Unit Objectives: Discuss the evolution and adaptations of seedless plants, both vascular and non-vascular; Discuss the evolution and adaptations of seed plants.
Lecture Objectives:
Compare structural, physiological, and reproductive adaptations that allowed plants to survive the transition from water to land.
Relate the origin of plants to green algae.
Compare the four major periods of plant evolution and the major adaptations associated with each stage.
Describe the life cycle and two key terrestrial adaptations of mosses.
Compare ferns and mosses.
Describe environmental conditions favoring the evolution of gymnosperms and three adaptations that first appeared in gymnosperms for life on land.
Describe flower structures and functions, including the adaptive significance of pollinator attraction.
Pre-Lecture Questions
Understanding Photosynthesis:
Chemical equation summarizing photosynthesis:
Correct Equation: Light Energy + $6 CO2 + 6 H2O o C6H{12}O6 + 6 O2$
Understanding Haploid and Diploid:
If diploid chromosome number of sexually-reproducing species is 58:
Correct Statement: The haploid chromosome number is 29.
What is a Plant?
A plant is a multicellular eukaryote that carries out photosynthesis and possesses adaptations for living on land.
Comparison with Animals and Fungi:
Animals and fungi are also eukaryotic and multicellular.
Large algae, such as seaweeds, are photosynthetic but classified as protists rather than plants due to a lack of terrestrial adaptations.
Terrestrial Adaptations of Plants
Challenges of Living on Land:
Upright bodies in buoyant water lose structural support and may shrivel in drying air.
Algae cannot obtain atmospheric carbon dioxide for photosynthesis easily, leading to extensive adaptations needed.
The transition from water to land took over 100 million years.
Adaptations of the Plant Body
Resource Distribution:
On land, resources are found in different environments:
Carbon dioxide: mainly in the air.
Mineral nutrients and water: primarily in the soil.
Specialized Organs:
Subterranean organs called roots anchor the plant and absorb minerals and water.
Above ground, shoots consist of photosynthetic leaves supported by stems.
Photosynthetic Organs
Main Photosynthetic Organs: Leaves, utilizing stomata (microscopic pores on leaves) for gas exchange (CO2 and O2).
Waxy Cuticle: A protective waxy layer on leaves prevents water loss.
Vascular Tissue: A network of tube-shaped cells branches throughout the plant for transport of vital materials between roots and shoots.
Vascular Tissue
Types of Vascular Tissue:
Xylem: Transports water and minerals from roots to leaves.
Phloem: Distributes sugars from leaves to roots and non-photosynthetic parts.
Lignin: A chemical that hardens many vascular tissue cell walls, crucial for structural strength and wood formation.
Reproductive Adaptations
Requirement of New Reproductive Modes:
Water ensures the gametes (sperms and eggs) and developing offspring do not dry out.
New adaptation needed for gamete protection and development outside of water.
Egg Fertilization:
In plants, the egg is fertilized while retained within the mother's body tissue.
Zygote develops into an embryo enclosed within protective ovule without dehydrating.
The Origin of Plants
Evolutionary History:
Algal ancestors of plants flourished on moist edges of water bodies over 500 million years ago.
Charophytes: A modern lineage of green algae that resembles early plant ancestors.
Adaptations for dry land began accumulating by about 470 million years ago, marked as the age of the oldest plant fossils.
Highlights of Plant Evolution
Chronicle of Four Major Periods:
470 Million Years Ago: Early diversification led to Bryophytes, such as mosses, liverworts, and hornworts. These lacked lignified walls, roots, and leaves.
425 Million Years Ago: Evolution of vascular plants with conducting tissues hardened with lignin.
360 Million Years Ago: First seed plants evolved with seeds containing embryos and food supply, notably gymnosperms like conifers.
140 Million Years Ago: Emergence of angiosperms with complex reproductive structures (flowers) enclosing seeds in ovaries.
Bryophytes
Moss Adaptations:
Key terrestrial adaptations:
A waxy cuticle prevents dehydration.
Embryo protection within the female gametophyte.
Reproduction: Require water for sperm to swim to eggs.
Distinct Forms:
Gametophyte: The recognizable green spongelike plant.
Sporophyte: Grows from gametophyte as a stalk with a capsule.
Life Cycle of Moss
Alternation of Generations:
Gametophytes produce gametes forming zygotes which develop into sporophytes.
Sporophytes produce spores giving rise to new gametophytes.
Moss Life Cycle Components
Includes parts such as:
Capsule, Seta, Foot, Venter, and Neck canal.
Fertilization resulting in meiospores that lead to next generation.
Ferns
Diversification through Vascular Tissue:
Ferns are diverse seedless vascular plants with over 12,000 species and can colonize various habitats.
Require water for sperm mobility similar to mosses.
Had a semi-reduced sporophyte generation.
Carboniferous Contributions:
Ancient ferns contributed to coal formation through dying and accumulating in wetlands.
Impact of Fossil Fuels
Fossil fuels (coal, oil, natural gas) are derived from ancient plant remains and contribute to climate change when burned.
Fern Life Cycle
Involves stages such as:
Diploid sporophyte producing haploid spores through meiosis and subsequent fertilization to form zygotes.
Gymnosperms
Adaptation to Dry and Cold Climate:
Evolved towards drier climate, enabling completion of life cycles and enduring harsh winters.
Descendants include conifers, the cone-bearing groups.
Terrestrial Adaptations of Gymnosperms
Three main adaptations compared to ferns:
Significantly more developed sporophyte generation.
Development of pollen for fertilization via wind.
Formation of seeds, consisting of plant embryo and food supply within a protective coat.
Angiosperms
Dominance in Modern Landscape:
Approximately 250,000 species of angiosperms versus 700 species of gymnosperms.
Success is attributed to refined vascular tissues and evolution of flowers for reproductive success.
Importance of attracting pollinators through showy flowers vs. wind-adapted smaller flowers.
Angiosperm Life Cycle
Flower Structure:
Comprised of modified leaves arranged in circles, with outer green sepals, colorful petals, male structures (stamens), and female structures (carpels).
Pollen grains develop in anthers and undergo fertilization leading to zygote development.
Produced seeds surrounded by nutritious endosperm, capable of dormancy.
Role of Fruit
Function of Fruit:
Ripened ovary helps protect seeds, enhances dispersal, and provides food for animals.
End of Lecture Review
Characteristics of Plants:
Correct option is: Multicellular, eukaryotic, and photosynthetic.