Introduction to Biology

• Biology is the study of life.
• There is no concise definition of "life".
• Scientists define life by a combination of characteristics.

Characteristics of Life:

• Organization: Atoms, molecules, organelles, cells, tissues, organs, and organ systems
• Sensitivity or Response to Stimuli: Organisms responding to diverse stimuli.
• Energy Use: Metabolism
• Maintenance of Internal Consistency: Homeostasis
• Reproduction, Growth and Development: Sexual and Asexual Reproduction
• Evolution: Natural Selection

Life's Organization Hierarchy

• Atom: The smallest chemical unit of a pure substance (element), e.g. Carbon atom.
• Molecule: A group of joined atoms, e.g. DNA.
• Organelle: A membrane-bounded structure that has a specific function in a cell.
• Cell: The fundamental unit of life, is Unicellular and Multicellular.
• Tissue: A collection of specialized cells that function in a coordinated fashion, e.g. Epidermis of a leaf.
• Organ: A structure consisting of tissues organized to interact and carry out specific functions, e.g. Leaf.
• Organ System: Organs connected physically or chemically which function together.
• Organism: A single living individual, e.g. One acacia tree.
• Population: A group of the same species of organisms living in the same place and time, e.g. multiple acacia trees.
• Community: Populations of different species that occupy the same region at the same time, e.g. all populations in the savanna.
• Ecosystem: The living and non-living components of the area, e.g. the savanna.
• Biosphere: The global ecosystem, the parts of the planet and its atmosphere where life is possible.

Sensitivity or Response to Stimuli

• Organisms respond to different stimuli, such as plants bending towards sunlight.
• Tiny bacteria move towards or away from chemicals (Chemotaxis) or light (phototaxis).
• Response to Stimuli can be positive or negative.
• Movement towards a stimulus is known as a positive response
• Movement away from a stimulus is known as a negative response.

Life requires energy

• Countless chemical reactions sustain life inside each cell, which are collectively called metabolism.
• Organisms use metabolism to acquire and use energy and nutrients to build new structures, repair old ones, and reproduce.
• Organisms are divided into broad categories based on their source of energy.
• Autotrophs/Primary producers: Make their own food by extracting energy and nutrients from non-living sources.
• Heterotrophs/Consumers: Obtain energy and nutrients by eating other organisms, living or dead.
• Decomposers: Heterotrophs that absorb energy and nutrients from wastes or dead organisms.

Life maintains constancy

• Conditions within a cell must remain within a constant range even if the surrounding environment changes.
• A cell must contain a certain temperature or it will die if it becomes too hot or cold.
• Cells must take in nutrients, excrete waste, and regulate chemical reactions to prevent shortages or surpluses of essential substances.
• Homeostasis: The state of internal constancy.
• Cells must maintain homeostasis by counteracting changes as they occur, sense stimuli, and react.

Life reproduces, grows, and develops

• Organisms reproduce other organisms that are similar to them.
• Reproduction transports DNA from generation to generation.
• Genetic information defines the inherited characteristics of offspring.
• Reproduction occurs in two basic ways: Asexually and Sexually.
• Asexually: Genetic information comes from one parent and all offspring are virtually identical, e.g., bacteria reproduce asexually by doubling and dividing the contents of the cell.
• Sexual reproduction: Genetic traits from two parents unite and have an offspring, which has a new combination of inherited traits.
• Mixing genes at each generation results in diversity in a population.
• Genetic diversity enhances the chances that some individuals will survive even if conditions change.
• Sexual reproduction is very successful, especially in environments where conditions change.
• Sexual reproduction is common among plants, animals, and fungi.
• Each organism has to develop into an adult before it can reproduce.

Life evolves

• Life ensures that organisms are well suited for their the environment. For example, teeth of organisms that feed on wood are structured to support that diet.
• Organisms evolve characteristics to fit their environment which will have greater reproductive success subject to the forces of natural selection.
• Evolution is the process of gradual change during which new species arise from older species.
• Adaptation: An inherited characteristic or behavior that enables an organism to survive and reproduce successfully in its environment.
• Offspring that outcompete others and live long enough to reproduce are those with the best adaptations.

