Important things to know:
Know and be able to explain the following:
- Redi's experiment and what it showed.
- The controversy over "spontaneous generation".
- Pasteur's experiment and his carefully worded conclusion.
- Oparin's theory, how he arrived at it, and his ideas about Earth's early atmosphere (a reducing atmosphere,
rich in H2, CH4, NH3, and H2O).
- Miller's experiment, how it tested Oparin's theory, and how he used a control to show that
his results could not have came from bacterial contamination.
- Modern ideas that draw upon the Oparin-Haldane theory, including the "RNA World" hypothesis.
- How procaryotic and eucaryotic cells differ
- Describe the symbiotic theory for the origin of eucaryotic cells, and the evidence for this theory
- The family tree of eucaryotes as currently understood.
The Origin of Life:
- Francesco Redi showed that flies only come from eggs laid by other flies; they do not generate spontaneously from rotting meat.
- Louis Pasteur perfected sterilization techniques and
proved that properly sterilized broth would remain sterile if bacteria were excluded,
but that ordinary air contained bacteria that could contaminate the broth. He proposed a theory of biogenesis—
life can originate only from pre-existing life.
- Alexander Oparin proposed that the origin of life was
impossible under present conditions, but that life had originated
spontaneously under very different conditions on the primitive Earth
(primary abiogenesis). He postulated that life could originate only
in a hydrogen-rich reducing atmosphere, which he thought contained
hydrogen (H2), methane (CH4), ammonia
(NH3), and water vapor (H2O). J.B.S. Haldane
proposed a similar theory independently.
- S.L. Miller tested Oparin's ideas by combining
H2, CH4, NH3, and H2O in
a sterile apparatus into which he could introduce a spark to simulate
lightning. After circulating this mixture for several days, he analyzed
the products and found many amino acids, a few small peptides, and other organic compounds.
- Modern ideas on the origin of life follow the Oparin-Haldane theory of chemical
evolution, in which life arose gradually in a reducing atmosphere.
- The solar system probably formed from a swirling nebula, which
formed into the sun at the center and the planets peripherally.
- Amino acids probably originated in a manner similar to the reactions
of Miller's experiment. The compounds dissolved in the primitive ponds
and oceans, forming a "hot, dilute soup."
- Proteins and DNA can form as polymers by linking smaller units
together, but not until the smaller units are concentrated. Several
concentration mechanisms (tidal pools, crystal surfaces, bubble-like
droplets, etc.) have been suggested.
- Molecules made without life are usually symmetrical or have equal
proportions of right-handed and left-handed forms, but biological
systems contain mostly asymmetrical molecules. Amino acids made by
organisms are mostly of the L- (left-handed) form, but experiments like
Miller's gave right- and left-handed amino acids in equal proportions.
Molecular asymmetry is an important property of life, but we don't know
exactly when or how it arose.
- At some point, biological systems formed tiny droplets with lipid or
protein membrane-like surfaces. Once these droplets formed, their contents could reach
concentrations very different from those prevailing outside or from one another (they had
individuality). Some were surely more stable than others, and were favored
by "protoselection," especially if they could increase in size and
fragment into smaller droplets, a primitive form of reproduction.
- Protein synthesis was surely much simpler originally than it is now
and was probably much less reliable in perpetuating sameness. Enzyme activity
may have originated by chance. The origins of DNA replication are obscure.
The most widely supported theory holds that RNA was
initially selected for its role in making protein synthesis more reliable,
and that an "RNA world" resulted. DNA came long afterwards, and was initially
selected for its role in copying RNA.
- Exobiology is the search for life elsewhere, outside planet Earth.
To date, much evidence exists for Miller-style synthesis of amino acids,
nitrogen bases, and other compounds elsewhere in our solar system.
Many stars outside our solar system have planetary systems, and some of those
planets are believed to have just the right temperature and other conditions
for life to have arisen (the "Goldilocks phenomenon").
No firm evidence has yet been found that life formed anywhere except
on Earth, but many scientists think such origins are very probable.
Evolution of life cycles:
Many organisms have life cycles in which diploid stages (sporophytes)
alternate with haploid stages (gametophytes)— an
alternation of generations.
