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What is Life?. What is the definition of life ?. There have been many definitions of life created over the years. There has yet to be a definition that has been broadly accepted. We need to understand what qualifies matter as living if we are to find life elsewhere in the Universe.
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What is the definition of life? • There have been many definitions of life created over the years. There has yet to be a definition that has been broadly accepted. • We need to understand what qualifies matter as living if we are to find life elsewhere in the Universe. • Can life exist somewhere other than earth? If so, where? Would it be anything like earth life?
In 1976, NASA landed two Viking landers on Mars in hopes of finding life on the planet
Viking Biological Experiments • The Gas Exchange Experiment (GEX) involved injecting gases (O2, CO2). into a test chamber containing a soil sample. Looking for changes in the makeup of gases in a test chamber that might indicate that the gases were taken up by living things. • The Labeled Release Experiment (LR) was set up to detect the uptake of a radioactively-tagged liquid nutrient by living things. The idea was that gases emitted by these living things (like CO2) would show the tag indicating that they consumed the nutrient. • The Pyrolytic Release Experiment (PR) involved "cooking" soil samples that had been exposed to radioactively-tagged gases to see if the chemical had been used by organisms to make organic compounds (food).
LR: The test sample released significant amounts of radioactivity, but the results could not be replicated.
Unifying Principles of Life Evolution: living things (populations) change over time through natural selection Homeostasis: living things maintain a stable internal environment Energy and Organization: living things are made up of highly organized matter (cells) that uses energy to carry out life processes Continuity: living things contain the genetic material DNA which is passed from parent to offspring during reproduction Development: living things grow and develop Ecology: living things interact with their living and non-living environment
Unifying Principles of Life Can you find the unifying principles in the above pictures?
Domains and Kingdoms of Life • Archaea, bacteria, fungi, and plant cells have a cell wall surrounding their cell membranes, but the structure of the cell wall differs between each group (not homologous). • Most autotrophs use sunlight to make food (photosynthesis), but several autotrophic archaea and bacteria use high energy chemicals to make food (chemosynthesis). • Multicellular protists and fungi lack specialized tissues and organs found in plants and animals. • Heterotrophy in animals is characterized by ingestion of food for internal digestion, unlike heterotrophy in bacteria and fungi where digestion occurs externally (decomposition).
