Transport Across Cell Membranes

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary requirement for active transport to occur?

Natural diffusion

Concentration gradient

Carrier proteins

ATP expenditure (correct)

Passive transport requires energy expenditure for molecules to move across a membrane.

False

What is the osmotic pressure of pure water?

180-g/L

290 mosm/L

360-g/L

Zero (correct)

Name one type of passive transport.

Facilitated diffusion Signup and view all the answers

Osmosis is the diffusion of water from a region of high ______ concentration to a region of low concentration.

water Signup and view all the answers

A hypertonic solution has a lower concentration of solutes than the extracellular fluid.

False Signup and view all the answers

Which type of transport requires specific carrier proteins?

Facilitated diffusion Signup and view all the answers

What is the normal osmolarity of body fluids?

290 mosm/L Signup and view all the answers

Active transport occurs against the ______, requiring energy.

gradient Signup and view all the answers

Match the following types of transport with their definitions:

Simple Diffusion = Movement from high to low concentration without energy Facilitated Diffusion = Movement aided by carrier proteins Endocytosis = Transport of large molecules into the cell Exocytosis = Transport of large molecules out of the cell Signup and view all the answers

Match the terms related to osmosis with their definitions:

Isotonic = Same concentration of solutes as extracellular fluid Hypotonic = Lower concentration than extracellular fluid Hypertonic = Higher concentration than extracellular fluid Osmolarity = Number of osmoles per liter of solution Signup and view all the answers

All types of active transport involve movement against a concentration gradient.

True Signup and view all the answers

Which type of active transport directly uses ATP for energy?

Primary active transport Signup and view all the answers

Give an example of a bulk transport mechanism.

Endocytosis or Exocytosis Signup and view all the answers

In secondary active transport, the transporter directly hydrolyzes ATP.

False Signup and view all the answers

What does the cotransport of Na+ and glucose require?

A lower intracellular concentration of Na+ Signup and view all the answers

Study Notes

Transport across Cell Membranes

Learning Objectives:
- Differentiate between passive and active transport.
- Identify types of passive transport and provide examples for each.
- Describe the mechanisms of water transport across membranes.
- Identify types of active transport and provide examples.
- Explain the transport of large molecules across membranes (bulk transport).

Plasma Membrane Structure

The plasma membrane is a phospholipid bilayer with embedded proteins, cholesterol, and glycoproteins/glycolipids.
Phospholipids have a hydrophilic (water-loving) head and hydrophobic (water-fearing) tails.
Proteins are embedded within the membrane and have various functions, including transport.
Cholesterol provides structural support and fluidity to the membrane.
Glycoproteins and glycolipids are involved in cell recognition and signaling.

Types of Transport

Passive Transport: Movement of molecules down a concentration gradient (high to low). No energy required.
- Simple Diffusion: Movement of nonpolar molecules (e.g., oxygen, carbon dioxide) directly through the lipid bilayer.
- Facilitated Diffusion: Movement of polar or charged molecules (e.g., glucose, ions) through channel or carrier proteins.
Active Transport: Movement of molecules against a concentration gradient (low to high). Energy (ATP) is required.
- Primary Active Transport: Directly uses ATP to move molecules against the gradient (e.g., Na+/K+ pump, Ca2+ pump).
- Secondary Active Transport: Uses the energy stored in an ion concentration gradient (e.g., Na+-glucose symport).
Bulk Transport: Transport of large molecules or large volumes of substances across the membrane.
- Endocytosis: Movement of substances into the cell by invagination of the plasma membrane (e.g. pinocytosis, phagocytosis).
- Exocytosis: Movement of substances out of the cell by fusion of vesicles with the plasma membrane.

Passive Transport Details

Simple Diffusion: Movement of molecules without protein assistance. Rate depends on concentration gradient, membrane permeability, and surface area.
Facilitated Diffusion: Needs membrane proteins (channels or carriers).
- Channels: Provide a pathway through the membrane for specific molecules.
- Carriers: Bind to molecules, change shape, and facilitate their movement across the membrane. This is important for larger molecules or charged substances.

Osmosis

Osmosis is the specific diffusion of water across a selectively permeable membrane, from a region of high water concentration to low water concentration.
Osmotic Pressure: The pressure required to prevent water movement across a semipermeable membrane. Higher solute concentration means higher osmotic pressure.

Active Transport Details

Primary Active Transport: Direct use of ATP for transport. (e.g., Sodium-Potassium Pump). This is crucial for maintaining osmotic balance and concentration gradients.
Secondary Active Transport: Takes advantage of electrochemical gradient created by primary active transport. The movement of one substance down its gradient provides the energy to move a second substance against its gradient (symport or antiport).

Bulk Transport Details

Endocytosis: Invagination of the membrane forms a vesicle around the substances to be moved into the cell. Phagocytosis (cell eating) and pinocytosis (cell drinking).
Exocytosis: Vesicles carrying molecules fuse with the plasma membrane, releasing their contents into the extracellular fluid. This is crucial for secretion and waste removal.

Concentration Gradients and Active Transport

The Na+-K+ pump is a crucial example of primary active transport, maintaining a low intracellular Na+ concentration and a high intracellular K+ concentration, which are essential for nerve impulse transmission and other cellular processes.
The Na+ concentration gradient is crucial for many secondary active transport mechanisms.
Different types of molecules traverse the plasma membrane through one of these various routes that maintain proper concentration and transport crucial substances for the upkeep of the cell.

Other Key Concepts

Isotonic: A solution has the same solute concentration as the inside of the cell.
Hypotonic: A solution has a lower solute concentration than the inside of the cell.
Hypertonic: A solution has a higher solute concentration than the inside of the cell.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz focuses on the mechanisms of transport across cell membranes, including the differentiation between passive and active transport. You'll explore the structure of the plasma membrane and the types of transport processes that occur, such as diffusion, osmosis, and bulk transport. Test your knowledge on the various components that facilitate transport in and out of cells.