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a group of scientists studying vegetation in a mountain range observe that a certain flowering plant grows taller at lower elevations and shorter at higher elevations. assuming the two populations of plants are genetically similar, those height variations are most likely due to developmental flexibility that allows the plants to assume tall or short growth forms.

(a) identify three biotic or abiotic factors that could differ at high and low elevations and cause the difference in plant height.

(b) using one of the factors listed in part (a) as an independent variable, write a hypothesis that proposes how this variable could cause the difference in plant height at high and low elevations.

(c) you are given seeds for this species of plant. design a procedure for a controlled experiment to test your hypothesis.

(d) describe the results that would support your proposed hypothesis, and the results that would refute your hypothesis.

Hi

Before answering the question, we need to understand the fact that there are some abiotic and biotic factors which affect the growth and development of plants, for example sunlight, wind, heat, presence of certain beneficial insects, bacteria etc. Although the height of plant is determined by its genetics mainly, however the effects of external factors cannot be ignored since they highly affect a plant's development.

Q 1( (a) Identify THREE Biotic or Abiotic factors that could differ at high and low elevations and cause the difference in plant height

In this question, we are asked about two plants of same specie which grow with different heights at low and high elevations. If we think about the abiotic factors of mountain, we know that thee are certain factors which differ at low and high elevation). These are:  

1: Concentration of Oxygen: Oxygen is low in concentration at high elevations and high in concentration in low areas. As we know oxygen is important for plant growth and development, therefore, oxygen a plenty of oxygen in lower elevations help plant to gain good and genetically pre-determined height.

2: Temperature: Temperature varies greatly at high and low elevations, In high elevated areas the temperature is lesser as compared to low elevations. Just like oxygen, temperature is also a key factor that controls the development of plant, a good temperature helps the plant to reach its genetically predetermined height.

3: Water: In hilly regions, water do not accumulate at the mountain tops and runs down from top to the bottom elevations of the hills, therefore more water is accumulated in lower elevations as compared to high elevated regions. Just like oxygen, water is also a key factor that controls the development of plant, a good amount of water helps the plant to reach its genetically predetermined height and therefore, plants in region of lower elevations grow taller because the regions receive more water.

2: (b) Using one of the factors listed in part (a) as an independent variable, write a hypothesis that proposes how this variable could cause the difference in plant height at high and low elevations.

If we talk about Independent variables, these are the factors that are varied or changed in an experiment as per our wish because we want to see the effect of this change on dependent variable (the other one that is being studied). We select Independent variable as water here and dependent variable as Plant height that is affected by change in water concentration. Now we propose the hypothesis:

Hypothesis: The more water concentrations can enhance the height of a plant as compared to a plant given lower quantities of water.

3: (c) You are given seeds for this species of plant. Design a procedure for a controlled experiment to test your hypothesis.

Now we take water as an independent variable and grow the plant seeds in green house in same pots, same temperature, same light intensity but only difference is the concentrations or quantities of water we give them daily. This will tell us, whether change in water quantities change the heights of plants or not. This sort of experiment is called a controlled experiment in which some factors are altered and others remain same.

4: (d) Describe the results that would support your proposed hypothesis, and the results that would refute your hypothesis.

Positive results: Suppose that we see a clear difference i heights of the plants grown with lower quantities of water (They are short) and higher quantities of water (They are tall). This is a positive and significant result which tells us that actually water is the factor which is responsible for altered plant heights at lower and higher elevations respectively.

Negative results: On the other hand, If height of both plant groups (grown in different water quantities) is same, it means that there is no remarkable difference between the plant heights and water is not a controlling factor, which refutes our hypothesis.

Hope it helps!

A. Three biotic/abiotic factors responsible for plant height

Justification:

- At higher elevations, low temperature reduces the plant growth significantly. Further, it has been well-established that temperature significantly impacts the expression of genes. In the presence of a cooler atmosphere, the plant height is expected to decrease.

- The availability of water at the top of the mountain is lesser because most of the water will flow down the hill. Therefore, it will affect the water content in the soil, thus affecting nutrients availability and soil quality parameters as well (total organic carbon, microbial activities, etc.). On the other hand, at lower elevations, there will be more water available for plant growth and nutrients bioavailability.

- At higher elevations, the wind/air pressure would be high compared to the lower elevations. Thus, the plants at higher elevations will often fall down and only smaller height plants will survive better.

- Biogeochemical transformation or high turn over of the soil ingredients is better expected at lower elevations due to the combined action of all of the abovementioned conditions. Briefly, microbial activities will be fast in the presence of high temperature, high moisture content and low wind pressure. The food will be abundantly available for microbes and their high turn over will increase the soil quality. This will ultimately impact the growth of the plants.

B. Hypothesis to test: Increasing the temperature of the soil obtained from elevations would improve the microbial activities thus supporting the bioavailability of nutrients, which are necessary for the plant growth (N, P, K).

N=Nitrogen, P=Phosphorus, K=Potassium

C. Soil will be obtained from the top of mountains (high elevations) for plant growth study. The changes in topsoil would improve plant growth in the presence of nutrients. Different treatments could be

D. Expected results:

Improving temperatures for soil obtained from higher elevations would improve biological activities. The nutrients (N, P, K) bioavailability will be increased and the growth of plants would be improved. Also, the relative proportion of total microbial counts (tested via 16S sequencing) will be high after improvement in temperature. Thus, the study would support that temperature is a crucial and driving factor for plant growth, which indirectly affects the microbial biogeochemical cycles and affect the soil quality.