Week 6 - Fungi and Intro to Animals

Week 6

Fungi & Intro to Animals

BIO182 - 29460 • Spring 2026 Dr. Rivera, CGCC

Learning Objectives

At the end of this week students should be able to,

• explain and identify the structures of a fungal cell.
• explain and draw the sexual life cycle of a fungus and compare and contrast the life cycle to the life cycles of plants and animals.
• name the five phyla of fungi, identify their main characteristics, and name examples.
• explain the ecological roles that different fungi have in the environment.
• provide examples of how humans use fungi.
• provide examples of fungal diseases that affect both plants and animals.
• identify the derived characteristics of animals.
• explain how the types of symmetry, tissue layers, body cavities, and zygote development are used to classify animals. Students will be expected to apply this knowledge to animal groups learned in subsequent chapters

Unikonts

Unikonts are diverse, containing animals, fungi, and many protists

Fungi Overview

• Diverse group of organisms
• ~150,000 species, but estimates over over 1 million

Fungi Characteristics

• Heterotrophic eukaryotes
• Can be single-celled (yeasts) or multicellular
• Reproduce with spores (unprotected embryos)
• The cell wall consists of complex carbohydrates, including chitin (which is also found in arthropod exoskeletons)

Fungal Body Plans

• Multicellular fungi (majority) form threadlike hyphae, collectively called mycelium
• Hyphae can have no barriers or cell walls with perforations; either way allows nutrients to flow across the individual
• Can grow on or through a variety of materials

Largest organism a fungus (Armillaria solidipes) in Oregon (*in terms of estimated biomass)

Fungi Nutrition

• Heterotrophs, but don’t ingest their food items
• They excrete enzymes to digest their food items, breaking them down to core components and then absorbing those smaller molecules through their cells
• Many are decomposers, breaking down hard-to-digest compounds like cellulose and lignin into glucose

Fungi Reproduction

• Most fungi reproduce by means of microscopic, nonmotile* spores which are formed in structures called sporangia
• The spores are dispersed by wind, water, or animals
• Spores are produced asexually (yeasts), or sexually on specialized aerial hyphae or in fruiting structures such as mushrooms
• When a spore germinates, it gives rise to a hypha, which then develops into a mycelium.
• Asexual reproduction via budding (in yeasts and single celled fungi) or when pieces of hyphae break apart (in multicellular fungi)

Fungi Sexual Reproduction

• Hyphae of two genetically compatible mating types come together and their cytoplasm fuses.
• Plasmogamy The two nuclei do not fuse together forming a cell that is Dikaryotic (n + n)
• Under the right conditions, Karyogamy (fusion of nuclei) occurs forming a diploid (2n) zygote nucleus.

Fungi Ecology

• Found almost everywhere, dominate in the dark
• Major decomposers – break down organic material
• Requires water to transfer molecules, decomposition much higher in moister environments
• Form frequent and successful symbiotic relationships, such as with algae and cyanobacteria as lichens, mycorrhizae and plant roots
• Some are parasites and pathogens that cause disease in animals or plants

Fungi Classification

• Systematists now view fungi as more closely related to animals than to plants
• Genetic and structural similarities support grouping fungi with choanoflagellates and animals in the Opisthokonta clade
• Five Phylum

• About 95% of named fungi are assigned to phyla Ascomycota and Basidiomycota
• *We will focus on the 3 major phyla (chytridiomycota, ascomycota, and basidiomycota)

Chytridiomycota

• Mostly unicellular, few multicellular
• Have flagella, a hair-like cellular protrusion which allow for movement in water, like other non-fungi protists
• Their spores also have flagella and can move, typically within water
• Chytrid fungus of amphibians

Chytridiomycota - Bd

• Batrachochytrium dendrobatidis (Bd.) – species of chytrid fungi that causes chytridiomycosis in amphibians
• Infects skin cells, reduces gas and water exchange; high mortality

