How are photosynthesis and breathing related?

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Habitats - In the forest

  • Plants can store the energy of sunlight (source: Colourbox)

The process of starch build-up under the influence of light is known as photosynthesis, because the formation (gr. Synthesis = formation, composition) of starch only takes place under the influence of light (gr. Phos = light). Photosynthesis involves complex biochemical reactions, but it can be summarized in a simplified way:

Photosynthesis is the most important metabolic process in nature because it is the basis of all life.

Today we know that the earth's atmosphere did not contain any oxygen until the first green plants appeared. It was only through the photosynthesis of the plants that the earth's atmosphere was slowly enriched with oxygen. This laid the foundation for the breathing of animals and humans and thus also for the appearance of these living beings on earth.

Photosynthesis enables plants to store the energy of sunlight in the form of organic compounds (e.g. starch). This energy is the basis of all life processes in plants, animals and humans. You can make yourself aware of this using the example of “bread for lunch”:

  • Without photosynthesis there would be no lunch break (source: Colourbox)

The main component of bread is flour, which is only available through the photosynthesis of the wheat plant. The plant converts the sun's energy into chemical energy. This energy is stored in the starch of the wheat grains. If we eat the bread, the starch provides our body with the energy it needs to function. But bread alone doesn't taste good. It can e.g. B. be topped with sausage, which also provides us with energy. Sausage is only available because there is photosynthesis. The pig from which the sausage comes from eats z. B. Potatoes. It can move because it has the energy from the potato and it can grow. The prerequisite for all of this is that the potato plant produces starch from light, water and carbon dioxide through photosynthesis and stores this in the potato tubers (their storage organs). So on the basis of the potato diet (and thus photosynthesis) pork is formed, from which the butcher makes sausage.

When it comes to energy production, there is a fundamental difference between plants and animals. Plants are called autotrophic (from Greek autos = self; trophé = nutrition) because they can meet their nutritional needs themselves. Animals and humans are heterotrophic (from Greek heteros = different), because they are dependent on the nutrients of others (animals or plants).

How can a tree survive without leaves in autumn and winter?

In our latitudes, most of the trees change their color in autumn. The green disappears, in its place are yellow, brown or red tones in many species. Ultimately, the deciduous trees shed the leaves entirely. You protect yourself against drying out. That seems absurd at first, because we experience the winter half-year as a rather humid time.

Still, leaf litter makes sense, because the ground often freezes in winter. The soil water cannot then be absorbed by the tree roots. However, trees are dependent on the water supply from the ground when their leaves transpire. By throwing leaves, they prevent excessive water loss, snow breakage and freezing.

But foliage discoloration and fallen leaves have another effect. The trees can no longer carry out photosynthesis without the "green" in the leaves, because for this they need leaf green (chlorophyll), which they break down shortly before the leaves fall. So already when they are still hanging on the tree but are no longer green, but already brown or yellow.

So what do trees live on in autumn and winter if they can't make starch and glucose? The answer is memory strength! This storage strength is produced during the "green season" and deposited in amyloplasts. Amyloplasts are cell organelles that are similar in structure to chloroplasts, but are colorless. The trees fall back on their storage strength when they sprout in spring enzymatically split into glucose and from this released sugar the tree builds up practically all the substances it needs for life.

A closer look: nutrients from the plant

Nutrients are the compounds that are used to generate energy and build up the body. These are carbohydrates, fats and proteins. The starch and grape sugar (glucose) produced in photosynthesis belong to the group of carbohydrates. But where do the other nutrients come from, such as B. the oil from sunflower seeds and olives, or the protein from wholemeal bread?

The basis of all these substances are the carbohydrates from photosynthesis. Some of it goes into complicated metabolic processes in which fats and proteins are formed. The fat that is formed in the sunflower is stored in the seeds, the protein of the wheat is stored under the seed coat of the grain.

Cellulose is also made from the synthesized grape sugar (glucose). Cellulose is the most important building material in plants, from which the cell walls are built. It is created by stringing together many pieces of glucose to form long chains.