Movement into and out of cells Flashcards
What is Diffusion?
Diffusion is the movement of molecules from a region of its higher concentration to a region of its lower concentration
Molecules move down a concentration gradient, as a result of their random movement
Diffusion Across the Cell Membrane: Principle of Movement
Same as non-living cells – movement down a concentration gradient.
Cell surrounded by a partially permeable membrane.
Diffusion Across the Cell Membrane: Cell Membrane
Nature: Partially permeable.
Function: Allows some molecules to cross easily, while others with difficulty or not at all.
Diffusion Across the Cell Membrane: Purpose of Diffusion
Benefits:
Obtain many requirements.
Get rid of waste products.
Carry out gas exchange for respiration.
Diffusion Across the Cell Membrane: Examples in Living Organisms
Plants:
Require oxygen for respiration continuously.
Need carbon dioxide for photosynthesis when conditions are suitable (e.g., adequate light and temperature).
Examples of Diffusion: Small intestine
Molecules Moving: Digested food products (glucose, amino acids, fatty acids, glycerol, etc.).
From: Lumen of the small intestine.
To: Blood/lymph in villi covering small intestine walls.
Examples of Diffusion: Leaf giving off
Molecules Moving: Oxygen.
From: Air spaces between mesophyll cells.
To: Mitochondria in all cells.
Examples of Diffusion: Leaf taking in
Molecules Moving: Carbon dioxide.
From: Air spaces between mesophyll cells.
To: Chloroplasts in mesophyll cells.
Examples of Diffusion: Leaf with water
Molecules Moving: Water vapor.
From: Stomatal pores.
To: Air outside stomata.
Examples of Diffusion: Lungs taking in
Molecules Moving: Oxygen.
From: Alveolar air space.
To: Blood in capillaries around alveoli.
Examples of Diffusion: Lungs giving off
Molecules Moving: Carbon dioxide.
From: Blood in capillaries around alveoli.
To: Alveolar air space.
Energy for Diffusion: Source of Energy
Energy for diffusion comes from the kinetic energy.
Kinetic energy originates from the random movement of molecules and ions.
Energy for Diffusion: Particle Movement:
All particles move randomly continually.
This random movement is termed Brownian motion
Factors Influencing Diffusion: Surface Area to Volume Ratio
Effect on Rate: Larger structures have a smaller surface area to volume ratio, slowing down substance movement.
Adaptations: Cells adapted for diffusion increase surface area, e.g., root hair cells in plants and ileum lining cells in animals.
Example: The highly folded surface of the small intestine increases its surface area.
Factors Influencing Diffusion: Distance
Influence on Transport: Smaller distances lead to faster transport.
Relevance: Blood capillaries and alveoli have thin walls (one cell thick) for rapid diffusion.
Factors Influencing Diffusion: Temperature
Impact: Higher temperature equals faster molecule movement due to increased energy.
Result: More collisions against cell membranes, enhancing the rate of substance movement.
Factors Influencing Diffusion: Concentration gradient
Relation to Movement: Greater concentration difference results in faster movement.
Explanation: Higher concentration causes more collisions, expediting movement across the membrane.
Water as a Solvent: Importance of Water
Water is crucial for all living organisms as it serves as a solvent.
Its role as a solvent is vital for life on Earth.
Water as a Solvent: Transport Within Organisms
Example: Xylem and phloem in plants.
Function: Dissolved substances are easily transported, facilitating essential processes.
Water as a Solvent: Distribution of Digested Food
Scenario: Digested food molecules in the alimentary canal.
Significance: Water as a solvent enables the movement of nutrients to cells throughout the body.
Water as a Solvent: Removal of Toxic and Excess Substances
Examples: Urea and excess salts.
Process: Water dissolves these substances, aiding in their removal from the body through urine.
Water as a Solvent: Role in the Cytoplasm
Importance: Water is a key component of the cytoplasm.
Function: Facilitates metabolic reactions within cells.
Osmosis: Cell membrane permeability
All cells are enclosed by a partially permeable cell membrane.
The membrane allows selective passage of substances.
Osmosis: Osmosis Definition
Process: Osmosis is the diffusion of water molecules.
