Sign In | Subscribe
Start learning today, and be successful in your academic & professional career. Start Today!
Loading video...
This is a quick preview of the lesson. For full access, please Log In or Sign up.
For more information, please see full course syllabus of AP Biology
  • Discussion

  • Study Guides

  • Download Lecture Slides

  • Table of Contents

  • Transcription

  • Related Books & Services

Bookmark and Share
Lecture Comments (3)

0 answers

Post by morgan franke on May 13, 2015

Can you help me identify what some analogies are between plants and fungi reproductive cycles? fungi and animals? and animals and plants?

1 answer

Last reply by: Dr Carleen Eaton
Tue Mar 25, 2014 3:12 PM

Post by JASON YUEN on February 27, 2014

THANK YOU SO MUCH ~


You are very Good

Fungi

  • Fungi are unicellular or multicellular eukaryotes with cell walls containing chitin.
  • Multicellular fungi are composed of microscopic thread-like structures called hyphae. Adjacent cells are separated from each other by septa. Coenocytic fungi lack septa and are multinucleated. Groups of hyphae form a mycelium, which is a visible structure.
  • Fungi play an important role in the environment. As decomposers, they break down organic materials, releasing the organic components for reuse.
  • Certain fungi form mycorrhizae in association with the roots of plants. This symbiotic relationship provides the plant with increased surface area for the absorption of water and minerals and provides the fungus with a source of carbohydrates.
  • Lichen are the result of a symbiotic relationship between fungi and either cyanobacteria or green algae. Lichen can survive in extreme conditions and are one of the first colonizers of a new area.
  • Plasmogamy is the fusion of the cytoplasm of two cells, without fusion of the two nuclei. Karyogamy is the fusion of the nuclei and may occur long after plasmogamy in fungi.

Fungi

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Introduction to Fungi 0:09
    • Introduction to Fungi
    • Mycologist
    • Examples of Fungi
    • Hyphae, Mycelia, Chitin, and Coencytic Fungi
    • Ancestral Protists
  • Role of Fungi in the Environment 5:35
    • Fungi as Decomposers
    • Mycorrrhiza
    • Lichen
  • Life Cycle of Fungi 11:32
    • Asexual Reproduction
    • Sexual Reproduction & Dikaryotic Cell
  • Chytridiomycota 18:12
    • Phylum Chytridiomycota
    • Zoospores
  • Zygomycota 19:07
    • Coenocytic & Zygomycota Life Cycle
  • Basidiomycota 24:27
    • Basidiomycota Overview
    • Basidiomycota Life Cycle
  • Ascomycota 28:00
    • Ascomycota Overview
    • Ascomycota Reproduction
  • Example 1: Fungi Fill in the Blank 31:02
  • Example 2: Name Two Roles Played by Fungi in the Environment 32:09
  • Example 3: Difference Between Diploid Cell and Dikaryon Cell 33:42
  • Example 4: Phylum of Fungi, Flagellated Spore, Coencytic 34:36

Transcription: Fungi

Welcome to Educator.com.0000

We are continuing on our discussion of the diversity of life with the kingdom Fungi.0002

Fungi are unicellular or multicellular eukaryotic organisms. Therefore, they have a nucleus and membrane-bound organelles.0011

Well, most of them are multicellular. As I mentioned, there are unicellular fungi, and these are called yeast.0022

Fungi are actually more closely related to animals than they are to plants.0029

Another term you should be familiar with is mycology or mycologist. Mycologists are scientists who study fungi.0034

Just to talk about some examples of different groups of fungi, you are familiar with these probably from day to day life.0047

For example baker's yeast is used in cooking and is the component that allows bread to rise. Mushrooms that you see around are produced by some fungi.0054

They are actually the fruiting body of certain groups of fungi, and certain species of mushrooms are edible.0066

Actually, fungi may also be parasites, and they can cause diseases in both humans and in plants.0073

There have been some species of trees that have actually been almost completely wiped out by fungal infections.0080

For humans, Candida albicans is a type of yeast that lives in humans.0088

The majority of humans are actually colonized with Candida, and it does not bother a person unless it overgrows.0098

And if it over grows, it can cause an infection called thrush, and this shows up for example in the mouth as whitish plaques, whitish areas.0105

