Living Things

Living Things

Middle School

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Learning Objectives

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

• Explain that the cell is the smallest unit of life and distinguish between unicellular and multicellular organisms.

• Identify the key characteristics shared by all living things, including growth and reproduction.

• Describe the basic needs for an organism's survival, including the concept of homeostasis.

Key Vocabulary

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Organism

An organism is any individual living being, such as a plant, an animal, or a bacterium.

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Cell

The cell is the smallest, most basic unit of life that makes up all living organisms.

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Unicellular

A unicellular organism is a living being that is made of only one single cell.

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Multicellular

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

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Microscope

A microscope is a scientific instrument used to see objects that are too small for the naked eye.

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Evidence

Evidence is information or facts that are used to support a claim or prove something is true.

Key Vocabulary

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Stimulus

A stimulus is any change or signal in the environment that an organism can react to.

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Response

A response is the reaction of a living organism to a stimulus from its environment.

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Homeostasis

Homeostasis is the process by which an organism maintains a stable internal environment to function properly.

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Autotroph

An autotroph is an organism that can produce its own food, usually through the process of photosynthesis.

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Heterotroph

A heterotroph is an organism that cannot make its own food and must eat other organisms.

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Reproduction

Reproduction is the biological process by which new individual organisms are produced from their parents.

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Characteristics of Living Things

• All living things, or organisms, are made of one or more cells.

• Living things use energy and contain chemicals like water and DNA.

• Organisms react to changes in their environment, which are called stimuli.

• All living things grow, develop, and reproduce to make new organisms.

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Multiple Choice

What is a fundamental characteristic shared by all living organisms?

• They are made of one or more cells.

• They can move from place to place.

• They live in water environments.

• They have hard skeletons.

Multiple Choice

Which statement best describes the relationship between an organism and a stimulus?

• An organism responding to a change in its environment.

• An organism making new organisms.

• An organism getting bigger over time.

• An organism containing water and DNA.

Multiple Choice

A complex robot can use energy and react to changes in its surroundings. Why is this robot not considered a living thing?

• It is not made of cells and cannot reproduce on its own.

• It uses energy from a battery to operate.

• It can move and respond to commands.

• It contains metal and plastic parts.

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The Cellular Basis of Life

Unicellular Organisms

• ​These living things are made of a single cell that carries out all of its life functions.

• ​​This single cell is responsible for all processes like movement, feeding, respiration, and even reproduction.

• ​A bacterium is a common example of a unicellular organism that exists as a single, simple cell.

Multicellular Organisms

• ​These organisms are made of many cells that work together to keep the organism alive and functioning.

• ​​Different types of cells are specialized for specific jobs, like nerve cells for messages or muscle cells for movement.

• ​Humans, animals, and plants are all examples of complex organisms that are made up of many cells.

Multiple Choice

What is the definition of a unicellular organism?

• It is a living thing made of a single cell that performs all life functions.

• It is a complex organism with many specialized cells.

• It is a type of plant that uses sunlight for energy.

• It is a system of organs working together in an animal.

Multiple Choice

How do the cells in a multicellular organism work together?

• They allow for different cells to perform specialized jobs.

• They make the organism smaller and simpler.

• They help the organism reproduce by dividing into two.

• They allow a single cell to do all the work for the organism.

Multiple Choice

A scientist observes an organism that has nerve cells for sending messages and muscle cells for movement. What conclusion can be drawn about this organism?

• It is a multicellular organism because it has specialized cells for different functions.

• It is a unicellular organism because it is a living thing.

• It is a bacterium because it has cells for movement.

• It is a plant cell because it can send messages.

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Observing Cells as Evidence for Life

• The invention of the microscope was essential to first observe the existence of cells.

• Microscopes provide evidence that living things have cells, while non-living things do not.

• This is an example of how science and technology are linked to make discoveries.

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Multiple Choice

What essential scientific discovery was made possible by the invention of the microscope?

• The existence of cells

• The structure of atoms

• The force of gravity

• The planets in the solar system

Multiple Choice

How do microscopes provide evidence to determine if an object is living?

• They show that living things have cells and non-living things do not.

• They measure the temperature of the object.

• They reveal the object's color and texture.

• They identify the chemicals the object is made of.

Multiple Choice

The discovery of cells happened after the microscope was invented. What does this suggest about the relationship between science and technology?

• Scientific discoveries can rely on advancements in technology.

• Technology is more important than scientific ideas.

• Science and technology are completely separate fields.

• All scientific discoveries require complex technology.

Life Cycles: Growth and Reproduction

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Growth and Development

• All living things grow and develop throughout their lifetime.

• Growth is the process of an organism becoming much larger.

• Development produces a more complex and mature individual over time.

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Asexual Reproduction

• This method of reproduction requires only one parent organism.

• The offspring are genetically identical to the single parent.

• There is no mixing of genetic material or DNA.

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Sexual Reproduction

• This process involves two different parents to create an offspring.