Direction: Moves from a dilute solution (high water concentration) to a more concentrated solution (low water concentration).
Medium: Occurs across a partially permeable membrane.
Osmosis: Concentration Gradient
Movement Direction: Water moves down its concentration gradient.
Explanation: From an area with a higher water concentration to an area with a lower water concentration.
Osmosis: Partially Permeable Membrane
Characteristic: Cell membrane is partially permeable.
Permeability: Allows small molecules (e.g., water) through but restricts larger molecules (e.g., solute molecules).
Osmosis Experiments: Immersing Plant Cells
Common Method: Use root vegetables like potato or radish.
Solutions: Place the cylinders in distilled water and sucrose solutions of varying concentrations.
Procedure:
Weigh the cylinders before immersion.
Leave in solutions for 20-30 minutes.
Remove, dry, and reweigh.
Osmosis Experiments: Observations - Plant Tissue Mass:
Gain in Mass:
Indicates water movement into the plant tissue by osmosis.
Surrounding solution is more dilute than the plant tissue.
Loss in Mass:
Indicates water movement out of the plant tissue.
Surrounding solution is more concentrated than the plant tissue.
No Change in Mass:
Implies no net movement of water.
Concentrations in the plant tissue and surrounding solution are equal.
Osmosis Experiments: Dialysis Tubing Experiment:
Membrane Characteristics: Non-living, partially permeable cellulose membrane.
Pores: Small enough to prevent large molecules (e.g., sucrose) but allow smaller ones (e.g., glucose and water).
Demonstration:
Fill tubing with concentrated sucrose solution.
Suspend in a boiling tube of water for a set period.
Observe changes in water level outside the tubing.
Osmosis Experiments: Osmosis in Dialysis Tubing
Principle: Water moves from higher water potential (dilute solution) to lower water potential (concentrated solution) through a partially permeable membrane.
Explanation: Demonstrates osmosis and diffusion across the membrane.
Osmosis in Plant Tissues: Water Entry in Plant Cells
When water enters a plant cell, the vacuole expands, pushing the cell membrane against the cell wall.
Water intake through osmosis contributes to cell rigidity, making it firm.
Cellular rigidity is vital for plant support, strength, and upright growth, enabling efficient sunlight exposure.
Cell wall pressure prevents excessive water entry, averting cell bursting.
Osmosis in Plant Tissues: Wilting Due to Water Shortage
Insufficient water leads to the loss of cellular rigidity (turgidity), resulting in wilting.
Osmosis in Plant Tissues: Osmosis Key Concepts
Definition: Net movement of water from higher water potential (dilute solution) to lower water potential (concentrated solution) through a partially permeable membrane.
Clarification: Dilute solution signifies high water potential; concentrated solution denotes low water potential.
Osmosis in Plant Tissues: Plant Cells in Varying Solutions
In a dilute solution (higher water potential), water moves into plant cells via osmosis, increasing turgor pressure and making cells turgid.
In a concentrated solution (lower water potential), water exits plant cells, causing flaccidity and potential plasmolysis.
Osmosis in Plant Tissues: Animal Cells and Osmosis
Animal cells undergo water loss and gain through osmosis.
Absence of a supporting cell wall in animal cells intensifies the impact of osmotic changes.
Active Transport: Definition of Active Transport
Active transport is the process of moving particles through a cell membrane from a region of lower concentration to a region of higher concentration, utilizing energy derived from respiration.
Active Transport: Importance of Active Transport
Energy Requirement: Active transport demands energy as particles move against their concentration gradient (opposite to diffusion).
Vital Processes: Essential for transporting molecules or ions across membranes, such as:
Uptake of glucose by epithelial cells in the villi of the small intestine.
Uptake of ions from soil water by root hair cells in plants.
Active Transport: Protein Carriers in Active Transport
Active transport employs carrier proteins embedded in the cell membrane for specific molecule transport.
Process:
Substance binds with the carrier protein in the cell membrane.
Carrier protein utilizes energy from respiration, inducing a change in shape to move the substance against the concentration gradient.
The substance is released into the cell.
