Plant Histology: Tissues and Growth

• Plants have evolved vascular tissues for water and nutrient transport, enabling survival on land.
• Xylem transports water, while phloem transports nutrients.
• The plant body consists of the root system (roots) and the shoot system (stems and leaves).

Plant Histology (Tissues and Growth)

• Meristematic tissues are areas of active growth through mitosis.

• Apical meristem gives rise to:

  • Protoderm becomes epidermis.
  • Ground meristem becomes parenchyma (storage and structural tissue).
  • Procambium becomes vascular tissues (xylem & phloem).

• Lateral meristem includes:

  • Vascular cambium provides support and protection.
  • Cork cambium forms protective bark with waterproof suberin.

• Parenchyma: Storage, photosynthesis, support, secretion, repair, water/food movement.

• Collenchyma: Flexible support in young plants and plant parts.

• Sclerenchyma: Thick, lignin-rich cells for support; dead at maturity.

• Dermal Tissue: Epidermis & periderm (outer protection).

• Vascular Tissue: Xylem & phloem (transportation).

Root Structure & Function

• Roots anchor plants, absorb water/minerals, store food, and produce growth hormones.

• Monocot root: Large vascular cylinder with scattered vascular bundles.

• Dicot root: Small, star/cross-shaped vascular bundles.

• Root Structures:

  • Epidermis: Outer protective layer.
  • Hypodermis: Below the epidermis.
  • Cortex: Storage and transport.
  • Endodermis: Regulates material flow into the vascular cylinder.
  • Pericycle: Initiates lateral root growth.
  • Xylem & Phloem: Transport water and nutrients.
  • Pith: Central core (in monocots).

• Taproot: Deep, main root with smaller lateral branches (e.g., conifers, eudicots).

• Fibrous Root: Many equal-sized roots (e.g., grasses).

• Adventitious Roots:

  • Prop roots (corn) for stability.
  • Haustoria (dodder) for parasitic nutrient absorption.
  • Buttress roots for wet environments.
  • Contractile roots pull bulbs deeper.
  • Aerial roots (various types).

• Edible Roots: Carrots, beets, radishes, etc.

Stem Structure & Function

• Stems support flowers and leaves.
• Stems transport water (xylem) and nutrients (phloem).
• Stems store and distribute food.
• Herbaceous stems: Soft, green, flexible.
• Woody stems: Hard, lignified.
• Monocot Stem: Scattered vascular bundles.
• Dicot Stem: Vascular bundles arranged in a ring.
• Woody Dicot Stem: Grows in annual rings.

Leaf Structure & Function

• Leaves contain chlorophyll (green), which breaks down in autumn to reveal other pigments.

• Leaves perform photosynthesis to create oxygen and glucose.

• Simple Leaf: Single blade attached to petiole.

• Compound Leaf: Leaflets in pairs along rachis.

  • Pinnately Compound: Leaflets in pairs along rachis.
  • Bipinnately Compound: Leaflets subdivided into smaller leaflets.
  • Palmately Compound: Leaflets attached at one origin.

• Leaf Arrangements (Phyllotaxy):

  • Opposite: Two leaves per node.
  • Alternate: One leaf per node.
  • Whorled: Three or more leaves per node.

• Leaf Venation (Vascular Arrangement):

  • Pinnately Veined: Midrib with branching veins.
  • Palmately Veined: Multiple primary veins from a single point.
  • Parallel Venation: Veins run parallel (monocots).
  • Dichotomous Venation: Forking veins, no midrib.

• Monocot Leaf: No palisade mesophyll layer.

• Dicot Leaf: Has palisade mesophyll layer.

• Stomates & Guard Cells: Control gas exchange.

• Trichomes: Hair-like structures on leaf epidermis.

Key Takeaways

• Vascular tissues (xylem & phloem) enable plants to transport essential resources.
• Roots anchor plants, absorb nutrients, and store energy.
• Stems support, transport, and sometimes store food.
• Leaves are the primary sites of photosynthesis, gas exchange, and food production.
• Differences between monocots and dicots exist in root, stem, and leaf structures.
• Adaptations like specialized roots, stems, and leaves help plants survive in various environments.
• Plants are eukaryotic, multicellular, photosynthetic autotrophs in diverse environments.
• Plants provide food, clothing, shelter, medicines, and support ecosystems.

Alternation of Generations

• All plants undergo alternation of generations:
  • Gametophyte generation (haploid) starts with a spore and ends with fertilization, producing a zygote.
  • Sporophyte generation (diploid) starts with the zygote and ends with spore production.
• Mature Sporophyte (2n) produces spores (1n).
• Spores (1n) germinate and grow into mature Gametophyte (1n).
• Gametophyte (1n) produces sperm (1n) and egg (1n).
• Fertilization of sperm (1n) and egg (1n) produces zygote (2n).

