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What makes one species different from another?

Look around your classroom and notice how much you and your classmates look alike. Each of you has a head, arms, legs, eyes, ears, a nose, hair, fingers, toes, and so on. Your classmates are all human beings. You could easily make a list of characteristics that most human beings have in common. Characteristics are distinctive qualities of living things. In this unit you will explore what determines different characteristics of living organisms and how characteristics are passed from generation to generation.

To study living things, both plants and animals, we sort them into groups that have similar characteristics. Think about your pets, for example. All cats have similar characteristics. You are able to recognize a cat when you see one. You could make a list of the characteristics of cats that set cats apart from other animals. Even though cats and dogs both have two ears and a tail, you probably don't confuse a cat with a dog. Dogs have characteristics that make them different from cats. What are some of the characteristics that help distinguish cats from dogs?

Plants also have characteristics that can be used to sort them into groups. You do not confuse oak trees and maple trees, even though both are trees. You can tell the difference between tulips and daffodils because they have different characteristics.

Figure 1.1 Cats and dogs have many similarities. but the differences in characteristics show that one is a cat and one is a dog.

Peanut Sort Select a peanut from a bag of peanuts with their shells. Write a description of your peanut. You may want to weigh or measure it to make the description more detailed. Please do not mark your peanut. Now mix your peanut with 5 or 10 other peanuts. Can you find your peanut? Explain how you can distinguish your peanut from the rest. Now mix your peanut with a whole bowl of peanuts. Can you still distinguish your peanut from the rest? Describe how.

Human Variations Traits are what make us human. Scientists who study heredity use the term trait to speak about characteristics that can be passed from generation to generation. Traits are common to all members of a species. In fact, traits are the characteristics that define a species. Observe your classmates again. This time, record how they are similar. Observe variations (differences) and record your observations. Review all of your observations. List those traits that are unique to human beings and, therefore, distinguish us from other species. List those traits that are shared with other kinds of animals.

"Like produces like"

One characteristic of living things that belong to the same group is that they can reproduce to produce offspring that have characteristics similar to those of the parents. For example, when cats reproduce, they have kittens. Dogs produce puppies, and horses produce foals. And two human beings reproduce a human baby, not a puppy.

The same phenomenon-like produces like-is true of plants, as well as animals. For example, a farmer's corn seeds produce corn. An acorn that is planted by a forest ranger will grow into a new oak tree that will produce more acorns. If you plant marigold seeds in your garden you expect more marigolds. These marigolds will in turn produce more marigold seeds.

A group of living things that has similar characteristics and can interbreed (reproduce among themselves) is called a species. The phenomenon of living things producing offspring with similar characteristics is continuity.

Look at your classmates again. They are all the same species. You are all members of the species Homo sapiens. Now take another good look around at your classmates. Though you are all the same species, you are different from one another in many ways. Some classmates may have blond hair. Some have black hair. There are probably many shades of brown hair among your classmates, too. Some have straight hair, while others have hair that is wavy or curly. Some classmates are probably taller than others are. Some are male and others are female. Some have dark skin while others have fair skin. Some have noses that are long and thin, while others have short, turned-up noses. Just as you have no difficulty distinguishing human beings from other groups of living things, you have no difficulty distinguishing individual human beings from one another. Even if there is a set of identical twins in your class, you probably can tell them apart.

It is possible to distinguish individuals belonging to the same species of all living organisms. If you have ever selected a new puppy from a litter, you know that each puppy is different, and you know that it is possible to tell the puppies apart. If you have chosen a pet parakeet from a cage with four or five parakeets, you knew which one you wanted-just any parakeet probably would not do. If you look carefully at a row of tulip plants, you will be able to describe each individual plant. Some have broader leaves than others do. Some have red petals, while others have petals that are pink.

Figure 1.2 Eye width.

Eye Variation To measure eye width, you need to work with a partner. You need a ruler (metric) and a piece of string about 25\;\mathrm{cm} long. While one partner closes his or her eyes, the other partner measures the eye width from the outside corner of one eye across the bridge of the nose to the outside corner of the other eye. Mark the string by holding it with the thumb and forefinger of each hand at the outside corners of each eye. While holding the string, move it to the table. Line up the string along a ruler and measure the length of the string. This is the eye width. Record the measurements on a class chart. Now reverse roles with your partner.

The difference among living organisms is called diversity. Diversity exists even among living organisms within the same species.

Did You Know?
Genes are regions of DNA that control traits and carry the trait from one generation to the next generation.

Genetics

Genetics is the study of the biological causes of continuity and diversity among living things. Geneticists are scientists who study genetics. They study the biological causes for the similarities and differences between members of the same species. Remember that the word trait means a characteristic that all members of the same species have. Geneticists use the word variation when they mean the characteristics that make members of the same species different from one another. Variations are the different forms of a trait. For humans, having hair is a trait, but the many colors of hair are variations of that trait. Your set of variations makes you special. There is no one else in the world exactly like you. Even if you have a twin, there are differences between you and your twin.

