Unit 2 · Transport, Excretion & Coordination
Unit 2 — Transport, Excretion and Coordination — Edexcel IGCSE Biology Modular - UNIT 2 Revision Notes & Topical Questions
5 min read 6 parts Lesson 1 of 4 Unit quiz
Transport, Excretion and Coordination: Overview — EDEXCEL MODULAR - OL notes: Summarise blood and circulation, excretion by the kidney, nervous and hormonal coordination and homeostasis.In humans, blood is pumped around a double circulation by the heart: right side to the lungs, …
- Worked example 1
- Worked example 2
- Worked example 3
- Reflex arc
- Ultrafiltration in the glomerulus: water, glucose, urea and salts are forced out of the blood into the capsule
- Urine (water, urea, salts) passes to the bladder
Section 1 of 6Transport
- In humans, blood is pumped around a double circulation by the heart: right side to the lungs, left side to the body.
- Blood consists of plasma (carries carbon dioxide, glucose, urea, hormones), red blood cells (haemoglobin carries oxygen), white blood cells (phagocytes and lymphocytes defend against pathogens) and platelets (clotting).
- Arteries carry blood away from the heart at high pressure and have thick, elastic walls;
- veins carry blood back at low pressure with valves;
- capillaries have walls one cell thick for exchange.
- In plants, xylem carries water and mineral ions up from the roots, driven by transpiration,
- and phloem carries sucrose and amino acids to where they are needed.
- Root hair cells have long extensions to increase surface area for absorption.
Section 2 of 6Excretion
- Metabolic reactions produce waste, for example carbon dioxide (lungs) and urea (kidneys).
- The kidneys filter the blood to form urine.
- Stages in the nephron:
- Ultrafiltration in the glomeruluswater, glucose, urea and salts are forced out of the blood into the capsule.
- Selective reabsorption in the proximal convoluted tubule: all glucose is reabsorbed by active transport (cells have many mitochondria), plus useful ions and some water.
- Water reabsorption in the loop of Henle and collecting duct by osmosis, controlled by antidiuretic hormone (ADH) from the pituitary gland.
- Urine (water, urea, salts) passes to the bladder.
- Homeostasis is the maintenance of a constant internal environment, using negative feedback.
- If blood is too concentrated, more ADH is released, the collecting ducts become more permeable and a small volume of concentrated urine is produced.
Section 3 of 6Coordination
| Nervous system | Hormonal system | |
|---|---|---|
| Signal | Electrical impulses | Chemical hormones in blood |
| Speed | Very fast | Slower |
| Duration | Short | Longer lasting |
| Target | Specific muscle or gland | Target organs anywhere in body |
- A reflex arc: stimulus, receptor, sensory neurone, relay neurone in spinal cord, motor neurone, effector, response.
- Reflexes are automatic and rapid, e.g. pain withdrawal, blinking and coughing.
- Neurones meet at synapses, where a chemical transmitter crosses the gap.
- The pancreas and liver control blood glucose, and the skin helps regulate body temperature.
Section 4 of 6Blood glucose control and temperature regulation
- After a meal blood glucose rises;
- the pancreas secretes insulin, which makes the liver convert glucose to glycogen, so blood glucose falls.
- If glucose falls too low, the pancreas releases glucagon and the liver breaks glycogen down to glucose.
- If glucose is too high, cells lose water by osmosis; if too low the brain lacks glucose for respiration.
- Diabetes is caused by inadequate insulin action.
| Body temperature too high | Body temperature too low |
|---|---|
| Vasodilation: more blood flows near skin surface | Vasoconstriction: less blood flows near skin |
| Sweating increases; evaporation cools | Sweating decreases |
| Hair erector muscles relax, hairs lie flat | Shivering releases heat from muscles |
- The brain (hypothalamus) monitors the temperature of the blood and coordinates these responses.
Section 5 of 6The eye and the reflex to light
- The pupil gets smaller in bright light (circular muscles contract, radial muscles relax) and larger in dim light.
- To focus on a near object, the ciliary muscles contract, the suspensory ligaments slacken and the lens becomes thicker;
- for a distant object the ciliary muscles relax, ligaments tighten and the lens becomes thinner.
- The retina has rods (dim light) and cones (colour), with cones most dense at the fovea.
Section 6 of 6Worked examples
Describe how glucose is dealt with in the kidney. [3]3 marks
It passes out of the blood in ultrafiltration but all of it is reabsorbed by active transport in the proximal convoluted tubule, so none appears in the urine.
State the sequence of a reflex arc. [3]3 marks
Stimulus, receptor, sensory neurone, relay neurone (CNS), motor neurone, effector, response.
Explain why the cells of the PCT have many mitochondria. [2]2 marks
They supply ATP (energy) for active transport of glucose.
Last updated:
🌳 Student Search Tree & Frequently Asked Exam Questions: unit 2
Step-by-step problem-solving guide, mark scheme criteria, and experimental error analysis curated by Dr. Khaled Dabour (DABOURHUB).
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.
Avoid confusing independent vs dependent variables in practical questions. In calculation questions, double-check percentage change formula: (change / original) × 100.
Where can I find unit 2 past paper questions by topic with the mark scheme?
On DABOURHUB every unit 2 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 unit 2 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 unit 2 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 unit 2 item here is written as a full-mark answer.
Is there an alternative to Save My Exams or Physics and Maths Tutor for unit 2?
Yes: the unit 2 notes, topical questions and MCQ quizzes on this site follow the same syllabus headings as the official specification, and they open straight from the search result with no download step.
How do I revise unit 2 in two weeks before the exam?
Three passes: read the unit 2 notes once, then do the topical questions and mark them against the mark scheme, then redo only the ones you missed. The quiz on the page gives instant feedback so the third pass takes minutes rather than an evening.