Meiosis marks the beginning of the
gametophyte stage and fertilization marks the beginning of the
sporophyte stage. The sporophyte generation has assumed greater and greater
importance in the course of plant and animal evolution.
Gametophyte: Any multicellular haploid body.
Gametophyte phase or generation: Haploid portion of life cycle, from meiosis to fertilization.
Sporophyte: Any multicellular diploid body.
Sporophyte phase or generation: Diploid portion of life cycle, from fertilization to the next meiosis.
Either the sporophyte or the gametophyte phase (or both) can be
conspicuous. Most microorganisms have dominant haploid phases. Higher plants
and most animals have dominant diploid phases.
- The unicellular green alga Chlamydomonas has a dominant haploid
phase. The diploid zygote exists only briefly before it undergoes meiosis
and releases new haploids. Gametes of opposite (+ and -) mating types look the same, a condition called isogamy.
- Life cycles vary greatly among other algae. Gametes are often dissimilar (anisogamy). Often, the male gametes are small and motile, while
eggs are much larger and nonmotile (oögamy).
- Moss plants are gametophytes, which contain sex organs and produce
gametes. Sporophytes grow as virtual parasites on the gametophytes.
Meiosis produces haploid spores, which grow into new gametophytes.
- The small fern gametophyte resembles a heart-shaped leaf; sex organs
are produced on its surface. Fertilization produces a sporophyte, which
is the conspicuous fern. Meiosis produces haploid spores, which grow into new gametophytes.
- In seed plants, the conspicuous plant is always a sporophyte.
Angiosperms produce microscopic female gametophytes of only a few cells within the ovaries of the flower.
Male gametophytes are even smaller and are contained in the pollen grains. The seed that results
after fertilization contains a young sporophyte.
Biological Diversity:
- Viruses are not true organisms. They are fragments of DNA or RNA (never both), often surrounded by protein,
that can replicate only with the help of intact cells.
- All viruses have a lytic cycle, in which they invade a cell,
replicate inside, then rupture the cell and release their progeny.
- Some viruses also have a lysogenic cycle, in which they lie
dormant and replicate as part of the host DNA.
- Viral shapes can be helical, icosahedral (20-sided), or complex (with head and tail).
- Viruses have very few characteristics of life; they cannot reproduce without the
gene-replicating machinery of the host cell.
- Viruses are classified by the the type of nucleic acid (either DNA or RNA).
- Procaryotes are one-celled organisms whose cells lack a true
(membrane-bounded) nucleus and other eucaryotic organelles. Procaryotes include:
- Archaea (Archaebacteria): A group of strict anaerobes (killed by
oxygen) that include methane-producers (methanogens), extreme halophiles, and extreme thermophiles.
Their RNA sequences have only minimal homology to the RNA of other procaryotic or eucaryotic
organisms, and the cell walls are also unique.
- True bacteria: The majority of procaryotes, with RNA sequences homologous to those of Cyanobacteria and eucaryotes (but not Archaebacteria). Most are
heterotrophs. A few autotrophs use various energy sources, but none contains chlorophyll a and none can split water in the Hill reaction.
A possible classification of Bacteria:
- Proteobacteria the majority of bacteria, further groupings are uncertain.
- Chlamidias: obligate energy parasites that can only survive inside animal cells
- Spirochetes: motile, corkscrew-shaped bacteria
- Gram-positive bacteria: a great variety of mostly pathogenic species
(Bacillus, Clostridium, Streptococcus, Staphylococcus, Streptomyces, Mycoplasma)
- Cyanobacteria (= Cyanophyta, blue-green bacteria, or blue-green algae):
All are similar to bacteria in structure and their RNA sequences are homologous.
All are oxygen-tolerant autotrophs that can use sunlight for energy and CO2 as a carbon source. They contain chlorophyll a
and can split water in the Hill reaction.
Procaryotic cells have no true nuclei and they lack many other
structures (such as mitochondria and endoplasmic reticulum) found in eucaryotic cells.
- Procaryotic cell walls contain substances like muramic acid, absent in eucaryotes.
- Gram-negative cell walls: two membranes, separated by a thin layer of peptidoglycan.
- Gram-positive cell walls: one membrane, surrounded by a very thick peptidoglycan layer.
