VIRUSES AND OTHER NONCELLULAR INFECTIOUS AGENTS – Viruses exhibit some, but not all, characteristics of living organisms. Viruses: Possess genetic material in the form of nucleic acids Are not cellular and cannot reproduce on their own.

Protein coat RNA Protein spike Membranous envelope Figure 10.28

– Prions are responsible for neurodegenerative diseases including: Mad cow disease Scrapie in sheep and goats Chronic wasting disease in deer and elk Creutzfeldt-Jakob disease in humans

Figure 10.34

– Avian flu: Infects birds Infected 18 people in 1997 Since has spread to Europe and Africa infecting 300 people and killing 200 of them

Figure 10.35

Prokarya--They’re Everywhere! – Prokaryotes Are found wherever there is life Far outnumber eukaryotes Can cause disease Can be beneficial – Compared to eukaryotes, prokaryotes are Much more abundant Typically much smaller – Prokaryotic cells Lack true nuclei Lack other membrane-enclosed organelles Have cell walls exterior to their plasma membranes – Prokaryotes come in several shapes: Spherical (coccus) Rod-shaped (bacillus) Spiral (spirillum)

Colorized SEM Figure 15.7

Plasma membrane (encloses cytoplasm) Cell wall (provides Rigidity) Capsule (sticky coating) Prokaryotic flagellum (for propulsion) Ribosomes (synthesize proteins) Nucleoid (contains DNA) Pili (attachment structures) Colorized TEM Figure 4.4

SHAPES OF PROKARYOTIC CELLS Spherical (cocci)Rod-shaped (bacilli)Spiral Colorized SEM Colorized TEM Figure 15.8

– Most prokaryotes can reproduce by binary fission and at very high rates if conditions are favorable. – Some prokaryotes Form endospores, thick-coated, protective cells that are produced within the cells when they are exposed to unfavorable conditions Can survive very harsh conditions for extended periods, even centuries Procaryotic Reproduction

The Two Main Branches of Prokaryotic Evolution: Bacteria and Archaea – By comparing diverse prokaryotes at the molecular level, biologists have identified two major branches of prokaryotic evolution: Bacteria Archaea (more closely related to eukaryotes) © 2010 Pearson Education, Inc.

– Some archaea are “extremophiles.” Halophiles thrive in salty environments. Thermophiles inhabit very hot water. Methanogens inhabit the bottoms of lakes and swamps and aid digestion in cattle and deer.

(a) Salt-loving archaea(b) Heat-loving archaea Figure 15.13

– Lyme disease is Caused by bacteria carried by ticks Treated with antibiotics, if detected early

“Bull’s-eye” rash Tick that carries the Lyme disease bacterium Spirochete that causes Lyme disease SEM Figure 15.15

Bioterrorism – Humans have a long and ugly history of using organisms as weapons. During the Middle Ages, armies hurled the bodies of plague victims into enemy ranks. Early conquerors, settlers, and warring armies in South and North America gave native peoples items purposely contaminated with infectious bacteria. In 1984, members of a cult in Oregon contaminated restaurant salad bars with Salmonella bacteria. In the fall of 2001, five Americans died from the disease anthrax in a presumed terrorist attack.

Figure 15.16

PROTISTS – Protists Are eukaryotic Evolved from prokaryotic ancestors Are ancestral to all other eukaryotes, which are – Plants – Fungi – Animals

(b) Origin of mitochondria and chloroplasts Photosynthetic eukaryotic cell Photosynthetic prokaryote Aerobic heterotrophic prokaryote Endosymbiosis (Some cells) Mitochondrion Chloroplast Figure 15.20b

– The classification of protists remains a work in progress. – The four major categories of protists, grouped by lifestyle, are Protozoans Slime molds Unicellular algae Seaweeds

Protozoans – Protists that live primarily by ingesting food are called protozoans. – Protozoans with flagella are called flagellates and are typically free-living, but sometimes are nasty parasites.

A flagellate: Giardia Colorized SEM Figure 15.21a

Another flagellate: trypanosomes Colorized SEM Figure 15.21b

– Amoebas are characterized by Great flexibility in their body shape The absence of permanent organelles for locomotion – Most species move and feed by means of pseudopodia (singular, pseudopodium), temporary extensions of the cell.

An amoeba LM Figure 15.21c

A foram LM Figure 15.21d

– Apicomplexans are Named for a structure at their apex (tip) that is specialized for penetrating host cells and tissues All parasitic, such as Plasmodium, which causes malaria

– Ciliates Are mostly free-living (nonparasitic), such as the freshwater ciliate Paramecium Use structures called cilia to move and feed

A ciliate LM Figure 15.21f

A flagellate: Giardia A foram An apicomplexan A ciliate An amoeba Another flagellate: trypanosomes Food being ingested Pseudopodium of amoeba Red blood cell LM TEM LM Colorized SEM Apical complex Cilia Oral groove Figure 15.21

Slime Molds – Slime molds resemble fungi in appearance and lifestyle, but the similarities are due to convergence, and slime molds are not at all closely related to fungi.

– Plasmodial slime molds Can be large Are decomposers on forest floors Are named for the feeding stage in their life cycle, an amoeboid mass called a plasmodium

Figure 15.22

– Cellular slime molds have an interesting and complex life cycle that changes between a Feeding stage of solitary amoeboid cells Sluglike colony that moves and functions as a single unit Stalklike reproductive structure

LM Amoeboid cells Slug-like colony Reproductive structure Figure 15.23

Unicellular and Colonial Algae – Algae are Photosynthetic protists Found in plankton, the communities of mostly microscopic organisms that drift or swim weakly in aquatic environments

– Unicellular algae include Diatoms, which have glassy cell walls containing silica Dinoflagellates, with two beating flagella and external plates made of cellulose

(a) A dinoflagellate, with its wall of protective plates SEM Figure 15.24a

(b) A sample of diverse diatoms, which have glossy walls LM Figure 15.24b

– Green algae are Unicellular Sometimes flagellated, such as Chlamydomonas Colonial, sometimes forming a hollow ball of flagellated cells, as seen in Volvox

(c) Chlamydomonas, a unicellular green alga with a pair of flagella Colorized SEM Figure 15.24c

(d) Volvox, a colonial green alga LM Figure 15.24d

Seaweeds – Seaweeds Are large, multicellular marine algae Grow on or near rocky shores Are often edible

– Seaweeds are classified into three different groups, based partly on the types of pigments present in their chloroplasts: Green algae Red algae Brown algae (including kelp)

Green algaeRed algaeBrown algae Figure 15.25