Viruses, Bacteria, Protists, and Fungi

Viruses, Bacteria, Protists, and Fungi

Middle School

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Learning Objectives

• Recognize that all living things are made of one or more cells.

• Explain that a cell is the smallest unit that can be considered alive.

• Differentiate between unicellular and multicellular organisms.

• Distinguish between living microorganisms and non-living viruses.

• Analyze the helpful and harmful roles of microorganisms.

Key Vocabulary

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Cell

A cell is the smallest, most basic building block of all living organisms.

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Unicellular

A unicellular organism is a living creature that is made up of just one single cell.

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Multicellular

A multicellular organism is a living creature that is composed of many different types of cells.

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Microscope

A microscope is a scientific tool used to see tiny things invisible to the naked eye.

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Virus

A virus is a tiny, non-living particle that must invade a host cell to reproduce.

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Host

A host is an organism that provides energy and a place for a virus to multiply.

Key Vocabulary

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Bacteria

Bacteria are unicellular prokaryotes, which are simple, single-celled organisms that famously lack a nucleus.

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Protist

Protists are a very diverse group of eukaryotic organisms that are typically found living in moist environments.

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Fungi

Fungi are eukaryotic heterotrophs, meaning they cannot make their own food and must absorb nutrients from others.

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Parasite

A parasite is an organism that lives on or inside another organism, called a host, often causing it harm.

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Hyphae

Hyphae are the long, branching, threadlike tubes that make up the body of a fungus, giving it structure.

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Binary Fission

Binary fission is a type of asexual reproduction where a single bacterial cell divides into two identical daughter cells.

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What are Microorganisms?

Prokaryotes

• The domains Archaea and Bacteria are made up of single-celled organisms called prokaryotes.

• Prokaryotic cells are very simple and do not have a nucleus or other complex parts.

• Their genetic material, or DNA, floats freely inside the cell’s main compartment, the cytoplasm.

Eukaryotes

• The domain Eukarya includes protists, fungi, plants, and animals, which are all eukaryotes.

• Eukaryotic cells are more complex and have a special compartment called a nucleus for their DNA.

• Protists are a very diverse group of eukaryotes that are simpler than plants or animals.

Multiple Choice

What is the main structural difference between a prokaryotic cell and a eukaryotic cell?

• The presence of a nucleus in a eukaryotic cell.

• The type of cytoplasm in a prokaryotic cell.

• The size of the genetic material in both cells.

• The number of cells each organism is made of.

Multiple Choice

Which statement best describes the group of organisms known as protists?

• They are prokaryotes because they are all single-celled organisms.

• They are eukaryotes because they are a diverse group of organisms with complex cells.

• They are prokaryotes because they do not have genetic material.

• They are eukaryotes because they are simpler than bacteria.

Multiple Choice

A scientist discovers a new single-celled organism. After studying its structure, the scientist finds that its genetic material is contained within a nucleus. How should this organism be classified?

• It should be classified as a prokaryote because it is a single-celled organism.

• It should be classified as a eukaryote because its DNA is inside a nucleus.

• It should be classified as a type of Bacteria because its DNA floats freely.

• It should be classified as a type of Archaea because all single-celled life belongs to this domain.

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Cells: The Building Blocks of Life

Multicellular

• Multicellular organisms are made of many different types of cells working together.

• Animals and plants are examples of complex organisms that are made of many cells.

• The presence of a cellular structure is what distinguishes living from non-living things.

Unicellular

• Unicellular organisms consist of just a single cell that performs all of its functions.

• Bacteria are a common example of a single-celled, or unicellular, organism.

• Since cells are so small, a microscope is needed to see these tiny organisms.

Multiple Choice

What is the key feature that distinguishes living things from non-living things?

• The presence of a cellular structure

• The ability to move independently

• The need for oxygen to breathe

• The complexity of its body parts

Multiple Choice

What is the main difference between a unicellular organism and a multicellular organism?

• A unicellular organism has one cell for all functions, while a multicellular organism has many cells working together.

• A unicellular organism is a type of plant, while a multicellular organism is a type of animal.

• A unicellular organism is large, while a multicellular organism is microscopic.

• A unicellular organism is complex, while a multicellular organism is simple.

Multiple Choice

A scientist observes a sample of water using a microscope and finds a tiny organism that performs all of its functions within one single cell. What is the best conclusion the scientist can make about this organism?