These types of infections are more common in individuals who are immunosuppressed.0115

It could be because they are in chemotherapy, or they have an underlying illness such as HIV.0119

Or sometimes when people are in antibiotics, it changes the balance of the flora in the body and allows the yeast to overgrow.0125

Another example of a fungus is mold.0133

Molds that you see on old food that has been sitting out too long like bread, that is another example of a fungus.0136

Talking about the structure of a fungus, fungi are composed of hyphae - singular is hypha - that sort of intertwine together to form mycelia.0143

Singular is mycelium.0161

Here is shown the structure of a hyphae, and what you see in this example is septa - here, singular, septum - separating these out into individual cells.0163

Now, a hypha is a microscopic structure. It is a microscopic thread-like structure.0177

It can be branched as shown, and here, is an example of a septated hypha. However, there are some groups of fungus that have unseptated hyphae.0186

This would just be essentially one large cytoplasmic mass with many nuclei, so multinucleated.0199

If there are no septa separating out an area of cytoplasm with a nucleus into individual cells, then, we call that type of fungus coenocytic.0207

Coenocytic fungi lack septums between the individual cells. Another attribute of fungi is that they have cell walls that contain chitin.0223

Recall that the cell walls in plants contain cellulose, so this is a different substance. This is a carbohydrate chitin.0241

As I mentioned, hyphae are microscopic, but they interweave together.0252

They grow, and various hyphae weave together to form what is called mycelia or mycelium. One would be a mycelium.0258

This is a structure that is visible with the naked eye, so hypha is microscopic. A mycelium would actually be visible.0268

If you look at a piece of moldy bread or moldy fruit, what you are seeing are the mycelia.0276

Fungi are heterotrophs, and they obtain nutrition through absorption, so digestion occurs externally.0285

What the fungi do is they secrete digestive enzymes, and they break down the nutrients externally and then, absorb them.0292

Fungi are believed to have evolved from a unicellular protist ancestor that lived in aquatic environments and had flagella.0301

So, an ancestral protist, and it lived in an aquatic environment; and it had flagella.0310

Well, some members of a phylum that we are going to discuss in a minute - Chytridiomycota - have a part of their life stage that includes flagella.0320

Most fungi are unflagellated.0331

The next thing that we are going to talk about before talking about individual phyla of fungi are the role of fungi in the environment.0337

Many fungi are decomposers, and this is extremely important because by breaking down dead plants,0344

they release the organic compounds in those plants so that they can be reused or recycled.0349

When we talk about plants, we are going to talk about lignin and cellulose, both components of plants, and these are very hard to breakdown.0355

However, fungus are able to break these down and, again, allow the organic components that would, otherwise, just be trapped in those plants to be used.0365

So, that is one role that fungus plays in the environment. A second role involves structures called mycorrhiza.0376

Some plants, many plants, actually, and fungi form a symbiotic relationship, and this is called a mycorrhiza.0386

You are maybe familiar with the word symbiosis or symbiotic.0395

And this means a relationship between two or more organisms in which they live closely together, so they have a close relationship to one another.0398

Some of these relationships are mutually beneficial, and we call these mutualistic. Mycorrhizae represent a mutualistic relationship.0408

What happens is that certain fungi have a special type of hyphae that extends over the root surface of plants and partly into the root.0420

It is specifically a relationship between fungi and the root of plants.0430

In order for this to be mutualistic, there has to be a benefit for both organisms.0436

What is the benefit for the fungus? Well, the fungus gets nutrients from the plant.0440

It actually takes carbohydrates from the plant root.0452

We are talking about mycorrhiza, which represents a mutualistic relationship, and the benefit for the fungus is that it gets the nutrients from the plants.0456

What is the benefit for the plant? Well, the plant has increased absorption of water and minerals as the result of the mycorrhiza.0470

These hyphae are essentially extending the surface area of the plant root, and that allows for more effective absorption of water and minerals.0491

And in fact, over 90% of plants have mycorrhiza associated with them.0499

Experiments have been done determining how well plant grows with mycorrhiza versus another same type of plant without mycorrhiza.0505

And those plants that have the mycorrhiza associated with them grow much better.0515

