottom
  • Helps regulate gas exchange
    • Stomata & guard cells
  • Typically one cell layer thick
• Cuticle: waxy layer that helps prevent water loss
• Trichomes: hair like structures
  • Prevent water loss
  • Protect plant

Leaf Structure & Function - internal

Mesophyll

• Located below epidermis (dicots)

Palisade parenchyma

• Tightly packed, column shaped cells

Spongy parenchyma

• Irregular shape
• Air between cells allows for gas exchange
• Contain xylem and phloem
• Contain chloroplasts

Leaf Adaptations

• Needle-like leaves
  • Plants that thrive in cold environments
  • Reduced water loss by shrunken stomata
• Spines
  • Leaves reduced dramatically to conserve water (cacti)

The Major Divisions of Land Plants

• Streptophyta
  • Includes green algae & land plants
  • Vascular = contains specialized cells for water and nutrient transport
  • Gymnosperms: produce naked seeds (pinecones)
  • Angiosperms: flowering plants, protect seed inside a fruit