Characteristics of Living Things

Defining Life

Living organisms are distinguished from non-living matter by a set of key characteristics. Understanding these features is fundamental to biology.

• Organization: Living things exhibit a complex, ordered structure. For example, cells are organized into tissues, tissues into organs, and organs into organ systems.

• Energy Use and Metabolism: All living organisms acquire and use energy to maintain their internal order. Metabolism refers to the sum of all chemical reactions that occur within an organism. For example, plants convert sunlight into chemical energy via photosynthesis.

• Adaptation and Evolution: Populations of living organisms evolve over generations through adaptation, which is a process driven by natural selection. For example, the beak shapes of Darwin's finches evolved to exploit different food sources.

• Homeostasis: Living organisms regulate their internal environment to maintain stable conditions necessary for survival. For example, humans maintain a constant body temperature through sweating and shivering.

• Reproduction: All living things have the ability to reproduce, passing genetic information to their offspring.

• Hereditary Material: DNA and RNA serve as the genetic material that stores and transmits hereditary information.

The Scientific Method

Steps in Scientific Inquiry

The scientific method is a systematic approach used to investigate natural phenomena.

1. Observation: Identifying a problem or phenomenon to study.

2. Hypothesis: Formulating a testable statement based on initial observations.

3. Experimental Design: Planning and conducting experiments to test the hypothesis.

4. Data Collection and Discussion: Gathering and analyzing data to interpret results.

5. Conclusion: Drawing conclusions based on the data and determining whether the hypothesis is supported or refuted.

Inorganic Chemistry in Biology

Basic Chemical Concepts

• Matter: Anything that has mass and occupies space. Exists in three forms: solid, liquid, and gas.

• Element: A pure substance consisting of only one type of atom. Common elements in living organisms include carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), and sulfur (S).

• Atom: The smallest unit of an element, composed of protons, neutrons, and electrons.

• Molecule: Two or more atoms bonded together. Represented by a molecular formula (e.g., for water).

• Compound: A substance formed when two or more different elements combine chemically.

Isotopes and Ions

• Isotope: Atoms of the same element with different numbers of neutrons. Biologically important isotopes include radioactive isotopes used in medical imaging and dating fossils.

• Ion: An atom or molecule that has gained or lost one or more electrons, acquiring a charge. Ions are formed through the process of ionization.

Electron Configuration and Chemical Bonds

• Duet and Octet Rules: Atoms tend to gain, lose, or share electrons to achieve a stable configuration of 2 (duet) or 8 (octet) electrons in their outer shell.

• Chemical Bonds:

  • Ionic Bonds: Formed when electrons are transferred from one atom to another, resulting in oppositely charged ions (e.g., NaCl).

  • Covalent Bonds: Formed when atoms share electrons.

    • Polar Covalent: Electrons are shared unequally, leading to partial charges (e.g., water).

    • Non-polar Covalent: Electrons are shared equally (e.g., ).

  • Hydrogen Bonds: Weak attractions between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom (e.g., between water molecules).

Water and Its Importance

• Unique Properties: Water is essential for life due to its high heat capacity, cohesion, adhesion, solvent abilities, and role in chemical reactions.

• Hydrophilic vs. Hydrophobic: Hydrophilic molecules interact with water (e.g., salts, sugars), while hydrophobic molecules do not (e.g., oils, fats).

Acids, Bases, pH, and Buffers

• Acid: A substance that increases the hydrogen ion () concentration in a solution.

• Base: A substance that decreases the hydrogen ion concentration, often by releasing hydroxide ions ().

• pH: A measure of hydrogen ion concentration; calculated as .

• Buffer: A substance that minimizes changes in pH by accepting or donating ions.

• Biological Importance: Proper pH is crucial for enzyme function and cellular processes.

Molecules and Compounds of Life

Organic vs. Inorganic Compounds

• Organic Compounds: Contain carbon and are typically found in living organisms (e.g., glucose, proteins).

• Inorganic Compounds: Do not contain carbon-hydrogen bonds (e.g., water, salts).

Role of Carbon in Organic Molecules

• Carbon atoms can form four covalent bonds, allowing for a diversity of stable, complex molecules essential for life.

Functional Groups in Biological Molecules

• Methyl (-CH3): Found in fats and oils.

• Hydroxyl (-OH): Present in sugars and alcohols.

• Carboxyl (-COOH): Found in fats and amino acids.

• Amino (-NH2): Present in amino acids and proteins.

• Phosphate (-PO42-): Found in phospholipids, DNA, and RNA.

Dehydration Synthesis and Hydrolysis

• Dehydration Synthesis: A chemical reaction in which two molecules are joined by removing a water molecule. This process forms polymers from monomers.

• Hydrolysis: The reverse reaction, where a water molecule is added to break a bond, splitting polymers into monomers.

Carbohydrates and Proteins

• Carbohydrates: Serve as energy sources and structural components (e.g., glucose in blood, cellulose in plant cell walls).

• Proteins: Function as enzymes, structural elements, and signaling molecules. Found in muscle (actin, myosin), enzymes (amylase), and antibodies.

Amino Acids and Protein Structure

• Basic Structure: An amino acid contains a central carbon, an amino group, a carboxyl group, a hydrogen atom, and a variable R group.

• Peptide Bond: A covalent bond formed between the amino group of one amino acid and the carboxyl group of another via dehydration synthesis.

• Levels of Protein Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Local folding into alpha-helices and beta-sheets.

  • Tertiary: Overall 3D shape of a single polypeptide.

  • Quaternary: Association of multiple polypeptide chains.

• Denaturation: Loss of protein structure (and function) due to changes in temperature, pH, or chemicals.

Lipids and Nucleic Acids

• Lipids: Include fats, oils, phospholipids, and steroids. Serve as energy storage, membrane structure, and signaling molecules. Found in adipose tissue, cell membranes, and hormones.

• Nucleic Acids: DNA and RNA store and transmit genetic information. DNA is found in the cell nucleus; RNA is involved in protein synthesis.

Additional info: This guide expands on the review points by providing definitions, examples, and context for each concept, ensuring a comprehensive understanding suitable for exam preparation.