Theme 3: Kingdom Plantae, Kingdom Fungi

Topic 13: Evolution of Plants

Outline

1. Identify traits of plants that are shared with other protists.

2. Describe the benefits, challenges, and adaptations of terrestrial life for plants.

3. Describe the shared derived traits of plants.

4. Summarize the origin and diversification of plants.

Topic 13 Notes

Evolution of Plants

Early Terrestrial Life

• Timeline: Earth's terrestrial surface was lifeless for over 3 billion years.

  • Around 1.2 billion years ago (bya): Simple algae began to colonize land.

  • By 470 million years ago (mya): Small plants emerged on land.

• Adaptations: Over time, plants evolved adaptations to terrestrial life, increasing in height to compete for sunlight by around 385 mya.

• Diversity: Approximately 325,000 living species of plants exist today.

• Ecological Role: Plants supply atmospheric oxygen and serve as the primary food source for land animals.

• Habitats: Plants occupy diverse terrestrial environments, such as deserts, grasslands, and forests. Some species have returned to aquatic environments, predominantly freshwater.

Plant Characteristics and Relationships to Algae

• Shared Features with Algae:

  • Plants are multicellular, photosynthetic eukaryotes; this is also characteristic of many protists (e.g., algae).

  • Plants have cell walls made of cellulose, similar to red, green, brown algae and some dinoflagellates.

  • Chloroplasts: Contain chlorophyll a and b; an ancestral trait shared with certain protists.

  • Classification: Plants belong to the protist supergroup Archaeplastida, descending from protists that underwent primary endosymbiosis with cyanobacteria.

Evolutionary Relationships

• Plants' Ancestors:

  • Freshwater Green Algae: Evidence from nuclear, chloroplast, and mitochondrial DNA suggests charophytes, specifically genera like Zygnema, are the closest living relatives of plants.

  • Charophytes share ancestral traits with plants, particularly in their adaptations for life in shallow and intermittently dry freshwater environments.

Adaptations for Terrestrial Life

Advantages of Terrestrial Life

• Benefits of Land Colonization:

  • Decreased competition and abundant sunlight for photosynthesis.

  • Rich carbon dioxide and nutrient-rich soils.

  • Early plants faced fewer herbivores and pathogens.

Challenges of Terrestrial Life

• Environmental Challenges:

  • Water Scarcity: Desiccation from limited water availability.

  • Structural Support: Lack of support structures needed for upright growth.

Key Adaptations Developed

1. Sporopollenin

   • A durable polymer secreted by charophyte zygotes, resistant to degradation, protecting against desiccation and UV light. Found in spores and pollen of plants, enhancing resilience.

2. Water Conservation Adaptations

   • Waxy Cuticle: Protective layer on epidermis to reduce water loss and prevent microbial attack.

   • Stomata: Tiny pores for gas exchange and water evaporation, capable of closing to minimize water loss.

3. Lignified Vascular Tissue

   • Xylem: Transports water/minerals and provides structural support through lignified walls.

   • Phloem: Distributes organic compounds produced during photosynthesis, enabling growth in dry conditions.

4. Functional Compartmentalization

   • Structural specialization with roots for water/mineral absorption and shoots for light and gas access, with growth patterns optimized for environmental resource utilization.

Plant Life Cycle and Reproductive Strategies

Alternation of Generations

• Life Cycle: Plants alternate between two multicellular generations:

  • Sporophyte (diploid): Produces haploid spores through meiosis.

  • Gametophyte (haploid): Produces haploid gametes by mitosis, facilitating fertilization.

• This evolution provides reproductive advantages, allowing spore dispersal through air, which benefits colonization of new areas.

Shared Derived Traits of Plants

1. Multicellular, Dependent Embryos: Nutrient transfer from gametophyte to embryos, called embryophytes due to this dependency.

2. Walled Spores in Sporangia: Spores formed by sporophytes in sporangia with resistant walls to desiccation, critical for terrestrial survival.

3. Apical Meristems: Regions that allow for continuous growth in root and shoot tips, evolving structural specialization.

4. Cuticle: Waxy surfaces reduce water loss, with stomata aiding in gas exchange while managing water retention.

Timeline of Plant Evolution

• ~1.2 bya: Photosynthetic organisms, including algae, began colonizing terrestrial habitats.