Ascomycota

• The majority of fungi,
• Diverse multicellular forms create a sac that contains their spores (ascus, asci)
• Contains the yeasts, powdery mildews, most molds, cup fungi, several edible species, and some parasites
• Economically/societally important species
• Yeasts
• Truffles
• Penicillin

Ascomycota - Yeasts

• Single-celled Ascomycota
• Saccharomyces cerevisiae – brewers' yeast
• Yeasts are of huge importance to humans,
• Fermentation
• Disease - thrush
• Molecular factories
• Model organism

Ascomycota - Cordyceps

• Genus of parasitic ascomycete fungi, many endoparasites (internal parasite) of arthropods
• Spores land on host, and enter the body
• Hyphae grow and digests host tissue, producing ascocarp (fruiting body) which grows outside the host’s body to release spores
• Often alter host behavior to increase spore dispersal

Zygomycota

• Most are decomposers; some form symbiotic mycorrhizae; a few cause disease in plants and animals
• The Zygomycetes are named for their sexually produced zygosporangia
• Ex. Rhizopus stolonifer, bread mold

Glomeromycota

• Symbionts that form mycorrhizae with the roots of most trees and herbaceous plants
• Roots supply the fungus with organic nutrients; fungus provides the plant with nutrient minerals
• Hyphae may grow directly into the plant cells to faciliate exchange of nutrients

Basidiomycota

• Form club-shaped fruiting bodies called basidia,
• Decomposers, mycorrhizae, pathogens
• Mushroom contain basidia to distribute spores
• Gill fungi – gill like structures under the caps
• Shelf fungi – grow off trees
• Smuts/rusts
• Most edible fungi are basidiomycete, some produce toxins

Fungi as Symbiotic Partners - Mycorrhizae

• Mycorrhizae – symbiotic mutualistic associations between roots and fungi.
• Ectomycorrhiza - fungi grows in root tissue but not inside cells
• Endomycorrhiza - fungal hyphae grow into cells!
• The fungi increase surface area for uptake of water and nutrients; the plants supply the fungi with carbohydrates.
• This relationship improves plant growth and survival in a wide range of habitats.

Fungi as Symbiotic Partners - Lichen

• Lichens – obligate mutualistic symbiotic association between a fungus and photosynthesizer (algae or cyanobacteria)
• Usually Ascomycota or Basidiomycota
• Fungi provides protection, photosynthesizer provides energy
• Disperse together via soredia a group of algae cells surrounded by lichen
• Sensitive to pollutants, used to monitor environmental health.

Fungi as Symbiotic Partners - Fungus Growing Ants

• Ants harvest leaves to feed to fungus to decompose, ants clean/mantain the fungal "garden"
• Fungus provides nutrients
• New queens disperse with piece of fungus to start new garden

Fungi as Pathogens

Fungi can cause serious diseases in humans, other animals and plants

• Athletes foot
• Valley Fever
• Ringworm
• Chestnut blight
• White nose syndrome (bats)

Characteristics of Animals

1. Multicellular eukaryotes
2. Heterotrophic
3. Have specialized body cells
4. Divers, but mostly fixed body plans
5. Most are capable of locomotion at some time during their life cycle.
6. Most have nervous systems and muscle systems
7. Most are diploid organisms that reproduce sexually
8. Most animals go through a period of embryonic development

Animal Diversity

• Animals are incredibly diverse and very well-studied
• >2 million species described
• An estimated 99% of all animal species that ever inhabited our planet are extinct.
• Taxonomists assign extant animals to about 35 phyla.
• Molecular studies confirm that many phyla are monophyletic.

Animal Evolution

• The ancestor of animals had more than 1500 genes not found in other eukaryotes
• The structure of genes that control development, RNA, and other molecules are similar among all animal groups
• Similarities between the feeding cells of sponges (choanocytes) and choanoflagellate protists have been used to suggest that animals evolved from a common ancestral organism that resembled the modern colonial choanoflagellates.

Evolution of Animals - Molecular Systematics

• Changes in animal body plan are linked to changes in patterns of embryonic development.

