1. What is Life?

2. 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?

3. In 1976, NASA landed two Viking landers on Mars in hopes of finding life on the planet

4. Viking Lander analyzing soil samples

5. Viking Biological Experiments The Gas Exchange Experiment (GEX) involved injecting gases (O 2, CO 2 ). 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 would show the tagging 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.

6. Results ExperimentResponse for sample Response for heat-sterilized control GEXno change LRlabeled CO 2 emitted none PRno organics detected

7. LR: The test sample released significant amounts of radioactivity but was determined to be a false positive

8. Unifying Principles of Life Evolution: living things change over time through natural selection Homeostasis: living things regulate their internal environment Energy and Organization: living things are made up of highly organized matter (cells) that use energy to carry out life processes Continuity Continuity: living things contain the genetic material DNA which is passed from parent to offspring during reproduction Development: living things grow and develop over their life Ecology: living things interact with their living and non-living environment

9. Unifying Principles of Life Can you find the unifying principles in the above pictures?

10. Domains and Kingdoms of Life DomainArchaeaBacteriaEukarya KingdomSeveral ProtistaFungiPlantaeAnimalia # of cells Type of cell Mode of nutrition Examples

11. Domains and Kingdoms of Life Domain ArchaeaBacteriaEukarya KingdomSeveral ProtistaFungiPlantaeAnimalia # of cells Unicellular Uni or Multi Multi Type of cell Prokaryotic Euk Mode of nutrition Autotrophic or Heterotrophic Auto or Hetero HeteroAutoHetero

12. Domains and Kingdoms of Life Archaea, bacteria, fungi, and plant cells have a cell wall surrounding the cell membrane, but the structure of the cell wall differs between each group (not homologous). Multicellular protists lack specialized tissues and organs found in fungi, plants, and animals. Most autotrophy occurs via photosynthesis, but some bacteria and archaea can use energy in chemicals to make food. Heterotrophy occurs by ingestion (internal digestion) in animals and absorption (external digestion) in fungi and bacteria. Most animals have a nervous system and can move.

13. Domains and Kingdoms of Life

14. Prokaryotes vs. Eukaryotes ProkaryoteEukaryote No nucleus (DNA not enclosed)DNA in nucleus No membrane-enclosed structures Membrane-enclosed structures 0.1-10 micrometers (µm)10-1000 micrometers (µm) Evolved 3.5 billion years agoEvolved 1.5 billion years ago Kingdoms: Bacteria, ArchaeaKingdoms: Protista, Fungi, Plantae, Animalia

15. Size of life

16. Domains and Kingdoms of Life

17. Are Viruses Alive?