Washington State University
Doctor Universe: How do flowers use sunlight and water to grow? - Jackie, 8 years old, Virginia
Dear Jackie,
When I was young, my family measured my height. They put a sign on the wall. It was amazing to see how much I had grown.
I was talking with Helmut Kirchhoff about how plants grow. He is a scientist at Washington State University. He studied plant chemistry and organic chemistry.
He told me that plants grow by creating new cells. To create a new cell, the existing cell is split into two parts. This is called cell division. Then new cells continue to grow. This is called cell growth. Thus, the plant can sharpen its stem or roots, and grow new cells in these places. When it's time to flower, the plant can produce new types of cells that make flowers.
Plants need the right nutrients for cell division and growth.
“We are all made up of carbohydrates, proteins, oils and special molecules in which our genetic information is encoded in the form of DNA or RNA,” says Kirchhoff. “They are the building blocks on which all life is built, and they take energy to build them.”
Plants get energy from sunlight, water and nutrients from the soil, and a gas called carbon dioxide from the air. The process is called photosynthesis.
Here's how it works. Everything in the universe is made of matter. Water consists of the elements hydrogen and oxygen. Carbon dioxide consists of the elements carbon and oxygen.
Each element is made up of tiny particles called protons, neutrons, and electrons. It is important to know that electrons are excited by light. Scientists call this absorption.
For photosynthesis, plants absorb everything they need – water, nutrients and carbon dioxide. Then a green pigment called chlorophyll in its leaves collects sunlight. Light excites electrons in chlorophyll. Excited chlorophyll transmits the sun's energy.
This energy has the ability to split water into oxygen, hydrogen ions and electrons. The excited hydrogen ions and electrons can then be thrown into carbon dioxide to form a sugar called glucose. It also produces a small electrical current in the plant. It converts light energy into chemical energy called adenosine triphosphate, or ATP for short.
“ATP is the energy currency used by all living cells, from the simplest bacteria to humans,” says Kirchhoff.
Have you ever played video games with energy bars? When the energy bar is full, your character can grow crops or fight enemies. When the energy bar runs out, your character may slow down or fall asleep.
Do you remember how cell division and growth require a lot of energy? ATP is the energy that living organisms use to carry out these activities. Photosynthesis is the way a plant replenishes its energy reserves.
The sugar produced during photosynthesis is used by plants to store energy for the future. Like a night without sunlight. When it needs energy, it can break down sugar and use the energy stored there.
Humans like you and cats like me grow by dividing and growing cells. But animals cannot perform photosynthesis to produce energy. This is why we eat plants like vegetables and fruits. When you eat a big bowl of spinach, you give your body the carbohydrates, protein and oil from the spinach. Your cells can break down sugar into energy that your body can use.
You can call it the sweet system.
sincerely,
Doctor of the universe
Adults can help children ask a question at Askdruniverse.wsu.edu/ask.