- Chemical diversity: Procaryotes have greater chemical diversity than
eucaryotes. They can subsist on a greater variety of foodstuffs, have
a greater range of chemical substances that can be tolerated, and can
subsist in a variety of atmospheres, both with and without oxygen.
- Energy sources: Phototrophic (sunlight) vs.
Chemotrophic (chemical energy)
- Carbon sources: Autotrophic (inorganic carbon incl. CO2)
vs.
Heterotrophic (organic molecules, mostly from other organisms)
- Anaerobic (oxygen-intolerant) vs. Aerobic (oxygen-dependent) vs.
Facultative (OK either way)
- Cell shapes: Commonly "rod"-shaped, but many are spherical ("cocci").
Less common shapes: bent rods, pear-like, gentle spirals, corkscrews ("spirochete")
- Procarytoic chromosomes are generally arranged in a single closed loop
containing DNA but no histone proteins. Most procaryotes also have small chromosome fragments
that can detach from the main chromosome and exist separately for long
periods as plasmids, small, circular samples of DNA similar to certain viruses.
- Eucaryotes are organisms whose cells have a true nucleus surrounded by a nuclear envelope,
and various other eucaryotic organelles including mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and sometimes plastids.
Eucaryotic cells have nuclei surrounded by double-layered membranes.
The several chromosomes each contain proteins as well as DNA. The cytoplasm of eucaryotic cells contains many organelles not found in procaryotic cells.
Much evidence indicates that eucaryotic cells originated by symbiosis, and, in particular, that mitochondria and plastids were once separate organisms.
- Chromosomes are usually separate, multiple, and linear; each contains protein
as well as DNA.
- Cytoplasm contains contractile proteins (actin, myosin), making possible
cytoplasmic streaming (cyclosis), amoeboid locomotion using pseudopods, and
ingestion of food by phagocytosis.
- Many types of cytoplasmic organelles are present, including membrane
organelles (like endoplasmic reticulum) and "9 + 2" arrangements of
microtubules. Mitochondria (and plastids in plant cells) contain their own DNA.
Theory of endosymbiosis: Most biologists now believe that eucaryotic
cells originated when small, energy-producing procaryotic cells lived inside
larger cells and became mitochondria by intracellular symbiosis
(endosymbiosis). Plastids may have arisen the same way. Similar origins
for other cell parts have been proposed but are less widely accepted. Perhaps
host cells originally phagocytized the energy-producing mitochondria; then
natural selection favored those host cells that maintained the mitochondria
as an energy source instead of digesting them.
- Evidence for endosymbiosis comes from the fact that both mitochondria and plastids have two membranes:
the outer membrane resembles a eucaryotic membrane, but the inner one resembles a procaryotic cell membrane.
- Mitochondria and plastids possess their own DNA and are self-replicating.
- Bacteria are known whose metabolic abilities are similar to those of
the postulated host cell, while other bacteria have the enzymes of the
Krebs cycle and are thus comparable in ability to mitochondria.
- CLASSIFICATION OF THE DOMAIN EUCARYA
Since 2004, the following major groups (subdomains) of eucaryotes are now recognized:
- UNIKONTA:
Most organisms in this group are motile, either by amoeboid locomotion or by a
single posterior (rear-facing) flagellum (or both). Many are predators that use their
pseudopods to engulf their prey. This large group includes the
Amoebozoa, the slime molds, the Fungi (Mycota), the choanoflagellates, and the
Animal Kingdom.
- EXCAVATA:
This small group includes the Diplomonads such as the parasite Giardia.
Two smaller groups, the Parabasalids, and the photosynthetic Euglenoids, may also
belong here. Many experts consider this group close to the ancestry of all Eucarya
(possibly excluding Unikonta).
- RHIZARIA:
These one-celled predators all secrete a hard shell enclosing a cell body from which
radiate numerous thin, needle-like pseudopods that are used to trap and engulf their prey.
- Radiolaria: shell is usually a beautiful sphere made of silica (SiO2).
- Foraminifera: shell is coiled, perforated with many tiny holes, and
usually made of calcium carbonate (CaCO3).
- CHROMALVEOLATA:
This large group is often subdivided into two subgroups:
- ALVEOLATA, with bubble-like spaces (alveoli) just beneath the plasma membrane.
Included here are:
- Ciliata, whose entire cell surface is
clothed in cilia. Paramecium is a familiar example.
