Biology Chapter on Plasma Membrane Function

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Questions and Answers

What is the primary role of transport proteins in cell membranes?

To facilitate the movement of hydrophilic substances across the membrane (correct)

To provide energy for cellular processes

To strengthen the membrane structure

To allow lipids to pass freely through the membrane

Which type of transport protein has a hydrophilic channel for specific molecules?

Channel proteins (correct)

Aquaporins

Carrier proteins

Gated proteins

What occurs during passive transport?

Transport proteins are unnecessary

Energy is required to facilitate movement

Substances diffuse down their concentration gradient without energy investment (correct)

Substances are moved against their concentration gradient

In the context of osmosis, water moves from areas of:

Lower solute concentration to higher solute concentration Signup and view all the answers

What is an isotonic solution in relation to cell water balance?

Solute concentration is the same as that inside the cell Signup and view all the answers

When a cell is placed in a hypertonic solution, what is the expected outcome?

The cell will lose water Signup and view all the answers

Which term describes the control of solute concentrations and water balance in organisms?

Osmoregulation Signup and view all the answers

Which type of environment poses problems for organisms regarding water balance?

Hypertonic and hypotonic environments Signup and view all the answers

What is the function of membrane proteins in relation to the plasma membrane?

They assist in the exchange of materials across the membrane. Signup and view all the answers

Which characteristic of phospholipids contributes to the formation of the bilayer in the plasma membrane?

They are amphipathic and possess both hydrophilic and hydrophobic regions. Signup and view all the answers

How do membrane carbohydrates assist in cell-cell recognition?

They bind to other cells and molecules on the extracellular surface. Signup and view all the answers

What is the main reason that the plasma membrane exhibits selective permeability?

Because of the arrangement and properties of phospholipids and proteins. Signup and view all the answers

Which statement about transmembrane proteins is accurate?

They penetrate deeply into the lipid bilayer and span the entire membrane. Signup and view all the answers

Why can HIV only infect certain individuals?

HIV requires the presence of CD4 and CCR5 surface proteins to infect cells. Signup and view all the answers

What describes the fluid mosaic model of membrane structure?

Membranes are dynamic and composed of various proteins and lipids. Signup and view all the answers

What defines the selective permeability of the plasma membrane?

It regulates the passage of certain molecules while prohibiting others. Signup and view all the answers

What occurs to a plant cell placed in a hypotonic solution?

The cell swells and becomes turgid. Signup and view all the answers

What is facilitated diffusion primarily aided by?

Transport proteins Signup and view all the answers

How does the sodium-potassium pump function?

It actively transports sodium out of the cell and potassium into the cell. Signup and view all the answers

Which statement describes plasmolysis in plant cells?

It is a lethal effect caused by losing water. Signup and view all the answers

What is the role of aquaporins in cell membranes?

To facilitate the diffusion of water. Signup and view all the answers

How does cotransport function in relation to plant cells?

It couples the active transport of one solute to drive the transport of another. Signup and view all the answers

What is primarily involved in the process of exocytosis?

Transport vesicles Signup and view all the answers

Which of the following statements is true regarding active transport?

It is performed by specific proteins embedded in the membranes. Signup and view all the answers

Study Notes

Plasma Membrane: Structure and Function

Separates the living cell from its surroundings.
Exhibits selective permeability, allowing some substances to cross more easily than others.

Fluid Mosaic Model

Membranes are fluid structures with a mosaic of proteins embedded in a phospholipid bilayer.
Phospholipids are amphipathic (hydrophilic and hydrophobic regions).
Protein distribution within the membrane is not random.

Membrane Proteins

Determine most membrane functions.
Peripheral proteins are bound to the membrane surface.
Integral proteins penetrate the hydrophobic core; transmembrane proteins span the entire membrane.

Six Major Functions of Membrane Proteins

Transport
Enzymatic activity
Signal transduction
Cell-cell recognition
Intercellular joining
Attachment to the cytoskeleton and extracellular matrix (ECM)
HIV infection requires binding to CD4 and CCR5 proteins on immune cells; individuals lacking CCR5 are resistant.

Membrane Carbohydrates

Involved in cell-cell recognition.
Covalently bonded to lipids (glycolipids) or proteins (glycoproteins).

Membrane Permeability

Selective permeability regulates molecular traffic.
Hydrophobic molecules cross easily; hydrophilic molecules do not.

Transport Proteins

Facilitate passage of hydrophilic substances.
Channel proteins provide hydrophilic channels.
Aquaporins are channel proteins for water.
Carrier proteins bind molecules and change shape to shuttle them across.
Transport proteins exhibit specificity.

Passive Transport: Diffusion

Movement of substances across a membrane without energy investment.
Substances diffuse down their concentration gradient (high to low concentration).
Dynamic equilibrium: equal movement in both directions.
No work is required; it’s passive.

Osmosis

Diffusion of water across a selectively permeable membrane.
Water moves from lower to higher solute concentration.

Tonicity

Isotonic solution: no net water movement.
Hypertonic solution: cell loses water.
Hypotonic solution: cell gains water.
Osmoregulation is crucial for maintaining water balance in different environments.

Water Balance in Cells

Plant cells with cell walls: turgid (hypotonic), flaccid (isotonic), plasmolysis (hypertonic).
Animal cells: cell lysis (hypotonic), crenation (hypertonic).

Facilitated Diffusion

Passive transport aided by proteins.
Channel proteins create corridors.
Gated channels open/close in response to stimuli.
Carrier proteins change shape to translocate solutes.

Active Transport

Moves substances against their concentration gradient.
Requires energy (usually ATP).
Maintains concentration gradients different from surroundings.
Sodium-potassium pump is an example.

Cotransport

Active transport of one solute indirectly drives transport of others.
Plants use proton pumps to drive nutrient uptake.

Bulk Transport

Exocytosis: vesicles fuse with membrane, releasing contents outside.
Endocytosis: substances are taken into the cell via vesicles (types: phagocytosis, pinocytosis, receptor-mediated endocytosis).

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Description

This quiz covers the structure and function of the plasma membrane, highlighting its role in cell separation and selective permeability. It also delves into the fluid mosaic model and the various functions and types of membrane proteins, emphasizing their importance in cellular processes. Test your knowledge on this fundamental biological concept!