Biology…What is it? Biology is the study of life. SO….What does it mean to be living?

Characteristics of Life To be considered living, an organism must….. 1. Be based on a universal genetic code. –DNA 2. Grow and develop

Characteristics of Life 4. Use materials and energy - Metabolism 3. Be able to R eproduce -Asexually -Sexually

Characteristics of Life 5. Be able to respond to their environment -stimulusresponse  Humans:  Plants:

Characteristics of Life 6. Maintain stable internal environment -Homeostasis

Characteristics of Life 7. Change over time, as a group. -Evolution 8.Made of units called Cells -Unicellular -Multicellular

Cell Theory Matthias Schleiden concluded that all plants are made of cells (1838) Theodore Schwann concluded that all animals are made of cells (1839) Rudolf Virchow concluded that all cells came from pre-existing cells (1855) Cell Theory all living things are made up of cells cells are the basic units of structure and function in an organism new cells are produced from existing cells

Levels of Organization LevelFunctionExample OrganismSingle living thing Organ SystemDifferent organs function together OrganDifferent tissues function together TissuesSimilar cells function together CellsSmallest unit of life Molecules Smallest unit of a substance with the same properties AtomSmallest unit of matter Nervous System Brain Nervous Tissue Nerve Cell Protein Carbon Human

Viruses…Living or not?  Now that we know what makes something living, let’s look at a virus. Viruses come in many different shapes and they cause many different diseases but, they all have something in common….

Viruses and Living Cells CharacteristicVirusCell StructureGenetic material surrounded by a protein capsid Cell membrane, cytoplasm; genetic material, ribosomes ReproductionOnly within a host cellYes, sexually and asexually Genetic CodeDNA or RNADNA Growth and Development NoYes Obtain and Use Energy NoYes Response to Environment NoYes EvolveYes HomeostasisNoYes

Verdict?  No, Viruses are not considered a living thing because they do not meet all of the living characteristics.