Chapter 26: Evolution of Land Plants

What event around 1 billion years ago contributed to the origin of land plants?

A cyanobacterium was engulfed by an early eukaryote and became a chloroplast.

What is primary endosymbiosis and its significance in plant evolution?

It led to the development of photosynthetic eukaryotes.

Which groups share chloroplasts but are not classified as plants?

Glaucophytes, red algae, and green algae.

What unique feature do glaucophytes possess in their chloroplasts?

Their chloroplast contains peptidoglycan, a characteristic of prokaryotes.

What pigment gives red algae their color?

Phycoerythrin reflects red light.

What role do some red algae play in marine ecosystems?

They produce CaCO3 and help build coral reefs.

What are the main characteristics of green algae?

They mostly contain chlorophyll, making them green, and exhibit a range of cellular arrangements (unicellular, colonial, multicellular).

When did plants move to land, and how many species are known?

Plants moved to land around 500 million years ago, with 290,000 known species.

What are the synapomorphies shared between Coleochaetophytes, Charaphytes, and land plants?

1. Retention of eggs in parental organism; 2. Possession of plasmodesmata; 3. Presence of phragmoplasts during mitosis; 4. Molecular data suggests monophyly.

What is the significance of phragmoplasts in plant cells?

They are a complex of microtubules formed between daughter nuclei during mitosis and serve as the starting point for cell plate formation during cytokinesis.

What are the two close relatives to land plants mentioned in the notes?

Chara ssp (a pond organism) and Coleochaete orbicularis (a disk-shaped charophyte).

What is an autapomorphy that distinguishes land plants from their algal relatives?

The retention of embryos within parental tissue, leading to the term 'embryophytes'.

What traits divide groups among embryophytes?

Presence of stomata, sporophyte appearance, vascular tissue, leaf type, existence of seeds, and existence of flowers.

What adaptations did land plants develop for survival on land?

1. Cuticle for water retention; 2. Stomata for gas exchange; 3. Gametangia to protect gametes from drying out.

What is the function of sporangia in land plants?

They are multicellular organs that contain spores walled with sporopollenin to prevent drying.

How do pigments in land plants help them survive in terrestrial environments?

They provide protection against the mutagenic effects of ultraviolet radiation.

What is the role of cuticles in land plants?

They provide a watertight covering for the plant's cells to retain water.

What are gametangia and their function in plants?

Multicellular organs that enclose and produce a plant's gametes, protecting them from drying out.

What is the significance of stomata in plant physiology?

They are small openings in leaves that regulate gas exchange and water loss.

What challenges did early land plants face when moving away from water?

They had to adapt to retain water and protect themselves from desiccation.

What does the term 'embryophytes' refer to?

It refers to land plants that retain embryos within parental tissue.

What is a mutualistic relationship in the context of land plants?

A mycorrhizal relationship between fungi and land plants that allows for the collection of water in terrestrial environments.

What is the alternation of generations in land plants?

A succession of multicellular haploid and diploid phases, specifically involving gametophyte (haploid) and sporophyte (diploid) generations.

What are the two multicellular generations in land plants?

Gametophyte (haploid) and sporophyte (diploid).

What is the role of the sporophyte generation in land plants?

The sporophyte generation is the multicellular diploid form that produces haploid spores by meiosis, which germinate into gametophytes.

How does the gametophyte generation develop in land plants?

The gametophyte generation is multicellular and haploid, producing haploid gametes by mitosis, which unite to form a diploid sporophyte.

What is a sporangium?

A diploid structure in the sporophyte that undergoes meiosis to produce numerous haploid spores.

What is the function of gametangia in land plants?

Gametangia are haploid structures that produce numerous haploid gametes through mitosis.

What is the male gametangium called, and what does it produce?

The male gametangium is called antheridium, which produces haploid sperm via mitosis.

What is the female gametangium called, and what does it produce?

The female gametangium is called archegonium, which produces haploid eggs via mitosis.

What are bryophytes?

nonvascular plants that are herbaceous, small, and ground-covering, requiring water for reproduction.

What are the three phyla of nonvascular plants?

1. Phylum Marchantiophyta (liverworts), 2. Phylum Bryophyta (mosses).

When did the first land plants appear?

Approximately 475 million years before present (MYBP).

What are some characteristics that form natural divisions among modern land plants?

Vascular tissue, seed presence, and flower presence.

What is the role of the sporophyte in the life cycle of land plants?

The sporophyte produces haploid spores that grow into the gametophyte generation.

What is syngamy in the context of land plants?

Syngamy, or fertilization, is the process where two haploid gametes unite to generate a diploid sporophyte.

How do nonvascular plants transport water and minerals?

Water and minerals move through dense mats of nonvascular plants via capillary action and diffusion.

What type of structure is an antheridium?

A multicellular structure that produces sperm in nonvascular plants and ferns.

What type of structure is an archegonium?

A multicellular structure that produces eggs in nonvascular land plants, ferns, and gymnosperms.

What is the significance of the alternation of generations in land plants?

It is a defining characteristic of all land plants, allowing for the transition between haploid and diploid phases.