This is a second benefit that fungi have in the environment that they increase the growth of plants.0520

And that, in turn, allows for food sources and habitats for other organisms.0528

Finally, we are going to talk about lichen. Lichen represents another symbiotic relationship.0533

This time, it is a symbiosis between a fungus and cyanobacteria or a fungus and green algae.0539

Both cyanobacteria and green algae are photosynthetic, and you may have seen lichen.0547

If you go into the woods, and you look on trees or rocks you can see lichen.0554

And with lichen, the fungi is actually layered on top, so now, we are talking about lichen.0559

So, the fungus is layered on top of the cyanobacteria or green algae, and we have cyanobacteria or green algae below.0569

The fungus provides protection for this lower layer of bacteria or green algae, so they are protected by the overlying fungus.0590

This helps the lower layer of organisms to retain water.0605

They are less likely to become desiccated, to dry out, and also, it allows them to more easily obtain minerals.0610

Just as with the mycorrhiza, the benefit to the fungus is that it can obtain nutrients.0618

It can obtain carbohydrates from the bacteria or green algae that are below.0627

One reason that lichen are very important to the environment is because they can live in extreme environments.0635

And they are often the first or very early colonizers of a habitat.0641

They can survive for long periods of time without water. They can live on rocks, even on the side of buildings.0645

If they colonize an area early on, they can break down the substrate such as a rock that they are on.0650

And that eventually makes the area that they are in, the habitat, more suitable for other organisms.0656

There will be an early settler. They will breakdown the substrate, and then, other plants and eventually animals and other organisms can settle that area.0664

However, lichen are particularly vulnerable to pollution.0673

Now that we have talked some general traits of fungi and their role in the environment, we are going to talk about the generalized fungus life cycle,0679

and then, focus on the life cycles of a few of the major phyla of fungi.0687

Again, this is just a generalized life cycle, so the details vary for different groups.0694

But what you see here is that there is possible asexual reproduction as well as sexual reproduction.0699

Asexual reproduction is very common, and most fungi reproduce this way. However, some have a more complex life cycle.0707

And they may have a life cycle were they usually reproduce asexually.0715

But in conditions where the environment is harsh, it is unfavorable to survival, they might switch over to sexual reproduction.0721

And this is similar to what we saw with some groups of protist.0729

And we will talk in a minute about why it can be beneficial to switch to sexual reproduction for survival.0731

Before we focus on this, let's talk a little bit more about yeast. Yeast are unicellular fungi, and they can reproduce asexually through budding.0739

Asexual reproduction involves budding- asexual reproduction through budding.0750

And budding, it is exactly what it sounds like that there is a smaller cell that will bud off the larger parent cell to reproduce an identical offspring.0762

Other types of asexual reproduction in fungi that we are going to talk about involves spores.0776

And that is what you see here. That hyphae form a mycelium.0783

Structures on that mycelium release spores. These spores germinate to produce hyphae and then, a mycelium.0788

Over here, there are a couple of aspects that I want to point out regarding the sexual reproduction of fungus.0797

Let's say that a fungus switches over to reproducing sexually, then, what will happen is two compatible mating types will join through plasmogamy.0805

When I say compatible mating types, this would be a plus and a minus.0819

We do not say male and female with fungi because although, there are biochemical differences between the two mating types,0825

there is not morphological differences, so we just say plus and minus, OK?0833

So, a plus and a minus, the two different mating types join. These spores join through plasmogamy.0837

This joining, though, involves fusion of the cell membranes, so with plasmogamy, the cell membranes fuse.0847

The nuclei remain separate, and that is what this term is all about- dikaryotic.0858

A dikaryotic cell is a cell that has two nuclei, and it is two separate nuclei.0864

Here, before these two fuse, you have two different cells. They are each haploid.0872

With sexual reproduction, you get two separate haploid cells, so they have one set of chromosomes.0881

This other cell has one set of chromosomes, then, they fuse.0887

Normally, what ends up happening is you end up with a diploid cell, a single nucleus with two sets of chromosomes.0890

That is not what happens here. It is a single cell with two nuclei, and what we say, then, is that this is a dikaryon or dikaryotic.0897

