Points to Consider
- The next lesson discusses photosynthesis.
- It is often said that plants make their own food. What do you think this means?
- What substances would need to move into a leaf cell?
- What substances would need to move out of a leaf cell?
4.2 Lesson 4.2: Photosynthesis.
Lesson Objectives
- Explain the importance of photosynthesis.
- Write and interpret the chemical equation for photosynthesis.
- Describe what happens during the light reactions and the Calvin Cycle.
Check Your Understanding
- How are plant cells different from animal cells?
- In what organelle does photosynthesis take place?
Introduction
Almost all life on Earth depends on photosynthesis. Recall that photosynthesis is the pro-
cess by which plants use the sun’s energy to make their own “food” from carbon dioxide and
water. For example, animals, such as caterpillars, eat plants and therefore rely on the plants
to obtain energy. If a bird eats a caterpillar, then the bird is obtaining the energy that
the caterpillar gained from the plants. So the bird is indirectly getting energy that began
with the “food” formed through photosynthesis. Almost all organisms obtain their energy
from photosynthetic organisms, either directly, by eating photosynthetic organisms, or indi-
rectly by eating other organisms that ultimately obtained their energy from photosynthetic
organisms. Therefore, the process of photosynthesis is central to sustaining life on Earth.
Overview of Photosynthesis
Photosynthesisis the process that converts the energy of the sun, or solar energy, into
carbohydrates, a type of chemical energy. During photosynthesis, carbon dioxide and water
combine with solar energy, yielding glucose (the carbohydrate) and oxygen. As mentioned
previously, plants can photosynthesize, but plants are not the only organisms with this
ability. Algae, which are plant-like protists, and cyanobacteria (certain bacteria which are