Biological system functions

Examples at different levels of organization

Cells: 

• acquire energy from the environment in the form of light radiation (autotrophs) or chemical potential energy (heterotrophs), and acquire carbon in the form of carbon dioxide (autotrophs) or organic food molecules (heterotrophs)

• exchange water and respiratory gases (oxygen and carbon dioxide) with the external environment by diffusion across the plasma membrane

• use specialized transport proteins to carry ions and molecules across the plasma membrane, both passively (according to concentration gradients) and actively (against concentration gradients, with an energy expenditure)

• oxidize carbohydrates through processes (cellular respiration, fermentation) that harness chemical energy to produce ATP

• perform a great variety of endergonic metabolic reactions, powered by coupling with ATP hydrolysis 

• perform a great variety of oxidation-reduction (redox) reactions, enabled by cofactors that readily accept and donate electrons

Organisms:

• complex multicellular organisms (e.g., plants, animals) move water and nutrients throughout their bodies by bulk flow within vascular systems

• heterotrophs (animals) acquire matter and energy from the environment by ingesting bulk food, which they digest extracellularly to absorb its nutrient molecules

• allocate matter and energy to different functions (such as growth, defense, and reproduction) in ways that maximize fitness.

Populations:

• ...

Examples at different levels of organization

Cells: 

• store genetic information in molecules of DNA (chromosomes)

• produce RNA molecules and proteins with specific functions, based on information encoded in genes

• replicate their genomes and pass them onto daughter cells through mitosis, meiosis, or binary fission

• check the integrity of their genomes and repair damage to DNA

• regulate the timing and intensity of expression of their genes; consequently, cells can:

  • • differentiate and acquire specialized forms and functions within multicellular organisms, 

    • activate or inactivate specific genes in response to stimuli

Organisms:

• display physical and behavioral traits dependent on their genotypes. 

• transmit genetic information to their offspring via asexual or sexual reproduction. 

Populations:

• hold repositories of genetic variation (gene pools, composed of all the alleles carried by all individuals in the population). 

• move alleles into and out of other populations by migration (gene flow).

Examples at different levels of organization

Cells: 

• perceive chemical signals through protein receptors on their surface (or inside the cytoplasm) and respond to these signals

• in response to environmental or developmental cues, produce signal molecules that influence the functions of other cells, nearby or distant.

Organisms:

• sense changes in their internal and external environment. 

• use chemical, electrical, or other forms of signaling to coordinate responses to internal/external stimuli at the cellular, tissue, organ, and/or system level. 

• regulate their internal conditions to achieve homeostasis

• communicate with individuals of their species or other species