General Biology Study Notes: Light, Vision, and Unifying Concepts of Life

Light and the Electromagnetic Spectrum

The Visible Region of the Electromagnetic Spectrum

The visible region of the electromagnetic spectrum refers to the range of wavelengths that human eyes can detect. This range is crucial for biological processes such as vision and photosynthesis.

• Visible Light: Wavelengths from approximately 400 nm (violet) to 710 nm (red).

• Shorter Wavelengths: Higher energy (e.g., gamma rays, X-rays, ultraviolet).

• Longer Wavelengths: Lower energy (e.g., infrared, microwaves, radio waves).

• Photons: Light behaves as particles called photons, which carry energy.

Equation:

$E = h\nu$

Where $E$ is energy, $h$ is Planck's constant, and $\nu$ is frequency.

Light Absorption by Molecules

Certain molecules have structures that allow them to absorb light energy, which is fundamental for processes like vision and photosynthesis.

• Pigments: Molecules that absorb specific wavelengths of light.

• Photoreceptors: Specialized cells containing pigments that detect light.

Structure and Function of the Eye

Anatomy of the Vertebrate Eye

The vertebrate eye is a complex organ that detects and processes light, enabling vision.

• Sclera: The white outer layer providing structure.

• Cornea: The transparent front part that refracts light.

• Lens: Focuses light onto the retina.

• Retina: Contains layers of cells, including photoreceptors (rods and cones).

Photoreceptors: Rods and Cones

Photoreceptors are the only cells in the retina that contain light-sensitive pigments. They convert light into electrical signals for the brain.

• Rods: Sensitive to low light; important for night vision.

• Cones: Responsible for color vision; function best in bright light.

Color Vision and Opsins

Mechanism of Color Vision

Color (chromatic) vision is enabled by cone cells in the retina, which contain different opsin proteins sensitive to various wavelengths.

• Opsins: Proteins in cone cells that determine wavelength sensitivity.

• Trichromatic Vision: Result of three different opsins:

  • Opsin S: Short wavelength (blue light)

  • Opsin M: Medium wavelength (green light)

  • Opsin L: Long wavelength (red light)

• Dichromatic Vision: Individuals with only two types of opsins (e.g., SWS and LWS) have dichromatic vision.

Example: Most humans have trichromatic vision, while some animals (e.g., dogs) have dichromatic vision.

Unifying Concepts of Biology

Fundamental Characteristics of Life

All living organisms share several fundamental characteristics that can be explained by unifying concepts in biology.

• Cells: All organisms are made up of cells.

• Replication: Cells and organisms reproduce.

• Information: Genetic information is stored and transmitted.

• Energy: Organisms acquire and use energy.

Scientific Theory in Biology

In science, a theory is a broad explanation supported by extensive evidence and capable of generating new hypotheses. This differs from the everyday use of 'theory' as a mere guess.

• Scientific Theory: Well-substantiated explanation (e.g., theory of evolution).

• Everyday Theory: Untested speculation or guess.

Major Unifying Theories in Biology

Cell Theory

Cell theory is one of the foundational principles of biology, describing the cellular basis of life.

• All organisms are made up of cells. (Pattern)

• All cells come from pre-existing cells. (Mechanism)

Example: In multicellular organisms, all cells descend from a single ancestral cell.

Theory of Evolution by Natural Selection

The theory of evolution by natural selection explains both the unity and diversity of life.

• Characteristics of populations change over time.

• Individuals with certain heritable traits produce more offspring.

• All species are related by descent from a common ancestor.

Equation:

$\text{Evolutionary change} = \text{Variation} + \text{Heritability} + \text{Differential Reproduction}$

Example: The diversity of finch species in the Galápagos Islands is a result of evolutionary processes.

Phylogeny and Biodiversity

Understanding Phylogeny

Phylogeny is the study of evolutionary relationships among species. Phylogenetic trees illustrate these relationships and help explain the unity and diversity of life.

• Phylogenetic Tree: Diagram showing evolutionary relationships.

• Common Ancestor: All organisms alive today descended from a common ancestor.

• Biodiversity: The variety of life forms resulting from evolutionary processes.

Domain	Characteristics
Bacteria	Prokaryotic, diverse metabolic pathways
Archaea	Prokaryotic, often extremophiles
Eukarya	Eukaryotic, includes plants, animals, fungi, protists

Example: The three domains of life (Bacteria, Archaea, Eukarya) are shown in phylogenetic trees to illustrate evolutionary relationships.

Additional info:

• Some content was inferred and expanded for clarity and completeness, such as the explanation of scientific theory and the structure of the eye.

• Table content on domains of life was logically grouped and expanded based on standard biology knowledge.