Science, Matter, Energy, and Systems 2 Science, Matter, Energy, and Systems Photo © Borut Trdina/iStockphoto

Case Study: Experimenting with a Forest In New Hampshire, scientists examined changes in water flow/soil nutrient content in a(n): Control area of an undisturbed mature forest Experimental area of a nearby deforested site Results showed lack of vegetation allows more water runoff, loss of nutrients from soil How might ecologists use basic chemistry and laws of matter to further study ecosystems?

2.1 What Do Scientists Do? The focus of science is to study how nature works and to use what is learned to predict what may happen in nature. Scientific methods, or practices, enable scientists to advance knowledge and understanding of how the world works. Scientific theory: well-tested and widely accepted explanation

The Practices of Science Asking questions Developing and using models Planning and carrying out investigations Analyzing and interpreting data Using math Forming explanations Forming arguments from evidence Obtaining, evaluating, communicating information

Observations, Experiments, and Models Answer Questions About Nature To answer questions about nature, scientists: Make careful observations. Develop hypotheses (possible/testable answers to scientific questions or explanations of what is observed). Take measurements (collect data, or information). Experiment and create models (representations of structures/systems). Use knowledge learned to describe and predict what happens in nature.

Values That Support Good Science Logic Critical thinking Objectivity Open-mindedness Honest reporting Collaboration Peer review: evaluation by others in one’s field (methods, results, reasoning, reliability)

Scientific Theories The goal of scientists is to develop theories and laws based on facts and data that explain how the physical world works. A scientific theory: Has been widely tested Is supported by extensive evidence Is accepted as being a useful explanation of some phenomenon by most scientists in a particular field or related fields of study

Scientific Laws A scientific law is a well-tested and widely accepted description of observations that have been repeated many times in a variety of conditions.

Science Has Limitations Scientific research cannot prove or disprove anything absolutely. There are inherent uncertainties in measurements, observations, and models. Scientists use words such as “overwhelming evidence” to clarify probability or certainty. Scientists must rely on statistical tools. As humans, scientists are not free from bias; peer review helps to reduce personal bias.

2.2 What Is Matter? Matter is anything that has mass and takes up space. Exists in three physical states: solid, liquid, gas Two chemical forms: elements (all the same atoms) or compounds (combinations of more than one type of atom)

Elements and Compounds Elements cannot be broken down into simpler forms by chemical means. Represented by a one- or two-letter symbol (C=carbon, Au=gold) Arranged in periodic table based on chemical behavior Currently 118 elements, not all of which occur naturally Compounds: two or more different elements held together in fixed proportions

Atom: Basic Building Block of Matter An atom is the smallest building block of matter that an element can have that will still retain its chemical properties. Each atom has three subatomic particles: Neutrons (no electric charge, inside nucleus) Protons (positive electric charge, inside nucleus) Electrons (negative electric charge, move rapidly outside nucleus) Each atom has a small central nucleus that contains its protons and neutrons.

Atomic Number, Atomic Mass, and Isotopes Atomic number: the number of protons in an atom’s nucleus Mass number: the total number of neutrons and protons in an atom’s nucleus Isotopes of an element have the same atomic number, but a different mass number (the same number of protons but a different number of neutrons).

Structure of Atoms Atom: This simplified model depicts a carbon-12 atom. The atom’s nucleus consists of six protons, each with a positive electrical charge, and six neutrons with no electrical charge. Six negatively charged electrons move rapidly outside its nucleus.

Molecule: Second Building Block of Matter A molecule is a combination of two or more atoms of the same or different elements held together by forces known as chemical bonds.

Ion: Third Building Block of Matter An ion is an atom or group of atoms with a net positive or negative charge. Subscript number: number of positive/negative electrical charges Important for measuring a substance’s acidity in a water solution (pH)

Acidity The concentration (amount) of hydrogen ions (H+) and hydroxide ions (OH−) in a substance Measured with a scale known as pH An acidic solution has a pH below 7 and a basic solution has a pH above 7 A neutral solution has a pH of 7

pH Scale pH Scale: The pH scale describes the acidity of solutions.

Molecules of Life In chemistry, organic compounds are carbon- based compounds that contain at least two carbon atoms combined with atoms of one or more other elements (except CH4). Hydrocarbons: compounds of carbon and hydrogen atoms Simple carbohydrates: contain carbon, hydrogen, and oxygen Polymers (complex carbohydrates): simple organic compounds (monomers) bonded together

Polymers Are Essential to Life What are the major types of polymers? Proteins: formed by amino acids Nucleic acids: formed by nucleotides (DNA and RNA) Lipids (fats, waxes): essential macromolecules not made of monomers

Monomers and Polymers Carbon-based Molecules: Glucose monomers (left) make up complex carbohydrate polymers, such as cellulose (right).

Physical and Chemical Changes Physical changes, such as changes in size or state (ice to water), do not involve changes in chemical composition. Chemical changes (reactions) involve changes in chemical composition of the substances involved. Chemists use a chemical equation to show how the chemicals involved are arranged in a chemical reaction. Chemists use a process of balancing the equation to account for all atoms involved in any reaction.

A Chemical Equation: Coal → CO2 Chemical Reaction: Chemical reactions can be modeled with words, symbols, or illustrations.

We Cannot Create or Destroy Atoms Law of conservation of matter Physical or chemical changes can take place in chemical reactions, but no atoms are created or destroyed in the process.

2.3 What Is Energy? Energy is the capacity to do work. Kinetic energy (associated with motion): Examples: flowing water, speeding car, electricity, wind Thermal energy (heat): total kinetic energy of all the moving atoms, ions, or molecules in a sample of matter, measured as temperature Electromagnetic radiation: wave energy resulting from changes in electrical/magnetic fields; includes solar energy, which fuels life on Earth Potential energy (stored energy): Can be converted to kinetic energy

Electromagnetic Radiation Electromagnetic Spectrum: The electromagnetic spectrum consists of a range of electromagnetic waves, which differ in wavelength and energy content.

Energy Quality High-quality, or concentrated energy, has a high capacity to do useful work. Examples: high-temperature thermal energy, concentrated sunlight, high-speed wind, energy released from burning fuels) Low-quality, or dispersed energy, has little capacity to do useful work.

Energy Changes Are Governed By Two Scientific Laws First law of thermodynamics (law of conservation of energy) Whenever energy is converted from one form to another in a physical or chemical change, no energy is created or destroyed. Second law of thermodynamics When energy is changed from one form to another, it always results in less high-quality energy.

2.4 What Are Systems? A system is a set of components that function/interact in some regular way. Inputs Throughputs Outputs Form of matter, energy, information Examples: cell, human body, river, forest, dam, economy

System Model Inputs, Throughputs, Outputs: This greatly simplified model shows the flow of matter, energy, and information into and out of a system.

Systems Respond to Change Through Feedback Loops Feedback is matter, energy, or information that is fed back into a system as input and can affect system behavior. Feedback loops Positive feedback loops cause systems to change further in same direction. Ecological tipping point: natural system locked into positive feedback loop Negative feedback loops cause systems to change in opposite direction.