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Chapter 8

Bio1000 chapter 8 notes

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BIOL 1000
Paula Wilson

Ch 1, Ch 2, Ch 3 (3.1, 3.4 3.5) 5.1 5.2 purple pages 40-43 2 important functions which light serves:  Source of energy that directly or indirectly sustains virtually all organisms  Provides organisms INFOMATION about the physical world that surrounds them Light is the portion of the electromagnetic spectrum that humans can detect with their eyes  No mass  Composed of a stream of energy particles called PHOTONSabsorbed by electrons Electromagnetic Radiation: A kind of radiation including visible light, radio waves, gamma rays, and X-rays, in which electric and magnetic fields vary simultaneously Wavelength of visible light is 400nm-700nm Wavelength and Energy Inversely Related: Shorter wavelengths  more energy (higher energy photons) Longer Wavelengths  less energy (lower energy photons) successive 3 possible fates which allows energy of light to be used by living things 1) Reflected off object 2) Transmitted through object 3) Absorbed by objectmust take place in order to be used by object, occurs when energy of photon is transferred to an electron within molecule *this can only happen if photon energy equals energy diff. b/w electrons ground state and excited state, if doesn’t match, it is transmitted or reflected. Pigments (Light absorbers)  Molecules that can absorb photons of light  Carbons linked by alternating single/double bonds  Bonding arrangement called Conjugated system of “delocalized” electrons, where none are associated with an atom or involved in bonding, therefore able to interact with a photon of light and used to do work  Pigment’s colour is result of photons of light which is not ABSORBED, instead reflected or transmitted Light as Energy: Photosynthesis: Light energyplants and organisms store it in the chemical bonds of sugars and other food moleculesCELLULAR RESPIRATION: plants, animals, and fungi release energy stored in chemical bonds of food molecules (sugar molecules) and use as energy. (trapping released energy as ATP) PHOTORECEPTORS:  Molecule that absorbs light, and generates a response Rhodopsin is the most common photoreceptor in nature, basis of vision in animals and other organisms. opsin protein +retinal absorption of photons of light causes retinal to change shape, which triggers changes to opsin it binds with, and then sends electrical signals to visual centres of brain allowing light to be seen Light captured by eye in humans involves about 125 million photoreceptors.. Eyespot-light sensitive structure found within chloroplast of cell : focuses and directs incoming light towards photoreceptors. It does not play role in photosynthesis as photoreceptors of eyespot causes cell to sense light direction +intensity. Phototaxis: cells respond to light by swimming toward or away from light sourceallows cell to stay in optimum light environment for photosynthesis. In plants, photoreceptor called phytochrome ( becomes active when exposed to wavelengths of red light and sends a signal that reaches nucleaus, where signals activate hundreds of genesleaf development and photosynthesis) senses light and critical for photomorphogenesis: developmental process activated when seedlings exposed to light. Eye: Organ animals use to sense light Process of vision : Requires eye (focus and absorb light) + brain (interpret signals) Simplest eye: OCELLUS (Ocelli) consists of a cup with up to 100 photoreceptors 2 Types of Image Forming Eyes: 1) Compounds eyes: found in arthropods (insects) built with hundreds of individual units OMMATIDIA fitted together, each samples only small part of visual fieldbrain receives mosaic image of world. THIS IS WHY they can detect the slightest motion (flies) 2) Single-Lens Eyes: some invertebrates and most vertebrates, including humans. Light enters transparent cornealens concentrates and focuses onto photoreceptor cells (retina)--.send into to brain through optic nerve. Shorter wavelengths of electromagnetic radiation absorbed by ozone, longer wavelengths absorbed by water vapour + carbon dioxide in atmosphere, therefore visible light most dominant form of electromagnetic radiation on earth’s surface. Radiation of shorter wavelengths will destroy chemical bonds which hold molecules together, while radiations of longer wavelengths are weak and not supply enough energy to move electron from diff states.  Light is form of energy, too much light can damage biological molecules. Photosynthetic apparatus constantly damaged by light and damage is repaired.  Ultraviolet light most harmful, strong enough to remove an electron from atom, resulting in ions. Also strong enough when reached DNA structure, can cause dimerchanges change shape of double helix structure DNA and prevent replication as well as delay gene transcription  Dimers can also result to skin cancer and genetic mutation Organisms synthesize MELANINpigment that strongly absorbs UV light. also the major component of the ink released by squid Spectrophotometer: tells specific wavelength of radiation pigment can absorb  Data from this can be used to produce an absorption spectrum plot of absorbance in relation to wavelength of light Humans synthesize melanin in specialize skin cells called melanocytes, and melanin synthesis increased upon sun exposure  people to suntan Circadian Rhythms: Governed by an internal biological clock. (sleep-wake cycles, body temp, metabolic processes, cell division, and behaviours for foraging for food and mating) Many physiological and behavioral responses are geared to daily changes in light and darkness and these daily changes are