27 Questions
What is the formula for flux in diffusion?
$J = \frac{M}{A \cdot t}$
According to Fick's first law of diffusion, what is the relationship between flux and concentration gradient?
Flux is directly proportional to the concentration gradient
How is the diffusion coefficient affected by temperature changes?
Diffusion coefficient increases with increasing temperature
What does Qd represent in the diffusion coefficient equation?
Activation energy
If the activation energy for diffusion is 20 kJ/mol, what will happen to the diffusion coefficient if the temperature increases?
Diffusion coefficient will increase
In steady-state diffusion, what does Fick's first law state about the rate of diffusion?
Rate of diffusion remains constant with time
What is the main reason for diffusion in a system?
To establish equilibrium
Which law is used to describe steady-state diffusion?
Fick's First Law
What is the focus of compartment modeling according to the text?
Solutes, compartments, and volumes
In vacancy diffusion, the rate of atoms exchange depends on all of the following EXCEPT:
Size of the atoms
Which type of diffusion involves smaller atoms moving between other atoms?
Interstitial diffusion
Which type of diffusion involves Fick's Second Law?
Non-steady State Diffusion
What does Fick's law of diffusion state?
Diffusion flux is directly proportional to concentration gradient
In relation to diffusion, what does Fick's First Law primarily address?
Rate of diffusion through a medium
Transport by diffusion is more effective for:
Short distances
How do we measure the amount or rate of diffusion?
Using Fick's law of diffusion
How does oxygen enter the cells in an Earthworm's body?
By diffusion through the skin
Why is diffusion through the skin insufficient for humans to obtain oxygen?
Only a small percentage of oxygen can diffuse through the skin
What structure in humans is responsible for oxygen exchange through diffusion?
Lungs
Which statement best describes the role of the cell membrane?
It controls the entry and exit of nearly all substances except oxygen and carbon dioxide.
What is the purpose of surfactants in the fluid coating the alveoli walls?
To reduce the surface tension and prevent alveoli collapse
Why have large organisms evolved transport systems despite the effectiveness of diffusion at the cellular level?
To overcome the limitations of slow diffusion in transporting substances across the whole body.
What is the main function of the diaphragm in the human respiratory system?
To regulate the volume of air inhaled and exhaled
What would happen if all substances in a cell could freely diffuse out?
The cell would lose essential substances needed for survival.
What is Laplace's law used to calculate in the context of alveoli?
Air pressure required to inflate the alveoli
Why is the distance from a cell membrane to the center of the cell kept small?
To maintain a rapid enough diffusion for oxygen and food supply.
What would be the consequence if the concentration of oxygen inside a cell were higher than outside?
Oxygen would stop diffusing into the cell.
Study Notes
Introduction to Diffusion
- Diffusion is a process that shows the uniform distribution of molecules of different substances over time, resulting in equilibrium.
- It is the reason why food coloring moves throughout a beaker of water and why odors smell strong at first and then disappear over time.
Diffusion Mechanisms
- Vacancy diffusion: atoms exchange with vacancies, applying to substitutional impurities.
- Interstitial diffusion: smaller atoms can diffuse between atoms, which is more rapid than vacancy diffusion.
Fick's Laws of Diffusion
- Fick's first law: diffusion flux (J) is proportional to the concentration gradient (dc/dx), J = -D(dc/dx), where D is the diffusion coefficient.
- Fick's second law: non-steady-state diffusion, describing how the concentration of a substance changes over time and space.
Quantifying Diffusion
- Diffusion flux (J) is the net number of moles crossing a unit area per unit time.
- Diffusion coefficient (D) is a measure of the rate of diffusion, which increases with increasing temperature.
- The relationship between D and temperature is given by the Arrhenius equation: D = Do exp(-Qd/RT).
Transport of Oxygen in Breathing
- In single-celled organisms, diffusion is rapid enough to supply oxygen and nutrients.
- In large organisms, diffusion is not sufficient, and specialized transport systems (e.g., blood circulatory systems) are needed to carry oxygen to cells.
- In humans, oxygen is obtained through diffusion in the lungs, which are made up of thousands of tiny air pockets called alveoli.
Transport of Substances across Membranes
- The permeability constant (p) describes the rate of transport across a membrane.
- The concentration gradient is maintained across the cell membrane, allowing oxygen to diffuse in and carbon dioxide to diffuse out.
- The cell membrane controls the exit and entry of substances to maintain homeostasis.
Compartmental Modeling
- Compartmental modeling describes the transport of substances between two compartments separated by a membrane.
- The volume of a cell and capillary diffusion are important in understanding compartmental modeling.
Test your knowledge on diffusion and Fick's first law with this quiz. Explore concepts such as mass diffusion, flux, concentration gradient, and the rate of diffusion. Understand the relationship between surface area, time, and diffusion rate.
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