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REVIEW 6 Adaptations to the Environment Some animals, such as chameleons and octopuses, can change the color of their skin. This ability is good for camouflage, or blending into the surroundings. Animals with the ability to change the color of their skin often use it to avoid predators and (if they kill and eat other animals) to surprise their prey. The ability to change skin color is one example of an adaptation. An adaptation is any trait that helps the individuals of a species survive within an environment. In this review, we will look at some common adaptations that help animals and plants survive in their environments. The ability to change skin color is useful for more than just camouflage. Describe one other reason why an animal such as a chameleon or octopus might change skin color. Words to Know adaptation angiosperm camouflage dormancy evolution gymnosperm hibernation homeostasis migration natural selection ovule pollen pollination 79 Homeostasis When you think of an organism interacting with its environment, you might first think of the external environment—the air, water, and/or land in which the organism lives. But an organism must also respond to changes inside itself, called its internal environment. In general, organisms must keep their internal environments fairly stable. Take the human body as an example. The human body works best when its temperature is around 37° C. If a human body gets too warm, it releases some of that heat by sweating. If a human body gets too cold, it produces more heat for itself by shivering. The ability to maintain a constant internal environment is called homeostasis. (Homeo- means "steady" and stasis means "state.") Name two other internal conditions to which your body responds. Different animals maintain homeostasis in different ways. Again, consider an animal's internal temperature. Mammals have bodies that automatically maintain their internal temperatures. For this reason, they are called warm-blooded animals. Other animals, such as reptiles, maintain their internal temperatures through behavior. If a lizard gets too warm, for example, it will go into the shade to cool off. If a lizard gets too cold, it will bask in the sun. Animals that maintain their body temperatures through behaviors are called coldblooded animals. Explain why mammals are found in polar regions but reptiles are not. Responses to seasonal change Of course, organisms must also respond to changes in their external environments, or the places in which they live. Many places on the Earth have seasons—months of rainy weather followed by months of dry weather, or months of cold temperatures followed by months of warm temperatures. Seasonal changes usually affect the amount of food available in an environment. Organisms have evolved different behavioral responses to the changing availability of food in their environments. 80 Hibernation is a condition in which an animal remains in a sleep-like state for weeks, months, or even years. Black bears, for example, fatten themselves up during the summer months when food is plentiful. During winter, they hibernate and slowly use up the food energy stored in their fat. Some insects and reptiles also hibernate when temperatures are low and food and water are scarce. Migration is another behavior for dealing with limited food availability. Birds, for example, rely on insects, nectar, and seeds for food. Because flowers and insects are not easy to find during cold or dry months, many species of bird migrate to areas where they can find such food. Some animals also migrate to special places for the purpose of mating and giving birth to their offspring. Explain why most animals in Arizona do not hibernate during the winter months. Are there circumstances when animals native to Arizona will enter a hibernation-like state? Explain your answer. Plant adaptations Most plants produce seeds. Seeds contain a plant embryo called a seedling. Warm, moist soil conditions help a seedling to grow and break out of the seed. Nutrients stored in the seed nourish the seedling until its leaves are large enough to begin photosynthesis. It may seem that a seed is similar to a bird egg about to hatch. However, baby birds must hatch when they grow too large for their egg, while seeds can lay dormant and not grow for many years. In deserts such as Death Valley, seeds wait in the soil for many years until a rare rain shower stimulates them to begin growing. Plant species develop seeds in different ways. Gymnosperms are plants that do not use flowers to produce seeds. A pine tree, which is a type of gymnosperm, uses pinecones to reproduce. A single pine tree makes both male and female pinecones. 