It is n + n.0906

So, if you had two different cells with nuclei, and they undergo a plasmogamy, now, we have one cell with two nuclei; and it is a dikaryon.0909

The fungus can exist in this dikaryotic stage for a long time- months, even years or decades.0924

During that time, the hyphae will continue to grow. The cells will divide.0932

The two nuclei will also divide. They will not fuse.0937

They will just divide, and the daughter cell will also have two nuclei; and that can go on for a long time.0941

Eventually, there will be, maybe a trigger for the two nuclei to fuse, and that process of the fusion of the nuclei is called karyogamy.0946

So, that is fusion of the nuclei, whereas, plasmogamy is just fusion of the cell membranes or fusion of the plasma membranes.0957

Once karyogamy occurs then, the cell is diploid. It is 2n.0969

We have haploid which is just n. We have dikaryotic, which is n + n because there are two sets of chromosomes, but they are in separate nuclei.0975

And then, when those two nuclei fuse, the cell becomes diploid. In fungi, the diploid stage is usually very brief.0984

We have a diploid zygote, and shortly, thereafter, usually meiosis occurs; and that is going to return the cells to their haploid state.0992

So, now that meiosis has occurred, this is back to being a haploid cell.1003

Hyphae will grow. Spores will be produced by these cells.1009

Excuse me. Meiosis will occur and produce spores.1015

Meiosis will occur, and this produces haploid spores. Those haploid spores will germinate and form hyphae and mycelium.1018

Hyphae of two different mating types can undergo plasmogamy.1026

And sexual reproduction or the mycelium may produce spores and reproduction continues on asexually.1030

So, these are some of the highlights of the fungal life cycle.1038

And we are going to go on now and just talk about some of the major phyla or as they are sometimes called divisions of fungi and their life cycles.1042

I want to note now, that the groupings that I am going to discuss, you may see, are slightly different in another source, another text,1049

because as with the protist, the molecular evidence points us in a different direction as far as categorizing organisms1059

and evolutionary relationships than morphological or life cycle data that we should use to originally categorize them.1067

Originally, many fungus were put into groups based on similarities of life cycle.1076

But these do not always align with what DNA sequencing and molecular evidence show us about their evolutionary relationships.1081

The first group we are going to cover are members of the phylum Chytridiomycota. These groups of fungus are among the oldest.1092

I mentioned before that fungi are believed to have descended from an ancestral protist that was flagellated.1102

And in fact, members of this group do have flagella during part of their life cycle, and they live primarily in aquatic environments.1110

So, you just need to know the basics about this group.1124

And now, we are going to go on and talk about some groups of fungus that have evolved more recently.1126

The other thing to know about this or just to keep in mind is that the name of these flagellated spores are zoospores, so these are spores with flagella.1131

The next group we are going to talk about are members of the phylum Zygomycota.1149

You are probably already familiar with members of this group because the mold that you see on breads and fruits that have sat out too long1154

especially if they are in a warm environment, and they start getting, kind of, fuzzy, those are mostly members of this phylum.1162

The hyphae of Zygomycota, these members are coenocytic.1170

Remember that coenocytic refers to the fact that there are no septa separating out the nuclei in the hyphae.1178

So, what you just end up with is a big cytoplasmic mass with many nuclei.1191

I also want to note that for those organisms, fungi, that have septa separating them out into individual cells,1198

they are actually pores in the cell wall so that nutrients and even organelles can pass from cell to cell.1207

Anyways, Zygomycota are coenocytic, and we are going to look at their life cycle.1215

As you can see here, they can reproduce both asexually and sexually, so right down here, this is asexual reproduction.1220

This occurs via haploid spores.1236

Hyphae that are part of the mycelium release haploid spores and these are all identical. They are genetically identical.1240

The spores germinate and form new hyphae, which interweave into larger mycelia.1249

The Zygomycota could go along, reproduce asexually, and it is going to stay in this haploid part of the life cycle.1260

However, it is possible for sexual reproduction to occur.1269

Sporangia is a structure where the spores develop, and we could get sporangia forming spores.1273

And those spores can go on through this asexual reproduction cycle, or the other possibility is that we get two different mating types.1282

I talked to you about hyphae that have two different mating types: plus and minus.1298

