Discovery Science: Earth – Morphology and Physiology – Photosynthesis

Earth Science: Morphology and Physiology – Photosynthesis

Plants create their own sustenance by converting sunlight into energy. Because of this ability, they are the nutritional foundation for most other living organisms.

Animals feed on other organisms while plants produce their own food. Most plants do this using photosynthesis, a process in which the sun’s energy is converted into chemical energy and stored.


Green plants annually remove about 200 billion tons of carbon dioxide from the atmosphere, while producing sugar and other nutrients and giving off vast amounts of oxygen as a waste product. There are two stages in this process: a light dependent stage, which requires visible light with wavelengths of between 400 and 700 nanometers and a stage that is independent of light.

Photosynthesis occurs in the chloroplasts, which are found in a plant’s leaves, giving them their green coloration. In fact, in an individual plant cell there are hundreds of these lens-shaped subcellular organelles. Many flat, disk-like structures containing the green pigment chlorophyll are stacked on top of each other within each chloroplast. Chlorophyll—the engine of photosynthesis—is a molecule that can absorb sunlight and use that energy to produce other molecules.

It produces the energy-carrying molecules adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH). To capture enough light to power photosynthesis, leaves usually grow toward the sun, a habit known as phototropism. The carbon dioxide needed for photo- synthesis is absorbed through microscopic openings in the leaves called stomata.

The water needed for photosynthesis is taken up by the roots and transported through the plant tissues. Excess water and the waste oxygen are released via the stomata.

The transfer molecules ATP and NADPH

Photosynthesis was not fully explained until the 1960s. Melvin Calvin-who won the Nobel Prize for chemistry in 1961 for his work—saw that it was a two-stage process. In the first stage, light energy from the sun is captured within the chloroplasts and used to split water molecules and create the carrier molecules ATP and NADPH.

In the second stage, the carrier molecules construct sugar molecules using carbon dioxide. The sugar is stored as a starch and transported to individual cells when energy is required. The waste product
is oxygen.


Stomata are tiny pores in the epidermis of leaves, stems, or flowers that consist of two bean-shaped guard cells. Numerous stomata connect the plant interior with the outside air and allow for the exchange of carbon dioxide and oxygen.

When open, the stomata also re lease water vapor, driving the transportation of water throughout the tissues (xylem) of the plant.