Nonvascular Plants

• Nonvascular plants lack specialized conducting tissue to transport water and nutrients.
• Three phyla of nonvascular plants:
  • Hepatophyta (liverworts)
  • Anthocerophyta (hornworts)
  • Bryophyta (true mosses)
• Thalloid liverworts have flat leaf-like lobed bodies (thalli), commonly found along creek banks.
• Leafy liverworts resemble mosses and are found on tree bark in tropical and subtropical environments.
• Marchantia can reproduce asexually and sexually.
  • Asexually through gemma cups containing gemmae, which splash out and grow.
  • Antheridia are plant structures that make sperm, while archegonia produce eggs.
• Hornworts are named for their sporophyte and live on moist ground in the shade.
• Hornworts reproduce asexually through fragmentation; Anthoceros is the most studied.
• True mosses are nonvascular plants in Phylum Bryophyta.
• Mosses reproduce asexually through fragmentation, and sexually through alternation of generations.

Seedless Vascular Plants

• Whisk Ferns, Club Mosses, Horsetails and Ferns
• True vascular tissues (xylem and phloem) are present, with true roots, stems, and leaves.
• Multicellular gametangia and embryos are present, stomata for gas exchange, and cutin to prevent moisture loss.
• Exhibit alternation of generations and bear sporangia on sporophylls.
• Can produce one type of spore (homosporous) or two types (heterosporous).
• Most are terrestrial; the sporophyte is dominant over the gametophyte.
• Possess above-ground stems (aerial) and below-ground stems (rhizome).
• Psilotum nudum is an example of whisk ferns.
• Lycopodium is an example of Club Mosses

Ferns

• Monecious Gametophyte
• Frond with Sori
• Sorus with Sporangium
• Sporangium contain Annulus, Lip Cells and Spores

Gymnosperms

• Seed plants (spermatophytes) are divided into gymnosperms and angiosperms.
• Gymnosperms consist of four phyla:
  • Cycadophyta (cycads and sago palms)
  • Ginkgophyta (Ginkgo biloba)
  • Gnetophyta (Ephedra, Welwitschia, and Gnetum)
  • Coniferophyta (pine, spruce, sequoia, juniper, cedar, and cypress)
• Life cycle is dominated by the sporophyte generation.
• Vascular plants (xylem/phloem), produce seeds but not in a fruit ("naked seed"), sporophyte dominant.
• Heterosporous, male gametophyte is the pollen grain, and pollination is aided by wind dispersal.
• Cycads are found in tropical and subtropical forests.
• Cycads are dioecious (separate sexes) and produce male pollen cones and female seed cones.
• Sperm of cycads is the largest known.
• Ginkgos were thought to be extinct but were found in China.
• Male Ginkgos are planted due to the odor produced by females.
• The only living species of Ginkgophyta is Ginkgo biloba.

Phylum Gnetophyta

• Composed of 71 species in 3 genera, most are monoecious.
• Gnetum are mostly vine-like plants; Welwitschia are native to deserts of southwestern Africa.
• Ephedra is commonly called a joint fir and is used medicinally.
• Pines, cypresses, spruce, redwoods, cedar, hemlock, junipers, and yews are common gymnosperms.

Life Cycle of Pine

• Male (Staminate) Cones made up of Microsporophylls arranged in a spiral around a woody axis.
• Pollen grain is the male gametophyte, released from the microsporangium.
• Female (Ovulate) Cones woody and made of Megasporophylls arranged around a woody central axis.
• Megasporophyll (scale) has two ovules on its upper surface.
• Ovules are enclosed, composite structure of the megasporangia plus integument.
• The integument of the ovule has an opening called the micropyle.
• The zygote develops into the pine embryo sporophyte plant.
• Pollination is wind-aided.
• Heterosporous—produces two types of spores
• Sporophyte—diploid plant form which is dominant in vascular plants
• Pollen—multicellular microgametophyte of cone-bearing trees and flowering plants; contains sperm
• Microspores—spores made in staminate cones; germinates into pollen grains
• Megaspores—spores made in ovulate cones; develop into megagametophytes
• Ovulate cone—female cones
• Staminate cone—male cones; also called pollen cones
• Pollen tube—structure produced by pollen grain at point of pollination; sperm travel from grain through pollen tube to ovule and fertilize egg
• Integument—outer layer of ovule; eventually becomes the seed coat
• Seed—a mature ovule, comprised of the embryo and seed coat
• Zygote—cell resulting from fertilization of egg by sperm; develops into embryo
• Embryo—the baby sporophyte plant housed within a seed
• Pollination—process by which pollen is carried from the male reproductive organs to the female reproductive organ, aided by wind, insects or birds