Allelopathy. Open Investigation Will increasing the number of allelopathic sunflower plants effect the height growth of a non-allelopathic bean plant when the two types of plants are grown next to one another?

Authors Avatar

High Level Biology

Plant Physiology

Open Investigation

Will increasing the number of allelopathic sunflower plants effect the height growth of a non-allelopathic bean plant when the two types of plants are grown next to one another?


  1. DESIGN

Aspect 1

Background Information

In biology, it is learnt that species competition ensures biodiversity of the ecosystems. Due to biology evolution all plants and animals have developed characteristics and techniques that will enable them to out-compete other species for nutrients, water, territory and other essential resources.

Allelopathic plants compete with other plant species through “chemical warfare”. A “chemical warfare” refers to the excretion of a collection of chemicals (allelopathy chemicals or allelochemicals) by the allelopathic plant to inhibit the growth on its competitors. Specifically, the height growth of plants is affected by the allelochemicals.  

The word allelopathy derives from two separate words – allelon which means "of each other", and pathos which means "to suffer". [1] Allelopathy plants releases different classes of chemicals such as phenolic compounds, flavonoids, terpenoids, alkaloids and amino acids. Due to the mixtures of different compounds the effect of allelopathy is greater than individual compounds alone. Plant tissues may contain up to several grams per kilogram of these compounds. [10]

Diagram 1.0: Tissue types of the plant stem [8]


External stimuli such as ultraviolent radiation from the sun and chemical stressors or fertilisers induce the synthesis of phenolic compounds in plants. [10]

Ultraviolent radiation is produced by the sun and also known as the sunlight or sunrays. Sunlight is the primary energy for all living things. When light energy (photons) gets trapped in the chloroplasts of plants it converts into chemical energy. The chloroplast is a structure with in the plant that carries on photosynthesis. The process of photosynthesis produces oxygen and organic compounds such as sugars which allows the plant to grow. [8]

Allelopathic substances work like herbicides. Common traced effects of allelopathy include –

  • Reduced seed germination
  • Restricted seedling growth, plant height growth and growth of leaves
  • Reduce the ability of plants to compete with allelopathic plants which are excreting the chemicals

Plants that are under stress from such things as the existence of pests and diseases, less than optimum access to nutrients, sun or moisture, possess a higher risk of being eliminated by allelopathic plants.

Diagram 1.1: Plant external structure [8]

Allelopathic chemicals can be released from any part of the plant, it merely depends of what type of plant it is.  Allelochemicals can be released from can plants’ leaves, flowers, roots, fruits, or stems. Some allelochemicals biodegrade over time and some allelochemicals continue to exist in the soil. Allelochemical concentrations in the producer plant may also vary over time and in the plant tissue produced. 

Due to the allelopathic substances retains many similarities to that of herbicides, allelopathic plants have been often used as “weedkillers”. Some examples of plants that have been proven to be allelopathic are Black Walnut, Tree-Of-Heaven, Broccoli, Eucalyptus and Sunflower plants.  

In this experiment, the allelopathic plant will be the sunflower plant and the non-allelopathic plant will be the bean plant. The bean plant will be the control in this experiment. [3]


Table 1.0: Description of a dwarf bean plant and sunflower. The scientific names of

the two plants are also included in the table.   

Rain water collected from the household water tank will be used to water the plants. Factors such as height of plant (mm), size of leaves, number of leaves, colour of leaves and the time it takes the seeds to germinate will be observed and recorded. To and prevent avoid any damage to the plant, daily inspection of bugs and pest will occur. This experiment will be carried outdoors where there is presence of full sunlight and plants are left to grow in an undisturbed area (refer to IV.Appendix to see location where plants will grow).

     


Focus Question

Will increasing the number of allelopathic sunflower plants effect the height growth of a non-allelopathic bean plant when the two types of plants are grown next to one another?

Hypothesis                (H1)

It is hypothesised that the height growth of the bean plant will increasingly decrease with increasing number of sunflower plants surrounding the single bean furthermore, the size and number of leaves will also decrease as the number of sunflower plants increase. It is hypothesised that the height of the control bean plant (no presence of sunflower plants) will attain the greatest height, number of leaves and largest sizes of leaves.

Null Hypothesis        (H0)

It is hypothesised that there will be no statistical difference between the height growth of bean plants surrounded by zero, one, two, three or four sunflower plants.  

Variables

Independent variables –

The number of sunflower seeds planted alongside the bean seed

  • 1 bean seed                         (control)
  • 1 bean seed                 +         1 sunflower seed
  • 1 bean seed                 +         2 sunflower seeds
  • 1 bean seed                 +         3 sunflower seeds
  • 1 bean seed                 +         4 sunflower seeds

Dependent variables

  • Height of plants from the surface level of the soil up to the tip of the stem (mm)


Aspect 2

Table 1.1: List of all the variables that will be controlled in this experiment and explanations and method of how the variables will be controlled.

Join now!


Aspect 3

Materials

  • Continuous supply of household rain water
  • 1  ×  Medium-sized trowel
  • 1  ×  1000mL measuring cup                                        ±  25 mL
  • 1  ×  The Green Gardener Potting Mix bag (25L)
  • 25  ×  Grower’s Pride Dwarf Bean Tender Green seeds
  • 50 ×  D.T Brown Sunflower seeds
  • 25  ×  REKO 6006 100mm STD Black plastic Pots  
  • 1  ×  Plastic box (L600mm × W400mm ×D200mm)  
  • 1  ×  300mm plastic ruler                                                ±  1 mm
  • 1  ×  Red permanent marker
  • 1  ×  Papermate Kilometrico Med Point pen
  • 1  ×  Kitchen ...

This is a preview of the whole essay