Chapter 1 Exploring Life

The phenomenon we call life Defies a simple, one-sentence definition Figure 1.1

Overview Biology Is the scientific study of life What are some properties that all living things have in common? Made of cells Display order/organization Utilize energy Reproduction Growth and development Maintain homeostasis = regulation thru adjustments Respond to the environment Adapt to their environment = evolve

A Closer Look at Cells The cell Is the lowest level of organization that can perform all activities required for life 25 µm Figure 1.5

All cells share certain characteristics Two Main Forms of Cells All cells share certain characteristics They are all enclosed by a membrane They all use DNA as genetic information There are two main forms of cells Eukaryotic Prokaryotic

Nucleus (contains DNA) Two Main Forms of Cells Prokaryotic cells Lack the kinds of membrane-enclosed organelles found in eukaryotic cells EUKARYOTIC CELL Membrane Cytoplasm Organelles Nucleus (contains DNA) 1 µm PROKARYOTIC CELL DNA (no nucleus) Eukaryotic cells Are subdivided by internal membranes into various membrane-enclosed organelles

Living things are organized Concept 1.1: Biologists explore life from the microscopic to the global scale The study of life Extends from the microscope scale of molecules and cells to the global scale of the entire living planet The hierarchy of life Extends through many levels of biological organization:

…another example of organization Order comes from DNA / RNA which stores information about organism This genetic information can be copied & transmitted from cell to cell, and to next generation Also has the ability to change (mutation)

The molecular structure of DNA Accounts for it information-rich nature DNA Cell Nucleotide A C T G (b) Single strand of DNA. These geometric shapes and letters are simple symbols for the nucleotides in a small section of one chain of a DNA molecule. Genetic information is encoded in specific sequences of the four types of nucleotides (their names are abbreviated here as A, T, C, and G). (a) DNA double helix. This model shows each atom in a segment of DNA.Made up of two long chains of building blocks called nucleotides, a DNA molecule takes the three-dimensional form of a double helix. Figure 1.7 Nucleus

Living things are highly organized Biological systems are much more than the sum of their parts A system is a combination of components that form a more complex organization The Emergent Properties of Systems Due to increasing complexity, new properties emerge with each step upward in the hierarchy of biological order

For study purposes, organization must be examined Reductionism Involves reducing complex systems to simpler components that are more manageable to study

The study of DNA structure, an example of reductionism Organization The study of DNA structure, an example of reductionism Has led to further study of heredity, such as the Human Genome Project Figure 1.9

Living things utilize energy Plants obtain energy from sun and store it (sugars, carbohydrates) = autotrophic Animals must eat other living things (heterotrophic) Food forms building blocks for growth, as well as fuel Organisms often convert energy into movement as well as for staying alive

Living things arise through reproduction Key: pass on information (genes) from one generation to next Reproduction involves copying (replication) of DNA Information in DNA codes for structures as well as processes (metabolism) within cell Often also involves sex- each parent contributes half offspring’s DNA. Offspring differs from both parents Some reproduce without a mate (asexually). Make new individual by duplicating own DNA. Offspring identical to parent (clones).

Living Things Grow and Develop Most start small and increase in size, and/or in numbers of cells, over their lives Large organisms start as single cell (zygote), that divides millions of times to form baby Cells divide many more times in a lifetime Some cell division results in growth, but some goes to repair and maintenance E.g. replacement of skin and hair Egg cell Sperm cell Nuclei containing DNA Fertilized egg with DNA from both parents Embyro’s cells with copies of inherited DNA Offspring with traits inherited from Figure 1.6

Living things are Homeostatic To survive, must maintain tolerable (relatively constant) internal environment Much of energy acquired is used to maintain homeostasis When balance is disturbed, organisms get sick or die Temperature pH etc

Feedback Regulation in Biological Systems A kind of supply-and-demand economy Applies to some of the dynamics of biological systems In feedback regulation The output, or product, of a process regulates that very process

In positive feedback The end product speeds up production W Enzyme 4 X Y Z Enzyme 4 Enzyme 5 Enzyme 6 Positive feedback Figure 1.12

Living things Respond to Stimuli Detect and respond to information about environment Plants turn leaves to sun; grow roots toward water Animals move toward food, away from predators or toward own species Organism’s responses form basis of “behavior” Usually focused on procuring food, finding mates and avoiding injuries (self-preservation)

Living things are adapted, have evolved: All living things are exquisitely suited to their habitats and the roles they play within them Adaptations reflect evolutionary history in which environment shaped species Each individual has different DNA Some are more successful than others More successful organisms pass on more genes so successful traits increase until most have successful adaptations Genetic similarities: Organisms share some basic traits because they descended from same original cell (common ancestry) Genetic differences: Organisms are different because they’ve adapted to different habitats