photosynthesisDr. Donna Howell

Biology IBlacksburg 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:

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.

The End