Seedless Plants: Bryophytes and Liverworts

Seedless Plants

• Bryophytes exhibit a life cycle with a dominant gametophyte (n) generation and a haploid ploidy

Bryophyte Life Cycle

• Spores undergo germination
• The protonema formation leads to the development of a mature gametophyte (n)
• Gametophytes produce sperm in antheridia and eggs in archegonia
• Fertilization in water results in a zygote (2n) formation
• The sporophyte (2n) grows from the gametophyte and produces spores (n) in a capsule

Liverwort Anatomy

• Thallus is the plant body
• Rhizoids are hair-like structures that aid in water and nutrient absorption

Liverworts

• Gametophyte is dominant (n)
• Has a thalloid structure that holds reproductive structures
• Sporophyte is dependent (2n)
• Is small and grows from the gametophyte, releasing spores
• Air pores facilitate gas exchange
• Antheridia are male structures requiring free water for sperm to swim to
• Archegonia are where eggs are fertilized by sperm, producing a zygote

Mosses

• Gametophyte (haploid n) is dominant
• Sperm is released to fertilize eggs.
• Sporophyte (diploid 2n) is dependent
• Zygote develops into a diploid sporophyte
• Antheridia are male structures requiring free water for sperm to swim to
• Archegonia are where eggs are fertilized by sperm, producing a zygote

Hornworts

• General characteristics include small, non-vascular plants with a thalloid body structure and photosynthetic tissue
• They produce horn-like sporophytes, engage in sexual reproduction using water for fertilization, fixate nitrogen with cyanobacteria, and have continuous sporophyte growth in moist environments

Pterophyta (Ferns)

• Homosporous, vascular plants with motile sperm
• External water is needed for fertilization
• Leaves are megaphylls that uncoil as they mature

Horsetails

• Homosporous, vascular plants with motile sperm with external water needed for fertilization
• Stems are ribbed and jointed
• Leaves are scalelike, in whorls, and non-photosynthetic at maturity
• Equisetum is the one genus

Whisk Ferns

• Vascular plants with motile sperm requiring external water for fertilization
• No differentiation between root and shoot, without leaves

Lycophyta (Club Mosses)

• Homosporous or heterosporous vascular plants with motile sperm who external water is needed for fertilization
• Leaves are microphylls

Vascular Seedless Plants Life Cycle

• Dominant generation is sporophyte
• Their ploidy is diploid

Fern Structures

• Sori are clusters of sporangia underneath fronds, producing spores
• Gametophyte is called prothallus, is small, heart-shaped, and photosynthetic (n)
• Sporophyte (2n) is the dominant plant form with fronds, rhizomes, and roots
• Antheridium has sperm that travels to archegonium for fertilization, producing a zygote
• Archegonium holds the eggs

Whisk Fern Sporangia

• Primary function is spore production, undergo meiosis, producing haploid spores
• Mature sporangium are released into the environment by wind or water, germinating and developing into prothallus.
• Zygotes develop into diploid sporophyte plants if fertilization occurs

Whisk Fern Photosynthesis

• Primarily occurs in the photosystemic stems
• Stems are green, contain chloroplasts, and are photosynthetic due to lack of true leaves

Horsetail Photosynthesis

• Primarily carried out by green, photosynthetic stems, with no true leaves present
• Leaves are located at nodes in whorls

Horsetail Strobili

• Reproductive structures produce spores by meiosis
• Sporangia is arranged in clusters called sporangiophores, allowing spore dispersal to grow into gametophytes and allowing reproduction

Club Mosses

• Small, vascular plants with needle-like leaves that reproduce via spores produced in strobili, lacking flowers or seeds

Club Mosses Strobili

• Reproductive structures produce spores by meiosis (sporangia in clusters called sporangiophores) for dispersal and gametophyte growth, resulting in a new diploid sporophyte

Gymnosperms

Monoecious

• Plants have both male and female reproductive organs on the same plant (e.g., most conifers like pines and spruces)

Dioecious

• Plants have male and female reproductive organs on separate plants (e.g., ginkgo and some cycads)

Seed and Pollen Advantages

• Increased reproductive success and embryo protection
• Pollen enables fertilization without water
• Easy dispersal by wind, animals, or other mechanisms increases genetic diversity

Cycads

• Recognized as Palm trees with big cones in the middle of the plant

Cycad Reproductive Structures

• Dioecious plants have separate reproductive structures on different plants

Gingkos

• Only one species left with fan-shaped leaves

Conifer Life Cycle

• Micro- and mega- sporocytes undergo meiosis, creating haploid gametes
• Archegonium has a sticky pollen trap near micropyle for pollination
• Pollen tube grows slowly toward the gametophyte
• A sperm nuclei fertilizes the egg ->embryo ->seed
• Entire process can take 1-2 years after pollination

