School of Life Sciences | Ask A Biologist

dropdown arrow downdropdown arrow upshow/hide menu

Why is Rudolp's nose red?
Photosynthesis Story Subpage

The Recipe for Plant Growth

show/hide words to know

  • Carbon dioxide: a chemical compound (a gas) that has two oxygen atoms and one carbon atom (CO2); carbon dioxide is a greenhouse gas... more
  • Chlorophyll: the pigment that gives plants their green color and allows them to absorb sunlight... more
  • Chloroplast: a part of a cell found in plants that converts light energy into energy plants can use (sugar). Other living organisms such as algae also have cells that contain chloroplasts.
  • Element: in chemistry a substance that cannot be broken down (separated) by a chemical process... more
  • Mass: is used to describe how much matter is in an object. If you know the number of atoms, the density of the atoms, and what type of atoms are in an object you can calculate its mass.
  • Oxygen: an element that makes up about 21% of air and that many organisms need to live.
  • Photosynthesis: a set of chain reactions that convert light energy into chemical energy. Photosynthesis also produces energy-rich carbohydrates like starch. Photosynthesis occurs in the chloroplast of a plant cell... more

Where Does a Plant's Mass Come From?

Have you ever wondered where plants get their mass? All those leaves and branches have to come from somewhere, but where? It turns out that the main ingredients for plant growth are water, air, and energy.Water, Air (CO2), energy are needed for plant mass.

The Story of Air

carbon dioxideThe air around you may seem empty, but it's not.

Air is made of tiny bits that we call molecules. If you had enough air molecules, you could even weigh them.

Two of the molecules in air are oxygen and carbon dioxide. You may think oxygen is the most important molecule—we need it to live. But carbon is important too. All living things on Earth are made of carbon.

If you removed the water from our bodies, you would find that carbon makes up most of the rest of our weight, or mass. The same is true for plants.

soil sun and waterWe get carbon from our food, but where do you think plants get carbon? They don't get their carbon from the soil, or from the sun, or from water.

Plants pull carbon out of the air.

Are Plants Made from Thin Air?

Inputs for photosynthesisAir is mostly made of nitrogen, oxygen, and carbon dioxide. So how do plants get the carbon they need to grow? They absorb carbon dioxide from the air. This carbon makes up most of the building materials that plants use to build new leaves, stems, and roots. The oxygen used to build glucose molecules is also from carbon dioxide.

Water is another important material plants need to grow, and they get it by absorbing it through their roots. Water is made of two hydrogen atoms and one oxygen atom. The hydrogen in water is used to help build glucose molecules.

A plant can be up to 95% water. Think of the water as the filler they use between carbon structures. If we take away the water from a plant though, and look at just the dry material, a large majority of that material comes from thin air.

They also need tiny bits of vitamins and minerals to grow properly, which they get through their roots.

Plants need a lot of energy to take care of their cells and to build new ones so they can grow. Plants get their energy from the sun.

cross section of a leaf showing stomata

The Carbon Story

Plant cell illustrationIf we zoom in on a plant leaf, so close that we can see the cells, we'll find tiny openings called stomata. Stomata are holes made from spaces between special cells. These holes are where plants absorb carbon dioxide from the air.

Once inside the leaf, the carbon dioxide can enter plant cells. Inside the plant cells are special cell parts called chloroplasts, where photosynthesis takes place.

Plant cells look green due to molecules in the chloroplasts that reflect green light. There are many, many chloroplasts in every green plant cell. Most of the rest of the cell usually looks clear. 

 

cellulose

In the chloroplasts, carbon, oxygen, hydrogen, and energy are used to make a sugar called glucose. The whole process of making glucose is called photosynthesis.

Next, glucose molecules combine to form long chains called cellulose. Cellulose is then used to build plant structures, like cell walls.

leaf growthThese structures and the materials they hold are also built with water.

When new cell structures are built, cells can grow and divide, making new cells. These new cells make for new plant growth. This lets the plants get bigger.

 So if you are creating a cookbook of life and want to include a recipe for plant growth you would add the following.

 

  • water treeWater, which can make up to 95% of the weight of a plant, enters the plant through its roots. 
  • Carbon, which makes up the most of the rest of the plant, comes from the air and enters the plant through holes in its leaves.
  • Oxygen from carbon dioxide, and hydrogen from water, enter through the leaves and roots, and are used to make glucose.

  • Energy, which the plant needs for photosynthesis to work, is absorbed from sunlight.

recipe for plant growth

 


This section was contributed by Karla Moeller and Charles Kazilek. Images are by Sabine Deviche.

 

Are plants made from thin air?

Check out our printable poster of the full carbon story.

Share to Google Classroom

Be part of Ask A Biologist

by volunteering, or simply sending us feedback on the site. Scientists, teachers, writers, illustrators, and translators are all important to the program. If you are interested in helping with the website we have a Volunteer page to get the process started.

dropdown arrow downdropdown arrow up  Learn More

Are plants made from thin air?

Check out our printable poster of the full carbon story.

Share to Google Classroom

Be part of Ask A Biologist

by volunteering, or simply sending us feedback on the site. Scientists, teachers, writers, illustrators, and translators are all important to the program. If you are interested in helping with the website we have a Volunteer page to get the process started.