The mesophyll consists of two types of cells: palisade parenchyma and spongy parenchyma. Palisade parenchyma cells are elongated and tightly packed, forming a compact layer just beneath the upper epidermis. They contain numerous chloroplasts, the organelles responsible for photosynthesis. Spongy parenchyma cells, located below the palisade layer, are irregularly shaped and loosely arranged, creating air spaces between them. These intercellular air spaces facilitate gas exchange, allowing carbon dioxide (CO2) to diffuse into the leaf and oxygen (O2) to diffuse out.
The function of the mesophyll is to absorb light energy from the sun and use it to power photosynthesis. Chloroplasts in the mesophyll cells contain chlorophyll, a green pigment that absorbs blue and red light from the spectrum, while reflecting green light, giving plants their characteristic color. The absorbed light energy is then used to drive the conversion of CO2 and water into glucose and oxygen.
Glucose is the primary energy source for plants, while oxygen is released as a byproduct of photosynthesis. The diffusion of gases through the intercellular air spaces in the spongy parenchyma allows for efficient gas exchange, ensuring a continuous supply of CO2 and removal of O2 to support photosynthesis.
In summary, the middle matter or mesophyll of a plant leaf consists of palisade and spongy parenchyma cells and plays a vital role in photosynthesis by capturing light energy and facilitating gas exchange. The intricate structure and specialized cells of the mesophyll allow plants to convert light energy into chemical energy, producing the food they need for growth and sustaining the intricate web of life on Earth.