INTRODUCTION

We are made up of complex interactions of various activities. Some of which we do consciously and others that we do without necessarily thinking about. One of such activities that we perform without thinking about is breathing. No one thinks before they breathe except they have some serious medical conditions that make breathing difficult. Breathing is one of the most important processes that take place in man as well as other living things. It is controlled by the part of the brain known as the medulla oblongata. Breathing like other involuntary actions take place without you consciously trying to control the process. Breathing involves the exchange of air; taking in oxygen into the lungs while releasing carbon dioxide as an end product of respiration. https://img.esteem.ws/amf9l0n77e.jpg ^{modified from original image - public domain: Wikipedia image} Breathing is a needed for respiration to be completed and it has to do with the taking in of oxygen and giving out carbon dioxide which is the end product of respiration. Respiration is a complex reaction that involves the breaking down of glucose using the oxygen inhaled to break down glucose to produce energy. This takes place every moment of our lives that we seldom take note of it. Oxygen is used for respiration and it is also very reactive. This means that oxygen is being constantly removed from the atmosphere and also very reactive we cannot be sure it will continuously be available in its useful state. Therefore, there is a need to constantly replenish this oxygen being used by man, the birds, the rodents, the lion, and even the fish in water. All thanks to photosynthesis, a process by which green plants manufacture their own food, oxygen is supplied back to the atmosphere while carbon dioxide is used up in the process. The cycling of both gases is controlled mainly by respiration and photosynthesis. Oxygen is abundant in our atmosphere, about 21% in volume. It is a colourless, odourless and tasteless gas. Oxygen is an element with the atomic number of 8 but too reactive that you don't usually find it in its free state. It can react with almost all the other elements and found in a combined state with them as oxide. The oxygen in the atmosphere is formed by the combination of two atoms of oxygen to form the diatomic gas written as O₂. , on the other hand, is less than 1% volume of the atmosphere. It is made up of 1 carbon atom and 2 oxygen atoms. In chemistry, it is written as CO₂. If our body is to be separated by the chemical elements that can be found in it, carbon will be the second most abundant element. CO₂ happens to be the most important source of this carbon to us. During photosynthesis (which I explained better later in this post), plants make use of the gas to produce glucose and they serve as the base of every food chain.

What are the small ones and what difference do they make?

https://img.esteem.ws/14r0wb1rkn.jpg ^{Diatom. Public domain: Wikipedia image}

From the introduction, you should have noticed that there is much emphasis on the two gases, oxygen, and carbon dioxide as well as the two processes of respiration and photosynthesis. These two processes are important for the cycling of these gases and, hence, important to life on earth. According to National Geographic, phytoplankton produce half of the earth's oxygen while another author estimated the number to be about 70%. While terrestrial plants supply the remaining volume. Either 50% or 70%, these small aquatic plants' contribution cannot be neglected. Phytoplanktons are still regarded to be more important in producing oxygen. As much potential the land plant have, when they die, they also release a considerable amount of CO₂ when they decay. Therefore, to me, I think phytoplanktons are the small ones that make the big difference and also the inspiration for writing this post.

What are phytoplankton?