All ciliates have two nuclei (macronucleus, micronucleus) and a unique type of
sexual conjugation in which two cells exchange micronuclei.
- Apicomplexa, a group of parasites that use a sharp apical complex
to penetrate host cells. Reproduction by spores. The malaria parasite Plasmodium belongs to this group.
- STRAMENOPILES,
characterized by two unequal flagella (one simple, one with feathery branches) and by
chloroplasts containing chlorophylls a and c and several unique xanthins and
other pigments not found in the Archaeplastida. This group is hypothesized to have originated
by a symbiotic capture of plastids, independently of the Archaeplastida.
Included are:
- Brown algae (Phaeophyta), often large, structurally complex; ecologically dominant
in temperate and colder marine waters.
- Dinoflagellates, unicellular, marine and planktonic,
with two flagella at right angles to one another.
Mitosis unusual: no histones, no centrioles, no spindle fibers; nucleolus and nuclear envelope
remain visible throughout mitosis.
- Diatoms, especially abundant in plankton; the major primary producers
in most marine (and several freshwater) ecosystems.
- ARCHAEPLASTIDA:
These organisms are all photosynthetic and all have plastids containing chlorophyll a
and either chlorophyll b or chlorophyll d, but never chlorophyll c.
Included here are the following:
- Red algae (Rhodophyta), containing chlorophylls a and d,
plus other pigments resembling those of Cyanobacteria. No "9 + 2" organelles
(centrioles or flagella); no motile cells, not even gametes. Unique storage
products include "floridean starch" in cell walls. Ecologically dominant
in tropical marine waters.
- Green algae (Chlorophyta), containing chlorophylls a and b,
xanthophylls, and α- and β-carotenes. Cellulose, pectins, and starch are also present.
Ecologically dominant in freshwater ecosystems, but many are also marine.
- Plants (Kingdom Plantae), sharing cellulose, starch, and all the pigments found
in green algae, but differing from algae in developing from multicellular embryos.
- Kingdom PLANTAE: Plants are organisms sharing the following derived characteristics:
- Autotrophic, using CO2 as the source of carbon for organic compounds
- Photosynthetic using chlorophylls a and b, plus several "accessory pigments," to capture solar energy.
- Generally non-motile, with some exceptions for male gametes.
- Presence of persistent embryonic tissue (meristem) capable of indeterminate growth throughout life.
- Development from multicellular embryos in which a reproductive cell (ovum) is surrounded by nonreproductive tissue.
Origin of Plant Kingdom = origin of multicellular embryos.
Embryophyta: Bryophytes and all higher plants are often
called Embryophyta because they develop from embryos
in which the zygote is surrounded by a protective layer of sterile,
nonreproductive cells. Multicellular sex organs are always present.
Bryophytes: Embryophyta without vascular tissues (xylem and phloem).
They develop from multicellular embryos in which sterile,
nonreproductive cells surround and protect the zygote.
However, because they lack vascular tissues or true roots, bryophytes cannot be
anchored very strongly in the soil or grow very tall.
Neither water nor
nutrients can be transported from one plant part to another except by
diffusion. This restricts bryophytes to small sizes and moist habitats;
it also means that all parts of the plant must carry out their own photosynthesis.
Bryophytes probably evolved from green algae. All bryophytes have well-marked
alternation of generations, with the gametophyte phase dominant.
There are two major types of bryophytes:
- Liverworts and hornworts: Bryophytes whose gametophytes are mostly
flat-lying plants with distinct upper and lower surfaces. Single-celled
absorptive rhizoids grow from the lower surface. Sporophytes vary but are generally simple.
- Mosses: Bryophytes whose gametophytes usually have an erect,
stem-like portion surrounded with leafy extensions arranged in a
circular pattern. Absorptive rhizoids are often multicellular,
with cross-walls. Sporophytes are typically more complex than in
liverworts, with a spore-bearing capsule supported by a stalk.
