The earliest forms of life on earth that we know date
back to about 3.5 billion years ago. These organisms were called bacteria and
blue-green algae. Photosynthesis is said to most likely have first appeared in
bacteria. The earliest land plants appeared on earth more than 400 million
years ago. The first ever seed plants appeared about 350 million years ago. Usually,
they are called seed ferns because they have large fernlike leaves.
Plants have four types of growth responses to the
things around them. These responses are called tropisms. There are types of
tropisms: phototropism, geotropism, thigmotropism, and chemotropism.
Phototropism refers to its response to the direction
of light, geotropism refers to its response to gravity, thigmotropism refers to
its response to water, and chemotropism refers to its response to a certain
chemical. One of the broad characteristics of plants is that they tend to grow
continuously throughout their lives. There are two sides of plant growth:
primary and secondary. Primary growth takes place in young organs, which gives
the result of the increase in length of the plant. Secondary growth refers to the
increase in the width of the plant.
Radiation refers to the transmission of energy in
the form of waves. Any kind of energy that is released through the form of
waves is called electromagnetic radiation. Each kind of electromagnetic
radiation follows the same physical laws as the rest. All of them travel in the
speed of light, and when they fall on a surface they release a pressure.
(Global Industries, 1991)
There are three types of radiation: alpha, beta, and
Alpha particles interact with matter due to their
charges and combined mass. Normally, alpha particles can only penetrate a few
millimeters of materials with low density, meaning that alpha particles cannot penetrate
the outer layers of dead skin cells and live tissues. There are a few high energy
alpha particles that are made up about 10% of cosmic rays. They can penetrate
the body and even thin metal plates.
Beta radiation can penetrate more than alpha
radiation can. Beta radiation from
radioactive decay can be stopped by a few centimeters of plastic or a few
millimeters of metal. Sometimes, beta radiation can be used in radiotherapy to
give treatment to external tumors.
Gamma radiation works to get rid of an unstable
nucleus of excess energy. Both alpha and beta particles have an electric charge
and mass, and can interact with other atoms along their way. However, gamma
radiation is made up of photons, which do not have mass or electric charge,
which makes it have the ability to penetrate much further through matter than
alpha and beta radiation. Gamma rays can be stopped by a thick or dense layer
of material, and it doesn’t matter whether the material has high or low
At low levels, radiation can have a positive effect
on plant growth, and at high levels, very harmful effects. Radiation can affect
the way a plant develops and germinates. The amount of damage is determined by the
amount radiation that is received by the plant. Because
of radiation, soil can become compact and can also lose the nutrients that are
needed for a plant’s growth. Intense radiation kills plants but in a different
way. Trees and shrubs change in the way they react to radioactive substances. (Taylor, 2017)