Biology: Plasma Membranes Overview

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Questions and Answers

Which of the following is a characteristic of passive transport across cell membranes?

Driven by the random motion of molecules. (correct)

Movement of substances against their concentration gradient.

Requires energy input from the cell.

Always involves the use of transport proteins.

What does the term "concentration gradient" refer to in the context of diffusion?

The difference in pressure between two regions.

The difference in electrical charge between two regions.

The difference in temperature between two regions.

The difference in the number of molecules of a substance per unit volume between two regions. (correct)

Which of the following substances would likely pass through a cell membrane most slowly?

Glucose

Sodium ions (Na+) (correct)

Oxygen gas (O2)

Water

Which of the following statements is TRUE about diffusion?

Diffusion is driven by the concentration gradient of the substance only, regardless of other substances present. (B) Signup and view all the answers

What is the main difference between passive and active transport?

Active transport moves substances down their concentration gradient, while passive transport moves them against their concentration gradient. (A) Signup and view all the answers

Which of the following statements accurately describes the fluid mosaic model of the plasma membrane?

The plasma membrane is a fluid structure with proteins embedded in or attached to a phospholipid bilayer. (B) Signup and view all the answers

What type of molecule is most abundant in the plasma membrane?

Phospholipids (D) Signup and view all the answers

Which of the following molecules can easily cross the plasma membrane without the need for transport proteins?

Carbon dioxide (CO2) (B) Signup and view all the answers

What is the primary reason for the lateral movement of phospholipids within the plasma membrane?

Hydrophobic interactions between phospholipid tails. (A) Signup and view all the answers

Which of the following is NOT a characteristic of integral membrane proteins?

They are primarily found on the exterior surface of the membrane. (D) Signup and view all the answers

What is the function of peripheral membrane proteins in the plasma membrane?

They provide structural support to the membrane. (D) Signup and view all the answers

Which of the following best describes the ability of the plasma membrane to regulate the passage of substances across it?

Selective permeability (D) Signup and view all the answers

Which of these best describes the movement of a phospholipid molecule from one leaflet of the plasma membrane to the other?

It is very rare and requires energy to occur. (D) Signup and view all the answers

What is the primary driving force behind simple diffusion?

The difference in concentration across the membrane (B) Signup and view all the answers

Which of the following molecules is most likely to cross a cell membrane via simple diffusion?

Oxygen (O2) (B) Signup and view all the answers

What is the key difference between open channels and gated channels?

Open channels always allow passage of molecules, while gated channels can open and close in response to stimuli. (A) Signup and view all the answers

Which of the following is NOT a characteristic of facilitated diffusion?

It requires energy input from the cell. (D) Signup and view all the answers

Which of the following best describes the role of carrier proteins in facilitated diffusion?

Carrier proteins bind to molecules and change shape to move them across the membrane. (A) Signup and view all the answers

What is the primary source of energy for most active transport processes?

ATP (D) Signup and view all the answers

What is the key difference between facilitated diffusion and active transport?

Facilitated diffusion moves molecules down their concentration gradient, while active transport moves them against it. (D) Signup and view all the answers

Which of the following is NOT a type of active transport?

Osmosis (C) Signup and view all the answers

How does ATP contribute to active transport?

ATP directly provides the energy used to pump molecules across the membrane. (B) Signup and view all the answers

What is the key difference between primary and secondary active transport?

Primary active transport uses ATP directly, while secondary active transport uses the energy stored in a concentration gradient. (A) Signup and view all the answers

What is the primary role of the sodium-potassium pump in animal cells?

To generate a membrane potential, essential for nerve impulse transmission. (C), To drive the active transport of other substances across the cell membrane. (D) Signup and view all the answers

How does the phosphorylation of the sodium-potassium pump carrier protein contribute to its function?

It changes the pump's shape, facilitating the movement of sodium ions across the membrane. (D) Signup and view all the answers

What is the main difference between symport and antiport cotransport mechanisms?

