Characteristics of Living Organisms

Metabolism and Energy Processing

All living organisms require energy to carry out cellular processes. The way organisms obtain and use energy is fundamental to life.

• Metabolism: The sum of all chemical reactions occurring within an organism. These reactions enable organisms to break down nutrients and build cellular components.

• Energy Transfer: Energy flows through ecosystems, typically entering as sunlight, being converted by producers (plants), and transferred through consumers (animals).

• Example: In a savanna ecosystem, plants capture sunlight, herbivores (like zebras) eat plants, and energy is transferred up the food chain.

Homeostasis: Maintaining Internal Balance

Organisms must maintain a stable internal environment to survive, despite changes in the external environment.

• Homeostasis: The process by which organisms regulate their internal conditions (such as temperature, pH, and water balance) to maintain equilibrium.

• Equilibrium: Equal amounts of substances on both sides of a membrane or within compartments; however, living systems often require dynamic balance rather than static equilibrium.

• Maintenance: Organisms constantly replace chemicals and repair structures (DNA, organelles, proteins) to sustain life.

• Example: Human bodies regulate blood glucose levels through insulin and glucagon.

Growth, Development, and Response to Stimuli

Growth and Development

All living things grow and develop during their lifetimes, often through complex processes involving cell division and differentiation.

• Growth: Increase in size and number of cells. For example, bacteria grow by enlarging and dividing, while plants and animals grow by cell division and differentiation.

• Development: The process by which organisms become more complex, forming specialized tissues and organs.

• Example: A seed develops into a mature plant with roots, stems, and leaves.

Response to Stimuli

Organisms detect and respond to changes in their environment, such as light, temperature, and chemicals.

• Stimulus: Any change in the environment that elicits a response from an organism.

• Response: The action or change in behavior resulting from a stimulus, such as plants bending toward light (phototropism).

• Example: Leaves of a plant droop when struck by a strong wind.

Reproduction and Genetic Information

Reproduction

Living organisms reproduce to pass on their genetic information to the next generation.

• Asexual Reproduction: Offspring are produced by a single parent, resulting in genetically identical individuals (e.g., bacteria dividing by binary fission).

• Sexual Reproduction: Offspring are produced by the combination of genetic material from two parents, increasing genetic diversity (e.g., plants producing seeds, animals bearing live young).

• Example: A plant produces seeds that grow into new plants.

Genetic Program: DNA and Genes

DNA is the molecule that stores genetic information in all living organisms.

• DNA (Deoxyribonucleic Acid): Composed of four nucleotide bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).

• Genes: Segments of DNA that encode instructions for building proteins and regulating cellular activities.

• Genetic Code: The sequence of DNA bases determines the traits of an organism, similar to how the arrangement of letters forms words and sentences.

• Example: The gene for eye color is determined by a specific sequence of DNA bases.

Evolution and Taxonomy

Evolutionary Theory

Evolution explains the diversity of life and is supported by extensive scientific evidence.

• Charles Darwin and Alfred Russel Wallace: Formulated the theory of evolution by natural selection.

• Natural Selection: Individuals with advantageous traits are more likely to survive and reproduce, passing those traits to offspring.

• Example: Peppered moths in England changed color in response to industrial pollution.

Taxonomy: Classification of Life

Taxonomy is the science of classifying living organisms based on evolutionary relationships.

• Three Domains of Life:

  • Bacteria: Prokaryotic, simple cell structure, no nucleus.

  • Archaea: Prokaryotic, distinct from bacteria, often found in extreme environments.

  • Eukarya: Eukaryotic, complex cells with a nucleus, includes plants, animals, fungi, and protists.

• Hierarchy of Classification: Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species

• Phylogenetic Tree: Diagram showing evolutionary relationships among species.

• Example: Bears and polar bears share a recent common ancestor.

Origin of Life: Hypotheses and Experiments

Primordial Earth and the Emergence of Life

The origin of life on Earth is a complex and intriguing scientific mystery. Early Earth had abundant compounds and energy sources but lacked free oxygen.

• Available Compounds: Carbon dioxide (CO2), water (H2O), methane (CH4), ammonia (NH3).

• Energy Sources: Lightning, volcanic activity, cosmic and ultraviolet radiation.

• Time Scale: Life began about 1.5 billion years after Earth formed.

Spontaneous Generation and Its Disproof

Historically, it was believed that life could arise spontaneously from nonliving matter. Experiments disproved this idea.

• Francesco Redi: Showed that maggots only appear on meat when flies can lay eggs on it.

• Louis Pasteur & John Tyndall: Demonstrated that microorganisms do not grow in sterile broth unless exposed to air.

• Stanley Miller & Harold Urey: Simulated early Earth conditions and produced organic molecules.

Origin of Organic Molecules: Hypotheses

Several hypotheses explain how organic molecules could have formed on early Earth.

• Primordial Soup Hypothesis: Proposed by A. Oparin and J. Haldane, suggests organic molecules formed in Earth's early oceans from simple compounds.

• Miller-Urey Experiment: Demonstrated that amino acids and other organic molecules could form under simulated early Earth conditions.

• Iron-Sulfur World Hypothesis: Suggests organic molecules formed at hydrothermal vents on the ocean floor, catalyzed by minerals like iron and hydrogen sulfide.

• Prebiotics: Organic compounds essential for life, which accumulated over time.

Table: Comparison of Origin of Life Hypotheses

RNA World Hypothesis

RNA may have been the first self-replicating molecule, preceding DNA and proteins in early life forms.

• RNA: Structurally similar to DNA but less stable; can catalyze chemical reactions (ribozymes).

• Ribozymes: RNA molecules that act as enzymes, discovered by Thomas Cech and Sidney Altman.

• Significance: RNA could both store genetic information and catalyze its own replication, making it a likely precursor to cellular life.

• Example: Laboratory experiments show RNA can join nucleotide fragments together.

Formation of Protocells

Protocells are simple, cell-like structures that may have been precursors to true cells.

• Vesicles: Hollow spheres formed from lipids that spontaneously assemble in water.

• Membrane Formation: Vesicles have boundaries separating internal and external environments, similar to cell membranes.

• Growth and Division: Under certain conditions, vesicles can absorb materials, grow, and divide.

• Example: Laboratory agitation of lipid solutions produces vesicles resembling living cells.

Summary Table: Key Characteristics of Life

Key Equations and Concepts

• Metabolic Rate Equation:

• Genetic Code: DNA sequence is composed of four bases: A, T, C, G.

• Homeostasis: Dynamic equilibrium maintained by feedback mechanisms.

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard biology curriculum.