Vascular plants (tracheophytes): Vascular tissue provides support that holds plants erect
and allows them to grow much taller; it also allows plants to transport materials from one part
to another. Vascular tissues include:
- Xylem: Plant tissue that conduct fluids upward through cells
with stiff cell walls (containing lignin). The stiff cell walls (wood) allow plants to grow
taller and erect, and the upward movement of water allows above-ground plant parts to receive water
and nutrients absorbed by the roots,
- Phloem: Conduct photosynthetic product to other parts of the plant (mostly downward). This allows
the parts that do not photosynthesize to receive sugars and other
products from the green, photosynthesizing parts.
(A root system is not possible unless photosynthetic products can reach underground parts.)
Vascular plants include:
- Early vascular plants (Rhyniophyta and Psilophyta):
The earliest vascular plants, like Rhynia and Asteroxylon, lived in moist, swampy places
during the Silurian period. Dichotomous (two-fold) branching characterized all plant parts.
Much of each plant grew out horizontally, but some parts turned upward and grew erect.
No true leaves were present; stems were green and photosynthetic.
Surviving relatives include only a few living genera (Psilotum, Tmesipterus) with
spore-forming structures (sporangia) terminal in position. Stems are green and photosynthetic;
no true leaves or roots are present. Stomates are distributed over the outside surface of the stems.
- Lepidophyta (lycopods): Club mosses and their relatives.
True roots are present and dichotomously branched. Leaves (mostly small) are microphylls— each has a
single vein in the middle, and the vascular bundle is not interrupted
where this vein arises. Some leaves bear reproductive sporangia in the
angle of attachment (axillary position). Modern lycopods are all small
plants, but some Carboniferous lycopods grew to tree-like heights.
- Arthrophyta or Sphenopsida: Horsetails, with spore-forming parts grouped in a cone-like
structure at the top, and spores hidden beneath scale-like sporophylls.
Small leaves are arranged in tiers or whorls; true roots are present.
Equisetum is the only living genus.
- Pterophyta: Ferns and fernlike plants, with true roots. Leaves are
megaphylls— each has many branching veins, and the vascular
bundle is interrupted by a leaf gap where the main vein arises.
Leaves carry sporangia on their lower surfaces or their margins. Life cycle has a dominant sporophyte.
- "Gymnosperms": Vascular plants with naked seeds, borne naked on the surface of reduced,
scale-like leaves and not enclosed within ovules (as in angiosperms).
Gymnosperms are placed in five or more phyla (divisions):
- Seed ferns (Pteridospermophyta): Extinct plants with large,
fern-like leaves, but reproducing by seeds; occasionally growing to the height of small trees. Devonian to Jurassic in age, dominant
during the Carboniferous (when they formed great coal swamps). Believed close to the ancestry of other seed plants.
- Cycads (Cycadophyta): Short, thick-stemmed plants with a crown of large fern-like or palm-like leaves. Seeds borne together in a structure
resembling a large pine cone. Flourished during the Mesozoic era; only a few tropical and subtropical genera persist today.
- Ginkgos (Ginkgophyta): A mostly Mesozoic group with one living species (Ginkgo biloba, an ornamental tree with fan-shaped leaves).
- Conifers (Coniferophyta): The most familiar and economically important gymnosperms, including pines, spruces, firs, etc. Leaves are typically
scale-like or needle-like, with reduced surface area. Seeds are borne in cone-like aggregates.
- Gnetophyta: This group includes only three living genera (Gnetum, Ephedra, Welwitschia), which differ greatly. All share a partially
enclosed type of seed that approaches the angiosperm condition but was probably derived independently.
- Angiosperms (flowering plants) have seeds enclosed in an ovary.
Angiosperms probably evolved in response to selection by insects; many flowers are fertilized by insects.
All angiosperms have double fertilization: one sperm nucleus fuses with the ovum to produce a zygote (true fertilization);
a second sperm nucleus fuses with two female "polar nuclei" to produce a triploid (3N) endosperm.
Angiosperms are the most diverse and most successful of all plants, arranged in two large groups:
- Class Dicotyledonae ("dicots", Magnoliophyta): Angiosperms with a
seed containing two "seed leaves" (cotyledons) in which food is stored. (The two halves of a dried peanut are a familiar example.)
- Flower parts are usually in multiples of 4 or 5.
- Veins in leaves and petals branch to form net-like patterns.
- Vascular bundles usually arranged in a circular ring.
- Includes the majority of angiosperms: buttercups (considered primitive), roses, beans (and other legumes),
daisies, oaks, maples, roses, apples, oranges, peaches, melons, and many others.
