Lecture 5 - Greening of the Earth - Plant Diversity (student)
Page 1: Introduction
Lecture Title: Greening of the Earth - Plant Diversity
Instructor: Dr. Colin Francis
Page 2: Learning Objectives
Define plants and distinguish them from multicellular protists.
List the basic resources required by plants and explain why each is needed.
Compare water and land as habitats for plants regarding:
availability of O2, CO2, mineral nutrients, and light
support
reproduction and dispersal
Describe the evolutionary history of plants, focusing on these four major events:
origin from plant-like protist ancestors
expansion onto land
development of vascular tissue
emergence of seeds, flowers, and fruit
Distinguish between vascular and non-vascular plants.
Describe key adaptations for life on land in major plant groups:
mosses
seedless vascular plants
gymnosperms
angiosperms
Identify limitations in exploiting terrestrial environments for each major plant group.
Compare and contrast monocots and eudicots.
Page 3: Definition of Plants
Characteristics of Plants:
Eukaryotic
Multicellular
Photoautotrophic (produce their own food through photosynthesis)
Possess cell walls made of cellulose
Note: Seaweed, which are multicellular plant-like protists, share these traits with plants.
Page 4: Similarities with Charophytes
Charophytes: A group of green algae closely related to plants.
Derived Traits: Unique traits that evolved in a group after diverging from a common ancestor.
Plants possess five derived traits that distinguish them from Charophytes.
Page 5: Derived Traits of Plants
Life Cycle - Alternation of Generations:
Distinct multicellular haploid (n) and diploid (2n) stages.
Sporophyte (diploid) produces haploid spores through meiosis.
Spores develop into multicellular gametophytes which produce gametes (sperm and eggs).
Fertilization results in a diploid zygote, developing into a new sporophyte.
Haploid: single set of unpaired chromosomes.
Diploid: two complete sets of chromosomes.
Page 6: Life Cycle - Uniqueness to Plants
Only plants exhibit two distinct multicellular generations within their life cycle.
Page 7: Dependent Embryos
Multicellular, Dependent Embryos:
Plants are classified as embryophytes.
Sporophyte embryos are nourished by the female gametophyte.
Page 8: Walled Spores
Walled Spores Produced in Sporangia:
Spores are produced in specialized structures called sporangia.
Example: Sporangium structure of Mnium (a moss).
Page 9: Gametangia
Multicellular Gametangia:
Female Gametangia: Archegonia containing eggs.
Male Gametangia: Antheridia producing sperm.
Example: Archegonia and antheridia of Marchantia (a liverwort).
Page 10: Apical Meristems
Apical Meristems:
Regions of rapid cell division at the tips of roots and shoots.
Allow continuous growth throughout the plant's lifespan.
Improve access to nutrients and water in the environment.
Page 11: Charophytes
Question: Which statement is likely true about Charophytes?
A. Aquatic plants
B. Ancestors to land plants
C. Close relatives to land plants
D. Unrelated to land plants
Page 12: Green Algae Groups
Question: Are green algae and their recent ancestor a clade?
A. True
B. False
C. More information required
Page 13: Origin of Plants
Objective 4(a): Plants evolved from Protist Ancestors:
Likely evolved in transitional habitats between red algae and green algae.
Page 14: Resources Required by Plants
Key resources:
Water (H2O)
Light
Carbon Dioxide (CO2)
Oxygen (O2)
Mineral nutrients
Page 15: Aquatic Habitat Limitations
Benefits for Algae:
Surrounded and supported by water.
Access sunlight at the surface.
Uptake nutrients and gases through diffusion.
Release gametes directly into water.
Page 16: Advantages of Colonizing Land
Initial advantages for the first land plants:
Less competition for resources
Abundant oxygen and carbon dioxide
More sunlight
Fewer predators
Page 17: Challenges in Colonizing Land
Major challenges faced by land plants:
Structural support against gravity (compared to water).
Risk of desiccation (drying out).
Environmental fluctuations (moisture and temperature changes).
Page 18: Land Plant Challenges (cont.)
Additional challenges for land plants:
Nutrient and water uptake requiring soil contact.
Need for effective transport systems for nutrients and water.
Reproductive challenges (gamete dispersal and fertilization).
Page 19: Importance of Adaptations
Adaptations: Traits that allow plants to exploit new habitats or resources, enhancing survival and reproduction.
Page 20: Plant Evolution
Early plant groups have fewer adaptations and are more similar to aquatic algae.
Later groups retain adaptations from earlier plants.
Page 21: Evolution of Plant Groups
Sequence of Evolution:
Bryophytes
Seedless vascular plants
Gymnosperms
Angiosperms
Page 22: Key Adaptations of Bryophytes
Bryophytes (≈470 mya):
Groups: Liverworts, hornworts, mosses
Key adaptations:
Waxy cuticle
Stomata for gas exchange to prevent water loss.
Page 23: Vascular vs. Non-Vascular Plants
Vascular Plants: Have vascular systems (xylem and phloem) for rapid nutrient and water transport.
Non-Vascular Plants: Lack vascular systems; rely on slow diffusion for transport.
Page 24: Limitations of Bryophytes
Bryophytes Major Limitations:
Height Restriction: Limited to under 20cm due to lack of vascular system.
Require moist environments for reproduction (sperm need water for fertilization).
Page 25: Adaptations of Seedless Vascular Plants
Seedless Vascular Plants (≈425 mya):
Groups: Ferns, club mosses, horsetails
Key adaptations:
Development of vascular tissue for nutrient transport.
Page 26: Key Adaptations of Seedless Vascular Plants
Advantages of vascular tissue and roots:
Supports greater heights and structural integrity.
Xylem conducts water; phloem distributes nutrients and sugars.
Page 27: Limitations of Seedless Vascular Plants
Limitations:
Require moisture for reproduction (sperm need water to reach eggs).
Page 28: Overview of Seeded Plants
Seeded Plants: Comprises Gymnosperms and Angiosperms.
Page 29: Seed Plants Overview
Introduction:
Seed plants include a protective seed containing an embryo, with two main groups:
Gymnosperms: seeds not enclosed
Angiosperms: seeds develop within ovaries.
Page 30: Advantages of Gymnosperms
Gymnosperms (≈305 mya):
Key adaptations:
Seeds over spores, supplying nutrients and protection.
Page 31: Pollen in Gymnosperms
Pollen:
Male structures enabling fertilization without water (wind-dispersed).
Page 32: Challenges Faced by Gymnosperms
Limitations:
Require high pollen production due to unreliable wind transfer.
Page 33: Angiosperm Overview
Angiosperms (≈140 mya):
Most diverse plant group (>250,000 species).
Page 34: Key Adaptations of Angiosperms
Advantages:
Flowers attract pollinators, enabling effective reproduction and dispersal.
Fruits provide protection and aid in dispersal of seeds.
Page 35: Cotyledons and Plant Groups
Cotyledons: First leaves in plants; not true leaves.
Monocots: one cotyledon
Eudicots: two cotyledons; the most diverse group of plants.
Page 36: Monocots vs. Eudicots
Comparison Table:
Include categories: seed leaves, leaf venation, stem structure, root system, pollen structure, floral organs.
Page 37: Summary of Major Events
Evolutionary Timeline:
Key events include the move to land, vascular tissue development, seeds, pollen, and flower and fruit evolution.