• The same basic set of genes (HOX genes) are used in a similar fashion to control early development in all animal groups.
• “Evo Devo” compares molecular events in various animal groups, such as gene regulation during development.
• Note how Hox gene expression, as indicated with various colors, occurs in the same body segments in the animals

Evolution of Animals - Fossil Record

• Molecular data indicate that most animal clades diverged over a very long period (2.5 bya to 542 mya).
• Animal phyla that first left fossils during the Cambrian radiation may have evolved several hundred million years before they appear in the fossil record.
• Animals evolved in the ocean and then moved to land

Animal Classification

• Animals are referred to as Metazoan
• Animals with true tissues are Eumetazoa
• Animals without true tissues are the Parazoa (sponges)
• Four traits are used to classify animals into groups:
• Type of symmetry
• Tissue Development
• Type of body cavity and presence of a coelom
• Embryonic development

Body Symmetry

Radial Symmetry - arranged as spokes from a central axis (Cnidarians, Ctenophora) Bilateral Symmetry - Animals can be divided through only one plane to produce right and left halves that are mirror images. Cephalization: the development of a head where sensory structures are concentrated.

Body Symmetry - Echinoderms

What's going on with Echinoderms (sea stars, urchins) Pentaradial Symmetry - A type of radial symmetry in which an organism can be divided into five equal parts. Echinoderms have bilateral symmetry as larvae and pentaradial as adults, like snakes being part of the quadrupeds they evolved changes to a defining characteristic

Tissues

• Tissues - groups of closely associated, similar cells that work together to carry out specific functions
• Germ layers - cell layers formed in early development of all animals, except sponges, that develop into specific types of tissues
• Ectoderm – gives rise to the tissues that form the outer covering of the body as well as to nervous tissue
• Endoderm - forms the lining of the digestive tube and other digestive structures.
• Mesoderm - gives rise to most other body structures, including muscles, skeletal structures, and organ tissues

Tissue Development

• Diploblastic - Have only two germ tissue layers: ectoderm and endoderm; Cnidarians and ctenophores
• Triploblastic - All animals with bilateral symmetry are triploblastic; Echinoderms are triploblastic - Have all three germ layers

Mesoderm is what forms the coelom or internal body cavity (see next few slides)

Body Cavity

• Evolution of the coelom provided a space where internal organs could develop and function.
• Tube-within-a-tube body plan—the coelom separates the body wall (outer tube) from the digestive (inner tube).
• Acoelomates have no body cavity; Phylum Platyhelminthes
• Pseudocoelomates have a body cavity that is not completely lined with mesoderm; Animals in Phylum Nematoda
• True coelomates have a body cavity that is completely lined with mesoderm.

Embryonic Development

• The zygote undergoes cleavage (cell division) and develops into a blastula.
• Gastrulation - the process where the hollow sphere of cells (blastula) is reorganized into 2 or 3 layered embryo (Gastrula)
• Blastopore - opening into the central cavity of the embryo, used to distinguish two main evolutionary lines of bilateral animals.

Protostomia vs Deuterostomia

Protostomia

• Blastopore develops into the mouth
• Spiral cleavage: early cell divisions are diagonal to the polar axis.
• Early cells typically undergo determinate cleavage.

Deuterostomia

• Blastopore develops into the anus; a second opening gives rise to the mouth.
• Radial cleavage: early cell divisions are parallel or at right angles to the polar axis.
• Early cells typically undergo indeterminate cleavage.
• Example: the embryo grows normally even if a few cells are removed from the blastula.
• Echinoderms and Chordates

Review Video

That was a lot! Here is a review video, first 5 mins cover the ways we classify animals.

Wrap Up

Last slide of this lecture

Blank

• Blank

Animals are extraordinarily diverse.More than two million species have been described — and that number is almost certainly an underestimate. What’s even more astonishing is that scientists estimate roughly 99% of all animal species that have ever existed are now extinct. So what we see today is just a snapshot — the surviving branches of a much larger evolutionary tree. Taxonomists currently classify animals into about 35 phyla. A phylum represents a major body plan difference — meaning fundamental structural organization changes. Modern molecular studies have confirmed that many of these phyla represent monophyletic groups — meaning they include an ancestor and all its descendants. So classification today reflects evolutionary history much more accurately than earlier systems based only on physical traits.

