provides information about the evolutionary relatedness of all extant (living) species, both to each other and to all extinct species. shows the order in which species 'split' from each other through time. One goal for biology is to have the hierarchical classification of taxonomic groups reflect the phylogenetic history as much as possible. contain information that is represented by the positions of the branches relative to each other, the points at which different branches join, and the lengths of the branches. Branch lengths can indicate very different things, however. First, branch lengths may indicate the amount of evolutionary change in the taxon since divergence from another lineage. In some cases, the longer the horizontal branches, the greater amount of genetic change within that branch. A given gene or genome can change at slightly different rates in different lineages. However, among all organisms alive today, in the tree of life, they all have been evolving and surviving for the same number of years.Branch lengths can also indicate time; the point at which two branches diverge in a phylogenetic tree can be connected to fossil/geologic events. (championed by Ernest Mayr): the concept most often used. a population or group of populations whose members have the potential to interbreed with each other in nature to produce viable, fertile offspring, but who cannot produce viable, fertile offspring with members of other species. drawbacks. The definition only applies to sexually reproducing species. Another problem is that individuals of two species may possibly interbreed (hybridize) such as a donkey and horse (mule), a donkey and zebra (a zebrass), zebras and horses, lions and tigers (ligers and tiglons), wolves, coyotes and domestic dogs, and so on. Some scientists would allow 'some' hybridization as allowable in this, others would not. A third problem is due to the allopatric nature of species, in other words, it is hard to know if you have two species if they do not overlap geographically and thus never have the opportunity to interbreed. Two biological species may be quite similar in appearance and difficult to distinguish. - cell size: large (10 to 100 microns)
- DNA and chromosomes: DNA in several chromosomes, more genes than in bacteria, histone and nonhistone proteins, DNA within the nuclear envelope, no plasmids
- cell division: mitosis
- sex: males and females that produce gametes from meiosis, gametes fuse to form zygote
- metabolism: mitochondria and chloroplasts, metabolism occurs in these organelles and in the cytoplasm
- intracellular movement: cytoplasmic streaming, phagocytosis, mitotic movements of chromosomes, all due to cytoskeleton of various protein filaments
- flagella, cilia, cell walls: '9 pairs + 2' pattern, cell wall if present does not have disaccharide polymers linked to peptides
1) Apical meristem
2) Multicellular embryos are dependent on the parent plant. -- Multicellular plant embryos develop from zygotes that are retained within tissues of the female parent. This distinction is the basis for a term used to describe all land plants, the embryophytes. The parent provides nutrients, such as sugars and amino acids, to the embryo.
3) Alternation of generations
4) Sporangia produce walled, resistant spores
5) The gametophytes of bryophytes, pterophytes, and gymnosperms produce their gametes within multicellular organs, called gametangia.
6) adaptations for acquiring, transporting, and conserving water.
7) Water and nutrient transport
8) Secondary compounds as terrestrial adaptations against UV, predators and microbes
1) The microspores, released from the microsporangium, develop into pollen grains.
2) Pollen grains are covered with a tough coat containing sporopollenin.
3) Pollen grains are carried away by wind or animals until pollination occurs, when they land near the ovule.
4) A pollen grain will elongate a fertilization tube into the ovule and deliver one or two sperm into the female gametophyte.
5) While some primitive gymnosperms have flagellated sperm cells, the sperm in most gymnosperms and all angiosperms lack flagella.
6) In seed plants, the use of resistant, far-traveling, airborne pollen to bring gametes together is an important terrestrial adaptation. In bryophytes and ferns, flagellated sperm must swim through a film of water to reach egg cells in archegonia. Therefore, the plants must be fairly close together to ensure fertilization. The evolution of pollen in seed plants led to even greater success and diversity of plants on land. Plants can then travel farther, and the distance between two plants involved in sexual reproduction can be greater.
1) begins with the appearance of cones on a pine tree. The pine tree, a sporophyte, produces its sporangia on scalelike sporophylls that are packed densely on cones.
2) 3 years for seeds to mature then disperse
3) A pollen cone contains hundreds of microsporangia held on small sporophylls. Cells in the microsporangia undergo meiosis to form haploid microspores that develop into pollen grains.
4)An ovulate cone consists of many scales, each with two ovules. Each ovule has a megasporangium inside.
5) During pollination, windblown pollen falls on the ovulate cone and is drawn into the ovule through the micropyle. The pollen grain germinates in the ovule, forming a pollen tube that digests its way through the megasporangium.
