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A characteristic of life is a high degree of order. Biological organization is based on a hierarchy of structural levels, with each level building on the levels below it
- With each step upward in the biological hierarchy, new properties emerge that were not present at the simpler organizational levels
- Life is difficult to define because it is associated with numerous emergent properties that reflect a hierarchy of structural organization
Some of the emergent properties and processes associated with life are the following:
1. Order - Organisms are highly ordered, and other characteristics of life emerge from this complex organization
2. Reproduction - Organisms reproduce; life comes only from life (Biogenesis)
3. Growth and Development - Heritable programs stored in DNA direct the species-specific pattern of growth and development
4. Energy Utilization - Organisms take in and transform energy to do work, including the maintenance of their ordered state
5. Response to Environment - Organisms respond to stimuli from their environment
6. Homeostasis - Organisms regulate their internal environment to maintain a steady state, even in the face of a fluctuating external environment
7. Evolutionary Adaptation - Life evolves in response to interactions between organisms and their environment
Because properties of life emerge from complex organization, it is impossible to fully explain a higher level of order by breaking it into its parts
Holism = The principle that a higher level of order cannot be meaningfully explained by examining components parts in isolation
It is also difficult to analyze a complex process without taking it apart
Reductionism = the principle that a complex system can be understood by studying its component parts
Cell - basic unit of structure and function
- Lowest level of structure capable of performing all activities of life
- All organisms composed of cells
- May exist singly as unicellular organisms or as subunits of multicellular organisms
The invention of the microscope led to the discovery of the cell and the formulation of the cell theory
- Robert Hooke (1665) - reported a description of his microscopic examination of cork. Hooke described tiny boxes which he called "cells"(really cell walls)
- Antonie van Leeuwenhok (1600's) used the microscope to observe living organisms such as microorganisms in pond water, blood cells, and animal sperm cells
- Matthias Schleiden and Theodor Schwann (1839) reasoned from their own microscopic studies and those of others, that all living things are made of cells. This formed the basis for the cell theory
The cell theory has since been modified to include the idea that all cells come from preexisting cells
Over the past 40 years, use of the electron microscope has revealed the complex ultrastructure of cells
- Cells are bounded by plasma membranes that regulate passage of materials between the cell and its surroundings
- All cells, at some stage, contain DNA
Based on structural organization, there are two major kins of cells: prokaryotic and eukaryotic
- Prokaryotic cell - cell lacking membrane-bound organelles and a membrane-enclosed nucleus
- Found only in archaebacteria and bacteria
- Generally much smaller than eukaryotic cells
- Contains DNA that is not separated from the rest of the cell, as there is no membrane-bound nucleus
-Almost all have tough external walls
Eukaryotic cell - cell with membrane-enclosed nucleus and membrane-enclosed organelles
- Found in protists, plants, fungi, and animals
- Subdivided by internal membranes into different functional compartments called organelles
- Contains DNA that is segregated from the rest of the cell. DNA is organized with proteins into chromosomes that are located within the nucleus, the largest organelle of most cells
- Cytoplasm surrounds the nucleus and contains various organelles of different functions
- Some cells have a tough cell wall outside the plasma membrane (plant cells). Animal cells lack cell walls
Biological instructions for an organism's complex structure and function are encoded in DNA
- Each DNA molecule is made of four types of chemical building blocks called nucleotides
- The linear sequence of these four nucleotides encode the precise information in a gene, the inherit unit from parent to offspring
- An organism's complex structural organization is specified by an enormous amount of coded information
Inheritance is based on:
- A complex mechanism for copying DNA
- Passing the information encoded in DNA from parent to offspring
All forms of life use essentially the same genetic code
- A particular nucleotide sequence provides the same information to one organisms as it does to another
- Differences among organisms reflect differences in nucleotide sequence
There is a relationship between an organism's structure and how it works. Form fits function.
