|
Photosynthesis
What Is It?
Photosynthesis is the process by which green plants (including trees) convert light energy to chemical energy and store it as food in bonds of glucose or sugar.
- The conversion takes place primarily in plant leaf structures, specifically in chloroplasts, where the plant processes light energy with CO2 (carbon dioxide) and H2O (water).
- This self-sufficient means of generating food is known as autotrophic nutrition.
Are Trees and Shrubs the Only Place Where We Can Find Photosynthesis?
No. Because chlorophyll, the green pigment of plants, is necessary to the process, we also find photosynthesis among Protista and Moneran Kingdom algaes. In fact, because the earth’s surface is predominated water, global photosynthesis takes place more in the seas than on land.
 How Do Tree Leaves Manage Photosynthesis?
In trees, photosynthesis occurs mostly in leaves, which are composed of upper and lower epidermis, the mesophyll, vascular bundles of veins, and stomates. (Note: Image on right)
- The upper and lower epidermis act as protective layers, and do not contain chloroplasts.
- Stomates are concentrated in the lower epidermis, appearing as a network of holes that allow for gas exchange, taking in CO2 and releasing O2 (oxygen)
- Vascular bundles form a leaf’s mobility system for the internal transport of water and nutrients.
- This circulatory system is broken into xylem, which transport water and minerals from the roots, through the stem, and into leaves.
- And phloem, which distribute glucose that is synthesized through photosynthesis.
- The mesophyll houses chloroplasts and is thus the site for photosynthesis.
 What About Chloroplasts?
Chloroplasts are made of outer and inner membranes, intermembrane space, stroma, and thylakoids that are stacked in structures called grana. (Note: Image on right)Chlorophyll gives plants their green color by absorbing red and blue light. It reflects the color green, and so this is the color that our eyes register. This absorption and reflective mechanism is not random, for it is the red and blue light energy transfer that plants use for photosynthesis.
Climate, Weather and Photosynthesis
Plants adapt and photosynthesis cycles change in response to climate changes. For example:
- Summertime
- Hot summer weather increases the amount of water a plant evaporates.
- To conserve water in hot weather, leaves will close their stomates, but this also restricts the exchange of carbon dioxide for oxygen, and photosynthesis decreases.
- This explains summer browning and wilting of plants and trees.
- Desert Heat
- Certain plants, such as cactus, have developed biological strategies to cope with hot, dry or desert climates.
- They open their stomates only at night and store captured CO2 in organic compounds until daybreak, when those compounds can be processed with light energy.
- Fall Colors
- As summer moves into autumn, days get shorter and shorter, leaving trees and plants less exposure and access to sunlight.
- In winter, trees must survive with far less light and water and resort to living off nutrients stored during the summer.
- Chlorophyll disappears from leaves as they shut down nutrient-generating processes.
- Yellow, gold and orange tones that are normally concealed by the abundance of chlorophyll-saturated green, rise to the visible surface.
- In some tree species, leaves also turn red from glucose trapped in the leaves after photosynthesis stops.
- The brown color noticed in trees, such as oaks, is made from waste left in the leaves.
- Human Benefits of Photosynthesis
- Photosynthetic organisms remove CO2 from our atmosphere and exchange it for oxygen.
- Leaves give off cooling vapor in the course of their photosynthetic chain.
- If we continue to stress or damage the ecosystems where photosynthesis occurs, oceans as well as forests, increased CO2 levels may promote global warming.
|