• 470 mya: Fossil evidence indicates early plant colonization on land based on spores and tissue fragments.

• 450 mya: Evidence of an increased presence of terrestrial plants.

• 425 mya: Larger fossilized plant structures like sporangia appear, supporting the evolution of diverse land plants.

• Molecular data suggests land plants may have originated between 425-490 mya.

Diversity of Plants

Classification of Plants

• Plants are classified into vascular and nonvascular groups, with key distinctions based on vascular tissue.

  • Nonvascular Plants (Bryophytes): Include liverworts, mosses, hornworts; unresolved relationships in some cases.

  • Seedless Vascular Plants: Comprised of lycophytes and monilophytes (ferns).

  • Seed Plants: Characterized by seeds; includes gymnosperms (e.g., conifers) and angiosperms (flowering plants).

Current Diversity

• Summary of Species: The number of known species within major plant groups:

  • Bryophytes: 22,225 total

  • Seedless Vascular: 13,200

  • Seed Plants: 290,000

• Vascular plants account for approximately 93% of all plants, indicating substantial diversity within this category.

Topic 13 Practice Questions

1. What did I learn?

2. How does this tie into the unit?

Topic 13 Reading

Campbell Biology, 2020, Canadian 3e: Ch. 29, pp. 657-674

Topic 14: Nonvascular Plants

Outline

1. Recall the phyla of nonvascular plants.

2. Describe the characteristics of bryophytes.

3. Explain the life cycle of a bryophyte.

4. Contrast the dependency of bryophytes on water for fertilization and dispersal with that of charophytes.

Topic 14 Notes

Topic: Nonvascular Plants - Bryophytes

Phylogenetic Relationships

• Bryophytes represent an unclear phylogenetic relationship, likely forming a paraphyletic group.

• They diverged before vascular tissues evolved, indicating their ancient lineage in plant evolution.

• Refer to Fig 29.10 for highlights of plant evolution.

Overview of Bryophytes

• Definition: Bryophytes are the earliest lineages branching from the common ancestor of land plants.

• Classification: They are a paraphyletic group comprising three phyla of small, herbaceous, nonvascular plants:

  • Liverworts (Phylum Hepatophyta)

    • Approx. 9,000 species.

    • Etymology: "Hepato" means liver, "phyt" means plant, and "wort" is Old English for herb.

  • Mosses (Phylum Bryophyta)

    • Approx. 12,000 species; the most diverse and widespread bryophytes.

    • Note: "Bryophyta" specifically refers to mosses, while "bryophyte" is a general term for all nonvascular plants.

  • Hornworts (Phylum Anthocerophyta)

    • Approx. 225 species.

    • Etymology: "Antho" means flower, "ceros" means horn.

Characteristics of Bryophytes

• Lack of Vascular Tissue:

  • Absence of true vascular systems limits size and structural support, leading to tissues only being a few cells thick.

  • They do not form roots; instead, they absorb water through surfaces, anchored by rhizoids.

  • This restriction confines them to habitats with abundant moisture.

• Sporophyte Structure:

  • Unbranched and lacks roots and leaves, contrasting with vascular plants that have branched structures.

  • Mosses and hornworts have stomata for gas exchange, while liverworts do not possess stomata.

  • No known extant gametophytes contain stomata.

• Gametophyte Dominance:

  • Gametophytes are the dominant phase; larger and longer-living compared to sporophytes.

  • Bryophytes have free-living haploid (1n) gametophytes; smaller diploid (2n) sporophytes are dependent on them.

Life Cycle of Mosses

• A spore germinates into a gametophyte (1n) consisting of protonema and gamete-producing gametophore.

• Mosses exhibit separate male and female gametophytes.

• Fertilization Process:

  • Flagellated sperm swim through a water film to fertilize eggs.

  • Antheridia: Produce and release flagellated sperm.

  • Archegonia: Produce eggs, being the site of fertilization.

  • Gametes are produced by mitosis in specialized organs called gametangia.

Asexual Reproduction

• Many bryophytes propagate asexually through mechanisms like brood bodies, which are small plantlets that detach from their parent and grow into genetically identical copies.

