Seed Plant Diversity in Adaptation

[Music] look closely at most any plant you see and your likely to find that it's a seed producer that's because seed plants such as coniferous trees are the largest plants seed plants are also the most plentiful both in number of individuals and species seed plants are the majority members of a deciduous forest most of the plants that compose tropical rain forests are seed plants cultivated plants of grassland lands are seed plants as our native grasses and the plants best adapted to a desert environment are also seed producers what makes the seed plants so successful to understand we'll compare seed plants with another group of plants slightly less efficient the ferns ferns like seed plants have root systems which absorb water and nutrients from the ground vascular systems which conduct materials to various parts of the plant and leaves for production of food but ferns do not have as efficient means of reproduction as seed plants this is the spor producing or sporify generation of the fern many dark specs are Spore cases each containing numerous microscopic spores each Spore can grow into another plant that looks looks quite different from the parent plant this is the alternate generation the gapy generation of the fern this tiny plant produces sexual cells gametes rather than spores this diagram of the underside of a fern gapy shows aragonia where egg cells are produced and antheridia where sperm cells are produced the surface of the plant must be moist for reproduction to occur the microscopic sperm cells represented here as dots swim through water to reach the eggs so ferns generally grow in places where plenty of moisture is available seed plants in contrast can grow almost anywhere consider the pine tree which is a sporify plant spores are produced inside the pine cones this particular cone produces one kind of spores microspores which grow into grains of pollen you can see the pollen falling on the card pollen does not germinate in the ground as do spores of the fern instead it is carried by the wind to cones which produce another kind of spores megaspores megaspores remain inside these cones where they grow in to female gametophytes contained within ovules each ovule contains female gametes egg cells for fertilization to occur one of the grains of pollen carried through the air must reach the opening at the tip of an ovule once it comes to rest against the ovule wall it grows a pollen tube this tube serves to carry sperm cells to the egg cells so the sperm do not have to swim through water as they do with the fern this is one of the principal adaptive advantages of a seed plant over other kinds of plants after the ovules develop into mature seeds the cone opens and the seeds are released seeds provide another adaptive advantage in that they are extremely durable structures each Pine seed has a tough covering that protects the the embryo plant until conditions are favorable for its growth food stored in the seed contributes further to the probability of the embryo surviving and eventually growing into a mature tree the pine is a representative of the simplest class of living seed plants the hemlock is a member of the same class as the Pine this tree has cones similar to pine cones in which the seeds develop these cones are open at the time of fertilization so that pollen lands directly on the ovules the seeds then are exposed at the beginning of their development thus the name naked seeds or gymnosperms which is what we call this class of plants the gko is another gymnosperm as is the psyched the seeds of the psyched also grow in a cone-like structure the psych Ginko and other gymnosperms are the most primitive and least widespread of the living seed plants the cucumber is a member of the most advanced and most prolific group of seed plants plants which have seeds enclosed in a fruit enclosed seeds or angiosperms is the name given to this class of plants angiosperms also include plants that have pod-like fruits a fruit is defined as the matured ovary of a flower ues of an angiosperm are enclosed within an ovary at the time of pollination so the seeds are enclosed and protected throughout their development the gemson weed is another angiosperm its fruit is a capsule again the fruit gives protection to the seeds another Advantage provided by the fruits of angiosperms is that they are easily dispersed squirrels store acorns for food and in the process May plant oak trees when birds eat fruits they are also spreading seeds some fruits have special devices that promote seed dispersal still other fruits have adaptations which allow dispersal by the wind and by the water the fact that a fruit is a matured ovary brings us to another adaptive advantage of angiosperms earlier in its development the ovary was a swelling at the base of a pistol and the pistol of course developed as part of a flower all angiosperms are flowering plants and may be fertilized in a variety of ways most angiosperms have pistols and stamin in the same flower and so produce both megaspores and microspores such flowers are often self- fertilized this flower has stamans and pistols in the same plant but with the stamman shorter than the pistols so self- fertilization is unlikely some flowers have stamans only and so produce just microspores others of the same species have pistols only producing megaspores such flowers can only be cross fertilized flowering plants are also diverse according to how they are pollinated some are pollinated by the wind flowers also attract a variety of animals which greatly increase the number of ways in which pollination can occur so flowers help explain the diversity of the angiosperms and their success in competing with other plants flowers also Supply a basis for classifying angiosperms into two subclasses flowers such as the Sweet Pea have their floral Parts arranged in groups of fours or fives five petals two United and three separate the seed of the pea plant and plant similar to it has have two leaf-like structures in which food is stored these are calans and such plants are called dicots two Calen plants dicots are one subclass of angiosperms the other subclass is represented by the day lily plants such as this have their floral Parts in threes or multiples of three the seeds of the day Lily and of plants which resemble it have only one structure for storing food and are called monocots one Coten plants the leaf of a monocot has veins which run parallel to one another a dcot leaf has an intertwined network of veins the stem of a dcot has vascular bundles arranged in a ring the monocot stem has vascular bundles distributed evenly throughout remember that both monocots and diots are angiosperms the most successful group of seed plants however both angiosperms and the more primitive gymnosperms are seed plants plants which have been far more successful than Ferns and other more primitive species in adapting to the widely varying conditions of a land [Music] 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