Plant Evolution, Structure, Nutrition, and Reproduction: Study Guide for BIOL 191A (Chapters 26, 28, 29, 30, 31)

Plant Evolution and the Colonization of Land

Evidence for Plant Descent from Green Algae

Plants are believed to have evolved from green algae, specifically charophytes, based on similarities in cell wall composition, chloroplast structure, and reproductive mechanisms. - Key Evidence: Presence of sporopollenin (a durable polymer) in both charophytes and land plants, preventing desiccation. - Shared Traits: Similarities in cellulose-synthesizing complexes, peroxisome enzymes, and structure of flagellated sperm.

Key Derived Characters of Land Plants

Land plants possess several adaptations for terrestrial life. - Alternation of generations: Life cycle alternates between multicellular diploid (sporophyte) and haploid (gametophyte) forms. - Multicellular, dependent embryos: Embryophytes retain embryos within parental tissues. - Walled spores: Produced in sporangia, protected by sporopollenin. - Apical meristems: Regions of cell division at tips of roots and shoots, enabling growth. - Cuticle: Waxy covering to prevent water loss.

Fungi and the Colonization of Land

Structure and Nutrition of Fungi

Fungi are heterotrophic organisms with unique structural features. - Hyphae: Filamentous structures forming the mycelium, increasing surface area for absorption. - Nutrition: Fungi absorb nutrients from their environment, often decomposing organic matter. - Mycorrhizae: Mutualistic associations between fungi and plant roots, enhancing nutrient uptake.

Role of Fungi in Colonization of Land

Fungi played a crucial role in enabling plants to colonize land by forming symbiotic relationships. - Mycorrhizal fungi: Aid in water and mineral absorption, especially phosphorus. - Decomposition: Fungi recycle nutrients, supporting plant growth.

Major Groups of Plants

Nonvascular Plants (Bryophytes)

- Characteristics: Lack vascular tissue, small size, require moist environments. - Examples: Mosses, liverworts, hornworts.

Seedless Vascular Plants

- Characteristics: Possess vascular tissue (xylem and phloem), reproduce via spores. - Examples: Ferns, club mosses.

Gymnosperms

- Characteristics: Vascular plants with "naked" seeds not enclosed in an ovary. - Examples: Conifers (pines, firs).

Angiosperms

- Characteristics: Flowering plants with seeds enclosed in an ovary (fruit). - Examples: Grasses, roses, oaks.

Plant Life Cycles and Reproductive Structures

Alternation of Generations

Plants exhibit a life cycle with alternating diploid and haploid stages. - Sporophyte (2n): Produces haploid spores via meiosis. - Gametophyte (n): Produces gametes via mitosis. - Fertilization: Gametes unite to form a diploid zygote, which develops into a sporophyte.

Key Plant Reproductive Structures

- Flower: Specialized shoot for sexual reproduction in angiosperms. - Stamen: Male organ (anther + filament), produces pollen. - Carpel: Female organ (stigma, style, ovary), produces ovules. - Fruit: Mature ovary, protects seeds and aids dispersal. - Pollen grain: Male gametophyte enclosed in a protective wall.

Structure and Organization of the Plant Body

Root System and Shoot System

The plant body is organized into two main systems: - Root system: Anchors plant, absorbs water and minerals, stores food. - Shoot system: Includes stems, leaves, and flowers; supports photosynthesis and reproduction.

Major Plant Organs and Their Functions

- Roots: Absorption, anchorage, storage. - Stems: Support, transport, growth. - Leaves: Main site of photosynthesis. - Flowers: Reproduction.

Plant Tissue Types

- Dermal tissue: Protective outer layer (epidermis, cuticle). - Vascular tissue: Transport of water, minerals, and nutrients (xylem, phloem). - Ground tissue: Storage, photosynthesis, support (parenchyma, collenchyma, sclerenchyma).

Plant Cell Types and Functions

- Parenchyma: Metabolism, storage, photosynthesis. - Collenchyma: Flexible support for growing tissues. - Sclerenchyma: Rigid support, thickened by lignin. - Xylem: Water and mineral transport (tracheids, vessel elements). - Phloem: Sugar and organic nutrient transport (sieve-tube elements).

Resource Acquisition, Nutrition, and Transport in Plants

Essential Minerals and Resources

Plants require various minerals and resources for growth. - Macronutrients: Needed in large amounts (N, P, K, Ca, Mg, S). - Micronutrients: Needed in small amounts (Fe, Mn, Zn, Cu, Mo, B, Cl, Ni).

Adaptations for Resource Acquisition

- Root hairs: Increase surface area for absorption. - Mycorrhizae: Symbiotic fungi enhance nutrient uptake. - Cation exchange: Roots release H+ ions to displace mineral cations from soil particles.

