Lab 5 - Observing Plants, part 1 (Exam 3 Unit 3)

What is a rhizoid?

A rhizoid is a very small hairlike structure at the bottom of the plant. Rhizoids are often so small that they are only composed of 1-2 cells. They help the plant anchor itself to surfaces. Although they can absorb some water, they are a poor source of water uptake and do not function the same as modern roots.

What is a Rhizome? How does it compare to a rhizoid? What are roots?

A rhizome is a lateral growth structure capable of propagating new stems and roots from it. Rhizomes can grow above or beneath the soil. This is in stark contrast to the similarly named rhizoids seen in primitive non-vascular plants as single-celled anchoring structures. True roots are vascularized and are capable of advanced water uptake into the vascular system.

Synapomorphic traits shared among all terrestrial Embryophytes (and that are not observed in the ancestral algaes)

Alternation of generations (haplodiplontic) life cycle Growth occurs at the tips in regions called apical meristems Optimized photosynthetic pigments for terrestrial life ☼ UV-shielding pigments to prevent DNA damage ☼ Waxy cuticle to prevent water loss through dermal tissues ☼ Stomata with guard cells (not seen in liverworts) ☼ Mutualisms with mycorrhizal fungi to improve water uptake ☼ Enclosed gametes inside multicellular gametangia ☼ Internal fertilization and enclosed embryos ☼ Enclosed, multicellular sporangia

What "unifying traits" define all members of Kingdom Plantae?

An embryophyte - also known as a land plant or terrestrial plant - is a photoautotroph (photosynthetic) organism. They are non-motile, multi-cellular eukaryotes. Their cell walls contain the carbohydrate cellulose which provides structure and protection against lysis.

Two prefixes are often used to describe male and female plant structures, "arche-" and "anthe." Which prefix applies to male structures, and which applies to female structures?

Arche-anything refers to the female structures. You can remember that Joan of Arc was a female if that helps. Anthe-anything refers to the male structures. My husband suggested remembering Ant-Man from the Marvel comics to remember this prefix.

What was Earth like prior to the evolution of terrestrial land plants? How did plants change the planet?

Before terrestrial plants, Earth was a rocky, barren wasteland So inhospitable, most life was restricted to the Oceans Terrestrial Earth in the Cambrian period had: No shade No soils, only rock Poor water retention Only habitable to the most hardy microbiota Plants and fungi are responsible for terraforming Earth Making it habitable for animals

What phase of the life cycle (sporophyte or gametophyte) is dominant in the vascular plants? Why?

The sporophyte dominates in all vascular plants including the seedless vascular plants, the gymnosperms, and the angiosperms. It is considered dominant because the sporophyte is the larger life phase and the phase that is recognized as being the plant. For example, if you look at a tree, and you recognize it as a tree, you are looking at the sporophyte). The gametophyte grows within the sporophyte and must be nourished by the sporophyte.

What is the sporophyte? What is the gametophyte?

The sporophyte is the mature plant phase responsible for asexually producing spores through the process of meiosis. The sporophyte is the diploid phase of the cycle. In vascular plants, the diploid sporophyte is the dominant life phase. The gametophyte is the mature plant phase responsible for producing gametes used in sexual recombination. The gametophyte and the gametes are haploid. The fusion of the haploid gametes produces a diploid zygote. In non-vascular plants, the gametophyte is the dominant life phase.

Of the four phyla of seedless vascular plants, which is the only group to have true fibrous roots, rhizoids, stems, and megaphyll leaves?

The true ferns are the most advanced of the seedless vascular plants and have all of those structures.

What are tracheids? What evolutionary trend did they cause?

The vascular tissue is composed of a new cell type called the tracheid cell. Tracheid cells function in transport of water and nutrients, but they also provide a considerable amount of structure within the plant. Because of this increased structure, plants grew taller and taller and competed for sunlight. In a short time span, plants like ferns quickly grew into tall, tree-like structures and formed dense forested areas.

Roughly how tall/large is the average moss?

They vary in size, but the average is under 15cm

Which adaptations are intended to help prevent desiccation in terrestrial habitats?

UV-shielding pigments to prevent DNA damage ☼ Waxy cuticle to prevent water loss through dermal tissues ☼ Stomata with guard cells (not seen in liverworts) ☼ Mutualisms with mycorrhizal fungi to improve water uptake ☼ Enclosed gametes inside multicellular gametangia ☼ Internal fertilization and enclosed embryos ☼ Enclosed, multicellular sporangia

What trait evolves in the seedless vascular plants that is not observed in their ancestors (the non- vascular plants)?

Vascular tissues evolve. The xylem is a vascular tissue for carrying water from the soil up to the top of the plant. Since it draws water and nutrients up, this tissue is single-directional and only allows for an upward flow. The phloem is an omnidirectional vascular tissue that allows for the transport of sugars produced during photosynthesis to other parts of the plant such as the roots.

What environmental conditions are required for successful transfer of gametes during sexual reproduction in non-vascular plants?

Water is required. Since non-vascular plants are restricted to damp environments, water is almost always present. A rain event in a dryer climate can also serve as a water source that leads to a sudden release of gametes in hopes of fertilization.

Is reproduction in the seedless vascular plants still water-dependent? Why or why not?

