photosynthesis Dr. Donna Howell Biology I Blacksburg High School
Energy • ALL organisms need a constant source of energy to survive. • The ultimate source of energy is the Sun. • Plants and other types of organisms are able to use light energy from the Sun to produce food.
Types of organisms • There are two types of organisms: • Autotrophs – organisms that make their own food from the Sun, such as plants • Heterotrophs – organisms that cannot use the Sun’s energy directly to make their food
Photosynthesis • Photosynthesis is the overall process by which sunlight (solar energy) chemically converts water and carbon dioxide into sugars, a source of energy. • Occurs in two stages in the chloroplasts.
Chloroplasts • Chloroplasts consist of: • Thylakoids – little “pancake-like” structures stacked on top of each other. Chlorophyll located here. • Granum – a stack of thylakoids • Stroma – the space outside the thylakoid membrane
Stage 1 • Stage 1 of the process is called the light-dependent reactions because require sunlight.. • This occurs in the plant’s chloroplasts. • Use energy from sunlight to produce ATP and NADPH, energy carrying molecules.
Stage 2 • Stage 2 of the process is called the dark reactions because doesn’t require sunlight. • This occurs in the plant’s chloroplasts. • Uses ATP and NADPH from the light-dependent reactions to produce high-energy sugars.
Photosynthesis • The chemical formula for photosynthesis is: 6CO2 + 6H2O C6H12O6 + 6O2 The above means that six molecules of carbon dioxide and six molecules of water react to form one glucose (sugar) molecule and six oxygen molecules. Solar energy
ATP • ATP stands for adenosine triphosphate. • It’s structure is: • Consists of nitrogen base (blue part) • Sugar – ribose (green part) • 3 Phosphate groups – orange part
ATP • ATP can be used to produce energy when one of the phosphate groups is removed. • Energy is contained in the chemical bonds that holds the phosphate groups together, and breaking a bond releases energy. That creates a molecule called ADP (di). • The loose phosphate group above can re-combine with the ADP molecule to form ATP again. Keeps cycling as needed.
Light-Dependent reactions • During the light-dependent reactions, solar energy is absorbed by chloroplasts and two energy storing molecules (ATP, NADPH) are produced. • The solar energy is used to split water molecules which results in the release of oxygen as a waste product.
Dark reactions (Calvin cycle) • During the dark reactions, energy stored in ATP and NADPH is used to produce simple sugars (glucose) from carbon dioxide. • These sugars store energy for use by the cell when it needs it. • The glucose can be used as an energy source, or can be used to produce organic molecules such as proteins, carbohydrates, fats, or nucleic acids.