Conifers

• Identified by pine cones, monoecious nature, and needle-like leaves (pine tree)

Conifer Reproductive Structures

• Monoecious
• Megastrobilus (female cone) makes megagametophyte
• Microstrobilus (male cone) makes microgametophyte

Angiosperms:

Flower Anatomy

• A complete flower has all four whorls
  • Sepals (Calyx)
  • Petals (Corolla)
  • Stamens (Androecium)
  • Carpel (Gynoecium)
• Flowers missing any of these parts are called incomplete flowers

Flower Types

• Perfect flowers contain both male (stamens) and female (carpel) reproductive organs.
• Imperfect flowers lack either stamens or carpels
  • Staminate: only male structures present
  • Carpellate: only female structure

Microsporogenesis

• Pollen slides
  • Male gametes

Microsporogenesis:

• Anther microsporocyte undergoes meiosis
• This results in the pollen tetrad microspores

Microgametogenesis:

• Microspores divide via mitosis Generative cell and tube cell
  • Generative cell produces two sperm cells through mitosis
  • Tube cell develops into pollen tube

Pollen Grain Development

• Pollen grains develop in the anther through meiosis, forming haploid microspores that mature into sperm cells inside the pollen grain.)

Megasporogenesis and Megagametogenesis:

• Lily ovary slides
• Female gametes are processed here

Megasporogenesis:

• Ovule megasporocyte undergoes meiosis, yielding 4 megaspores - 3 small 1 large

Megagametogenesis

• Large megaspore survives division via mitosis
• Division result : 8-nucleate, 7 celled gametophyte (embryo sac)
• 3 cells at each end of embryo sac ( antipodal cells, synergids and egg- micropylar end) Central cell contains polar nuclei
• result : endosperm of seed (Ovules in the ovary undergo meiosis, forming haploid megaspores, one of which develops into an egg cell.)

Double Fertilization

Two sperm cells are involved

• Pollen lands on stigma
• Pollen tube begins to grow (synergids guide pollen tube to egg)
• 1 sperm + 1 egg= 1st fertilization event: One sperm fertilizes the egg, forming a diploid zygote (embryo). The second sperm fuses with polar nuclei, forming the triploid cell -> endosperm (food reserve)
• Result : Zygote develops into embryo with radicle and one or two cotyledons

Monocot vs Dicot Differences

Table 31.1

Monocots:

• One cotyledon (seed leaf)
• Long narrow leaf (parallel veins)
• Vascular bundles scattered in stems. Floral parts in multiples of three.
• Examples: Grasses, Lilies.

Dicots:

• Two cotyledons
• Broad leaf (network of veins)
• Vascular bundles in a ring in stems
• Floral parts in multiples of four or five.
• Examples: Roses, Sunflowers.

Embryo Development

Seen in the Capsella embryo slide - Figure 31.14

• Heart-shaped Stage:
• Early stage where cotyledons begin to form, and the embryo takes a rounded, bilateral shape
• Torpedo Stage: The embryo elongates and becomes torpedo-shaped, with the root and shoot axis visible, and the cotyledons elongate
• Mature Embryo Stage:
• The embryo becomes fully formed with distinct cotyledons, root, and shoot
• ready for dormancy until germination

Bean Seed vs Corn Seed

• Bean Seed (Dicot): Two cotyledons (energy storage) Embryonic:

  • Axis Radicle (root) & Plumule (shoot) Hypocotyl:

• Below cotyledons, connects root and shoot Epicotyl: Above cotyledons, forms stem and leaves Stored in cotyledons Protective outer layer

• Corn Seed (Monocot): One cotyledon (scutellum) Protective sheath for the radicle Protective sheath for the plumule Radicle (root) & Plumule (shoot) Not distinct in monocots Forms stem and leaves above cotyledon Surrounds embryo provides nutrients Protective outer layer

Corn Grain Structures

Use the corn grain embryo slide - Figure 31.16

• Scutellum: Single cotyledon, absorbs nutrients during germination.
• Embryonic Axis: Contains both the plumule (shoot) and radicle (root).
• Plumule: Young shoot, becomes stem and leaves.
• Radicle:
• Young root, will develop into the root system
• Coleoptile: Protective sheath, covers plumule during early growth.
• Coleorhiza:
• Protective sheath, covers radicle during early growth

Fruits - Types

Figure 31.18

• Simple fruits:

• Develop from a single ovary

• Berries: grape, berries, peaches, almonds, zucchini, tomatoes Blueberries, cranberries, grapes, tomatoes, passion fruit

• Pepos- Type of berry w/ hard rind (usually) Watermelons squashes, pumpkins

• Hesperidium- type of berry w/ leathery rind, fruit interior is separated into segments Most citrus varieties Each section is one carpel in flower

