Plant Adaptations and Life Cycles

Flashcards covering key vocabulary related to plant adaptations for life on land, plant life cycles (alternation of generations), and characteristics of nonvascular plants, based on the provided lecture notes.

Vascular System (Plants)

A system of pipes in plants that provides structural support and facilitates the circulation of materials throughout the body, essential for living on land.

Challenges of Living on Land (for Plants)

Include scarcity of water, lack of structural support, intense UV radiation, and difficulty for flagellated sperm to achieve fertilization in dry environments.

Opportunities of Living on Land (for Plants)

Include unfiltered sunlight (photosynthetically active wavelengths), increased access to carbon dioxide, rich soil resources for nutrients, and abundant available space.

Cuticle

A waxy, water-resistant substance secreted by the outer layer of plant cells, serving as an ancestral adaptation in all land plants to prevent water loss (drying out).

Stomata (Stoma, singular)

Openings or pores on the surface of most plants, flanked by two guard cells, that can open and close to regulate air exchange (for photosynthesis) and water loss.

Flavonoids

Chemical compounds in plants that absorb UV light, protecting the plant's DNA from damaging effects of intense UV radiation on land.

Ancestral Condition for Early Land Plants

Small body size, allowing for simple diffusion of water and materials without a complex circulatory system, a characteristic seen in early diverging plant groups like mosses.

Sporangia (Sporangium, singular)

Multicellular structures or containers in plants where spores are produced, offering a protective environment for spore development on land.

Sporopollenin

A durable, water-resistant polymer that coats plant spores, protecting them from desiccation and allowing them to remain dormant until favorable conditions arise.

Gametangia (Gametangium, singular)

Multicellular structures in plants that protect and produce gametes.

Archegonia (Archegonium, singular)

Female gametangia that produce and contain a single egg cell.

Antheridia (Antheridium, singular)

Male gametangia that produce and release numerous flagellated sperm.

Multicellular Embryos (Embryophytes)

A defining characteristic of land plants, where the embryo is multicellular, initially dependent on, and protected by the parent gametophyte, receiving resources.

Alternation of Generations

The life cycle unique to plants, involving a regular alternation between a multicellular haploid gametophyte stage and a multicellular diploid sporophyte stage.

Gametophyte

The multicellular haploid (n) stage in the plant life cycle that produces haploid gametes (egg and sperm) by mitosis.

Sporophyte

The multicellular diploid (2n) stage in the plant life cycle that produces haploid spores by meiosis.

Numerical Advantage of Multicellular Diploid Stage

An evolutionary adaptation where a plant zygote undergoes mitosis to produce a multicellular sporophyte before meiosis, significantly increasing the number of spores produced from a single fertilization event.

Spores (Plant Life Cycle)

Haploid (n) single cells produced by meiosis within the sporophyte, coated in sporopollenin, that can germinate and grow into new gametophytes via mitosis.

Gametes (Plant Life Cycle)

Haploid (n) cells (egg and sperm) produced by the gametophyte through mitosis, which fuse during fertilization to form a diploid zygote.

Gametophyte-Dominant Life Cycle

A life cycle characteristic of nonvascular plants where the gametophyte stage is larger, longer-lived, and the sporophyte is physically dependent on it for nutrients and support.

Nonvascular Plants

A paraphyletic group of early-diverging land plants (liverworts, hornworts, mosses) that lack a true vascular system, limiting their size and requiring reliance on diffusion for transport.

Paraphyletic Group

A taxonomic group that includes an ancestral species and some, but not all, of its descendants (e.g., nonvascular plants as a group excluding vascular plants).

Protonema (Protonemata, plural)

The initial, two-dimensional, filamentous growth structure produced when a haploid spore of a nonvascular plant germinates, eventually developing into a mature gametophyte.

Rhizoids

Hair-like filamentous structures (not true roots) found in nonvascular plants and fern gametophytes, whose primary function is to anchor the plant to the substrate.

Liverworts (Stomata Implications)

A lineage of nonvascular plants that possess simple pores for gas exchange but lack guard cells, meaning their pores cannot close, making them highly susceptible to dry conditions and often restricting them to moist, sprawling habitats.

Fertilization Dependence (Nonvascular Plants)

Due to flagellated sperm, nonvascular plants require a film of environmental water (e.g., rain, dew) for sperm to swim to the egg, making reproduction reliant on moist conditions.

Gamete Production by Mitosis (in Plants)

In the plant life cycle, haploid gametophytes produce haploid gametes directly through the process of mitosis, rather than meiosis.