Inhale, exhale

(Continuation of #5)

Animation showing the 12-month cycle of all plant life on Earth - whether on land or in the ocean. Rather than showing a specific year, the animation shows an average yearly cycle by combining data from many satellite instruments and averaging them over multiple years. Credit: NASA’s Goddard Space Flight Center

Pr. Sahoo: “Now Jacqueline, take a deep breath: inhale, exhale! Once more. Inhale, exhale. Very good. Well, the second breath we took, we owe it to the algae which every day renew more than half of the oxygen in the atmosphere of our planet.”

More than half of the oxygen in the air?! This a breathtaking information isn’t it? Dr. Sahoo explained to me that like all plant organisms, algae perform photosynthesis.

Basically, photosynthesis is a process by which plants make their own food. It sounds a bit magical actually! In their tiny kitchen inside their cells, they use and mix special ingredients : water, carbon dioxide CO₂ (a gas taken from the air) and minerals (tiny elements that compose the rocks). Instead of using a stove or an oven for creating a reaction, they have some special equipment which allow them to take the energy of the sunlight. And from this recipe, they make sugars! Wow! That is quite impressive!

They will then use these sugars as an ingredient for making all the other substances (such as proteins, fats or hormones) that they need for feeding, growing, reproducing, in short: living!

Sugars and these other substances which are made by living organisms are organic matter, while minerals, carbon dioxide and water are inorganic matter.

Plants are indispensable to us. They are able to produce organic matter from inorganic compounds, we are not! We - humans - also manufacture our own organic matter to live and ensure our basic needs. We do that through complex reactions in our cells but but we can’t do it from sunlight, we need the organic components made by plants. Because of this capability, scientists call plants autotrophic organisms (able to feed themselves), while animals like us we are called heterotrophic organisms (feeding from other food).

Except for a few groups of bacteria¹, plants and algae are the only groups of living organisms capable of synthesizing organic matter from mineral elements. We, and all other animals, are completely dependent on photosynthesis. This is why plants are irreplaceable!

In addition, plants are a carbon sink: the photosynthesis reaction fixes the carbon dioxide from the atmosphere and reject the **oxygen O_{2. Carbon dioxide is the famous **CO2 we hear a lot about in the news and ads for cars on TV and the dioxygen O2 is a molecule that we take from the air we breath and which is essential to the functioning of all our cells.}

Pr. Sahoo added that algae have played a fundamental role in the history of the evolution of life on our planet.

Apparently, 3.8 billion years ago, the first plants which appeared and performed photosynthesis were algae, called cyanobacteria. They were the only ones able to do that and took the opportunity to proliferate and occupy the place… for 2 billion years! Because of that, they transformed their environment: they trapped the carbon dioxide, rejected dioxygen and this led to the establishment of the atmosphere and of the ozone layer at the surface of the planet.

OK. I can make an effort to make Pr Sahoo and Anne-Gaëlle believe that I believe them but I remain very doubtful: 3.8 billion years ago? I wonder who are the eyewitnesses of that time!².

To be continued in #7

Adapted from the interview of Dr. Sahoo, click here !