Those hyphae can undergo plasmogamy where their cell membranes fuse, and the result is a dikaryon, so it is a hyphae that has two unfused nuclei.1303

There can actually be more than two nuclei in a cell sometimes, and that is called a heterokaryon.1318

This dikaryon that results from plasmogamy is called a zygosporangium.1334

And this is the dikaryotic structure resulting from plasmogamy of two compatible mating types.1343

Now, zygosporangium have very thick tough walls.1350

And this helps to explain why the fungus would exit this asexual reproduction cycle and start reproducing sexually.1354

Let's say that it is very dry. The environment becomes dry.1364

There is not enough rain, and the fungus is, then, threatened. Its survival is threatened1368

What it can do is switch over to sexual reproduction and end up forming zygosporangia,1376

which have this tough wall and will allow for survival until conditions are better.1382

Once condition is improved, karyogamy is triggered.1387

So, if it starts to rain again, or there are more nutrients around, and conditions are favorable to survival again, karyogamy will be triggered.1391

At this point, the two nuclei fuse, so the nuclei fuse.1399

This cell is, then, diploid, so the zygote is diploid.1408

Shortly, thereafter, meiosis will occur, and haploid spores will eventually grow into hyphae that can, again,1416

be of two mating types and then, undergo sexual reproduction or produce spores and just continue to reproduce asexually.1429

The spores that we are talking about are called zygospores. It is the specific name for them.1441

Alright, so important points here are just understanding that there is three different phases.1450

One is the dikaryotic phase. The other is the diploid phase, which tends to be short.1454

The other is the haploid phase.1458

Also, that reproduction can occur asexually or sexually, and that sexual reproduction is a means to allow for survival under difficult conditions.1460

The next phylum we are going to discuss is the phylum Basidiomycota.1468

These are also referred to as club fungi because of the shape of spore-producing cells known as basidia, so the basidia are club-shaped.1472

These include many types of fungi that you may be familiar with such as mushrooms and puffballs.1486

Some members of this group are decomposers. Others are plant parasites known as rusts, and still, others form mycorrhiza.1492

When you see a mushroom, what you are looking at is actually the fruiting body of the fungus.1501

A lot of the fungus structure lies within the ground absorbing nutrients, growing outward as it seeks more nutrients, water and minerals.1506

But above the ground, pops up these mushrooms that are important for the reproduction of the fungus.1517

Just to talk about the structure of a mushroom or basidiocarp, that is the formal name, but these are actually known usually as mushrooms.1524

Here, we have what is called either the stock or the stipe - I will just write stock here- and the cap.1540

The cap protects cells on the underside called basidia, so that is where the basidia are located, and spores are formed within the basidia.1547

The basidia are actually located within what is called gills, so on the underside of the cap are gills; and then, within the gills are the basidia.1562

Looking at the life cycle, if you start out, again, we can have asexual or sexual reproduction.1573

Here is the asexual reproduction where hyphae form spores which germinate, form more hyphae and mycelia, again, forming spores, and that goes on.1579

However, if conditions are unfavorable to survival, hyphae of two compatible mating types can undergo plasmogamy.1588

Again, during plasmogamy, the cell membranes fuse, and now, you have a hypha that is a dikaryon: n + n. It has unfused nuclei.1597

Here is where the mushrooms come in.1613

When the environment returns to better conditions, so let's say that there was not enough water,1614

there was not enough nutrients, and now conditions are favorable again, that will trigger the formation of mushrooms.1620

So, the hyphae will grow into these structures above ground, and you will see mushrooms pop up.1630

The basidia located here on the underside of the cap will fuse during karyogamy, so the basidia fuse, and now, what we have is a cell that is diploid.1637

These undergo meiosis returning them into their haploid state.1655

Spores can be produced. Spores are produced from this, haploid spores.1663

They grow into hyphae, and then, asexual reproduction can occur or sexual reproduction.1667

Again, this is a mechanism for survival in harsh conditions.1674

Ascomycota is a very large and diverse phylum. There are over 60,000 species that are members of this phylum.1681

They are sometimes called the sac fungi because of the sac-shaped structure called an ascus.1689

So, there is a structure called an ascus that is a site of the production of sexual spores.1698