6)The megaspore mother cell undergoes meiosis to produce four haploid cells, one of which will develop into a megaspore. The megaspore grows and divides mitotically to form the immature female gametophyte.
7) Two or three archegonia, each with an egg, then develop within the gametophyte.
8) At the same time that the eggs are ready, two sperm cells have developed in the pollen tube which has reached the female gametophyte. Fertilization occurs when one of the sperm nuclei fuses with the egg nucleus, producing the zygote. In most gymnosperms and in all angiosperms, the sperm do not have flagella; the sperm do not swim to the egg.
9) The zygote undergoes mitosis to produce the embryo. The pine embryo (the new sporophyte) already has a rudimentary root and several embryonic leaves by the time it matures and the seed is dispersed.
10) The female gametophyte surrounds and nourishes the embryo. The ovule develops into a pine seed, which consists of an embryo (new sporophyte), its food supply (derived from gametophyte tissue), and a seed coat derived from the integuments of the parent tree (parent sporophyte). The seed coat protects the young seed from the environment. Under the right conditions, the seed germinates and the embryo produces the young sporophyte seedling.
1) The mature sporophyte produces flowers, with stamens and/or carpels.
A microsporocyte (2N) in the anther undergoes meiosis and produces four haploid (N) microspores. A
microspore in turn produces a pollen grain (the male gametophyte, haploid). It consists of only a few cells or nuclei.A megasporocyte (2N) in the ovules undergoes meiosis and produces four megaspores (N). Only one survives, and it undergoes mitosis to produce the embryo sac (female gametophyte). It consists of only a few cells or nuclei.
2) After its release from the anther, pollen is carried to the sticky stigma of a carpel. The pollen grain produces a pollen tube that grows from the stigma down towards the ovary. When the pollen tube reaches the micropyle, a pore in the integuments of the ovule, the pollen tube discharges two sperm cells (without flagella) into the female gametophyte.
3) In a process known as double fertilization, one sperm unites with the egg to form a diploid zygote and the other sperm fuses with two haploid nuclei in the large center cell of the female gametophyte. This forms a triploid cell that will produce the endosperm.
4) The zygote develops into a sporophyte embryo packaged with food and surrounded by a seed coat. The embryo has a rudimentary root and one or two seed leaves, the cotyledons.
5) Corn and many monocots store most of the food for the developing embryo in endosperm which develops as a triploid tissue (3N) in the center of the embryo sac. Beans and many dicots transfer most of the nutrients from the endosperm to the developing cotyledons.
6)As the ovules develop into seeds, the ovary develops into a fruit.
7) After dispersal by wind or animals, a seed germinates if environmental conditions are favorable. During germination, the seed coat ruptures and the embryo emerges as a seedling. The seedling initially uses the food stored in the endosperm and cotyledons to support development.
1) Ovules, each containing a single sporangium, form within the chambers of the ovary.
2) One cell in the sporangium of each ovule, the megasporocyte, grows and then goes through meiosis, producing four haploid megaspores. In many angiosperms, only one megaspore survives.
3) This megaspore divides by mitosis three times, resulting in one cell with eight haploid nuclei. Membranes partition the cytoplasm into a multicellular female gametophyte, also called the embryo sac or egg sac.
a) At one end of the embryo sac, two synergid cells flank the egg cell. The synergids function in the
attraction and guidance of the pollen tube.
b) At the other end of the embryo sac are three antipodal cells of unknown function.
c) The other two nuclei, the polar nuclei, share the cytoplasm of the large central cell of the embryo sac. d) The ovule now consists of the embryo sac and the surrounding integuments (from the sporophyte).
The ovule develops into a seed containing an embryo and a supply of nutrients --
1) after double fertilization, ovule to seed and ovary to fruit
2) embryo develops, seed gets nutrients into endosperm then the cotyledons (storage leaves)
3) triploid nucleus of the ovule's central cell divides, forming a multinucleate "supercell" that has a milky consistency. The 'supercell' becomes multicellular when cytokinesis partitions the cytoplasm between nuclei and cell walls form and the endosperm becomes solid. Coconut "milk" is an example of liquid endosperm and coconut "meat" is an example of solid endosperm.
4) In most monocots and some dicots, the endosperm also stores nutrients that can be used by the seedling after germination.
