Cells and Life

Cells and Life

Middle School

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Learning Objectives

• Define a cell and explain the three main principles of the Cell Theory.

• Describe how cells, tissues, and organs work together as systems in the body.

• Compare different types of cells and explain the functions of their organelles.

• Explain how the invention of the microscope was critical for discovering cells.

Key Vocabulary

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Cell

The cell is the smallest, most basic building block of all living things.

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Cell Theory

The Cell Theory states that all living organisms are made up of one or more cells.

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Homeostasis

Homeostasis is the process by which an organism maintains a stable, constant internal environment.

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Prokaryote

A prokaryote is a simple, single-celled organism that does not have a membrane-bound nucleus.

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Eukaryote

A eukaryote is an organism whose cells contain a nucleus enclosed within a membrane.

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Organelle

An organelle is a tiny, specialized structure found inside a cell that performs a specific job.

Key Vocabulary

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Microscope

A microscope is an instrument that makes very small objects look bigger so that they can be studied.

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Nucleus

The nucleus is a large organelle in a cell that acts as the control center, containing the cell's genetic material.

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Mitochondrion

This organelle is the powerhouse of the cell, responsible for generating most of the cell's supply of chemical energy.

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Chloroplast

Found only in plant cells, the chloroplast is the organelle where the process of photosynthesis happens to create food.

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Tissue

A tissue is a group of similar cells that work together to carry out a particular job in the body.

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Organ

An organ is a body structure composed of different types of tissues that work together to perform a specific task.

Key Vocabulary

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Organ System

An organ system is a group of different organs that all work together to perform specific jobs.

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What Makes Something Alive?

• Living things, called organisms, have seven characteristics that make them different from nonliving things.

• An object must have all seven characteristics to be considered a living thing.

• These include being made of cells, organization, growth, and using energy.

• They also include reproduction, responding to stimuli, and maintaining internal balance (homeostasis).

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Multiple Choice

What is the primary condition that must be met to classify something as a living organism?

• It must have all seven of the characteristics of life.

• It must be able to move on its own.

• It must have at least three of the characteristics of life.

• It must be made of cells and use energy.

Multiple Choice

Which of the following is not one of the seven characteristics of living things?

• Using energy

• Responding to stimuli

• Having a shiny outer surface

• Being made of cells

Multiple Choice

A remote-controlled car uses energy from a battery and responds to a controller. Is the car a living organism according to the scientific definition?

• Yes, because it uses energy, which is a key characteristic of life.

• No, because it does not show all seven characteristics of life, such as growth and reproduction.

• Yes, because it responds to stimuli, which proves it is a living organism.

• No, because only things made by nature can be considered living.

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Discovery of the Cell & Technology

• In 1665, Robert Hooke first used the term 'cells' while observing cork.

• Anton van Leeuwenhoek improved the microscope, seeing living single-celled organisms.

• This shows how science and technology depend on one another for advances.

• These observations proved that all living things are composed of cells.

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Multiple Choice

Which statement best describes the relationship between science and technology?

• Science and technology rely on each other to make new discoveries.

• Technology is more important than science for making discoveries.

• Scientific discoveries happen without the need for new technology.

• Technology is only used for observing things that are very large.

Multiple Choice

How did the improvement of the microscope affect the scientific understanding of living things?

• It allowed scientists to see that living things are made of tiny units called cells.

• It helped prove that cork comes from living trees.

• It was used to create the first single-celled organism.

• It showed that all living things are exactly the same.

Multiple Choice

Based on the advancements made by Hooke and Leeuwenhoek, what is the most likely outcome if the microscope had not been improved?

• The discovery that all living things are made of cells would have been delayed.

• Scientists would have focused on studying larger organisms instead.

• Robert Hooke would have used a telescope to study cork.

• Living things would no longer be composed of cells.

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The Cell Theory

• The Cell Theory is a key principle in biology, defining life's basic unit.

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

• The cell is the smallest and most basic unit of all living things.

• All new cells are formed from cells that have already existed.

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Multiple Choice

Which statement best describes the main idea of the Cell Theory?

• It states that all living things are composed of cells.

• It describes the different types of animals on Earth.

• It explains how to use a microscope to see small objects.

• It lists the chemical elements found in living things.

Multiple Choice

According to the Cell Theory, what is the origin of all new cells?

• They must come from other cells that already exist.

• They are formed spontaneously from non-living matter.

• They are created by the organism as it grows larger.

• They can be built from simple molecules like water.

