Plant Biology - How Plants Drink
Most people are aware of the crucial need of plants for water, but not of all the different ways in which water helps a plant. Since plant biology lectures don't normally approach their physiology from the point of view of water, then this article should provide a new look for many people.
Here are some of the ways in which water contributes, both inside and outside of a plant, to its overall health:
Water inside the plant transports nutrients to cells and wastes away from them.
Helps create energy to fuel plant activities (photosynthesis).
Contributes to turgidity, keeping the plant sturdy.
Makes nectar that attracts bees and birds to help pollinate.
Cools the plant via transpiration.
Moistens the air to help distribute scent.
- Supplies extrafloral nectaries that protect the plant against insects.
- Rainwater washes the outside of the plant clean.
Softens the soil so roots can penetrate down and out.
Softens the seed cover so a seed can take root.
Absorption of Water by Plants
The first five functions above require a plant to be able to absorb water inside of itself. Plants obtain water through their root systems via osmosis. When the ground around a plant's roots is saturated, the roots suck water in by absorbing it into the root cells, then transporting it up into its stems (or trunk), out into the leaves, and out the rest of the way into the air as transpiration (plant sweat). This process happens more often with some types of plants, and hardly at all with others, depending on the type of plant and the atmosphere in which it grows.
Here is another way to look at it. Ninety percent (90%) of a plant's water evaporates from the leaves, so the plant is continually being dried out. Dry cells pull water in from more saturated areas like wetter cells below and, further down, the wet soil. As a plant dries out then, it creates a subtle suction that pulls fresh water up from the roots to slake its thirst, as long as water is available down there.
A Plant's Internal Watery Functions
Transportation: As water is subtly pushed and pulled into and out of a cell membrane it moves nutrients into the cell and pulls wastes out of it. The nutrients, including nitrogen, have come from the soil. Wastes are transported to the leaves to be discarded into the air, if they are gaseous, or they stay in the leaf structure to be discarded when the leaf grows old.
Photosynthesis: 6H2O + 6CO2 ----> C6H12O6 + 6O2 Water plus carbon dioxide - six molecules of each - make one molecule of sugar, with six of oxygen left over. The sugar is the plant's food, the oxygen its discards. This is the formula for photosynthesis. You can see the integral role that water plays, and also how plants produce the oxygen that we breathe.
The trigger for this conversion is sunlight. Sunlight is absorbed by the plant's chlorophyl - its green pigment - which starts the chemical conversion from water and carbon dioxide to sugar and oxygen. The plant creates its sugary energy in this two stage process, discarding leftover oxygen into the air.
Turgidity: Water provides volume that bolsters the cells and walls of a plant's stems, helping them to stand up straight. Water flows up a series of tubules called "xylem vessels" on its way to the leaves. It fills all the plant's cells, creating pressure against cell walls and making them stiff. Without water most plants become flaccid or wilt.
Nectar Production: Nectaries located inside flowers produce a sweet-tasting, insect attractant called nectar. Nectar is a combination of water and sugars made by the plant. This nectar becomes food for insects like bees and tiny birds like hummingbirds. The plant benefits from their accidental brush against plant pollens as they feed on the nectar. When they fly away they carry the pollen with them and deposit it on the next plant they feed on. The pollen is what plants use to fertilize other plants, so they can make seeds. Without this sweet nectar, most plants would not be able to reproduce.
Transpiration: Water that leaves the plant via transpiration serves the same purpose as sweat in a human body. It removes gaseous wastes (including oxygen) and helps cool the plant. Stomata are little openings in the plant leaf, like air pockets, that let used air and water evaporate out into the atmosphere and let carbon dioxide in to be utilized by the plant in photosynthesis. The stomata are flanked by neighboring "guard cells," which open and close, depending on how much water is in them.
When the plant is dry and there is no water in the guard cells, they automatically close, preventing the plant from transpiring, so it can retain its moisture. When the air is hot outside, the plant and its water heat up too, which makes the water travel to the surface, where some of it enters and opens the guard cells to let the rest of it out as cooling vapor.
External Functions of Water for Plants
Leaf Cleaning: Rainwater and irrigation water falling on a plant cleans the leaves and stems. Without this service, the plant would have a hard time carrying out photosynthesis. Similar to solar panels (which were designed from a plant's ability to photosynthesize), the plant needs its surfaces to be clean in order to function optimally.
Air Humidifier: Humid air around a plant provides two helpful functions. One is to help prevent the plant's sensitive leaves from drying out. The other is to carry scent to foraging insects and birds. Scent carries much further in moist air, which is why roses smell stronger right after it rains. Because plants produce some of their own humidity through transpiration, they are often used as small humidifiers indoors.
Extrafloral Nectary Supply: Extrafloral nectaries do the same thing as nectaries in flowers, but serve a different purpose. In this case, nectaries are positioned on leaves, stems, and sometimes on the outsides of flowers to attract predatory insects that will eat the plant's enemy bugs. Again, water is used to produce the nectar in these outdoor nectaries.
Soil Softening: Water softens and cools hard soil. Softer soil makes it easier for plants to push their roots down and out further, giving them greater access to nutrients and providing a more stable base to hold them up. This is why soil should be soaked before planting baby plants. In turn, roots provide underground tunnels through which water can flow down into the aquafir when it rains. Water stored in the aquafir (underground) becomes future food for trees and larger bushes.
Seed Penetration: The last main service water provides to plants exterior to itself is to soften and penetrate the protective covering of its seeds. This starts the germination process. Many plants produce seeds that can last years and even decades under very dry conditions. When water finally arrives it soaks the seed, softens its walls, and the plant sprouts, thereby perpetuating its species.
Growing Plants with Hydroponics
Hydroponics is a way of growing plants in water without soil, to which nutrients have been added. The Hanging Gardens of Babylon is an example of a well known hydroponic garden. Hydroponic plants grow faster and yield more than their "ensoiled" brethren. Nutrients are delivered several times a day, so the plant doesn't have to search for them, and the energy it saves can be used for plant growth. Because the plant is more vigorous, there are also fewer problems with bugs, fungus, and disease. Watch the video below to learn how cities can use hydroponics to feed their residents.
A Little More Depth:
- Extrafloral Nectaries and Ants - Wild About Ants
- Hydroponic Gardening for Beginners - Greentrees Hydroponics
- The Healthy Human Water Body
You've heard that our bodies are vessels, with water constituting 60% of it, but have you ever wondered where all that water is? This article shows why the human body needs so much.