Sporophyte Structure and Function

• Sporophyte consists of:

  • Foot: Site of attachment to the gametophyte.

  • Seta: Stalk that elevates the capsule.

  • Capsule (Sporangium): Produces thousands of haploid spores (1n) via meiosis; these spores disperse into the air.

  • Spore cell walls contain sporopollenin, which provides durability.

Environmental Needs and Ecology

• Water Requirement: Fertilization in bryophytes necessitates water; however, spore dispersal is independent of water.

• Bryophytes thrive in moist forests and wetlands, with mosses often dominating the ground cover.

• Example: Sphagnum (peat moss) plays a crucial role in regulating water flow in peat bogs, especially in Arctic and boreal regions.

• Sphagnum can lose significant amounts of water and rehydrate to reactivate.

• Peat Formation: Peat originates from accumulated undecayed organic material in peatlands, characterized by low temperatures, pH level, and oxygen.

• Ecological Role: Peatlands serve as carbon reservoirs, stabilizing atmospheric CO2 levels.

Topic 14 Practice Questions

1. What did I learn?

2. How does this tie into the unit?

Topic 14 Reading

Campbell Biology, 2020, Canadian 3e: Ch. 29, pp. 657-674

Topic 15: Seedless Vascular Plants

Outline

1. Define the shared derived traits of vascular plants.

2. Describe the characteristics of extant vascular plants and seedless vascular plants.

3. Explain the life cycle of a fern.

4. Identify the taxa of seedless vascular plants.

Topic 15 Notes

Origin of Vascular Plants

• Bryophytes as Dominant Vegetation:

  • Dominated for first 100 million years of plant evolution.

  • Earliest vascular plant fossils date to approximately 425 million years ago.

• Early Vascular Plants:

  • Example: Aglaophyton.

  • Exhibited anatomical features intermediate between bryophytes and fully developed vascular plants.

  • Characteristics:

    • Possessed independent, branching sporophytes.

    • Sporophytes were not continuously reliant on gametophytes for sustenance.

    • Lacked leaves or roots and true vascular tissues.

• Evolution of Vascular Tissue:

  • Subsequent discoveries revealed gradual evolution of vascular tissues, leading to development of leaves and roots.

Shared Derived Traits of Vascular Plants

1. Vascular Tissues:

   • Evolved exclusively in sporophytes of vascular plants.

   • Allowed sporophytes to grow tall, providing an evolutionary advantage over nonvascular plants.

   • Xylem:

     • Conducts water and minerals via dead, hollow cells forming continuous conduits throughout the plant.

     • Strengthened by lignin for structural support.

   • Phloem:

     • Consists of living cells that distribute nutrients and organic products.

2. Life Cycles with Dominant Sporophytes:

   • Sporophytes are larger, more complex, and longer-lasting than gametophytes.

   • Not continuously reliant on gametophytes.

3. Well-Developed Roots and Leaves:

   • Roots:

     • Complex multicellular structures anchor sporophytes and aid in absorption of water and nutrients from the soil.

     • Roots may have evolved from subterranean stems.

   • Leaves:

     • Complex multicellular structures increase surface area for photosynthesis.

     • Bryophytes lack true roots and leaves.

Characteristics of Living Vascular Plants

• Leaf Types:

  • Microphylls:

    • Small leaves with single veins; possibly evolved from stem outgrowths.

  • Megaphylls:

    • Large leaves with highly branched vascular systems; potentially evolved from webbing between flattened branches.

• Sporophylls:

  • Modified leaves that bear sporangia (spore-producing organs).

  • Sori:

    • Clusters of sporangia on the underside of sporophylls (e.g., ferns).

  • Strobili:

    • Cone-like structures formed from groups of sporophylls (e.g., lycophytes and most gymnosperms).

Variation in Spore Sizes among Taxa

• Most seedless vascular plants are homosporous, producing a single type of spore that develops into a bisexual gametophyte.

• Some seed plants and a few seedless vascular plants are heterosporous, producing:

  • Megaspores: develop into female gametophytes.

  • Microspores: develop into male gametophytes.

Characteristics of Seedless Vascular Plants

• Height Attainment:

  • Vascular tissue enables height in seedless vascular plants.

