Origin of Life and Terrestrial Adaptations

Origin of Life

• Earth originated 4.6 billion years ago (Ga)
• Life originated approximately 3.7-4 Ga
• Early colonization of land began with fungi, followed by early embryophytes and animals

Challenges of Terrestrial Life

• Desiccation: organisms needed protection from drying out.
• Respiration: organisms needed new structures to breathe in the absence of dissolved oxygen and carbon.
• Reproduction: organisms needed to adapt to reproduce under dry conditions.
• Locomotion: organisms needed new features to defy gravity.
• Senses: organisms needed to adapt to new light, sound, and smell conditions.

Algal Mats, Non-vascular Plants, and Arthropods

• Algal mats were the first organisms to colonize water edges.
• Non-vascular plants were the first truly terrestrial organisms.
• Arthropods were the first terrestrial animals.

Adaptations to Desiccation

• Waxy Cuticles:
  • Prevents water loss.
  • Composed of layers, including an outer epidermal layer.
  • Contains fatty acids.
• Stomata:
  • Pores that allow gas exchange across the leaf surface.
  • Opening and closing controlled by guard cells.
  • Guard cells regulate turgor pressure, opening and closing based on water availability and sunlight.
  • Found in early land plants, including non-vascular plants.

Adaptations for Growth and Transport

• Vascular Tissue:
  • Cell walls thickened with lignin, allowing for vertical growth.
  • Facilitates water transport through elongated conducting cells.
  • Contains xylem, which dies at maturity.
  • Xylem includes tracheids (ferns and gymnosperms) and vessels (angiosperms).
• Root System:
  • Non-vascular plants (mosses) have rhizoids.
  • Rhizoids are also present in fern gametophytes.

Evolutionary Timeline

• Mosses (non-vascular plants) already had stomata.
• Vascular tissues with lignified cells and leaves evolved in lycophytes.
• Non-swimming sperm and seeds evolved in gymnosperms.

Key Points

• Water Availability: A key factor in the evolution of plants.
• Free Living Zygote: Only present in algae.
• Gametophyte (n) Generation: Algae > Mosses > Ferns > Conifers (Gymnosperms)
• Sporophyte (2n) Generation: Algae < Mosses < Ferns < Conifers (Gymnosperms)
• Gametophyte (n) Size: Relative size decreases from mosses to ferns to conifers.
• Sporophyte (2n) Size: Relative size increases from mosses to ferns to conifers.
• Protection of Zygote/Embryo (2n): Protection strategies evolve over time, leading to the development of seeds in gymnosperms.

Origin of Life & Plants

• Earth originated approximately 4.6 billion years ago (Ga)
• Life emerged on Earth around 3.7-4 Ga
• Early colonization of land began with fungi, followed by early embryophytes (plants) and then animals

Adaptation to Terrestrial Life

• Desiccation: Organisms needed protection from drying out, leading to the development of outer coverings to prevent water loss.
• Respiration: Exchange of gases, like oxygen and carbon, required new structures for breathing in the air.
• Reproduction: Organisms had to adapt to reproduce in dry conditions, evolving new methods for fertilization and embryo protection.
• Locomotion: Land animals required new features for movement, while plants needed ways to grow erect and defy gravity.
• Senses: Organisms on land had to develop adaptations for detecting changes in light, sounds, and smells.

Algal Mats and Early Terrestrial Life

• Algal mats were the first organisms to colonize land, living in water edges.
• The first fully terrestrial organisms were non-vascular plants (e.g., mosses)
• Arthropods were the first terrestrial animals.

Adaptions for Plant Life on Land

• Desiccation:
  • Waxy Cuticles: These layers help prevent water loss and consist of fatty acids with an outer epidermal cell layer.
  • Stomata: Pores on leaf surfaces that allow gas exchange and are controlled by specialized guard cells that regulate opening and closing based on water availability and sunlight.
• Vascular Tissue:
  • Developed to support vertical growth and efficiently transport water with lignin-thickened cell walls.
  • Xylem: A type of vascular tissue involved in water transport, cells die at maturity.
  • Tracheids: Elongated conducting cells with openings in their secondary walls, found in ferns and gymnosperms.
  • Vessels: Shorter and wider conducting cells, primarily found in angiosperms.
• Root Systems:
  • Rhizoids: Present in non-vascular plants (e.g., mosses) and fern gametophytes.