- Class Monocotyledonae ("monocots," Liliophyta): Angiosperms with a seed containing only one "seed leaf" (cotyledon)
in which food is stored (such as a kernel of corn, which cannot be divided into halves).
- Flower parts are usually in multiples of 3 or 6.
- Leaves and petals have parallel veins that branch only occasionally.
- Vascular bundles usually scattered throughout cross-section of stem.
- Includes the more advanced angiosperms: orchids, lilies, palms,
and grasses (including wheat, corn, rice, and other cereal grains).
- Structure and Function in Vascular Plants:
- Roots: Absorptive parts, usually underground, absorbing water and dissolved ions.
From the outside inward, they contain:
- Epidermis, from which absorptive root hairs develop.
- Cortex, often a thick layer.
- Endodermis, containing a waterproof Casparian strip.
- Vascular bundles, with xylem, phloem, and cambium surrounded by a pericycle.
- Stems: Supporting structures which contain, from the outside inward:
- Epidermis
- Cortex (bark)
- Vascular bundles whose tissues provide both structural support and transport of fluids:
- Phloem: tissue that transports photosynthetic
products from the leaves to other parts of the plant, principally
downward through the stem. The principal transport cells in phloem are
seive tube cells.
- Cambium: a type of meristem, or persistently embryonic tissue,between the xylem and phloem, that helps the
stem increase in girth throughout the life of the plant.
- Xylem and its function:
- The stiff cell walls of xylem contain lignins that allow the stems to support the plant.
"Xylem" is the Greek word for wood.
- Water and dissolved minerals (ions, including K+, Ca2+, Mg2+,
NO3-, PO43-) ascend from roots through stems to upper parts of the plant, traveling
through tube-like tracheids of the xylem.
- Loss of water from leaves is called transpiration.
- The ascent of sap seems to be governed largely by
transpiration pull, or reduced pressure from above,
a process requiring long, unbroken chains of fluid with no
air bubbles. Root pressure also helps a bit.
- Pith (not always present) in the innermost parts of the stem.
- Leaves are the principal organs of photosynthesis in most plants, arranged as follows:
- Upper epidermis, coated with a waxy cuticle.
- Palisade layer, containing the highest density of
chloroplasts. The "light" (light-dependent) reactions of
photosynthesis are most efficient here.
- Spongy mesophyll: The "dark" (light-independent)
photosynthesis reactions are most efficient here because
air spaces facilitate gas exchange.
- Veins (extensions of xylem + phloem) run through the
spongy mesophyll layer.
- Lower epidermis, coated with a waxy cuticle, contains
pores for gas exchange called stomates or stomata.
- Seeds are easily dispersed structures developed from a zygote and enclosing an embryonic sporophyte.
Seeds evolved in gymnosperms and are enclosed in ovaries among angiosperms.
- Flowers develop in angiosperms only. They include ovaries and surrounding structures:
- Petals and sepals surround and protect the other flower parts,
especially in undeveloped flowers. In many species, these parts may have colors or odors that attract insects or other species that pollinate the plant or disperse its seeds.
- Male flower parts include stamens, each made of a filament and a pollen-producing anther. Pollen grains contain male gametophytes.
- Female flower parts include stigma (whose sticky surface catches pollen), style (a stalk-like part supporting the stigma),
and ovary, enclosing one or more ovules within modified leaves called carpels. Each ovule develops into an 8-celled
gametophyte containing 1 egg, 2 polar nuclei, and 5 other cells.
Ripened ovaries make up a fruit.
- "Complete" flowers have all the parts listed above, but many species have separate male flowers and female flowers.
- Fertilization in angiosperms: First, a thin, long pollen tube grows from the
pollen grain down the style. Two nuclei (tube nucleus and generative nucleus migrate down the pollen tube as it grows. The generative nucleus
then divides into two sperm cells: one fertilizes the egg (syngamy or true fertilization; the other fuses with the 2 polar nuclei to form
a triploid (3N) endosperm, containing stored food that supports the embryo later. This so-called double fertilization is characteristic
of all angiosperms. After fertilization, the new embryo and its endosperm and protective coverings make up a seed.