What is the difference between the sporophyte and gametophyte generations?

The sporophyte is diploid and produces spores, while the gametophyte is haploid and produces gametes.

What is the primary reproductive requirement for nonvascular plants?

Nonvascular plants require water for reproduction.

What is the dominant stage of the life cycle in nonvascular plants?

Haploid gametophytes are the dominant stage.

What is the role of the diploid sporophyte in nonvascular plants?

present for a short period and is nutritionally dependent on the gametophyte.

What do spores from the sporophyte of nonvascular plants germinate into?

Spores germinate into a one-cell thick mass of filaments called a protonema.

How do gametophytes anchor themselves in nonvascular plants?

They are anchored by rhizoids, which are long, tubular single cells used only for anchoring.

What is a key characteristic of Phylum Marchantiophyta (Liverworts)?

Most have elevated gametophytes resembling miniature trees and can reproduce asexually via gemmae.

What is the significance of the sporophyte in Phylum Bryophyta (Mosses)?

The sporophyte grows up from the female gametophyte to gain elevation for spore dispersal.

What unique feature do mosses possess for gas exchange?

Mosses possess stomata.

What is the role of the genus Sphagnum in the ecosystem?

forms dense mats that decompose in water to create peat, which is flammable and used as fuel.

What are the two phyla of seedless vascular plants (SVPs)?

Phylum Lycophyta and Phylum Monilophyta.

What is a key synapomorphy of seedless vascular plants?

Vascular tissue capable of efficiently transporting materials over long distances.

What are the main cells in xylem responsible for transporting water and minerals?

Tracheids, which are hardened by lignin.

What does phloem transport in seedless vascular plants?

Phloem transports sugars, amino acids, and other organic products.

How did the evolution of vascular tissue affect plant height?

It allowed plants to grow taller, leading to increased competition for sunlight and spore dispersal.

What is the relationship between sporophytes and gametophytes in seedless vascular plants?

Sporophytes are branched, diploid, and independent of gametophytes for nutrition, making sporophytes the dominant stage.

What evolutionary advancement is associated with seedless vascular plants?

The evolution of true roots, which contain vascular tissue.

What is the ecological significance of peat formed from Sphagnum moss?

used as fuel and, if compressed over time, can become coal.

How do nonvascular plants differ from vascular plants in terms of size and structure?

Nonvascular plants are typically short and ground-covering, while vascular plants can grow much larger due to vascular tissue.

What is the common name of Phylum Anthocerophyta?

Hornworts.

What is a distinctive feature of hornworts?

They have a horn-like long tapered shape of the sporangium.

What type of chloroplast do hornwort cells contain?

A single, large plate-like chloroplast.

What symbiotic relationship do hornworts engage in?

They have a symbiotic relationship with nitrogen-fixing bacteria.

What are leaves in the context of vascular plants?

Flattened portions of a plant that increase surface area and perform photosynthetic functions.

What type of leaves do Lycophytes have?

Very small, spine-shaped leaves called microphylls supported by a single vascular bundle.

What type of leaves do Monilophytes have?

Larger leaves with a highly branched vascular system known as megaphylls.

What is the Phylum Lycophyta known for?

Includes club mosses, spike mosses, and quillworts, with 1,200 species, mostly small and serving as ground cover or epiphytes.

What was the size of Lycophytes during the Carboniferous period?

They were giant trees, reaching 2 meters in diameter and 40 meters tall.

What are strobili in Lycophytes?

Clusters of spore-bearing microphylls at the tip of a stem.

What is a sporophyll?

A leaf that has specialized to house sporangia.

What is the significance of Phylum Monilophyta?

Includes ferns and horsetails, which were dominant during the Carboniferous period with much more diversity and size.

How many extant members are there in Phylum Monilophyta?

12,000 extant members, mostly found in tropical regions.

What is unique about horsetails?

Once diverse, now only one genus (Equisetum) with 15 species remains, featuring jointed growth and silica deposits in stems.

What are fronds in ferns?

Megaphylls that unfurl from a structure called a fiddlehead.

Where are sori located in ferns?

On the underside of fronds, where clusters of sporangia produce spores.

What is the classic form of a fern?

The sporophyte, which houses sori under its fronds.

What is the role of gametophytes in ferns?

They have both gametangia and achieve fertilization via water.

What are sporophylls in seedless vascular plants (SVPs)?

Leaves modified to bear sporangia, with fern sporophylls resembling normal leaves but having sori.

What is a strobilus?

A cone-like structure formed by sporophylls in lycophytes and gymnosperms.

What are the two types of spore formation in SVPs?

Homosporous (one type of sporangium producing one spore) and heterosporous (two types of sporangia producing two types of spores).

What is a megaspore?

A spore produced in a megasporangium on a megasporophyll that develops into a female gametophyte.

What is a microspore?

A spore produced in a microsporangium on a microsphorphyll that develops into a male gametophyte.

What is the early condition of spore formation in SVPs?

Homosporous, where one type of sporangium produces one spore that develops into a bisexual gametophyte.

What evolutionary advancement is represented by heterospory in SVPs?

The evolution of two types of sporangia that produce two types of spores.