11-2-17 Models Practice

Do Now: Answer the following questions in your science notebook Why are models useful in science? Some processes or events are too complex to understand. What are some limitations of using models? Models can only approximate; models are never exactly correct. Models may work in some cases, but not others.

Homework Start Reviewing for the UNIT TEST ON THURSDAY, 11/9 (1 week from today!!!)

Scientific Models SC.7.N.3.2: Identify the benefits and limitations of the use of scientific models. This will be the last topic before the NATURE OF SCIENCE UNIT TEST ON THURSDAY, 11/9/17 Write this down in your agenda!!!

Lesson Objectives I can explain how scientists use models. I can explain the benefits and limitations of scientific models.

We often want to predict or explain things that are pretty complicated. For example, this basketball player might want to know how many points he will score in his next game. That will depend on many factors, including how many minutes he plays, if he stays healthy, and whether the person guarding him is good at defense. These things, and more, will decide how many points he will eventually score. We often want to predict or explain things that are pretty complicated. For example, this basketball player might want to know how many points he will score in his next game. That will depend on many factors, including how many minutes he plays, if he stays healthy, and whether the person guarding him is good at defense. These things, and more, will decide how many points he will eventually score. Wouldn’t it be nice to simplify this list of things to make it easier to predict the number of points he will score?

Why we need scientific models? Scientists face the same problem as our basketball player. Their job is to explain and predict complicated processes in nature. These processes often involve many factors. For example, astronomers want to know the structure of our universe, which consists of billions of stars, planets, and other objects. Science also tries to understand processes like how the climate on Earth is changing, or the relationships between different species in a habitat. Science also tries to understand the inner workings of a single species, including their cells and DNA. All of these things are so complex that we need to simplify them in order to understand them, or to make useful predictions about them. This is one of the main tasks of scientists.

Models in Science Scientific Model: a simplified representation of an object, event, or process. Examples include a 3-dimensional object, diagram, graph, equation, map, or written description Scientific models simplify an object or process into only its most important parts, which makes it easier to understand.

Examples The models of the atom and food web show relationships between different objects, like atomic particles or animals. They show how different parts of a whole are positioned or related to one another.

Examples Other types of models may represent an event or process. Ex: a diagram of the movement of Earth’s crust by plate tectonics. Ex: an equation that represents evolution from one generation to the next by natural selection.

Practice: Think-Pair-Share True or false, a model is always a 3-dimensional, physical representation of an object or process? Explain your answer. Answer: False, a model doesn’t have to be a 3D object. It can be a graph, map, equation, or diagram.

Practice: Think-Pair-Share (with a different person) Which of these scientific discoveries are models? The solar system, water cycle, temperature graph, and population equation are all examples of models. The discoveries about water and cheetahs are observations.

A more specific example: Mendel’s question about inheritance To understand how models are created, and how they can be useful, let’s look at a specific example. You may have heard of the scientist and monk Gregor Mendel and his model of inheritance.

Mendel’s question about inheritance Mendel had a very specific purpose. He wanted to be able to predict what the offspring of two parents would look like. Specifically, he wanted to help animal or plant breeders predict what would happen when two specific parents were bred with one another. The process of inheritance is obviously very complicated. So what Mendel wanted to do was create a simple model - based on math - that enabled him to understand how inheritance worked.

Mendel’s Experiment What Mendel did was cross - or mated - many different pea plants. He then grew the seeds from these crosses and compared the features of the parents with their offspring. Mendel did this with thousands of pea plants and noticed a pattern.

Mendel’s Experiment When he started by crossing a purple- flowered pea plant with a white- flowered pea plant, he found that all of the offspring had purple flowers. But when he crossed all of the offspring with purple flowers to each other, one- fourth, or 25%, of them had white flowers, and the rest had purple flowers. The white flower skipped generations!

Mendel’s Model of Inheritance To explain these puzzling results, Mendel created a model. Flower color: two factors – purple and white Each factor is inherited randomly from each parent To explain these puzzling results, Mendel created a model. He predicted that a characteristic like flower color is controlled by two factors. In this case, the two factors are purple and white. An individual plant inherits one factor at random from each parent. These plants inherited a purple factor from one parent and a white factor from the other.

Mendel’s Model of Inheritance To explain these puzzling results, Mendel created a model. Flower color: two factors – purple and white Each factor is inherited randomly from each parent One factor dominates the other Dominant trait = P Recessive trait = p Finally, one factor is dominant over the other. This means that when both are inherited, the dominant factor is shown. In this case, purple is dominant over white. We identify the dominant trait with the capital letter P for purple and the recessive trait with a lower case letter p. Since these plants have one white and one purple factor, or big P little p, they have purple flowers.

