1. Principles of Life. Chapter 1 Principles of Life. Key Concepts 1.1 Living Organisms Share Common Aspects of Structure, Function, and Energy Flow 1.2 Genetic Systems Control the Flow, Exchange, Storage, and Use of Information 1.3 Organisms Interact with and Affect Their Environments.
1.4 Evolution Explains Both the Unity and Diversity of Life
1.5 Science Is Based on Quantifiable Observations and Experiments
Characteristics shared by all living organisms:
Composed of a common set of chemical components and similar structures
• Contain genetic information that uses a nearly universal code
• Convert molecules obtained from their environment into new biological molecules
• Extract energy from the environment and use it to do biological work
Regulate their internal environment
• Replicate their genetic information in the same manner when reproducing
• Share sequence similarities among a fundamental set of genes
• Evolve through gradual changes in genetic information
Earth formed between 4.6 and 4.5 billion years ago.
It was some 600 million years or more before the earliest life evolved.
Complex biological molecules possibly arose from random associations of chemicals in the early environment.
Experiments that simulate conditions on early Earth show that this was possible.
Critical step for evolution of life—formation of nucleic acids
Biological molecules were enclosed in membranes, to form the first cells.
Fatty acids were important in forming membranes.
For 2 billion years, organisms were unicellular prokaryotes.
Early prokaryotes were confined to oceans, where they were protected from UV light.
There was little or no O2 in the atmosphere, and hence no protective ozone (O3) layer.
Photosynthesis evolved about 2.7 billion years ago.
The energy of sunlight is transformed into the energy of biological molecules.
Earliest photosynthetic cells were probably similar to cyanobacteria.
O2 was a byproduct of photosynthesis, and it began to accumulate in the atmosphere.
O2 was poisonous to many early prokaryotes.
Organisms that could tolerate O2 evolved aerobic metabolism (energy production using O2), which is more efficient than anaerobic metabolism.
Organisms were able to grow larger. Aerobic metabolism is used by most living organisms today.
O2 also produced a layer of ozone (O3) in the upper atmosphere.
This layer absorbs UV light, and its formation allowed organisms to move from the ocean to land.
Some cells evolved membrane-enclosed compartments called organelles.
Example: The nucleus contains the genetic information.
These cells are eukaryotes.
Prokaryotes lack nuclei and other internal compartments.
Some organelles may have originated by endosymbiosis, when larger cells engulfed smaller ones.
Mitochondria (site of energy generation) probably evolved from engulfed prokaryotic organisms.
Chloroplasts (site of photosynthesis) probably evolved from photosynthetic prokaryotes.
Multicellular organisms arose about 1 billion years ago.
Cellular specialization—cells became specialized to perform certain functions.
Evolution of species:
Mutations are introduced when a genome is replicated.
Some mutations give rise to structural and functional changes in organisms, and new species arise.
Each species has a distinct scientific name, a binomial:
• Genus name
• Species name
Example: Homo sapiens
Evolutionary relationships of species can be determined by comparing genomes.
A phylogenetic tree documents and diagrams evolutionary relationships.
Relationships in the tree of life are determined by fossil evidence, structures, metabolic processes, behavior, and molecular analyses of genomes.
Three domains of life:
• Bacteria (prokaryotes)
• Archaea (prokaryotes)
• Eukarya (eukaryotes)
Because all life is related, discoveries made using one type of organism can be extended to other types.
Biologists use model systems for research, such as the green alga Chlorella to study photosynthesis.
Genome—the sum total of all the information encoded by an organism’s genes
DNA consists of repeating subunits called nucleotides.
Gene—a specific segment of DNA that contains information for making a protein
Proteins govern chemical reactions in cells and form much of an organism’s structure.
Mutations alter nucleotide sequences of a gene, and the protein is often altered as well.
Mutations may occur during replication, or be caused by chemicals and radiation.
Most are harmful or have no effect, but some may improve the functioning of the organism.
