principles of life a chapter 1. chapter 1 principles of life key concepts 1.1 living organisms share...

Principles of Life

A Chapter 1

Chapter 1 Principles of Life

• Key Concepts• 1.1 Living Organisms Share Common Aspects

of Structure, Function, and Energy Flow• 1.2 Life Depends on Organization and Energy• 1.3 Genetic Systems Control the Flow,

Exchange, Storage, and Use of Information

Chapter 1 Principles of Life

• 1.4 Evolution Explains the Diversity as Well as the Unity of Life

• 1.5 Science Is Based on Quantitative Observations, Experiments, and Reasoning

Concept 1.1 Living Organisms Share Common Aspects of Structure, Function, and Energy Flow

• Biology: the scientific study of living things or organisms.

• Living things are all descended from a single-celled ancestor (a single common ancestor).

• The characteristics shared by all organisms logically lead to the conclusion that all life has a common ancestry.


• Characteristics shared by all living organisms:• Composed of a common set of chemical

components and similar structures (e.g., cells)• Depend on interactions among structurally

complex parts to maintain the living state – 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 for life functions

• Replicate their genetic information in the same manner when reproducing

– Share structural 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.

• The earliest life evolved about 600 million years later.

Figure 1.1 Life’s Calendar


• 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 that could

reproduce themselves and contain the information to produce proteins.


• The next step: • Biological molecules were enclosed in a

membranes, to form a cell.• Fatty acids, which form membrane-like films in

water, were important in forming membranes.• Membranes separate the cell from the

surrounding environment.


• 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.

Figure 1.2 The Basic Unit of Life Is the Cell


• Photosynthesis evolved about 2.7 billion years ago.

• The energy of sunlight is transformed into the chemical-bond energy of biological molecules.

• Earliest photosynthetic cells were probably similar to cyanobacteria.

• O2 was a by-product of photosynthesis, and it began to accumulate in the atmosphere.

Figure 1.3 Photosynthetic Organisms Changed Earth’s Atmosphere

Stromalites


• 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, where specialized functions can be performed.

• The nucleus contains the genetic information.• These cells are called eukaryotes.• Prokaryotes lack nuclei and other internal

compartments.


• Some organelles may have originated by endosymbiosis, when larger cells engulfed smaller ones.

• Mitochondria (sites of energy generation) probably evolved from engulfed prokaryotic organisms.

• Chloroplasts (sites of photosynthesis) probably evolved from engulfed photosynthetic prokaryotes.


• Multicellular organisms arose about 1 billion years ago. Groups of eukaryote cells probably failed to separate after division.

• Cellular specialization—cells became specialized to perform certain functions.

• This allowed multicellular eukaryotes to become larger and adapt to specific environments.


• Evolution of species:– Mutations (changes) 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

Concept 1.1 Living Organisms Share Common Aspects of Structure, Function, and Energy Flow• Evolutionary relationships of species can be

determined by comparing genomes.• Genome sequencing and other molecular

techniques have added molecular evidence to knowledge from the fossil record.

• Phylogenetic trees document and diagram evolutionary relationships.

Figure 1.4 The Tree of Life

Concept 1.1 Living Organisms Share Common Aspects of Structure, Function, and Energy Flow• Relationships in the tree of life are based on

fossil evidence, structures, metabolic processes, behavior, and molecular analyses.

• Three domains of life:• • Bacteria (prokaryotes)• • Archaea (prokaryotes)• • Eukarya (eukaryotes)


• All organisms that are alive today descended from common ancestors in the past.

• Living species did not evolve from other species living today.

Concept 1.1 Living Organisms Share Common Aspects of Structure, Function, and Energy Flow• Because all life is related, discoveries made

using one type of organism can be extended to other types.

• Biologists use model organisms for research, such as the green alga Chlorella to study photosynthesis.

Concept 1.2 Life Depends on Organization and Energy

• The second law of thermodynamics states that, left to themselves, organized entities tend to become more random.

• Energy is required for cells to combat the tendency for their molecules, structures, and systems to lose organization.

• Energy is required by cells throughout their lives.


• Organization is apparent in a hierarchy of levels from molecules to ecosystems.

• Cells use energy to synthesize complex molecules by assembling atoms into new, highly organized configurations.

• Organization is essential for cells to function in a multicellular organism, which has many levels of organization.

Figure 1.5 Life Consists of Organized Systems at a Hierarchy of Scales (1)


• Organisms also interact with their physical environment and with each other, resulting in hierarchy in the larger biological world.

Figure 1.5 Life Consists of Organized Systems at a Hierarchy of Scales (2)

ECOSYSTEM


• A system is a set of interacting parts (components) in which neither the parts nor the whole can be understood without taking into account the interactions (processes).

