MAVO Year 4 · Plants · Section 9.3

Glucose as a raw material

Energy-rich and energy-poor substances

Organisms contain organic substances, including glucose, fats and proteins, as well as water and mineral nutrients. The organic substances contain chemical energy that can be released by metabolism. Water, carbon dioxide and mineral nutrients are described as energy-poor in this course because they do not provide food energy in the same way.

Photosynthesis and cellular respiration

Plants make glucose and oxygen by photosynthesis. They also carry out cellular respiration, using organic fuels and usually oxygen to release usable energy. Under sufficient light, photosynthesis can exceed respiration, producing a net uptake of carbon dioxide and release of oxygen. At night there is no light-driven photosynthesis, but respiration continues, taking up oxygen and releasing carbon dioxide.

Making other substances from glucose

Carbohydrates: glucose can be used to make transport sugars, cellulose for walls and starch for storage. Starch often accumulates in seeds, storage roots and tubers.
Proteins: plants use carbon-containing substances derived from glucose and nitrogen obtained from compounds such as nitrate to make amino acids and then proteins. Proteins occur in cells and may be stored in seeds.
Fats: plants make fats from carbon-containing raw materials derived from glucose. Oil-rich seeds include peanuts and sunflower seeds.

Assimilation

Assimilation, in this course, means building an organism's organic substances. Photosynthesis builds glucose, and further reactions convert it into other compounds for growth and maintenance. These reactions require energy and additional raw materials where necessary. Photosynthetic production supplies organic food for most ecosystems; oxygen release specifically occurs during oxygen-producing photosynthesis, not every assimilation reaction.

Uses of assimilation products

Fuels are broken down to release usable energy. Building materials, such as proteins and cellulose, form cell structures and tissues. Reserves, such as starch and fats, are stored for later use.

Glossary

Assimilation: Building the organic substances of an organism from simpler raw materials.
Fuels: Substances broken down during respiration to release usable energy, such as glucose.
Building materials: Substances used to form and repair cells and tissues.
Proteins: Complex molecules built from amino acids; plants make them using carbon-containing substances and nitrogen compounds.
Carbohydrates: Substances including sugars, starch and cellulose, with energy, storage or structural roles.
Reserves: Substances stored for later use, such as starch and fats.
Fats: Energy-rich substances used in structures, as fuels and as reserves, often abundant in some seeds.
Starch: A carbohydrate composed of glucose units and used as a storage substance in plants.