Cell Structure and Function

Cell Structure and Function

Middle School

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Learning Objectives

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

• Compare plant and animal cells and describe the function of their main parts.

• Explain how cells group together to create tissues and organs in organisms.

• Understand why a cell's size is important for transporting materials.

Key Vocabulary

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Cell

A cell is the most basic and smallest unit of all life.

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Unicellular

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

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Multicellular

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

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Cell Membrane

The cell membrane is the flexible barrier that controls what substances enter and leave a cell.

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Cell Wall

The cell wall is the rigid outer layer that supports and protects a plant cell.

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Nucleus

The nucleus is the cell's control center, which directs all of the cell’s activities.

Key Vocabulary

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Mitochondria

Mitochondria are the powerhouses of the cell, converting the food we eat into usable energy.

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Chloroplast

Chloroplasts are found in plant cells and use sunlight to make their own food.

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Tissue

A tissue is a group of similar cells that work together to perform a specific job.

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Organ

An organ is made of different types of tissues that all work together to function.

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Organ System

An organ system is a group of organs that cooperate to perform major functions.

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SA:V Ratio

The surface-area-to-volume ratio compares the outside surface of an object to its internal volume.

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Living Things are Made of Cells

Unicellular Organisms

• Unicellular organisms are living beings that are made of only one single cell.

• This single cell must carry out all essential functions of life to survive.

• Bacteria and amoebas are common examples of unicellular organisms you can find.

Multicellular Organisms

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

• Different cells are specialized to perform specific jobs within the organism's body.

• Plants, animals, and fungi are all complex examples of multicellular organisms.

Multiple Choice

What is the fundamental difference between unicellular and multicellular organisms?

• The number of cells they are made of.

• The environment where they can be found.

• The type of food they consume to live.

• The way they produce their own energy.

Multiple Choice

How does the way essential functions are carried out differ between unicellular and multicellular organisms?

• In unicellular organisms, one cell does everything; in multicellular organisms, different cells have specific jobs.

• Unicellular organisms do not need to perform life functions, while multicellular organisms do.

• Unicellular organisms have cells that work alone, while multicellular cells compete with each other.

• In unicellular organisms, all cells are the same; in multicellular organisms, all cells are different.

Multiple Choice

If a single skin cell from an animal is separated from the body, why can it not survive on its own?

• The cell is specialized and depends on other cells to perform all the functions needed for life.

• The cell is a type of bacteria that cannot live outside of an animal.

• The cell is too large to survive without being part of a bigger structure.

• The cell needs to be in a unicellular organism to carry out its job.

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The Cell as a System

• A cell is a complete system where each part, or organelle, has a job.

• The cell membrane controls what materials are able to enter and leave the cell.

• The nucleus is the control center, while mitochondria work to produce its energy.

• In plant cells, chloroplasts have the important job of creating the cell's food.

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Multiple Choice

What does it mean to say that a cell is a 'complete system'?

• Each part of the cell has a specific job to do.

• The cell is the smallest part of an animal.

• The cell's main job is to create food.

• A cell is a simple structure with only one part.

Multiple Choice

What is the relationship between the nucleus and the mitochondria within the cell system?

• The nucleus acts as the control center, while the mitochondria produce energy.

• The nucleus produces energy, while the mitochondria act as the control center.

• The nucleus allows materials to leave the cell, while the mitochondria create food.

• The nucleus creates food, while the mitochondria allow materials to enter the cell.

Multiple Choice

If a plant cell's membrane were damaged and could no longer control what enters the cell, what is the most likely consequence for the chloroplasts?

• The chloroplasts would not be able to get the materials needed to make food.

• The mitochondria would start making food instead of energy.

• The nucleus would send signals to the cell to find a new source of energy.

• The cell would produce more energy to fix the cell membrane.

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What Surrounds a Cell?

Cell Membrane

• ​The cell membrane is a flexible barrier that surrounds and protects every type of cell.

• ​​It forms a boundary between the cell and its environment, keeping cell parts contained.

• ​It controls what substances are allowed to enter or leave the cell, like a gatekeeper.

Cell Wall

• ​The cell wall is a tough, rigid layer found outside the cell membrane in plants.

• ​​It provides the strong structural support that helps give plant cells their fixed shape.

• ​This sturdy outer layer also provides the cell with much-needed protection from outside harm.

Multiple Choice

What is the main function of the cell membrane?

• To provide the cell with a fixed, rigid shape.

• To control what substances enter and leave the cell.

• To create energy for the cell to use.

• To help the cell move around its environment.

Multiple Choice

How do the cell wall and cell membrane differ in their structure and function?

• The cell wall is a rigid layer that provides structural support, while the cell membrane is a flexible barrier.

• The cell membrane is a rigid layer, while the cell wall is a flexible barrier.

• Both the cell wall and cell membrane are rigid layers that provide a fixed shape.

• Both the cell wall and cell membrane are flexible barriers that control what enters the cell.

Multiple Choice

A plant is not watered for several days, causing its cells to lose water. What best explains why the plant's cells keep their basic shape?

• The flexible cell membrane can easily stretch to hold the cell together.

• The rigid cell wall provides a strong outer layer that prevents the cell from losing its shape.

• The cell membrane will let all the water out to keep its shape.

• The cell wall can absorb all the extra water.

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Powering the Cell

Mitochondria

• Found in both animal and plant cells, they are the powerhouses of the cell.

• They perform cellular respiration to get energy from food.

• This process creates a usable energy form for the cell called ATP.

Chloroplasts

• Found only in plant cells, these are the food factories for the plant.

• They perform photosynthesis by using light energy from the sun.

• They make a sugar called glucose from water and carbon dioxide.

Multiple Choice

What is the primary function of mitochondria within a cell?