• Flagellated Sperm:

  • Require a film of water for fertilization, similar to bryophytes.

  • Mainly found in damp habitats.

• Sporophyte Dominance:

  • In seedless vascular plants, the sporophyte is the larger and dominant generation.

  • Gametophytes are small, independent plants often growing on or below the soil surface.

The Life Cycle of a Fern

• Most ferns produce a single type of spore (homosporous) that develops into a bisexual photosynthetic gametophyte.

• Spore Wall:

  • Contains sporopollenin, spores are dispersed in the air.

• Sporangia:

  • Produce spores via meiosis.

• Fertilization:

  • Sperm swim to eggs in archegonia (using flagella).

• Zygote Development:

  • Grows into a new sporophyte from the archegonium of the gametophyte.

• Sporophyte Features:

  • Produces clusters of sporangia (sori) on the underside of leaves (sporophylls).

  • Gametophyte dies as sporophyte becomes independent.

Classification of Seedless Vascular Plants

• Two Clades:

  • Phylum Lycophyta:

    • Includes club mosses, spike mosses, and quillworts (~1,200 species).

  • Phylum Monilophyta:

    • Includes ferns, horsetails, and whisk ferns (~12,000 species).

• Phylogenetic Note:

  • Seedless vascular plants are paraphyletic.

Lycophytes

• Once giant lycophyte trees dominated Carboniferous swamps; became extinct as the climate cooled and dried.

• Surviving species are small herbaceous plants.

  • All are microphyllous and can be either homo- or heterosporous.

  • Club mosses and spike mosses possess vascular tissues, despite the name "mosses."

Monilophytes

• Morphologically diverse, includes:

  • Whisk Ferns:

    • Resemble ancestral vascular plants but are closely related to modern ferns; lack true roots or leaves (lost secondarily).

  • Horsetails:

    • Characterized by brushy stems, once grew to 15 m during Carboniferous but now limited to the genus Equisetum (15 species).

    • Have leaves with a single vein but are secondarily microphyllous.

Ferns

• Most diverse seedless vascular plants (~12,000 species); thrive in tropical and temperate forests.

• Characteristics:

  • Megaphylls (large leaves with branched vascular systems).

  • Produce clusters of sporangia (sori) on the undersides of sporophylls, with spring-like structures for spore release.

  • Most are homosporous.

Significance of Seedless Vascular Plants

• Ancestors of extant lycophytes, horsetails, and ferns dominated during the Devonian and Carboniferous periods, forming the first forests.

• Partially decayed plant material formed coal deposits during the Carboniferous period.

• Increased plant growth and photosynthesis may have contributed to global cooling by reducing atmospheric CO2 levels (5-fold decrease during Carboniferous period).

Topic 15 Practice Questions

1. What did I learn?

2. How does this tie into the unit?

Topic 15 Reading

Campbell Biology, 2020, Canadian 3e: Ch. 29, pp. 657-674

Topic 16: Seed Plants - Gymnosperms

Outline

1. Define the shared derived traits of seed plants (gymnosperms and angiosperms).

2. Contrast pollination in seed plants with fertilization in seedless plants.

3. Explain the evolutionary benefits of seed dispersal as compared to spore dispersal.

4. Identify the taxa of gymnosperms.

5. Explain the life cycle of a conifer.

Topic 16 Notes

Seed Plants Overview

• Seed plants originated around 360 million years ago (mya).

• They have become the dominant primary producers in terrestrial ecosystems.

• Seeds provide:

  • An embryo and nutrients in a protective coat.

  • Enabled long-distance dispersal.

• Domestication began approximately 8,000 years ago, facilitating permanent human settlement.

Diversity of Plant Kingdom

Number of Known Species

• Nonvascular Plants (Bryophytes)

  • Phylum Hepatophyta (Liverworts): 9,000 species

  • Phylum Bryophyta (Mosses): 13,000 species

  • Phylum Anthocerophyta (Hornworts): 225 species

• Vascular Plants

  • Seedless Vascular Plants

    • Phylum Lycophyta (Lycophytes): 1,200 species

    • Phylum Monilophyta (Monilophytes): 12,000 species

  • Seed Plants

    • Gymnosperms

      • Phylum Ginkgophyta (Ginkgo): 1 species

      • Phylum Cycadophyta (Cycads): 350 species

      • Phylum Gnetophyta (Gnetophytes): 75 species

      • Phylum Coniferophyta (Conifers): 600 species

    • Angiosperms

      • Phylum Anthophyta (Flowering plants): 290,000 species

Shared Derived Traits of Seed Plants

1. Reduced Gametophytes

• Gametophytes develop within spore walls retained in parental sporophyte tissues.

