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How does water help plants grow?

Asked by: Anna Korchak
School: St. James Middle School
Grade: 5
Teacher: Mr. Martinkovic
Hobbies/Interests: Basketball, tennis, piano, chess
Career Interest: Medicine, law, law enforcement, chemist, engineer, scientist, pediatrician, teacher, health care professional, president

Answer from Laurie Kasperek

Manager, E.W. Heier Teaching and Research Greenhouses

Research area: Integrated Pest Management, Beneficial Insect Pest Control
Interests/hobbies: Friesian horses, dancing, hot rods
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Water is essential to plant growth, in fact, it is essential to all living beings. Plants are able to make what they need to survive from water, air and the nutrients their roots absorb from the soil. Green plants require sugar in the form of glucose and the synthesis of this sugar is performed primarily in the leaves. This process is called photosynthesis. The raw materials for photosynthesis are carbon dioxide absorbed from the air, and water absorbed primarily from the soil. The product of the process of photosynthesis is a sugar (glucose). This is shown as:

6CO2 + 6H2O + 673kcal (light energy) yields C6H12O6 (glucose) + 6O2

For every 6 molecules of carbon dioxide absorbed by the leaf through its small openings, called stomates, 6 molecules of water are needed, plus energy from light, in order to yield a molecule of sugar, while 6 molecules of oxygen are released to the atmosphere through the same stomates. The production of glucose is essential for green plants as it is broken down in another chemical process (respiration) to release energy needed for growth. 

Plants absorb light with their leaves, and large flat leaves have more surface area in which to catch that light. But this can also mean more surface area for the loss of water. If the plant is stressed, by drought for instance, the stomates close to prevent the loss of water through evaporation. Air, which normally enters the leaves through the small stomates, now cannot enter the leaf. This is important to keep in mind because if those stomates close to conserve water, photosynthesis and sugar production stops! At that time it wouldn’t matter how much light is available to the plant; all growth has stopped!

Growth is linked with water in a more complex manner in green plants. The “building blocks” of plants, plant cells, grow by division and expansion. Cell division creates more cells and cell expansion increases the size of cells. Cells increase in size by taking up water. The young cells expand and produce cell walls, increasing in size until they are limited by the cell walls. If there is a lack of water during this process the cell cannot expand to full size and growth stops. This translates into smaller plants, fewer leaves, smaller fruit, thinner stems, and fewer roots.

Roots are plant organs that take up water. At the root tip is a zone of active cell division, where new cells are being formed. Behind this is a zone were the root cells are expanding, the zone of elongation. Water moves readily into and out of the root tips. The zone of elongation pushes the roots down into the soil and as the soil dries out, root growth slows or stops. This creates water loss in the plant.

Proper watering is critical to the plant collection of the E. W. Heier Teaching Greenhouse on campus and is a daily practice. Visitors are welcome at the Greenhouse; hours are normally 8:30am to 4:00pm weekdays.

Last Updated: 3/1/17