• To convert food into a usable form of energy called ATP.

• To create a hard outer layer for protection.

• To store water and nutrients for later use.

• To use sunlight to produce food for the cell.

Multiple Choice

Which statement correctly compares the location and function of chloroplasts and mitochondria?

• Chloroplasts are only in plant cells and make glucose, while mitochondria are in both and make ATP.

• Chloroplasts are only in animal cells and make ATP, while mitochondria are in plant cells and make glucose.

• Chloroplasts use food to make energy, while mitochondria use sunlight to make food.

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

Multiple Choice

If a healthy plant was moved into a completely dark room, what would be the most likely immediate effect on the plant's ability to power itself?

• The plant would not be able to produce glucose, its food source.

• The plant's cells would not be able to convert energy into ATP.

• The plant would start performing cellular respiration to create food.

• The plant's animal cells would begin to shrink.

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Controlling the Cell: The Nucleus

• The nucleus is a large organelle that directs all of the cell's activities.

• It acts as the main control center for the entire cell system.

• Inside, genetic information is stored in a special molecule called DNA.

• DNA provides instructions for making the proteins a cell needs to function.

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Multiple Choice

What is the main function of the nucleus in a cell?

• To act as the main control center for the cell

• To produce energy for the cell to use

• To store water and nutrients for the cell

• To control what enters and leaves the cell

Multiple Choice

How does the nucleus direct a cell's activities?

• It stores the cell's genetic information in DNA, which contains instructions for making proteins.

• It creates energy by breaking down DNA molecules.

• It uses proteins to send messages out of the cell.

• It absorbs instructions from outside the cell and stores them in DNA.

Multiple Choice

Based on the role of the nucleus, what would be the most likely consequence if it were damaged?

• The cell would not be able to create the proteins needed for it to function.

• The cell would immediately run out of water and nutrients.

• The cell would lose its shape and structure.

• The cell would be unable to absorb energy from sunlight.

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Plant Cells vs. Animal Cells

Animal Cells

• These cells are typically round or have an irregular shape.

• They have a flexible cell membrane but do not have a cell wall.

• Animal cells have many small vacuoles and no chloroplasts.

Plant Cells

• These cells are more rigid and have a fixed, rectangular shape.

• They have a strong cell wall outside of the cell membrane for support.

• Plant cells have chloroplasts and one large central vacuole.

Multiple Choice

What is a key structural difference between plant and animal cells?

• Plant cells have a rigid cell wall, while animal cells do not.

• Animal cells have chloroplasts, while plant cells do not.

• Plant cells have many small vacuoles, while animal cells have one large one.

• Animal cells are rectangular, while plant cells are round.

Multiple Choice

How does a cell wall contribute to the characteristics of a plant cell?

• It provides a rigid structure that gives the cell a fixed shape.

• It allows the cell to be flexible and change its shape easily.

• It contains chloroplasts for making food.

• It stores water in many small vacuoles.

Multiple Choice

A scientist observes a cell that is irregularly shaped and has a flexible cell membrane but no cell wall. What conclusion can be drawn about this cell?

• A plant cell, because it has a cell membrane.

• An animal cell, because it has an irregular shape and lacks a cell wall.

• A plant cell, because it is a living organism.

• An animal cell, because it contains a large central vacuole.

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The Surface-Area-to-Volume Ratio

• A cell needs a large surface area compared to its volume to be efficient.

• This is known as the surface-area-to-volume ratio.

• As a cell grows, its volume increases faster than its surface area.

• This is why most cells are small, ensuring efficient transport of materials.

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Multiple Choice

What does a cell need in order to transport materials efficiently?

• A large surface area compared to its volume

• A large volume compared to its surface area

• An equal amount of surface area and volume

• A very thick cell membrane

Multiple Choice

What is the relationship between a cell's surface area and volume as it grows?

• Its volume increases faster than its surface area.

• Its surface area increases faster than its volume.

• Its volume and surface area increase at the same rate.

• Its volume and surface area both decrease.

Multiple Choice

What is the best explanation for why most cells are small?

• To maintain an efficient surface-area-to-volume ratio for material transport.

• Because large cells have a more efficient surface-area-to-volume ratio.

• Because small cells require more energy to function.

• To prevent the cell from dividing too quickly.

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From Cells to Organisms

• In multicellular organisms, the body is a system that begins with individual cells.

• Cells with similar functions group together to form specialized tissues like muscle tissue.

• Different tissues work together to form organs that perform specific jobs, like the heart.

• Organs team up in organ systems to carry out complex bodily functions.

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Multiple Choice

What is the basic unit that groups together to form all other parts of a multicellular organism?

• Cells

• Tissues

• Organs

• Organ systems

Multiple Choice

How is an organ, like the heart, formed?

• A single cell divides many times.

• Different tissues work together.

• An organ system creates them.

• Similar organs are grouped together.

Multiple Choice

If an organ within an organ system is damaged, what is the most likely consequence for the system?

• The organ system may not be able to carry out its complex function.

• The cells in the organ will start performing a different job.

• The tissues in the organ will turn into a different type of tissue.

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

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Common Misconceptions

Misconception	Correction
Living things must be large.	Many living things are microscopic and have only one cell, like bacteria.
Only animal cells have mitochondria.	Plant cells also have mitochondria to convert food into usable energy.
Bigger cells are more efficient.	Smaller cells are more efficient due to a larger surface-area-to-volume ratio.

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Summary

• Living things are made of cells, which form tissues, organs, and systems.

• Organelles work together; the membrane controls entry and the wall provides support.

• Plant cells have a cell wall, chloroplasts, and a large central vacuole.

• Cells are small to maintain a large surface-area-to-volume ratio for transport.

Poll

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

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