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Biology: Ecology and Sustainability - Biodiversity, Habitats, and Ecosystems

Grade 8IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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An Ecosystem consists of all the living organisms (biotic factors) in a particular area interacting with the non-living (abiotic) parts of their environment like H2OH_{2}O, soil, and sunlight.

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Biodiversity is the variety of life in the world or in a particular habitat. It is usually measured at three levels: genetic diversity, species diversity, and ecosystem diversity.

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Trophic Levels represent the position an organism occupies in a food chain. Energy flows from producers (autotrophs) to consumers (heterotrophs), following the 10%10\% rule where only approximately 10%10\% of energy is transferred to the next level.

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Habitats are the specific physical environments where an organism lives, providing necessary resources like food, water, and shelter. A Niche is the functional role or 'job' the organism has within that habitat.

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Sustainability refers to the ability to maintain ecological processes over time. It involves the responsible management of natural resources so that the needs of the present are met without compromising the ability of future generations to meet their own needs.

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Interactions between species include Predation, Competition, and Symbiosis (Mutualism, Commensalism, and Parasitism).

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Photosynthesis is the primary process by which energy enters most ecosystems: 6CO2+6H2O→lightC6H12O6+6O26CO_{2} + 6H_{2}O \xrightarrow{light} C_{6}H_{12}O_{6} + 6O_{2}

📐Formulae

Efficiency of Energy Transfer=Energy available after transferEnergy available before transfer×100\text{Efficiency of Energy Transfer} = \frac{\text{Energy available after transfer}}{\text{Energy available before transfer}} \times 100

Population Density=NA\text{Population Density} = \frac{N}{A} where NN is the total number of individuals and AA is the unit of area.

Simpson’s Index of Diversity (D)=1−∑n(n−1)N(N−1)\text{Simpson's Index of Diversity (D)} = 1 - \frac{\sum n(n-1)}{N(N-1)}

Percentage Change in Population=New Value−Old ValueOld Value×100\text{Percentage Change in Population} = \frac{\text{New Value} - \text{Old Value}}{\text{Old Value}} \times 100

💡Examples

Problem 1:

In a local grassland ecosystem, the total energy stored in the producers (grass) is measured at 25,000 kJ25,000 \text{ kJ}. Based on the 10%10\% rule of energy transfer, calculate the energy available to the secondary consumers (e.g., snakes that eat mice that eat grass).

Solution:

  1. Primary Consumers (Mice): 25,000×0.10=2,500 kJ25,000 \times 0.10 = 2,500 \text{ kJ}.
  2. Secondary Consumers (Snakes): 2,500×0.10=250 kJ2,500 \times 0.10 = 250 \text{ kJ}.

Explanation:

According to the 10%10\% rule, only 10%10\% of the energy from one trophic level is passed to the next. The rest is lost as heat, used for metabolic processes, or remains unconsumed. Therefore, the secondary consumer receives 1%1\% of the original producer energy (10%10\% of 10%10\%).

Problem 2:

An ecologist uses a 1 m21 \text{ m}^2 quadrat to estimate the population of daisies in a field. In 55 random samples, they find 12,15,10,18,12, 15, 10, 18, and 1515 daisies. Calculate the average population density.

Solution:

Average=12+15+10+18+155=705=14 daisies/m2\text{Average} = \frac{12 + 15 + 10 + 18 + 15}{5} = \frac{70}{5} = 14 \text{ daisies/m}^2

Explanation:

Population density is calculated by taking the sum of all individuals found in the sample areas and dividing by the number of samples taken.

Problem 3:

A forest area had 450450 deer in 20102010. Due to habitat fragmentation, the population dropped to 360360 by 20202020. Calculate the percentage decrease in the deer population.

Solution:

450−36090\begin{array}{r} 450 \\ - 360 \\ \hline 90 \end{array} Percentage Decrease=90450×100=20%\text{Percentage Decrease} = \frac{90}{450} \times 100 = 20\%

Explanation:

The change is 90 individuals. Dividing the change by the original population (450450) and multiplying by 100100 gives the percentage decrease.