Question

Please critique the following experimental design: An ecologist with the Environmental Protection Agency (EPA) wants to investigate the effects of acid rain on the reproductive output of mustard plants. The scientist grows 1 mustard seed in mildly acidic water (pH = 6) and 1 mustard seed in neutral water (pH = 7). The temperature and photoperiod was kept the same between both treatment and control. All plants were given 40 days to develop to seed.

Answer 1

Acidity or alkalinity in a plant’s soil is measured by pH. The pH scale goes from 1 to 14 -- a pH of 1 is highly acidic and a pH of 14 is highly alkaline. The soil's pH varies depending on geographical location. Many plants, including common garden and houseplants, prefer a neutral pH level of around 7.

When a plant’s soil pH increases, which is what would happen when its food’s pH is too high, the plant’s ability to absorb certain nutrients is disrupted. As a result, some nutrients cannot be absorbed properly. For example, if a plant’s leaves become yellow between the veins, this indicates an iron deficiency. Low iron in the soil is not the culprit. The soil’s high pH prevents the iron present in the soil from changing into a form the plant can absorb.

Most plant nutrients are at their most available state at a pH of 6.0 to 6.5. At a higher pH, soil builds up toxic levels of certain nutrients. For example, molybdenum, typically a plant nutrient, becomes poisonous to plants in large amounts. Molybdenum soil levels increase in a high pH environment. Introducing a plant food that results in high pH levels can be toxic to that plant.

When soil has a neutral pH near 7.0, microorganisms beneficial to the surrounding plants flourish and provide vital nutrients to the soil. For example, earthworms live best in a neutral or slightly lower soil pH. When the soil's pH becomes too high due to a high-pH food, earthworms do not perform well and cannot convert the nitrogen present in the soil into a form that plants can absorb

Unless they have adapted, plants do not thrive in extreme conditions. As with an excess of heat, water or light, an excessively high pH soil will not provide an ideal environment for most plants. Creating high pH conditions by feeding a plant the wrong type of food will have an adverse effect.

Certain plants thrive at the higher end of the pH scale, so feeding them a plant food with a high pH level will be good for them. Because rain can lower soil pH, these plants are usually found in areas that receive less rainfall.