Unit IV: Form and Function, Modularity and Incremental Change

The function of a biological structure can be inferred from its shape.
Similar structures across different species will have similar shapes and properties if they perform the same function.

Sclera: The white outer layer of the eye.
Iris: The colored part of the eye that controls the size of the pupil.
Pupil: The opening in the center of the iris through which light passes.
Cornea: The transparent outer layer that covers the iris, pupil, and anterior chamber; part of the eye's focusing system.
The cornea has no capillaries.
Anterior chamber: Filled with aqueous humor.
Posterior chamber
Suspensory ligaments: Hold the lens in place.
Ciliary body and muscle: Control the shape of the lens.
Lens: Focuses light onto the retina.
Eyelid: Protects the eye.
Lacrimal caruncle: Contains glands that produce tears.
Tear duct: Drains tears from the eye.
Lateral rectus muscle: Controls eye movement.
Vitreous body: Filled with vitreous humor.
Choroid: The vascular layer of the eye, providing nutrients to the retina.
Retina: The light-sensitive layer at the back of the eye.
Macula lutea: The central area of the retina.
Fovea centralis: The central depression within the macula, responsible for sharp, central vision.
Optic disc: The blind spot where the optic nerve exits the eye.
Medial rectus muscle: Controls eye movement.
Optic nerve and retinal blood vessels: Transmit visual information to the brain.

The cornea, unlike many other tissues, does not contain capillaries.
Scientists at Harvard's Schepens Eye Research Institute and Massachusetts Eye and Ear Infirmary (MEEI) discovered that the presence of large amounts of the protein VEGFR-3 (vascular endothelial growth factor receptor-3) on the top epithelial layer of healthy corneas is the reason why the cornea is free of blood vessels.

Engineering definition of a module: A functional unit capable of maintaining its intrinsic properties.
Modularity enables defined and predictable outcomes by connecting different modules.
It reduces costs and simplifies the design process.

Biological systems are modular, using simple building blocks for multiple and complex purposes.
Hierarchy: Cells → Tissues → Organs → Systems.
Cells are parts of tissues, which are parts of organs, which are parts of systems, and so on.
Biological organisms share a close relationship due to their modular nature.
This similarity is reflected at each hierarchical level, including the molecular level.
There's a high degree of similarity (commonality) even at the molecular level.
The same genetic code is used throughout the biological universe.

Plants and Animals: 50% similarity
Fruit flies and Humans: 44%
Chickens and Humans: 60%
Primates and Humans: 99%
The difference between individuals (e.g., "me and you") is only 0.1% at the DNA level.

Perform a defined function in a better way:
- Unique functions can be achieved by assembling existing forms in new ways.
- Each cell in early embryo development can become nerve, bone, or liver.
Act as units for evolution:
- Modularity allows evolution to occur by forming components that can be individually modified.

A new species is formed or evolved from an existing species through incremental change.
The old species is not discarded but is changed.
Evolution occurs from one form to another.
Progression from less adapted to more adapted.
Biological organisms adapt much better to small changes compared to large ones.

Nasal Drift in Whales:
- Ancient whales spent more time immersed, so their nostrils were at the tip of the nose.
- Over time, as they migrated to seas, the nostrils moved higher on the skull.
- Modern whales can break the surface of the sea because their nostrils are on the top of the skull. This is an example of incremental morphological change.
Evolution of Hemoglobin:
- Billions of years ago, the earth was devoid of life and oxygen.
- The first life developed about 3.8 billion years ago, using water vapor, nitrogen, methane, and ammonia for food and energy.
- Metabolic reactions were likely catalyzed by metals such as iron and magnesium.
- With the emergence of photosynthetic organisms around 3.5 billion years ago, oxygen was released into the atmosphere, becoming a major constituent.
- Life forms appeared utilizing this oxygen.
- Oxygen needs to bind to a carrier without reacting with it, then be transported to cells.
- Chlorophyll, which evolved earlier for photosynthesis, is a porphyrin ring containing magnesium.
- Heme is another porphyrin ring containing iron. Heme bound to a globin molecule is called hemoglobin.
- Hemoglobin binds to oxygen in the lungs and gives blood its red color.
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