Major Objectives of this Lab
1. Understand the distinguishing features of fungi, algae and plants.
2. Understand the concept of Alternation of Generations in plants.
3. Identify the gametophyte and sporophyte generations in plants.
4. Determine the features that facilitate or retard the movement of plants from water to a terrestrial environment.
Fungi: Food source
- More than 100,000 species of fungi are known. Fungi, are heterotrophs and obtain their food as saprophytes or parasites
- Saprobes obtain their nutrition by breaking down and feeding on dead or decaying organic matter.
- Thus, fungi are extremely important as decomposers which recycle nutrients back into the biosphere.
- These organisms are not photosynthetic (why, then were they once classified with the plants?).
Fungi: Structure
- primarily terrestrial, filamentous and possess a cell wall made of chitin which is similar to the polysaccharide found in the exoskeletons of arthropods
- The majority of the fungi are usually composed of filaments known as hyphae (hypha = singular)
- Many hyphae, when joined together, form a mycelium (mycelia = plural)
- Mushrooms consist of densely packed hyphae.
- This filamentous form provides a high surface-to-volume ratio that greatly enhances its mode of nutrition.
Rhizopus (bread mold)
Zygomycetes
- saprophytic fungus whose mycelium grows rapidly on bread and soft fruits
- At certain times the hyphae form sporangia, containing numerous black spores which are easily spread by the wind
- These sporangia are the result of either asexual or sexual reproduction
- Rhizopus are Zygomycetes (about 600 species known) with reference to the zygospores which they produce as result of sexual reproduction.
Fungi: Sexual Structure
- Fungi are classified into four divisions ("phyla" in the animal kingdom) based on their sexual structures
1. Zygomycetes
2. Basidomycetes
3. Ascomycetes
4. Deuteromycetes
Fungi: Agaricus bisporous (common, store-bought edible mushroom)
Basidomycetes
- The mushroom is the characteristic sexual reproductive structure of the Basidomycetes (about 25,000 species known)
- The hyphae making up the mushroom are dikaryotic (n+n) and form a diffuse mat hidden from view in substrates such as soil or rotting wood
- In an open area the mycelium expands evenly in all directions and may grow as large as 100 feet in diameter
- Mushrooms usually form at the outer edges of the mycelium because this is where the freshest nutritive material is located and hence the most active growth.
- As a consequence, mushrooms may be arranged in circular formation (the so-called "fairy rings" of legend).
- Mushrooms develop very quickly, some- times overnight.
- This is possible because for a much longer period of time the hyphae were assimilating large amounts of food and producing new protoplasm underground.
Fungi: Human Pathogens
Ascomycetes
- Many skin and lung (pulmonary) diseases are caused by fungi
- vaginitis, involves infection of the mucous membrane of the female reproductive system by C. albicans. In the popular press, this disease is said to be caused by a "yeast", but in fact, what we commonly call yeast (involved in beer and bread making) belongs to an entirely different group
- these "yeasts" are members of the Ascomycetes
Fungi: Penicillium
Deuteromycete
- is a Deuteromycete which was found to produce an antibiotic which could significantly retard the growth of other living organisms such as bacteria.
- This accidental discovery by Sir Alexander Fleming in 1928 resulted in countless lives being saved.
- Many other Deuteromycetes are important as producers of antibiotics that are essential in the fight against disease pathogens.
1. Zygomycetes
- Ex. Bread mold
- Mostly reproduces asexually
- During sexual reproduction, they produce zygospores
- Zygospores - structures that develop after 2 hyphae combine and fuse their nuclei together
2. Basidomycetes
They are short-lived structures called basidiocarps
They produce spores called basidiospores on club-shaped hyphae called basidia
3. Ascomycetes
Includes:
Powdery mildews on leaves
Truffles & morels used in cooking
Single-celled yeasts
They have small finger-like sacs called asci, which they develop during sexual reproduction
4. Deuteromycetes
Only reproduce asexually
Produce spores called conidia
Is a diverse group
Ex. Penicillium (first produced penecillin)
Not Fungi: aprolegnia (the fly fungus)
- is a water mold
- This organism consists of many fine thread-like hyphae which appear as a white fuzzy growth on the body of the fly.
- Water molds have flagellated reproductive cells and are the cause of several major crop diseases, such as the mildews.
- Water molds are now part of the group known as the Stramenopiles.
Not Fungi: Slime molds
- Protista
- cool, shady, moist places in the woods on decaying logs, dead leaves and other damp organic matter
- non-reproductive stage, forms a large, multinucleate masses of streaming protoplasm known as a plasmodium (plural = plasmodia) which moves in an "amoeboid" fashion
- As the plasmodium travels, it engulfs bacteria, yeast, fungal spores and small particles of decayed animal and plant matter.
- The ability to migrate exposes the plasmodium to new feeding areas.
- Depletion of the food supply stimulates movement.
- When food is in short supply, the plasmodium creeps to an exposed location and forms several masses of protoplasm, each of which develops into a sporangium consisting of a stalk and a sporangium in which spores are borne.
- Plasmodia come in a variety of colors and can be quite beautiful. It is probable that the pigments function as photoreceptors since only pigmented plasmodia require light for spore reproduction.
Physarum, a typical slime mold
- produces two macroscopic stages:
1) the vegetative plasmodium
2) the reproductive sporangium which contains numerous spores.
- Examine the rapid protoplasmic streaming within the "veins" of the plasmodium.
- Each vein is coated with a thick sheath of slime, hence the name slime mold.
