Transport Mechanisms in Human and Social Biology

Introduction to Transport Mechanisms

Transport mechanisms are biological processes that move substances into, out of, and within cells and organisms. These mechanisms are essential for maintaining homeostasis, distributing nutrients, removing wastes, and facilitating communication between cells.

Overview of Transport Mechanisms

Passive Active Bulk

Figure 1: Major categories of transport mechanisms

Passive Transport

Passive transport moves substances without energy input, following concentration gradients.

1. Diffusion

The movement of particles from high to low concentration:

High Low

Figure 2: Diffusion process showing movement from high to low concentration

2. Osmosis

The diffusion of water across a semi-permeable membrane:

Low Solute Concentration High Solute Concentration Semi-permeable Membrane

Figure 3: Osmosis across a semi-permeable membrane

3. Facilitated Diffusion

Passive transport using membrane proteins:

Channel Protein

Figure 4: Facilitated diffusion through a channel protein

Active Transport

Active transport moves substances against concentration gradients, requiring energy (ATP).

1. Protein Pumps

Membrane proteins that move specific molecules:

Sodium-Potassium Pump ATP

Figure 5: Active transport via protein pumps

Bulk Transport

Movement of large particles or quantities of materials using vesicles.

1. Endocytosis

Import of materials by engulfing:

Endocytosis Process Particle

Figure 6: Endocytosis process

2. Exocytosis

Export of materials by vesicle fusion:

Exocytosis Process Vesicle

Figure 7: Exocytosis process

Comparison of Transport Mechanisms

Mechanism Energy Required Direction Example
Diffusion No High to low concentration O2 and CO2 exchange
Osmosis No Low to high solute Water absorption in roots
Facilitated Diffusion No High to low concentration Glucose uptake
Active Transport Yes (ATP) Low to high concentration Na+/K+ pump
Bulk Transport Yes (ATP) Either direction White blood cell engulfing bacteria

Glossary of Terms

Concentration Gradient
The difference in concentration of a substance between two areas.
Semi-permeable Membrane
A membrane that allows certain molecules or ions to pass through by diffusion.
ATP (Adenosine Triphosphate)
The energy currency of the cell used in active transport.
Homeostasis
The maintenance of stable internal conditions despite external changes.
Phagocytosis
A type of endocytosis where cells engulf large particles like bacteria.
Pinocytosis
A type of endocytosis where cells take in extracellular fluid.
Turgor Pressure
The pressure of water pushing the plasma membrane against the cell wall in plant cells.
Plasmolysis
Shrinking of the cytoplasm away from the cell wall due to water loss.

Self-Assessment Questions

1. What is the main difference between passive and active transport?
Passive transport moves substances along the concentration gradient without energy input, while active transport moves substances against the concentration gradient requiring energy (ATP).
2. Explain why osmosis is considered a special case of diffusion.
Osmosis is specifically the diffusion of water molecules across a semi-permeable membrane from an area of low solute concentration to high solute concentration, while diffusion refers to the movement of any particles from high to low concentration.
3. Describe two adaptations of root hair cells for water absorption.
1) Long, thin extension increases surface area for absorption. 2) Large vacuole maintains concentration gradient for water uptake by osmosis.
4. Why does the sodium-potassium pump require ATP?
The sodium-potassium pump moves sodium ions out of the cell and potassium ions into the cell against their concentration gradients, which requires energy provided by ATP.
5. Compare endocytosis and exocytosis.
Endocytosis brings materials into the cell by forming vesicles from the cell membrane, while exocytosis releases materials from the cell by fusing vesicles with the cell membrane. Both require energy and are forms of bulk transport.
6. What would happen to a red blood cell placed in distilled water? Explain why.
The red blood cell would swell and possibly burst (lyse) because water would enter the cell by osmosis. The distilled water has higher water potential (lower solute concentration) than the cell's cytoplasm.
7. Explain the importance of transport mechanisms in maintaining homeostasis.
Transport mechanisms regulate the movement of nutrients, wastes, and other molecules to maintain optimal internal conditions. They ensure cells receive needed materials while removing harmful substances, keeping concentrations within required ranges.
8. How does facilitated diffusion differ from simple diffusion?
Facilitated diffusion uses specific protein channels or carriers to move molecules across membranes, while simple diffusion occurs directly through the phospholipid bilayer. Both move substances down their concentration gradient without energy.
9. Why can't large molecules like proteins diffuse through cell membranes?
Large molecules like proteins are too big to pass between the phospholipid molecules of the membrane. They require specific transport mechanisms like vesicular transport.
10. Describe how oxygen and carbon dioxide are exchanged in the lungs.
Oxygen diffuses from the alveoli (high concentration) into the blood (low concentration), while carbon dioxide diffuses from the blood (high concentration) into the alveoli (low concentration). This occurs by simple diffusion across the alveolar and capillary membranes.

Summary of Key Points