Mutations are the raw material of evolution.
Complete genome sequences have been determined for many organisms.
Genome sequences are used to study the genetic basis of everything from physical structure to inherited diseases, and evolutionary relationships.
Biological systems are organized in a hierarchy.
Traditionally, biologists concentrated on one level of the hierarchy, but today much biology involves integrating investigations across many levels.
Living organisms acquire nutrients from their environments.
Nutrients supply energy and materials for biochemical reactions.
Some reactions break nutrient molecules into smaller units, releasing energy for work.
Examples of cellular work:
Synthesis—building new complex molecules from smaller chemical units
Movement of molecules, or the whole organism
Electrical work of information processing in nervous systems
Metabolism is the sum total of all chemical transformations and other work done in all cells of an organism.
The reactions are integrally linked—the products of one are the raw materials of the next.
In multicellular organisms, cells are specialized, or differentiated.
Differentiated cells are organized into tissues.
Tissue types are organized into organs, and organ systems are groups of organs with interrelated functions.
Multicellular organisms have an internal environmentthat is acellular—an extracellular environment of fluids.
Homeostasis—maintenance of a narrow range of conditions in this internal environment
Regulatory systems maintain homeostasis in both multicellular organisms and in individual cells.
Population—group of individuals of the same species that interact with one another
A community—populations of all the species that live in the same area and interact
Communities plus their abiotic environment constitute an ecosystem.
Individuals may compete with each other for resources, or they may cooperate (e.g., in a termite colony).
Plants also compete for light and water, and many form complex partnerships with fungi, bacteria, and animals.
Interactions of plants and animals are major evolutionary forces that produce specialized adaptations.
Species interaction with one another and with their environment is the subject of ecology.
Evolution is a change in genetic makeup of biological populations through time—a major unifying principle of biology.
Charles Darwin proposed that all living organisms are descended from a common ancestor by the mechanism of natural selection.
Natural selection leads to adaptations—structural, physiological, or behavioral traits that enhance an organism’s chances of survival and reproduction
In science, a theory is a body of scientific work in which rigorously tested and well-established facts and principles are used to make predictions about the natural world.
Evolutionary theory is:
(1) a body of knowledge supported by facts
(2) the resulting understanding of mechanisms by which populations have changed and diversified over time, and continue to evolve
Evolution can be observed and measured by:
Changes in genetic composition of populations over short time frames
The fossil record—population changes over very long time frames
Scientific investigations are based on observation and experimentation.
Understanding the natural history of organisms—how they get food, reproduce, behave, regulate internal environments, and interact with other organisms—facilitates observation and leads to questions.
Observation is enhanced by technology: microscopes, imaging, genome sequencing, and satellites.
Observations must be quantified by measurement and mathematical and statistical calculations.
The scientific method (hypothesis–prediction (H–P) method):
Inductive logic leads to tentative explanations called hypotheses.
Deductive logic is used to make predictions.
Experiments are designed to test these predictions.
Controlled experiments manipulate the variable that is predicted to cause differences between groups.
Independent variable—the variable being manipulated
Dependent variable—the response that is measured
Comparative experiments look for differences between samples or groups.
The variables cannot be controlled; data are gathered from different sample groups and compared.
Statistical methods help scientists determine if differences between groups are significant.
Statistical tests start with a null hypothesis—that no differences exists.
Statistical methods eliminate the possibility that results are due to random variation.
Not all forms of inquiry into nature are scientific.
Scientific hypotheses must be testable, and have the potential of being rejected.
Science depends on evidence that comes from reproducible and quantifiable observations.
Religious or spiritual explanations of natural phenomena are not testable and therefore are not science.
Science and religion are nonoverlapping approaches to inquiry.
Scientific advances that may contribute to human welfare may also raise ethical questions.
Science describes how the world works; it is silent on the question of how the world “ought to be.”
Contributions from other forms of human inquiry may help us come to grips with such questions.