Phytoplanktons can best be described by explaining the name itself. Let me start by splitting the name into parts, ‘phyto' and ‘plankton'. The name plankton describes those aquatic organisms that cannot swim at their own will. Their movement simply depends on the water current. The Greek word for planktons means drifter. While the Greek word for ‘phyto' simply means plant. This should give you an idea of what these organisms are. They are the photosynthetic free-floating aquatic organisms and are usually microscopic which means you don't always get to see them like your garden plants. However, when conditions are very favourable and these organisms bloom, they may appear greenish on the surface of the water due to the presence of the green pigment – chlorophyll in their cell component. They also serve as the base of the oceanic food chain. The zooplankton feed on them and smaller organisms can feed on both the zooplankton and phytoplankton and larger organisms will then in turn feed on these smaller organisms. My teacher once said jokingly that if you can imagine a shape then there is probably a plankton that looks like that. They are abundant and of diverse form inhabiting the surface of the water where sunlight penetration can reach as it is needed for photosynthesis to take place. Along with the light energy obtained from sunlight for photosynthesis, phytoplankton needs nutrients like nitrogen and phosphorous from the water for their growth. There are three major groups of phytoplankton which I will briefly highlight. - The blue-green phytoplankton also known as the cyanobacteria can occur either as single-celled or filament and also can come together to live as a colony. - The planktonic green algae also are known as the Chlorophyceae is also another important group of planktons. They are also mostly cultured as food for zooplankton in feeding fish larvae. Also, they are more of freshwater than the marine waters. - The diatoms which are the third major group is also an important group of phytoplankton. According to live science, diatom contributes 20% of the oxygen we breathe. This is indeed a small organism with a big difference in my own opinion. Another characteristic worth knowing about them is their cell wall made of silicate. - There are other examples of phytoplankton that do not fall into these major categories such as the dinoflagellates, the brown algae, the red algae, and etcetera.

Oxygen production by phytoplankton through photosynthesis

Phytoplanktons, like plants, are autotrophs which means they produce their own food through the process of photosynthesis. Their cell consists of a green pigment known as chlorophyll. It serves the function of trapping solar energy from sunlight. The phytoplankton gets the needed water for photosynthesis by absorbing water from their environment and the carbon dioxide from the atmosphere produced which can be an end product of respiration or released during decay or decomposition. This process results in the production of glucose and oxygen gas. Although these organisms are individually very small, they collectively contribute immensely to the oxygen equilibrium. The equation below illustrates the process of photosynthesis in a plant: 6H₂O + 6CO₂ + Light energy ---> C₆H₁₂O₆ + 6O₂ The same equation written in words only is shown below Water + Carbon dioxide + Light energy ---> Glucose + Oxygen

Biological pump, an action influenced by phytoplankton

https://img.esteem.ws/qkmch0qdb9.jpg ^{biological and physical pump of carbon dioxide : Creative Commons
Attribution-Share Alike 2.5 Generic}

The biological pump is an important process of the Oceanic carbon cycle. It simply means how the living component of the ocean circulates carbon from the atmosphere through the ocean body and ocean floor and this is about half of the total carbon fixation. The major source of carbon that the phytoplankton body contains is from the atmosphere. They make use of carbon dioxide from the air to produce organic carbon compound like carbohydrate stored in the body of this phytoplankton. These organisms can be eaten and removed into the food chain or can either die and continue into the next phase of the biological pump. The dead planktons will continue to sink until they reach the ocean floor. However, their rate of sinking is slow but can become faster when more dead planktons come together. In the process of sinking, some are decomposed while only a few percentage of it makes it to the ocean floor. At the ocean floor, some others are still decomposed while others escape the process and become stored away in the sediment where it can remain for millions of years. The decomposed organic matter continues the biological pump and it is again being used for primary production through photosynthesis.

Primary productivity in the ocean by phytoplankton

https://img.esteem.ws/mptvhhdmvi.jpg ^{file available under CC BY 2.0: source}

Although the process of primary productivity by these organisms have been highlighted in the explanation of photosynthesis above, it is important to note that this organism makes it possible for production to take place in the ocean. Although not all fish feeds on the phytoplankton, they ultimately rely on them to obtain their own food. And even some big ocean dwellers feed on these tiny organisms. Take for example, the baleen whale whose feeding preference includes the planktons. The phytoplankton are fed on by the zooplankton and those are in turn fed on by smaller fish and the process continues where the smaller ones are eaten by the bigger ones. This, however, will be determined by the feeding habit of the individual organism and not necessarily their size.

Reference

https://en.m.wikipedia.org/wiki/Oxygen
https://en.m.wikipedia.org/wiki/Phytoplankton
https://en.m.wikipedia.org/wiki/Biological_pump
Marine Plants: A Unique and Unexplored Resource
Source of Half Earth's Oxygen Gets Little Credit
The Air You're Breathing? A Diatom Made That
Importance of phytoplankton