D CONTINUITY and CHANGE

Genes transmitted from one generation to the next ensure the perpetuation of life across all species. The remarkable diversity in chromosomal combinations resulting from meiosis, coupled with the occurrence of gene or chromosomal mutations, ensures that offspring are not only distinct from their parents but also from one another. These variations in alleles, and occasionally the emergence of new alleles, enable natural selection to drive the development of novel adaptations. Consequently, the characteristics of any species evolve gradually over time.

At the cellular or organismal level, the concept of continuity and change is exemplified by the dynamic systems of homeostasis. For instance, the concentration of glucose in the blood fluctuates during periods of feeding and fasting, yet remains remarkably stable within narrow limits, thanks to the regulatory actions of insulin and glucagon hormones interacting with liver hepatocytes.

On a larger scale, biomes and ecosystems exhibit profound continuity and resilience. Rainforests, some of Earth’s oldest ecosystems, have persisted for at least 70 million years. At the organism level, trees often outlive animals, with many species thriving for centuries. One notable example is the Patagonian cypress in Chile, which can live for over 3,000 years. However, these ancient systems are now facing unprecedented threats from climate change and unsustainable human exploitation, with changes occurring at a pace potentially too rapid for natural adaptation.
 

These topics have been chosen to illustrate the theme of Continuity and change:

 

D1.1 DNA replication
D1.2 Protein synthesis
D1.3 Mutations and gene editing
D2.1 Cell and nuclear division
D2.2 Gene expression [HL only]
D2.3 Water potential
D3.1 Reproduction
D3.2 Inheritance
D3.3 Homeostasis
D4.1 Natural selection
D4.2 Stability and change
D4.3 Climate change