10.2. Pisum sativum: Pea Plant http://www.ck12.org
Mendel’s law of segregation. This law states that there are two factors controlling a given characteristic, one of
which dominates the other, and these factors separate and go to different gametes when a parent reproduces.
Additional experiments analyzing two pea plant characteristics, such as pod shape and color, resulted in Mendel
developing his second law, the law of independent assortment. This law states that factors controlling different
characteristics are inherited independently of each other.
Evolution
Evolutionary scientists believe that theP. sativumfirst evolved in Egypt in the Nile Delta area around 4800-4400 BC.
The Pea Plant has not evolved over time or from a specific organism but it has made adaptations. The adaptations
that it has made over time are self-pollination, nitrogen fixation, and the development of xylem and phloem. Self-
pollination allows the pea plant to reproduce without the need of an organism to move its pollen. The downside to
self-pollination is that there is less of a chance for greater genetic variability and change.
Ecology
The pea plant’s ecological role in the environment is a producer.
The pea plant is able to carry-out nitrogen fixation because of a symbiotic relationship relationship with certain
bacteria and fungus. The bacteria receive extra sugars that the pea plant has made through photosynthesis, and the
bacteria provides the plant with nitrogen. The plant, like all organisms, incorporates the nitrogen into its nucleic
acids. The fungus provides the plant with additional nutrients that it usually receives from the soil. The fungus also
receives glucose from the plant.
Physiology
Like all plants,P. sativumhas an alternation of generations life cycle. This type of life cycle has separate times when
either the haploid or diploid organism is dominant. Like all angiosperms, the pea plant has separate male and female
reproductive structures, though both are located in the same flower.
Like most vascular plants,P. sativummaintains homeostasis through the use of xylem and phloem, self-pollination,
and nitrogen fixation. Since the pea plant is a legume, it has developed a relationship with the bacteriaRhizobium.
This bacteria enters the roots of the pea plant and forms nodules. Through this symbiotic relationship, the bacteria
receive carbohydrates and other substances in exchange for fixing/converting nitrogen gas. The pea plant obtains
and produces glucose during the process of photosynthesis, which it supplies to the bacteria. The pea plant has also
developed a symbiotic relationship with a fungus. The fungus provides the plant with additional nutrients from the
soil, and the fungus receives sugars from the plant.
The development of plant vascular tissue, xylem and phloem, occurred when plants migrated onto land. This vascular
system allowed for the movement of water up the plant, and sugars made in their leaves during photosynthesis down
the plant. The xylem moves water and the phloem moves dissolved solutes like sugars and amino acids. With this
adaptation, the pea plant, like all plants is able to grow taller.
Photosynthesis converts water and carbon dioxide into sugars and oxygen, with the help of sunlight.P. sativumhas
two separate layers in the walls of the pods that are involved in photosynthesis. The outer layer is used to collect
carbon dioxide from the atmosphere, and the inner layer is used to collect carbon dioxide that is coming off from the
developing seeds inside the pod.