2.3.7Inquiry Process
Active Transport and Bulk Transport — IB Biology HL Revision Notes & Topical Questions
5 min read 6 parts Lesson 53 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 6Active Transport
Cells use energy to maintain concentrations that differ from their surroundings.
Direction
- Direction Moves substances from low to high concentration, against the gradient.
Energy
- Energy Requires ATP, which is hydrolysed to supply energy for protein shape change.
Pump proteins
- Pump proteins Specific carrier proteins bind the substance, change shape and release it on the other side.
Example
- Example The sodium-potassium pump moves 3 Na⁺ out of the cell and 2 K⁺ in for each ATP used.
| Feature | Passive transport | Active transport |
|---|---|---|
| Gradient | Down | Against |
| ATP | Not needed | Needed |
| Proteins | Sometimes | Always |
Section 2 of 6Endocytosis
Endocytosis
Process
- Process The plasma membrane folds inwards, engulfs material and pinches off a vesicle inside the cell.
Phagocytosis
- Phagocytosis Bulk uptake of solids, such as a white blood cell engulfing bacteria.
Pinocytosis
- Pinocytosis Bulk uptake of liquid droplets with dissolved substances.
Energy
- Energy The process uses ATP and relies on a fluid membrane.
Section 3 of 6Exocytosis
Exocytosis releases products such as hormones and digestive enzymes.
1
Proteins are made and processed in the rough endoplasmic reticulum and Golgi apparatus.
2
The Golgi packages them into secretory vesicles.
3
Vesicles move along the cytoskeleton to the plasma membrane.
4
A vesicle membrane fuses with the plasma membrane and releases its contents outside.
5
The vesicle membrane becomes part of the plasma membrane, increasing its area.
Section 4 of 6Comparing Methods
All these processes need energy and a flexible membrane.
Size of cargo
- Size of cargo Pumps move ions and small molecules, while vesicles move large particles and bulk fluid.
Membrane change
- Membrane change Bulk transport changes the area of the plasma membrane, but pumps do not.
Energy
- Energy Both active transport and bulk transport need ATP.
Examples
- Examples Neurotransmitter release is an example of exocytosis at synapses.
Section 5 of 6Worked Example
Question
- The sodium-potassium pump moves 3 Na⁺ out and 2 K⁺ into the cell for each ATP hydrolysed.
- How many ions of each type are moved when 100 ATP molecules are used?
- Sodium ions moved out = 100 × 3 = 300.
- Potassium ions moved in = 100 × 2 = 200.
- Net movement is 500 ions in total, with a net loss of one positive charge from the cell for each cycle.
Answer 300 Na⁺ are pumped out and 200 K⁺ are pumped in.
Section 6 of 6Exam Checklist & Tips
2.3.7 – Key Points for the Exam
- Active transport Movement of substances against their concentration gradient using ATP.
- Endocytosis Uptake of material into the cell by invagination of the plasma membrane.
- Exocytosis Release of material from the cell by fusion of vesicles with the plasma membrane.
- Phagocytosis Endocytosis of solid particles.
- Vesicle A small membrane-bound sac used to transport material.
Common Mistakes
- Saying active transport moves substances down a gradient.
- Believing exocytosis does not use energy.
- Confusing phagocytosis (solids) with pinocytosis (liquids).
- Forgetting that exocytosis adds membrane to the cell surface.
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