Members of this group include decomposers such as morels as well as some plant parasites.1705

The first antibiotic discovered was penicillin, and that is actually produced by a mold that is a member of this group.1711

Some species of Ascomycota also are part of the association that forms lichen along with photosynthetic bacteria or green algae.1720

Again, we see the two possibilities for reproduction.1730

Mycelia with hyphae of opposite mating types can fuse.1736

Their cell membranes can fuse to form a dikaryon, and an ascus forms on the hyphae where this process has taken place.1741

The two hyphae of opposite mating types undergo plasmogamy, and then, an ascus is formed.1753

So, the ascus is part of this dikaryotic structure.1761

The nuclei inside the ascus undergo karyogamy, so those nuclei fuse to from a diploid zygote, which undergoes meiosis.1766

This is going to produce four nuclei that are haploid, so you are going to end up with four haploid nuclei.1779

This is followed by a round of mitosis, so meiosis followed by - let's put this right here - mitosis.1788

So, we had four haploid nuclei. Mitosis occurs, and then, that is going to result in 8 haploid nuclei.1796

Cell walls are going to grow to separate out the nuclei so that there is only one nuclei per cell, and each nuclei will end up as part of a haploid spore.1802

So, for each cell that undergoes meiosis, the result is going to be 8 haploid spores, and these are called ascospores.1816

These spores are released and undergo germination, form hyphae, and sexual reproduction could occur or asexual reproduction.1829

You will note this term down here- conidia. These are actually pigmented haploid spores.1839

So, asexual reproduction involves conidia, which are just pigmented spores, so it is a slightly different term.1847

OK, so that covers the material for this lecture, and what we are going to do now is go over some examples.1855

In the first example, example one, fill in the blanks with the correct terms below.1863

Recall, and when I talk about the structure of fungi, I said that the cell walls do not contain cellulose like plants.1872

In fact, they contain chitin, which is a carbohydrate.1878

Two: hyphae become interwoven to form a visible mass called a, well, singular would be mycelium, so to form a mycelium.1885

No. 3: blank is the process of fusion of haploid hyphae without fusion of their nuclei.1898

So, with just the cell membranes fused, remember that that process is called plasmogamy.1903

Finally, hyphae found in the symbiotic association with the roots of plants are known as mycorrhiza, so chitin, mycelium, plasmogamy and mycorrhiza.1913

Example two: name two roles played by fungi in the environment. There are more than two roles, but you are just asked to name two.1930

Well, one is that they function as decomposers, and this allows for recycling of organic materials.1937

So, they breakdown dead plants.1945

And allow those organic materials to enter back into the cycle and be used by other organisms, so recycle organic materials.1947

The second is that they can form mycorrhiza. They are one component of mycorrhiza.1962

And this is important because mycorrhiza allow plants to grow much more effectively.1972

They increase the surface area available for absorption of water and minerals, and plants that have mycorrhiza grow taller.1978

They grow faster. They grow better than the plants that do not.1987

Finally, they are a component of lichen.1993

And remember that lichen is an association between a fungus and cyanobacteria1996

or fungus and green algae and that these are early colonizers of a new environment.2001

They are also capable of settling in very harsh environments since they can go without water for a long time.2008

They can set the stage for other organisms to settle.2014

So, you only had to name two, but here is three.2018

Example three: describe the difference between a cell that is diploid and one that is a dikaryon.2022

Recall that diploid who we often say as 2n, and that means that there are two sets of chromosomes in the nucleus.2030

So, a cell possesses two set of chromosomes.2045

A dikaryon also has two sets of chromosomes, but they are not within a single nucleus.2049

So, there are two separate nuclei each with a set of chromosomes.2054

Example four: some members of which phylum of fungi have flagellated spores?2077

So, we went over four phyla today, and remember the most primitive group or the earliest of evolved group are the Chytridiomycota.2084

And they have some remnants of their ancestry in the form of flagellated spores.2097

Members of which phylum of fungi are coenocytic meaning that they do not have septa between the various nuclei in the hyphae?2104

Well, that is the phylum Zygomycota.2113

That was the final example and concludes this lesson of Educator.com.2119

Thanks for visiting.2123