Molecular data suggest animal lineages began diverging long before they appear in the fossil record.Many animal phyla first appear during the Cambrian radiation about 542 million years ago. But genetic evidence suggests those lineages diverged hundreds of millions of years earlier. The Cambrian period likely represents a time when animals evolved hard body parts — shells and skeletons — which fossilize more easily. Animals first evolved in marine environments and later colonized land. Moving to land required major innovations — support structures, desiccation resistance, new reproductive strategies — and we’ll see those adaptations as we explore different groups

The evolution of a coelom — a fluid-filled body cavity — was a major innovation.It provides space for internal organs and allows them to move independently of the body wall. In a tube-within-a-tube body plan, the outer tube is the body wall and the inner tube is the digestive tract. The coelom lies between them. Acoelomates lack a body cavity. Pseudocoelomates have a body cavity not completely lined with mesoderm. True coelomates have a body cavity fully lined with mesoderm. The coelom can also function as a hydrostatic skeleton — muscles push against fluid to generate movement

Basidiomycota includes the mushrooms most people are familiar with.They produce spores on club-shaped structures called basidia. Many form large, visible fruiting bodies — mushrooms — that elevate spores into the air for efficient dispersal. This group includes: Gill fungi Shelf fungi Rusts and smuts, which infect crops Most edible mushrooms belong to this phylum — but so do some toxic species. It’s important to remember: the mushroom is just the reproductive structure. The majority of the organism is underground as mycelium.

Fungi are heterotrophic eukaryotes. That means they have nuclei and membrane-bound organelles, and they cannot produce their own food like plants do.They can be unicellular — like yeasts — or multicellular. One key defining feature is their cell wall composition. Unlike plants, which have cellulose cell walls, fungi have cell walls made of chitin — the same material found in arthropod exoskeletons. They reproduce using spores — microscopic reproductive cells. Unlike plant embryos, fungal spores are not protected by specialized tissues.

Fungi are grouped into several phyla, but about 95% belong to two: Ascomycota and Basidiomycota. You may notice a pattern as we move across taxa that the diversity is concentrated in a few taxa. For example the majority of plants are angiosperms, the majority of fungi are in ascomycota and basidiomycota. Think about what features they have that have allowed them to be so diverse.

The ancestor of animals had over 1,500 genes not found in other eukaryotes. Many of these genes are involved in cell communication, adhesion, and development — features critical for multicellular organization.There are also striking similarities between sponge feeding cells — called choanocytes — and choanoflagellate protists. Choanoflagellates are considered the closest living relatives of animals. Their collar-like feeding structures resemble sponge choanocytes almost exactly. This suggests that animals likely evolved from a common ancestor resembling modern colonial choanoflagellates. So animals didn’t appear suddenly — they evolved from single-celled ancestors that gradually developed cell cooperation and specialization

Lichens are not single organisms — they are partnerships.A fungus — usually an ascomycete — forms a structure that houses a photosynthetic partner, either algae or cyanobacteria. The fungus provides structure, moisture retention, and protection. The photosynthetic partner provides carbohydrates. Lichens can survive extreme environments — deserts, arctic tundra, bare rock. They are also sensitive to pollutants, especially sulfur dioxide. Because of this, they are used as bioindicators of air quality.

Fungi can infect both plants and animals.In humans, common infections include athlete’s foot and ringworm — both affecting keratinized tissues like skin. More serious fungal infections, like Valley Fever, affect the lungs and can become systemic. In plants, fungal diseases such as chestnut blight have reshaped entire forests. Fungal diseases are difficult to treat because fungal cells are eukaryotic — like ours. Drugs that target fungal cells may also damage human cells. And remember — spores can persist for long periods in dry conditions, waiting for favorable environments.