Symport moves both substances in the same direction, while antiport moves them in opposite directions. (C) Signup and view all the answers

Which of the following is an example of a cotransport mechanism?

The uptake of glucose from the small intestine into the bloodstream. (B) Signup and view all the answers

What is the role of vesicles in bulk transport?

They facilitate the movement of large molecules and particles across the plasma membrane. (C) Signup and view all the answers

Which type of endocytosis specifically involves the uptake of specific molecules?

Receptor-mediated endocytosis (B) Signup and view all the answers

What is the main difference between exocytosis and endocytosis?

Exocytosis involves the release of substances from the cell, while endocytosis involves the uptake of substances into the cell. (C) Signup and view all the answers

Which of the following is NOT a type of endocytosis?

Osmosis (D) Signup and view all the answers

Study Notes

Plasma Membranes

Plasma membranes are approximately 8nm thick (8000 times the thickness of paper).
They control the passage of substances into and out of cells.
They exhibit selectivity in chemical exchange, a fundamental characteristic of living cells.

Membrane Structure

Membranes are primarily composed of phospholipids and proteins, with carbohydrates also playing a role.
Phospholipids are the most abundant molecules, forming a bilayer.
Phospholipids are amphipathic, possessing hydrophilic heads and hydrophobic tails.
Proteins are also amphipathic, with both hydrophilic and hydrophobic regions.

Fluid Mosaic Model

Membranes are fluid structures with a mosaic of embedded proteins within (or attached to) a phospholipid bilayer.
Proteins and phospholipids are not rigidly fixed in place, but the tails of the phospholipids are held together by hydrophobic interactions.

Membrane Protein Diversity

Membrane proteins are categorized into integral and peripheral proteins.
Integral proteins penetrate the hydrophobic interior of the membrane, often traversing the entire membrane (transmembrane proteins).
Peripheral proteins are not embedded within the membrane but are loosely associated with the hydrophilic portions of integral proteins or other membrane surfaces.

Membrane Transport

Biological membranes are selectively permeable, meaning they regulate the movement of substances across their boundaries.
Nonpolar molecules (e.g., hydrocarbons, O2, CO2) readily cross the lipid bilayer.
Polar molecules (e.g., water) and ions diffuse more slowly through the membrane or via membrane proteins.

Passive Transport

Passive transport does not require energy input from the cell.
It follows the concentration gradient, moving substances from high to low concentration.
Simple diffusion - molecules move across a membrane without assistance.
Facilitated diffusion - molecules move across a membrane through proteins.

Active Transport

Active transport requires energy input from the cell.
It moves solutes against their concentration gradient (from low to high concentration).
The most common energy source is ATP.
Includes several types: primary, secondary, bulk (exocytosis, endocytosis).

Osmosis

Osmosis is the diffusion of water across a selectively permeable membrane.
It moves water from high to low water concentration.
Key terms: isotonic, hypertonic, hypotonic solutions. Cell response to different solutions vary depending on if the cell has or does not have a cell wall

Types of Transmembrane Proteins

Channels – allow molecules to pass through by providing a tunnel.
Carriers – bind to molecules and change shape, facilitating their movement across the membrane.

Other Forms of Bulk Transport

Exocytosis – materials are released from the cell in vesicles.
Endocytosis – materials are taken into the cell in vesicles. There are three types:
- Phagocytosis (“cell eating”) – solids
- Pinocytosis (“cell drinking”) – liquids
- Receptor-mediated endocytosis – specific molecules.

Sodium-Potassium Pump

Active transport mechanism that moves Na+ out of the cell and K+ into the cell (against their concentration gradients).
Crucial role in maintaining cell volume and nerve impulse transmission

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Description

This quiz explores the structure and function of plasma membranes, including their composition and key features such as the fluid mosaic model. Understand the importance of membrane selectivity and the diversity of membrane proteins. Test your knowledge of how substances are regulated in and out of cells.