The Theme of Levels of Organization in Plant Biology
From cell to leaf to plant to population, species and ecosystem, plants have a lot of different levels of organization, like other organisms. The great redwood forests exist only on the western coast of the United States, in California and Oregon. They live in places with coastal fog, and the redwood trees are the tallest living things. A redwood forest is a whole ecosystem, but it is made up of many individual trees, which are made up of cells.
Starting with cells, what makes plants unique? Plant cells have rigid cell walls, and they have special machinery to allow them to convert sunlight to food:
chloroplasts. The chloroplasts are organelles that supply energy for the cell and the plant, by converting using solar energy to make sugars. It would be pretty easy to tell a plant cell from an animal cell, assuming you have a microscope to look through.
Of course cells don’t exist in a vacuum—cells make up different tissues and plant structures that we have already discussed in this unit: shoot and root systems, including stems, leaves, flowers, fruits, and roots. When light hits a redwood leaf, chloroplasts in the palisade parenchyma start converting the light into energy the plant can use. But not all leaves are created equal; leaves at the top of a tree look and act differently than their counterparts closer to the ground.
If you walk around a redwood forest, you’ll notice it is pretty dark on the ground. The extremely tall trees with all their branches don’t let a lot of light reach down to the forest floor, though some plants cope with the low light and grow there anyway. Because of the difference in light, leaves on top of a redwood tree are much thinner and smaller. At the top of the tree, these leaves get plenty of light but also have to deal with wind, which wicks water away from the leaves. Smaller leaves have less surface area, which means less water can evaporate from them. Further down the tree, leaves are wider. These leaves grow in shade, so they have a large surface area that maximizes the amount of light they get. These leaves also aren’t as exposed to wind since they are protected by the trees around them. The bigger leaves growing in the shade are actually more efficient at photosynthesis than sun leaves are; the shade leaves have to be, since they don’t get much sun.
The vascular tissue (phloem in this case) carries the products of photosynthesis (photosynthates) to other areas of the plant. In the meantime, xylem carries water up from the roots to the shoot system. However, redwoods are extremely tall; can the vascular tissue really carry water all the way up the tree trunk? Redwoods actually have another way of dealing with their thirst needs. They don’t just rely on water in the ground to reach the tops of their trunks. They have found another solution: fog! Redwood trees drink in the fog that surrounds their canopies as another water source, and circumvent the problem of getting water all the way up to the top of the tree.
Redwoods and support whole ecosystems by creating habitat for a variety of animal life, scavengers, herbivores and predators. The holes left when branches fall off a tree are perfect nesting spots for these animals. In Redwood National Park in California, a whole bunch of threatened or endangered animals make redwood forests their home, including bald eagles, marbled murrelets, northern spotted owls, Coho salmon, Chinook salmon, and Steelhead trout. That’s right, fish can live in redwood forests—as long as a stream runs through.