Copy of Fungi
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Fungi
Chapter 21
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Learning Objectives
Define the terms:
Saprophytic: Organisms that obtain nutrients from dead organic matter.
Parasitic: Organisms that extract nutrients from living hosts.
State the structure & life cycle of Rhizopus.
Explain nutrition in fungi.
Outline the structure & reproduction of Yeast.
Name 2 Beneficial & 2 Harmful fungi.
Mention that there are Edible and Poisonous fungi.
Identify and state functions for:
Rhizoid
Sporangium
Gametangium
Zygospore
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Mycology
The study of fungi is called mycology.
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Introduction
Examples of fungi include:
Mushrooms,
Mildews,
Molds,
Yeasts.
Fungi are eukaryotic. This means they have membrane-enclosed organelles and nuclei.
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Features of Fungi
Nutrition: Fungi do not make their own food (i.e., they are heterotrophic).
Cell Structure: Mostly multicellular.
Reproduction: Reproduce by means of spores.
Hyphae: Made up of threads called hyphae.
Mycelium: Hyphae combine in masses to form mycelium.
Cell Walls: Their walls are made of a carbohydrate called chitin.
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Nutrition
All fungi are heterotrophs, meaning they take in food made by other organisms.
Types of fungi:
Parasitic: Take food from live hosts.
Saprophytic: Take food from dead organic matter.
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Saprophytic Fungi
Most fungi are saprophytic and take food from dead organic matter.
Commonly found in soil and on decaying matter.
As they digest substances, minerals are released and recycled.
Play a vital role in the environment as they are responsible for decay.
Example: Mushrooms and molds.
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Parasitic Fungi
Absorb their food from live hosts.
In plants, the fungus penetrates between plant cells to absorb food.
They primarily get their food from plants, but some can live on animals (e.g., athlete’s foot and ringworm).
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Types of Parasitic Fungi
Obligate parasites: Live on hosts but do not normally kill them (e.g., mildews).
Facultative parasites: Can kill the host and feed on the remains (e.g., fungi causing soft rots in fruit).
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Symbiosis
Some fungi form symbiotic relationships with other organisms.
Lichen: An organism that is a combination of a fungus and an alga, indicating mutual benefit.
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Edible and Poisonous Fungi
Some fungi are edible, but many are poisonous if consumed.
It is often difficult to distinguish between edible and poisonous varieties growing in the wild.
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Edible vs Poisonous Fungi
Edible Poisonous | |
Standard field mushroom | Death cap |
Truffle (found near tree roots) | Destroying angel |
Ingesting both poisonous types can damage the intestinal lining and liver, often leading to liver failure.
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Learning Check
Define saprophytic fungi.
Give an example of saprophytic fungi.
Define parasitic fungi.
What is an obligate parasite?
What is a facultative parasite?
Give an example of a parasitic fungi.
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Rhizopus
Commonly known as Common Bread Mould.
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Rhizopus Growing on Agar
Observation of Rhizopus colonies growing on agar medium.
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Nutrition of Rhizopus
Common bread mould is a saprophyte, primarily feeding on starchy foods such as bread and vegetable peelings.
The fungus secretes enzymes into the starchy substances, leading to external digestion.
Digested nutrients are then absorbed by the fungus.
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Structure of Rhizopus
Commonly referred to as pin mould.
Key structures include:
Sporangium
Spores
Columella (feeds spores)
Apophysis
Sporangiophore
Stolon
Substrate
Mycelium
Hypha
Rhizoids
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Hyphae
Consists of thread-like structures known as hyphae.
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Nuclei of Hyphae
Hyphae are tubular with no cross walls and are multinucleate, with each nucleus being haploid.
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Mycelium and Function of Structures
Large numbers of hyphae form a mycelium.
Hyphae digest the substrate on which they grow.
Rhizoids: Provide extra surface area for absorption of nutrients.
Stolons: Aerial hyphae that allow Rhizopus to spread laterally.
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Structure of Rhizopus (Diagram)
Illustrative diagram of Rhizopus showing:
Sporangiospores
Sporangium
Columella
Apophysis
Sporangiophore
Stolon
Rhizoid
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Sporangium Structure
Key structures:
Columella (feeds spores)
Apophysis
Sporangiophore
Sporangium
Spores
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Learning Check
Can you draw and label the structure of Rhizopus?
Define hypha.
Define mycelium.
What is the function of a rhizoid?
What is a stolon?
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Life Cycle of Rhizopus
Overview of Rhizopus life cycle stages.
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Asexual Reproduction
Sporangiophores grow from the substrate after several days.
Cells within the sporangium divide by mitosis to produce haploid spores.
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Asexual Reproduction Details
The sporangium dries under certain conditions, eventually opening and releasing numerous spores.
Each spore can germinate into new hyphae and mycelium upon landing on a suitable substrate.