- Biological structure gives clues about what it does and how it works
- Knowing a structure's function gives insights about its construction
*This correlation is apparent at many levels of biological organization
Organisms interact with their environment, which includes other organisms as well as abiotic factors
- Both organism and environment are affected by the interaction between them
- Ecosystem dynamics include two major processes:
1. Nutrient cycling
2. Energy flow
Regulation of biological processes is critical for maintaining the ordered state of life
Many biological processes are self-regulating: that is, the product of a process regulates that process (=feedback regulation)
- Positive feedback speeds process up
- Negative feedback slows process down
Organisms and cells also use chemical mediators to help regulate processes
- The hormone insulin, signals cells in vertebrate organisms to take up glucose. As a result, blood glucose goes down
- In certain forms of diabetes, insulin is deficient and cells do not take up glucose as they should, as a result glucose levels remain high
Biological diversity is enormous
- Estimates of total diversity range from 5 million to over 30 million species
- About 1.5 million species have been identified and named, including approximately 260,000 plants, 50,000 vertebrates, and 750,000 insects
To make this diversity more comprehensible, biologist classify species into categories
Taxonomy = branch of biology concerned with the naming and classifying organisms
-Taxonomic groups are ranked into a hierarchy from the most to least inclusive category:
domain
kingdom
phylum
class
order
family
genus
species
The three domain are:
Archaea
Bacteria
Eukarya
- The kingdoms of life recognized in the traditional five-kingdom system are:
Monera
Protista
Plantae
Fungi
Animalia
There is unity in the diversity of forms at the lower levels or organization. Unity of life form is evident in:
- A universal genetic code
- Similar metabolic pathways
- Similarities of cell structure
Evolution is the one unifying biological theme:
- Life evolves. Species change over time and their history can be described as a branching tree of life
- Species that are very similar share a common ancestor at a recent branch point on the phylogenetic tree
- Less closely related organisms share a more ancient common ancestor
- All life is connected and can be traced back to primeval prokaryotes that existed more that three billion years ago
In 1859, Charles Darwin published On the Origin of Species in which he made two major points
1. Species change, and contemporary species arose from a succession of ancestors through a process of "descend with modification"
2. A mechanisms of evolutionary change is natural selection
Darwin synthesized the concept of natural selection based upon the following observations
- Individuals in a population of any species vary in many inheritable traits
- Populations have the potential to produce more offspring than will survive or the environment will support
- Individuals with the best suited traits will leave a large number of offspring which increases the proportion of inheritable variations in the next generation
Organism's adaptations to their environments are a product of natural selection
- Natural selection does not create adaptations; it merely increases the frequency of inherited traits by chance
- When exposed to environmental pressures, certain traits might favor reproductive success
Darwin proposed that cumulative changes in a population over long time spans could produce a new species from an ancestral one
- Similarities between two species may be a reflection of their descent from a common ancestor
- Differences may be the result of natural selection modifications
Science is a way of knowing. It is a human endeavor that emerges from our curiosity about ourselves, the world, and the universe
Good scientists are people who:
Scientific method = process which outlines a series of steps used to answer questions
- It is not rigid
- Based on the conviction that natural phenomena have natural causes
- Requires evidence to logically solve problems
The key ingredient of the scientific process is the hypothetico-deductive method, which is an approach to problem-solving that includes:
1. Asking a question and formulating a tentative hypothesis by inductive reasoning
2. Making hypothesis and then testing the validity of those predictions
Inductive reasoning = making an inference from a set of observations to reach a conclusion
Deductive reasoning = making an inference from general premises to specific consequences, which logically follow if the premises are true
- If... then logic
- Usually involves predicting experimental results that are expected if the hypothesis is true
Usefully hypothesis have the following characteristics:
- Are probable causes
- Reflect past experience
- Multiple hypotheses should be proposed whenever possible
- Must be testable via the hypothetico-deductive method
- Can be eliminated, but not confirmed with absolute certainty
Another feature of the scientific process is the controlled experiment
Control group = the group in which all variables are held constant
- Necessary for comparison with experimental group which has been exposed to a single changed variable
- Allows conclusions to be made about the effect of experimental manipulation
- Good controls = good experimental design
Variable = condition of an experiment that is subject to change and that may influence an experiments outcome
Experimental group = the group in which one factor is varied
Science is a never ending process that is a self-correcting way of knowing. Scientists:
- Build on prior knowledge
- Try to replicate observations and experiments of others to check their conclusions
- Share information
Science and technology are interdependent
- Technology extends our ability to observe and measure, which enables scientists to work on new questions that were previously unapproachable
- Science in turn, generates new information that makes new technological inventions possible
We have a love/hate relationship with technology
- Technology has improved our standard of living
- Technology has also created new problems
A better understanding of nature must remain the goal of science. Scientists should:
- Try to influence how technology is used
- Help educate the public about the benefits and hazards of technology
- Includes chemistry, physics and mathematics
- As well as humanities and the social sciences
There are levels of organization beyond the individual organism:
Population = Localized group of organisms belonging to the same species
Community = Populations of species living in the same area
Ecosystem = An energy-processing system of community interactions that include abiotic environmental factors such as soil and water
Biomes = Large scale communities classified by predominant vegetation type and distinctive combinations of plants and animals
Biosphere = The sum of all the planet's ecosystems
The study of biology balances the reductionist strategy with the goal of understanding how the parts of cells, organisms, and populations are functionally integrated
Though structurally different, eukaryotic and prokaryotic cells have many similarities, especially in their chemical processes