B1.6B1. Characteristics of Living Organisms and Cells
Active transport — Combined Science 0653 - Biology Revision Notes & Topical Questions
5 min read 8 parts Lesson 8 of 14 Unit quiz
Lesson summary
B1.6 Active transport (Part 2) — COMBINED SCIENCE notes: Compare active transport with diffusion and osmosis and describe what affects its rate.FeatureDiffusionOsmosisActive transportParticlesAny small moleculesWater onlyIons, glucose and amino acidsDirectionHigh to low concentra…
- Mitochondria
- Respiration inhibited
- Temperature
- Oxygen supply
- Carrier proteins
- Root hair cells
Section 1 of 8Comparison of the three processes
| Feature | Diffusion | Osmosis | Active transport |
|---|---|---|---|
| Particles | Any small molecules | Water only | Ions, glucose and amino acids |
| Direction | High to low concentration | High to low water potential | Low to high concentration |
| Energy from respiration | Not needed | Not needed | Needed |
| Membrane | Not essential | Partially permeable | Carrier proteins |
Section 2 of 8Evidence that active transport uses energy
Mitochondria
- Mitochondria cells that carry out a lot of active transport, such as root hair cells and cells lining the small intestine, have many mitochondria.
Respiration inhibited
- Respiration inhibited active transport slows or stops when respiration is stopped.
- A lack of oxygen or a poison such as cyanide has this effect.
Section 3 of 8Factors that affect the rate
Temperature
- Temperature the rate rises with temperature, up to the point where proteins denature.
- A higher temperature raises the rate of respiration, which supplies energy.
Oxygen supply
- Oxygen supply more oxygen allows faster aerobic respiration, so more energy is available.
Carrier proteins
- Carrier proteins the number in the membrane limits the rate.
- Cells specialised for absorption have many carriers.
Section 4 of 8Examples in context
Root hair cells
- Root hair cells take up mineral ions such as nitrate from dilute soil water.
Small intestine
- Small intestine absorbs glucose when its concentration in the gut is lower than in the blood.
Kidney tubules
- Kidney tubules reabsorb glucose back into the blood.
Section 5 of 8Choosing the process
1Down a gradient
- Down a gradient use diffusion or osmosis, with no energy.
2Against a gradient
- Against a gradient use active transport, with energy from respiration.
Section 6 of 8More from the specification
1Active transport definition
- Active transport is the movement of dissolved substances or ions across a cell membrane from a region of lower concentration to a region of higher concentration, requiring cellular energy from ATP.
- (against a concentration gradient)
2Active transport in plants
- Root hair cells in plants use specialized carrier proteins to absorb mineral ions from dilute soil water solution into plant root tissue against a steep concentration gradient.
- (such as nitrates and magnesium)
3Diffusion through Visking tubing
- In model laboratory experiments, dialysis (Visking) tubing demonstrates passive diffusion and selective permeability,
- where smaller solute molecules diffuse across pores into external water solution while large macromolecules are retained.
4Importance in living organisms
- Living organisms depend on active transport for vital physiological functions,
- including glucose reabsorption in the mammalian nephron and nutrient absorption across intestinal epithelial tissue.
5Solvent
- Liquid in which a solute dissolves.
6Solute
- Substance that dissolves in a solvent.
7Carbon dioxide
- Gas that turns limewater cloudy.
8Dialysis tubing
- A non-living partially permeable membrane.
9Tissue
- A group of similar cells working together to do one job.
10Organism
- A whole living thing made of organ systems.
Section 7 of 8Key terms
| Term | Meaning |
|---|---|
| Active transport | Movement against a concentration gradient using energy. |
| Respiration | The release of energy from food in cells. |
| Concentration gradient | A difference in concentration between two regions. |
| Mitochondrion | The organelle that releases energy in respiration. |
| Carrier protein | A membrane protein that carries particles across. |
| Passive | Not needing energy from respiration. |
Section 8 of 8Exam technique
1
Saying osmosis needs energy — osmosis is passive.
2
Saying solutes move in osmosis — only water moves.
3
Writing that active transport is from high to low concentration — it is low to high.
4
Forgetting carrier proteins — active transport needs them.
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