Class 12 Biology - Ecosystem

Activity 12.1: Study of Decomposition Kinetics in a Controlled Microcosm

Aim: To observe the rate of decomposition of organic matter under different environmental conditions (moisture and temperature).

Materials Required:

Leaf litter (Dry leaves)
3 Large Glass Jars (A, B, and C)
Moist Garden Soil
Thermometer
Balance
Mesh bags (Nylon)

Procedure:

Weigh exactly 10g of leaf litter and place it in three separate mesh bags.
Prepare Jar A: Fill with dry soil and place in a cold environment (5°C).
Prepare Jar B: Fill with moist soil (60% field capacity) and place in a warm environment (30°C).
Prepare Jar C: Submerge the litter in water (Anaerobic condition) at 30°C.
After 15 days, retrieve the mesh bags, dry the contents at 60°C to a constant weight, and calculate the Mass Loss Percentage.

Scientific Note Decomposition is an oxygen-consuming process. The rate is determined by the C:N ratio and the chemical composition of the detritus. Materials rich in Lignin and Chitin decompose very slowly, while those rich in nitrogen and water-soluble substances (like sugars) decompose rapidly. Anaerobic conditions inhibit the activity of aerobic decomposers, significantly slowing down the process.

Observation: Jar B (Warm and Moist) will show the highest rate of decomposition (highest mass loss). Jar C (Anaerobic) will show the lowest rate due to limited microbial respiration.

Lab Best Practice Drying the litter to a "constant weight" is essential to ensure that you are measuring the loss of organic matter and not just changes in water content.

Activity 12.2: Constructing Ecological Pyramids of Biomass

Aim: To quantify the transfer of biomass across different trophic levels in a local ecosystem.

Materials Required:

Data from Activity 11.2 (Quadrat sampling)
Oven for dry weight measurement
Bomb calorimeter (optional, for energy calculation)

Procedure:

Collect all plants (Producers) from a 1 $m^2$ quadrat, dry them at 80°C for 24 hours, and record the dry weight (Biomass).
Estimate the biomass of Primary Consumers (e.g., insects) and Secondary Consumers (e.g., frogs/birds) in the same area through sampling.
Represent the data graphically as a Pyramid of Biomass.

Scientific Note In terrestrial ecosystems, the pyramid of biomass is usually upright. However, in aquatic ecosystems, the pyramid of biomass can be inverted (e.g., the biomass of a small population of phytoplankton supports a much larger biomass of zooplankton/fish due to high turnover rates).

Safety First When collecting insects or small animals for biomass estimation, use specialized tools (sweep nets/pitfall traps) and ensure that no endangered species are harmed. Always release non-target organisms immediately.

Activity 12.1: Study of Decomposition Kinetics in a Controlled Microcosm

Aim: To observe the rate of decomposition of organic matter under different environmental conditions (moisture and temperature).

Materials Required:

Leaf litter (Dry leaves)

3 Large Glass Jars (A, B, and C)

Moist Garden Soil

Thermometer

Balance

Mesh bags (Nylon)

Procedure:

Weigh exactly 10g of leaf litter and place it in three separate mesh bags.

Prepare Jar A: Fill with dry soil and place in a cold environment (5°C).

Prepare Jar B: Fill with moist soil (60% field capacity) and place in a warm environment (30°C).

Prepare Jar C: Submerge the litter in water (Anaerobic condition) at 30°C.

After 15 days, retrieve the mesh bags, dry the contents at 60°C to a constant weight, and calculate the Mass Loss Percentage.

Observation: Jar B (Warm and Moist) will show the highest rate of decomposition (highest mass loss). Jar C (Anaerobic) will show the lowest rate due to limited microbial respiration.

Lab Best Practice Drying the litter to a "constant weight" is essential to ensure that you are measuring the loss of organic matter and not just changes in water content.

Activity 12.2: Constructing Ecological Pyramids of Biomass

Aim: To quantify the transfer of biomass across different trophic levels in a local ecosystem.

Materials Required:

Data from Activity 11.2 (Quadrat sampling)

Oven for dry weight measurement

Bomb calorimeter (optional, for energy calculation)

Procedure:

Collect all plants (Producers) from a 1

m^2

quadrat, dry them at 80°C for 24 hours, and record the dry weight (Biomass).

Estimate the biomass of Primary Consumers (e.g., insects) and Secondary Consumers (e.g., frogs/birds) in the same area through sampling.

Represent the data graphically as a Pyramid of Biomass.

Class 12 Biology - Ecosystem (Activities)

Class 12 Biology - Ecosystem

Activity 12.1: Study of Decomposition Kinetics in a Controlled Microcosm

Activity 12.2: Constructing Ecological Pyramids of Biomass

On this page

Class 12 Biology - Ecosystem (Activities)

Class 12 Biology - Ecosystem

Activity 12.1: Study of Decomposition Kinetics in a Controlled Microcosm

Activity 12.2: Constructing Ecological Pyramids of Biomass

On this page