5) dicots, the food reserves of the endosperm are completely exported to the cotyledons before the seed completes its development
6) first mitotic division
7) After the cotyledons appear, the embryo elongates. Cradled between cotyledons is the apical meristem of the embryonic shoot. At the opposite end of the embryo axis, is the embryonic root, also with an apical meristem.
8) After the seed germinates, the apical meristems at the tips of the shoot and root will sustain primary growth as long as the plant lives. The three primary meristems ( protoderm, ground meristem, and procambrium) are also present in the plant embryo.
9) During the last stages of maturation, a seed dehydrates until its water content is only about
5 to 15% of its weight. The embryo stops growing until the seed germinates. The embryo and its food supply are enclosed by a protective seed coat formed by the integuments of the ovule.
1) In the seed of a common bean, the embryo consists of an elongate structure, the embryonic axis, attached to fleshy cotyledons. Dicots have two cotyledons, the monocots one. In the monocot grasses, the specialized cotyledon, the scutellum, is a thin shield that absorbs nutrients from the endosperm.
2) Below the point at which the fleshy cotyledons are attached, the embryonic axis is called the hypocotyl and above it is the epicotyl.
3) At the tip of the epicotyl is the plumule, consisting of the shoot tip with a pair of miniature leaves. 4) The hypocotyl terminates in the radicle, or embryonic root.
5) In monocots such as grasses, the coleoptile is a protective sheath or covering of a embryonic/young shoot in a monocot. The coleorhiza is a sheath that covers the young root.
As the seeds are developing from ovules, the ovary of the flower is developing into a fruit, which protects the enclosed seeds and aids in their dispersal by wind or animals.
1) Pollination triggers hormonal changes that cause the ovary to start transforming into a fruit.
2) If a flower has not been pollinated, fruit usually does not develop, and the entire flower withers and falls away.
3) The wall of the ovary becomes the pericarp, the thickened wall of the fruit, while other parts of the flower wither and are shed. However, in some angiosperms, other floral parts contribute to what we call a fruit. In apples, the fleshy part of the fruit is derived mainly from the swollen receptacle, while the core of the apple fruit develops from the ovary.
1) As a seed matures, it dehydrates and enters a dormancy phase, a condition of extremely low metabolic rate and a suspension of growth and development.
2) Conditions required to break dormancy and resume growth and development vary between species. a) Some seeds germinate as soon as they are in a suitable environment.
b) Others remains dormant until some specific environmental cue causes them to break dormancy.
3) Seed dormancy increases the chances that germination will occur at a time and place most advantageous to the young seedling.
a) For example, seeds of many desert plants germinate only after a substantial rainfall, ensuring enough
water to support growth and reproduction.
b) For other plant seeds, where natural fires are common, many seeds require intense heat to break
dormancy, taking advantage of new opportunities and the open space.
c) For other seeds of plants in areas where winters are harsh, seeds may require extended exposure to
cold before germinating.
d) Other seeds require a chemical attack or physical abrasion as they pass through an animal's digestive
tract before they can germinate.
4) The length of time that a dormant seed remains viable and capable of germinating varies from a few days to decades or longer. This depends on species and environmental conditions.
a) Most seeds can last for a year or two until conditions are favorable for germinating.
b) The soil has a pool of thousands of nongerminated seeds per square meter that may have accumulated
for several years. This is one reason that vegetation reappears so rapidly after a fire, drought, flood, or some other environmental disruption.
1) This causes the expanding seed to rupture its seed coat and triggers metabolic changes in the embryo that enable it to resume growth.
2) Enzymes begin digesting the storage materials of endosperm or cotyledons, and the nutrients are transferred to the growing regions of the embryo.
3) The first organ to emerge from the germinating seed is the radicle, the embryonic root.
4) The shoot tip then must break through the soil surface. In garden beans and many other dicots, a hook forms in the hypocotyl, and growth pushes it aboveground. Stimulated by light, the hypocotyl straightens, raising the cotyledons and epicotyl.
5) As it rises into the air, the epicotyl spreads its first foliage leaves (true leaves). These foliage leaves expand, become green, and begin making food for photosynthesis.
6) After the cotyledons have transferred all their nutrients to the developing plant, they shrivel and fall off the seedling.
Kenneth R. Miller, Levine Kenneth R. Miller, Levine Christy C. Hayhoe, Doug Hayhoe, Jeff Major, Maurice DiGiuseppe