Lab 7 – Effects of pH on Radish Seed Germination


Learning Objectives

  • Define ecology as interactions amongst organisms and their environment
  • Analyze the effects of abiotic and biotic factors in an ecosystem
  • Assess how generalists and specialists define habit tolerance


Figure 1: Note the relationship between an organism, populations, communities and ecosystems.

Ecology is the scientific study of both the interactions among organisms and the interactions between organisms and their environment. It is an interdisciplinary field that blends Earth science, evolutionary biology and general biology. Ecology explores the adaptations of organisms, the distribution of organisms and biodiversity.

Ecology can be divided into different levels or categories. Ecosystem ecology looks at the “big picture”. It focuses on the cycling of chemicals and the energy flow within an ecosystem. Ecosystem ecology includes all the abiotic factors and species within an ecosystem. Community ecology is concerned with the interactions between species and how those interactions affect the structure and organization of the community. As the name implies, population ecology is concerned with populations. A population is a group of individuals of the same species living in the same area at the same time. Population ecology focuses on factors that affect population density and growth. Ecology of organisms, or organismal ecology, is the study of individual organisms and the evolutionary adaptations that have enabled them to survive in their environments.

Abiotic and Biotic Factors

Environments encompass abiotic and biotic components. Abiotic components include the physical and chemical aspects. Physical factors that affect an ecosystem include sunlight, temperature, water currents, wind, nature of soil, latitude and altitude. Chemical factors include pH levels, available nutrients (in soil or water), water salinity, toxicity concentrations and water levels in soil. Biotic components refer to the living factors in an environment and include the producers, consumers and decomposers. Producers are the organisms that convert inorganic material to organic substances. Plants are an example of a producer. By converting sunlight and carbon dioxide to carbohydrates, they are producing food for the consumers.

Figure 2: Creatures have learned to thrive in a variety of extreme environments, such as the desert climate pictured above.

Consumers and decomposers are completely dependent on producers for nourishment. Since plants are an important producer, it follows that sunlight powers nearly all ecosystems (aquatic and terrestrial).

Organisms have adapted and evolved anatomical, physiological, and behavioral characteristics that compensate for variation within the environment. The blending of ecology and evolutionary biology is probably most evident when examining organismal ecology. In this way, the environment shapes the organisms.

Habitat Tolerance

Adaptations that organisms have developed allow them to compensate for minimal temporal and spatial variation within their environment. This is accomplished, for example, by regulating body temperature or controlling the rate at which water is transpired. Nevertheless, there are limits to an organism’s ability to compensate for environmental factors. No single species can tolerate all of Earth’s environments. The geographic distribution of a species is thus limited by the physical environment. That is, species distribution is limited by an environment’s abiotic factors.

Figure 3: Dandelion (Taraxicum officionale)- species like the dandelion are very common and show no aspects of rarity making them very common handling a broad range of tolerances.

Although living organisms are found all over the planet, all species have a defined habitat tolerance assigning a viable range of environmental conditions. For example, some plant species can tolerate a broad range of soil variability, while others are confined to a single soil type. If a species has a narrow habitat tolerance because of one or more abiotic factors, then they are limited in their distribution range. Species with a broad range of tolerance are usually distributed widely, whereas those with a narrow range have more restricted distribution. Species can be categorized as specialists or generalists. Specialist species are those that have a limited diet or cannot tolerate a wide range of environmental conditions. Consider a cactus. A cactus has a limited tolerance for soil conditions, water levels and temperatures. Generalists, on the other hand, have a wider range of tolerance for environmental conditions and diet. For example, omnivores are typically generalists, whereas herbivores tend to be specialists. Interestingly, invasive species are frequently generalists.

Habitat tolerance along with a species’ geographic range (limited vs. widespread) and its local population size (large vs. small) determines a species’ commonness or rarity. These classifications can be very significant to industries such as agricultural production and wildlife management.

As mentioned above, the environment shapes the organisms. What is the effect of organisms on the environment? Environmental changes are influenced by the organisms that inhabit that environment. In this way, organisms shape the environment. A change in species distribution can modify interactions within the environment. The loss of a native species or the invasion of a non-native species can alter the survival of other organisms within the environment. Therefore, control of invasive species and conservation of endangered species are important to maintain the balance of the entire system.



