Ch 34 - Plant Form and Function

Define Autotroph

• Any organism that can synthesize reduced organic compounds from simple inorganic sources such as CO2 or CH4

• Ex: most plants and some bacteria

Define Heterotroph

• Any organism that cannot synthesize reduced organic compounds from inorganic sources and that must obtain them from other organisms

• Ex: some bacteria, some archaea, and virtually all fungi

• AKA a consumer

Morphological Diversity

• Different species have varied root structures; diversity allows plants to coexist without competing directly for resources

• Ex: prairie plants show a range of root depths and types

  • Some have deep taproots, like the compass plant, which can reach over 4 meters deep, while

  • Others, like Junegrass, have fibrous roots that spread widely but remain shallow

Phenotypic Plasticity

• Roots can change form based on environmental conditions

• Ex: spruce trees in wet soils develop shallow roots due to low oxygen levels, while the same species in dry soils grow deeper roots

Modified Roots

• Some roots have specialized functions beyond absorption

• Ex: Adventitious roots, like those in ivy, grow from the shoot system to anchor plants to surfaces

• Ex: Corn's prop roots brace the plant against wind.

Root Support

• Anchor Roots: These adventitious roots grow from stems, helping plants like ivy cling to walls or other structures

  • Stabilize the plant by anchoring it securely.

• Prop Roots: Found in plants like corn, these roots emerge from the stem and enter the soil, providing additional support to withstand windy conditions.

Root Gas Exchange

Pneumatophores

• Seen in mangroves

• Specialized roots that grow upwards allowing oxygen to diffuse into the root system

• Crucial adaptation for survival in submerged, oxygen-poor environments.

Root Nutrient Storage

AKA Storage Roots

• Ex: carrots and sugar beets,

  • Have thick taproot that stores carbohydrates

  • These nutrients are used for energy during the plant's reproductive phase

Roots & Shoot Growth: Environmental Impact

• Bc plants exhibit phenotypic plasticity, plant shoot growth is highly influenced by environmental conditions like light, water, nutrients, and temperature (their shoot systems can greatly vary)

• Hormones (auxin) play a crucial role in regulating these growth responses

  • Auxin = responsible for phototropism (shoots grow towards light) and gravitropism (adjust growth in response to gravity)

• Ex of variance: in lush environments, tall woody plants are favored to compete for light, while in dry, windy areas, shorter plants thrive due to reduced water needs and stability against wind

Varying Arrangement of Leaves

• Alternate Leaves: Leaves are staggered on alternating sides of the stem, each emerging at different heights

  • Allows for optimal sunlight exposure.

• Opposite Leaves: Pairs of leaves grow directly across from each other at the same level (symmetrical sets)

• Whorled Leaves: Multiple leaves (three or more) radiate outward from the same point on the stem, encircling it in a ring-like patter.

• Rosette: Leaves form a circular pattern low to the ground, with very short internodes, giving a compact appearance

Modified Leaves: Bulbs

Onion bulbs consist of thickened leaf bases that store nutrients

• The layers of an onion are modified leaves, with the stem visible at the base

• These leaves are designed to store food efficiently.

Modified Leaves: Succulents

• Plants like aloe vera have thick leaves that store water

• A crucial adaptation for survival in arid environments.

Modified Leaves: Tendrils

• Modified leaves that help the plant climb by wrapping around supports

• Ex: tendrils found on pea plants

Modified Leaves: Floral Mimics

• I.e. Poinsettia leaves are bright red and mimic flowers to attract pollinators to the actual small flowers they surround.

Modified Leaves: Traps

• Pitcher plants have tubular leaves that trap insects

• The hood prevents escape, and digestive enzymes or bacteria break down the insects for nutrient absorption

Plant Tissues: Big Picture

• Vascular Tissue System: includes xylem and phloem; xylem transports water and nutrients while phloem distributes sugars and other organic compounds

• Dermal Tissue System: protects the plant and facilitates gas exchange

• Ground Tissue System: involves parenchyma for storage and synthesis, collenchyma for support, and sclerenchyma for protection

Plant Tissues: Dermal

• Epidermis: Composed of epidermal cells, guard cells, trichomes, and root hairs

• Provides protection and facilitates gas exchange in shoots and water and nutrient absorption in roots

Plant Tissues: Ground

• Parenchyma: simple tissue with primary cell walls, involved in synthesis and storage of sugars

• Collenchyma: simple tissue with unevenly thickened primary cell walls, providing flexible support

• Sclerenchyma: composed of sclereids and fibers, with primary and secondary cell walls, offering protection and support

Plant Tissues: Vascular

• Xylem: Complex tissue with tracheids and vessel elements

  • Dead at maturity

  • Transport water and nutrients via transpiration (in one direction)

• Phloem: Contains sieve tube elements and companion cells

  • Alive at maturity

  • Transports sugars and other compounds via translocation (both directions)

Cell Structure + Function: Wall

• Composed of cellulose

• Provides structural support and defines the cell's shape

• Some cells develop a secondary cell wall for added rigidity

Cell Structure + Function: Plasmodesmata

Channels that connect adjacent cells, allowing the movement of molecules between them

• Think of translocation

• When a companion cell gets turgid, it must dump its sugar into another cell (through plasmodesmata) to avoid exploding

Cell Structure + Function: Chloroplasts

• Sites of photosynthesis (converting light energy into sugars)

• Crucial for energy production in plants

Cell Structure + Function: Vacuoles

• Large organelles that store water, nutrients, and waste

• Also contain pigments and toxins to deter herbivores

Outer Cell Layer: Gas Exchange

• Stomata: pores surrounded by guard cells that regulate the opening and closing

• Open: allow carbon dioxide to enter and oxygen to exit, facilitating photosynthesis

