Download Chapter 13 – Review

Chapter 13 – Review
Origin of Life
13.1 How Cells Arose
Primordial soup – early ocean in which the chemicals of life may have arisen
Experiment performed by Stanley Miller and Harold Urey supported this hypothesis
Life on earth may have arisen in bubbles in the ocean. The “bubble model” suggests that biological molecules
were captured in bubbles where they underwent chemical reactions leading to the origin of life (figure 13.2)
(144.0K) . The first cells may have formed from bubble-enclosed molecules, such as RNA.
Prokaryotes
13.2 The Simplest Organisms
Prokaryotes have very simple internal structures, lacking a membrane-bound nucleus and other membrane-bound
compartments, such as mitochondria and chloroplasts. The plasma membrane of prokaryotes is encased in a cell
wall. The cell wall of bacteria is made of peptidoglycan, and the cell wall of archaea lacks peptidoglycan, being
made of protein and/or polysaccharides. Bacteria are divided into two groups, gram-positive and gram-negative,
based on the construction of their cell walls, including the presence of an outer membrane in gram-negatives
(figure 13.3) (111.0K) .
Bacteria reproduce by splitting in two, called binary fission, and may exchange genetic information through
conjugation (figure 13.4) (79.0K) .
13.3 Comparing Prokaryotes to Eukaryotes
Prokaryotes are different from eukaryotes in many ways, including that they lack interior compartments, such as
membrane-bound nuclei, and are more metabolically diverse (figure 13.1) (99.0K) .
Viruses
13.4 Viruses Infect Organisms
Viruses are not living organisms, but are parasitic chemicals that enter and replicate inside cells. They contain a
nucleic acid core (either RNA or DNA, usually not both) surrounded by a protein coat, called a capsid. Some
viruses have an outer membrane-like envelope (figure13.6) (94.0K) . Viruses cause many diseases, often
spreading from animals to humans.
The Protists
13.5 The Origin of Eukaryotic Cells
The endosymbiosis theory proposes that energy-producing bacteria became incorporated into the cells of early
eukaryotic cells, giving rise to mitochondria. Similarly, photosynthetic bacteria became incorporated, giving rise
to chloroplasts (figure 13.7) (117.0K) .
13.6 General Biology of Protists
Protists are a very diverse group of eukaryotes, having diverse cell surfaces, modes of locomotion, and modes of
acquiring nutrients. Some protists form cysts and most reproduce asexually except for times of stress. Some exist
as single cells (figure 13.8) (145.0K) , whereas others form colonies (figure 13.9) (191.0K) or aggregates,
but only a few exhibit true multicellularity like that seen in plants, fungi, and animals. This is found in some of
the algae.
13.7 Kinds of Protists
The classification of the organisms in the kingdom Protista is in a state of flux. The 15 phyla of protists are often
grouped into five categories based on modes of locomotion, photosynthetic capabilities, and spore-formation
(figure 13.10) (76.0K) and (table 13.2a) (109.0K) and (table 13.2b) (113.0K) .
Fungi
13.8 A Fungus Is Not a Plant
Fungi are nonmobile heterotrophs. The body of a fungus is composed of long slender filaments, called hyphae,
that pack together to form a mycelium (figure 13.11) (161.0K) . Most fungi have nonmotile sperm, unlike
some plants. They have cell walls made of chitin, which is different from plant cell walls, and they undergo
nuclear mitosis, where the nuclei divide but not the cell. Most fungal cells are separated by an incomplete wall
called a septum, which allows cytoplasm to pass between cells.
Sexual reproduction takes place between two genetically different “mating types” where two haploid hyphae
fuse.
Fungi obtain nutrients through external digestion (heterotrophic by absorption). They grow on their food,
releasing enzymes that digest the food. The products of digestion are then absorbed by the fungus.
13.9 Kinds of Fungi
There are four phyla of fungi— Zygomycota, Ascomycota, Basidiomycota, and Chytridiomycota— classified
according to their mode of sexual reproduction. A fifth group, the imperfect fungi, is a “catch-all” category of
fungi in which sexual reproduction has not been observed (table 13.3) (118.0K) .
Fungi play key roles in the environment. They are decomposers. They are involved in symbiotic associations
with the roots of some plants, called mycorrhizae, and with cyanobacteria or algae, called lichens (figure
13.14) (351.0K) .