Download Plant Life Essay, Research Paper The kingdom Plantae

Plant Life Essay, Research Paper
The kingdom Plantae encompasses water-dwelling red and green algae as well as terrestrial
plants, which have evolved to support themselves outside of the aquatic environment of their
ancestors. This SparkNote focuses on the terrestrial plants, which include bryophytes (mosses) as
well as the more highly evolved vascular plants, called tracheophytes. As a consequence of their
move onto land, terrestrial plants require structures that support their weight, prevent desiccation
(drying out), aid in reproduction, and transport water, nutrients, and the products of
photosynthesis throughout the parts of the plant. Bryophytes have not yet made the complete
transition to land, and are thus still dependent upon a moist environment to assist in reproduction
and nutrient transport. The more highly evolved tracheophytes, on the other hand, have
developed internal systems of transport and support called vascular systems, which have allowed
them to become fully terrestrial.
A.1 Plant Characteristics
As explored in Common Plant Characteristics , most terrestrial plants (both bryophytes and
tracheophytes) share some general structural and functional features. Plant bodies are divided
into two regions, the underground root portion and the aerial shoot portion (including stem,
leaves, flowers, and fruits). These different regions of the plant are dependent on each other, as
each performs different essential functions. Land plants also share certain more specific
adaptations that are essential to survival out of water. These include an impermeable waxy
cuticle on the outer aerial surfaces, jacket cells around the reproductive organs, and stomata that
allow gas exchange without risking excessive water loss. All Plants are also autotrophic,
meaning that they produce their own food and do not use other organisms to supply organic
nutrients the way animals do. Finally, the life cycle of plants follows a pattern called the
alternation of generations, in which they fluctuate between haploid and diploid generations and
sexual and asexual modes of reproduction.
A.2 Plant Classification
Terrestrial plants, as noted above, are classified as bryophytes and tracheophytes. Bryophytes,
such as mosses and liverworts, are still dependent on a moist environment for reproductive and
nutritive functions even though they are technically “terrestrial.” Bryophytes also have very little
internal support, limiting the heights to which they can grow. As a phylum, Bryophytes, are
lower on the evolutionary scale than tracheophytes, which have adapted completely to life on
land.
Tracheophytes (also known as vascular plants) possess well-developed vascular systems, which
are comprised of tissues that form internal passageways through which water and dissolved
nutrients can traverse the entire plant. Vascular plants are thus far less reliant on moist
environments for survival. At the same time, Vascular systems also provide a strong system of
support to the plant, allowing some tracheophytes to grow to immense heights. The vascular
system will be discussed in far more detail in Vascular Tissues.
The tracheophytes can be further broken down into two kinds of seed-producing plants,
gymnosperms (conifers) and angiosperms (flowering plants). The male gametes of gymnosperms
and angiosperms are carried by pollen; each of these types of plants also produce seeds, which
protect the embryos inside from drying out in a terrestrial environment. Angiosperms, with their
flowers and fruits, have adapted even further to the terrestrial environment: flowers, by attracting
insects and other pollen-bearing animals, aid in the transfer of pollen to female reproductive
organs. Angiosperm fruits, developed from ovaries, protect the seeds and help in their dispersal.
Finally, angiosperms themselves are divided into two classes–monocots and dicots–based on
differences in embryonic development, root structure, flower petal arrangement, and other
factors.
A.3 Structures and Functions
The seed, which develops from an ovule after fertilization has occurred, surrounds the plant
embryo and protects it from desiccation. Each seed consists of an embryo, food source, and
protective outer coat, and can lie dormant for some time before germinating. The roots of a plant
function in the storage of nutrients, the acquisition of water and minerals (from the soil), and the
anchoring of the plant to the substrate. Tiny root hairs, which extend from the root surface,
provide the plant with a huge total absorptive surface and are responsible for most of the plant’s
water and mineral intake. Plant stems (or trunks, as they are called in trees) function primarily in
nutrient transport and physical support. The leaves contain chlorophyll and are the major sites of
photosynthesis and gas exchange. Flowers contain the reproductive organs of angiosperms.
A.4 Essential Processes Plants carry out a number of processes that are essential to their survival.
Internal water and sugar transport are largely carried out within the vascular system, ensuring
that the entire plant receives water and food even though these materials are brought in or
produced only in certain parts of the plant. Plant hormones determine the timing and occurrence
of many of the processes of the plant, from germination to tissue growth to reproduction. Plants
can also respond to light, touch, and gravity in various ways.
A.5 Life Cycle
The life cycle of plants depends upon the alternation of generations, the fluctuation between the
diploid (sporophyte) and haploid (gametophyte) life stages. Reproduction in most plants can
occur both sexually and asexually. In sexual reproduction, fertilization occurs when a male
gamete (sperm cell) joins with an egg cell to produce a zygote. In gymnosperms and
angiosperms (the seed plants), the ovule containing the egg cell becomes a seed after fertilization
has occurred. In angiosperms (flowering plants), the embryo is given added protection by an
ovary, which develops into a fruit. Plants can also reproduce asexually through vegetative
propagation, a process in which plants produce genetically identical offshoots (clones) of
themselves, which then develop into independent plants. This asexual means of reproduction can
occur naturally through specialized structures such as tubers, runners, and bulbs or artificially
through grafting.
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