Multiple Choice

A scientist claims to have discovered a new life form. According to the Cell Theory, what must be true for this claim to be correct?

• The object is composed of at least one cell.

• The object is found in a natural environment.

• The object is too small to be seen without a microscope.

• The object is capable of moving on its own.

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Unicellular vs. Multicellular Organisms

Unicellular Organisms

• These living things are made up of only one single cell.

• This single cell must carry out all of the essential functions for life.

• A common and well-known example of a unicellular organism is bacteria.

Multicellular Organisms

• These are living things that are made of many different types of cells.

• The cells work together in specialized groups to perform different specific functions.

• For example, humans have specialized nerve cells and strong muscle cells.

Multiple Choice

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

• The number of cells they are made of.

• The environment where they live.

• The type of food they eat.

• Whether they are a plant or an animal.

Multiple Choice

How does the way a unicellular organism functions differ from the way a multicellular organism functions?

• A single cell performs all functions in a unicellular organism, while specialized cells perform different functions in a multicellular one.

• Unicellular organisms rely on other cells to live, while multicellular organisms are independent.

• Unicellular organisms have many specialized cells, while multicellular organisms have only one cell.

• Both types of organisms have a single cell that performs all essential functions for life.

Multiple Choice

An organism needs to be able to move using muscle tissue and send signals using nerve tissue. What can you conclude about this organism based on this evidence?

• It is a multicellular organism with specialized cells for different tasks.

• It is a very large unicellular organism like a bacterium.

• It is made of many cells that all perform the exact same function.

• It is an organism that does not need to carry out essential functions.

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Prokaryotic vs. Eukaryotic Cells

Prokaryotic Cells

• These cells are simple in structure and do not have a nucleus.

• Their genetic material is not contained within a nucleus and floats in the cytoplasm.

• Most organisms with these cells are unicellular, such as bacteria.

Eukaryotic Cells

• These cells are more complex and have a distinct nucleus to hold genetic material.

• They contain many specialized, membrane-bound structures called organelles.

• Plants, animals, fungi, and protists are all examples of eukaryotic organisms.

Multiple Choice

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

• A eukaryotic cell has a nucleus, while a prokaryotic cell does not.

• A prokaryotic cell is always larger than a eukaryotic cell.

• Eukaryotic cells are only found in bacteria.

• Prokaryotic cells contain more organelles than eukaryotic cells.

Multiple Choice

Which statement best compares a simple prokaryotic organism, like a bacterium, to a complex eukaryotic organism, like an animal?

• The animal cell is more complex, with a nucleus and specialized organelles.

• The bacterium is more complex, containing a nucleus and other organelles.

• Both cells are simple and lack a nucleus or specialized organelles.

• Both cells are complex and contain a nucleus and specialized organelles.

Multiple Choice

A scientist discovers a new single-celled organism. Upon inspection, they find that its genetic material floats freely in the cytoplasm. What is the most logical conclusion the scientist can make?

• The organism is a prokaryote because its genetic material is not in a nucleus.

• The organism is a eukaryote because it is a single-celled organism.

• The organism is a plant cell because it has genetic material.

• The organism is an animal cell because it lives in water.

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Cell Boundaries: A System's Edge

Plant Cell

• Has a strong, rigid cell wall for extra support and protection.

• A flexible cell membrane is located just inside the cell wall.

• The cell wall provides a fixed shape to the plant cell system.

Animal Cell

• Surrounded only by a flexible cell membrane that holds the cell together.

• The cell membrane controls all materials that enter and leave the cell.

• This lack of a rigid cell wall allows animal cells to be flexible.

Multiple Choice

What is the main purpose of a cell's outer boundary?

• To provide support and control what enters and leaves the cell.

• To help the cell move from one place to another.

• To store food and water for the cell's energy.

• To create energy for the cell to carry out its functions.

Multiple Choice

What is the key structural difference between the boundary of a plant cell and an animal cell?

• Plant cells have a rigid cell wall, while animal cells only have a flexible cell membrane.

• Animal cells have a cell wall, while plant cells only have a cell membrane.

• Both plant and animal cells are surrounded by a rigid cell wall.

• The cell membrane in a plant cell is rigid, while it is flexible in an animal cell.

Multiple Choice

A scientist observes a cell that can change its shape easily. Based on this evidence, what is the most likely conclusion?

• It is an animal cell, because the lack of a cell wall allows it to be flexible.

• It is a plant cell, because its cell wall has become soft.

• It is an animal cell, because its cell membrane has been removed.

• It is a plant cell, because it is storing a large amount of water.