Mendel’s Model: Limitations Model can only approximate Factors are passed on by chance

Model Limitations: not always exact Models are never exactly correct; they are simplifications Chance events can affect results Best models = best approximation of reality Models will never be exactly correct every time. This is because all models are simplified representations of complex things. There are always chance events that can make an actual outcome different from what is predicted by a model. The best models are the best approximation of what actually occurs

Model limitations: not always exact Scientists can account for this uncertainty by allowing their models to predict a range of values that are most likely. For example, we know that electrons orbit around the nucleus in particular paths, but can never know the exact location of an electron in an atom. Therefore, atomic models like the one shown here highlight the areas where an electron is most likely to be found.

Practice: Think-Pair-Share Choose the correct statement about the predictions of scientific models. One model of Earth’s climate predicts that global temperatures will rise by 2.5 – 5.0 F. The model gives a range, because there are some uncertainties about future human behavior. A model that is not exactly correct is useless. An evolutionary model says that orangutans evolved between 12 and 16 million years ago. Because this model does not give an exact value, it must be wrong. If I cross two pea plants and get something slightly different than predicted by Mendel, his model should be thrown away because it is incorrect.

Model Limitations: Simplification Mendel’s model, and other scientific models, have another limitation. Mendel’s model worked well for predicting inheritance in pea plants. But many organisms’ characteristics are not inherited in the way he proposed for pea plants. For example, some characteristics in humans like freckles or dimples are controlled by two factors, just like flower color in pea plants.

Model Limitations: Simplification But human features like height and hair color are controlled by more than two factors. Therefore, we cannot use a Punnett square to understand how these traits are passed from parent to child.

Model Limitations: Simplification Many models work in some cases but not others. For example, a model of Earth’s climate would not work on Mars. Or a model of human behavior might not work for birds. This is okay, as long as we know exactly what we are trying to understand. Models are supposed to be simplified representations. No model can explain everything about the universe, or it would be too complex to use or understand.

Practice: Think-Pair-Share Choose all the statements that are correct about this model of a dolphin’s body parts. This model is useful for comparing positions of the heart, kidney, and liver of the dolphin. This model should not be used to understand a shark’s anatomy, since sharks don’t have a bony skeleton like dolphins. This model does not show the dolphin’s muscles, so it is incorrect and should not be used for any purpose.

Benefits of Scientific Models 1. They simplify complex processes. Inheritance is quite complicated, it involves cell division, genes, and DNA. But Mendel’s model allows us to predict the outcome very accurately.

Benefits of Scientific Models 2. They lead to new discoveries Using Mendel’s model of inheriting factors, a scientist named Thomas Hunt Morgan studied fruit flies and discovered that these factors, now called genes, were found on chromosomes. Chromosomes were eventually found to be made of DNA.

Benefits of Scientific Models 3. They can be improved upon Ex: discovering a new fossil can improve a model of evolution. Ex. Dr. Morgan found Mendel’s model of inheritance did not work for eye color in flies. But, he was able to build upon Mendel’s model to create a new one to better predict inheritance of fly eye color.

Practice: Think-Pair-Share Choose all ways in which Mendel’s model was beneficial. Mendel’s model simplified the complex process of inheritance. Mendel’s model allows us to accurately predict the inheritance of characteristics ranging from flower color to freckles. Mendel’s model eventually led to the discovery of genes, chromosomes, and DNA. Thomas Hunt Morgan improved Mendel’s model so that he could predict inheritance of fruit fly eye color.

Lesson Review

Lesson Review Accuracy How they can be applied They are simple Models are limited by: Models are beneficial because: Accuracy How they can be applied They are simple They lead to new discoveries They can be improved upon

Planet Distance from the Sun Mercury 0.39 AU Venus 0.723 AU Earth 1 AU Mars 1.524 AU Jupiter 5.203 AU Saturn 9.539 AU Uranus 19.18 AU Neptune 30.06 AU Practice In assigned groups, design a scale drawing of the solar system. Use the scale 5 cm = 1 AU (this means you will have to practice solving ratios!!!) Use the following chart of distances of each planet from the Sun.

Closure The solar system scale diagram is useful for determining the order of the solar system and for determining how close planets are to each other. Though, it does not include important features such as the asteroid belt. Exit Ticket: On the provided notecard, identify another benefit and limitation of the solar system diagram.