Biology 121 Lab 4

All members of the kingdom Plantae are united by these following features:

1) an alternation of generations life cycle, 2) gametangia and sporangia with multicellular walls, and 3) embryos nourished and protected by a gametophyte. The multicellular walls are an adaptation to prevent the embryos and reproductive cells from desiccation.

Describe each process of the transition to land- step 1.

1) prevent of desiccation. The outermost layer of plant cells, the epidermis, secretes a waxy covering called the cuticle which prevents water loss. Since the early plants lacked leaves, photosynthesis was accomplished by the stem. The cuticle prevents gas exchange necessary for photosynthesis from occurring; therefore, specialized structures called stomata (minute pores) developed along the length of the stem. Stomata allow the exchange of gases necessary for photosynthesis.

Step 2.

2) absorption of water and inorganic nutrients. Since the earliest plants lacked roots, water was absorbed by hairlike extensions called rhizoids borne on the horizontal stem (rhizomes).

Step 3.

3) transport of water and nutrients. All vascular plants possess specialized conducting tissue which transport water, minerals, and sugars to all parts of the plant body. Conducting tissue called xylem transport water and dissolved minerals, whereas phloem transports sugars.

Step 4.

4) support. Plants evolved from algae, which are aquatic. Both green algae and plants have cell walls made of cellulose. In certain types of vascular plants there is an additional thick cell wall which is composed of a very tough polymer called lignin which provides support to the plant body.

Step 5.

5) dispersal. The spores of all plants are produced in sporangia with multicellular walls. Plant spores are covered in an extremely tough, decay-resistant polymer called sporopollenin. Sporopollunin is the most resistant polymer known and is nearly indestructible to microbial attacks. This tough outer covering on spores protects them from damage and desiccation and enables them to survive dispersal through the air. It is interesting to note that charophycean algae do possess sporopollenin on the walls of their zygotes (but not their spores)

What are the two types of stems in Lycopodium?

Aerial (upright) stem- clothed with small green leaves and bears a cone (or strobilus) at its apex. The leaves are called microphylls (typically small leaves that have a single, unbranched vein) and are unique to the Lycopodiophyta. Rhizome- horizontal stem which grows underground.

Why are mosses important?

Among the first organism to colonize newly exposed soil, where they contribute to organic soil development and prevent erosion. They are sensitive to atmospheric pollution and are used as indicators of pollution levels.

What was the earliest known vascular plant?

An extinct plant called Cooksonia. Small, dichotomously-branching plant.

How does asexually reproduction occur?

Can also occur by fragmentation, with small pieces of gametophytes breaking off to produce entire new gametophytes.

What is a major adaptation for Polytrichum?

The spores are small and light and therefore well adapted for wind dispersal. Because the sporophyte stalk is elongate, the spores are released well above the gametophyte where they are exposed to more air currents. If a spore lands on a suitable substrate, it germinates and grows to produce a haploid gametophyte.

Describe a gametophyte and attached sporophyte of Polytrichum.

The sporophyte arises from the gametophyte as a long stalk with a single sporangium, called a capsule, at its apex. Within the capsule, cells undergo meiosis to produce haploid spores. If your specimen has an immature sporangium, it will be covered with a protective, hair cep called the calyptra, which is composed of old, dry archegonial tissue. The calyptra is shred when the sporangium is mature. The apex of the sporangium has a lid or operculum which protects the entrance to the spore-producing region, until the spores are mature.

Describe the alternation of generations life cycle.

The sporophyte is dominant, most conspicuous stage in the life cycle of vascular plants and the gametophyte is inconspicuous and short-lived.

Describe how Polypodium grow?

The stems called rhizomes grow horizontally along or understand the ground. Only their large leaves grow upright. Polypodium was named for its branching rhizomes.

What is the function of the sterile hairs?

The sterile hairs retain water, which functions to prevent desiccation of the antheridia. The antheridia and sterile hairs are surrounded by protective leaves that partially enclose the stem tip.

Why are Bryophytes restricted to moist habitats?

They have few structural adaptations to withstand drought and are dependent on water for fertilization.