• Guard cells change shape based on water availability, opening the stomata when water is abundant and closing them to prevent water loss during dry conditions

Outer Cell Layer: Water Retention

• The outer surface of leaves is covered by a waxy cuticle that minimizes water loss through evaporation

• Cuticle is crucial for maintaining the plant's internal moisture levels, especially in dry environments

Outer Cell Layer: Protection

• Specialized epidermal cells (e.g. trichomes) provide protection by reflecting sunlight, reducing water loss, and deterring herbivores with barbs or toxic compounds

• These adaptations help protect the plant from environmental stressors and predators

Fundamental Plant Cell Types: Vessel Elements

• Cells that are part of the xylem tissue and are dead at maturity

• Have thick cell walls and are responsible for transporting water from roots to other parts of the plant under negative pressure

Fundamental Plant Cell Types: Sieve-Tube Elements

• Cells found in the phloem tissue and always accompanied by a companion cell

• Alive at maturity but contain few organelles

• They transport sugars throughout the plant under positive pressure

Fundamental Plant Cell Types: Parenchyma Cells

• Simple cells with only a primary cell wall

• Involved in the synthesis and storage of sugars and other compounds

Fundamental Plant Cell Types: Collenchyma Cells:

• Cells with unevenly thickened primary cell walls

• Provides flexible support, mainly in stems and leaves

Fundamental Plant Cell Types: Sclerenchyma Cells

• Cells comprised of sclereids or fibers

• Have both primary and secondary cell walls and are dead at maturity

• Provide protection and support

Growth Process (Roots and Shoots)

1. Cell Division: apical meristems contain cells that continuously divide

• Some daughter cells remain in the meristem to maintain its population, while others differentiate into various cell types.

2. Cell Enlargement and Differentiation: as new cells form, they enlarge and differentiate into specialized cells, contributing to the extension of the plant body.

• AKA primary growth

3. Exploration of New Space: this primary growth allows roots and shoots to extend outward

• Allows the plant to explore new areas for resources like light, water, and nutrients.

Importance of Cell Division (Apical Meristems)

• Apical meristems (located at the tips of roots and shoots) = crucial for plant growth

  • Contain undifferentiated cells that continuously divide, allowing plants to grow all throughout their lives

  • Cells divide: some remain in the meristem, others differentiate into various cell types → forms primary plant body

• Growth Zones in Roots: cellular division, elongation, and maturation

  • Apical meristem = in the division zone (active cell division occurs)

  • Cells then elongate/mature, become specialized

Vascular Tissue Arrangement

• Dicot Stem: vascular bundles are arranged in a ring near the stem's perimeter

  • Ring formation (highly organized) allows for secondary growth

• Monocot Stems: (i.e. corn) vascular bundles are scattered throughout the ground tissue

  • No secondary growth occurs

• Leaves: vascular tissue forms veins that network throughout the leaf and are surrounded by ground tissue

  • Arrangement facilitates efficient transport of water and nutrients

• Roots: vascular tissue is centrally located within the root and is surrounded by ground tissue

  • Central arrangement supports the transport of water and nutrients from the soil

Woody Plant Tissues: Growth/Development

1. Primary Growth: Occurs at the apical meristems which results in increase in length

• It allows plants to extend their reach for light, water, and nutrients.

2. Secondary Growth: crucial for woody plants and involves the increase in width of roots and shoots.

• Facilitated by the vascular cambium and cork cambium

• Vascular cambium: located between the xylem and phloem; produces new layers of vascular tissue, contributing to the thickening of stems and roots

• Cork cambium: forms the outer protective layer (bark)

Cell Division in Lateral Meristems: Diameter

• Lateral meristems consist of undifferentiated cells that can divide and differentiate into various cell types

  • When dividing: contribute to the thickening of the plant body by producing new cells that differentiate into epidermal, ground, and vascular tissues

• Newly formed cells grow in specific directions and differentiate into specialized tissues

  • Process is influenced by environmental cues and cell-cell signals (ensures plant can adapt to its surroundings)

• Tissue Formation: epidermis forms the protective outer layer; ground tissue supports functions like photosynthesis and storage; vascular tissue (central location) facilitates the transport of nutrients and water

Lateral Meristem Growth (Width)

• Vascular Cambium: meristematic tissue that produces two types of tissues: secondary xylem (wood) and secondary phloem

  • Secondary Xylem: produced toward the interior of the cambium; consists of tracheids, vessels, parenchyma cells, and sclerenchyma cells; responsible for water/ion transport and provides structural support

  • Secondary Phloem: produced toward the exterior of the cambium; includes sieve tube elements, companion cells, and sclerenchyma cells, all involved in transporting nutrients.

• Cork Cambium: located near the outer perimeter and produces cork

  • Forms part of the bark and provides protection

• Annual growth: these processes result in the thickening of the tree trunk as new layers of xylem and phloem are added each year

Annual Growth Rings in Wood

• Dormancy periods (e.g. winter in cold climates or dry seasons in tropical areas): vascular cambium ceases growth

  • Once growth resumes (i.e,. spring or rainy season) cambium produces large, thin-walled cells (early wood)

  • Season progresses/less favorable conditions: smaller, thicker-walled cells called (late wood) form

  • Alternation between early and late wood results in distinct growth rings.

• Wider rings suggest favorable conditions like abundant moisture

• Narrower rings indicate stress factors such as drought or pollution

A. Oak Tree

B.

A. Oak Tree

A. Oak Tree

B. Baobab Tree

A.

B.

Yes

C. Both

B. Phenotypic Plasticity

A. Genetic Differences