Fungi are an incredibly diverse kingdom. We’ve described about 150,000 species so far, but estimates suggest there may be over a million species. That means most fungal diversity is still undiscovered.They range from microscopic yeasts to massive underground networks. In fact, the largest known organism on Earth by estimated biomass is a fungus — Armillaria solidipes in Oregon — spanning miles underground. When you think of fungi, don’t just think of mushrooms. Think of molds, yeasts, lichens, decomposers, pathogens, and symbiotic partners.

Tissues arise from germ layers formed early in development.Most animals, except sponges, form germ layers during gastrulation. There are three primary germ layers: Ectoderm — forms the outer covering and nervous system Endoderm — forms the digestive tract lining Mesoderm — forms muscles, skeleton, circulatory systems, and more

blank

One chytrid species, often abbreviated as Bd, has had devastating ecological consequences.Bd infects amphibians — particularly frogs — by attacking keratin in their skin. Amphibians rely heavily on their skin for gas exchange and water balance, so when the fungus disrupts skin function, it can lead to death. This pathogen has been linked to dramatic amphibian population declines worldwide.

Fungi are found almost everywhere, but they thrive in dark, moist environments.They are major decomposers. They break down organic material — not for the benefit of the ecosystem, but to obtain nutrients for themselves. Ecosystem recycling is a byproduct. They also form important symbiotic relationships: Mycorrhizae with plant roots Lichens with algae or cyanobacteria And some are parasites or pathogens. Moisture is critical because digestion and nutrient transport require water — which is why decomposition rates are much higher in humid environments.

blank

Now we’re transitioning from fungi to animalsAnimals are multicellular, ingestive heterotrophs. That means instead of secreting enzymes onto their food like fungi, animals take food into their bodies and digest it internally. And what’s remarkable is their diversity. From microscopic marine invertebrates to blue whales, animals have radiated into nearly every environment on Earth. As we move forward, we’re going to focus not just on listing groups, but on understanding the evolutionary innovations that allowed this diversity to emerge. Let’s define what makes an animal an animal. Animals are multicellular eukaryotes. Their cells lack cell walls, which allows for flexibility and the development of specialized tissues. They are heterotrophic — meaning they obtain energy by consuming other organisms. Most animals have specialized cells organized into tissues, and many have organs and organ systems. This level of organization allows for increased complexity and efficiency. Most animals are capable of locomotion at some stage of their life cycle — even if the adult form becomes sessile, like corals or barnacles. They also typically possess nervous and muscle tissue, enabling rapid response and coordinated movement. And importantly, animals undergo embryonic development. That developmental process — especially early cell divisions — tells us a lot about evolutionary relationships, which we’ll explore shortly.

Animals are often referred to as Metazoans.Animals with true tissues are called Eumetazoans. To classify animals into major groups, we focus on four key traits: Type of symmetry Tissue development Body cavity type Embryonic development pattern

Today we’re going to explore two incredibly important groups of organisms: fungi and animals.Fungi are often overlooked — they’re not plants, they’re not animals, and for a long time scientists weren’t quite sure where to place them. Yet they’re essential to ecosystems, agriculture, medicine, and even your dinner plate. Then we’ll transition into animal diversity — how animals evolved, how we classify them, and the major body plan differences that define the animal kingdom. By the end of today, I want you to start thinking less in terms of memorizing names and more in terms of patterns — body plans, evolutionary relationships, and shared developmental pathways.” Before we dive into fungi themselves, we need to zoom out evolutionarily. Fungi belong to a larger group called the Unikonts. This group includes fungi, animals, and certain protists. Being in the same clade means animals and fungi are more closely related to each other. So despite fungi looking plant-like — growing out of soil, forming structures that resemble stems — genetically and evolutionarily, they’re closer to us than to trees. That relationship becomes important when we talk about fungal infections later — because similarities at the cellular level make them harder to treat.

