Topic in Plants: Reproduction, Life Cycles, and Plant Evolution

Comprehensive flashcards covering plant evolution, ploidy levels, alternation of generations, heterospory, floral anatomy, double fertilization, and seed dispersal mechanisms.

What is the evolutionary sequence of plant groups outlined in the study notes?

Green algae $\rightarrow$ land plants $\rightarrow$ bryophytes $\rightarrow$ vascular plants $\rightarrow$ seed plants $\rightarrow$ gymnosperms $\rightarrow$ angiosperms.

How are haploid and diploid ploidy levels defined?

Haploid ($n$) means having one set of chromosomes, whereas diploid ($2n$) means having two sets of chromosomes.

What are the two multicellular stages involved in plant alternation of generations?

The gametophyte stage ($n$) and the sporophyte stage ($2n$).

What is the complete sequence of steps in the plant alternation of generations life cycle?

Sporophyte ($2n$) $\rightarrow$ meiosis $\rightarrow$ Spores ($n$) $\rightarrow$ mitosis $\rightarrow$ Gametophyte ($n$) $\rightarrow$ mitosis $\rightarrow$ Gametes ($n$) $\rightarrow$ fertilization $\rightarrow$ Zygote ($2n$) $\rightarrow$ mitosis $\rightarrow$ Sporophyte ($2n$).

Why do gametophytes produce gametes through mitosis rather than meiosis?

Because the gametophyte is already haploid ($n$), undergoing mitosis ($n \rightarrow n$) allows it to produce $n$ sperm and $n$ eggs without changing the chromosome number.

How do spores and gametes differ in their production and function?

A spore ($n$) is produced by meiosis and grows into a gametophyte, whereas a gamete ($n$) is produced by mitosis in a gametophyte and must fuse with another gamete.

How does the life cycle of green algae differ from that of land plants?

Green algae lack a multicellular diploid phase (only the zygote is $2n$), and their dominant stage is the haploid gametophyte.

What are the main features of the gametophyte and sporophyte stages in bryophytes?

Bryophytes have a large, free-living gametophyte and a small sporophyte that stays attached to and depends on the gametophyte.

What are the specific definitions of sporangium, antheridium, and archegonium?

Sporangium is where meiosis produces spores, antheridium is the male reproductive structure producing sperm, and archegonium is the female reproductive structure producing eggs.

How do the gametophyte and sporophyte stages change in vascular plants compared to bryophytes?

In vascular plants, the gametophyte becomes smaller while the sporophyte becomes larger and more dominant.

Do seedless vascular plants like ferns require water for reproduction?

Yes, seedless vascular plants like ferns have a dominant $2n$ sporophyte, but they still require water for reproduction.

What is heterospory, and what two types of spores does it produce?

Heterospory is the production of two distinct types of spores: microspores (which become male gametophytes) and megaspores (which become female gametophytes).

How did heterospory contribute to the evolution of the seed and ovule?

Instead of releasing the megaspore into the environment, the plant retains and protects the female gametophyte inside the sporophyte, forming the ovule which eventually becomes the seed.

Why are gymnosperms independent of water for reproduction?

Gymnosperms use pollen grains and pollen tubes to deliver sperm directly to the female reproductive structure.

What is an angiosperm, and what is the primary role of a flower?

An angiosperm is a flowering plant with modified stems and leaves, where the flower serves as a reproductive structure designed to help the plant reproduce.

What are the functions of sepals and petals in flower structure?

Sepals (typically green) protect the flower bud, whereas petals (often colorful) help attract pollinators.

What components make up the stamen, and what occurs inside the anther?

The stamen consists of the anther and filament; inside the anther, microsporangia undergo meiosis to produce microspores, which develop into pollen grains.

What structural components make up the carpel or pistil?

The carpel/pistil consists of the stigma (receives pollen), style (path for the pollen tube), and ovary (contains ovules).

What is the cellular and nuclear composition of the female gametophyte inside an angiosperm ovule?

The female gametophyte inside the ovule has 7 cells containing 8 nuclei total, with one cell containing the egg and another containing two polar nuclei.

What is a pollen grain in angiosperms, and how many cells does it contain?

A pollen grain is a male gametophyte containing 3 cells, including 2 sperm cells.

What is the difference between pollination and fertilization?

Pollination is strictly the transfer and placement of pollen onto the stigma, whereas fertilization is the fusion of sperm with the egg and polar nuclei.

What events occur after pollen is deposited on the stigma before fertilization takes place?

The pollen grain germinates, grows a pollen tube down through the style, and carries 2 sperm cells toward the ovule.

What occurs during double fertilization in angiosperms?

Sperm #1 fuses with the egg to form a diploid zygote ($2n$) that becomes the embryo, while Sperm #2 fuses with two polar nuclei to form triploid endosperm ($3n$).

What is the primary function of the endosperm in an angiosperm seed?

Its job is to provide nutrition for the developing seed.

What are the key ploidies of the embryo, endosperm, and seed coat in an angiosperm?

Embryo is diploid ($2n$), endosperm is triploid ($3n$), and the seed coat is maternal sporophyte tissue.

What tissues and ploidies are found in a gymnosperm seed?

A gymnosperm seed contains an embryo that is $2n$ and female gametophyte tissue that is $n$.

What structures do the ovule and ovary develop into after fertilization?

The ovule becomes the seed, and the ovary becomes the fruit.

How do flowers facilitate pollination and prevent self-fertilization?

Flowers offer nectar, pollen, rewards, or trickery to attract insect pollinators; plants prevent self-fertilization using mechanisms such as having separate male and female structures or individuals.

What is the distinction between self-pollination and cross-pollination?

Self-pollination occurs when pollen comes from the same plant, whereas cross-pollination occurs when pollen comes from another plant.

How are seeds dispersed away from the parent plant?

Seeds are dispersed by wind, water, or animals, with some seeds having hooks, barbs, spines, hairs, or sticky coverings that attach to animals.