81 Male pinecones produce pollen (male sex cells), and female pinecones produce ovules (female sex cells). You have probably noticed female pinecones because they are large. The smaller male pinecones are easier to overlook. For a seed to develop, pollen must come in contact with an ovule. Gymnosperms use the wind to blow large amounts of pollen from the male pinecones to the ovules of female pinecones. The movement of pollen is called pollination. Once pollen comes into contact with an ovule, a seed can develop. After a time, the female pinecones open and release their seeds. Either the wind or animals then move the seeds to the new locations where they may grow into new pine trees. "The sidewalks are covered by pollen from those pine trees, and the pollen is really bothering my allergies," said Tom. "Why do those trees have to be so messy?" How would you answer Tom's question? Angiosperms are plants that use flowers to produce seeds. Many angiosperms have both male and female parts in the same flower. The male parts of the flower produce pollen; the female parts of the flower produce ovules. Pollen must reach an ovule so that seed development may begin. Flowers often use animals such as birds and insects to help them move pollen from one flower to another. Flowers use their colors, smells, and a sugar substance called nectar to attract animal pollinators. In most cases, pollinators move from flower to flower looking for a snack of nectar. Moving from plant to plant, pollinators carry the pollen from one flower to the flower of another. For example, bumblebees moving in and out of flowers are often covered in yellow plant pollen. 82 Why do angiosperms make less pollen than gymnosperms? Once a flowering plant is pollinated and produces seeds, these seeds must be dispersed to a place that they can grow. Plants will usually produce seeds that are adapted to the type of environment in which they live. Plants that live in windy environments are likely to produce seeds with wings that are easily carried by the wind. Plants that live in wet, rainy environments are more likely to develop hard, water-resistant seeds that can be carried but not destroyed by water. Based on their structures, how are the following seeds most likely dispersed? Explain your answer. The flowers of angiosperms develop into fruit once the seeds are mature. Either an animal eats the fruit and moves the seeds away from the parent plant, or the fruit opens and the seeds are moved away by wind and rain. If the seeds end up in a good location, they may develop into new plants. Apples, green peppers, and blueberries are examples of angiosperm fruit. Eating an apple before it is ripe can give a person a stomachache. Why wouldn't the tree "want" you to eat an unripe apple? 83 Adaptations and evolution Offspring that inherit a helpful adaptation have a better chance of surviving than offspring that do not inherit the trait. This process is called natural selection. Over many generations, helpful traits may become more common within a population, and unhelpful or harmful traits may become less common. When the traits of an entire population change over several generations, such change is called evolution. A famous example of evolution through natural selection is Darwin's finches. (A finch is a type of bird.) In the 1830s, Charles Darwin traveled to the Galapagos Islands, a group of islands about 700 km off the eastern coast of South America. Traveling from island to island, Darwin discovered 13 species of finches. Each species was adapted to particular ways of eating. For example, the species named the warbler finch ate only insects; the species named the vegetarian tree finch ate only plants. Other species of finch had different eating habits. Darwin asked himself: Why were there so many species of finch on the Galapagos Islands? He reasoned that, millions of years ago, a single finch species had traveled to the islands and stayed there. The individuals in that population competed with each other for food in many different types of environments. Some islands had many insects, and other islands had many plants. Some islands had trees that produced many nuts, and other islands had plants that produced seeds and fruits. All species have a natural amount of variation among their members. Therefore, the finches in the original population were not identical. The finches had beaks of different lengths, strengths, and so on. Describe a beak that would be good for breaking open hard nuts. Describe a beak that would be good for digging insects out of cracks in rocks. Darwin reasoned that some birds within the original finch population had more success in some environments than in others. The finches with the strongest beaks could break open and eat hard seeds. Those finches outcompeted other finches on an island where hard seeds were the main food source. The finches with the longest beaks could catch and eat insects. Those finches outcompeted other finches on an island where insects were the main food source. Over several generations, the population of finches on a seed island came to have strong beaks, and a population of finches on an insect island came to have long beaks. 