photosynthesis Dr. Donna Howell Biology I Blacksburg High School

Energy and Life

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 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: 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 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.

The End