Lesson 3.3 - Acidity: An Abiotic Limiting Factor 

You learned about abiotic limiting factors of a population.  The next investigation will test whether the pH of water can affect the germination of seeds. 

Read Investigation 13-A: Abiotic Limiting Factors on pages 262 and 263 in your textbook.

A student performed the investigation and recorded the following results.

Petri Dish 1
(Vinegar)

Petri Dish 2
(tap water)

 Petri Dish 3
(sodium hydroxide)

pH

3
7
11

Acid, Base, or Neutral?

acid
neutral
base

Appearance of seeds after 1 day

  • seeds pale in colour
  • no seeds germinated
  • no change in colour
  • 1 seed germinated
  • seeds dark in colour
  • no seeds germinated

Appearance of seeds after 2 days

  • seeds pale in colour
  • no seeds germinated
  • no change in colour
  • 2 seeds germinated
  • seeds dark in colour
  • no seeds germinated

Appearance of seeds after 2 days

  • seeds pale in colour
  • no seeds germinated
  • no change in colour
  • 2 seeds germinated
  • seeds dark in colour
  • no seeds germinated

Appearance of seeds after 4 days

  • seeds pale in colour
  • no seeds germinated
  • no change in colour
  • 8 seeds germinated
  • seeds dark in colour
  • no seeds germinated

Use the student results to answer the following questions. 

Question 1. Answer questions 1 and 2 of Analyze on page 263.

Question 2. How does this student's results show that an abiotic factor can limit the size of a population?

Question 3. Answer questions 1 and 2 of Check Your Understanding on page 263.



Check your answers with those that follow.

 

 

 

 

 

 

 

 

 

 

 

 

Answers to Questions:

Question 1. Answer questions 1 and 2 of Analyze on page 263.

        1. The most seeds germinated in petri dish #2.  The pH of the water in this dish was 7.
        2. No seeds germinated in petri dishes #1 and #3.  The pH of the water in these dishes was 3 and 11 respectively.

Question 2. How does this student's results show that an abiotic factor can limit the size of a population?

pH is an abiotic factor because it is non-living.  The results show that a pH that is low or high will affect severely germination of plant seeds.  Germination of seeds is critical to the size of the population; poor germination results in few plants growing.

Question 3. Answer questions 1 and 2 of Check Your Understanding on page 263.

        1. a.  Lack of light reaching the forest floor limits the growth of seedlings.
          b.  Soil conditions and weather limit the growth of trees on a mountainside.
          c.  Water and weather limit the growth of plants in a desert.
        2. a.  The warm weather between June and September results in a large mosquito population.
          b.  The colder weather between September and November results in a decreased mosquito population.
          c.  If this were a tropical climate, the curve would be flatter and likely quite high because the temperature in tropical climates is always warm.  Likely, the curve would depend more on water than temperature.

 


Now, do Assignment 13C.  Page forward to access it.