• Protection from environmental stresses.

• Comparisons:

  • Nonvascular plants (bryophytes): dominant and independent gametophyte.

  • Seedless vascular plants: dominant sporophyte, independent gametophyte.

  • Seed plants: dominant sporophyte, microscopic and sporophyte-dependent gametophyte.

2. Heterospory

• All seed plants are heterosporous, producing:

  • Megaspores (female gametophytes) from megasporangia.

  • Microspores (male gametophytes) from microsporangia.

• Spores are retained within the sporophyte.

3. Ovules

• An ovule consists of:

  • Megasporangium (2n), megaspore (1n), and protective integuments (2n).

• Gymnosperm ovules: 1 integument; angiosperm ovules: usually 2 integuments.

• Develop into seeds post-fertilization.

4. Pollen

• Microspores develop into male gametophytes in pollen grains.

• Pollen grains have outer walls of sporopollenin, protecting them from desiccation, UV, and damage.

• Utilized for fertilization without the external release of sperm.

5. Seeds

• Seeds develop from fertilized ovules, containing:

  • Embryo, food supply, and seed coat.

• Variation in seed size based on gametophyte-derived storage reserves (e.g., orchid seeds < 1 µg to coco de mer palm seed up to 30 kg).

Pollination and Fertilization

• Pollination transports pollen to ovules for fertilization.

• Key changes in seed plant fertilization strategies:

  • Pollen eliminates the need for water during fertilization.

  • Entire male gametophyte transported via pollen grain.

  • Pollen can be dispersed by wind or animals.

• If germination occurs, pollen develops into a pollen tube delivering sperm nuclei to female gametophyte within the ovule.

Seed Dispersal

• Seeds are a significant adaptation for dispersal, contrasting with spores in seedless plants.

• Advantages of seeds:

  • Protection for embryos through outer coats.

  • Dormancy capabilities until favorable conditions arise.

  • Energy-dense food supply aiding early seedling growth.

  • Trade-offs between seed size and number.

Evolutionary Changes in Fertilization

• Overview of fertilization modes:

  • Earlier plants (Charophytes, chlorophytes, non-vascular plants, vascular plants) relied on water for sperm movement.

  • In contrast, seed plants utilize air (via pollen) for fertilization.

Clades of Seed Plants

• Two main clades:

  • Gymnosperms: ~1,000 species (e.g., conifers).

  • Angiosperms: ~290,000 species (flowering plants).

Evolution of Gymnosperms

• Gymnosperms feature "naked seeds" on sporophyll cones.

• Originated approximately 360 mya with "seed ferns."

• Dominated ecosystems during the Mesozoic era, adapting to drier conditions.

• Angiosperms started replacing gymnosperms late in the Mesozoic, with conifers prevailing in specific climates.

Extant Gymnosperms

Main Phyla

1. Cycadophyta: ~350 species; slow-growing with large cones, mainly tropical.

2. Ginkgophyta: One living species (Ginkgo biloba), widely used in urban settings.

3. Gnetophyta: Diverse forms adapted to varying environments (~75 species).

4. Coniferophyta: Leading phylum in species richness (~600 species), primarily found in colder areas.

Adaptations in Conifers

• Evergreens capable of year-round photosynthesis; some are deciduous.

• Adapted to cold, dry habitats; features include:

  • Resistant xylem; thick waxy cuticles; reduced leaf surface area.

Life Cycle of Gymnosperms

• Dominant sporophyte generation.

• Development of seeds from fertilized ovules.

• Transfer of male gametophytes occurs through pollen, which has a resistant outer layer (sporopollenin).

