2.1 A Microscopic Look at Life’s Organization -in unicellular organisms (bacteria) structural diversity exists at the cellular level -in multicellular organisms, division occurs in order to reproduce and grow -two types of cell division; -mitosis: cells divide to form new cells that are identical to the parent cell -meiosis: produces the reproductive cells (egg and sperm), have half the chromosomes from each parent cell (contributes to genetic diversity) Prokaryotes and Eukaryotes Characteristic Prokaryotes: Eukaryotes: Bacteria, Archaea Protists, Plants, Fungi, Animals Size 1-10 µm (nanometers) 100-1000 µm (nanometers) Genetic Material -circular DNA, not bound by membrane -DNA in nucleus bounded by -genome made up of a single membrane chromosome -genome made up of several chromosomes Cell Division -not by mitosis and meiosis -mitosis and meiosis Reproduction -commonly asexual -commonly sexual Number of Cells -unicellular -mostly multicellular Organelles -mitochondria and other membrane -mitochondria and other membrane bound organelles absent bound organelles present Metabolism -many are anaerobic (do not require -most are aerobic (require oxygen to oxygen to carry out cellular respiration) carry out cellular respiration) Viruses -viruses are a structure that contains strands of DNA or RNA surrounded by a protective protein coat -cannot live independently outside of cells -differ from both prokaryotes and eukaryotes -outside a cell, they are dormant -not cellular, do not contain cytoplasm, membrane bound organelles or a cell membrane Classifying Viruses -are not formally considered organisms since they are not cellular -they have genetic material and are able to reproduce -one method used by scientists to classify viruses are by shape and size of the capsid -a capsid is the outer protein later that surrounds the genetic material of a virus -they are also grouped by the types t ypes of diseases they cause -these groups differ in their genomes (sets o f genes) and their method of replication Reproduction in Viruses -they undergo replication within a host cell since they are not cellular and do not reproduce by cell division -the host cell depends on the virus type and can be in both eukaryotic and prokaryotic cells -there are two kinds of replications cycles: -the lytic cycle is the replication process in which the virus’s genetic material uses the copying machinery of the host cell to make new viruses -the virus produces multiple copies of its parts and then assembled itself in th e host cell -it is the typical replication cycle -the lysogenic cycle is the replication process in which the viral DNA enters the host cell’s chromosome; it may remain dormant and later activate and instruct the host cell to produce more viruses -basically, the viral DNA becomes a part of the host cell’s chromosome (called a provirus) and controls it to produce more viral cells -when the host cell divides by mitosis, it replicates the provirus in the chromosomes, spreading the virus
Viruses and Diseases -in a lytic cycle, newly formed viruses burst out of the host cell, usually killing the host cell -in multicellular hosts, the new viruses can infect neighbouring cells which causes damage to the host -viruses that go through the lysogenic cycle, the effects m ay not be immediate due to the fact t hat the viral DNA might stay dormant when entering the host cell -retroviruses are RNA viruses that insert a DNA copy of its genome into the host cell in order to replicate -at any time, the provirus can separate fr om the host chromosome and undergo the lytic cycle Patterns of Disease -replication strategies of viruses help explain certain patterns of disease For example, the herpes simplex virus causes cold sores in humans; these cold sores appear and disappear on infected people throughout their life. They appear when the viral cycle destroys cells and disappear when the virus is in its provirus stage, when it is dormant. Prions: Non-viral Disease-causing Agents -a prion is an infectious particle that causes damage to nerve cells in t he brain and consists mostly or entirely of a single protein -they are normally found in the body -are the only known disease-causing agent that lack RNA or D NA -they become disease-causing agents when they convert from their normal form to their more harmful form which consists of the same chemical composition, but with a different molecular shape
2.2 Comparing Bacteria and Archaea -prokaryotes are represented by two domains; bacteria and archaea Bacterium (bacteria) is an individual prokaryotic cell or a single species that is in the domain Bacteria Archaeon (archaea) is an individual prokaryotic cell or single species that is in the domain Archaea Comparing Morphology -most common forms in bacteria and archaea are spheres and rods -the spherical forms are called coccus (sing. cocci ) -the rod forms are called bacilli (sing. bacillus) -there are also a part that is spiral -some bacteria are shaped like cubes, pyramids, and rods with star -shaped cross sections -some Archaea are shaped like plates and r ectangular rods Comparing Nutrition -all Archaea are methanogenesis which means that they produce methane-gas as a by-product -methanogenesis is an anaerobic process that occurs in environments that lack oxygen -often one of the final stages of o f decomposition -methane producing Archaea live in the digestive tracts of many animals, such as cattle -bacteria are photosynthetic -they absorb solar energy to convert to carbon dioxide and water to sugar Comparing Habitats -both bacteria and Archaea live in aerobic (with oxygen) and anaerobic(without anaer obic(without oxygen) habitats -archaea generally live in extreme habitats, they ar e usually referred to as extremophiles -bacteria generally live in moderate conditions, they are referred to as mesophiles There are three types of Extremophiles: -thermophiles live in hot springs and deep sea vents, temperatures over 100⁰C - acidophiles live in volcanic craters and mine drainage lakes, pH levels lower than 3 -halophiles live in salt lakes and inland seas, enduring salt concentrations above 20% Comparing Reproduction -they both reproduce asexually -since both domains are prokaryotic and lack a nucleus, both produce by binary fission where a cell just divides into two genetically identical -DNA can be exchanged instead of reproducing by binary fission with a process called conjugation -one cell links to another by a pilus a pilus(tube) (tube) and transfers a copy of some or all chromosomes
