Biology Chapter on Cell Membranes

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Questions and Answers

What is the primary function of channel proteins in facilitated diffusion?

To actively pump ions against their concentration gradient

To chemically alter the molecules they transport

To provide a specific pathway for certain ions and molecules to diffuse (correct)

To increase the thickness of the membrane

How do carrier proteins differ from channel proteins during facilitated diffusion?

Carrier proteins can alternate between different shapes (correct)

Carrier proteins function only in hyperosmotic solutions

Carrier proteins remain static and do not change shape

Carrier proteins only transport water molecules

Which type of environment causes a human red blood cell to shrivel?

Isosmotic solution

Isotonic solution

Hyperosmotic solution (correct)

Hypoosmotic solution

What characterizes an isosmotic solution in relation to cell membranes?

It maintains equal solute concentrations on both sides of the membrane Signup and view all the answers

What triggers the opening of gated channels, such as aquaporins?

Signal molecules like hormones Signup and view all the answers

What occurs during osmosis?

Movement of water from low solute concentration to high solute concentration Signup and view all the answers

Which of the following statements is true regarding hyperosmotic solutions?

They draw water out of the cell towards the area of higher solute concentration Signup and view all the answers

Which condition describes the function of ion channels during facilitated diffusion?

Ion channels allow selective transport based on ion size and charge Signup and view all the answers

What happens to a cell in a hypoosmotic solution?

The cell swells as water enters. Signup and view all the answers

Which active transport mechanism requires a carrier protein to function?

Active transport Signup and view all the answers

What primarily allows for the selective permeability of the cell membrane?

Phospholipid bilayer structure Signup and view all the answers

What is the function of the sodium-potassium pump?

To control osmotic balance and maintain cell potential. Signup and view all the answers

Which of the following statements about cotransport is true?

It can couple the transport of two different solutes. Signup and view all the answers

Facilitated diffusion across the cell membrane primarily involves which type of molecule?

Transmembrane proteins Signup and view all the answers

What type of solution causes animal cells to experience no net change in size?

Isotonic solution Signup and view all the answers

Which process describes the movement of substances against their concentration gradient, requiring energy?

Active transport Signup and view all the answers

How does cholesterol affect the cell membrane?

Enhances flexibility and stability Signup and view all the answers

During which process are glucose and amino acids absorbed into the bloodstream from the gut?

Active transport and diffusion Signup and view all the answers

Which of the following best describes active transport mechanisms?

Requires ATP and can move substances against their concentration gradient. Signup and view all the answers

What effect would placing animal cells in a hypertonic solution have?

Cells will shrink Signup and view all the answers

Which of the following can be classified as an example of antiport in transport processes?

Exchange of sodium and potassium across the membrane. Signup and view all the answers

Which characteristic of the fluid mosaic model highlights the movement of proteins within the membrane?

Fluidity of the membrane Signup and view all the answers

What type of molecules are typically restricted from easily crossing the phospholipid bilayer?

Polar molecules and ions Signup and view all the answers

Which type of transport requires no energy and occurs when molecules move down their concentration gradient?

Simple diffusion Signup and view all the answers

Study Notes

Cell Membrane and Transport Mechanisms

Membranes must be thin for efficient diffusion of molecules and ions.
Oxygen, carbon dioxide, and water easily cross membranes via diffusion.
Large polar molecules (e.g., amino acids, sugars) and ions are repelled by hydrophobic regions and diffuse slowly.
Facilitated diffusion allows these molecules to pass through channel proteins that have hydrophilic channels tailored to specific ions or molecules.
Gated channels can be opened or closed, facilitating ion transport in response to signals (e.g., hormones).
Aquaporins are examples of gated water channels in human kidneys that enable water transport.
Channel proteins maintain fixed shapes, while carrier proteins change shape rapidly (up to 100 cycles per second) to transport molecules.
Carrier proteins alternate between two states called ping and pong during transport.

Osmosis and Solute Concentration

Osmosis is the movement of water from areas of higher to lower concentration through a partially permeable membrane.
Osmotic potential is the solution's ability to draw water when separated by a semi-permeable membrane.
Hyperosmotic solutions have a higher solute concentration; hypoosmotic have a lower concentration; isosmotic indicates equal concentrations.
Hyperosmotic solutions cause cells to shrivel by drawing water out; isosmotic solutions maintain cell size; hypoosmotic solutions lead to cell swelling due to water influx.

Active Transport Mechanisms

Active transport requires energy (ATP) to move molecules or ions against their concentration gradient.
The sodium-potassium pump is a classic example: it moves 2 potassium ions into the cell while expelling 3 sodium ions, essential for osmotic balance and electrical activity in cells.
Bacteria, fungi, and plant cells (with cell walls) do not rely on the sodium-potassium pump.
Nutrient absorption in the intestine occurs via both diffusion and active transport for efficient nutrient uptake.

Types of Active Transport

Active transport in plants involves transporting sugars produced during photosynthesis into the phloem.
Transport types include:
- Uniport: transport of one solute.
- Cotransport: coupling transport of one solute with another.
  - Symport: different solutes transported in the same direction.
  - Antiport: different solutes transported in opposite directions.
Examples of cotransport include the concurrent transport of glucose and sodium ions.

Eukaryotic Cell Structure

Eukaryotic cells (in protists, fungi, plants, and animals) range from 10-100 µm in diameter and are significantly larger than prokaryotic cells.
The cell membrane follows the fluid mosaic model, being 7nm thick, with key components including phospholipids and various proteins.

Components of the Cell Membrane

Phospholipids: form bilayers with hydrophilic heads facing outward and hydrophobic tails facing inward. This amphipathic nature is crucial for membrane structure.
Membrane Proteins: include integral (transmembrane) proteins for passageways and peripheral proteins that partially penetrate the membrane.
Supporting Fibers: reinforce membrane shape and direct protein movement within the membrane.
Glycoproteins and Glycolipids: feature short carbohydrate chains that extend from proteins/lipids.
Cholesterol: increases membrane flexibility and stability; without it, membranes can break apart.

Fluid Mosaic Model

The membrane is depicted as a mosaic due to the diverse types of embedded proteins and cholesterol, giving it a dynamic structure.
The fluidity of the membrane allows lateral movement of embedded molecules, emphasizing that membranes are not solid.

Functions of Cell Membranes

Cell membranes are partially permeable, controlling entry and exit of polar molecules and ions.

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Description

This quiz covers the limitations on cell size related to membranes and the processes of diffusion. It explores how small molecules like oxygen and water pass through, as well as the mechanisms for larger polar molecules. Test your knowledge on facilitated diffusion and membrane dynamics.