Life Cycle of Conifers (Pinus)

Topic 16 Practice Questions

1. What did I learn?

2. How does this tie into the unit?

Topic 16 Reading

Campbell Biology, 2020, Canadian 3e: Ch. 30, pp. 678-686

Topic 17: Seed Plants - Angiosperms

Outline

1. Define the shared derived traits of angiosperms.

2. Describe the structure and function of flowers.

3. Explain the life cycle of angiosperms.

4. Explain the adaptive advantages of angiosperm fertilization.

5. Describe self-fertilization and the mechanisms angiosperms have evolved to avoid self-fertilization.

6. Differentiate between sexual and asexual reproduction in angiosperms.

7. Identify angiosperm taxa.

Topic 17 Notes

Topic 17: Seed Plants - Angiosperms

• Angiosperms (flowering plants) are seed plants characterized by two major adaptations: flowers and fruits.

• They represent the most diverse group of plants, with over 290,000 species, classified under the phylum Anthophyta (from Greek anthos, meaning flower).

  • Range exemplifying diversity spans from tiny duckweed (2-3 mm) to giants like Eucalyptus regnans (131 m in height).

Angiosperm Life Cycle

• Life Cycle Characteristics:

  • Alternates between multicellular haploid (1n) generation and multicellular diploid (2n) generation.

  • Diploid sporophytes (2n) generate spores (1n) through meiosis, which develop into haploid gametophytes (1n).

  • Gametophytes produce haploid gametes (1n) via mitosis leading to the formation of a diploid sporophyte through fertilization.

Dominant and Dependent Generations

• In angiosperms:

  • The sporophyte is the dominant generation, which is the large plant visible to us.

  • Gametophytes are microscopic and depend on the sporophyte for nourishment.

  • Both spores and gametophytes are retained on the sporophyte.

• Key features denoted as the “three Fs”:

  • Flowers

  • Double Fertilization (leading to seed endosperm)

  • Fruits

  • These are shared derived traits (synapomorphies) that distinguish angiosperms from other plant categories.

Flower Structure and Function

• Flowers are specialized structures for sexual reproduction in angiosperms:

  • They facilitate pollen transfer and reception.

  • Pollination strategies include animal and wind pollination; flowers attract animal pollinators with rewards.

• Flower Composition: Typically includes four types of modified leaves:

  • Sepals: protect the flower

  • Petals: often brightly colored for attracting pollinators

  • Stamens: comprise anther to produce pollen

  • Carpels: contain ovules for reproduction

  • Sepals and petals protect and attract, whereas stamens and carpels directly involve in reproduction.

Flower Sporophyll Structure and Function

• Stamens: (microsporophylls)

  • Composed of stalk (filament) and anther with pollen sacs (microsporangia) producing pollen.

  • Pollen sacs yield microspores via meiosis forming male gametophytes in pollen grains.

• Carpels: (megasporophylls)

  • Structure comprises an ovary, style leading to stigma for pollen reception.

  • Multiple carpels can fuse to form a pistil, containing ovules that develop into seeds post fertilization.

  • The megaspore develops into a female gametophyte.

Flower Classification and Arrangement

• Majority of angiosperm flowers are complete, containing all four floral organs.

• Approximately 12% are incomplete, lacking one or more reproductive organs.

  • Incomplete flowers may only have either male (stamens) or female (carpels), often relying on wind pollination.

• Clusters of flowers are termed inflorescences, exemplified by sunflowers where multiple individual flowers form a composite.

Male Gametophyte Development in Pollen Grains

• A pollen grain consists of a two-celled male gametophyte protected by a sporopollenin-rich outer wall.

• Development begins in pollen sacs, with microspores undergo mitosis leading to:

  • Generative cell: forms sperm nuclei.

  • Tube cell: develops into a pollen tube essential for fertilization.

Female Gametophyte Development

• The female gametophyte (embryo sac) forms within an ovule in the flower's ovary:

  • Each ovule typically has two integuments around the megasporangium.

  • The megasporocyte undergoes meiosis forming four megaspores, with one surviving to develop into a seven-celled female gametophyte, featuring polar nuclei.

Pollination Mechanism

• Pollination involves pollen transfer from an anther to a stigma via agents like wind, water, or animals:

  • If successful:

    • The tube cell produces a pollen tube.

    • The generative cell undergoes mitosis creating two sperm nuclei.