-both bacteria and Archaea house small DNA loops called plasmids which contains genes that differ from the ones in the chromosomes -they are transferred through conjugation -bacteria form hard walled structures called endospores to protect and store genetic material Classifying and Identifying Bacteria and Archaea -the following characteristics can be used to classify and identify bacteria and Archaea: -size and shape -nutrition -movement -genetic components -gram staining (separates bacteria into two major divisions based on the cell wall’s response to staining) Bacteria, Human Health and Environment -some bacteria will harm human health -bacteria are decomposers; breaks down organic molecules and releases carbon, nitrogen and sulfur -supports nutrient cycles -cyanobacteria are major producers of oxygen due to photosynthesis -some Archaea have enzymes that are special to humans -they can withstand extreme temperatures, salinity and acidity -biotechnologists use some of the enzymes for various procedures in DNA research
2.3 Eukaryotic Evolution and Diversity About 2 million years ago, eukaryotes evolved and this led an increase to diversity in life. These organisms are more complex than prokaryotes. They include more genes, allowing for greater cellular diversity in terms of size, shape, mobility and specialized functions. Scientists examined the important question how eukaryotic cells evolved and have come up with theories supported by evidence and observations. Endosymbosis -endosymbosis is a theory that ex plains how eukaryotic cells evolved from the symbiotic relationship between two or more prokaryotic cells -in endosymbosis, one cell engulfs a different type of cell and the e ngulfed cell becomes an internal part of the engulfing cell -the engulfed cell is called an endosymbiont Chloroplasts and Mitochondria -chloroplasts and mitochondria may have been free -living prokaryotes They continued to perform cellular activities while surviving and serving the host cell. A comparison of chloroplasts and mitochondria and prokaryotes show: -similar types of membrane -similar types of ribosomes -each reproduces by binary fission -each contains circular chromosomes -gene sequences match Multicellularity -scientists believe that large and complex eukaryotes first developed 550 million years ago -they have found red algae that date eukaryotes 1.2 to 1.5 billion years ago Scientists believe that multicellular organisms arose from colonies created by individual cells that divided; the genes in these cells contained information for some cells to become specialized. With time, groups of cells developed different functions Life Cycle and Re production Eukaryotes reproduce by a number of methods: -simple asexual reproduction -multiple fission asexual reproduction; where multiple copies of a cell are made at once -sexual reproduction preformed by a diploid organism (one set of chromosome per cell) -sexual reproduction preformed by a haploid organism (two sets of chromosome per cell)
-sexual reproduction preformed by an organism with both a haploid and a diploid stage of li fe -in the case of sexual reproduction, the timing of the production of the egg and sperm differs as the organism may be a haploid or a diploid -sexual reproduction is not possible without meiosis, meiosis, which is unique to eukaryotes -meiosis is the type of cell division that results in two daughter cells each with half the number of chromosomes as the parent cell
2.4 Protists: Unicellular Eukaryotes Most protists are unicellular. They are diverse and essentially grouped into one kingdom because they do not fit well into other kingdoms. There is still debate about whether multicellular algal species fit into this kingdom or belong in the plant kingdom. The rest of the kingdom can be gro uped into three types of protists: -animal like protists -fungus like protists -plant like protists Animal-like Protists -are often called protozoans called protozoans -are heterotrophic, consumes prokaryotes and other protists or organic wastes -some are parasites and consume nutrients from the organism they live in -parasites are organisms that benefit by living in or on another or ganism at the expense of that organism or ganism There are four different phyla: phyla : Cercozoa -includes amoebas -uses pseudopods (fake feet) and they change shape for mobility and to engulf food -inhabits various environments (freshwater, saltwater and humans) Ciliophora -includes paramecia -surface has cilia (hair-like projections) -cilia used for motion and food sweeping -inhabits various environments, some are parasites -large and complex organisms Zoomastigina -contains species with hard, protective covering over outer membrane -are called flagellates since they have one or more flagella used for movement -live in a variety of environments and conditions -can live in mutualistic relationships where both organisms can benefit Sporozoa -includes parasitic protists -unique and alternate between sexual and asexual reproduction -one species can cause malaria in humans
Fungus-like Protists -these protists absorb nutrients from living organisms, dead organisms and wastes -are heterotrophic (gets its nutrients and e nergy by consuming other organisms) -similar to fungi due to the fact they produce spores -structure of cell differs from fungi -classified into two categories; water moulds and slime moulds There are three different phyla: Myxomycota -plasmodial slime moulds -visible to unaided eye -creep and stream over decaying plant matter and e ngulf small particles -plasmodium contains many nuclei
Acrasiomycota -cellular slime moulds -differ from myxomycota in many ways; only contain one nucleus -live as separate cells and behave like amoebas until food is scares, then they join together as a slime mould Oomycota -filamentous water moulds -consumes dead organic matter -some are parasitic and draw nutrients out of their hosts by extending fungus like threads into their t issues and release digestive enzymes
Plant-like Protists -includes diatoms, dinoflagellates and euglenoids -contain photosynthetic pigments in their chloroplasts, which contain chlorophyll There are three phyla: Chrysophyta -also called phytoplankton called phytoplankton -free-living aquatic diatoms that are an important source of food for many marine organisms -all contain a rigid cell wall with an outer layer o f silica -can produce both sexually and asexually Pyrrophyta -also called dinoflagellates (two flagellas) -flagellas produce a spinning movement during locomotion -with plentiful food, they reproduce quickly and cause great algal bloom -a ride tide is a coastal phenomenon in which dinoflagellates that contain red pigments are so concentrated that the seawater has a distinct red colour -are photosynthetic -mutualistic relationship with coral Euglenophyta -mostly freshwater species -autotrophs (can produce own food) in sunlight -contains chloroplasts for making food by day -heterotrophs in the dark -absorbs nutrients at night
