Sources of Energy

• All living things need energy• All cells need energy to carry out their functions

Photosynthesis• Photo (light) + synthesis (putting

together)• Process by which a cell captures energy

in sunlight to make food• Living things can obtain energy either

directly or indirectly from the energy of sunlight captured during photosynthesis

Organisms

autotroph• Organism that makes

its own food (uses sunlight directly)

• Plants, some bacteria

heterotroph• Organism that cannot

make its own food (uses sunlight indirectly)

• Animals that eat plants or other animals

Photosynthesis is a complex process that takes two stages:

Stage 1:Capturing the Sun’s

energy

Stage 2:Producing sugars

Stage 1• Chloroplasts in the leaves capture energy

from sunlight• The main pigment in chloroplasts is

chlorophyll (a colored chemical compound that absorbs light)

Stage 2• Need water (H2O) and carbon dioxide (CO2)

• water soil roots stem leaves• carbon dioxide (gas in the air) enters from

stomata (small openings on back side of leaf)

Inside the chloroplasts, the H2O and CO2 undergo a complex series of

chemical reactions:PRODUCTS:• sugar with 6 carbon atoms (C6H12O6), a type of carbohydrate which fuels cells• oxygen (O2) which exits the leaf through the stomata *Almost all the oxygen in Earth’s atmosphere was produced by living things through photosynthesis

Photosynthesis Equation:6 CO2 + 6 H2O C6H12O6 + 6 O2

raw materials products

= “yields” (or gives)

Light energy

Uses for sugar?• Some is used for food• Can be converted into other compounds (such as cellulose)• Some stored in plant for later use…