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Sexual Reproduction
Sexual reproduction in Rhizopus occurs only between a plus and a minus strain.
Triggered by adverse environmental conditions like dehydration.
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Hyphal Interaction
When hyphae from opposite strains come into proximity, swelling occurs on both strains, leading to contact.
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Nuclei Movement
Nuclei from both hyphae migrate into the swellings, now termed progamiangia.
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Formation of Gametangia
Cross-walls form, producing gametangia from the earlier swelling.
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Fertilization in Gametangia
The walls of gametangia dissolve, allowing fertilization and resulting in diploid zygote nuclei formation.
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Zygospore Formation
A zygospores forms surrounding the diploid nuclei.
When conditions are optimal, the zygospore germinates via meiosis.
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Germination Process
Similar to previous section: zygospore germinates once favorable conditions return.
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Growth from Zygospore
A hypha emerges from the zygospore, culminating in a sporangium at the tip, opening to release new haploid spores.
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Summary of Sexual Reproduction
Nuclei migrate into the suspensor, linking hyphae from different mycelia.
Crosswalls dissolve, allowing the formation of progametangia.
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Diagram of Reproductive Events
Illustrative representation of zygote fertilization, meiosis, and subsequent growth towards sporangium.
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Review of Sexual Reproduction Process
Review steps of reproduction, emphasizing the inter-strain interactions and zygote developments.
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Continued Review
Additional insights into gametangia formation and the emergence of new individuals post-spore release.
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Learning Check
Describe Rhizopus reproduction.
Define progametangia.
Explain gametangia formation.
Define zygospore formation.
What structure is produced at the tip of a hypha?
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Yeast
Characterized as unicellular (single-celled).
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Structure of Yeast
Yeast cells are:
Oval/Round in shape.
Contain food vacuoles, nucleus, cell wall, cytoplasm, and cytoplasmic membrane.
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Yeast Cell Features
Cell walls are made of chitin.
The cytoplasm contains many food storage vacuoles, giving it a grainy appearance.
Usually has one large vacuole and typically one nucleus per cell.
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Yeast Respiration
Yeasts primarily respire anaerobically.
Word equation for yeast respiration:
Glucose ➜ 2 Ethanol + 2 Carbon Dioxide
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Reproduction in Yeast
Process of budding begins with a bud growing to full size then pinching off to form a new cell.
The nucleus divides through mitosis, with one daughter nucleus moving into the bud.
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Asexual Reproduction Process
Asexual reproduction occurs mainly via budding, where the parent cell's nucleus divides and one nucleus enters a developing bud.
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Budding Growth
The bud can separate from the parent, forming a new individual.
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Colonial Budding
In some cases, the bud does not separate but continues to bud again, forming long colonies of yeast cells.
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Visual Representation of Budding
Illustrative diagram of the budding process in yeast.
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Economic Importance of Fungi
Beneficial Fungi
Yeasts are used in:
Bread making.
Alcohol production (e.g., wine and beer).
Some fungi serve as food sources (e.g., mushrooms).
Production of antibiotics, such as Penicillin.
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Economic Importance of Fungi
Harmful Fungi
Fungi that can harm:
Attack crops like corn and wheat, leading to financial losses.
Infect humans and animals (e.g., athlete's foot, thrush, ringworm).
Spoil food, as seen in Rhizopus growing on bread.
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Learning Check
Draw the structure of yeast.
Describe yeast reproduction.
Economic importance of yeast with examples.
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Syllabus Focus
Saprophytic and parasitic forms.
Structure and life cycle of Rhizopus.
Nutrition.
Yeast structure and reproduction (budding).
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Contemporary Issues and Technology
Awareness of edible vs poisonous fungi.
Importance of fungi in economy: examples of beneficial and harmful fungi.
Practical Activities
Investigate growth of leaf yeasts using agar plates and controls.
Learning Objectives
Saprophytic: Organisms that derive their nutrients from the decomposition of dead organic matter, thereby playing a crucial role in nutrient recycling within ecosystems.
Parasitic: Organisms that obtain nutrients by living on or within a host organism, often harming the host in the process.
The structure of Rhizopus includes specialized components for reproduction and nutrient absorption, as well as a complex life cycle that showcases its adaptability.
Nutrition in fungi occurs through absorption rather than photosynthesis, allowing them to extract essential nutrients from their environment, whether through parasitism or saprophytism.
Yeast reproduction is characterized by budding, a method where new cells develop from a parent cell, which is essential for their propagation.
Beneficial fungi include species used in food production and medicine, while harmful fungi can cause diseases in plants, animals, and humans.
Fungi can be categorized as either edible or poisonous, with distinguishing characteristics that require careful consideration.
Rhizoids, Sporangium, Gametangium, and Zygospore are all essential structures in fungal biology, each serving distinct functions related to survival, reproduction, and nutrient acquisition.