• The organism is unicellular because it is a complete living thing within a single cell.

• The organism is multicellular because all living things are made of many cells.

• The organism is a non-living particle because it can only be seen with a microscope.

• The organism is part of a larger plant that was in the water.

Viruses: The Non-Cellular Invaders

• A virus is a tiny, non-living particle that is not a cell.

• All viruses have a protein coat and a core of genetic material.

• They must invade a living host cell to reproduce.

Multiple Choice

Which statement best describes a virus?

• A type of microscopic living cell.

• A non-living particle that is not a cell.

• A complex organism with many cells.

• A simple single-celled animal.

Multiple Choice

What is the relationship between a virus and the host cell it invades?

• It provides the host cell with energy.

• It uses the host cell's machinery to make copies of itself.

• It protects the host cell from other invaders.

• It helps the host cell absorb nutrients.

Multiple Choice

A scientist observes a particle that has a protein coat and genetic material. The particle cannot make copies of itself unless it enters a living cell. Based on this evidence, what is the most logical conclusion?

• The particle is a cell, because it contains genetic material.

• The particle is a virus, because it needs a host to reproduce.

• The particle is living, because it has a protein coat.

• The particle is a bacterium, because it is a tiny particle.

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Bacteria: The Unicellular Prokaryotes

• Bacteria are single-celled prokaryotes, appearing in ball, rod, or spiral shapes.

• A cell wall offers protection, while a membrane controls what enters and exits.

• Genetic material directs cell functions, and a flagellum may provide movement.

• Some bacteria make their food, while others form endospores to survive.

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Multiple Choice

Which statement best describes the fundamental characteristic of bacteria?

• They are single-celled prokaryotes.

• They always have a spiral shape.

• They form complex multicellular organisms.

• They can only survive by making their own food.

Multiple Choice

What is the relationship between a bacterium's cell wall and its cell membrane?

• The cell wall provides protection, and the membrane controls transport.

• The cell wall helps with movement, and the membrane makes food.

• The cell wall stores genetic material, and the membrane provides shape.

• The cell wall captures food, and the membrane helps the cell move.

Multiple Choice

If a bacterium that cannot make its own food is exposed to an environment with no nutrients, what is its most likely response?

• It would form an endospore to survive the harsh conditions.

• It would use its flagellum to find a new environment.

• It would change its shape from a rod to a spiral.

• It would start making its own food immediately.

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Bacterial Reproduction and Roles

Binary Fission

• ​This is a form of asexual reproduction where one cell divides.

• ​​It results in two daughter cells that are genetically identical to the parent.

• ​This process allows for the very rapid growth of bacterial populations.

Conjugation

• ​Bacteria can exchange genetic material directly with each other.

• ​​This allows spreading traits like antibiotic resistance between different bacteria.

• ​Most bacteria are helpful decomposers, while less than 1% are harmful.

Multiple Choice

What is the direct result of a single bacterium undergoing binary fission?

• Two daughter cells that are genetically identical to the parent

• Two cells that have different genetic material

• A single cell with new traits like antibiotic resistance

• A group of bacteria that are all helpful decomposers

Multiple Choice

What is the relationship between binary fission and conjugation in bacteria?

• Binary fission leads to rapid population growth, while conjugation allows for the exchange of genetic material.

• Conjugation is a form of asexual reproduction, while binary fission is a form of sexual reproduction.

• Binary fission is only used by harmful bacteria, while conjugation is used by helpful decomposers.

• Conjugation creates two identical daughter cells, while binary fission spreads traits like antibiotic resistance.

Multiple Choice

If a few bacteria in a large population have a trait for antibiotic resistance, what is the most likely way for that trait to spread to other existing bacteria in the population?

• Through conjugation, where a resistant bacterium shares its genetic material with others.

• Through rapid binary fission, which creates new traits in the daughter cells.

• Because most bacteria are helpful and can fight off antibiotics naturally.

• Because the bacteria stop being decomposers and become harmful.

Protists: The Diverse Eukaryotes

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Animal-like Protists

• ​They are heterotrophs, consuming other organisms to get their required energy.

• ​​Most are able to move around freely to hunt for their food.

• ​A common example is the amoeba, which constantly changes its body shape.