Evolutionary Timeline of Plants

• Vascular tissues with lignified cells and leaves evolved in lycophytes.
• Non-swimming sperm and seeds evolved in gymnosperms.

Comparing Plant Groups

• Algae: Free-living zygote, dominant gametophyte generation
• Mosses: Shorter gametophyte generation than algae, dominant gametophyte generation
• Ferns: Shorter gametophyte generation than mosses, dominant sporophyte generation
• Gymnosperms (conifers): Shortest gametophyte generation, dominant sporophyte generation

Key Features of Plant Evolution

• Water Availability: Plants adapted to varying water availability conditions.
• Length of Gametophyte Generation: Ranges from dominant in algae to very short in gymnosperms.
• Length of Sporophyte Generation: Increases from algae to gymnosperms.
• Zygote & Embryo Protection: Evolved from no protection in algae to advanced protection in gymnosperms.

Origin of Life and Colonization

• Earth formed approximately 4.6 billion years ago (Ga).
• Life originated on Earth around 3.7-4 Ga.
• Colonization of land began with fungi, early embryophytes, and then animals.

Adaptations for Terrestrial Life

• Organisms needed to adapt to terrestrial conditions, including:
  • Desiccation: Preventing water loss from the body.
  • Respiration: Acquiring oxygen and releasing carbon dioxide.
  • Reproduction: Producing offspring in a dry environment.
  • Locomotion: Moving and supporting the body against gravity.
  • Senses: Detecting light, sound, and smell.

Early Terrestrial Organisms

• Algal mats were among the first organisms to live at water edges.
• Non-vascular plants were the first fully terrestrial organisms.
• Arthropods were the first terrestrial animals.

Plant Adaptations for Terrestrial Life

• Desiccation:

  • Waxy cuticles: A protective layer on the surface of leaves to prevent water loss.
    • Includes an epidermal layer and a wax layer containing fatty acids.
  • Stomata: Pores on the leaf surface for gas exchange.
    • Controlled by specialized cells called guard cells.
    • Opening and closing depends on factors like water availability and sunlight.

• Growth and Support:

  • Vascular tissue: A network of cells that transports water and nutrients.
    • Contains thickened cell walls with lignin.
    • Allows for vertical growth.
  • Xylem: A type of vascular tissue that conducts water.
    • Composed of dead cells at maturity.
  • Tracheids: Elongated cells with openings in their secondary walls, found in ferns and gymnosperms.
  • Vessels: Wider and shorter than tracheids, found in angiosperms.

• Root System:

  • Rhizoids: Root-like structures found in non-vascular plants like mosses.
  • Rhizoids are also present in the gametophyte stage of vascular plants like ferns.

Evolutionary Timeline of Plants

• Stomata: Present in early non-vascular plants like mosses.
• Vascular tissue with lignified cells and leaves: Evolved in lycophytes.
• Non-swimming sperm and seeds: Evolved in gymnosperms.

Evolution of Plant Life Cycles

• Water Availability: Increased reliance on water for reproduction.
• Free-living zygote: Only present in algae.
• Length of gametophyte (n) generation:
  • Algae > mosses > ferns > conifers (gymnosperms).
• Length of sporophyte (2n) generation:
  • Algae < mosses < ferns < conifers (gymnosperms).
• Relative size of gametophyte (n) and sporophyte (2n): The sporophyte generation becomes increasingly dominant.
• Protection of zygote/embryo (2n): Development of protective structures for the embryo, such as seeds.

Origin of Life and Evolution

• Earth formed approximately 4.6 billion years ago (Ga).
• Life on Earth originated between 3.7-4 Ga.
• The first organisms to colonize land were fungi, followed by early embryophytes (plants) and then animals.
• Organisms faced challenges like desiccation (drying out), respiration, reproduction, locomotion, and senses when moving from water to land.

