VMBO Year 2 · HAVO/VWO Years 2–3 · Cellular respiration and breathing · Section 1.1

Metabolism

Metabolism is the set of chemical reactions in organisms that change substances into other substances. These reactions take place continually in cells, including human cells.

Metabolism allows organisms to move, maintain body temperature, grow and repair damage. It is essential for survival.

Photosynthesis

In the light, photosynthesis takes place in green plant parts. Chloroplasts, containing the green pigment chlorophyll, use light energy to make glucose from carbon dioxide and water.

Water + carbon dioxide + light energy → glucose + oxygen

Glucose is an energy-rich substance.
Energy from sunlight is stored as chemical energy in glucose.
Plants use glucose to make other substances needed for growth and building tissues.
Oxygen is released during the process.

Breaking down glucose

Sugars made by photosynthesis are transported to other parts of the plant. Both plants and animals break down glucose in their cells to release energy.

Much of aerobic respiration takes place in mitochondria, organelles involved in supplying usable energy to the cell.

Breaking down glucose releases stored chemical energy.
Cells use this energy for many processes.
Both plant and animal cells contain mitochondria.
Cells with high energy needs, such as muscle cells, often contain many mitochondria.
Mitochondria can be seen with suitable light-microscopy methods, but an electron microscope reveals their internal structure much more clearly.

Glossary

Glucose: An energy-rich sugar made during photosynthesis from water and carbon dioxide using light energy. Cells use it as a fuel.
Mitochondria: Organelles in plant and animal cells where much of aerobic respiration takes place, releasing energy for cellular activities.
Metabolism: All the chemical reactions in cells that change substances into other substances and support life processes.
Photosynthesis: The process in which plants use light energy to make glucose and oxygen from water and carbon dioxide.
Chloroplast: A plant-cell organelle containing chlorophyll, in which photosynthesis takes place.