• Drupes-

• simple fruit, endocarp forms hard enclosure (pit) surrounding the seed Mangos, olives, pistachios

• Multiple fruits- accessory fruit: formed, result of fused ovaries and other structures of multiple nearby flowers

• Aggregate fruits:

• Form from one flower w/ many carpels Raspberries, blackberries

• Pomes-

• accessory fruit, formed from receptacle

Plant Anatomy

• Compare the primary and secondary growth
• The increase in length of the shoot and root due to the cell division in the apical meristem
• All vascular plants have primary growth at apical meristems Herbaceous plants are primary.
• Monocots cannot go through 2nd growth, therefore they will lack wood

Secondary Growth

• Increase in girth occurs due to cell division in the lateral meristem
• Woody plants: secondary, wood: secondary growth of xylem, conifers produce "softwood" through secondary growth due to tracheids
• Eudicots produce "hardwood" via 2nd growth due to vessel elements

Primary Tissues of the Root

• Epidermis The outermost layer of cells, protects from diseases, absorbs water and nutrients
• Endodermis Extra protective layer, found only in roots, Forces water and solutes to cross the plasma membrane of endodermal cells to protect against toxins and pathogens
• Cortex Lies below the epidermis but outside of the vascular bundles

Vascular Bundle Arrangements

• In monocot roots Vascular: tissue is scattered
• In Eudicot roots Vascular: tissue is arranged in a ring; tissue in center forms an x

Apical Meristem Function

• Increases the length of roots and shoots=Growth at tips (NOT found in most bryophytes)
• Allows plant to concentrate energy for upwards growth so they can reach sunlight)
• Meristematic cells give rise to different tissue types (differentiation)

Vascular Bundle Arrangement in Stems

Monocot Stem Vascular bundles: scattered randomly throughout the stem

• Xylem and phloem are: in individual bundles scattered in the stem
• No cambium
• Limited secondary growth (intercalary growth) Grass, corn, lilies, and other monocots

Dicot Stem

• Vascular bundles -arranged in a ring around the pith
• Xylem is: toward the center.
• Phloem is: toward the outside in each bundle
• Vascular cambium present, Secondary growth (thickening of the stem)
• Bean, oak, rose, and other dicots

Vascular Bundle Arrangement in Roots vs Stems

Feature Roots Monocots Dicots Vascular tissue arranged in a central cylinder with radial arrangement (xylem in the center and phloem surrounding) Vascular tissue arranged in a radial pattern (xylem in a star shape and phloem between the arms) Phloem is toward the outside of the stem, within the vascular bundles Absent in most roots (except in lateral roots) Xylem in the center of the root

Stems . Vascular bundles are scattered throughout the stem without a clear pattern Vascular bundles form a ring around the pith, with a vascular cambium present for secondary growth. Present in dicots, allowing for secondary growth and thickening of the stem. Xylem is toward the inside of the stem, within the vascular bundles

Anatomy of a Tree Ring

Feature Location Function

Activity Cell Color

Chemical Constitution Composition

Decay Resistance Age Sapwood Outer portion of xylem, beneath the bark Active in water and nutrient transport Contains living cells Lighter in color Contains more water and nutrients More susceptible to decay Younger xylem cells

Heartwood Inner portion of xylem, at the center of the trunk Primarily for structural support, no longer involved in transport

Contains non-living cells Darker in color Contains resins, oils, and tannins More resistant to decay due to chemicals

Older xylem cells Modified: Stems

Type of Description Function Examples

Rhizomes: Horizontal underground stems storage are vegetative, reproduction Rhizome: Ginger, Bamboo, Fern Tubers Stems: Swollen underground stems Storage are vegetative reproduction Potato, Yams, Jerusalem artichoke Corms Stems: Short, thickened underground stems Storage: (energy reserves) Crocus, Gladiolus, Taro Stolons Stems: Horizontal stems along the ground vegetative reproduction Strawberries, Spider plant Tendrils Stems: Coiled, slender stems Climbing are support Grapevines, Peas, Cucumbers Cladodes Stems: Flattened, leaf-like stems photosynthesis, water storage Cacti, Asparagus, Ruscus Thorny Sharp Stems: Pointed stems Protection: (herbivores) orages Hawthorn, Citrus Rose Bulbs Stems: Swollen undergroun stems Modified- leaves, Storage, energy Onion, Garlic, Tulip reserves Orchid- Cattleya Pseudobulbs stems: Thickened, swollen stems (orchids) Storage water/nutrients, vegetative reproduction Catlleya Creeping stems Stems: Prostrate stems Vegetative/vegetative reproduction Creeping Jenny, Mint, Buttercup