Zygomycota includes familiar molds like Rhizopus — the black bread mold you may have seen growing on old bread.They’re named for their zygosporangia — thick-walled structures formed during sexual reproduction. These thick-walled spores are resistant to harsh conditions, which helps the fungus survive periods of environmental stress. Most zygomycetes are decomposers, breaking down sugars and starches. Some form symbiotic relationships, and a few can cause disease.

Early development begins with cleavage — rapid cell divisions — forming a blastula.Some animals develop directly into miniature adults. Others develop into larval stages that look very different from adults. Many larvae undergo metamorphosis. Cleavage patterns and blastopore fate distinguish two major lineages: Protostomes and Deuterostomes

Fungi are heterotrophs — but they don’t ingest food like animals do.Instead, they secrete digestive enzymes into their environment. These enzymes break down complex molecules — like cellulose and lignin — into smaller components. Then the fungus absorbs those small molecules directly through its cell walls. This external digestion is incredibly powerful. Fungi are among the only organisms capable of breaking down lignin — a major component of wood. Without fungi, forests would be buried in undecomposed plant matter like what occurred in the Carboniferous

Changes in body plans are closely linked to changes in embryonic development.Many genes that control early development — especially HOX genes — are highly conserved across all animals. HOX genes act like master control switches. They determine where structures develop along the head-to-tail axis. If you look at the diagram, you’ll see that different colors represent HOX gene expression in similar body segments across very different animals. This tells us something profound: the same genetic toolkit builds a fruit fly, a mouse, and a human. The field of ‘Evo Devo’ — evolutionary developmental biology — studies how changes in gene regulation produce evolutionary diversity. Often, evolution doesn’t invent new genes — it repurposes and modifies existing ones

Plasmogamy — the fusion of cytoplasm between two compatible mating types. The nuclei don’t immediately fuse, resulting in a dikaryotic stage — meaning two separate nuclei per cell.This has some benefits, the cell has access to 2 copies of the genome, and potentially 2 different alleles per genes, like normal diploids. And they don’t have the increased risks during genome duplication associated with normal diploids. Later, under the right conditions, karyogamy occurs — the nuclei fuse to form a diploid zygote nucleus. That diploid stage is usually brief, followed by meiosis to produce spores. The dikaryotic stage is a defining feature in many fungi and can last a long time.

Now we move to Ascomycota — the largest fungal phylum.The defining feature here is the ascus — a sac-like structure that contains spores. If you look at the image, you’ll likely see microscopic sacs with spores lined up inside. Ascomycota includes an enormous range of forms: Multicellular molds Single-celled yeasts Truffles and morels Many plant pathogens fungi that produce antibiotics And let’s take a second to think why fungi might be good sources for antibiotics. Because they digest then ingest the nutrients from decomposing mater, there is strong selective pressure for them to exclude competitors like bacteria and other microbes.

Let’s revisit mycorrhizae briefly, because they are so important.These mutualistic relationships occur in the vast majority of plant species. The fungal hyphae extend far into the soil, increasing the plant’s ability to absorb water and nutrients. In exchange, the plant shares sugars produced via photosynthesis. This relationship enhances plant survival in nutrient-poor soils and can even improve resistance to drought.

These fungi infect arthropods. The spores land on an insect, penetrate its exoskeleton, and grow inside the body.The hyphae digest host tissues, effectively replacing much of the internal structure. Eventually, a fruiting body emerges from the host’s body to release spores. While cordyceps don’t infect humans (unlike in the Last of Us) many fungal diseases do. Watch this short video and then answer why fungal diseases are difficult to treat for humans, plants, and other animals.

We begin with Chytridiomycota, we’re looking at what many biologists consider the most basal, or earliest-diverging, fungal lineage. Most chytrids are unicellular, though a few form simple multicellular structures. What really sets them apart — and you’ll probably see this in the diagram — is that they produce flagellated spores. That means their spores can actually swim. This is unusual for fungi. Most fungi have non-motile spores that rely on wind or animals for dispersal. The presence of flagella suggests chytrids evolved in aquatic environments and retain that ancestral trait. Many chytrids are decomposers in freshwater ecosystems. They help break down organic matter, especially plant material. However, some are parasitic — and that brings us to one of the most ecologically significant examples.

