5 LIFE HOW DO WE DEFINE LIFE AND WHAT DO WE KNOW ABOUT IT?

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1 5 LIFE HOW DO WE DEFINE LIFE AND WHAT DO WE KNOW ABOUT IT?

2 UNIT 5 OVERVIEW Key Disciplines: Biology Timespan: The first life forms appeared about 3.8 billion years ago Key Question: How do we define life and what do we know about it? Threshold for this Unit: Threshold 5: Life

3 UNIT 5 LEARNING OUTCOMES By the end of Unit 5, students should be able to: 1. Compare life to non-life and why life indicates another threshold of increasing complexity. 2. Describe the conditions that made it possible for life to emerge on Earth. 3. Trace the major events in the development of life on Earth and explain what is meant by the term biosphere. 4. Use evidence to explain adaptation and evolution, including Darwin s theory of natural selection and DNA. 5. Use multiple documents and the notion of claim testing to explain the influence of personal beliefs and historical context on people s interpretation and application of scientific ideas.

4 UNIT 5 CONCEPT CARDS (you will complete these in class tomorrow) 1. adaptation 2. biology 3. biosphere 4. brains 5. DNA 6. eukaryotes 7. evolution 8. homeostasis 9. life 10.mammals 11.metabolism 12.natural selection 13.photosynthesis 14.reproduction

5 LOOKING BACK

6 WHAT HAPPENED IN UNIT 4? Unit 4 focused on the formation of our Solar System and our planet, Earth. We learned: How Earth and the rest of our Solar System formed over a very long period of time. About the Earth s violent and unstable beginning. How plate tectonics keep the Earth s surface in constant motion. How we learn about the Earth s changes over time through the science of geology.

7 KEY CONTENT VIDEO: Threshold 5: Life

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10 Threshold 5: Life on Earth Living organisms represent a new type and level of complexity. Chemically, they are much more complex than stars or planets, but they are also smaller and more delicate, because they are shaped mainly by the electromagnetic force, which acts only over small distances. They can only form under very particular Goldilocks Conditions. And they have to constantly adjust the way they relate to their environments in order to survive, which is why living organisms, unlike stars or rocks, seem to have a purpose. Living organisms are constantly changing so they have generated far more diversity than any earlier forms of complexity.

11 Learning About Evolution The goal of this World History course is to tell the story of the Universe from the Big Bang to the present. The story is based on the best, currently available evidence from the major academic disciplines, and presents evidence that is testable. You are being asked to study the evidence from these disciplines and see how the evidence fits together to create a coherent narrative. Another goal of this course is to make you better thinkers (think about our Common Core discussion on Friday). You are not being asked to blindly accept this story, and you are encouraged to challenge and question the resources. You are not being asked to discard your personal religious beliefs in this short unit and replace them with the scientific claims about life s origins. You are not being asked to choose between the origin story of your faith and the scientific origin story presented in the course.

12 What makes life different? Defining what it means to be a living thing has proved very difficult for biologists. The dynamism of life is due to four linked qualities, all instructed by deoxyribonucleic acid (DNA): Metabolism: making or taking energy for survival. Living organisms need fuel to keep themselves going Homeostasis: regulating internal functions to maintain health and survive. As the environment is always changing, living organisms adapt to new information BIG HISTORY PROJECT / UNIT 5 / LIFE

13 What makes life different? Reproduction: making copies of themselves. Since all living organisms die, they need to reproduce to perpetuate their species. Adaptation: adjusting each generation to better survive in a changing environment. The theories of Charles Darwin and the nature of DNA are critical to our understanding of life and how it works. Members of each species compete for resources, mates, and survival: those who survive pass on the traits that made them successful to their offspring. BIG HISTORY PROJECT / UNIT 5 / LIFE

14 Charles Darwin 19 th century biologist Published On the Origin of Species in 1859 His greatest achievement was to explain how life changes and adapts. He observed that slight changes were constantly occurring and those that favored survival persisted. Over time, this led to a more viable species. He surmised that since environments were constantly changing, biological change is an endless process. BIG HISTORY PROJECT / UNIT # / UNIT TITLE

15 Evidence for Evolutionary Change Darwin knew that fossils provided evidence of changes in living organisms over time, and today we can track such changes over 3.5 billion years. He also saw that there were subtle links between different species that showed that they were related.

16 Evidence for Evolutionary Change In the twentieth century more evidence emerged to support Darwin s theories. Geologists realized that the Earth is old enough for such processes to have generated the huge variety we see around us Biologists have learned how reproduction works, and what causes the tiny errors that drive evolutionary change.

17 Evidence for Evolutionary Change We now know that the code for all living organisms is contained in huge molecules of DNA, billions of atoms in length, organized in a long double helix that contains and preserves the information needed to make new copies of each organism.