Animals Directions: Read, highlight, and answer the question. What is an animal? It's a simple enough question, but the answer is kind of difficult (isn’t everything in cell biology?). Below, we'll walk through the characteristics that make a living thing an animal and attempt to figure out what exactly an animal is. So what is an animal? It's easy to say that a giraffe, a whale, or a dog is an animal. But when it comes to making a list of animal characteristics—identifying things shared by all animals—it’s kind of difficult (but we are still going to try ☺). The list that follows describes characteristics shared by all animals, from snails and zebras to mongooses and sea stars. These characteristics help us to say that coral is an animal but not plants. That seems kind of weird saying that coral is an animal, but it meets the characteristics below. With this type of biology, everything is grouped based on their characteristics. Plants, fungus, and animals all have similar characteristics. The one odd ball we’ve mentioned before is protists. They are grouped based on how they are different than plants, fungus, and animals. All animals are eukaryotes. If you recall, all living organisms can be sorted into two groups depending on one organelle, the nucleus. These two groups are called prokaryotes and eukaryotes. Prokaryotes have no nucleus while eukaryotes have a nucleus. In eukaryotes, the nucleus holds the cell's genetic material in an organelle called the chromosome (DNA). In prokaryotes, the chromosomes are located in the middle of the cell and just float around inside that area. Since animal cells have a nucleus, that makes them eukaryotes. Their DNA is organized into chromosomes which are located inside the nucleus. Keep in mind that the reverse is not true — not all eukaryotes are animals. Plants, fungi, and protists—in addition to animals—are eukaryotes. All animals are heterotrophs. All living things need energy in the form of an element called carbon to help them grow, develop, and reproduce. There are two ways an organism can get the food they need: •
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An organism can get food from the air they breathe (carbon dioxide) and combine it with sunlight to make energy. They can also get the food chemically from the ground absorbing it into their bodies. The term autotroph describes these organisms. We’ve talked about autotrophs before being chemoautotrophs (chemical) and photoautotrophs (sun). An organism can get the food they need by getting it from other living organisms that are made up of carbon. They get it this way by scavenging and eating other organisms. The term heterotroph describes this type of organism. Green plants are autotrophs. They take energy from the sun and use it along with carbon dioxide in the air to produce sugar. In contrast, all animals are heterotrophs. They eat plants and other organisms as a way to get their carbon, the energy they need to live. Animals are multicellular. Most animals (with the exception of sponges) have bodies that are differentiated into tissues. Animals' bodies are made up of many cells (which is why we are multi‐cellular). In most animals, those cells are organized into different tissues that perform different functions. During the development of an animal (the very early part of reproduction), cells differentiate so they can perform different jobs. Groups of cells with similar jobs that perform a common function are referred to as a tissue. One exception to this is sponges which do not possess tissues (they don't have muscles or nerves). Plants also have cells that form tissues and performing special jobs. Bacteria, protists, and fungi do not have the cells that form tissues. Most animals are capable of movement. Unlike plants, which are fixed to where they grow, most animals are able to move. One exception is again sponges and coral, which are fixed in one place. Animals that do move can move quickly which is of great benefit when compared to other organisms. Most animals undergo sexual reproduction although a small number are capable of asexual reproduction. Most animals reproduce sexually (egg and sperm). This means genetic information is combined between parents and the offspring has an equal blend of chromosomes from both parents. Remember from our reproduction discussion that this is a benefit since the offspring are now slightly different. There are a few animals that are capable of asexual reproduction. These include sharks, frogs, and snakes to new a few. Keep in mind though that this type of event only happens during extreme moments. It’s not a normal/typical way of reproducing. Directions: Compare and contrast the different groups of cells (note: it may require you to find your previous reading assignments or to look through your notes to complete). Bacteria Protist Fungi Plants Animals Cell Type (eukaryote or prokaryote) How do they obtain energy? (heterotroph, autotroph or both) Unicellular or Multi‐cellular or both Typical Reproduction (asexual, sexual or both) Body system (none, radial, or bilateral) Can cells form tissues? Yes or no? Capable of movement?