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Biology 1000 Mid Term 1 Study Notes.docx

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BIOL 1000
David Stamos

Biology Mid-Term Study Notes Chapters 1, 2, 3, 13, and 21 Chapter 1: Light and Life Light can be defined as the portion of the electromagnetic spectrum that humans can detect with their eyes Visible radiation is a narrow band of electromagnetic spectrum spanning wavelengths in nonometers from 400 nm to 700 nm Composed of discrete particles or packets of energy referred to as photons the amount of energy in a photon is inversely related to its wavelength Photons either can be reflected off an object, transmitted through an object, or absorbed by the object A molecule that absorbs photons of light is called a pigment, and individual pigments differ in the wavelengths of light that they can absorb Upon absorption of a photon of light, the energy is transferred to the electron, moving it from the ground state to a higher energy, excited state The excited state electron is a source of potential energy that can be used to do work The colour of a pigment is determined by the wavelengths of light it cannot absorb (chlorophyll reflects green) Photoreceptors is the basic light-sensing system, the most common photoreceptor in nature is rhodopsin Each rhodopsin molecule consists of a protein called opsin that binds a single pigment molecule called retinal Absorption of a photon of light causes the retinal pigment molecule to change shape In humans, capturing of light by the eye involves about 125 million photoreceptor cells that line the retina Eye is the organ animals use to sense light Eyespots differ in allowing some organisms to have vision, those that have a brain or at least a simple nervous system that interprets signals sent from the eye (we see with our brain) Simplest form of eye is ocellus which consists of up to 100 photoreceptor cells lining a cup or pit The greatest advance in vision came with more sophisticated eyes that produced an actual image of the lighted environment for discerning objects and shapes. These image forming eyes are found in two distinctly different typed: compound eyes and single-lens eyes Compound eyes are common in anthropoids such as insects and contain hundreds to thousands of ommatidia (each samples only a small part of the visual fields as each only contains a bundle of photoreceptors) In single lens eyes, light enters this eye through the transparent cornea, a lens concentrates the light, a layer of photoreceptors at the back of the eye, the retina, records the image Light from the sun is potentially harmful to life. DNA is particularly vulnerable to damage. Damage results in dimers which is when two neighbouring bases become covalently linked. This can change the shape of DNA and prevent replication Absorption spectrum is a plot of the amount of light a pigment absorbs in relation to the wavelength of light The presence of melanin prevents the DNA damage in skin cells that is linked to the development of skin cancer The many physiological and behavioural responses geared to earths day-night cycle are called circadian rhythms. This biological clock is set by the external light environment, but it can run a long time without input from outside the organism Organisms that produce light are bioluminescent When an electron returns to the ground state, the energy is released as a photon of light Bioluminescence used for communication, attract mate, camouflage, attract prey Organisms that use bioluminescence light must have light-sensing organs Chapter 2: Origins of Life The Fundamental Unit of Life is the Cell Cell Theory: all organisms are composed of one or more cells, the cell is the smallest unit that has properties of life, and cells arise only from the growth and division of pre-existing cells The Origin of the Information Center All organisms contain DNA The information in DNA is copied onto molecules of a related substance, RNA, which then directs the production of protein molecules (common to all life) Early Life Earliest evidence of life is stromatolites (type of layered rock that is forms when microorganisms bind particles of sediment together, forming thin sheets All forms of life are based on two fundamentally distinct types of cells: prokaryotic and eukaryotic Prokaryotic organisms are found in two domains of life: the bacteria and the Archaea Major difference is the lack of a nucleus that a prokaryotic cell does not have. Otherwise the two types of cells share many of the same fundamental features. DNA is organized into chromosomes. Prokaryotes have much less internal membrane organization Eukaryotic Cells Differences from prokaryotic cells: the separation of DNA and cytoplasm by a nuclear envelope, the presence in the cytoplasm of membrane bound compartments with sp
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