Role of Bacteria and Fungi in Plant Nutrition

- Nitrogen fixation: Bacteria convert atmospheric N2 to ammonia (NH3), usable by plants. - Nodules: Structures on legume roots housing nitrogen-fixing bacteria. - Mycorrhizae: Fungi form mutualistic relationships with roots, aiding mineral uptake.

Angiosperm Reproduction and Life Cycle

Major Steps of Angiosperm Reproduction

- Pollination: Transfer of pollen to stigma. - Pollen tube formation: Delivers sperm to ovule. - Double fertilization: One sperm fertilizes egg (zygote), another forms endosperm. - Seed development: Embryo and endosperm form within seed coat. - Fruit formation: Ovary matures into fruit, aiding seed dispersal.

Stages of Angiosperm Life Cycle

- Flower formation - Pollination and fertilization - Seed development - Fruit maturation

Abiotic vs. Biotic Pollination

- Abiotic: Pollination by wind or water. - Biotic: Pollination by animals (insects, birds, bats).

Floral Adaptations for Pollination

- Colorful petals: Attract pollinators. - Nectar: Rewards for pollinators. - Shape and scent: Specialized for specific pollinators.

Seed Adaptations

- Seed coat: Protects embryo. - Dormancy: Allows seeds to survive unfavorable conditions.

Sexual vs. Asexual Reproduction

- Sexual: Genetic diversity, adaptation to changing environments. - Asexual: Rapid colonization, offspring genetically identical to parent.

Plant Responses to Internal and External Signals

Plant Hormones and Their Functions

- Auxin: Cell elongation, root formation, fruit growth. - Cytokinins: Stimulate cell division, delay aging, control apical dominance. - Gibberellins: Stem and leaf growth, seed germination, fruit development. - Abscisic acid (ABA): Inhibits growth, promotes dormancy, closes stomata. - Ethylene: Response to stress, fruit ripening, leaf abscission.

Triple Response to Mechanical Stress

- Slowing of stem elongation - Thickening of the stem - Curvature causing horizontal growth

Senescence, Leaf Abscission, and Fruit Ripening

- Senescence: Programmed cell death. - Leaf abscission: Shedding of leaves. - Fruit ripening: Ethylene promotes ripening.

Light Receptors and Circadian Rhythms

- Blue-light photoreceptors: Mediate phototropism and other responses. - Phytochromes: Regulate seed germination, shade avoidance, flowering. - Circadian rhythms: 24-hour cycles in plant physiology, independent of external cues.

Comparison of Monocots and Eudicots

Feature	Monocots	Eudicots
Seed leaves (cotyledons)	One	Two
Leaf venation	Parallel	Net-like
Flower parts	Multiples of 3	Multiples of 4 or 5
Vascular bundles	Scattered	Arranged in a ring
Root system	Fibrous	Taproot

Major Characteristics of Plant Groups

Group	Vascular Tissue	Seeds	Flowers
Nonvascular plants	No	No	No
Seedless vascular plants	Yes	No	No
Gymnosperms	Yes	Yes (naked)	No
Angiosperms	Yes	Yes (enclosed)	Yes

Key Terms and Definitions

• Alternation of generations: Life cycle with both multicellular diploid and haploid forms.

• Angiosperm: Flowering plant with seeds enclosed in an ovary.

• Apical meristems: Regions of cell division at plant tips.

• Carpel: Female reproductive organ of a flower.

• Conifer: Cone-bearing gymnosperm.

• Cuticle: Waxy covering preventing water loss.

• Embryophyte: Land plant with multicellular, dependent embryos.

• Flower: Specialized shoot for reproduction.

• Fruit: Mature ovary protecting seeds.

• Gametophyte: Haploid form producing gametes.

• Gymnosperm: Vascular plant with naked seeds.

• Hypha: Filament of a fungus.

• Leaves: Main photosynthetic organ.

• Lignin: Structural polymer in cell walls.

• Mycelium: Network of fungal hyphae.

• Mycorrhiza: Mutualistic association of plant roots and fungi.

• Nonvascular plant: Plant lacking vascular tissue.

• Ovary: Structure producing ovules.

• Petal: Colorful flower part attracting pollinators.

• Phloem: Tissue transporting sugars.

• Pollen grain: Male gametophyte in seed plants.

• Pollination: Transfer of pollen to ovules.

• Root: Anchors plant, absorbs water/minerals.

• Seed: Embryo with food and protective coat.

• Seedless vascular plant: Vascular plant lacking seeds.

• Sepal: Protects flower bud.

• Spore: Haploid cell for reproduction.

• Sporophyte: Diploid form producing spores.

• Sporopollenin: Durable polymer in spores.

• Stamen: Male reproductive organ.

• Stoma: Pore for gas exchange.

• Vascular plant: Plant with vascular tissue.

• Vascular tissue: Transport system in plants.

• Xylem: Tissue transporting water/minerals.

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