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Photosynthesis

Why are trees and plants so important to us?

Try it like this

1
Explore the marble runs and guess where, how, and towards where the marbles will travel.
2
Guide the marbles through the tracks and observe whether you guessed their path correctly.
3
Notice that the individual marbles change color along the way, and name them according to the legend on the Koumio® board.
4
Decipher the cycle of photosynthesis and respiration. Find out how the individually named marbles journey through the Koumio® board.
5
Tell a story by the Koumadlo about a tree and a little bird. Discover their endless cycle of photosynthesis and respiration. Try telling this story about other plants, animals, and humans as well.
6
Explore further to find out what happens inside trees and plants during photosynthesis.

How do photosynthesis and breathing work?

Green plants (including mosses), algae and cyanobacteria can photosynthesise. It is a process in which plants produce the sugars they need to grow and convert light energy into chemical energy.

Photosynthesis takes place in chloroplasts, tiny green "factories" inside plant cells. They contain chlorophyll, a green pigment that captures light. Photosynthesis is essential for life on Earth, because it produces the oxygen that most living organisms need to breathe. But a plant doesn't do it so that we can breathe easily. It does it mainly for itself, so that it has something to live and grow on.

What does a plant need for photosynthesis to work properly?

light (usually sunlight) – the source of energy
water – taken up by the roots
carbon dioxide (CO₂) – taken from the air. It gets inside through the stomata, microscopic openings found mainly on the underside of the leaves
chloroplasts with chlorophyll – tiny parts of plant cells that contain the green pigment

How does photosynthesis work?

lImagine a plant as an amazing factory with two production lines:

1) Light-dependent phase (charging the batteries)

This takes place in the chloroplasts, on membranes called thylakoids. Chlorophyll captures light energy (photons) and passes it on to other molecules in the chloroplast. Using this energy, the plant splits water molecules into oxygen, electrons and hydrogen ions. This part produces the energy-carrying molecules ATP and NADPH, which work like charged "batteries".

The oxygen created when water is split is released by the plant into its surroundings. It is a by-product of a process whose main purpose is to obtain the energy needed to make sugars.

2) Second phase (technically the Calvin cycle) (making sugars)

This takes place in the stroma, the fluid inside the chloroplast. This phase does not use the incoming light directly, but the energy stored in the ATP and NADPH created during the light-dependent phase. That is why it is also known as the light-independent reactions.

The plant takes the charged "batteries" from the first phase and uses their energy to capture carbon dioxide from the air and gradually build carbohydrates (sugars) from it. These then serve as fuel for growth, as material for making cellulose, or as storage substances — for example starch, which we find in potatoes.

The overall equation of photosynthesis

using light energy captured by chlorophyll


: 6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂

💡Why are there sixes in the equation? Think of it as a baking recipe. For a plant to build one "cake" (one molecule of sugar), it needs exactly 6 portions of carbon dioxide and 6 portions of water. These sixes tell us how many "ingredients" we must supply to the plant for one molecule of sugar and 6 molecules of oxygen to be created.

Breathing = cellular respiration (the engine of the cell)

While photosynthesis is about building and storing reserves, cellular respiration is the "engine" that puts the energy to use. For a plant (and for us) to stay alive, it has to "burn" the sugars it has made.

It takes place in the mitochondria, which are like tiny power stations inside cells.

During cellular respiration, the plant takes sugar (the fuel) and oxygen and "burns" them. In doing so it obtains the energy (ATP) it needs for life. The waste products are carbon dioxide and water.

❗Important: Cellular respiration goes on all the time, day and night. If a plant stopped respiring, it would have no energy for its basic life processes and would die.

The overall equation of cellular respiration

in the mitochondria


: C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + energy (ATP)

💡The recipe rule applies here too. To "burn" one molecule of sugar we need exactly 6 molecules of oxygen, and these produce 6 molecules of carbon dioxide and 6 molecules of water.

Why is the circuit closed?

The closed circuit is a reminder that nothing in nature is lost — everything keeps going round.

The exhibit shows that photosynthesis is not a static picture in a textbook but a dynamic process that needs a threshold amount of energy and material before the chemical change happens. That is exactly what the hidden lever stands for.

What is the lever inside for?

The lever inside is like a chemical balance in a chloroplast. The plant has to collect enough energy from the sun and enough material before it can switch over and make something new.

Once your movement tips the lever, the process is complete. On one side sugar appears — energy for the plant; on the other, oxygen is released for us.

Does photosynthesis always happen at the same rate?

No, photosynthesis is not a machine that runs at a constant rate. Its speed depends on the "weather" inside the plant and around it. It needs enough light, a suitable temperature, water, enough CO₂ and also minerals from the soil, such as nitrogen or magnesium. When one of these is missing, the plant "changes down a gear".

