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Terms in this set (261)

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.
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) 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.