84 People in Science Charles Darwin studied plant and animal life. He is famous for coming up with the idea that all animals, including humans, developed from life-forms that lived millions of years ago. We call his idea the theory of evolution. Darwin spent five years on a boat at sea working on his ideas. He was very unhappy; he was seasick all the time. When his trip ended, Darwin decided he would never travel again. He married, had 10 children, and took only short vacations within Great Britain. He did all his scientific study at home, using the information and materials he had collected during his sea voyage. He built a big house with a large study and designed a special microscope. For the first eight years, he studied only barnacles. When his children were young, they thought all fathers worked at home and studied barnacles. Later in life, he decided to study earthworms. For a while, he even kept live worms on top of the piano. He liked to watch the worms' activity when the piano was played. Darwin published many books about his research. His most famous book is On the Origin of Species, which explains his theory of evolution. Charles Darwin (1809-1882) Keys to Keep An adaptation is a trait that increases the chances that an organism will survive and reproduce. Homeostasis describes how animals and plants keep their internal conditions constant. Gymnosperms are plants that make seeds without using flowers. Angiosperms are plants that use flowers and pollinators to make seeds. Evolution is the change in the traits of a population of a species over many generations. Charles Darwin developed the theory of evolution based on years of observation. 85 Explore It Yourself In this activity, you will explore how an organism's trait—in this case, its coloring—can aid or hinder the organism's survival within an environment. You will also investigate how a natural pressure—in this case, predators—can increase or decrease the frequency of a trait within a population over several generations. In other words, you are going to simulate how natural selection causes evolution within a species. Your teacher will put you in groups of three or four. Each group gets a tub with a layer of black aquarium gravel at the bottom. Laying on the gravel are 50 white beans and 50 black beans. Each group also needs a stopwatch. Step 1: Pick two students to be hungry birds and one student to be the timer. Beans represent the prey. Step 2: When the timer says "go," the hungry birds have 30 seconds to capture their prey. The hungry birds should pick out their prey as quickly as possible, one bean at a time, and then put beans outside the tub. Step 3: After 30 seconds, the timer says "stop." The hungry birds are full. Step 4: Count the number of white and black beans remaining in the tub. Surviving black beans: Surviving white beans: Step 5: Suppose that each surviving individual produces two offspring of its own color, then dies. The population that remains is generation 2. How many black beans would be in generation 2? How many white beans would be in generation 2? 86 What Does It Mean? 1. Which color provided better camouflage against the birds? How do you know? 2. Suppose that the birds eat the organisms and the survivors keep reproducing several more times. Over several generations, what change will occur in the coloration of the population? Explain why this change takes place. 3. Suppose that, after several generations, you introduce some simulated pollution to the environment by painting the gravel white. What will happen to the overall coloration of the population after several more generations? 4. Some people think that evolution involves individual plants or animals somehow "choosing" to adapt to a change in the environment. Use this simulation to explain why that understanding of evolution is incorrect. 87 AIMS Science Practice 1 When an animal sweats to keep cool, which of the following processes is the animal exhibiting? A evolution B hibernation C homeostasis D migration 2 The following pictures show the talons of four different types of bird. Which bird has the best talon structure for walking on muddy ground? A W B X C Y D Z 88 3 When the seeds of an angiosperm are mature, what do the flowers develop into? A pollen B ovules C leaves D fruit 4 Maple trees use the specialized structure below to transport their seeds. How are the seeds transported? A by animals B by wind C by water D by erosion 5 A certain species of plant produces seeds without the use of flowers. What type of plant is this? A a gymnosperm B an angiosperm C a pollinator D a stamen 89 6 Suppose two populations of a single species of squirrel are put in different environments for hundreds of generations. What will most likely happen to the two populations? A Both populations will become extinct. B Both populations will develop new sets of traits. C Both populations will develop larger muscles. D Both populations will become carnivorous. 7 In which population of organisms could scientists most likely observe direct evidence of evolutionary change? A blue whales B elephants C fruit flies D oak trees 8 What characteristic of a population of organisms would most likely be subject to evolutionary change within 10 generations? A protective coloration B type of skeleton C reproductive strategy D respiratory organs 90