Describe the prepared slide of a longitudinal section of a female gametophyte of Mnium with archegonia.

This gametophyte is narrower with two or three long, flask-shaped, multicellular archegonia surrounded by sterile hairs. The archegonia and sterile hairs are surrounded by protective leaves. Each archegonium has a long, narrow neck and a swollen base containing a single, haploid, non-motile egg cell.

What does the conducting tissue do in vascular plants?

Transports water, minerals and sugars to all parts of the plant body.

Describe the alternation of generations cycle in Polytrichum.

Two multicellular generations: the haploid generation called the gametophyte because its produces gametes, and the diploid generation called the sporophyte because it produces spores. The dominant, most conspicuous stage in the life cycle of all bryophytes, including Polytrichum, is the gametophyte.

Describe the phylum Lycopodiophyta (club mosses)

Vascular plants. Inhabit forests floors in temperate regions, grow as epiphytes (a plant which grows on another plant) on trees in tropical forests.

What are tracheids?

Vascular tissue contains specialized thick-walled, water-conducting cells called tracheids, which are part of xylem tissue. Vascular plants are also called tracheophytes. Also contain specialized food-conducting cells called sieve elements, which are part of phloem tissue.

What are nonvascular plants?

Commonly called bryophytes and include mosses (Bryophyta), liverworts (Hepatophyta), and hornworts (Anthocerophyta). They lack tissue (the specialized conducting tissue which transports sugars, water, and minerals throughout the plant body) possessed by all other phyla of the kingdom Plantae. They diverged early. They remained small in size and restricted to moist habitats.

What does the rhizome function in?

Functions in asexual reproduction by producing new aerial stems at regular intervals, allowing the plant to spread horizontally across the forest floor. The rhizome bears scale-like leaves and roots.

What type of liquid do you put on top of your sample of a sorus?

Glycerine.

Describe Lycopodium.

Has an alternation of generations life cycle with a dominant sporophyte generation. Depending on the species, the tiny gametophytes are either photosynthetic and grow above ground, or are non-photosynthetic and subterranean.

Describe the phylum Pteridophyta.

Includes plants such as ferns, horsetails, and whisk ferns. Seedless vascular plants that have dominant sporophytes and both homosporous and heterosporous members. Depend on water for fertilization, so restricted to moist habitats. They have leaves called megaphylls which have vascular tissue in the form of extensively branched veins.

What is a sporophyte?

Inconspicuous, typically non-photosynethic at maturity, and completely dependent on the gametophyte for nourishment. It is short-lived, functioning only to produce spores.

Describe asexual reproduction in Polypodium.

Is accomplished by rhizomes. Has an alternation of generations life cycle with the sporophyte being the dominant stage. Gametophytes are tiny, green and photosynthetic.

Why is peat moss so important?

It can absorb 20 times its own weight in water therefore enhances moisture retention in garden soil.

When looking at the slide, what do you see?

It contains a central mass of flagette, haploid sperm cells (the flagella cannot be discerned on your slide), enclosed by a multicellular antheridial wall.

What happens if a spore lands in a suitable environment?

It will grow into a bisexual gametophyte. The gametophyte produces both archegonia and antheridia, which produce eggs and flagette sperm. Fertilization results in a diploid zygote which develops into an embryo, which subsequently forms a new sporophyte plant.

Describe the appearance of a gametophyte.

Leafy appearance. These plants consist of short stems with tightly-packed, poorly developed leaves. Fine hair-like rhizoid grow out and down from the stems to absorb water the anchor the plant. (These are not roots, although their function is similar). When the gametophyte is mature, the sexual structures, antheridia (male gametangia) and archegonia (female gametangia) develop at the top of the leafy gametophytes. This species is unisexual; the antheridia and archegonia are on separate gametophytes.

What organism represents the phylum Lycopodiophyta?

Lycopodium which belongs to the domain Eukarya, kingdom Plantae, phylum Lycopodiophyta, and genus Lycopodium.

Where does Polypodium live?

Mainly in the tropical forests of South and Central America, although they can be found in BC. Big ferns that often grow in large stands forming the undergrowth in boreal forests.

Who are the friends of Polytrichum?