known as circadian rhythms circa: around diem: day examples : insectsemergence as adults from pupil case occurs close to dawn when humidity of air is highest which prevents desiccation of insects(drying out)  In organisms, proteins required for DNA replication and are synthesized at dusk, allows DNA replication to occur at night and not get damaged by UV radiation during day Photoperiod organisms that can keep track of changing seasons Chapter 2: Cell Theory: 1. All organisms are composed of one or more cells 2. Cell is basic structural and functional unit of all living organisms 3. Cells arise only from division of pre-existing cells 1) Natural Selection Theory: 1. Characteristic of a population change over time 2. Evolution occurs through natural selection Basic Features of Cell Structure and Function (2.1)  Cells carry out the essential processes of life. They use chemical molecules/light as energy sources.  Unicellular organismsfunctions independently  Multicellular organisms activities of life are divided among varying number of specialized cells.  All forms of life grouped into one of 3 domainsBacteria, Archaea, and the Eukarya  All cells bounded by plasma membrane, bilayer made of lipids + protein molecules  Parts between plasma membrane and central regioncytoplasmcontains organelles, cytosol  (aq. Solution which contains ions and organic molecules), and cytoskeleton (protein framework that helps maintain proper cell shape and plays key roles in cell division and chromosome segregation from cell generation to generation)  All major eukaryotic cytoskeletal proteins have function equivalents in prokaryotes  Many of cell’s vital activities happens in the cytoplasm (synthesis and assembly of most molecules for growth and reproduction, conversion energy into forms that cells can use, conducts stimulatory signals carry out chemical reactions to respond)  TWO TYPES OF CELLS: 1. Prokaryotic (pro=before, karyon=nucleus): Cells lacking nucleus, surrounded by plasma membrane. DNA is located in the nucleoidno boundary membrane separating it from cytoplasm. Cytoplasm contains masses of ribosomeuses info in mRNA to assemble amino acids into proteins. 3 most common shapes: spherical, rodlike and spiral. Prokaryotic chromosomeDNA, single circular molecule that unfolds when released from cell. Cell wall provides rigidity to prokaryotic cells + protects cell from physical damage. 2. Eukaryotic: Have cells where DNA is contained within membrane called NUCLEUS. Four major groups: animals, plants, fungi, and protists. Cytosol participates in energy metabolism and molecular synthesis + performs specialized functions in support and motility. Have larger ribosomesuse info in mRNA to make a.a into proteins. E.K cells characterized by endomembrane systemcollection of interrelated internal membranous sacs that divide the cell into functional and structural compartments (system includes nuclear envelope, endoplasmic reticulum, golgi complex, lysosomes, vesicles, and plasma membrane.  Eukaryotic nucleus contains more DNA than prokaryotic nucleoid. The nucleus and cytoplasm separated by nuclear envelopeconsist of 2 membranes  NUCLEAR PORE COMPLEXlarger structure formed by many types of proteins, exchanges components b/w nucleus and cytoplasm preventing material not meant to cross in  Most of the nucleus is filled with chromatincombination of DNA and proteins  ENDOPLASMIC RETICULUM: interconnected network of membranous channels and vesicles called cisternae formed by single membrane called ER lumen. Two types: 1. Rough ER-ribosomes stud it outer surface, makes proteins that become part of cell membranes or released from cell. 2. Smooth ER-synthesizes lipids and breaks down toxic substances so they can be easily removed from body (BOTH MEMBRANES CONNECTED)  GOLGI COMPLEX: chemically modifies proteins made in rough ER and sorts finished proteins into vesicles (regulates movement of several types of proteins)  LYSOSOMES: vesicles containing hydrolytic enzymes, digest complex molecules that enter cell by endocytosis, cellular organelles that no longer function correctly (RESTRICTED to animal cells)  Cytoskeleton is supportive structure built from microtubules, intermediate filaments, and microfilaments. (Largest to smallest) (ALL of these are made from proteins; 1 one tubulins, 2nd rd intermediate filament proteins, and 3 actins)  Keratins from animal hair contain common form of intermediate filament protein known as CYTOKENATINS.  Motor proteins produce most movements of animal cellssliding of microtubules generates the movements of flagella and cilia  Microtubules-assembled from dimers of a and b tubulin proteinsseparate and move chromosomes during cell division, determine orientation for growth of new cell wall, maintain shapes of animal cells, move animal cells. (Animal cell movement generated by motor proteins)  Intermediate filament: eight protein chains wind together to form each subunit provide structural support in many cells and tissues  Microfilaments: assembled from 2 linear polymers of actin proteins wound around eachother into a helical spiraloccur in all EK cells and involved in structural and locomotor functions. Involved in actively flowing motion of cytoplasm called cytoplasmic streaming (transport nutrients, proteins, organelles in both animals + plant cells. When animal cell divide, micro.fila. Responsible for dividing cytoplasm. 2.4 Types of PLASTIDS:  CHLOROPLASTSsite of photosynthesis. Surrounded by two membranes (outer and inner) which enclose the stroma. Within stroma is third membrane called THYLAKOIDScontain molecules that absorb light which convert to chemical e
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