Active and Passive Transport

Active and Passive Transport

High School

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Learning Objectives

• Compare active and passive transport based on energy use and concentration gradients.

• Describe the three types of passive transport: diffusion, facilitated diffusion, and osmosis.

• Explain the role of the cell membrane and ATP in cellular transport.

• Explain how cellular transport is essential for maintaining homeostasis.

Key Vocabulary

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Passive Transport

Movement of molecules across the cell membrane without using cellular energy, from high to low concentration.

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Active Transport

Movement of molecules from low to high concentration, which requires the use of cellular energy (ATP).

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Osmosis

The specific diffusion of water across a selectively permeable membrane to balance water concentration on both sides.

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Diffusion

The movement of molecules from a high concentration area to a low concentration area until equilibrium is reached.

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Cell Membrane

A semi-permeable barrier that controls which substances can move in and out of a cell based on size.

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Facilitated Diffusion

The movement of specific molecules across cell membranes through protein channels without the use of cellular energy.

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Introduction to Cellular Transport

Passive Transport

• Molecules naturally move from an area of higher concentration to one of lower concentration.

• This process of moving substances across the cell membrane does not require any cellular energy.

• It is a key way cells maintain internal stability, also known as homeostasis, without effort.

Active Transport

• Molecules are moved from an area of lower concentration to one of higher concentration.

• This movement against the concentration gradient requires the cell to use energy, usually from ATP.

• This is vital for cells to gather necessary nutrients and expel unwanted waste products.

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Solved Example 1
A cell with an internal salt concentration of 0.9% is in a solution with 2.5% salt. Will water move into or out of the cell, and is this solution hypotonic, hypertonic, or isotonic to the cell?

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Step 1: Analyze and Sketch the Problem

• Goal: Determine water movement and classify the solution.

• Knowns: Internal concentration = 0.9% salt; External concentration = 2.5% salt.

• Formula: Water moves via osmosis from a high water concentration (low solute) to a low water concentration (high solute).

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Solved Example 1
A cell with an internal salt concentration of 0.9% is in a solution with 2.5% salt. Will water move into or out of the cell, and is this solution hypotonic, hypertonic, or isotonic to the cell?

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Step 2: Solve for the Unknown

• Compare concentrations: The outside solution (2.5% salt) is more concentrated than the inside of the cell (0.9% salt).

• This means the outside has a lower water concentration.

• Therefore, water will move out of the cell to the area of lower water concentration.

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Solved Example 1
A cell with an internal salt concentration of 0.9% is in a solution with 2.5% salt. Will water move into or out of the cell, and is this solution hypotonic, hypertonic, or isotonic to the cell?

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Step 3: Evaluate the Answer

• A solution with a higher solute concentration than the cell is called a hypertonic solution.

• Since water leaves the cell, the cell will shrivel. This confirms our analysis that the external solution is hypertonic.

Multiple Choice

According to the slide, what is the primary purpose of cellular transport?

• To replicate the cell's DNA.

• To generate energy for the cell.

• To maintain homeostasis by moving substances.

• To create new proteins for the cell.

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Passive Transport

• Molecules move across the cell membrane without using cellular energy like ATP.

• This movement is driven by a difference called the concentration gradient.

• Substances naturally move from a higher to a lower concentration.

• Think of it like sliding down a slide—it requires no effort.

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Multiple Choice

What are the two defining characteristics of passive transport?

• It requires no energy and moves from high to low concentration.

• It requires ATP and moves from low to high concentration.

• It requires a protein and moves from low to high concentration.

• It requires no energy and moves from low to high concentration.

Types of Passive Transport

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Simple Diffusion

• Small molecules like O₂ and CO₂ move directly across the membrane.

• Movement is from a high concentration area to a low concentration area.

• The process continues until equilibrium is reached on both sides of membrane.

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Facilitated Diffusion

• Helps larger molecules like glucose and ions cross the cell membrane easily.

• It uses special protein channels or carriers embedded in the cell membrane.

• This type of transport process does not require any cellular energy.

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Osmosis

• Osmosis is the specific diffusion of water across a permeable membrane.

• Water moves from an area of higher to lower water concentration.

• This movement helps to balance the water levels on both sides.

Multiple Choice

Which type of passive transport requires protein channels to move substances like glucose across the membrane?

• Facilitated Diffusion

• Simple Diffusion

• Osmosis

• Active Transport

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What Is Active Transport?

• This process moves molecules against their concentration gradient from low to high concentration.

• It requires the cell to use energy in the form of ATP.

• The energy molecule, ATP, is produced by the cell’s mitochondria.

• Carrier proteins in the cell membrane are also required to move the molecules.

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Multiple Choice

What is required for active transport to move molecules against their concentration gradient?

• A selectively permeable membrane only

• Movement from high to low concentration

• Energy in the form of ATP and carrier proteins

• The diffusion of water only

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The Cell Membrane and Receptors

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

• It is selectively permeable, allowing only certain substances to pass through.

• Receptor molecules are proteins in the membrane that act as gatekeepers.

• They recognize and respond to specific signals from outside the cell.

Multiple Choice

What is the function of receptor molecules in the cell membrane?

• To produce energy for the cell.

• To allow all substances to pass freely into the cell.

• To give the membrane a rigid structure.

• To recognize, receive, and respond to specific substances.

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Common Misconceptions about Cell Transport

Misconception	Correction
All cell transport requires energy.	Passive transport does not require energy; it follows the concentration gradient.
Diffusion and osmosis are the same.	Osmosis is a special type of diffusion that only involves water.
Molecules only move from high to low concentration.	Active transport moves molecules from low to high concentration, requiring energy.

Multiple Choice

What is the key difference in how passive transport and active transport use the concentration gradient?

• Active moves down the gradient, while passive moves against it.

• Neither process is affected by the concentration gradient.

• Passive moves down the gradient, while active moves against it.

• Both move against the gradient, but only active transport uses ATP.

Multiple Choice

Why is facilitated diffusion considered a type of passive transport, even though it uses protein channels?

• Because it moves substances from low to high concentration.

• Because the protein channels require ATP to function.

• Because it does not require cellular energy (ATP) to move substances.

• Because it only transports water across the membrane.

Multiple Choice

A human red blood cell is placed in pure, distilled water. What is the most likely outcome, and why?

• The cell will shrink because water will move out via active transport.

• The cell will shrink because salt will move in via diffusion.

• The cell will not change because the membrane is impermeable to water.

• The cell will swell and may burst because water will move in via osmosis.

Multiple Choice

How would a failure in a cell's mitochondria most directly impact cellular transport?

• Simple diffusion would reverse direction, moving from low to high concentration.

• Facilitated diffusion would halt because protein channels would break down.

• Osmosis would stop because water movement requires mitochondrial energy.

• Active transport would stop due to the lack of available ATP energy.

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Summary

• Cellular transport maintains homeostasis by moving substances across the semi-permeable membrane.

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

• Osmosis is the passive transport of water across a membrane.

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

Poll

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