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.