Adapting to Land

• Desiccation: Organisms needed a way to prevent water loss.
  • Waxy cuticles, a layer of fatty acids and other compounds, evolved to protect plants against water loss.
  • The outer layer of a waxy cuticle is called the epidermal layer.
• Respiration: Organisms needed different structures to breathe air.
  • Stomata: Pores on the leaves allow gas exchange.
    • Specialized cells called guard cells regulate the opening and closing of stomata.
    • The opening and closing depend on environmental cues like water and sunlight.
      • Stomata will close if water is scarce.
• Growth: Plants needed structures to grow erect and access sunlight.
  • Vascular tissue: Helps plants transport water and nutrients.
    • Lignin: A rigid polymer that strengthens cell walls.
    • Xylem: A type of vascular tissue that transports water.
      • Xylem cells die at maturity.
    • Tracheids: elongated, dead cells that transport water.
    • Vessels: Another type of xylem cell (found in angiosperms) that is wider and shorter than tracheids.
• Root system: Provides support and anchors plants to the ground.
  • Rhizoids: Root-like structures found in non-vascular plants and fern gametophytes.

Evolutionary Timeline

• Mosses: The first land plants; have stomata but lack vascular tissue.
• Lycophytes: Evolved vascular tissue with lignified cells and leaves.
• Gymnosperms: Evolved non-swimming sperm and seeds.

Comparison of Plant Groups

• Water availability: Algae thrive in water, whereas land plants need adaptations to survive in drier environments.
• Free-living zygote: Only found in algae.
• Gametophyte (n) generation: The length of the gametophyte generation decreases from algae to conifers.
  • Algae: Long gametophyte generation
  • Mosses: Shorter than algae, but still relatively long
  • Ferns: Shorter than mosses
  • Conifers: Very short gametophyte generation
• Sporophyte (2n) generation: The length of the sporophyte generation increases from algae to conifers.
  • Conifers: Very long sporophyte generation
• Relative size of gametophyte (n): Decreases from algae to conifers
• Relative size of sporophyte (2n): Increases from algae to conifers
• Protection of zygote/embryo (2n): Protection increases from algae to conifers.

Early Life on Earth

• Earth formed approximately 4.6 billion years ago (Ga), with life emerging around 3.7-4.0 Ga.
• Early life forms primarily existed in aquatic environments.

Transition to Land

• The transition to land presented significant challenges for organisms, including desiccation (drying out), gaseous exchange, reproduction, locomotion, and sensory adaptations.
• Algal mats were among the first organisms to colonize water edges.
• Non-vascular plants were the first truly terrestrial organisms.
• Arthropods were the first terrestrial animals.

Adaptations to Terrestrial Life

Desiccation

• Waxy cuticles:
  • Prevent water loss, forming a protective barrier.
  • Composed of epidermal layers and fatty acids.
• Stomata:
  • Pores on leaf surfaces for gas exchange.
  • Controlled by specialized guard cells that respond to water availability and sunlight.
  • Found in both non-vascular and vascular plants.

Respiration

• Vascular tissue:
  • Allows for upright growth and efficient water transport.
  • Consists of lignified cell walls, xylem (dead at maturity), tracheids (found in ferns and gymnosperms), and vessels (found in angiosperms).

Root System

• Non-vascular plants (mosses) have rhizoids.
• Vascular plant gametophytes, such as ferns, also possess rhizoids.

Evolutionary Timeline of Plant Adaptations

• Mosses (non-vascular) - Possess stomata.
• Lycophytes - Evolution of vascular tissue with lignified cells and leaves.
• Gymnosperms - Development of non-swimming sperm and seeds.

Plant Life Cycle Comparison

• Algae:

  • Free-living zygote.
  • Long gametophyte (n) generation.
  • Short sporophyte (2n) generation.

• Mosses:

  • Shorter gametophyte (n) generation than algae.
  • Longer sporophyte (2n) generation than algae.

• Ferns:

  • Shorter gametophyte (n) generation than mosses.
  • Longer sporophyte (2n) generation than mosses.

• Conifers (Gymnosperms):

  • Very short gametophyte (n) generation.
  • Very long sporophyte (2n) generation.

• Gametophyte (n) size:

  • Decreases from algae to conifers.

• Sporophyte (2n) size:

  • Increases from algae to conifers.

• Zygote/embryo (2n) protection:

  • Increases from algae to conifers.