- Fruits: One or more ripened ovaries together constitute a fruit,
enclosing one to many seeds. Many fruits are eaten (and their seeds dispersed)
by animals; other seeds are dispersed by wind, etc.
- Biological Diversity (continued):
- Kingdom MYCOTA (FUNGI):
General characteristics: The Mycota or Fungi are non-photosynthetic eucaryotes adapted to absorptive nutrition.
Plastids and chlorophyll are absent. Cell walls are made of chitin, not cellulose.
Cell membranes sometimes break down to form binucleated cells or multinucleated aggregates. Nutrition is usually absorptive; many fungi live on dead or decaying matter (saprophytic),
but some are parasitic instead. Fungi are important as decay organisms in freshwater and terrestrial ecosystems. Most prefer moist conditions for optimal growth.
True fungi form branched filaments (hyphae) that invade dead
or decaying material. All fungi form spores; the various groups of fungi are distinguished by their means of spore formation.
- Chytrids: Primitive, aquatic fungi that reproduce by flagellated cells (zoospores).
- True fungi (Eumycota): Fungi whose vegetative structure typically consists of a series of branching filaments (hyphae) forming a tuft (mycelium).
In most cases, the cells of the hyphae are dikaryotic, containing two nuclei that fuse only when ready to undergo meiosis.
- Glomerulomycota: Fungi that are often attracted to plant roots, where they
form symbiotic associations (mycorrhizae) that benefit both species.
- Zygomycota (black bread molds, etc.): Reproduce by conjugation of hyphae that come together and form nonmotile spores.
- Ascomycetes (Ascomycota) (yeasts, common bread molds, cup fungi, truffles, etc.):
spores are produced, 4 or 8 at a time, in sacs (asci). The genus Saccharomyces
is used commercially in the production of both bread and beer.
- Basidiomycetes (Basidiomycota) (mushrooms, puffballs, rusts, smuts, etc.): spores
are produced, usually 4 at a time, at the tips of club-like organs (basidia).
- Deuteromycetes ("fungi imperfecti"): Fungi with no known sexual stages. Important genera
include: Penicillium (responsible for penicillin, also roquefort and camembert cheeses),
Candida (responsible for vaginal yeast infections), and fungi responsible for ringworm and athlete's foot.
- Lichens are very intimate symbiotic associations of fungi with either
algae or cyanobacteria. The fungus absorbs and retains sufficient moisture
for both partners; the green partner photosynthesizes and provides food.
Lichens are often the first colonizers of bare rock surfaces.
- Kingdom ANIMALIA:
General characteristics: Animals are multicellular, non-photosynthetic eucaryotes
that develop from a hollow ball of cells (blastula);
motility usually present at some life stages or in certain cells.
Know the various animals phyla and their characteristics, as follows:
- Porifera: sponges, organized as a single tissue, with numerous pores and many sharp spicules.
- Cnidaria: radially symmetrical animals with two tissue layers (ectoderm and endoderm),
separated by a jelly-like mesoglea; and an all-purpose gastrovascular cavity with a
single opening (mouth). Tentacles surround mouth and have stinging cells (cnidocytes)
containing stingers (nematocysts).
- Class Hydrozoa: Life cycle includes both asexual polyps (solitary or colonial) and
sexually reproducing medusae (usually small).
- Class Scyphozoa: Solitary "jellyfish" with dominant medusa stage.
- Class Anthozoa: Sea anemones and corals, with polyp stage (solitary or colonial) dominant; no medusa.
- Ctenophora ("comb jellies"): Marine anmimals with biradial symmetry, 2 large tentacles,
and 8 comb-like rows of cilia.
- VOCABULARY TO KNOW:
Spontaneous generation (abiogenesis): The idea that life could arise suddenly and easily from nonliving matter.
Biogenesis: The theory that life can only come from preexisting life ("from parents similar to themselves").
Primary abiogenesis: The theory that life originally came from nonliving matter, but can now only come
from preexisting life ("biogenesis now, but abiogenesis originally").
Reducing conditions: Conditions with abundant hydrogen gas or other molecules that easily donate electrons.
Phototrophic: Using sunlight as an energy source.
Chemotrophic: Using chemical energy as an energy source.
Autotrophic: Using CO2 (or carbonates) as a carbon source.