    • The pollen tube reaches the ovary to release sperm for fertilization.

Double Fertilization

• Occurs when the pollen tube delivers two sperm nuclei into the female gametophyte:

  • One sperm fertilizes the egg to form the zygote (2n).

  • The second sperm fuses with two polar nuclei to create a triploid cell (3n) that develops into endosperm, providing nourishment to the embryo.

Seed Development Post-Fertilization

• After double fertilization:

  • Each fertilized ovule develops into a seed.

  • The ovary matures into a fruit enclosing the seed(s).

• Seed Development:

  • Endosperm forms before embryo, generating starchy tissues for seedling nourishment.

  • Nutrients are sourced from the megagametophyte and sporophyte.

  • Certain species utilize endosperm as a nutrient reserve, while others transfer reserves to cotyledons.

  • The zygote divides to form an elongated embryo comprising cotyledons, shoots, and roots.

Fruit Development

• Following fertilization, each ovule becomes a seed and the ovary matures into the fruit:

  • Fruits serve two primary purposes:

    1. Protect seeds during development.

    2. Facilitate seed dispersal via various means (wind, water, animals).

• Fruit Types:

  • Dry fruits (e.g. dandelions).

  • Fleshy fruits (e.g. cherries).

Adaptive Advantages of Angiosperm Fertilization

1. Resource Conservation: Nutrient stores in seeds only develop post fertilization.

2. Resource Efficiency: Fruit development initiated by fertilization avoids waste if fertilization fails.

3. Reduced Resource Requirement: Smaller female gametophytes require fewer resources.

4. Rapid Development: Female gametophytes mature quickly, allowing completion of life cycles within a growing season.

Angiosperm Pollination Types

• Abiotic Pollination:

  • Water and wind (20% of species), involves significant pollen production.

• Biotic Pollination:

  • ~80% rely on animals, with variations in floral morphology adjusted to attract specific pollinators.

  • Insects, especially bees, as primary pollinators, are attracted to certain colors and scents.

Coevolution of Flowers and Pollinators

• Interactions lead to coevolution, where flowering plants and their pollinators evolve in response to each other's adaptations.

• Shapes and sizes correlate with pollinators' morphology ensuring effective pollen transfer.

• Mutual benefits:-

  • Plants produce rewards, while pollinators obtain food.

Reproduction in Flowering Plants

• Flowering plants can reproduce both sexually and asexually:

  • Sexual reproduction provides genetic diversity, whereas asexual reproduction leads to clones.

  • Methods include fragmentation and apomixis, where seeds develop without fertilization.

Advantages and Disadvantages of Reproduction Types

• Asexual reproduction enables rapid establishment but poses risks due to lack of genetic diversity.

• Sexual reproduction enhances variability and adaptability, yet fewer offspring may survive to maturity.

Mechanisms Preventing Self-Fertilization

• Self-compatibility favors isolated environments.

• Strategies evolved include:

  1. Self-incompatibility prevents fertilization by own pollen.

  2. Floral Structure: Incomplete flowers reduce self-pollination.

  3. Temporal and Spatial Separation prevent simultaneous maturation of reproductive structures.

Angiosperm Evolution and Diversity

• Angiosperms represent ~90% of plant diversity, dominating the Cretaceous.

• Their adaptive radiation was rapid post origination (140 mya), linked to various advantages:

  • Enhanced xylem vessels allowed for increased photosynthetic efficiency.

  • Pollinator-driven speciation reduced extinction rates.

• Phylogenetic studies reveal Amborella as the earliest angiosperm representative.

Eudicot vs. Monocot Seeds

• Eudicots feature seeds with two cotyledons, whereas monocots have one and larger endosperms.

Topic 17 Practice Questions

1. What did I learn?

2. How does this tie into the unit?

Topic 17 Reading

Campbell Biology, 2020, Canadian 3e: Ch. 30, pp. 686-696; Ch. 38, pp. 873-887

Topic 18: Kingdom Fungi

Outline

1. Define the characteristics of fungi.

2. Explain how fungal body structures support absorptive nutrition.

3. Describe the generalized life of fungi (incl. asexual and sexual reproduction).

4. Distinguish between fungal phyla using their characteristics.

5. Describe ecological interactions involving fungi.

Topic 18 Notes

Kingdom Fungi

• More closely related to Animalia than Plantae.

