Table of contents

1. Introduction to Anatomy & Physiology5h 43m
2. Cell Chemistry & Cell Components12h 36m
3. Energy & Cell Processes10h 6m
4. Tissues & Histology10h 3m
5. Integumentary System2h 20m
6. Bones & Skeletal Tissue2h 16m
7. The Skeletal System2h 35m
8. Joints2h 17m
9. Muscle Tissue2h 33m
10. Muscles1h 11m
11. Nervous Tissue and Nervous System1h 35m
12. The Central Nervous System1h 6m
- Introduction to the Central Nervous System
  18m
- The Cerebrum
  48m
13. The Peripheral Nervous System1h 26m
14. The Autonomic Nervous System1h 38m
15. The Special Senses2h 41m
16. The Endocrine System2h 48m
17. The Blood3h 22m
18. The Heart3h 42m
19. The Blood Vessels3h 35m
20. The Lymphatic System3h 16m
21. The Immune System14h 37m
22. The Respiratory System3h 20m
23. The Digestive System2h 5m
24. Metabolism and Nutrition4h 0m
25. The Urinary System2h 39m
26. Fluid and Electrolyte Balance, Acid Base Balance37m
27. The Reproductive System2h 5m
28. Human Development1h 21m
29. Heredity3h 32m

2. Cell Chemistry & Cell Components

Introduction to Membrane Transport

Anatomy & Physiology

2. Cell Chemistry & Cell Components

Introduction to Membrane Transport

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2:21 minutes

Problem 27

Textbook Question

The transport of a certain molecule exhibits the following characteristics:
(1) The molecule moves down its concentration gradient;
(2) at concentrations above a given level, the rate of transport does not increase; and
(3) cellular energy is not required for transport to occur.
Which transport process is at work?

Verified step by step guidance

Identify the key characteristics of the transport process described: (1) the molecule moves down its concentration gradient, (2) the rate of transport plateaus at higher concentrations, and (3) no cellular energy is required.

Understand that movement down a concentration gradient without energy input suggests a passive transport mechanism.

Recognize that the plateau in the rate of transport at higher concentrations indicates that the transport process involves a carrier protein that becomes saturated, which is characteristic of facilitated diffusion.

Differentiate facilitated diffusion from other passive transport processes like simple diffusion, which does not involve carrier proteins and does not exhibit saturation.

Conclude that the transport process described is facilitated diffusion, as it matches all the given characteristics: passive, carrier-mediated, and saturable.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Passive Transport

Passive transport is a biological process where molecules move across cell membranes without the need for cellular energy. This movement typically occurs down a concentration gradient, meaning substances move from areas of higher concentration to areas of lower concentration until equilibrium is reached.

Facilitated Diffusion

Facilitated diffusion is a specific type of passive transport that involves the use of transport proteins to help move molecules across the cell membrane. This process is essential for larger or polar molecules that cannot easily pass through the lipid bilayer, allowing them to move down their concentration gradient without energy expenditure.

Saturation Kinetics

Saturation kinetics refers to the phenomenon where, at high concentrations of a substrate, the rate of transport reaches a maximum and does not increase further, despite increases in concentration. This occurs because all available transport proteins are occupied, illustrating a limit to the transport capacity of the system.

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Related Practice

Textbook Question

For diffusion to occur, there must be:

a. A selectively permeable membrane

b. Equal amounts of solute

c. A concentration difference

d. Some sort of carrier system

e. All of the above

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Textbook Question

List five important factors that influence diffusion rates.

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Textbook Question

When a cell is placed in a(n)___solution, the cell will lose water through osmosis. This process results in the___ of red blood cells

(a) hypotonic; crenation

(b) hypertonic; crenation

(d) hypotonic; hemolysis

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Textbook Question

The sodium–potassium exchange pump

(a) Is an example of facilitated diffusion

(b) Does not require the input of cellular energy in the form of ATP

(d) Is composed of a carrier protein located in the plasma membrane

(e) Is not necessary for the maintenance of homeostasis

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Textbook Question

Solutions A and B are separated by a selectively permeable barrier. Over time, the level of fluid on side A increases. Which solution initially had the higher concentration of solute?

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Textbook Question

In the following diagram, identify the type of solution (hypertonic, hypotonic, or isotonic) in which the red blood cells are immersed.

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Textbook Question

The process that transports solid objects such as bacteria into the cell is called

(a) Pinocytosis

(b) Phagocytosis

(d) Receptor-mediated endocytosis

(e) Channel-mediated transport

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Textbook Question