Characteristics of Living Organisms

Defining Features of Life

All living organisms share a set of fundamental characteristics that distinguish them from non-living matter. Understanding these features is essential for studying anatomy and physiology.

• Organization: Living things are made up of one or more cells, the basic units of life. Cells are organized into tissues, organs, and systems in multicellular organisms.

• Metabolism: Organisms carry out chemical reactions to obtain and use energy. This includes processes like respiration and photosynthesis.

• Responsiveness: The ability to respond to stimuli from the environment (e.g., light, temperature, touch).

• Growth and Development: All living things grow and develop according to genetic instructions coded in their DNA.

• Reproduction: The ability to produce new individuals, either sexually or asexually.

• Homeostasis: Maintaining a stable internal environment (e.g., body temperature, pH).

• Evolution: Populations of living organisms evolve over time through changes in their genetic material.

Energy in Living Systems

The Sun as the Primary Energy Source

The sun provides solar energy, which is the primary source of energy for most life on Earth. Plants and other photosynthetic organisms capture this energy and convert it into chemical energy.

How Plants and Animals Obtain Energy

• Photosynthesis (Plants):

  • Plants absorb solar energy using their leaves.

  • They use this energy to convert carbon dioxide (CO2) and water (H2O) into glucose (C6H12O6) and oxygen (O2).

  • This process stores energy in chemical bonds (chemical potential energy).

• Cellular Respiration (Animals):

  • Animals obtain energy by consuming plants (or other animals that have eaten plants).

  • They break down glucose and other molecules during cellular respiration to release stored energy.

  • Plants also use cellular respiration to release energy from glucose.

Energy Flow: The flow of energy can be summarized as: sun → plants → animals.

Types of Work Performed by Organisms Using Energy

Definition of Work in Biology

In biological terms, work refers to any process that requires energy to move or change something within an organism.

Main Types of Work

• Chemical Work: Building and breaking down molecules (e.g., synthesizing proteins, breaking down glucose). Includes anabolism (building up) and catabolism (breaking down).

• Transport Work: Moving substances across cell membranes, often against a concentration gradient (e.g., active transport using ATP to move ions like Na+ and K+).

• Mechanical Work: Physical movement, such as muscle contraction or movement of cilia and flagella.

Kinetic and Potential Energy

Definitions and Examples

• Kinetic Energy: The energy of movement. Example: Blood flowing through vessels, a muscle contracting, or a person running.

• Potential Energy: Stored energy due to an object's position or structure. Example: Energy stored in the chemical bonds of glucose, or a ball held at the top of a hill before it rolls down.

Thermodynamics in Biological Systems

The First and Second Laws of Thermodynamics

• First Law (Conservation of Energy): Energy cannot be created or destroyed, only transformed from one form to another. In biological systems, this means energy from food is converted into other forms such as heat, movement, or stored energy.

• Second Law (Entropy): Every energy transformation increases the entropy (disorder) of the universe. Some energy is lost as heat, increasing the randomness or disorder in the surroundings.

Summary:

• First Law: Energy is conserved; it changes form but is never lost.

• Second Law: Energy transformations increase entropy; systems become more disordered over time.

Chemical Reactions in Living Organisms

Basic Format of a Chemical Reaction

• Chemical reactions are written as: Reactants → Products

• Reactants: Starting materials (left side of the arrow).

• Products: Substances formed (right side of the arrow).

Types of Chemical Reactions

• Synthesis (Combination) Reaction: Two or more reactants combine to form one product. Example:

• Decomposition Reaction: One reactant breaks down into two or more products. Example:

• Exchange (Replacement) Reaction: Parts of reactants are swapped to form new products. Example:

Identifying Reactants and Products

• Look at the left side of the arrow for reactants.

• Look at the right side for products.

• Use the reaction type to describe what is happening (building up, breaking down, or swapping parts).

Energy Changes in Chemical Reactions

Key Terms

• Free Energy: The energy available to do work in a system.

• Activation Energy: The initial input of energy required to start a chemical reaction. It helps reactants reach a "transition state" so the reaction can proceed.

• Exergonic Reaction: Products have less free energy than reactants; energy is released (e.g., cellular respiration).

• Endergonic Reaction: Products have more free energy than reactants; energy is absorbed or required (e.g., photosynthesis).

How Energy Changes Relate to Reactions

• Every chemical reaction needs activation energy to get started, even if it will release energy overall.

• If the reaction releases free energy (exergonic), it can proceed spontaneously after activation energy is supplied.

• If the reaction requires free energy (endergonic), it will only proceed if energy is supplied from another source.

Nucleotides and Energy Coupling

Role of ATP, NADH, and FADH2 in Metabolism

• ATP (Adenosine Triphosphate): The main energy currency of the cell. Stores and transfers energy for cellular processes.

• NADH and FADH2: Electron carriers that store energy released during exergonic reactions (such as the breakdown of glucose in cellular respiration).

• Energy Coupling: Endergonic reactions (which require energy, like building proteins or DNA) use the energy stored in ATP, NADH, and FADH2. ATP donates a phosphate group (and energy) to drive these reactions. NADH and FADH2 donate electrons and hydrogen to help produce more ATP or drive other biosynthetic processes.

Summary Table: Types of Chemical Reactions

Key Equations

• Photosynthesis:

• Cellular Respiration:

Additional Info

• Anabolism and catabolism are two types of metabolic pathways. Anabolism builds complex molecules from simpler ones (requires energy), while catabolism breaks down complex molecules into simpler ones (releases energy).

• Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy. They are specific to the reactions they catalyze.