1.1Unit 2 · Transport, Excretion & Coordination
Transport Systems — Unit 2 — Edexcel IGCSE Biology Modular - UNIT 2 Revision Notes & Topical Questions
10 min read 4 parts Lesson 2 of 4 1 quiz
Lesson summary
Explain why multicellular organisms need transport systems.Single-celled organisms rely on diffusion because their surface area to volume ratio is large.Mineral ions are absorbed into root hairs by active transport, using energy from respiration.A potometer measures water uptake,…
- Antibodies are specific
- The need for a transport system
- Role of xylem and phloem
- Absorption of water by root hair cells
- Transpiration
- White blood cells and immunity
Section 1 of 4Transport Systems — Unit 2
The need for a transport system:
small organisms have a large surface area to volume ratio and short diffusion distances, so diffusion alone is enough.- Large organisms have a small SA:V ratio and long distances, so they need mass transport systems (the circulatory system in animals, xylem and phloem in plants).
Role of xylem and phloem:
xylem vessels are dead, hollow and strengthened with lignin; they carry water and mineral ions upwards.- Phloem is living tissue that transports sucrose and amino acids from leaves to where they are used or stored, both up and down.
Absorption of water by root hair cells:
- the long extension gives a large surface area.
- Soil water is more dilute than the cell sap, so water enters by osmosis;
- mineral ions are taken up by active transport against their concentration gradient.
Transpiration:
- water evaporates from mesophyll cells and diffuses out of stomata.
- This pulls water up the xylem in a continuous column.
- It supplies water for photosynthesis, carries minerals, cools the leaf and keeps cells turgid.
Practical — factors affecting transpiration:
cut a shoot underwater, fit it into a potometer with airtight seals, introduce an air bubble and measure how far it moves in a set time.- Change one factor (e.g. use a fan for wind, a lamp for light, a plastic bag for humidity) and keep others constant;
- repeat and calculate mean rates.
- Change one factor (e.g. use a fan for wind, a lamp for light, a plastic bag for humidity) and keep others constant;
The blood:
- blood consists of plasma, red blood cells, white blood cells and platelets.
- Red cells are adapted with a biconcave shape (large surface area), no nucleus (more room for haemoglobin) and flexibility.
White blood cells and immunity:
- phagocytes engulf and digest pathogens.
- Lymphocytes recognise antigens and produce specific antibodies, which cause pathogens to clump or mark them for destruction.
- Some lymphocytes become memory cells.
Vaccinations:
a vaccine contains dead, weakened or inactivated pathogens or their antigens.- Lymphocytes produce antibodies and memory cells.
- On later infection, memory cells cause a rapid, large production of antibodies,
- (secondary response)
- so the pathogen is destroyed before symptoms develop.
- High vaccination rates give herd immunity.
Platelets and blood clotting:
At a cut, platelets release chemicals that turn soluble fibrinogen into insoluble fibrin threads.- The fibrin mesh traps red blood cells to form a clot, which hardens into a scab.
- This limits blood loss and stops pathogens entering while new skin grows.
Structure of the heart:
The heart is a double pump separated by the septum.- The right side sends deoxygenated blood to the lungs; the left side sends oxygenated blood to the body,
- so the left ventricle wall is thicker to generate higher pressure.
- Valves prevent backflow, and coronary arteries supply the heart muscle with oxygen and glucose.
Route of blood through the heart:
1Vena cava2right atrium3tricuspid valve4right ventricle5semilunar valve6pulmonary artery7lungs8pulmonary vein9left atrium10bicuspid valve11left ventricle12semilunar valve13aorta14bodyHeart rate and exercise:
Resting heart rate is set by the pacemaker cells in the right atrium.- During exercise muscles respire faster,
- so heart rate and the volume pumped per beat increase to deliver more oxygen and glucose and remove CO2.
- Rate stays high afterwards to repay the oxygen debt.
- Adrenaline also raises heart rate.
Coronary heart disease:
Fatty deposits (plaque), mainly cholesterol, build up inside the coronary arteries and narrow the lumen.- Less blood reaches the heart muscle, so it gets less oxygen: partial blockage causes chest pain (angina) and complete blockage stops aerobic respiration in that area, causing a heart attack.
Risk factors for CHD:
- Obesity (strain on the heart, risk of type 2 diabetes), high blood pressure (damages artery walls), high blood cholesterol (faster plaque formation) and smoking (chemicals increase plaque and blood pressure;
- carbon monoxide lowers the oxygen carried by red cells).
