Youth Science Lessons – Forms of Life – Lesson 1 Unicelluar Life
To our knowledge, Earth is the only planet with life forms. Many believe there must be other locations in the universe that support life, but we have not found them yet. Of course, they could look completely different from what we think we are looking for. For us, life are masses of organic based cells that need energy and can reproduce. Much of what they do during the day focuses on one of these two needs. And after decades of exploring life on our planet, we have found literally millions of different species and designs to try and out complete others seeking the same needs.
The diversity of life can be attributed to the changes and adaptations species make to be able to co-exist. Some species who have common needs accomplish this by existing in different locations within the habitat – what is called resource partitioning. For example, certain creatures who might feed on similar foods could live in different parts of a marsh. One could live at the waters edge, where the other might live higher in the marsh where the water does not reach. By doing this, they are not in direct competition and thus can live together. One form might be nocturnal another diurnal in their habits, thus reducing the chance they will compete directly for the same resource. Some species could occupy the same niche (a role/job within the community – such as apex predator) but in different habitats – say a desert and a forest. However, Earths creatures do this, they have been doing it for about 3 billion years.
Of course, not all species make it. Some are too specialized and cannot adapt to changing conditions. It is believed that most new life forms do become extinct – look at any dinosaur book to see some examples of really strange creatures from the past. Some are so successful that they have changed very little over millions of years. This course curriculum divides all life forms into three categories – unicellular, plants, and animals. This lesson will look at the unicellular creatures.
All life forms on our planet are made of cells, but some exist only as a single one. However, the need for energy (food), defense from becoming food, and reproduction are still part of their lives. It would make sense that unicellular creatures would only feed on unicellular creatures, but there are many who are decomposers and feed on large dead carcasses of things such as raccoons and whales. Others can actually photosynthesize and produce food from the sun. Some chemosynthesize producing food from organic and inorganic compounds expelled from volcanic vents on the ocean floor.
Single celled creatures have a variety of methods of defense. Some produce shells, some are even made from glass. Others can produce and release toxins, such as those responsible for red tide and other harmful algal blooms. Some can produce cysts. These are like protective shields (like superheroes) which protect them from extreme environmental changes and can last for several days.
With reproduction, asexual reproduction is the rule – but sexual reproduction can be found. In asexual reproduction simple binary fission, mitosis, can produce numerous new members of the community in a very short period of time. Sexual reproduction calls for the exchange of genetic information between one individual and another. This genetic exchange can generate new forms of the species that may be able to tolerate changes in the environment that their parents could not. In the process of conjugation genetic information from one cell can literally be exchanged with that from another. Once completed, the cell can then go through binary fission to produce numerous offspring with a little genetic twist to them.
So, now we understand that they do have the same needs as larger creatures in the ocean, how many are there? And what kinds exist?
There are multiple ways to divide the unicellular creatures into groups. The Swedish botanist Carlos Linnaeus developed a classification system that allowed you to categorize all creatures into one of seven categories. Kingdom, Phylum, Order, Family, Genus, and Species. The system works in a similar fashion as your identity. For example, Kingdom could be analogous to the United States. You are an American and, in a sense, related (or similar) to all Americans. Another “Kingdom” could be European, or African.
Your phylum would be analogous to being from Florida. You can be an American and a Floridian at the same time as a creature could be an Arthropod and a Crustacean at the same time. For class we have your county. You are from Escambia County. So… you are an American, a Floridian, and an Escambian. Order… order would be analogous to being from Pensacola. Family would be analogous from being from East Hill. Genus would be analogous to being from Blount Street. And Species would be analogous to being from 2001 Blount Street – your house.
The taxonomic system created by Linnaeus is sometimes confusing to students, but when seen in this light – maybe not. You can be an American and a Pensacolian at the same time. And 2001 Blount breaks it down you individually.
Now we need to collect these unicellular creatures and categorize all of the different types. How do you collect them? Better yet, how do you even know they are there? These guys are small… I mean REALLY small. Bacteria can run between 10 – 750 microns (µm). A micron is 1/1,000,000 of a meter – and a meter is 3.4 feet long.
How tiny is that?
Well let’s say you have a unicellular creature that is 1 µm (some are). You know how long a millimeter is – you can see it on any standard ruler. Between the two-millimeter marks on your ruler you could have 1000 unicellular creatures lying end of end. A typical ruler might be 300 mm long. So, if laid end to end, how many 1 µm unicellular creatures could you line up along your ruler? IT’S A LOT?
Now think of how many could lie just along the top of your ruler – imagine how many could be along the bottom of your local bay? The Gulf of Mexico? The Pacific Ocean? Unicellular creatures are one of the most abundant creatures on the planet.
So, how to collect these?
Well, if they are on the bottom, or in the sediment, you can just collect a sediment sample. Ocean engineers have developed many tools to do this in shallow or deep water. So, now you have a tube of sediment. What now?
What many microbiologists do at this point is culture them. They place a nutrient material (food) on the bottom of a petri dish. A petri dish is actually two dishes, one slightly larger than the other. You place the nutrient material (usually a gelatin material from seaweed called agar) in the bottom of the smaller diameter half (called a plate). You would then take an inoculating loop (small metal wire in the shape of a loop sort of like what you use to blow bubbles with) and heat it in a Bunsen burner. This is to kill any unicellular creatures that may be on the loop already. You do not want to contaminate you bottom sample thinking these creatures live on the seafloor when they actually live in your desk drawer.
