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Investigating the propagation of Mentha with varying concentrations of salicylic acid as a rooting hormone. IB DP Biology IA - Level 6 IA. May 2023 Examination Batch
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Title:Investigating the propagation of Mentha with varying concentrations of salicylic acid as a rooting hormone
Research Question:
How does increasing the concentration of salicylic acid (0%, 1%, 2%, 3%, 4%), a rooting hormone, impact the
mean root growth of Mentha over the course of 2 weeks?
Introduction:
Plants have a significant role in today's world due to their numerous benefits, and we can use them to produce
medicine, paper, furniture, and food. The leaves of plants such as mint, coriander, and curry leaves, are also
used in numerous Indian dishes. As an individual from a family full of restaurant proprietors, exploring the
world of cooking has allowed me to understand the significance of substituting altered and processed
ingredients with fresh foods, not only in hopes of establishing the best-tasting dishes but also the most
nutritional ones possible. Over time, I was introduced to gardening, an opportunity to grow foodstuffs that could
help us start an initiative towards more nutritious food. After a few months of experimentation and trial and
error with fruits and vegetables, I planted my first herb – Mint (Mentha). As it is an herb commonly used in my
favourite dishes, I was extensively inquisitive about the development and agriculture of the plant.
Mentha is a perennial runner herb that belongs to the Lamiaceae family. Other herbs in the Lamiaceae family
include basil, sage, thyme, and rosemary. There are over 20-30 different plant species that are grown in many
regions of the world, such as Europe, North America, parts of Asia, North Africa, and the Middle east. Mentha
is widely used in the culinary world. It provides a fragrant aroma in cooked dishes and a deep vivid flavour in
beverages, sauces, chewing gums, jellies, syrups, etc. Mentha oil is easily extracted and widely used in
aromatherapy; its medicinal property helps heals common disorders such as IBS (irritable bowel syndrome),
nausea, muscle discomfort, headache, cold, mild digestive difficulties, and certain forms of skin allergies, this is
because Mentha consists of methanol which has various analgesic, antispasmodic, and anti-inflammatory
properties [Peppermint oil, healthline.com]. Mentha is a fumigant that repels a variety of stored-grain pests
such as Tribolium castaneum, Sitophilus Oryza, Acanthoscelides, Obtectus, and others (Sardoei and
Shahdadneghad 2015). Studies have proven its effectiveness as an adulticidal, larvicidal, and
growth/reproduction inhibitor.
Salicylic acid can be used as a rooting hormone that can stimulate root growth in plants. However, the
concentration of salicylic acid required to achieve optimal root growth can vary depending on the plant species
,and other factors, such as the growth medium, temperature, and light conditions. In general, increasing the
concentration of salicylic acid may result in an increase in root growth. Moreover, it is also possible that
salicylic acid may become toxic to the plant at very high concentrations and inhibit root growth. Therefore, it is
essential to use the correct concentration of salicylic acid to obtain optimal root growth.
Background Information:
I picked mentha for this experiment because it is the most widely available and accessible herb to grow in an
indoor garden. Mentha can either be grown through stem cuttings or stolon cuttings; both propagation methods
take around two to four weeks for new roots to develop. Stolons, also known as rhizomes, allow the plant to
grow horizontally, developing adventitious roots and lateral shoots, thus increasing ground cover. Mentha can
be grown by cutting the stolons at strategic points so they can grow into new plants. Instead of
propagating mentha through stolons, I have chosen to grow it through stem cuttings. This is because it is
easier to measure the growth of Mentha cuttings than a stolon. Stem cutting of mentha involves cutting 5" from
the top growth of the stem. Furthermore, as the cuttings on mentha do not have any leaves, we do not have to
worry about transpiration through the leaves. If transpiration were to occur, the plant's growth rate could differ
as the loss of water from the plant would instill a transpiration pull which in turn will require the roots to
maintain a higher concentration of minerals using active transport, which would result in the plant using energy.
This loss of energy could stun the growth of the plant.
Salicylic acid was formerly the most popular drug in the world and was first developed in Germany in 1898.
Salicylic acid is a member of a very diverse class of plant phenolics containing an aromatic ring and a hydroxyl
group (Figure 1), or one of its functional derivatives. It is classified under the group of plant hormones and is
widely dispersed throughout the whole plant kingdom (Raskin et al., 1990).
Figure 1: Structure of Salicylic Acid
2
, It is generally known that phenolic chemicals have an impact on a variety of biological and physiological
functions of plants, such as photosynthesis, enzyme activity, membrane permeability, and plant growth and
development. Salicylic acid is one such natural substance that can function as a regulator of plant growth.
Although it is beneficial to plants, due to its acidic nature in high concentrations, only controlled amounts of
salicylic acid should be used as a plant rooting hormone. Hence, small concentrations of salicylic acid, 0%,
1%, 2%, 3%, and 4% will be used in this experiment.
Additionally, a rooting hormone will be used in this experiment as a control in order to ensure plant root growth.
Hormex is a well-known brand that produces plant growth stimulants and rooting powders. Hormex rooting
hormone powder is used to root new plants from cuttings easily. In this experiment, the same amount of
Hormex rooting powder will be added to all the trials. This is to make sure that the rooting hormone doesn't
have a different effect on each trial, which could cause anomalies in the results. To obtain optimal results from
the rooting hormone, 2 cm of the root of the cutting should be dipped in the rooting powder ["Rooting
Hormones Improve Uniformity Among Vegetative Cuttings"].
Hypotheses:
The research hypothesis: An increase in the concentration of salicylic acid (%) will result in an increase in the
mean root length growth of Mentha (cm), but only for controlled concentrations of salicylic acid. This is
because, in certain concentrations of salicylic acid, the optimum environment for growth enzymes can be
achieved whereas if concentrations are too high for the plant it can negatively affect the metabolic process,
resulting in an overreactive immune response, and can stunt plant growth.
Null Hypothesis: An increase in the concentration of salicylic acid (%) will either result in a decrease or non-
existent correlation in the growth of Mentha (cm). This is due to the acidic nature of salicylic acid which has a
low pH level. Low levels of pH will denature the enzymes of the plant, therefore, stopping growth.
Variables:
Table 1: Independent, Dependent and Control variables table
Independent Variable Percentage of Rooting hormone (Salicylic Acid)
present in water (0%, 1%, 2%, 3%, 4%),
Dependent Variable Length of Root Growth (millimetres)
Control Variables
Factor Controlled Significance Method of Control
3
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