The earliest forms of life that are known to us dateback to about 3.5 billion years ago. These beings are called bacteria andblue-green algae. Photosynthesis most likely first appeared in bacteria. Theearliest land plants developed a little more than 400 million years ago. The firstseed plants appeared about 350 million years ago and were referred to as seedferns because of their large fernlike leaves.Plants have different types of growth responses tothe things around them.
These responses are called tropisms. There are fourmain types of tropisms: phototropism, geotropism, thigmotropism, andchemotropism.Phototropism is the response to light direction,geotropism is the response to gravity, thigmotropism is the response to water,and chemotropism is the response to a particular chemical. One of the generalcharacteristics of plants is that they tend to grow continuously throughouttheir lives. There are two aspects of plant growth: primary and secondary.Primary growth takes place in young organs, which gives the result of theincrease in length of shoots and roots of the plant. Secondary growth refers tothe increase in the plant’s width.
Radiation is the transmission of energy in wave formand to the transmission of streams of atomic particles through space. Anyenergy that is emitted through the form of waves is called electromagneticradiation. All kinds of electromagnetic radiation follow the same physicallaws, all of them travel as fast as light, and when they fall on a surface theyrelease a pressure. (Global Industries, 1991)There are three types of radiation: alpha, beta, andgamma.
Alpha particles are helium-4 nuclei (two protons andtwo neutrons). They interact with matter strongly because of their charges andcombined mass. Usually, alpha particles can only penetrate a few millimeters oflow density material. Therefore, this means that alpha particles do not penetratethe outer layers of dead skin cells and do not damage live tissues. There are afewvery high energy alpha particles that are made up about 10% of cosmic raysand they can penetrate the body and even thin metal plates.Beta radiation can penetrate more than alpharadiation can.
Beta radiation fromradioactive decay can be stopped by a few centimeters of plastic or a fewmillimeters of metal. Sometimes, it is used in radiotherapy to give treatmentto superficial tumors. Gamma radiation works to get rid of an unstablenucleus of excess energy. Both alpha and beta particles have an electric chargeand mass, and can probably interact with other atoms along their path. However,gamma radiation is made up of photons, which do not have either mass orelectric charge, which makes it be able to penetrate much further throughmatter than alpha and beta radiation.
Gamma rays can be stopped by a thick ordense layer of material, and it doesn’t matter whether the material has high orlow density. (Nowicki)Radiation can have a positive effect on plant growthat low levels and harmful effects at high levels. Radiation can affect thegrowth and sprouting of a plant. The amount of damage is proportional to theradiation that is received by the plant.
Becauseof radiation, soil can become compact and can also lose the nutrients that areneeded for a plant’s growth. Intense radiation kills plants but in a differentway. Trees and shrubs change in their reactivity and sensitivity towardsradioactive substances. (Taylor, 2017)