ZOOMING IN
ANATOMY OF A LEAF
FIGURE 23–15 Leaves absorb light and carry out most of the photosynthesis in a plant. Compare and Contrast Compare the structure of the two types of mesophyll cells in a leaf.
Photosynthesis The mesophyll tissue in most leaves is highly specialized for photosynthesis. Beneath the upper epidermis is a layer of cells called the palisade mesophyll, containing closely packed cells that absorb light that enters the leaf. Beneath the palisade layer is a loose tissue called the spongy mesophyll, which has many air spaces between its cells. These air spaces connect with the exterior through stomata (singular: stoma). Stomata are small openings in the epidermis that allow carbon dioxide, water, and oxygen to diffuse into and out of the leaf.
Transpiration The walls of mesophyll cells are kept moist so that gases can enter and leave the cells easily. The trade-off to this feature is that water evaporates from these surfaces and is lost to the atmosphere. Transpiration is the loss of water through leaves. This lost water may be replaced by water drawn into the leaf through xylem vessels in the vascular tissue. Transpiration helps to cool leaves on hot days, but it may also threaten the leaf's survival if water is scarce.
BUILD Vocabulary
WORD ORIGINS Mesophyll comes from two Greek words: meso, meaning “middle,” and phyllon, meaning “leaf.” Stomata comes from the Greek word meaning “mouths.”
In Your Notebook Make a two-column table in which you list structures found in a leaf cross section and describe their functions.
Table of Contents
- Formulas and Equations
- Applying Formulas and Equations
- Mean, Median, and Mode
- Estimation
- Using Measurements in Calculations
- Effects of Measurement Errors
- Accuracy
- Precision
- Comparing Accuracy and Precision
- Significant Figures
- Calculating With Significant Figures
- Scientific Notation
- Calculating With Scientific Notation
- Dimensional Analysis
- Applying Dimensional Analysis