Cells: Here, There, Everywhere

Lesson 2 Reading One: Cells: Here, There, Everywhere

Getting Ready

Were you surprised to see living things in yogurt and we eat? How about those little organisms in pond water? In class, you were able to see these tiny organisms that are made up of only one cell with the help of a microscope.

Can you think of some other places single-celled organisms might be in our environment?

In this lesson, you learned that there are living things that are made entirely of one cell. You saw bacteria in yogurt and an amoeba in pond water. Even though these are only a single cell, too small to be seen without a microscope, they do all the things that make something a living thing. These organisms use food for energy, grow and reproduce, and respond to stimuli. So these organisms made of a single cell are living things.
You also saw in these first two lessons that there are cells that are parts of larger organisms. How are these single-celled organisms related to the cells in larger organisms? Today’s reading is about the cells all around you and how they compare with the cells in your bodies.

Where Are These Single-Celled Organisms?

The amoeba in the pond water was not something unusual in nature. Single-celled organisms can be found just about everywhere. They are in the soil, in water, and even in the air. In the last lesson, you read that Leeuwenhoek found single-celled organisms living in the plaque on his teeth. In fact, there are bacteria living on many parts of your body.
There are many species of single-celled organisms. The most well known are the bacteria, but there are also others, such as single-celled fungi and algae. Pick up a fistful of garden soil and you are holding hundreds, if not thousands, of different kinds of single-celled creatures in your hand. One teaspoon of that soil contains over 1,000,000,000 bacteria cells, about 120,000 fungi cells, and 25,000 algae cells. Even though they have only one cell each, single-celled creatures come in a wide range of shapes, sizes, and colors.

What Can Bacteria Do to Other Organisms?

Did you ever happen to drink spoiled milk? Not a pleasant experience, right? Well, food does not spoil by itself. It is organisms that caused the damage. When food spoils, it is usually because single-celled organisms have started to grow in it. When milk is expired or is left outside the refrigerator for too long, harmful bacteria can grow. These bacteria feed on the milk’s sugars and produce substances that make the milk “sour.” The substances may also be poisonous. What is usually called “food poisoning” is due to consuming food containing harmful bacteria and/or the substances they produce.
Single-celled organisms may also infect food as it is being grown. During the 1840s, a terrible plant disease caused by a single-celled organism ruined potato crops all over Europe, especially in Ireland. At that time in Ireland, potatoes were the main food crop. With so many of the potato crops destroyed, many people starved. This was called the Irish Potato Famine that led to the death of about one million people through starvation and disease.

Single-Celled Organisms Are Often Helpful

Did you know that most of the oxygen you breathe is produced by single-celled organisms? Although plants generally get the credit for making the oxygen you breathe, most of it is actually produced by single-celled organisms that live in the oceans. In the IQWST LS1 unit, you learned about plankton, which form the foundation of the food webs for both freshwater and saltwater ecosystems. The name plankton is used for a collection of different kinds of organisms, including some multicellular organisms and a large number of single-celled organisms, including algae and bacteria. These algae and bacteria make their own food using energy from sunlight, just like plants, and give off oxygen. So not only are these single-celled organisms food for all the fish in the world, but they contribute a large part of the oxygen in the atmosphere. Without them, people might not have enough oxygen to survive.
Single-celled creatures are involved in yet another important environmental process—recycling. Single-celled creatures in the soil can feed on almost everything. They feed on dead leaves and twigs, scraps of food, and anything organic (matter from living things) in garbage. When they do that, they break down the organic materials, releasing minerals that plants can use. Today, many people use this process to recycle organic waste and turn it into compost. Putting the compost into gardens returns nutrients to the soil and keeps the garbage used in the compost out of landfills. In the IQWST LS1 unit, you learned about interactions between organisms. You learned about one type of organism preying on another or about two kinds of organisms competing for the same resources, such as food or living space. With single-celled organisms, you see another kind of relationship. These organisms are called decomposers. Their role in helping dead plants and animals to decay and recycling their nutrients back into the soil is essential in ecosystems.

What Are the Differences between the Cells in You and Single-Celled Organisms?

You saw that you have cells that are in, or on, your body. You looked at skin cells and cheek cells and a picture of heart cells. Are these cells like the single-celled organisms? This can be confusing when learning about cells. You use the same word for the cells in your heart as for a single-celled organism like the bacteria you saw. Both are called cells.

In Your Notebook

Answer the following questions in your science notebook:

Are there any differences between the cells of single-celled organisms and the cells in your body?
List the important characteristics of organisms that are true of a single-celled organism.
Which of these characteristics do you think a cell that is part of the human body has?

Conclusion

The important differences are all connected to what it means to be an organism. As you will see in the next several lessons, cells in your body do a number of things that organisms do. But there is one thing they cannot do—they cannot be a living thing on their own. They cannot get what they need unless they are part of a larger organism. A single-celled bacterium can get energy from food, grow, reproduce, and get rid of waste, all by interacting with its environment. The cells in your body need the other parts of the body to stay alive.