C INTERACTION and INTERDEPENDENCE

The dynamic interactions between molecules and cells are fundamental to understanding biological processes. For instance, the diffusion of oxygen across a cell membrane and its role in accepting electrons within the mitochondria exemplify crucial molecular interactions that sustain life. These interactions are pervasive across all levels of biological organization.

As we scale up from molecules to cells, we observe complex interactions such as neurons communicating through synapses, which collectively contribute to the emergence of consciousness in the brain. Similarly, at the level of organisms and populations, interactions become evident in different contexts. Viruses like HIV or COVID-19 spread through human contacts, illustrating how organism-level interactions can influence disease dynamics. 

Furthermore, ecological interactions, such as those driving populations toward carrying capacities, underscore the impact of density-dependent factors within ecosystems. The carbon cycle is a prime example of how entire ecosystems are interconnected at the largest scale of biological organization.

Exploring these themes further, it becomes intriguing to compare how the concentration of enzymes and substrates affects the rate of biochemical reactions to how population density influences competition and predation within communities. Both scenarios reflect the profound impact of quantitative factors on biological systems, providing a fascinating parallel that highlights the universal principles governing interactions from microscopic to macroscopic levels.

 

These topics have been chosen to illustrate the theme of Interaction and interdependence:

 

C1.1 Enzymes and metabolism
C1.2 Cell respiration
C1.3 Photosynthesis
C2.1 Chemical signalling [HL only]
C2.2 Neural signalling
C3.1 Integration of body systems
C3.2 Defence against disease
C4.1 Populations and communities
C4.2 Transfers of energy and matter