- Obesity (strain on the heart, risk of type 2 diabetes), high blood pressure (damages artery walls), high blood cholesterol (faster plaque formation) and smoking (chemicals increase plaque and blood pressure;
Arteries:
Carry blood away from the heart at high pressure (usually oxygenated, except the pulmonary artery).- Thick walls with muscle and elastic fibres withstand the pressure and recoil to keep blood moving;
- the narrow lumen helps maintain pressure.
- Thick walls with muscle and elastic fibres withstand the pressure and recoil to keep blood moving;
Veins:
- Carry blood back to the heart at low pressure (usually deoxygenated, except the pulmonary vein).
- They have thin walls, a wide lumen and valves to stop blood flowing backwards.
Capillaries:
Tiny vessels in tissues with walls only one cell thick, giving a short diffusion distance for exchange of substances with cells.- Blood flows slowly at low pressure, and their leaky walls let plasma escape to form tissue fluid, which is later returned to the blood by lymph vessels.
Main blood vessels to and from organs:
Heartin by vena cava and pulmonary vein, out by aorta and pulmonary artery.- Lungsin by pulmonary artery, out by pulmonary vein.
- Liverin by hepatic artery and hepatic portal vein (from the gut), out by hepatic vein.
- Kidneysin by renal artery, out by renal vein.
Section 2 of 4Process & sequence
- Water enters root hair cells from soil by osmosis.
- Water moves across the root cortex cell to cell into the xylem.
- Water rises up xylem vessels in a continuous column.
- Water leaves xylem into leaf mesophyll cells.
- Water evaporates from mesophyll cell surfaces into air spaces.
- Water vapour diffuses out through stomata, pulling the column up (transpiration stream).
Water through a plantwrite these steps in this order; each step is a marking point.
- Osmosis into root hair
- Across root to xylem
- Up xylem vessels
- Into leaf mesophyll
- Evaporation into air spaces
- Diffuses out of stomata
Section 3 of 4Compare
| Component | Structure | Function |
|---|---|---|
| Red blood cells | Biconcave, no nucleus, contain haemoglobin | Carry oxygen as oxyhaemoglobin |
| Phagocytes | Lobed nucleus, can change shape | Engulf and digest pathogens |
| Lymphocytes | Large round nucleus | Produce antibodies; form memory cells |
| Platelets | Cell fragments | Help blood clot, sealing wounds |
| Plasma | Liquid, mostly water | Transports CO2, glucose, urea, hormones, heat |
| Factor increased | Effect on rate | Reason |
|---|---|---|
| Temperature | Increases | Water molecules have more kinetic energy; faster evaporation and diffusion |
| Humidity | Decreases | Smaller concentration gradient of water vapour |
| Wind speed | Increases | Water vapour blown away, keeping gradient steep |
| Light intensity | Increases | Stomata open wider for photosynthesis |
Section 4 of 4Worked examples
In a potometer, the bubble moves 45 mm in 5 minutes. The capillary tube has a cross-sectional area of 0.8 mm2. Calculate the rate of water uptake in mm3 per minute.
- Volume = distance × area = 45 × 0.8 = 36 mm3. Rate = 36 ÷ 5 = 7.2 mm3 per minute.
Explain why a person who has been vaccinated does not become ill when infected with the pathogen.
- The vaccine caused lymphocytes to produce memory cells specific to the antigen.
- On infection, memory cells rapidly trigger production of large amounts of specific antibodies,
- which destroy the pathogen before it can multiply enough to cause symptoms.
- The vaccine caused lymphocytes to produce memory cells specific to the antigen.
Marked practiceQuizzes for this lesson
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🌳 Student Search Tree & Frequently Asked Exam Questions: transport systems
Step-by-step problem-solving guide, mark scheme criteria, and experimental error analysis curated by Dr. Khaled Dabour (DABOURHUB).
Q1: How to solve transport systems examination questions step-by-step?
1. Identify all given values and convert non-standard units, 2. State the primary formula or physiological/chemical principle, 3. Calculate to 3 significant figures and clearly state units.
Q2: What are the common mistakes and experimental sources of error for transport systems?
Avoid confusing independent vs dependent variables in practical questions. In calculation questions, double-check percentage change formula: (change / original) × 100.
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On DABOURHUB every transport systems question is grouped by syllabus point and shown with the mark-scheme wording, so you can see exactly which sentence earns the mark instead of scrolling through whole year papers.
What is the most common transport systems exam question and why do students lose marks on it?
The repeated pattern on Edexcel papers is a short stem that asks you to apply transport systems and then justify it with a command word (explain, suggest, compare). Marks are lost by stating the fact without linking it back to the wording of the question, so each transport systems item here is written as a full-mark answer.
Is there an alternative to Save My Exams or Physics and Maths Tutor for transport systems?
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How do I revise transport systems in two weeks before the exam?
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