Where on Earth is photosynthesis greatest?

Surprisingly, not in the rainforests but in the oceans. About half of all photosynthesis on Earth takes place in the seas and oceans, thanks to the enormous numbers of microscopic algae and cyanobacteria.

Can photosynthesis and cellular respiration happen together?

Yes, and they even happen at the same time. A plant respires continuously, day and night. Photosynthesis, however, needs light, and so it only happens when light is available.

During the day, a plant both respires and photosynthesises. Photosynthesis is usually more intense, though, so the plant produces more oxygen than it uses up itself. At night it only respires and uses oxygen up.

What would a world without trees and plants look like? Did you know that Earth was once exactly like that?

What had to happen before it took on the living form we know today?

A world without plants would be a wasteland of rock and sand, rather like the surface of Mars or the Moon. On ancient Earth there really were no plants growing. Gradually, though, organisms capable of photosynthesis appeared and began to produce oxygen. It took hundreds of millions of years for the atmosphere to change enough to allow more complex forms of life to arise.

Who was the first to produce oxygen?

It wasn't trees or flowers. The first oxygen producers were probably cyanobacteria, tiny organisms living in water. They began to use light energy and released oxygen as they photosynthesised. It is thanks to them that the Earth's atmosphere gradually changed, and the conditions arose for life as we know it today.

Cyanobacteria are microscopic organisms that were among the first on Earth able to photosynthesise and produce oxygen. They significantly changed the composition of the atmosphere and made more complex life possible. Without cyanobacteria, animals and humans might never have appeared on Earth at all.

Why are leaves almost always green? Are there plants that aren't green? Can they photosynthesise too?

The green colour comes from chlorophyll, which works like a "solar panel". Chlorophyll absorbs mainly blue and red light, while it reflects green light. That is why we see plants as green.

Many plants with red, burgundy or yellow leaves contain chlorophyll as well. It is simply masked by other pigments. There are, however, parasitic plants that have no chlorophyll and obtain their nutrients from other plants. These cannot photosynthesise.

Do plants look different at night than during the day?

At first glance they look the same, but inside they switch to "night mode". They stop photosynthesising and carry on with cellular respiration only. Some flowers also close for the night and open again in the morning.

How many trees would we need in a room to have enough oxygen just for ourselves?

That's a great trick question. In ideal conditions, one large tree can produce enough oxygen for several people. In a room, though, it wouldn't work that simply. A tree needs enough light, water and space. What's more, oxygen and carbon dioxide are constantly mixing and being exchanged in nature. That is why; to live, we don't need a single tree in a pot but healthy ecosystems — forests, meadows, oceans and other natural environments.

DID YOU KNOW?

Photosynthesis produces oxygen, which is released into the atmosphere.
Photosynthesis forms the basis of most food chains, because plants, algae and cyanobacteria are primary producers.
Every year, photosynthesis creates roughly hundreds of billions of tonnes of new biomass.
About half of all photosynthesis on Earth takes place in the oceans, thanks to cyanobacteria and algae.

RELATED TERMS

Chloroplast: A tiny "green factory" inside a plant cell. Photosynthesis takes place precisely in the chloroplasts. They are filled with membranes called thylakoids and contain the green pigment chlorophyll, which captures light. The thylakoids form what are known as grana — stacks of thylakoids lying on top of one another, looking a little like a pile of pancakes. The space around the thylakoids is filled with the stroma, the fluid environment inside the chloroplast. It is here that the second phase of photosynthesis takes place, in which sugars are made from carbon dioxide.
Stomata: Stomata are tiny openings in the outer skin of leaves, most often on their underside. Through them a plant takes in the carbon dioxide it needs for photosynthesis, and releases water vapour and oxygen. When it is too hot, too dry or too cold, the stomata can close so that the plant loses less water.
Glucose: A simple sugar created during photosynthesis. It serves as a source of energy and as a building material for making other substances in the plant. Plants store surplus sugar in the form of starch. In it, plants store surplus energy for later. Cellulose is another form of sugar, the substance from which most plant cells are built. It forms wood, stems and the firm parts of leaves, for example.
Mitochondria: Tiny organelles inside cells, in which cellular respiration takes place. They obtain energy from the sugars the plant has created by photosynthesis.
ATP (adenosine triphosphate): A molecule that stores the energy needed for life. It is created during the light-dependent phase of photosynthesis, and the plant uses it as a source of energy for making sugars. It is a kind of battery that the cell has available.
NADPH: A molecule that carries energy and hydrogen during photosynthesis. It helps to convert carbon dioxide into sugars. If we imagine ATP as a battery, then NADPH is the lorry carrying energy and materials for building sugar.