Topics: Osmosis, Photosynthesis, Cell Pages: 13 (5542 words) Published: November 1, 2014

Big Idea 2
Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to maintain dynamic homeostasis. Living systems require both free energy and matter to maintain order, grow and reproduce. Organisms employ various strategies to capture, use and store free energy and other vital resources. Energy deficiencies are not only detrimental to individual organisms; they also can cause disruptions at the population and ecosystem levels. Biological systems must both capture free energy and then transform the energy into usable forms. Autotrophic cells capture free energy through photosynthesis and chemosynthesis. Photosynthesis traps free energy present in sunlight that, in turn, is used to produce carbohydrates from carbon dioxide. Chemosynthesis captures energy present in inorganic chemicals. Cellular respiration and fermentation harvest free energy from sugars to produce free energy carriers, including ATP. The free energy available in sugars drives metabolic pathways in cells. Photosynthesis and respiration are interdependent processes. Cells and organisms exchange matter with the environment. For example, water and nutrients are used in the synthesis of new molecules; carbon moves from the environment to organisms where it is incorporated into carbohydrates, proteins, nucleic acids or fats; and oxygen is necessary for more efficient free energy use in cellular respiration. These processes release matter to the environment as waste products. For example, cellular respiration will release carbon dioxide. In addition, programmed cell death (apoptosis) plays a role in normal development and differentiation (e.g., morphogenesis). Differences in surface-to-volume ratios affect the capacity of a biological system to obtain resources and eliminate wastes. Membranes allow cells to create and maintain internal environments that differ from external environments. The structure of cell membranes results in selective permeability preventing molecules with certain characteristics from passing through the membrane while allowing others to pass. Processes that maintain dynamic homeostasis by allowing the movement of molecules across membranes include osmosis, diffusion and active transport. In eukaryotes, internal membranes partition the cell into specialized regions. Each region provides a localization of chemical reactions allowing the cell processes to operate with optimal efficiency. Feedback mechanisms maintain dynamic homeostasis within an organism by regulating responses to changes in both internal and external environments. Negative feedback loops maintain optimal internal environments while positive feedback mechanisms amplify responses. Changes in a biological system’s environment, particularly the availability of resources, influence an organism’s responses and activities. Organisms use various means to obtain nutrients and remove wastes. Homeostatic mechanisms across phyla reflect both continuity due to common ancestry and change due to evolution and natural selection. Examples of homeostatic mechanisms that have evolved in plants and animals include defense mechanisms as well as the timing and coordination of developmental, physiological and behavioral event regulation. These mechanisms increase the fitness of individuals and long-term survival of populations. Units in AP Biology Course

Be sure to know the following:
01A – Viruses and Cells
How organelles use and produce ATP.
How organelles maintain homeostasis within cells.
01B – Homeostasis in Cells
All the notes in the unit.
How to use the water potential formula to calculate water potential values. 01C – Replication of Viruses and Cells
The cell cycle and regulation of the cell cycle via check points (cyclins, CDKs, MPFs, and PDGFs) Three phases of interphase and alternation of interphase with mitosis The sequence of events in mitosis (replication, alignment, separation) How the reduction division of meiosis...
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