CLASS: SS 1
SUBJECT: BIOLOGY PERIOD(S) 2
DURATION: 45 MINUTES
TOPIC: TOLERANCE
SUBTOPIC 1: MINIMUM AND MAXIMUM RANGE OF TOLERANCE
SUBTOPIC 2: GEOGRAPHIC RANGE
PREVIOUS KNOWLEDGE: STUDENTS AND FAMILIAR WITH THE
TOPIC
OBJECTIVES: At The End Of The Period(s), students should be able to:
Period 1: Discuss why living organisms possess a range of tolerance to environmental factors
Period 2: List the abiotic factors that impose tolerance on organisms
REFERENCES
Modern biology for senior secondary school page
Essential biology for senior secondary schools by M.C. Michael pg
CONTENT
Tolerance can be defined as the ability of a living organism to withstand or tolerate little unfavourable changes in the environment which affect their survival. Abiotic factors such as temperature, humidity, light, intensity, rainfall etc play very crucial part in the distribution of organisms in the various terrestrial and aquatic habitats of the world because they occur over a range in the various habitats. Therefore, living organisms can only inhabit a particular habitat it they can tolerate the ranges of abiotic factors that operate in it (minimum and maximum limit). For example, temperature can range from 15 – 500C in hot desert and – 250-00C in polar areas.
TOLERANCE RANGE
Living organisms can only survive within certain minimum and maximum limits for each factor. The tolerance range refers to the range between upper and lower limits. Anything beyond this range will result to the organisms’ death. Tolerance range for a given abiotic factor varies from species to species and within species from population to population depending on their ecological niche e.g. most animals have a tolerance range from temperature between 00C (lower lethal temperature) and 420C (upper lethal temperature).
The optimum range can be found within the tolerance range and at this range, species activities (growth and reproduction ) are at an optimum or at their peaks. Beyond the optimum range, this species face physiological stress because it cannot function well.
The tolerance range may also differ as an organisms passes through its various stages in life. The minimum and maximum tolerance limits for all abiotic factors may vary geographically and seasonally. One factor may affect the tolerance ranges of other factors e.g. lobsters can withstand temperatures up to 290C when the oxygen level of water is low but at higher oxygen levels, they can withstand temperatures up to 420C
GEOGRAPHIC RANGE
This refers to the areas where a species of organisms can only be found within the minimum and maximum limits of its tolerance. Different abiotic factors (e.g. food availability, light intensity, daylength time, wind etc) play arole in the geographic boundaries fo a species e.g. a given platn species may be prevented from growing by low temperature at its northern boundary and low rainfall at its southern boundaries. Tolerance ranges of various plant types determine the main biome of the world.
INSTRUCTIONAL MATERIALS: A map of the world, charts, showing distribution of living organisms according to their tolerance.
TEACHING METHODS PROCEDURES
Step 1: Teacher revises the last topic with the students
Step II: Teacher introduced the new topic by defining tolerance and explaining how tolerance influence living organisms distribution.
Step III: Teacher explained geographic range
Step IV: Teacher allows students to ask questions and writes note under content on the board.
ACTIVITIES
Period 1: Students discuss tolerance and tolerance range
Period 2: Students discuss geographica range
EVALUATION
Period 1: What is a biome? Define Tolerance
Period 2: What do you understand by the term “tolerance range”?
SUMMARY: Teacher summarizes the topic, marks the students note s and makes corrections where necessary.
Assignment(s):
- Describe the tolerance range of most animals in an ecosystem.
- Write a 200 word essay on the distribution of living organisms in relation to their tolerance.