Life on earth is composed of cells. Highly complex and often quite specialized, cells of organisms belonging to each of the kingdoms of life (such as plants, animals, and prokaryotes) have distinctive features, organelles and functions. All cells, however, share certain common properties. Biological equilibrium (homeostasis) is maintained by cells. In particular this function is served by the cell membrane as it regulates the movement of materials into and out of the cell by passive (diffusion and osmosis) and active transport. Cells must process energy to function (respiration), with some cells having the capability to capture solar energy and store it in chemical form for later use (photosynthesis). The chemical processes of photosynthesis and respiration form the biological basis of the global carbon cycle.
Our understanding of the structure and function of cells has been dependant on the development of scientific tools. Light microscopes, electron microscopes, and other technologies that allow exploration at cellular scales have been critical in the development of our current concept of the living cell.
The structure and function of living cells is determined by DNA. Understanding the structure of DNA and its primary and critical function to control and direct cellular protein synthesis is central to an understanding of the nature of living cells. The processes of cellular reproduction, whether mitosis (production of diploid daughter cells) or meiosis (production of haploid sex cells), are strongly linked to the cells’ need to produce precise and accurate copies of the original DNA prior to cell division. In eukaryotic cells, DNA is organized into separate strands called chromosomes. Chromosomes abnormalities, or change in DNA base sequences that make up the chromosomes (mutations) can cause significant changes in organisms.
Our current understanding of DNA, genes, and chromosomes, along with Mendel’s laws of inheritance and tools such as Punnett squares and pedigrees allows us to trace inheritance of many traits through generations, and can sometimes allow us to predict the probabilities of traits in future generations as well. Moreover, modern genetic engineering technology can alter and/or determine inherited traits.
Ecosystems consist of multiple organisms interacting in a complex web of relationships strongly influenced by the characteristics and constraints of the surrounding environment. These relationships control both the ecosystem structure and flow of energy and matter through the system as well. Because of the importance of species interactions and interdependence in a balanced ecosystem, changes in the system, either through the introduction or elimination of species or through direct human activity, may powerfully alter the balance of living and nonliving resources.
Genetic variability of offspring within a species is due to mutation and/or the recombination of genes. These new variations within a species are naturally selected when they help the organism to better survive in their environment. Organisms with these beneficial new variations will have greater reproductive success thus affecting the nature of future generations. Over time this natural selection may lead to the development of new species.
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