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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

📚 IB Biology HL Hub / Topical Revision
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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.
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Part 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.
FeaturePassive transportActive transport
GradientDownAgainst
ATPNot neededNeeded
ProteinsSometimesAlways

Part 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.

Part 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.

Part 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.

Part 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?

  1. Sodium ions moved out = 100 × 3 = 300.
  2. Potassium ions moved in = 100 × 2 = 200.
  3. 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.

Part 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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