This section will help you to review all the new information from the unit as well as to connect what you’ve learned about plants to what you learned in Unit 1 about homeostasis in human beings.
1. Read the following information about plant activity. Circle any terms that are still new to you.
Photosynthesis (photo = light; synthesis = to make) is the process used by plants and other autotrophs (producers) to capture light energy and use it to power chemical reactions that convert water (H2O) and carbon dioxide (CO2) into oxygen (O2) and sugar (glucose: C6H12O6). Photosynthesis takes place in the chloroplasts of plant cells.
Cellular respiration is the process of capturing energy found in carbon compounds from the food we eat (glucose: C6H12O6) and using that energy to make cellular energy in the form of ATP (Adenosine triphosphate) in the presence of oxygen (O2). Cellular respiration occurs in the mitochondria of autotrophs (producers) AND heterotrophs (consumers).
As photosynthesis takes place in plants, cellular respiration occurs as well. Both processes help the plant maintain homeostasis. Remember, all living things must maintain a relatively steady state (maintaining a stable or balanced internal environment is called homeostasis). During the day, some of the oxygen produced during photosynthesis is immediately used during cellular respiration. In addition, some of the carbon dioxide made during cellular respiration is immediately used in photosynthesis.
Summary of the molecules used during photosynthesis and cellular respiration:
2. Write three questions for a quiz you could give to another student after reading that section.
3. Read about the process of transpiration on this page. You should read forward to learn what you’ll have to do in the writing assignment below so you can take notes as needed.
4. Evidence shows plants have evolved from aquatic algae. Read this excerpt describing the adaptations plants have made to living on dry land.
Over time, plants had to evolve from living in water to living on land. In early plants, a waxy layer called a cuticle evolved to help seal water in the plant and prevent water loss. However, the cuticle also prevents gases from entering and leaving the plant easily. Recall that the exchange of gasses—taking in carbon dioxide and releasing oxygen—occurs during photosynthesis.
To allow the plant to retain water and exchange gases, small pores (holes) in the leaves called stomata also evolved. The stomata can open and close depending on weather conditions. When it's hot and dry, the stomata close to keep water inside of the plant. When the weather cools down, the stomata can open again to let carbon dioxide in and oxygen out.[1]
5. What are stomata?
6. What do you think happens to photosynthesis when the stomata are closed?
7. What do you think causes a plant to wilt?
8. Write a paragraph based on what you’ve learned explaining how a plant maintains homeostasis.