The Study of Life Chapter 1

Bio logy Life Knowledge Biology is the branch of science that studies living things So.... What is “life?” How do scientists study it?

Living vs. Non-living or Alive vs. Dead When talking about the qualities of “living things,” we are often talking about the species level rather than the individual level. “Skunks are living things,” rather than, “That skunk is living, the one on the road is dead.”

What is Life? The concept of “living” can be difficult to define, since many qualities of living things can be seen in non-living things: Crystals (non-living) can grow. A thermostat (non-living) responds to the environment.

Qualities of Living Things are complex, organized, and made up of cells. maintain homeostasis. respond to stimuli. reproduce and grow. use materials and energy. as species, adapt and evolve.

Cells are the basic unit of living things. Complex and organized All living things have DNA, which contains information to build cell parts. Cells are the basic unit of living things. Organisms can be single-celled, or cells can organize into tissues and organs.

Maintain Homeostasis Living organisms need to maintain an internal environment, such as maintaining temperature.

Respond to stimuli All living things have ways of sensing the environment that allow them to respond to threats and find food or favorable environments.

Reproduce and grow Living things produce more of their kind through reproduction. The young grow to maturity and the cycle begins again.

Use materials and energy In order to maintain complexity, maintain homeostasis, to grow, and to respond to the environment, organisms must take in energy and materials. Living things have a metabolism and give off waste products as they use materials.

Still a relevant question “What is life?” isn’t just a question that you left behind in Kindergarten. Astrobiologists who search for signs of life on other planets look for many of the same characteristics of terrestrial life. Microbiologists studying nanobacteria may challenge our current understanding of “life.”

Scientists classify living organisms into three broad Domains based on physical characteristics.

Scientific Inquiry Science is an investigation of the natural world, using evidence from nature to support explanations. The methods used by scientists to investigate the natural world are called Scientific Inquiry. Scientific Laws and Theories are products of scientific inquiry.

Hypothesis Testing Scientific Inquiry is often used to test hypotheses. A hypothesis is a tentative explanation for an observation. A valid hypothesis must be specific, testable, and falsifiable.

Hypotheses often begin with an observation that leads to questions.

Questions invite possible explanations. These possible explanations are hypotheses. To be valid, a hypothesis must be specific, testable, and falsifiable – but it doesn’t have to be correct! In fact, you don’t know if it is correct or not until you test it.

Each possible explanation — hypothesis — can give rise to a prediction, often stated in an IF...THEN format.

A good prediction suggests a procedure that can test the hypothesis. Scientists test hypotheses and accept or reject hypotheses based on data. They do not set out to prove hypotheses or they may bias their results.

Notice that the hypothesis is supported rather than “proven.” Once the procedures are carried out, scientists use the data to reach a conclusion regarding the hypothesis. Notice that the hypothesis is supported rather than “proven.”

Experiments are one type of scientific inquiry Experiments are one type of scientific inquiry. Experiments test variables to try to find the cause of natural events.

Observational studies are also part of scientific inquiry Observational studies are also part of scientific inquiry. Much of Astronomy and Paleontology, for example, involves observational science.

Laws and Theories In general: Scientific Laws and Theories are both products of Scientific Inquiry. Laws tend to be descriptions of natural phenomena in given circumstances. Theories tend to be explanations of how natural phenomena work.

Law of Gravity describes what happens when you drop a rock or launch a rocket at the moon. Gravitational Theory explains why dropped objects fall toward the center of the mass of the Earth.

Mendel’s Laws of Heredity: Describe patterns of inheritance in terms of probability. Darwin’s Theory of Natural Selection: Explains why inherited traits change in populations over generations.

A Unifying Theory The gene pool of populations changes over time. Changing environmental conditions favor different gene combinations at different times. Change in the genetics of a population from generation to generation is called “evolution.” Evolution explains species diversity and underlies all of modern Biology.

Modern evolutionary theory explains why organisms are so diverse, yet all are related. Three processes underlie evolution: genetic variability, inheritance, and selection.

Genetic variability in populations is normal.

Genetic variation is inherited when DNA is passed from one generation to the next. Our DNA contains the code for all of our inheritable traits.

Natural Selection, one mechanism that causes evolution, is a tendency for genes for traits that help an organism survive and reproduce to be passed on from generation to generation. Traits that interfere with reproductive success tend not to be passed on.

Recap Living things are complex, organized, and maintain homeostasis. Scientists study living things using scientific inquiry to make observations and test hypotheses. Laws and theories are the products of science. Evolution is the unifying theory of modern biology.