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“If you want to understand function, study structure.” – Francis Crick This quote means that in biology, what something does can only be understood by examining how it is built. Throughout this course, we repeatedly saw that biological function is determined by physical structure at every level of organization. Throughout the course, we were constantly looking at, analyzing, and labeling diagrams. At first, this seemed repetitive, but over time it became clear why this was so important: to understand how something works, we must first understand its structure. This directly connects to Crick’s idea that structure is the key to understanding function. In genetics, the structure of DNA explains its function. It took many years of research by scientists such as Watson, Crick, and Rosalind Franklin to study and analyze the structure of DNA before scientists could fully understand how it works. DNA’s double helix shape and complementary base pairing—adenine with thymine and guanine with cytosine—allow it to replicate accurately during mitosis and meiosis. Because the bases pair in a specific way, each strand can act as a template for copying genetic information. Without this precise structure, we would not be able understand dna In human and animal body systems, the relationship between structure and function strongly supports Francis Crick’s idea that we must study structure to understand function. Organ systems contain specific anatomical structures that have evolved to perform particular jobs, and their functions can only be understood by examining how those structures are built. For example, in the digestive system, the muscle layers of the esophagus and intestines are arranged in a way that allows peristalsis, a wave-like squeezing motion that pushes food forward. Studying the structure of these muscle layers explains how food moves through the digestive tract. The small intestine contains villi, which are finger-like structures that increase surface area. This structural adaptation explains how nutrients can be absorbed efficiently into the bloodstream. In the respiratory system, the alveoli are microscopic air sac structures in the lungs. Their thin walls, moist surface, and large surface area are structural features that explain how oxygen and carbon dioxide can diffuse efficiently. In the circulatory system, arteries, veins, and capillaries are all structures with different designs. Arteries have thick, elastic walls to handle high pressure blood from the heart. Capillaries have walls that are only one cell thick, which explains how oxygen and nutrients can pass easily into tissues. These examples clearly show that biological function can only be understood by first studying biological structure, directly supporting Francis Crick’s statement. These examples show that when we study structure, we can clearly understand function, directly reinforcing Crick’s statement. In plants, structure also explains function and shows deep evolutionary origins shaped by natural selection. All plants evolved from green algae, and over time, natural selection favored structures that improved survival and efficiency. Important plant structures were passed down because they helped plants function better in their environments. For example, xylem tissue is made of long, hollow, dead cells with thick cell walls that form continuous tubes. This structure allows water to move upward through the plant using the transpiration–cohesion–adhesion mechanism, even against gravity and without a pump. Plants with more efficient xylem were more likely to survive and reproduce, so this structure became common over generations. The function of water transport can only be fully understood by examining the structure of the xylem. Across genetics, animals, and plants, this course consistently showed that structure determines function. By studying how biological structures are built, scientists can understand how systems work, why they are effective, and what happens when they fail. This strongly supports Francis Crick’s statement that to understand function, we must first study structure. Evolution is at the heart of explaining biological processes and development because it shows why organisms have the traits and structures they do, how variation arises, and how development is shaped over time. Evolution relies on genetic variation, which comes from DNA, mutations, and meiosis. DNA stores genetic information in the form of nucleotides (A, T, G, C), and complementary base pairing ensures accurate replication. Mutations create new alleles, and meiosis increases variation through crossing over and independent assortment. Without this variation, natural selection could not act, and biological processes could not evolve. This directly links evolution to the existence and adaptation of biological processes. Evolution also explains why biological structures and processes are suited to their environment. Structures evolve because they improve survival or reproduction. For example, alveoli in the lungs have thin walls and large surface area, allowing efficient gas exchange, and xylem tissue in plants has long hollow tubes that transport water against gravity. These structures exist in their current forms because natural selection favored individuals with efficient structures, showing that evolution shapes how biological processes work. Furthermore, evolution explains developmental patterns and common ancestry. Homologous structures, like human arms and whale flippers, share the same underlying bone structure but have different functions, showing how evolution modifies structures over time. Vestigial structures, such as whale pelvic bones, reveal ancestral traits retained in development. Early embryonic similarities across species exist because developmental pathways are inherited from a shared ancestor. This shows that evolution explains not just traits, but how organisms develop over time. In conclusion, evolution is central to biology because it explains variation, inheritance, structure, and development, which together determine how biological processes work and why they exist in their current forms. Studying DNA, organ structures, and developmental patterns demonstrates that all biological processes and developmental pathways are the result of long-term evolutionary change, making evolution truly at the heart of biology. Evolution is at the heart of explaining biological processes and development because it explains why organisms have the structures they do and why they develop and function the way they do. Evolution depends on genetic variation, which comes from DNA, mutations, and meiosis. DNA stores genetic information using the bases A, T, G, and C, and complementary base pairing allows DNA to be copied accurately. Mutations create new alleles, and meiosis increases variation through crossing over and independent assortment. This variation allows natural selection to occur, meaning traits that improve survival and reproduction become more common over generations. Without evolution acting on this variation, biological processes and development would not change or adapt over time. Evolution also explains how biological processes developed over long periods of time, especially in plants. Early plants did not have specialized structures, but over many generations, natural selection favored plants with beneficial traits. Structures such as stomata and guard cells evolved to control gas exchange and water loss, cuticles evolved to reduce dehydration, and xylem and phloem evolved to transport water and nutrients efficiently. These structures improved key biological processes such as photosynthesis, water regulation, and transport. This shows that biological processes exist in their current form because evolution gradually shaped structures that made those processes more efficient. Evidence for evolution further explains development and biological processes. The fossil record shows that organisms have changed gradually over time, meaning structures and functions developed step-by-step. Embryology shows that many organisms have similar early embryos, which means their developmental processes come from a shared ancestor. Comparative anatomy shows that homologous structures share a common origin but develop different functions, proving that development is modified over time by evolution. Vestigial structures show that development can still follow ancestral patterns even when a structure is no longer useful. Overall, evolution explains where biological structures come from, how biological processes developed, and why organisms develop the way they do. By connecting genetics, natural selection, plant and animal structures, and evidence such as fossils and embryology, evolution provides the framework that makes all biological processes and development understandable. 1. Genetic variation → drives evolution Evolution depends on genetic variation Variation comes from: DNA Bases: A, T, G, C Complementary base pairing allows accurate copying Mutations Create new alleles (new traits) Meiosis Crossing over Independent assortment Increases variation Natural selection Traits that improve survival/reproduction become more common Without evolution acting on variation: Biological processes would not change Development would not adapt over time 2. Plants show how evolution shaped biological processes Early plants had no specialized structures Over generations, natural selection favored better traits: Stomata & guard cells Control gas exchange and water loss Cuticle Reduces dehydration Xylem & phloem Transport water, nutrients, sugars efficiently These structures improved biological processes: Photosynthesis Water regulation Transport Shows that: Structures and processes exist today because evolution shaped them for efficiency 3. Evidence for evolution explains development Fossil record Shows organisms changed gradually over time Structures and functions developed step-by-step Embryology Similar early embryos = shared ancestors Developmental patterns come from evolution Comparative anatomy Homologous structures: Same origin, different functions Shows development changes over time Vestigial structures Remains of ancestral traits Shows development still follows evolutionary history Conclusion Evolution explains: Where structures come from How biological processes developed Why organisms develop the way they do Genetics + natural selection + plant structures + fossil/embryo evidence → All connect to prove evolution is central to biology