Yes, all seedless vascular plants have flagellated sperm cells which must swim from the antheridium to the archegonium. This can only be accomplished in a wet environment or after a rain event.

Primitive traits seen only in Charophycean green algae (the ancestors/outgroup to the land plants)

Called charophytes, charophyceans, or stoneworts Obligate aquatic organism, typically freshwater near streams and ponds Capable of surviving only brief periods of desiccation No turgor pressure; cannot stand upright out of the water

Triassic and Jurassic Periods (250mya)

Domination of Gymnosperms

What is the function or outcome of fertilization in all life cycle diagrams?

Fertilization implies the fusion of compatible gametes, which are typically haploid. The fusion of haploid gametes produces a diploid zygote or embryo.

Ordovician Period (480mya)

First terrestrial non-vascular plants

Silurian Period (450mya)

First vascular plants

When is the plant in a sexual phase? When is the plant in an asexual phase?

Generally, the gametophyte is the sexual phase that allows for sexual recombination of gametes. The asexual phase is the sporophyte phase, which produces a large quantity of identical spores from a sporangium.

What do the terms haploid and diploid mean?

Haploid means the cells in the organism have one copy of each chromosome. Diploid means the cells contain two copies of each chromosome.

Which groups of seedless vascular plants are homosporous? Which are heterosporous?

Homosporous: Lycophyta (club mosses), Psilophyta (whisk ferns), Equisetophyta (horsetails), Pterophyta (true ferns) Heterosporous: Lycophyta (spike mosses and quillworts) Note: All non-vascular plants are homosporous and all seed-bearing plants (gymnosperms and angiosperms) are heterosporous. Only the seedless vascular plants are a mixed group.

Devonian Period (420mya)

Large forests of ferns and woody trees

Which four taxa are seedless vascular embryophytes?

Lycophyta (club mosses) Psilotophyta (whisk ferns) Pteridophyta (ferns) Equisetophyta (horsetails)

What do the prefixes "mega" and "micro" mean when applied to plant reproductive structures?

Mega refers to female structures, like the megasporangium or megastrobilus. Micro refers to male structures, like the microsporangium and microstrobilus.

What is the function or outcome of meiosis in all life cycles?

Meiosis is a process that divides the chromosome number in half. Typically, this means taking a diploid cell and, though a cell division process, producing multiple haploid cells.

Do non-vascular plants have roots or leaves?

No, these structures are not present in the non-vascular plants. Water enters the plant through all parts of its body including its "leaflets" or thallus and its rhizoids. Photosynthetic tissue is spread out in all the green parts of the plant.

Plesiomorphic traits shared between Charophycean green algae and the terrestrial Embryophytes

Non-motile, multicellular eukaryotes Capable of photosynthesis; contain chloroplasts with chlorophyll pigments Cell walls are made of cellulose by structures in the plasma membrane Cell-to-cell junctions called plasmodesmata ☼ Sporopollenin coating on their reproductive spores Flagellated sperm cells Shared nuclear, chloroplast, and mitochondrial DNA

What major events occurred in the history of the evolution of plants, and when did each event occur in Earth's history (both period and rough date)?

Ordovician Period (480mya) - First terrestrial non-vascular plants Silurian Period (450mya) - First vascular plants Devonian Period (420mya) - Large forests of ferns and woody trees Carboniferous Period (350mya) - Rapid radiations of all plants - So many plants on Earth; When they died, they formed fossil fuel deposits Triassic and Jurassic Periods (250mya) - Domination of Gymnosperms Cretaceous Period (150mya) - Rise of the Angiosperms, including grasses

Which three taxa are non-vascular embryophytes?

Phylum Hepatophyta (Liverworts) Phylum Anthocerophyta (Hornworts) Phylum Bryophyta (Mosses)

Carboniferous Period (350mya)

Rapid radiations of all plants. - So many plants on Earth; When they died, they formed fossil fuel deposits.

Cretaceous Period (150mya)

Rise of the Angiosperms, including grasses

In the context of biology, what is sex? What is reproduction? What is the difference between sexual and asexual reproduction?

Sex is any process that increases genetic variation. Reproduction is any process that creates offspring. The two acts can occur separately, with a sexual process not leading to the production of offspring, or the production of offspring not requiring sexual recombination. Asexual reproduction produces offspring that are genetically identical to the parent. Sexual reproduction produces offspring that are genetically diverse/different from the parents.

Roughly how tall/large is the average hornwort?

Sporophyte is around 5cm tall

Roughly how tall/large is the average liverwort?

Thallus is less than 10cm

Where would fertilization and the growth of the sporophyte occur in a non-vascular plant?

The egg is fertilized inside the archegonium, where it develops into a zygote/embryo and ultimately produces the sporophyte. The sporophyte grows directly from the archegonial head and obtains nutrients from the female gametophyte.

What phase of the life cycle (sporophyte or gametophyte) is dominant in non-vascular plants? Why?

The gametophyte dominates in the non-vascular plants. It is considered dominant because it is larger, and because the sporophyte must grow off of or out of it and receive nutrition from it.

Of the three clades of non-vascular plants, which one is the most likely outgroup (with the closest shared common ancestry) to the seedless vascular plants?

The hornworts (Anthocerophyta) are the most likely ancestor to the seedless vascular plants like the ancient Cooksonia and Rhynia species.