The diversity of life

• There is tremendous diversity of life on Earth, all originating from evolution.
• In the 18th century Carl Linnaeus first proposed organizing organisms into a hierarchical system, where similar organisms are grouped together

Taxonomy

• Taxonomy: The science of branching and classifying organisms.
• Species: The basic unit of classification which designates a distinctive "type" of organism.
• Genus: Closely related species grouped into the same genus.
• Genus species: Together, they denote the unique two-word scientific name of each species, for example: Homo sapiens, Musca domestica, and Felis catus (can be italicized or underlined).
• Binomial nomenclature: Biological system of naming organisms in which the name is composed of two terms, where the first term indicates the genus and the second term indicates the species of the organism.
• Taxonomy involves more than simply naming organisms.
• Taxonomists strive to classify organisms by evolutionary relationships.
• How recently one type of organism shared an ancestor with another type.
• The more recently diverged from a common ancestor, the more closely related they are presumed to be.

Domains

• Broadest taxonomic category is the Domain.
• Prokaryotes: Single-celled organisms whose cells lack a nucleus and other membrane-bounded organelles. Most are Unicellular. Included in this group are Archea and Bacteria.
• Eukaryotes: Organisms composed of one or more cells containing a nucleus and other membrane-bounded organelles. Can be Unicellular or Multicellular.
  • Domain Eukarya Kingdoms: Kingdom Protista, Kingdom Animalia, Kingdom Fungi and Kingdom Plantae
• Genetic evidence suggests all species fall into one of three domains.
• Classifying an organism occurs from the Domain to the species being classified.
• Each classification category is based on certain characteristics in an organism.

The Scientific Method

• Scientists use evidence to answer questions about the natural world.
• Biology is a rapidly changing field.
• Scientific knowledge arises from the application of the Scientific Method.
• Scientific Method: A general way of using evidence to answer questions and test ideas.
• Science combines: Thinking, detective work, collaboration with other scientists, learning from mistakes, and noticing connections.

Observations and asking questions

• The Scientific Method begins with observations and asking questions.
• Observations and asking questions can rely on what we can see, hear, touch, taste or smell, or existing knowledge/experimental results.
• Connections between previously unrelated observations can take place by combining multiple points of information.

Hypothesis and Predictions

• Hypothesis: A tentative explanation for one or more observations. Essential for scientific inquiry.
• Hypotheses must be testable with data that can support or reject it.
• Hypotheses become more widely accepted when multiple lines of evidence support them.
• Hypotheses cannot be proven true.
• Hypotheses should lead to a specific prediction.
• Prediction: Anticipated outcome of the test of a hypothesis. Often written as an "if" statement.

Data collection

• Conclusion are drawn based on the data collected.
• Data may come from careful observation of the natural world.
• Data can also be collected by carrying out an experiment to test the hypothesis under controlled conditions.
• Discovery and experimentation work hand-in-hand.

Analysis and peer review

• After collecting and interpreting data, investigators decide whether the evidence supports or falsifies the hypothesis.
• Often, the most interesting results are unexpected, which can provide new observations that force scientists to rethink their hypothesis.
• Science advances as new information arises and explanations continue to improve.
• Once a scientist has enough evidence to support or reject a hypothesis, they write a paper and submit it for publication in a relevant journal.
• Journal editors send the paper to anonymous reviewers who are knowledgeable about the topic to conduct a peer review.
• Scientists evaluate the validity of the methods, data, and conclusions.
• Peer reviews ensure that journal articles are of high quality.

Experiment Design

• An experiment's design should be clear and follow a specific plan.
• Sample size: One of the most important decisions which must be made when designing an experiment.
• Variables: A changeable element of an experiment.
• Independent variable: Factor that the investigator manipulates to determine whether it causes another variable to change.
• Dependent variable: Any response that depends on the value of the independent variable.
• Standardized variable: Anything the investigator holds constant for all subjects in the experiment, ensuring the best chance of detecting the effect of the independent variables.
• Control: Provides a basis for comparison in measuring the effect of the independent variable.
• Sometimes the experiment evidence may lead to multiple interpretations.
• Sometimes the carefully planned experiment can fail to provide a definitive answer.
• Even though scientists may make mistakes, science is self-correcting because it remains open to new data and interpretations.

Science ethics

• Scientists must ensure that their efforts do not cause undue damage to humans, animals, or the environment.
• Efforts also include ensuring that research and communication are free of bias.
• Bioethics define the guidelines to current practice, originating from unethical practices where biologists did not treat research subjects with dignity and harmed them, such as the 1932 syphilis study (399 African American men).
• Bioethicists have to weigh the positive with the negative, balancing the benefits with harm, and considering the dignity of the person.
• Even with animals, ethics clearance is required, e.g., frog dissections.