Module 5 Intro

Module 5—Photosynthesis and Cellular Respiration

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Plant Productivity and Types of Photosynthesis

In Module 2: Lesson 1 you were introduced to productivity. Plant productivity can be related to biomass. Biomass is produced by photosynthesis and is measured in units of dry organic matter (kg/m2/ yr). The higher the biomass, the greater the productivity. When farmers talk about crop yields, they are hoping for high levels of plant productivity. Plant productivity is directly related to the metabolic process of photosynthesis.

The ability for farms and orchards to produce large amounts of food is of great importance to people. In 2008, it was reported that there may be a global food-shortage crisis. There is not enough food, such as wheat and corn, being stored or grown to support both human consumption and biofuel production. Booming populations and a switch to meat-rich diets in the developing world have increased the demand for wheat and rice.

How can photosynthesis-related technologies help this potential crisis?

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TR 1. Types of Photosynthesis

Ninety-five percent of plants follow the Calvin-Benson cycle that you examined in Lesson 3. These plants form 3-carbon molecules of PGAL, which are then used to make glucose. Scientists refer to these plants as C3 plants. A birch tree is an example of this type of plant.

In climates with intense sunlight and high temperatures, C3 plants are not very efficient. Gas exchange in the leaves of plants is controlled by the stomata. In warmer temperatures, plant leaves must keep their stomata closed to reduce water loss. Closing the stomata prevents carbon dioxide from being absorbed into cells for use during photosynthesis. In addition, the buildup of oxygen as a waste gas in leaves inhibits carbon fixation.

Plants in these conditions may open their stomata at night to release waste oxygen and store carbon dioxide. In hot, dry conditions, plants with other mechanisms to convert carbon dioxide into glucose are more efficient. These plants, such as C4 and CAM plants, have evolved by adapting to their environmental conditions.

How have scientists applied their knowledge of the different types of photosynthesis to plant productivity (agricultural technologies)?

Use the Internet or print resources, such as your textbook, to research C3, C4, and CAM plants. You will be placing your findings in a chart found in  your Module 5: Lesson 4 Assignment. Be sure to save your information to your course folder.

Self-Check

SC 2. Complete this phrase: Productivity and sustainability are influenced by______________. Perform a web search with the keywords “sustainability plant productivity grasslands.”

Studies suggest that species richness, in producers and consumers, maintains a sustainable environment. Jot down some of your ideas about the effect of biodiversity on plant productivity and photosynthesis. Save your ideas in your course folder. It is beneficial to review past topics and apply them to new information.

Watch and Listen

In Module 2: Reflect on the Big Picture, you were asked to create a list of technologies related to photosynthesis. You may have explored biofuels, agriculture, greenhouse gas reduction, and hydrogen gas production. But you may not have considered herbicides as a technology related to photosynthesis. Watch the video of the time-lapsed effects of herbicides on a plant. Since many herbicides interfere with the process of photosynthesis, they are considered to be metabolic toxins. You will be taking a closer look at metabolic toxins in Lesson 7.