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The Cell as a System: Energy

Mitochondria

• Mitochondria perform cellular respiration to provide the cell with energy for all its functions.

• They are known as the "powerhouses" of the cell because they generate most of its energy.

• These important organelles are found in both animal cells and plant cells.

Chloroplasts

• Chloroplasts are special organelles responsible for photosynthesis and are found only in plant cells.

• Photosynthesis is the process of converting light energy into food for the plant.

• This food is then used by mitochondria to produce usable energy for the cell.

Multiple Choice

What is the main function of the mitochondria, the 'powerhouses' of the cell?

• To generate most of the cell's energy.

• To convert light energy into food.

• To store water and nutrients for the cell.

• To control all of the cell's activities.

Multiple Choice

What is a key difference between mitochondria and chloroplasts?

• Mitochondria are in both plant and animal cells, while chloroplasts are only in plant cells.

• Chloroplasts are in both plant and animal cells, while mitochondria are only in animal cells.

• Mitochondria create food from light, while chloroplasts create energy from food.

• Chloroplasts are found in all cells, while mitochondria are only found in 'powerhouse' cells.

Multiple Choice

Which statement best explains how chloroplasts and mitochondria work together in a plant cell?

• Chloroplasts make food using light energy, and mitochondria use that food to produce energy.

• Mitochondria make food using light energy, and chloroplasts use that food to produce energy.

• Chloroplasts and mitochondria both create energy directly from sunlight.

• Mitochondria produce food for the plant, and chloroplasts turn that food into energy.

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Plant vs. Animal Cells

Animal Cells

• They are typically round or irregular in shape and have a flexible cell membrane.

• Animal cells have mitochondria to get energy but do not have a cell wall.

• They don't have chloroplasts because animals get food from what they eat.

Plant Cells

• They are usually rectangular or box-shaped due to a rigid cell wall outside the cell membrane.

• Plant cells have both mitochondria for energy and chloroplasts to make their own food.

• Chloroplasts are where photosynthesis happens, which is how plants create their food from sunlight.

Multiple Choice

What is a primary function of the cell wall in a plant cell?

• To provide a rigid, box-like shape

• To create energy from food

• To make food from sunlight

• To allow the cell to be flexible

Multiple Choice

What is the main reason that plant cells have chloroplasts while animal cells do not?

• Plants make their own food using sunlight, while animals get food by eating.

• Chloroplasts are needed to absorb water from the soil.

• Animal cells use mitochondria for energy, but plant cells do not.

• The cell wall prevents chloroplasts from fitting inside animal cells.

Multiple Choice

A scientist observes a cell that is irregular in shape and contains mitochondria but no chloroplasts. What is the most logical conclusion about this cell?

• It is an animal cell that gets energy from the food it eats.

• It is a plant cell that lives underground, away from sunlight.

• It is an animal cell that can perform photosynthesis.

• It is a plant cell that has a flexible cell membrane instead of a cell wall.

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Levels of Organization

• In multicellular organisms, the body is organized in several interacting levels.

• ​Cells are the basic units of life that group together to form tissues.

• Organs are different tissues that work together for a specific function.

• Organ systems are groups of organs that perform major functions together.

Multiple Choice

What are the basic units of life that group together to form tissues?

• Cells

• Tissues

• Organs

• Organ systems

Multiple Choice

How is an organ best described in the levels of organization?

• A single cell divides into many smaller cells.

• Different tissues work together for a specific function.

• An organ system breaks down into several organs.

• A group of organs with different functions combine.

Multiple Choice

Based on the concept of interacting levels, what is the most likely outcome if a major organ within an organ system stops working?

• The organism will immediately create a new organ to replace it.

• The entire organ system may not be able to perform its major function.

• The cells in the other organs will stop working completely.

• The tissues in that organ will form a new, different organ.

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Common Misconceptions

Misconception	Correction
Plant cells have a cell wall instead of a cell membrane.	Plant cells have both a cell wall and a cell membrane.
Bigger organisms have bigger cells.	Larger organisms have more cells, not bigger cells.
Organs and organ systems work independently.	Organ systems constantly interact and work together.

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Summary

• Cells are the basic unit of life and organize into tissues and organs.

• Engineering advances like the microscope were essential for discovering cells.

• Organelles like the nucleus and mitochondria perform important jobs in the cell.

• Plant cells contain a cell wall and chloroplasts, which animal cells do not.

Poll

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

• 1 (Not confident at all)

• 2 (A little confident)

• 3 (Mostly confident)

• 4 (Very confident)