Big Idea 2: Biological Systems Utilize Free Energy and Molecular Building Blocks to Grow, to Reproduce, and to Maintain Dynamic Homeostasis.



Living systems require 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.

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 must 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. Differences in surface-to-volume ratios affect the capacity of a biological system to obtain resources and eliminate wastes. Programmed cell death (apoptosis) plays a role in normal development and differentiation (e.g. morphogenesis).

Membranes allow cells to create and maintain internal environments that differ from external environments. The structure of cell membranes results in selective permeability; the movement of molecules across them via osmosis, diffusion and active transport maintains dynamic homeostasis. In eukaryotes, internal membranes partition the cell into specialized regions that allow cell processes to operate with optimal efficiency. Each compartment or membrane-bound organelle enables localization of chemical reactions.

Organisms also have feedback mechanisms that maintain dynamic homeostasis by allowing them to respond to changes in their internal and external environments. Negative feedback loops maintain optimal internal environments, and positive feedback mechanisms amplify responses. Changes in a biological system’s environment, particularly the availability of resources, influence responses and activities, and organisms use various means to obtain nutrients and get rid of wastes. Homeostatic mechanisms across phyla reflect both continuity due to common ancestry and change due to evolution and natural selection; in plants and animals, defense mechanisms against disruptions of dynamic homeostasis have evolved. Additionally, the timing and coordination of developmental, physiological and behavioral events are regulated, increasing fitness of individuals and long-term survival of populations.



Enduring understanding 2.A: Growth, reproduction and maintenance of the organization of living systems require free energy and matter.

Essential knowledge 2.A.3: Organisms must exchange matter with the environment to grow, reproduce and maintain organization.




Chapter 3 Presentation-Water and The Fitness of The Environment



Enduring understanding 2.A: Growth, reproduction and maintenance of the organization of living systems require free energy and matter.
Enduring understanding 1.D: The origin of living systems is explained by natural processes.


Essential knowledge 1.D.1: There are several hypotheses about the natural origin of life on Earth, each with supporting scientific evidence.
Essential knowledge 2.A.3: Organisms must exchange matter with the environment to grow, reproduce and maintain organization.




Chapter 4 Presentation-Carbon and The Molecular Diversity of Life

Enduring understanding 3.A: Heritable information provides for continuity of life.
Enduring understanding 4.A: Interactions within biological systems lead to complex properties.
Enduring understanding 4.B: Competition and cooperation are important aspects of biological systems.
Enduring understanding 4.C: Naturally occurring diversity among and between components within biological systems affects interactions with the environment.


Essential knowledge 3.A.1: DNA, and in some cases RNA, is the primary source of heritable information.
Essential knowledge 4.A.1: The subcomponents of biological molecules and their sequence determine the properties of that molecule.
Essential knowledge 4.B.1: Interactions between molecules affect their structure and function.
Essential knowledge 4.C.1: Variation in molecular units provides cells with a wider range of functions.




Chapter 5-The Structure and Function of Macromolecules

Peptide Bond Formation


Enduring understanding 2.A: Growth, reproduction and maintenance of the organization of living systems require free energy and matter.
Enduring understanding 2.B: Growth, reproduction and dynamic homeostasis require that cells create and maintain internal environments that are different from their external environments.
Enduring understanding 4.A: Interactions within biological systems lead to complex properties.
Enduring understanding 4.B: Competition and cooperation are important aspects of biological systems.


Essential knowledge 2.A.3: Organisms must exchange matter with the environment to grow, reproduce and maintain organization.
Essential knowledge 2.B.3: Eukaryotic cells maintain internal membranes that partition the cell into specialized regions.
Essential knowledge 4.A.2: The structure and function of subcellular components, and their interactions, provide essential cellular processes.
Essential knowledge 4.B.2: Cooperative interactions within organisms promote efficiency in the use of energy and matter.




Chapter 6 Presentation-A Tour of The Cell

Enduring understanding 2.B: Growth, reproduction and dynamic homeostasis require that cells create and maintain internal environments that are different from their external environments.

Essential knowledge 2.B.1: Cell membranes are selectively permeable due to their structure.
Essential knowledge 2.B.2: Growth and dynamic homeostasis are maintained by the constant movement of molecules across membranes.




Chapter 7 Presentation-Membrane Structure and Function

Enduring understanding 2.A: Growth, reproduction and maintenance of the organization of living systems require free energy and matter.
Enduring understanding 4.B: Competition and cooperation are important aspects of biological systems.


Essential knowledge 2.A.1: All living systems require constant input of free energy.
Essential knowledge 4.B.1: Interactions between molecules affect their structure and function.




Chapter 8 Presentation-An Introduction to Metabolism

Enduring understanding 2.A: Growth, reproduction and maintenance of the organization of living systems require free energy and matter.

Essential knowledge 2.A.1: All living systems require constant input of free energy.
Essential knowledge 2.A.2: Organisms capture and store free energy for use in biological processes.




Chapter 9 Presentation-Cellular Respiration: Harvesting Chemical Energy

Enduring understanding 2.A: Growth, reproduction and maintenance of the organization of living systems require free energy and matter.

Essential knowledge 2.A.1: All living systems require constant input of free energy.
Essential knowledge 2.A.2: Organisms capture and store free energy for use in biological processes.




Chapter 10 Presentation-Photosynthesis


Enduring understanding 3.A: Heritable information provides for continuity of life.

Essential knowledge 3.A.2: In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization.




Chapter 12 Presentation-The Cell Cycle

The Cell Cycle and Mitosis Animation

The Cell Cycle and Mitosis Animation II