BioSec: Text: Unit 1: Setting the Stage

Light and Life

The book starts out talking about Monet, the French impressionist painter, and the reason why his later paintings lacked light blue, and appeared to be toned towards red-yellow. This was due to a physical ailment of cataracts. The opaqueness of a cataract affected lens causes it to absorb certain wavelengths of light.

The way in which you see the world is affected by biological processes. The way in which you view a computer is similar – an operating system on a machine is effectively a map to the internal workings of the machine. It gives you a perspective view of how to interact and process information stored within a computer.

The Physical Nature of Light

Light functions: Light is a source of energy that sustains life. Light provides organisms with information about the physical world.

Photosynthesis – biological process to create energy rich molecules (algae)

Light is defined as the portion of the electromagnetic spectrum that humans can detect with their eyes. It is hard to characterize because it although it can be described as a wave it also behaves like a stream of energy particles. When light interacts with matter three things can happen – it can be reflected off of the object, transmitted through the object or absorbed by the object. Absorption occurs when the energy of a photon is transferred to the electron of the pigment molecule. Pigments are molecules that can absorb photons of light – each differ in the wavelengths that they can absorb. The feature critical to light absorption is a region where carbon atoms are covalently bonded with alternating single and double bonds (conjugated system) which results in the delocalization of electrons. A single photon results in the excitation of one and only one, electron in the pigment molecule and secondly the energy of the photon must match the energy difference between the ground state and one of the excited states in order for the photon to be absorbed.

Why is cholorophyll green in color? The color of a pigment is determined by the wavelengths of light it cannot absorb.

Photosynthesis sustains almost all life – uses the energy in sunlight to build sugar molecules from carbon dioxide and water – releasing oxygen as a by-product.

Light as a Source of Energy

The excited electron state is a source of potential energy that can be used to do work. This energy is used to synthesize energy rich compounds (NADPH and ATP) which are used to convert CO2 into carbohydrates. Other biological molecules such as lipids, proteins, and nucleic acids from simple building blocks found in the environment.

Light as a Source of Information

Organisms use light to sense their environment. Not every person – and not every species sees the world in the same way. Rhodopsin - the most common photoreceptor found in nature – mystery as to why – perhaps it developed very early in the evolution of life consists of a protein called opsin that binds a single pigment molecule called retinal absorption of a photon causes the retinal pigment to change shape – causing chain reaction - alteration of protein, intracellular ion concentrations and electrical signals which are then sent to the brain even things without eyes can sense light direction and intensity eye – can be defined as the organ animals use to sense light – what distinguishes the eye from an eyespot of an invertibrate is the vision process – requires not only an eye but also a brain or simple nervous system that interprets signals sent from the eye

image forming eyes come in two varieties: compound eyes and single lens eyes -

compound eyes can be found in insects and crustaceans – hundreds to thousands of ommatidia units fitted closely together – each one samples only a small part of the visual field. Enables even slight motion detection.

Lens eyes (camera) – light enters through the transparent cornea – a lens concentrates the light and a layer of photoreceptors at the back of the eye, the retina – records the image.

Darwin proposed that the eye as it exists in humans and other animals did not appear suddenly but evolved by variation (mutation) and natural selection over time from a simple, primitive eye.

Any application during it's development life cycle evolves to hopefully become better at the task it was designed to perform. Not only programs, but operating systems, and hardware are selected and chosen by respective audiences somewhat based upon the usability, and performance of the system.

Computer scientists not only program, but attempt to imitate life in many ways as well. Robots were initially designed to perform specific tasks, but have evolved over time to complete more interesting behaviours. Sensors are designed to provide input in a variety of different ways to affect the behaviour of a robot. Cameras contain lenses. Touch screens, keyboards and mice provide the ability to provide stimuli.