Algae
- diverse group of both unicellular and multicellular autotrophic organisms which have photosynthetic pigments
- Algae are classified in part depending on the pigments they possess
- concerned primarily with the green algae in this lab as they are the probable precursors to the land plants
Green algae
- have chlorophyll pigments which are identical to the ones found in plants
- Members of the green algae range from the microscopic to several hundred feet in length and are mostly aquatic, most are found in freshwater habitats but many are marine. A few are terrestrial.
- Some are symbiotic with lichens, protozoa and even various invertebrates
Green algae: Spirogyra
- is a microscopic and filamentous green alga common in cool ponds where some movement of water occurs.
- It has a single spiral chloroplast in each cell.
- Pyrenoids, small round structures "decorate" the chloroplast. These store starch.
Green algae: Volvox
- is a microscopic and colonial green alga.
- This group includes spectacular colonies composed of 512 to 50,000 cells.
- Each colony is motile.
- Within some of the mature colonies you may find daughter colonies which are eventually liberated to form new mature colonies.
Green algae: Ulva
- (known as sea lettuce), is a large green marine alga that is found along the Pacific coast.
- It has a sheetlike growth habit and is often found on rocks that are exposed at low tide.
- A holdfast anchors it to the substrate.
brown algae
- many of the familiar sea weeds, including the kelps
- The brown algal body (thallus) takes on a range of forms and may be highly branched
- thallus can often be subdivided into distinct regions: a holdfast, a stipe, a blade, and often a bladder.
- A bladder is an enlarged, hollow structure at the tip of a blade that allows it to float at or near the surface of the water.
- Examples of red algae (4,000 species, mostly marine) include the "sea weed" that is used for making sushi.
Not algae: Blue-green algae (cyanobacteria)
- autotrophic bacteria which are prokaryotes
- Prokaryotes have no nuclear membrane and thus lack a defined nucleus
- They possess chlorophyll and evolve oxygen via photosynthesis although their pigments are not bounded by membranes into organelles like chloroplasts
- formation of our oxygen atmosphere; evolution of organisms having aerobic respiration
- serial endosymbiosis
Symbiotic relationship: Lichen (between fungi and certain green algae or cyanobacteria)
- The fungus is usually an Ascomycete.
- Because of this symbiotic relationship, lichens are able to inhabit some of the harshest environments on earth.
- However, they are particularly sensitive to toxic compounds in the atmosphere. Thus they are natural indicators of polluted air.
Characteristics of Land Pants
- waterproof waxy cuticle layer that protects against desiccation
- a layer of sterile (non-reproductive) cells protects the gamete producing cells (and embryo) of plants from drying out
- Plants also have stomata (absent in liverworts and some mosses) that control the loss of water that result from necessary gaseous exchange for photosynthesis and respiration
- Plants also share some features with their progenitors, the green algae in having chloroplast, food storage as starch and cell walls of cellulose
Classifying Land Plants
- morphology, anatomy, cytology, biochemistry, physiology and life cycle pattern
- fossil evidence is also used
Major trends in life cycles as one moves from the "primitive" to the "advanced" plants
- Many of the trends involve the transition from life in an aquatic to a terrestrial environment.
- Examples of these trends include a waxy waterproof cuticle, the development of spores with their protective walls to tolerate dry conditions, conducting systems for the transport of water and food and the development of seeds to protect the embryo.
Spore vs Gamete
Spore: Spores are units of asexual reproduction
Gamete: gametes are units of sexual reproduction, as two gametes need to fuse to create a new organism.
a sporophyte vs a gametophyte
sporophyte: Among organisms which display an alternation of generations (such as plants, fungi, and certain algae), the individual diploid organism that produces spores. A sporophyte develops from an embryo resulting from the union of two gametes. Each of its cells has two sets of chromosomes, as opposed to the haploid gametophyte generation.
gametophyte: Among organisms which display an alternation of generations as part of their life cycle (such as plants and certain algae), the haploid organism that produces gametes. Each of its cells has only one, unpaired set of chromosomes, as opposed to the corresponding diploid form of the organism, called the sporophyte. A gametophyte develops from spores produced by the sporophyte. The gametophytes of homosporous plants are bisexual (produce both eggs and sperm), while the gametophytes of heterosporous plants, such as all seeds plants, are unisexual (produce only eggs or only sperm)
Alternation of Generations
- Complete life cycle showing Alternation of Generations. All plants will exhibit these phases but the diploid and haploid phases may vary in duration in different plant groups.
Bryophyte: Liverwort (Marchantia)
- Note the prominent midrib and the way the flat body (thallus) branches (known as dichotomous branching) in Marchantia
- On top of each "umbrella" (antheridiophore) sperm are produced, and under the arms of the other "umbrella" (archegoniophore) an egg is formed.
- Water carries the sperm to the egg, and following fertilization, a new sporophyte develops (attached to the underside of the arm of the archegoniophore).
Moss Life cycle
- In a representative moss life cycle (below), spores are released from a capsule, which opens when a small lid (operculum) bursts.
- The spore germinates to form a branched, filamentous protonema, from which a leafy gametophyte develops.
- Sperm, which are expelled from the mature antheridium, are attracted into the archegonium, where one fuses with the egg cell to produce the zygote.
- The zygote divides mitotically to form the sporophyte
Bryophyte
- is considered to have retained many features of the first plants to move from the water onto the land
- All these plants are small, and are usually found in an environment either periodically or permanently moist
- The Bryophytes are usually divided into
three divisions: the liverworts (6,500 species), the hornworts (100 species), and the mosses (12,000 species)
- what is the gametophyte and what is the sporophyte, and which is dominant?
Bryophyte: peat moss
is probably the most important economically, forming vast peat bogs which are "harvested" and used for fuel