Unit 5: Plants - Vocabulary Review

## Evolution of Land Plants

1.a) Phylogenetic Tree & Evolution:

• Plants evolved from green algae called charophytes; Molecular and structural comparisons have identified charophytes as the closest living relatives of land plants. Examples include Coleochaete and Chara.

• Phylogenetic trees are constructed using DNA evidence and shared traits, illustrating evolutionary relationships.

- Evolutionary sequence: mosses -> ferns -> gymnosperms -> angiosperms; This progression marks key adaptations to terrestrial environments.

1.b) Features of Plant Groups:

• Bryophytes:

  • Lack vascular tissue, restricting their size and habitat range; Examples: mosses, liverworts, and hornworts.

  • Gametophyte-dominant life cycle, with the sporophyte dependent on the gametophyte for nutrition.

• Ferns:

  • Possess vascular tissue (xylem and phloem), enabling larger size and more efficient transport.

  • Lack seeds, reproducing via spores; Example: Polypodium (common fern).

  • Sporophyte-dominant life cycle, with the gametophyte reduced in size.

• Gymnosperms:

  • Have seeds and cones, protecting the embryo and aiding dispersal; Examples: conifers, cycads, and ginkgos.

  • Lack flowers and fruits, which limits their reproductive strategies compared to angiosperms.

• Angiosperms:

  • Possess flowers and fruits, enhancing pollination and seed dispersal; Represent the most diverse and abundant plant group.

- Undergo double fertilization, a unique process where one sperm fertilizes the egg, and another fuses with polar nuclei to form the endosperm.

1.c) Alternation of Generations:

• Plants alternate between a haploid (gametophyte) and a diploid (sporophyte) phase; This alternation is a defining feature of plant life cycles.

• Evolutionary trend: shift from gametophyte to sporophyte dominance; This shift reflects adaptation to terrestrial conditions, with the sporophyte better suited for structural support and protection.

## Transport in Plants

2.a) Key Terms:

• Xylem: Vascular tissue that transports water and minerals from roots to aerial parts of the plant.

• Phloem: Vascular tissue that transports sugars (produced during photosynthesis) from source to sink tissues.

• Transpiration: Evaporation of water from plant leaves, creating a tension that pulls water up the xylem.

• Cohesion-tension model: Explanation of how water moves up the xylem, driven by transpiration, cohesion, and adhesion.

• Pressure-flow model: Explanation of how sugars move through the phloem, driven by differences in turgor pressure between source and sink.

- Root pressure: Upward force of water in xylem due to water entering roots, particularly at night when transpiration is low.

2.b) Xylem vs Phloem:

• Xylem:

  • Transports water and minerals; Essential for hydration and nutrient distribution.

  • Unidirectional transport (upward); From roots to leaves.

  • Composed of dead cells; Provides structural support and efficient water flow.

• Phloem:

  • Transports sugars; Supplies energy to non-photosynthetic parts of the plant.

  • Bidirectional transport; Allows movement of sugars to various sinks as needed.

- Composed of living cells; Requires metabolic energy for active transport.

2.c) Cohesion-Tension Model:

• Water is pulled upward through the xylem due to transpiration; Evaporation from stomata drives this process.

- Cohesion (water molecules sticking to each other) and adhesion (water molecules sticking to xylem walls) are crucial; These properties maintain a continuous water column.

2.d) Pressure-Flow Model:

• Sugars are actively loaded into the phloem; Typically in the form of sucrose.

• Water follows, increasing pressure; Turgor pressure increases in the phloem.

- This pressure drives the flow of sugars to areas of need; Sugars move from source (e.g., leaves) to sink (e.g., roots, fruits).

2.e) Leaf Structures:

• Stomata: Pores for gas exchange; Regulate CO_2 uptake and water vapor release.

• Cuticle: Waxy layer that reduces water loss; Provides a barrier against evaporation.

• Mesophyll: Tissue where photosynthesis occurs; Contains chloroplast-rich cells.

• Veins: Contain xylem and phloem for transport; Provide structural support and facilitate efficient transport.

## Plant Reproduction

3.a) Key Terms:

• Alternation of generations: Life cycle alternating between haploid and diploid phases; Characteristic of all plants and some algae.

• Sporophyte: Diploid, spore-producing phase; Undergoes meiosis to produce haploid spores.

• Gametophyte: Haploid, gamete-producing phase; Produces gametes via mitosis.

• Diploid: Having two sets of chromosomes (2n); Result of fertilization.

• Haploid: Having one set of chromosomes (n); Produced by meiosis.

• Stamen: Male reproductive structure in flowers; Composed of anther and filament.

• Pistil: Female reproductive structure in flowers; Composed of stigma, style, and ovary.

• Ovary: Structure containing ovules; Develops into fruit after fertilization.

• Style: Stalk connecting stigma to ovary; Facilitates pollen tube growth.

• Ovules: Structures that develop into seeds after fertilization; Contain the embryo sac.

• Anther: Part of the stamen that produces pollen; Contains microsporangia.

• Pollen: Contains the male gametes; Carried by wind, water, or pollinators.

• Sepals: Protective leaves enclosing the flower bud; Collectively called the calyx.

• Petals: Often colorful part of the flower that attracts pollinators; Collectively called the corolla.

• Pollination: Transfer of pollen to the stigma; Can be self-pollination or cross-pollination.

- Endosperm: Nutritive tissue in seeds; Provides nourishment to the developing embryo.

3.b) Evolution of Reproduction:

- Trend: Shift from water-dependent fertilization to seed and pollen-based mechanisms; This adaptation allowed plants to colonize drier environments.

3.c) Flowering Plants:

• Pollination -> Fertilization -> Zygote -> Embryo

• Double fertilization: One sperm fertilizes the egg (zygote), and another sperm fuses with two polar nuclei forming the endosperm; This process is unique to angiosperms.

Summary & Big Ideas

• Plants adapted from aquatic to terrestrial life through vascular and reproductive adaptations; These adaptations allowed them to thrive in diverse habitats.

• Alternation of generations is central to plant

## Evolution of Land Plants

Dicots vs. Monocots

Dicots and monocots differ in their petal arrangement: dicots typically have petals in multiples of four or five, while monocots usually have petals in multiples of three.