  • Molecular phylogeny places fungi in Opisthokonts (Unikonta protist supergroup), alongside animals.

  • Shared common protist ancestor was single-celled with posterior flagella.

• Fungal Diversity and Importance:

  • Approximately 145,000 described species; estimated 2.2-3.8 million species in total.

  • Vital for nutrient cycling and decomposition, critical for ecosystem function.

  • Predominantly found in soil, where they decompose organic material.

Characteristics of Fungi

• Common Structural Features:

  1. Hyphae and Mycelium:

     • Long, thread-like filaments (hyphae) form a network (mycelium).

     • Increases surface area for nutrient absorption.

  2. Chitinous Cell Wall:

     • Majority have cell walls made of chitin, providing structural support and protection.

• Functional Characteristics: 3. Absorptive Nutrition:

  • Fungi are absorptive chemoheterotrophs; absorb nutrients directly from the environment.

  • Secrete enzymes that degrade complex organic materials into simpler forms for uptake.

  • Contrasts with animals which are phagotrophic.

  4. Spore Production:

     • Reproduce by producing spores through asexual (mitosis) and sexual (meiosis) reproduction.

• Exceptions in early-diverging fungal lineages exist.

Fungal Nutrition and Digestion

• Absorptive Nutrition:

  • Chemoheterotrophic eukaryotes absorb dissolved organic compounds directly from the environment.

  • Secrete exoenzymes for external digestion, breaking complex substrates into smaller organic molecules.

  • Versatile enzyme production allows digestion of cellulose, lignin, chitin, and keratin.

Fungal Body Structure

• Non-motile; create networks to find and absorb nutrients.

• Characterized by hyphae and mycelium:

  • Hyphae are cylindrical, branched, multicellular and adapt for nutrient absorption.

  • Growth occurs primarily at tips, allowing for rapid elongation (up to 1 km of hyphae/day).

  • Mycelium's filamentous structure optimizes surface area-to-volume ratio for efficient absorption.

• Coenocytic vs. Septate Fungi:

  • Coenocytic Fungi: lack septa, forming continuous compartments with multiple nuclei.

  • Septate Fungi: have septa with single nuclei per cell, allowing for better regulation of cytoplasm.

Reproduction in Fungi

• Spores: reproductive units that can be produced asexually or sexually.

  • Asexual spores arise from mitosis while sexual spores arise from meiotic processes.

  • Fungal mycelia are typically haploid (1n) and produce haploid spores.

• Generalized Life Cycle: includes stages of plasmogamy (cytoplasmic fusion) and karyogamy (nuclear fusion).

  • Heterokaryotic Stage: genetically distinct haploid nuclei coexist before karyogamy.

Diversity of Fungi

• Major Lineages:

  • Nine major clades identified, including Chytrids, Zoopagomycetes, and Dikarya.

  • Fungi are critical in early land colonization, forming mutualistic associations with plants.

• Basal Fungal Lineage: includes Cryptomycetes and Microsporidians which are unicellular and spore-forming parasites.

• Chytrids: aquatic fungi with flagellated spores that can be free-living decomposers.

Ecological Roles of Fungi

• Decomposers:

  • Fungi play crucial roles in recycling nutrients by decomposing organic matter. Examples include mold and wood-rot fungi.

• Mutualists:

  • Fungi form beneficial associations, like mycorrhizae with plant roots, enhancing nutrient uptake,

    • Ectomycorrhizae: envelop roots without penetrating cells; limited to certain tree species.

    • Arbuscular Mycorrhizae: penetrate root cells, forming structures that facilitate nutrient exchange.

  • Lichens: symbiotic relationship between fungi and photosynthetic microorganisms.

• Pathogens:

  • Fungal pathogens are responsible for significant agricultural diseases, affecting crop yield and plant health.

  • Fungi can also infect animals, causing disease. Common human fungal diseases include candidiasis and histoplasmosis.

Topic 18 Practice Questions

1. What did I learn?

2. How does this tie into the unit?

Topic 18 Reading

Campbell Biology, 2020, Canadian 3e: Ch. 31, pp. 698-715

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