Chapter 1- Biology: The Study of Life

1.1 What Does It Mean to Say that Something is Alive

• An organism is a life form- a living entity made up of one or more cells.
• ==Organisms share a suite of five fundamental characteristic:==
  • Cells: Organisms consist of membrane-bound units called cells
  • Replication: Almost everything an organism does contributes to one goal: replicating itself.
  • Information: Organisms process hereditary, or genetic, information encoded in units called genes. Cells throughout your body are using information stored in your genes to make the substances, or molecules
  • Energy: To stay alive and reproduce, organisms have to acquire and use energy.
  • Evolution: Organisms are the products of evolution, and their populations continue to evolve today.
• Three of the greatest unifying ideas in all of science are:
  • (1) the cell theory
  • (2) the chromosome theory of inheritance
  • (3) the theory of evolution.
• Scientists define a theory as an explanation for a veηr broad class of observed phenomena that is supported by a wide body of evidence.

1.2 Life is Cellular and Replicates through Cell Division

• ==All organisms are made of cells==
• The complete cell theory builds on this concept: All organisms are made of cells, and all cells come from preexisting cells.
• The all-cells-from -cells explanation was a hypothesis: a testable statement to explain a set of observations.
• Experiments are a powerful scientific tool because they allow researchers to test the effect of a single, well-defined factor on a particular phenomenon.
• An experimental prediction describes a measurable or observable result that must be correct if a hypothesis is valid.
• Biologists now have evidence that life arose from nonlife early in Earth’s history, through a process called chemical evolution

1.3 Life Processes Information and Requires Energy

• Chromosome theory of inheritance:  Inside cells, hereditary or genetic information is encoded in units called genes 1at are located on chromosomes.
• A chromosome consists of a molecule of deoxyribonucleic acid, or DNA. To sum up, DNA is 1e hereditary material.
• ==Genes consist of specific segments of DNA that code for products in the cell.==
• Each strand of the double helix is made up of varying sequences of four molecular building blocks, each containing a different kind of base
• The central dogma-first articulated by Crick-describes the flow of information in cells.
• Molecular machinery in cells makes a copy of a particular gene’s information in the form of a closely related molecule called ribonucleic acid, or RNA.
• Proteins are crucial to most tasks required for a cell to exist, from forming structural components to promoting the chemical reactions that sustain life.
• Organisms have two fundamental nutritional needs-chemical energy in the form of a molecule called ATP ( or adenosine triphosphate) and molecules that can be used as building blocks

1.4 Life Evolves

• Evolution is a change in the characteristics of a population over time.
• A population is defined as a group of individuals of the same species living in the same area at the same time.
• The great insight by Darwin and Wallace was in proposing a process, called natural selection, that explained how evolution occurs.
• ==Natural selection occurs whenever two conditions are met:==
  • (1) Individuals within a population vary in characteristics that are heritable-meaning, traits that can be passed onto offspring.
  • (2) In a particular environment, certain versions of these heritable traits help individuals survive better and reproduce more than do other versions.
• Fitness means an individual’s ability to produce viable offspring relative to that ability in other individuals in the population.”
• Adaptation is a heritable trait that increases the fitness of an individual in a particular environment relative to individuals lacking that trait.

1.5 The “Tree of Life” Depicts Evolutionary History

• The theory of evolution by natural selection predicts that biologists should be able to construct a tree of life-a family tree of organisms.
• Their goal was to understand the phylogeny of all organisms and their actual genealogical relationships.
• A diagram that depicts evolutionary history in this way is called a phylogenetic tree.
• Researchers who study the origin of life propose that the tree’s root extends all the way back to a “last universal commonαncestor of cells, or LUCA.
• ==There are three fundamental groups or lineages of organisms:==
  • (1) the Bacteria
  • (2） the Archaea
  • (3) the Eukarya
• In all eukaryotes (literally,“true-kernel”), cells have a prominent component called the nucleus
• The vast majority of bacterial and archaeal cells lack a nucleus, they are referred to as prokaryotes
• In science, the effort to name and classify organisms is called taxonomy.
• Any named group at any level of a classification system is called a taxon
• Based on the tree of life, Woese proposed a new taxonomic category called the domain.
• Biologists today often use the term phylum (plural: phyla) to refer to major lineages within each domain.
• Each type of organism is assigned a two-part name:
  • Genus The first part of 1e two-part name indicates the organism’s genus (plural: genera). A genus is made up of a closely related group of species.
  • Species name The second term in the name identifies the organism’s species.
• An organism’s genus and species designation is called its scientific name, or Latin name.

1.6 Doing Biology

• A null hypothesis specifies what should be observed when the hypothesis being tested isn’t correct.
• A control checks for factors, other than the one being tested, that might influence the experiment’s outcome.
• ==The experimental conditions must be as constant or equivalent as possible.==
• ==The experimental conditions must be as constant or equivalent as possible.==
• Hypothesis testing is a two-step process:
  • Step 1: State the hypothesis as precisely as possible and list the predictions it makes.
  • Step 2: Design an observational or experimental study that is capable of testing those predictions.

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