Mnium Sphagnum Marchantia- belongs to a group of bryophytes called liverworts. They are restricted to moist areas and live in similar environments. Their gametophytes are flat and broad, not leafy like mosses. Asexual reproduction in liverworts is by little discs of gametophyte tissue (gemmae) that are produced in cups on the surface of gametophytes.

Define sporophylls.

Modified leaves that compose the cone and each sporophyll bears a single round sporangium on its upper surface.

Describe the algae Coleochaete.

Multicellular, freshwater alga, grows on the surface of submerged rocks or aquatic plants, two growth forms- branched filament or a flat thallus. Belongs to the group called charophycean algae, which shares similar features of sexual production, cell structure, and cell division.

Where does Polytrichum grow?

One of the largest species of mosses, grows in the boreal forests of Northern SK, usually on acidic soil.

Define homosporous.

Plants that produce spores of only one size that germinate into bisexual gametophytes.

Define heterosporous.

Plants that produce two types of spores called megaspores and small spores called microspores. Each spore will produce a unisexual gametophyte. Megaspores and microspores are produced in separate sporangia and germinate to form separate female and male gametophytes. Lycopodiophyta contains both homosporous (club mosses) and hetersporous members (spike mosses, quillworts)/

What is the representative organism of the phylum Pteridophyta?

Polypodium which belongs to the domain Eukarya, kingdom Plantae, phylum Pteridophyta, and genus Polypodium.

What organism represents the phylum Bryohphyta?

Polytrichum which belongs to the domain Eukarya, kingdom Plantae, phylum Bryophyta, and genus Polytrichum.

Define oogamy.

Reproduction involving flagellate sperm non-motile eggs, and is also found in the charophycean algal relatives, like Coleochaete.

Who are the friends of Polypodium?

Salvinia- aquatic fern. Floats by trapping air in the hairs on its leaves. Psilotum- not a fern, but most distant relative called a whisk fern. Unusual plant which has underground rhizomes and erect, bright green stems with no leaves. It produces yellowish sporangia on the erect stems. Equisetum- can be found in SK. Its sporophyte consists of erect stems growing up from underground rhizomes.

Describe the groups of vascular plants.

Seedless vascular plants- possess vascular tissue, better adapted to terrestrial conditions than bryophytes, they have flagellate sperm thus require water for fertilization. Although they are reliant for water to reproduce sexually, they have developed methods of asexually reproduction so they can reproduce in drier areas.

Who are the friends of Lycopodium?

Selaginella- live getersporous plant, the spike moss. The small cones are borne at the tips of the branches.

What are gametophytes?

Small, leafy plants which are photosynthetic, green, and long-lived.

What are the brown spots on the underside of the leaves called?

Sori. Each sorus is composed of a cluster of sporangia, where meiosis occurs to produce haploid spores.

What was the advantage of vascular tissue?

Terrestrial plants could now transport water and food internally and also (due to thick walls of tracheids) gave considerable physically support to the plant.

Why do mosses grow on the north side of tree trunks?

The environment is moister and cooler on the side of the trunk that receives the least sunlight.

Vascular plants had to overcome several obstacles such as:

1) prevent desiccation (drying out), 2) absorb water, 3) transport water and nutrients, 4) support themselves against gravity, 5) disperse/reproduce on dry land

Describe the phylum Bryophyta.

Commonly referred to as mosses. Small in size, inhabit moist terrestrial environments (bogs, tree trunks, along the banks of streams, etc.).

Where can Lycopodium be found?

Short plant that forms part of the undergrowth in forested areas of North America, including SK.

What happens when the flagellate sperm are mature?

They are released from the antheridium and swim through a film of water to the archegonium to fertilize the egg cell. This reliance on external water to the archegonium to fertilize the egg cell. This reliance on external water for fertilization is one of the major factors which restricts mosses to moist areas. The resulting diploid zygote divides mitotically to form a diploid embryo, which remains within the archegonium. The embryo grows upward out of the archegonium to form a diploid sporopyte, which remains permanently attached to and nourished by the gametophyte.

Know the drawings of Polytrichum.

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Know the moss life cycle diagram.

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