• Parents combine their genetic material, also known as their DNA.

• The new organism has a unique mix of parental characteristics.

Multiple Choice

Which statement best describes the difference between growth and development?

• Growth is the process of getting larger, while development is the process of becoming more complex.

• Growth is the process of becoming more complex, while development is the process of getting larger.

• Growth involves one parent, while development involves two parents.

• Growth creates genetically identical organisms, while development creates unique organisms.

Multiple Choice

What is the primary difference between how offspring are produced in asexual versus sexual reproduction?

• Asexual reproduction involves one parent, while sexual reproduction involves two parents.

• Asexual reproduction results in unique offspring, while sexual reproduction results in identical offspring.

• Asexual reproduction involves the mixing of DNA, while sexual reproduction does not.

• Asexual reproduction produces a more mature organism, while sexual reproduction produces a larger one.

Multiple Choice

A bacterium divides and produces two new bacteria. The new bacteria have the exact same genetic material as the original bacterium. What conclusion can be drawn about this process?

• It is a form of asexual reproduction because the offspring is genetically identical to the parent.

• It is a form of sexual reproduction because a new, unique organism is created.

• It is a form of development because the new plant is more complex than the parent.

• It is a form of growth because the total size of the plant population has increased.

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What Living Things Need to Survive

Autotrophs

• ​Autotrophs are also called producers because they make their own food.

• ​​Most autotrophs use energy from the sun in a process called photosynthesis.

• ​Plants, algae, and some bacteria are common examples of autotrophs in ecosystems.

Heterotrophs

• ​Heterotrophs are also known as consumers because they eat other organisms for energy.

• ​​They cannot produce their own food and must obtain it from other sources.

• ​Animals, fungi, and humans are all examples of heterotrophs found in nature.

Multiple Choice

What is the main difference between how autotrophs and heterotrophs obtain energy?

• Autotrophs make their own food, while heterotrophs get energy by eating other organisms.

• Autotrophs get energy from water, while heterotrophs get energy from sunlight.

• Autotrophs are also known as consumers, while heterotrophs are also known as producers.

• Autotrophs are only plants, while heterotrophs are only animals.

Multiple Choice

Based on the information, why are organisms like plants and algae called 'producers'?

• Because they consume other organisms for energy.

• Because they produce their own food using energy from the sun.

• Because they are the most common types of living things in an ecosystem.

• Because they move around to find resources.

Multiple Choice

What would be the most likely long-term consequence for heterotrophs in an ecosystem if all autotrophs were eliminated?

• The heterotrophs would learn to make their own food through photosynthesis.

• The heterotrophs would not be affected because they only eat other heterotrophs.

• The heterotrophs would eventually be unable to survive because their primary food source would be gone.

• The heterotrophs would switch to consuming non-living things like water and rocks for energy.

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Disproving Spontaneous Generation

Redi's Experiment

• An old and mistaken idea, called spontaneous generation, was believed for many years.

• Francesco Redi performed an experiment showing that maggots on meat came from flies.

• He proved that the maggots did not just appear from the meat by itself.

Pasteur's Experiment

• Louis Pasteur's later experiment with flasks finally disproved the old idea of spontaneous generation.

• He showed that microorganisms, or germs, in the air caused the broth to spoil.

• This confirmed that living things can only come from other living things, a key idea.

Multiple Choice

What was the idea of spontaneous generation?

• The mistaken idea that living things can appear from non-living things.

• The idea that living things can only come from other living things.

• The process by which germs in the air cause broth to spoil.

• The theory that maggots are created by flies laying eggs on meat.

Multiple Choice

What was the main conclusion from the experiments performed by Redi and Pasteur?

• They showed that living organisms come from other living organisms.

• They proved that meat and broth will always spoil over time.

• They discovered that flies and microorganisms are the same thing.

• They found that sealing a jar can prevent flies from getting in.

Multiple Choice

Based on the conclusions from Pasteur's experiment, what would most likely happen if a flask of sterile broth was kept completely sealed from the air?

• The broth will become cloudy because germs will be created from the broth itself.

• The broth will remain clear because no microorganisms can enter to cause spoiling.

• The broth will turn into maggots because there are no flies to eat them.

• The broth will only spoil if it is heated to a high temperature first.

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Common Misconceptions

Misconception	Correction
Things that move, like fire, must be alive.	Living things have all life characteristics and are made of cells.
All parts of a living thing are alive.	The cell is the smallest unit of life; hair is not alive.
The idea of spontaneous generation is valid.	Life can only come from other pre-existing life.
Humans are autotrophs if they cook their food.	Autotrophs make food internally. Humans are heterotrophs and eat for energy.

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Summary

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

• Living things use energy, grow, reproduce, and respond to stimuli.

• All life needs water, food, and a place to live.

• Life can only come from other pre-existing life.

Poll

On a scale of 1-4, how confident are you about the cellular basis of life?

• 1

• 2

• 3

• 4