Heterotrophic: Using organic compounds as a source of carbon (especially by eating other organisms).
Anaerobic: Oxygen-intolerant.
Aerobic: Oxygen-dependent.
Facultative: Capable of living either with or without oxygen.
Procaryotic cells: Cells without true nuclei, lacking many other structures found in eucaryotic cells.
Eucaryotic cells: Cells with true (membrane-bounded) nuclei, with multiple linear chromosomes, and with many
internal compartments or organelles (including mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, etc.).
Unikonta: A proposed grouping of animals, amebozoans, slime molds, and fungi, united by their common posession of lobe-like pseudopods and/or
a single whiplike flagellum.
Plankton: All aquatic organisms that drift at the mercy of currents (as opposed to active swimmers).
Animalia: Kingdom of multicellular organisms that develop from a hollow ball of cells (blastula);
motility usually present at some life stages or in certain cells.
Blastula: An early embryo consisting of a hollow ball of cells.
Blastocoel: The hollow cavity inside the blastula.
Gastrula: A 2- or 3-layered embryo derived from a blastula by tucking-in (invagination).
Archenteron: The inside cavity ("primitive gut") of a gastrula.
Blastopore: The entrance to the archenteron from the outside.
Diploblastic: Containing 2 germ layers (ectoderm and endoderm), as in Cnidaria.
Triploblastic: Containing 3 germ layers (ectoderm, mesoderm, and endoderm), as in Bilateria.
Ectoderm: Outermost germ layer, giving rise to outer epidermis and in many cases also to nervous system.
Mesoderm: Middle germ layer, giving rise to muscles, bones (when present), kidneys,
reproductive organs, and most connective tissues.
Endoderm: Innermost germ layer, giving rise to inner lining of the gut (also to lungs, liver, pancreas, etc.).
Tissue: A group of similar cells and their products, built together (structurally integrated) and
working together (functionally integrated).
Spicules: Sharp needles or more complex shapes embedded within sponges, functioning in support and
as a defense against predators.
Mesoglea: Jelly-like layer between ectoderm and endoderm in Cnidaria.
Polyp: Cnidarian body form with the mouth directed upward, mesoglea thin, animal usually attached
(as in corals).
Medusa: free-swimming "jellyfish" body form some Cnidaria, with thick mesoglea;
mouth directed downward.
Radial symmetry: Structure that looks the same when viewed from any angle around a circle.
Biradial symmetry: Symmetry of a 2-armed pinwheel, looking the same if rotated 180 degrees.
Bilateral symmetry: Structure in which the right half is a mirror image of the left half; symmetry
** Also the following taxonomic groups (listed under "Biological Diversity" above): **
Viruses, Archaea (=Archaebacteria), Proteobacteria, Chlamydia, Spirochetes, Gram-positive bacteria, Cyanobacteria;
Unikonta, Amoebozoa, Slime molds, Excavata, Diplomonads, Euglenoids, Rhizaria, Foraminifera, Radiolaria, Chromalveolata, Alveolata, Ciliata, Apicomplexa,
Stramenopiles, Brown algae, Dinoflagellates, Diatoms, Archaeplastida, Red algae, Green algae
Plantae (=Embryophyta), Bryophyta, Tracheophyta, Rhyniophyta, Psilophyta, Lepidophyta, Arthrophyta (=Sphenopsida), Pterophyta,
"Gymnosperms", Pteridospermophyta, Cycadophyta, Ginkgophyta, Coniferophyta, Gnetophyta,
Angiospermae (=Anthophyta), Dicotyledonae (=Eudicotyledonae), Monocotyledonae;
Mycota (=Fungi), Chytrids, Eumycota, Glomerulomycota, Zygomycota, Ascomycetes (Ascomycota), Basidiomycetes (Basidiomycota), Deuteromycetes
Animalia, Porifera, Cnidaria, Hydrozoa, Scyphozoa, Anthozoa, Ctenophora
- MORE DETAILS are contained in the following outlines:
12.Origin 13.Procaryotes 14.EucaryoteOrigins
15.EucaryoteDiversity 16.LifeCycles
17.Bryophytes 18.Vascular 19.SeedPlants
20.Fungi 21.Sponge
- THIS GUIDE will continue to be revised.
It is still tentative.
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