Active and Passive Transport

Active and Passive Transport

Middle School

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Learning Objectives

• Define active and passive transport and the cell membrane's role in these processes.

• Compare diffusion, osmosis, and facilitated diffusion as types of passive transport.

• Explain how active transport uses energy to move substances against a concentration gradient.

• Describe endocytosis and exocytosis for transporting large molecules across the cell membrane.

• Understand homeostasis and how cell transport helps maintain this stable internal environment.

Key Vocabulary

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Passive Transport

Substances move across the cell membrane from high to low concentration without using any energy.

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Active Transport

Substances move across the cell membrane from low to high concentration, a process that requires energy.

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Homeostasis

An organism or cell maintains a stable internal environment to ensure it can function normally.

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Concentration Gradient

This measures how the concentration of a substance changes from one area to another across space.

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Selective Permeability

A property of cell membranes that allows certain substances to pass through while blocking others.

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Osmosis

A special type of diffusion involving the movement of water molecules across a semipermeable membrane.

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The Cell Membrane: A Gatekeeper

• The cell membrane controls what gets in and out of the cell.

• This function helps maintain a stable internal balance called homeostasis.

• It is selectively permeable, choosing what substances can pass through.

• Hydrophobic molecules pass easily, but hydrophilic and large molecules cannot.

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Multiple Choice

Why is the cell membrane described as 'selectively permeable'?

• It allows all substances to pass through freely.

• It only allows water molecules to pass through.

• It allows some substances to pass through but blocks others.

• It blocks all substances from entering or leaving the cell.

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Types of Passive Transport

Simple Diffusion

• Substances move across the cell membrane without the cell using any energy.

• This movement is down a concentration gradient, from a high to low concentration.

• Osmosis is a special type of diffusion involving only water molecules.

Facilitated Diffusion

• Special transport proteins are used to help certain substances cross the cell membrane.

• Channel proteins form small pores or tunnels for small ions and water to pass.

• Carrier proteins change their shape to carry specific, larger molecules across the membrane.

Multiple Choice

What is the key difference between simple diffusion and facilitated diffusion?

• Facilitated diffusion requires energy, while simple diffusion does not.

• Facilitated diffusion uses transport proteins to help substances cross the membrane.

• Facilitated diffusion moves substances against the concentration gradient.

• Simple diffusion only moves water molecules.

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Effects of Osmosis on Cells

• Water diffuses out of a cell when solute concentration is higher outside.

• This causes an animal cell to shrivel and a plant cell membrane to pull away.

• Water diffuses into a cell when the solute concentration is lower outside.

• Animal cells may burst, while plant cells become firm, or turgid.

Multiple Choice

What happens to an animal cell when it is placed in a solution with a lower solute concentration than the cell's interior?

• The cell shrivels.

• The cell swells and may burst.

• There is no change in the cell.

• The cell's plasma membrane pulls away from the cell wall.

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Active Transport

• Active transport uses energy from a molecule called ATP to move substances.

• ​It moves particles against their concentration gradient, from low to high concentration.

• The sodium-potassium pump moves sodium ions (Na⁺) out of the cell.

• It also pumps potassium ions (K⁺) into the cell to maintain balance.

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Multiple Choice

Which statement accurately describes active transport?

• It moves substances from high to low concentration without using energy.

• It is a type of passive transport that uses carrier proteins.

• It moves substances from low to high concentration and requires energy (ATP).

• It only transports water molecules across the cell membrane.

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Vesicle Transport

Endocytosis

• Endocytosis is the process of moving a large substance into the cell.

• The plasma membrane surrounds the material, forming a pocket around it.

• This pocket pinches off from the membrane, creating a vesicle inside the cell.

Exocytosis

• Exocytosis is the process of moving a large substance out of the cell.

• A vesicle containing the material moves towards the cell membrane.

• The vesicle fuses with the membrane and releases its contents outside the cell.

Multiple Choice

A cell needs to expel a large protein waste product. Which process would it most likely use?

• Endocytosis

• Osmosis

• Facilitated diffusion

• Exocytosis

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Common Misconceptions About Cell Transport

Misconception	Correction
All forms of cell transport require energy.	Passive transport, like diffusion and osmosis, does not require cellular energy.
Facilitated diffusion is active transport because it uses proteins.	It's passive transport that uses proteins but no cellular energy (ATP).
Osmosis and diffusion are the exact same process.	Osmosis is a specific type of diffusion for water across a membrane.
Only small molecules can cross the cell membrane.	Large molecules are transported via vesicles through endocytosis and exocytosis.

Multiple Choice

What is the primary difference in how facilitated diffusion and active transport function?

• Both require energy, but they move substances in opposite directions.

• Facilitated diffusion moves substances against the concentration gradient, while active transport moves them down the gradient.

• Active transport requires energy to move substances against their concentration gradient, while facilitated diffusion does not.

• Both are passive processes, but active transport uses carrier proteins.

Multiple Choice

How does the sodium-potassium pump demonstrate the principle of active transport?

• It uses water movement to balance the concentration of sodium and potassium ions.

• It uses energy (ATP) to move both sodium and potassium ions from a low concentration area to a high concentration area.

• It allows sodium and potassium ions to naturally diffuse down their concentration gradients.

• It creates protein channels for sodium and potassium to pass through without using energy.

Multiple Choice

A cell's ability to produce ATP is completely blocked. What would be the most immediate and significant consequence for cell transport?

• Osmosis would stop, and the cell would be unable to regulate its water content.

• Simple diffusion of oxygen into the cell would cease.

• The sodium-potassium pump and other active transport processes would stop functioning.

• Facilitated diffusion would reverse direction, moving substances out of the cell.

Multiple Choice

Analyze the impact on a plant cell if it is moved from a freshwater environment to a saltwater environment.

• Water will move into the cell, causing it to become more turgid.

• The cell will not be affected due to its rigid cell wall.

• The cell will burst due to the high influx of salt.

• Water will move out of the cell, causing the plasma membrane to pull away from the cell wall.

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Summary

• The cell membrane is selectively permeable, controlling transport to maintain homeostasis.

• Passive transport moves substances down the concentration gradient without using energy.

• Active transport uses energy (ATP) to move substances against the concentration gradient.

• Facilitated diffusion uses proteins, while endocytosis and exocytosis move large molecules.

Poll

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

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