“Protozoa: Kingdom of Protists” Discovery Education Video Transcript
Protozoa, a word meaning "first animals," are classified as members of the kingdom of protists.
Protozoa are usually smaller than the many-celled invertebrate animals in a pond community. But protozoa are much larger than bacteria. Comparing bacteria and protozoa, we find that both are one-celled organisms. But a bacterial cell doesn't have a separate nucleus within its cytoplasm...While a protozoan cell will have one or more distinct nuclei within its cytoplasm. Later in this program, we will learn to recognize nuclei, as well as other structures of protozoan cells.
As a group, the protozoa have long provided biologists with a wonderful source of material for scientific study. The protozoa can be divided into two basic groups - -Those that are like animals and cannot make their own food and those that are like plants and can make their own food by photosynthesis from sunlight, Water, and carbon-dioxide gas. Plant-like protozoa, also called "algae,” are major food producers in the pond community. And for this reason, many of the other life-forms that dwell there depend on algae, either directly or indirectly, for their survival. When the algae are eaten, the energy they captured from the sun is passed on to the primary food consumers, usually animal-like protozoa. Even if an alga dies, the energy it captured from the sun while it was alive is still passed on to scavenging organisms that feed on the dead remains of once-living things.
But photosynthesis does even more than create food. It causes oxygen to be released into the environment. Most of the earth's oxygen is created by one-celled algae. Animals could not exist without oxygen, which is needed for cellular respiration. During cellular respiration, the energy stored in food is released In order to keep an organism's life processes going. Because algae are important sources of both food and oxygen to other organisms, we will look at them in more detail. If you dip a stick into an algae-filled pond, you will find that some of the algae come out in long threads. These threads are actually long groups of identical cells Called "cell colonies.”
One of the most common thread-like algae’s called "spirogyra.” Under the microscope, Spirogyra has a very unusual appearance because the chloroplasts inside the cells Wind around and around in a beautiful spiral pattern. At a higher magnification, we can see these chloroplasts very clearly. Chloroplasts are the little organs, or organelles, where photosynthesis takes place. They are found in all protest algae and in higher plant cells. Animals and animal-like protists do not have chloroplasts. Besides spirogyra, Thread-like algae of many other types are also very commonly found in pond communities, where they shelter and feed all sorts of creatures.
Another very common type of colony found in greenish waterier the beautiful spinning spheres called "volvox."Under a microscope at low power, we can see the smaller daughter colonies living inside the large mother colonies. At a certain stage of their lives, the mother colonies burst open and release the colonies of daughter cells to the water outside. The movement of a volvox colony is beautiful to watch. Each cell of a colony has a pair of whip-like projections That are called flagella That are wiggled in a well-coordinated wait is not unusual to find the simpler cousins of volvox living with them in the same drop of water. With this group of creatures, each genus, or type, shows a step going from the simplest to the most complicated type of colony. The simplest types are just one-celled algae with flagella. Next are the four-celled colonies, whose beating flagella can be seen very clearly here. Even more complicated are members of this genus that can form solid, ball-shaped colonies Of 16 identical cells. Then another type forms a small, hollow sphere of about 32 cells. Finally, hundreds of identical cells can be found in the colonies of volvox.
Biologists believe that the ability of cells to make colonies the formation of the many-celled creatures Found in the kingdoms of plants, animals, and fungi. Another group of algae are called "diatoms.” They are very important as food and oxygen producers. Diatoms are recognized by the fact that their cells are covered with a hard, mineralized coating. Diatoms can be found living both as colonies of identical cells and as slow-moving, single-celled creatures of many different sizes, shapes, and colors. This organism, called a euglena, doesn't form colonies. It seems to be a link between the plant and animal worlds. The euglena we see here is green because it contains chlorophyll. Chlorophyll is the chemical needed for photosynthesis that is found in all plants. When enough sunlight exists, a euglena can make its own food by photosynthesis, just like a plant. But when light is not available they can capture food just like animals.