FORM FITS FUNCTION
The specific structure of a biological mechanism is closely related to its purpose. This specialization of parts facilitates the smooth interactions of life on three levels:
(a substrate's shape is specific to the active site of its enzyme)
(a hummingbird's long, thin beak is perfectly designed to get nectar from flowers)
(an elephant's long, muscular trunk facilitates drinking and food-getting)
Molecules and Cells
The plasma membrane is composed of phospholipids, proteins, and cholesterol. The phosphate component is hydrophilic, while the fatty acid tails of the lipid portion are hydrophobic. Because the membrane is a bilayer, the fatty acid tails face in towards each other and the phosphates face out. This construction allows for the insertion of protein carriers that transport molecules into and out of the cell.
Ion pumps, a specific type of protein carrier, are specifically shaped to carry the ions that the cell needs.
DNA consists of two long strands of phosphates and deoxyriboses with nitrogenous bases attached to the sugars. Simply, DNA is composed of a sequence of nucleotides. However, if DNA were left in this elementary state, the amount needed to code for an entire organism would not fit into the nucleus. DNA must be twisted into a helical state and then folded around histones and condensed further into looped domains. The form resulting from this folding is a chromosome.
The increased surface area created by the shape of the mitochondria, mitochondrial membrane, and the thylakoids found in chloroplasts, allows for an optimum rate of cellular respiration or photosynthesis.
The fibrous structure of cellulose provides the necessary rigidity for the cell wall of a plant cell.
The electron transport system consists of a sequence of electron carriers lined up one after the other. This construction allows for the movement of electrons through each cytochrome, thereby releasing the energy needed to make ATP.
Each enzyme has a specific nucleotide sequence which is the restriction site, or cut site.
Cell differentiation allows cells to specialize to correspond to their specific function. In this way every cell can carry out a specific function correctly by using this unique division of labor.
Heredity and Evolution
As a result of natural selection, all adaptations are the best design for their function.
One example of an important adaptation is the fact that birds have hollow bones to facilitate flight.
The structure of the complementary gametes, the egg and sperm, is such that their fusion is possible. The egg is large and immobile with more cytoplasm than the small flagellated sperm cell. This fusion is vital to the creation of a new zygote. If the structure of the gametes did not serve their function, sexual reproduction would not be possible.
The tRNA molecules are folded so that they have a sequence of three nucleotides (anticodon) in the clover-leaf structure. The opposite end of the molecule is designed to carry the amino acid that corresponds to the the anticodon.
As DNA is ready to be transcribed, the two strands of DNA separate at a specific site. The separation remains localized so that the entire chromosome does not have to be unraveled.
Viruses consist of a nucleic acid core and a protein coat. This simplistic structure means that the virus's only function is to manipulate the functions of the host cell by using the host cell DNA and proteins to replicate its own. The virus only has what it requires to infect a cell and directs the cell to do everything else - reproduction and protein synthesis.
Organisms and Populations
**This is not an exhaustive list of examples of form fitting function.
The Integumentary System
The Nervous System
The Muscular System
The Endocrine System
The Reproductive System
-Lack of nucleic and cytoplasmic fluid
-Flagella for propulsion against the pull of gravity
-Penetrates the egg and contributes chromosomes
-Protects the sperm
-Keeps testes away from body and at a lower temperature
-Produces and houses eggs
-Releases egg during ovulation
-Moves egg through Fallopian tube
-Draws egg into the uterus
-Nurtures and protects embryo
-Secrete milk produced by mammary glands
-Formed to fit mouth of offspring
The Respiratory System
The Circulatory System
ex: Capillaries are only a single layer of cells thick to allow for easy exchange between cells.
The Immune System
The Excretory System
The Digestive System
The Skeletal System
Since xylem transports water against gravity, its walls are thicker than those of phloem. The explanation for the transport of water is known as the cohesion-tension model.
The tracheids and vessel elements of xylem are non-living, and at their junctions, the cell walls have deteriorated, so they form a long tube. Because the cells are not alive, the xylem cells cannot perform active transport.
The walls of the phloem are thinner since there is no tension or pressure imposed upon them as it is in the xylem.
The sieve-tube elements and companion cells actively transport the products of photosynthesis and other organic molecules. The explanation for the movement of organic materials through a plant is the pressure-flow hypothesis.
Stomates are the "holes" through which water transpires and gases flow (CO2 flows in and O2 flows out). Guard cells regulate the opening and closing of these holes. Because of their thicker inner cell wall, the hole will open when the cells are turgid.
Not only does the branching network of roots anchor the plant, it also extends far enough into the soil to reach underground reservoirs of water. Root hairs provide extra surface area for the absorption of water and minerals. The root cap at the tip of a root allows the root to push through tightly packed soil without damaging the meristematic cells.
Flowers are colorful, fragrant and nectar-rich to attract pollinators (i.e. insects and birds). Some flowers even have special patterns on the petals to guide the pollinators to the pollen. Flowers often complement the structures of their pollinators.
Self-pollinating flowers have the anther higher than the pistil so that pollen grains can fall directly onto the pistil to facilitate fertilization.
Seeds consist of the embryo, food for the embryo, and a hard coat which serves as protection for the embryo.
Fruits are designed to facilitate dispersal of seeds. (e.g. apples taste good so deer will eat them)
Some parasites exist in more than one form, depending on their life cycle and host. According to which host they are in, they change form and function. One example of this polymorphism is malaria; it exists as a trophozoite, merozoite, and sporozoite depending on whether it is in its human or mosquito host. (Don't worry about the details of the life cycle, just be aware that malaria is an example of a polymorphic parasite.)