Did you ever wonder?
America’s tallest trees are the California Redwoods. Some tower well over 350 feet. To put in perspective, Allentown’s PPL Building is about 320 feet. Did it ever make you wonder how a plant this large (tall) is able to get water to all of its cells? Nature has found a way and it’s not how water gets to the top floors of the Lehigh Valley’s tallest building.
First, let’s discuss some basic biology. Green plants (those with chlorophyll) are able to produce their own food through the process of photosynthesis (to make food with light.) In very basic terms, those green plants use sunlight for energy, they take in carbon dioxide from the air, water from the ground, and produce food. The food is actually glucose. A waste product of photosynthesis is oxygen. Of course we are aware that oxygen is needed for animals to breathe. Actually, the correct terminology is respiration.
Respiration is the process where animals, and plants too, combine sugar with oxygen to produce energy. The byproduct of respiration is carbon dioxide. Simply put, plants produce oxygen that animals, while animals through respiration, produce carbon dioxide which plants need to make food. Note: All living things respire; green plants, fungi, bacteria, and animals. Green plants though produce more oxygen in photosynthesis than they use in their respiration.
Now the question. How do the cells in needles of redwoods get water to the top of the tree? Very tall “skyscrapers” can’t pump water 5, 6, or 8 hundred feet to the upper floors. The pumps would fail from the pressure. Architects have designed these building to have “reservoirs/tanks” at various floors. Here water is stored temporarily until different pumps push water to the next level of tanks, etc.
Trees don’t have pumps, and water doesn’t flow up hill, or does it? Plants amazingly, use transpiration pull to solve this problem. Transpiration is the process where water molecules are released through tiny openings in leaves (stomata) and as a molecule of water evaporates, it tugs another molecule upward.
This amazing event works to pull molecules of water (one tugging the next, and the next, and the next) from the roots and eventually to all the leaves (needles) throughout a plant or a 300-foot tall redwood. Trees, shrubs, flowers, etc. have special tissues called xylem through which the water travels upward. The official scientific term for this tugging of water molecules is called Cohesion Tension Theory.
Plant leaves are usually waxy on the top to protect from evaporation loss. The underside of the leaves is where the plant takes in carbon dioxide, releases oxygen, and critically, where molecules of water are released. If you have house or garden plants that get too dry, the leaves wilt because the loss of water lowers the turgor pressure. Waxy leaf surfaces of oak or maple leaves help control water loss. The underside of leaves has the openings needed for transpiration and respiration.
Desert plants have gone to the extreme. They either have very small leaves, like mesquite, or cacti that have no leaves at all. (Technically they do have leaves, the leaves through evolving have become spines.). The cactus’ thick, green waxy skin protects it from water loss and makes the food. The cactus spines keep desert animals from chewing into cacti to get the moisture they would need.
Test Your Outdoor Knowledge: True/False: Pines or spruce retain most of their leaves through winter because their narrow leaves lose less water in cold, drying winds.
Last Week’s Trivia Answer: Loons, with legs set much farther back on their bodies, struggle to move about on land and thus must “run” across the water’s surface in order to take flight.