1) What are key grand challenges in our field-- both scientific and technical? A complete mechanistic understanding of function and structure of living systems -- integrating bottom up (constructive) approaches scaling up from ab-initio and molecular models, to top-down (deconstructive) approaches that work down from funciton/phenotype (disease) to underlying structures. While bottom-up techniques have received significant research attention (with complex codes capable of scalable parallel performance now available), relatively lesser attention has been focused on a systems-level, deconstructive approach to modeling. It is in this realm that significant potential for radical advances appears likely. Within systems level modeling, the key technical challenges include high-throughput data generation, curation, and publication for large number of species, effective and efficient tools for analysis, inference, and modeling, statistical and computational tools for bridging phenotype, genotype, and the associated interaction cascades, and techniques for guiding experimental studies. The high-level goal, of ocurse, is a comprehensive computational model of a living cell, modeling all of the processes in complete detail, with the ability to instrument change and observe behavior all the way from atomistic detail to phenotype. 2) What is the impact of achieving them? 3) Which of these have computation as a bottleneck and what new theory or algorithms need to be developed to achieve them? 4) What day-to-day science in our area could be aided by extreme computing- not grand challenges but things we have to do anyway that are leading to great science and important technological advance?