Once the loop has been sterilized you wipe, or stick it, through the sediment sample. Afterwards you swipe the loop over the agar and place the larger plate (dish) over to cover the petri dish and you have them. Many microbiologists will sometimes tape the edge of the two plates to assure no unicellular creatures enter. Many will now place it in a low heat oven for a day or so. Warmer temperatures encourage micro growth (hence you place a lot of food in the refrigerator or freeze it). Once they start growing colonies you can actually see a colored mass. But which species do you have?
Enter the microscope.
Invented by Antone von Leeuwenhoek, a Dutch Draper, in the mid-1600s, scientists were now able to see the small world of life on our planet. Protozoans, bacteria, and rotifers were all discovered by simply looking at a drop of water. The famous English scientist Robert Hooke published a book of the small world at that time – Micrographia – and coined the term “cell” to describe what he was seeing.
With the microscope scientists could view these tiny unicellular creatures. They could see what they looked like and how they behaved. As microscope technology improved, so did the science of the unicellular. And it would be the microscope you would use to view the organisms that formed the colored mass in your petri dish.
Seeing these creatures, you could now begin to note their structure and begin to classify them.
At first unicellular creatures were placed into one of two kingdoms: Monera or Protista. The difference… whether you had a nucleus or not. As the microscope technology improved scientist could see small “organelles” within the cells. The cell was basically a membrane surrounding a gelatinous material they called the cytoplasm – which was mostly water. Suspended within the cytoplasm were small “organelles” which act like organs in our bodies. Some aided in digestion, others for storage, and the nucleus acted almost like a “brain” controlling all actions within the cell. Later it would be discovered that our genetic material (DNA and RNA) were found within the nucleus.
Those that lacked a nucleus (Monerans) did have DNA, it was just not encased within a nucleus. These Monerans are primarily what we call bacteria. When we hear the term bacteria we immediately think “bad”. Bacteria are associated with uncleanliness and disease. Though some species do cause disease, many are quite beneficial to the environment and life on the planet. Some convert inorganic forms of nitrogen into useful forms for plants to utilize, and eventually animals when they eat the plants. They are a crucial part of the production of crops. As mentioned, they decompose dead animals and sort of “clean up the planet” of all the dead organisms converting them into nutrients utilized by other forms of life. They are found everywhere. On the ocean floor, in the slime of fish, in your intestines, on rocks at the top of the world and in Antarctica. They create the “chimneys” we see on the ocean floor and the beautiful colors of the geysers at Yellowstone National Park. They are classified further by their shapes. Rod shaped are known as Bacillus, spherical ones are known as Coccus, and spiral shaped ones are known as Spirillum. Some can photosynthesize, the blue-greens, and others can produce bioluminescent light in the ocean. Some are associated with sewage and are used as indicators of sewage spills in local waterways. And, yes, some can produce toxins and cause disease. They are a fascinating group and one of the most abundant forms of life on the planet.
Those with a nucleus (Protists) are considered more advanced. These are basically sub categorized by whether they are photosynthetic (autotrophs – “self-feeders”) or whether they consume other protists (heterotrophs – “feed on something different”). Within the ocean we call the autotrophs phytoplankton and the heterotrophs zooplankton. Many of these unicellular creatures actually live in the water column and not on the bottom. To collect these, they developed what is called a plankton net. There are a variety of styles and designs of these, but the basics is a fine mesh net connected to a sample bottle at one end and a line connected to the boat at the other. These nets can be dragged at a variety of depths for a any period of time the scientists wish. Once back on board, the sample can be collected using the loop as mentioned before.
The majority of the phytoplankton collected in the ocean belongs to one of two groups – diatoms or dinoflagellates. Diatoms possess a silica shell that fits together similar to a petri dish. It is called a frustule and their remains (after the diatom dies) sinks and becomes diatomaceous earth – a valuable product for humans.
The other are the dinoflagellates. Their shells are calcium carbonate (a popular material for shell building in the sea) and they possess two flagella. These are whip-like structures that allow them to swim, or least turn themselves around.
Most of the zooplankton in the ocean are actually multicellular and will be discussed later. But there are some unicellular forms. These are sub categorized by the way they move. Mastigophorans are those that use the whip-like flagella to move. Ciliophorans possess numerous cilia. Cilia are basically very short flagella and ciliophorans are very fast. Sarcodinids lack any sort of whip or tail. They move VERY slowly by expanding their cytoplasm in a direction and sort of “blob” their way around the world. These would include the group we call amoebas.
This was meant to be an introduction to this group. Microbiology is a full course in on itself and there is too much to teach in this one lesson. We will cover more later in the course. But they are pretty cool.
As you can imagine, doing activities with unicellular creatures will be tough – unless you have a microscope. But here are some ideas.
- If coli are 600 µm, how many could you line up end to end along a 300 mm ruler? How many would you think live in Pensacola Bay?
- Take a small glass jar down to a local waterway. Scoop a little of the surface mud just beneath the water near the shoreline. Wait a few minutes and then look for any tiny specks swimming about. If you can see them, they are most likely multi-cellular, but it does give you the chance to see a tiny world that few know about.
- If you have a microscope you could repeat the above, place a few drops on a cover slide (deep well slides work best) and observe under the microscope. It will take a lot training and practice to identify what you are seeing but it is fun to just watch them swim around. They sometimes eat each other!
- If you have a microscope you can observe the unicellular world from a variety of locations. Scrap the scum off of a seagrass blade, off the back of a blue crab, from dry sand, from wet sand, anything you can think of – unicells are everywhere! It is fun to look.
- Another idea is to visit a local marine lab – such as the Estuarium at Dauphin Island Sea Lab. They may have an exhibit where you can observe the micro world.
- And there is always the internet. You can search for bacteria, dinoflagellates, or any of the others mentioned in this lesson and you might find photos and videos of these guys.