• Systems are found at every level of biological organization.

Figure 1.6 A Generalized System

Figure 1.7 Organized Systems Exist at Many Levels


• Biological systems are dynamic: • Characterized by rapid flows of matter and

energy.• They constantly exchange energy and matter

with their surroundings.• But even though there is constant turnover of

atoms, molecules, etc., the organization of the systems persist.


• Feedback: the amount of one component in a system affects the rate of an earlier process in the system.

• Positive feedback occurs when a product of the system speeds up an earlier process.

• Negative feedback occurs when a product of the system slows down an earlier process.

Figure 1.8 Feedback Can Be Positive or Negative


• Positive feedback tends to destabilize a system (sometimes advantageous, provided it is ultimately brought under control).

• Negative feedback tends to stabilize systems and is very common in regulatory systems.


• Systems analysis is used to understand how biological systems function.

• The system components are identified, and processes by which the components interact are determined.

• Rates of interactions can be affected by feedback.

• Then we can analyze how the system will change through time.


• Mathematical equations express amounts of the different components and include processes and their rates, resulting in a computational model.


• If a computational model is well grounded in factual knowledge of the biological system, it will mimic the biological system.

• Computational models can be used for prediction, for instance, the future behavior of a system in a warming world.

• Parameters of the model are adjusted to take into account the expected increases in temperature.

Concept 1.3 Genetic Systems Control the Flow, Exchange, Storage, and Use of Information

• The genome is the sum total of all the information encoded by an organism’s genes.

• DNA consists of repeating subunits called nucleotides.

• A gene is a specific segment of DNA that contains information for making one or more proteins.

• Proteins govern chemical reactions in cells and form much of an organism’s structure.

Figure 1.9 DNA Is Life’s Blueprint


• All cells in a multicellular organism contain the same genome, but different cells have different functions.

• The different types of cells must express different parts of the genome.

• How cells control genome expression is a major focus of biological research.


• 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.

• They are used to study the genetic basis of everything from physical structure to inherited diseases and evolutionary relationships.

• Bioinformatics is the field of study that developed to organize and process the immense amount of data resulting from genome sequencing.

Concept 1.4 Evolution Explains the Diversity as Well as the Unity of Life

• Evolution is a change in genetic makeup of biological populations through time—a major unifying principle of biology.

• A common set of evolutionary mechanisms applies to all organisms.

• The constant change that occurs among populations gives rise to all the diversity of life.


• 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.

Figure 1.10 Adaptations to the Environment


• Two kinds of explanations for adaptations:

– Proximate explanations—immediate genetic, physiological, neurological, and developmental processes that explain how an adaption works.

– Ultimate explanations—what processes led to the evolution of an adaptation.


• 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 processes 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

Concept 1.5 Science Is Based on Quantifiable Observations and Experiments• Scientific investigations are based on

observation, experimentation, and reasoning.• Understanding the natural history of organisms

—how they get food, reproduce, behave, regulate functions, and interact with other organisms—facilitates observation and leads to questions.

Concept 1.5 Science Is Based on Quantifiable Observations and Experiments

• Observation is enhanced by technology—microscopes, imaging, genome sequencing, satellites.

• Observations must be quantified by measurement and mathematical and statistical calculations.

Concept 1.5 Science Is Based on Quantifiable Observations and Experiments• The scientific method (hypothesis–prediction

method):

1. Observations

2. Questions

3. Hypotheses

4. Predictions

5. Testing

Figure 1.11 Scientific Methodology


• To answer questions, biologists look at what is already known to form possible answers, or hypotheses.

• Predictions are made based on observations, and experiments are designed to test these predictions.


• Controlled experiments manipulate the factor, or variable, that is predicted to be causing the phenomenon being investigated.

• A method is devised to manipulate only that variable in an “experimental” group, which is compared with an unmanipulated “control” group.

Figure 1.12 Controlled Experiments Manipulate a Variable (Part 1)

Figure 1.12 Controlled Experiments Manipulate a Variable (Part 2)


• 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.

Figure 1.13 Comparative Experiments Look for Differences among Groups (Part 1)

Figure 1.13 Comparative Experiments Look for Differences among Groups (Part 2)


• 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.

Concept 1.5 Science Is Based on Quantifiable Observations and Experiments• Religious or spiritual explanations of natural

phenomena are not testable and therefore are not science.

• Science does not say that untestable religious beliefs are necessarily wrong, just that they cannot be addressed using scientific methods.

• Many advances in science raise ethical concerns. Science can not tell us how we should address these concerns.

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