Obtaining and Removing Materials

Obtaining and Removing Materials

Middle School

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Learning Objectives

• Explain how the cell membrane controls what enters and leaves the cell.

• Differentiate between passive transport and active transport.

• Predict the movement of water based on hypotonic, hypertonic, and isotonic solutions.

• Describe the roles of the four major biomolecules in cellular transport.

Key Vocabulary

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Homeostasis

Maintaining a stable internal environment within a cell or an organism.

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Selectively Permeable

Allowing some substances to pass through a membrane more easily than others do.

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Concentration Gradient

The difference in the concentration of a substance between two separate areas.

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Passive Transport

The movement of substances across a cell membrane without using any cellular energy.

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Active Transport

Moving materials across a cell membrane against a concentration gradient, which requires energy.

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Osmosis

The diffusion of water molecules through a selectively permeable or semipermeable membrane.

Key Vocabulary

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Tonicity

Tonicity is the comparison of solute concentration on the outside of a cell to the inside.

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Endocytosis

Endocytosis is the process of capturing a substance from outside the cell by engulfing it completely.

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Exocytosis

Exocytosis is the process of vesicles fusing with the plasma membrane to release their contents outside.

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The Cell Membrane: A Smart Barrier

• The cell membrane is a phospholipid bilayer with hydrophilic heads (facing outwards) and hydrophobic tails (embedded inside).

• ​Proteins embedded in the membrane act as channels or pumps for transport.

• Carbohydrate chains are ID tags; cholesterol provides flexibility in animal cells.

• It is selectively permeable, meaning it controls what enters and exits the cell.

Multiple Choice

What is the primary function of the cell membrane?

• To control what enters and leaves the cell.

• To provide the cell with a rigid structure.

• To create energy for the cell's activities.

• To store all of the cell's genetic information.

Multiple Choice

How is the phospholipid bilayer structured to form an effective barrier in a watery environment?

• The water-loving heads face outward and the water-fearing tails face inward.

• The water-fearing tails face outward and the water-loving heads face inward.

• The heads and tails are mixed together randomly throughout the layer.

• The entire layer is made of water-loving parts to attract water.

Multiple Choice

If a cell's membrane lost its proteins but kept its phospholipid bilayer, what would be the most likely consequence?

• The transport of specific substances into and out of the cell would be disrupted.

• The membrane would completely dissolve in the surrounding water.

• The cell would no longer have a double layer of phospholipids.

• The cell would lose its ability to identify other cells.

Passive Transport: Movement Without Energy

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Simple Diffusion & Osmosis

• ​Particles move from a high concentration area to a low concentration area.

• ​​Small molecules like O₂ and CO₂ slip through the cell membrane.

• ​Osmosis is the special term for the diffusion of water across membranes.

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Tonicity & Water Flow

• ​Tonicity compares a solution’s solute concentration to what's inside a cell.

• ​​In hypotonic solutions, water enters the cell, causing it to swell.

• ​In hypertonic solutions, water exits the cell, causing it to shrink.

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Facilitated Diffusion

• ​Some molecules like glucose need help to cross the cell membrane.

• ​​Channel and carrier proteins create a specific pathway for these molecules.

• ​This process does not require any energy from the cell to work.

Multiple Choice

What is the defining characteristic of all forms of passive transport, including simple diffusion, osmosis, and facilitated diffusion?

• They occur without the cell using energy.

• They require special proteins to move molecules.

• They only move water across the cell membrane.

• They move particles from low to high concentration.

Multiple Choice

What is the key difference between how small molecules like oxygen move across the membrane and how larger molecules like glucose move?

• Oxygen slips through the membrane, while glucose needs a protein pathway.

• Oxygen requires energy to move, while glucose moves freely.

• Glucose is a type of osmosis, while oxygen moves by diffusion.

• Oxygen moves into the cell, while glucose only moves out.

Multiple Choice

If a cell is placed into a solution that has a much higher concentration of solutes than the cell's cytoplasm, what is the most likely result?

• Water will diffuse out of the cell, causing it to shrink.

• Water will diffuse into the cell, causing it to swell.

• Solutes will move into the cell until the concentrations are equal.

• The cell will use energy to pump water out of the cell.

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Active Transport: Pushing Against the Flow

• Active transport moves materials from a low to a high concentration area.

• This process requires energy from a molecule called ATP to work.

• Endocytosis brings materials into the cell, while exocytosis pushes them out.

• These bulk transport methods use vesicles to move large particles.

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Multiple Choice

What is the primary function of active transport?

• To move materials from an area of low concentration to an area of high concentration.

• To move materials from an area of high concentration to an area of low concentration.

• To allow materials to enter the cell without using energy.

• To break down large particles into smaller ones for storage.

Multiple Choice

What is the relationship between endocytosis and exocytosis?

• They are both forms of bulk transport that use vesicles to move large particles.

• Endocytosis creates energy for the cell, while exocytosis uses energy.

• Endocytosis moves materials out of the cell, while exocytosis brings them in.

• They both move materials from a high concentration area to a low one.

Multiple Choice

What would be the most likely consequence if a cell's ability to produce ATP was suddenly blocked?

• The cell would be unable to move materials from low to high concentration areas.

• The cell would rely on exocytosis to bring in more energy.

• The cell's vesicles would start producing their own ATP.

• The cell would move materials much faster to save energy.

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The Biomolecule Team for Transport

Lipids & Proteins

• Phospholipids form the main structure of the cell membrane, creating a protective hydrophobic barrier.

• This essential lipid barrier is effective at keeping many unwanted substances out of the cell.

• Proteins act as channels, carriers, and pumps to move specific materials across the membrane.

Carbs & Nucleic Acids

• Carbohydrates attach to proteins and lipids, serving as unique ID tags for the cell.

• These special tags help cells recognize each other and bind to necessary transport materials.

• Nucleic acids like DNA provide the genetic instructions for building the cell’s transport proteins.

Multiple Choice

What is the main function of phospholipids in the cell membrane?

• To form a protective barrier that controls what enters and leaves the cell.

• To provide the genetic instructions for building cell parts.

• To act as channels and pumps for moving materials.

• To serve as ID tags for cell recognition.

Multiple Choice

What is the relationship between proteins and carbohydrates in their roles for the cell membrane?

• Carbohydrates identify materials for transport, and proteins create pathways for them to cross the membrane.

• Proteins form the main barrier, while carbohydrates provide the genetic instructions.

• Both proteins and carbohydrates attach to the membrane to make it stronger.

• Both proteins and carbohydrates store the energy the cell needs for transport.

Multiple Choice

If a cell's DNA has a mutation that prevents it from building the correct transport proteins, what is the most likely consequence?

• The cell would not be able to move specific materials across its membrane.

• The cell's phospholipid barrier would dissolve.

• The cell would lose its ability to recognize other cells.

• The cell would create the wrong kind of nucleic acids.

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Common Misconceptions

Misconception	Correction
Particles stop moving at equilibrium.	Particles are in constant motion, but with no net change at equilibrium.
Osmosis is the movement of salt or sugar.	Osmosis is the specific movement of water across a membrane.
All membrane transport requires energy.	Only active transport requires energy; passive transport does not.
The cell membrane is a solid, rigid wall.	The cell membrane is fluid and flexible, not rigid.

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Summary

• The cell membrane is selectively permeable, maintaining homeostasis.

• Passive transport requires no energy, while active transport uses ATP.

• Water moves via osmosis based on tonicity, and bulk transport moves large particles.

• Lipids, proteins, and carbohydrates are key biomolecules in the membrane’s function.

Poll

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