Cell Membrane Control - Middle School Life Science

What is the main function of the cell membrane in controlling cell contents?

It selectively regulates what enters and leaves the cell. Acts as a gatekeeper, maintaining cell homeostasis.
What is diffusion across a membrane called when it requires no energy from the cell?

Passive transport. Molecules move naturally down their concentration gradient.
What type of membrane protein provides a passageway for specific ions or molecules?

Channel protein. Acts like a tunnel for specific ions or small molecules.
What is active transport?

Movement against the gradient using energy (ATP). Pumps molecules from low to high concentration areas.
What type of membrane protein changes shape to move a substance across the membrane?

Carrier protein. Binds and releases molecules through conformational changes.
What type of transport moves substances from high to low concentration without energy input?

Passive transport. No ATP needed; molecules move down concentration gradient.
Identify the transport type: glucose enters a cell down its gradient using a membrane protein.

Facilitated diffusion. Protein assists but no energy needed for downhill movement.
What is diffusion?

Movement from high concentration to low concentration. Molecules naturally spread out to reach equilibrium.
What type of transport moves substances from low to high concentration and requires energy?

Active transport. Uses energy to pump molecules against concentration gradient.
Identify the transport type: a cell uses ATP to pump $\text{Na}^+$ out where $\text{Na}^+$ is already higher outside.

Active transport. Energy required to pump ions against concentration gradient.
What is the basic structure of the cell membrane that forms a barrier?

Phospholipid bilayer. Two layers of phospholipids create the membrane's foundation.
What is a channel protein, in terms of membrane transport function?

A protein pore that lets specific ions or water pass. Forms tunnel for passive movement of specific molecules.
Which direction does water move by osmosis relative to solute concentration?

Toward the side with higher solute concentration. Water dilutes concentrated solutions to reach equilibrium.
Identify the transport type: a cell uses ATP to pump sodium ions out against the concentration gradient.

Active transport. ATP powers uphill movement against concentration gradient.
What phrase describes the cell membrane property of allowing some substances through but not others?

Selectively permeable (semipermeable). Like a filter that blocks some molecules while letting others pass.
Which part of a phospholipid avoids water: the head or the tails?

The hydrophobic fatty acid tails avoid water. Nonpolar tails repel water, forming the membrane's interior.
Which part of a phospholipid is hydrophobic and points inward away from water?

Fatty acid tails (hydrophobic tails). Water-fearing tails cluster together in membrane's interior.
Which part of a phospholipid faces water: the head or the tails?

The hydrophilic head faces water. Polar heads are attracted to water molecules.
What is exocytosis?

Cell releases substances when vesicles fuse with the membrane. Vesicles merge with membrane to expel contents outside.
Identify the transport type: oxygen moves into a cell from higher outside concentration to lower inside concentration.

Simple diffusion (passive transport). Small gas molecules diffuse freely without proteins or energy.
What property of the cell membrane describes allowing some substances through but not others?

Selective permeability (semipermeable). Allows only certain molecules through while blocking others.
What is the cell membrane mainly made of that forms a barrier between cell and environment?

A phospholipid bilayer with embedded proteins. Proteins help transport specific molecules across the lipid barrier.
What is endocytosis?

Cell takes in substances by forming membrane vesicles. Membrane pinches inward to engulf external materials.
What is diffusion across a membrane without transport proteins called?

Simple diffusion. Small molecules pass directly through the lipid bilayer.
What term describes a concentration difference across a membrane?

Concentration gradient. The difference drives passive transport processes.
What is a carrier protein, in terms of membrane transport function?

A protein that binds a substance and changes shape to move it. Undergoes conformational change to transport molecules.
Identify the transport type: a white blood cell engulfs a bacterium into a vesicle.

Endocytosis (phagocytosis). Cell eating - membrane surrounds and engulfs large particles.
Which cellular molecule usually provides the energy for active transport?

ATP. Cell's energy currency powers uphill molecular transport.
What is the main structural model that explains cell membrane organization?

Fluid mosaic model. Describes membrane as flexible with proteins embedded in lipids.
Which option describes facilitated diffusion: movement with or against the gradient?

With the gradient (high to low) using a membrane protein. Proteins help large or polar molecules cross without energy.
Identify the transport type: glucose crosses the membrane through a specific protein with no ATP used.

Facilitated diffusion. Protein channels help polar molecules move down gradient.
Identify the transport type: a white blood cell engulfs a bacterium by surrounding it with membrane.

Endocytosis (phagocytosis). Cell eating: membrane surrounds and engulfs large particles.
Identify the transport type: oxygen moves directly through the bilayer from high to low concentration.

Simple diffusion (passive transport). Small, nonpolar molecules cross the lipid bilayer freely.
Which part of a phospholipid is hydrophilic and faces the water on each side of the membrane?

Phosphate head (hydrophilic head). Water-loving heads face outward toward aqueous environments.
What is osmosis?

Diffusion of water across a selectively permeable membrane. Water moves to balance solute concentrations.
Which molecule provides energy for many active transport processes?

ATP. The cell's energy currency powers transport pumps.
Which type of transport uses a membrane protein to move molecules down their concentration gradient?

Facilitated diffusion. Proteins help larger molecules cross without using energy.

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