Experiment 1: Effects of pH on Radish Seed Germination

Natural soil pH depends on the parent rock material from which it was formed and processes like climate. Soil pH is a measure of the acidity or alkalinity of the soil. Acidic soils are considered to have a 5.0 or lower pH value whereas 10.0 or above is considered a strong basic or alkaline soil. The pH of soil affects the solubility of nutrients in soil water and thus it affects the amount of nutrients available for plant uptake. Different nutrients are available under differing pH conditions.

In this experiment we will look at the effect of pH on the germination and growth rate of radish seeds in order to determine the range of pH tolerance for the seed. Acidic or basic water will be used in order to simulate acidity or alkalinity in soil.


2 mL 4.5% Acetic Acid (Vinegar), C2H4O2
Permanent Marker
(3) 5 cm Petri Dishes
3 pH Test Strips
Radish Seed Packet
2 mL 15% Saturated Sodium Bicarbonate (Baking


Soda) Solution, NaHCO3
*Paper Towel Sheets (cut to fit into the Petri dish)
*Sunny Location

*You Must Provide


  1. Use the permanent marker to label the top of each of the three Petri dishes as Acetic Acid, Sodium Bicarbonate, or Water.
  2. Carefully cut three small circles from the paper towel sheets. The circles should comfortably fit within the bottom of the Petri dish.
  3. Place the circles in the dishes, and wet them with approximately 2 mL of each respective solution (acetic acid, sodium bicarbonate, or water).
  4. Gently press the reaction pad of three, pH test strips onto the wet paper towels. Record your data in the first row of Table 1.
  5. Arrange 10 radish seeds on each paper towel in each Petri dish. Make sure the seeds have space and are not touching. Then, place the top of the Petri dish on the bottom.
  6. Place the Petri dishes in a sunny or well-lit, warm place. Be sure to keep the paper towels moist for the length of the experiment with the appropriate solution if any of the towels dry out.
  7. Observe the seeds daily for seven days, and record the number of seeds that germinate in Table 1. Note when the seeds crack and roots or shoots emerge). On the seventh day, record the lengths of radish seed sprouts (mm or cm).



Pre-Lab Questions


  1. Would you expect endangered species to be more frequently generalists or specialists? Explain your answer.




  1. How does temperature affect water availability in an ecosystem?




  1. Identify a generalist species and explain why it is considered a generalist. Identify a specialist and describe some adaptations that species developed that allow them to survive in their native habitat.



Experiment 1: Effects of pH on Radish Seed Germination

Table 1: pH and % Radish Seed Germination

Stage/Day Observations Acetic Acid Sodium Bicarbonate Water
Initial pH pH – 4 (Faded Orange color) pH – 7 (Green) pH – 5 (light yellow, color barely changed)
Day 1 0 – no growth 0 – no growth (the color of the seeds turned black) 10 – All Shoots Emerged
Day 2 0 – no growth 0 – no growth 10 – Sprouting
Day 3 0 – no growth 0 – no growth 10 – Sprouting
Day 4 0 – no growth 0 – no growth 10 – Sprouting
Day 5 0 – no growth 0 – no growth 10 – Sprouting
Day 6 0 – no growth 0 – no growth 10 – Sprouting
Day 7


Record Lengths of radish seeds sprouts

0 – there were no germinated seeds. 0 – there were no germinated seeds. Seed #1 – 6cm

Seed #2 – 6cm

Seed #3 – 7cm

Seed #4 – 6.5cm

Seed #5 – 3cm

Seed #6 – 5cm

Seed #7 – 5cm

Seed #8 – 2cm

Seed #9 – 2cm

Seed #10 – 2cm





Day 1 – Feb. 17th

Day 7 – Feb. 23rd


Post-Lab Questions


  1. Compare and contrast the growth rate for the control with the alkaline and acidic solutions.



  1. According to your results would you consider the radish a generalist or a specialist? Why or why not? Use your data to support your answer.



  1. Research the internet and report on a crop species that is currently being affected by acid rain and along with any proposed solutions. Provide your citations in APA format.


  1. Research the internet and report on another toxin found in rain water and its effect on the environment.   Provide citations in APA format.


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