Understanding Biology: Structure and functions in living organisms: Nutrition to Transport: Edexcel IGCSE Science Single Award Explained

Nutrition, respiration, gas exchange and transport are the four topics that form the core of how organisms obtain, process and distribute the substances they need to survive. Here is a systematic breakdown of each one for the Edexcel IGCSE (4SS0) Science Single Award.

These four topics sit at the centre of the biology component in the Pearson Edexcel IGCSE Science Single Award. They connect to almost everything else in the specification: enzymes from the previous section reappear in digestion, diffusion reappears in gas exchange, and the circulatory system ties transport to every organ in the body. If you invest time here, it pays dividends across both your understanding and your exam performance.

This article provides edexcel igcse science single award revision notes for the edexcel igcse science single award biology: structure and functions in living organisms: nutrition to transport section, including worked calculations, common pitfalls and self-check questions. Whether you are revising for the first time or revisiting these topics before the exam, the material below covers every learning objective the specification requires.

Nutrition: photosynthesis

Photosynthesis is the process by which green plants convert light energy into chemical energy stored in glucose. The specification requires you to know both the word equation and the balanced chemical symbol equation.

Word equation: carbon dioxide + water (+ light energy) -> glucose + oxygen

Symbol equation: 6CO₂ + 6H₂O -> C₆H₁₂O₆ + 6O₂

Three factors affect the rate of photosynthesis: carbon dioxide concentration, light intensity and temperature. Each can act as a limiting factor. If you increase light intensity but carbon dioxide is in short supply, the rate will plateau because CO₂ is limiting. The leaf is adapted for photosynthesis in several ways: a broad, flat shape to maximise light absorption; a thin structure to keep diffusion distances short; stomata on the underside to allow gas exchange; and palisade cells packed with chloroplasts near the upper surface where light hits first.

Nutrition: the human alimentary canal

The digestive system breaks large, insoluble food molecules into small, soluble ones that can be absorbed into the blood. You need to know the structure and function of each part of the alimentary canal.

Digestive enzymes: a worked example

Question: A student investigates the effect of amylase on starch at 37 degrees Celsius. After 10 minutes, she tests the mixture with iodine solution and it stays brown. What does this tell her? (2 marks)

Answer: The iodine solution remaining brown (rather than turning blue-black) indicates that starch is no longer present in the mixture. Amylase has broken down the starch into maltose (a simple sugar), so there is no starch left to react with the iodine.

Respiration

Respiration is the process by which cells release energy from glucose. It happens in every living cell, all the time. The energy released is used to make ATP, which powers cellular activities.

Aerobic respiration uses oxygen.

Word equation: glucose + oxygen -> carbon dioxide + water (+ energy released)

Symbol equation: C₆H₁₂O₆ + 6O₂ -> 6CO₂ + 6H₂O

Anaerobic respiration occurs without oxygen.

In animals: glucose -> lactic acid (+ energy released)

In plants and yeast: glucose -> ethanol + carbon dioxide (+ energy released)

Aerobic respiration releases significantly more energy per glucose molecule than anaerobic respiration because glucose is completely broken down. Anaerobic respiration only partially breaks down glucose, so less energy is transferred. The exam often asks you to compare the two processes, so learn the table below.

Gas exchange

The lungs are where oxygen enters the blood and carbon dioxide leaves it. Gas exchange happens in the alveoli, tiny air sacs at the ends of the bronchioles. You need to describe the structure of the thorax and explain how alveoli are adapted for efficient gas exchange.

Key structures: ribs, intercostal muscles, diaphragm, trachea, bronchi, bronchioles, alveoli and pleural membranes. The trachea divides into two bronchi, one for each lung, and each bronchus branches into smaller bronchioles that end in clusters of alveoli. The pleural membranes surround the lungs and reduce friction during breathing movements.

Ventilation (breathing):

• Inhaling: Intercostal muscles contract, pulling the ribs up and out. The diaphragm contracts and flattens. The volume of the thorax increases, the pressure inside decreases, and air rushes in.
• Exhaling: Intercostal muscles relax, the ribs move down and in. The diaphragm relaxes and curves upward. The volume decreases, the pressure increases, and air is pushed out.

Alveolar adaptations: Large surface area (millions of alveoli), thin walls (one cell thick for short diffusion distance), rich blood supply (maintains a steep concentration gradient), and moist lining (gases dissolve before diffusing across).

Transport

Simple, unicellular organisms can rely on diffusion alone because their surface area to volume ratio is large enough and the distances involved are small. As organisms grow larger, the surface area to volume ratio decreases, diffusion distances increase, and a dedicated transport system becomes essential. In humans, the circulatory system fulfils this role.

Blood composition

• Red blood cells: Contain haemoglobin, which binds oxygen. No nucleus (more room for haemoglobin). Biconcave shape increases surface area.
• White blood cells: Part of the immune system. Phagocytes engulf pathogens. Lymphocytes produce antibodies specific to particular pathogens.
• Platelets: Cell fragments involved in blood clotting.
• Plasma: Liquid portion that transports dissolved substances: carbon dioxide, digested food (glucose, amino acids), urea, hormones and heat energy.

The heart

The heart is a double pump. The right side pumps deoxygenated blood to the lungs (pulmonary circulation). The left side pumps oxygenated blood to the rest of the body (systemic circulation). The left ventricle has a thicker muscular wall than the right because it needs to generate higher pressure to push blood around the entire body.

Blood vessels

Self-check questions

1. Write the balanced symbol equation for photosynthesis.
2. Name two adaptations of the ileum for absorption.
3. What is the difference between aerobic and anaerobic respiration in terms of products?
4. Explain how alveoli are adapted for gas exchange. Give three adaptations.
5. State the function of plasma in the blood.

Answers:

1. 6CO₂ + 6H₂O -> C₆H₁₂O₆ + 6O₂
2. Villi increase the surface area for absorption. The villi have thin walls (one cell thick) for a short diffusion distance. Each villus has a rich network of blood capillaries to maintain a concentration gradient and carry absorbed nutrients away.
3. Aerobic respiration produces carbon dioxide and water. Anaerobic respiration in animals produces lactic acid; in plants and yeast it produces ethanol and carbon dioxide.
4. (i) Large total surface area from millions of alveoli. (ii) Walls are one cell thick, giving a short diffusion distance. (iii) Rich blood supply maintains a steep concentration gradient for oxygen and carbon dioxide.
5. Plasma transports dissolved carbon dioxide, digested food molecules (glucose, amino acids), urea, hormones and heat energy around the body.

Self-check questions

1. State two differences between the structure of a plant cell and an animal cell.
2. Describe the process of osmosis and explain why it is important in living organisms.
3. Explain the difference between an exothermic and an endothermic reaction, giving one example of each.
4. A car accelerates from rest to 20 m/s in 5 seconds. Calculate its acceleration and the resultant force if the car has a mass of 1200 kg.
5. Describe the structure of an atom, naming each subatomic particle and stating its relative charge and mass.

In the igcse 4ss0 biology: structure and functions in living organisms: nutrition to transport section, these four topics collectively account for a substantial share of the biology exam content. The biology: structure and functions in living organisms: nutrition to transport edexcel igcse material rewards students who understand the connections between topics, not just the individual facts. The edexcel igcse science single award explained through worked problems like those above is a qualification that tests application, not just recall. Use the edexcel igcse science single award practice questions and edexcel igcse science single award notes on the Green Bridge CBT platform to reinforce each area systematically and build exam confidence.