Geneticists are interested in the biological causes of continuity and diversity. They are concerned with traits and variations that are inherited. Inherited characteristics can be passed from parents to their offspring (from one generation to the next). For example, a geneticist would not study human hair length, since humans style their hair differently, which often includes cutting hair. Hair length is not inherited in humans. A geneticist might be interested in hair color, but would have to make sure the hair color was natural and not dyed.

Identify each of the following as either a trait or a variation.

  1. Parrot has feathers.
  2. Cat has a striped coat.
  3. Geranium plant has flowers.
  4. Jasmine has two arms.
  5. Dog has droopy ears.
  6. Rosebush has thorns.
  7. Jamie has freckles.

Activity 1-1: Fingerprinting

Introduction

What is your unique fingerprint pattern? One way to tell the difference between human beings is to look at their fingerprints. Even the fingerprints of identical twins are different. However, there are only 4 patterns of fingerprints-the whorl, the loop, the arch, and the composite. One of these patterns is on each finger. If you examine all ten of your fingers, you might find all of the patterns, or you might find only one of the patterns. In this activity you determine the fingerprint pattern of each of your fingers.

Figure 1.3 The four patterns of fingerprints.

Materials

  • Stamp pad
  • Magnifying glass
  • Ruler (metric)
  • Clear tape
  • Paper towels and soap, or packaged hand wipes
  • Activity Report

Procedure

Step 1 Look carefully at the four basic fingerprint patterns shown in Figure 1.3. Note the differences among the four patterns.

  • In the whorl pattern, ridges circle around a point.
  • In the loop pattern, ridges enter from one side, form a loop in the center, and exit from the same place.
  • In the arch pattern, ridges flow across the finger with a rise in the center.
  • In the composite pattern, there is a combination of two or more of the other three patterns.

Step 2 Wash and dry your hands.

Step 3 Have your partner press each of your fingers onto the pad. DO NOT ROLL YOUR FINGER.

Step 4 Have your partner press each finger onto the appropriate section of the chart on your Activity Report. You might want to practice on a plain piece of paper first.

Step 5 Wash your hands before you continue. Protect your fingerprints by covering them with clear tape.

Step 6 Examine each of your fingerprints carefully. You may need the magnifying glass. Decide which of the four patterns is most like yours. Your fingerprints will not look exactly like the patterns in the figure, but should be close enough for you to decide.

Step 7 Write the name of the pattern below each box on your Fingerprint Chart on the Activity Report.

Step 8 Look at the fingerprints of other people in your group and notice how they are the same and how they are different.

Step 9 Enter your prints on a class tally either on the board or on the overhead projector.

Continuity and Diversity in Art Illustrate your knowledge of the terms continuity, diversity, trait, and variation in a drawing, cartoon, or painting. Make sure your final product reflects your knowledge of the relationships among these terms.

Wrist Variation In this activity you measure wrist circumference. To measure the wrist, work with a partner. You need a ruler (metric) and a piece of string about 25\;\mathrm{cm} long. Have one partner wrap a piece of string once around the other partner's wrist. With the fingers, mark where the string meets. Move the string to the ruler and measure the length of the marked string. This is the wrist circumference. Record the measurement on a class chart and make a graph. Now reverse roles with your partner.

Figure 1.4 Wrist measurement.

Describe what everyday life would be like if there were less variety among living things. How would your life be different? What would be the drawbacks to having less diversity, and what are the benefits to having more diversity?

Environment

The external environment plays an important role in shaping (influencing) variations in humans. Sometimes scientists argue which is more important in determining some variations-the genes or the environment. Scientists refer to this argument as the nature versus nurture argument-where nature refers to the genes and nurture to the environment. Both environment and genes play an important part in causing variations. Let's look at an example. The mother's body is the environment for the unborn child, so it is important that a woman takes especially good care of herself before and during her pregnancy. If a woman drinks alcohol when she is pregnant, her baby can be born with abnormal characteristics that are referred to as fetal alcohol syndrome. One of the abnormal characteristics is mental retardation.

Review Questions

  1. What is unique about a species?
    1. What term refers to the phenomenon of living organisms producing offspring with similar characteristics?
    2. What term refers to the phenomenon that all living organisms, even those from the same species, are different from each other?
  2. What is the difference between traits and variations?
  3. What is genetics? What are geneticists most interested in? Why wouldn't a geneticist be interested in hair length in humans?

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Grades:

6 , 7 , 8

Date Created:

Feb 23, 2012

Last Modified:

Nov 10, 2014
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