Glomeromycota are specialized symbionts.They form mycorrhizae — associations with plant roots. If you look at the diagram, you’ll likely see fungal hyphae penetrating or surrounding plant root cells. This increases the surface area available for nutrient absorption. The fungus helps the plant absorb phosphorus and other minerals from the soil. In return, the plant provides carbohydrates

Symmetry describes how body parts are arranged around an axis.Some animals, like sponges, are asymmetrical — they lack defined symmetry. Radial symmetry means body parts radiate from a central axis. Think of a jellyfish. This arrangement is common in organisms that interact with the environment from all sides. Bilateral symmetry allows only one plane that divides the organism into mirror-image halves. Bilateral symmetry is associated with cephalization — the concentration of sensory organs and nervous tissue at the anterior end, forming a head. This is evolutionarily significant because bilateral symmetry supports directional movement. There’s also pentaradial symmetry — seen in adult echinoderms like sea stars. Interestingly, echinoderm larvae are bilaterally symmetrical, revealing their evolutionary history

Fungi reproduce using spores, which are usually microscopic and nonmotile.Spores can be dispersed by wind, water, or animals. Reproduction can be asexual — such as budding in yeasts — or sexual, involving specialized reproductive structures like mushrooms. When a spore lands in a suitable environment, it germinates and produces a hypha, which grows into a mycelium. Because spores are small and numerous, fungi are very effective at colonizing new environments.

Yeasts are single-celled ascomycetes.One of the most important species is Saccharomyces cerevisiae — brewer’s yeast. Yeasts perform fermentation. In low-oxygen conditions, they convert sugars into carbon dioxide and alcohol. That carbon dioxide is what makes bread rise. The alcohol is what produces beer and wine. Beyond food production, yeast is a major model organism in research. Because it’s eukaryotic but simple and fast-growing, it’s ideal for studying cell division, genetics, and metabolism. However, not all yeasts are beneficial. Some species can cause infections such as thrush, particularly in immunocompromised individuals.

Tissues arise from germ layers formed early in development.Most animals, except sponges, form germ layers during gastrulation. There are three primary germ layers: Ectoderm — forms the outer covering and nervous system Endoderm — forms the digestive tract lining Mesoderm — forms muscles, skeleton, circulatory systems, and more Diploblastic animals have only two layers — ectoderm and endoderm. These include cnidarians and ctenophores. Triploblastic animals have all three germ layers. All bilaterally symmetrical animals are triploblastic. The addition of mesoderm allowed for greater complexity — including internal organs and advanced organ systems

In protostomes, the blastopore becomes the mouth.Cleavage is spiral, and development is typically determinate — meaning early cell fate is fixed. In deuterostomes, the blastopore becomes the anus. Cleavage is radial, and development is typically indeterminate — meaning early cells retain the potential to develop into a complete organism. This distinction represents one of the deepest splits in bilateral animal evolution. Deuterostomes include echinoderms and chordates — the group that includes vertebrates.

If we look at multicellular fungi, they’re made of threadlike filaments called hyphae. A mass of hyphae is called a mycelium.Think of the mycelium as the real body of the fungus. The mushroom is just the reproductive structure. Hyphae may be divided by cross-walls or may lack them entirely. Even when walls are present, they often have perforations that allow cytoplasm and nutrients to flow freely. This makes the organism function almost like a continuous network rather than isolated cells. This structure allows fungi to grow through soil, wood, food — almost any organic material It is this ability to be joined up in a network that allows so fungi to grow incredibly large. The world largest organisms in terms of biomass was recorded in an oregon forest, a species of fungi in the genius armillaria, which has a network of mycelium several miles long. How did researchers know this was the same organisms? The fed it with some radioactively labeled sugars on one end, and were able to track its transmission through the network.