Chapter 4, Section 1

Cell Processes and Energy

PHOTOSYNTHESIS

KEY IDEA

How do cells obtain the energy they needto carry out their functions?

Photosynthesis • The process by which a cell captures energy in sunlight and uses it to make food

• Nearly all living things depend on the energy of the sun

STAGE 1: Capturing the sun’s energy

• The sun’s energy is taken in by the leaves of a plant

• This is done by the photosynthetic pigment, chlorophyll, in the chloroplasts of the plant cell

• CHLOROPHYLL gives plants their GREEN color

• This energy is then used in the second step of photosynthesis

The Two Stages of Photosynthesis

Chloroplasts in a plant cell

STAGE 2: Using energy to make food

• The captured sun energy is used to make sugars and oxygen from water and carbon dioxide.

• The plant roots take in water (H₂O) from the soil

• Tiny pores on the leaves, called stomata, take in carbon dioxide (CO₂) from the air

• Once in the leaves, the H₂O and CO₂ move into the chloroplasts in the cells

Magnified stomata in a pine needle Table Talk: What do stomata remind you of in the human body?

Table Talk: Summarize the two stages of photosynthesis

What happens to the sugar produced in photosynthesis?

• Plants use some of it for food

• Some sugar molecules are converted into other compounds such as cellulose, which is used to form the plant cell wall

• Other sugar molecules are stored in the plant’s cells for later use

• When we eat fruits and vegetables, we are eating the plant’s stored energy

QUICKWRITE: SUMMARIZEIn your own words, write a short paragraph describing the

process of photosynthesis. Include and underline the following words:

Carbon dioxideWatersugar

OxygenPhotosynthesis

SunlightChloroplasts

stomata

See BrainPop, “Photosynthesis” end