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Plant-like Protists

• ​Plant-like protists are autotrophs, making their own food like most plants.

• ​​They produce their food through a process you know called photosynthesis.

• ​Algae are a very common and important example of plant-like protists.

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Fungi-like Protists

• ​These protists are heterotrophs and absorb nutrients from their surroundings.

• ​​They have cell walls and reproduce by forming spores, similar to fungi.

• ​Slime molds are a great example of this interesting protist group.

Multiple Choice

What is the main characteristic used to classify protists into plant-like, animal-like, or fungi-like groups?

• How they obtain their energy.

• The environment where they live.

• Whether they have a nucleus.

• The way they change their body shape.

Multiple Choice

Which statement correctly compares two different groups of protists?

• Animal-like protists consume food, while plant-like protists make their own food through photosynthesis.

• Fungi-like protists move to hunt, while animal-like protists absorb nutrients.

• Plant-like protists have cell walls, while fungi-like protists do not.

• Animal-like protists are autotrophs, while fungi-like protists are heterotrophs.

Multiple Choice

A scientist discovers an organism that absorbs nutrients from a decaying log, has cell walls, and reproduces using spores. Which conclusion is best supported by this evidence?

• It is likely a fungi-like protist, such as a slime mold.

• It is likely an animal-like protist because it is a heterotroph.

• It is likely a plant-like protist because it has cell walls.

• It is likely an amoeba that is hunting on the log.

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Fungi: The Great Absorbers

• Fungi are heterotrophs with cell walls, either unicellular or multicellular.

• Most fungi are made of threadlike tubes called hyphae that grow into food.

• Hyphae release chemicals to break down the food and then absorb the nutrients.

• Fungi reproduce with spores from a fruiting body, carried by wind or water.

Multiple Choice

How do fungi, as heterotrophs, get the energy they need to live?

• By absorbing nutrients from their environment

• By making their own food using sunlight

• By catching and eating small insects

• By drinking water through a root system

Multiple Choice

What is the relationship between a fungus's hyphae and its ability to eat?

• They form a network to absorb nutrients from the fungus's surroundings.

• They create spores that are carried by the wind.

• They provide a hard outer layer for protection.

• They allow the fungus to move from place to place.

Multiple Choice

If a fungus's fruiting body developed in an environment without any wind or moving water, what would be the most likely outcome?

• The fungus would likely be unable to spread and reproduce in new locations.

• The fungus would develop roots to find water instead.

• The fungus would not be able to form hyphae to absorb nutrients.

• The fungus would start making its own food like a plant.

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The Roles of Fungi

• Fungi can be a source of food, such as edible mushrooms.

• ​They are used to make important medicines like the antibiotic Penicillin.

• As decomposers, they break down dead organisms, returning nutrients to the soil.

• Harmful fungi can spoil food and cause diseases like athlete's foot.

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Multiple Choice

Which statement best summarizes the different roles of fungi?

• Fungi can be both helpful and harmful to other organisms.

• Fungi are only useful for making important medicines.

• Fungi primarily exist to break down dead organisms.

• Fungi are only known to spoil food and cause diseases.

Multiple Choice

What is the main function of fungi when they act as decomposers?

• They are a source of food, such as edible mushrooms.

• They are used to produce medicines like Penicillin.

• They break down dead material, returning nutrients to the soil.

• They cause common diseases, such as athlete's foot.

Multiple Choice

Based on their role as decomposers, what would most likely happen in a forest ecosystem if all fungi disappeared?

• The supply of medicines like Penicillin would increase.

• Dead organisms would pile up, and nutrients would not be returned to the soil.

• More types of edible mushrooms would become available as food.

• Cases of food spoilage would completely stop.

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Common Misconceptions

Misconception	Correction
Viruses are a type of living cell.	Viruses are not cells. They are non-living and need a host to reproduce.
All living things are visible.	Many living things are microscopic and can only be seen with special tools.
All bacteria are harmful.	Most bacteria are not harmful. Many are actually helpful to us.
Fungi are plants.	Fungi are not plants because they absorb food, while plants make their own.

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Summary

• All living things are composed of one or more cells.

• Viruses are not made of cells and require a host to reproduce.

• Bacteria, protists, and fungi reproduce in diverse ways.

• Microorganisms and viruses have both helpful and harmful effects on the environment.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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