# Using Models to Explain Phenomena or Make Predictions

Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

In this lesson, we'll learn how to apply models to explain phenomenon in science. We'll explain what models are, how they're used, and look at specific examples, including mathematical models.

## What Are Models?

Imagine wanting to study a big problem in the world. Maybe you're thinking of finding the cure for cancer, developing next year's flu vaccine, or even predicting the weather more reliably. As scientists, we know the way to solve our problems is through conducting scientific investigations where we propose a prediction based on past data, test one variable at a time, collect, and finally analyze our data.

But what do you do if the system in question is too big to test? We can't just experiment on every person with cancer, or control aspects of the weather during an investigation. So how are scientists supposed to figure out these mysteries if they can't conduct classic investigations? They get around this problem by constructing models. Models are representations of real scientific phenomenon that may be difficult to study in the real world. Models may be physical representations, diagrams, theories, or mathematical equations.

Although models vary in their structure, they serve common purposes for scientists. Sometimes models help scientists visualize something, such as the Bohr model of atomic structure. Other times, models are designed to analyze past data and make predictions about the future, such as models of seismic activity to predict future earthquakes. Some other models are designed to recreate a problem, such as an animal model of human disease, so scientists can test possible treatments. Today, we're going to look at some examples of models and their uses in science.

## Examples

### DNA Structure

One of the greatest models in scientific history is the Watson and Crick model of DNA. DNA is the genetic material of the cell and contains all information to code for our traits. But prior to the work of James Watson, Francis Crick, and their colleagues Rosalind Franklin and Maurice Wilkins, the structure of this molecule of heredity was a mystery. These scientists discovered the DNA structure was a double helix, composed of two strands of complementary DNA with the genetic information coded in the base sequence inside the helix. This DNA model opened the doors to understand how information is coded in the molecule and how our traits can change. Today, it is still widely accepted and used to understand aspects of molecular biology.

### Evolution

Sometimes models are used not to visualize structures, but rather to explain phenomena. Have you ever wondered why kangaroos have such strong legs, or why rhinos have horns? What if there was an overarching scientific model to explain any biological adaptation? This model is known as the biological theory of evolution, and it was originally developed by Charles Darwin.

Throughout careful observation of natural populations, Darwin concluded that any trait that would allow an organism to survive and reproduce would be passed on through its DNA. The new generation would also be more likely to have that trait. Over time and with selective pressure from a changing environment, new species would evolve in this way. This model explains all biodiversity on Earth today, from microscopic bacterial populations to the most beautiful animals and plants in tropical rainforests.

### Climate Change

Other times, qualitatively applying a model isn't enough. Scientists want to predict concrete numbers to use as data. This is where mathematical models come in. Mathematical models describe phenomenon using mathematical equations. Mathematical models are very helpful in the study of climate change.

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