krit.club logo

Human Influences on Ecosystems - Food supply and habitat destruction

Grade 12IGCSEBiology

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

🔑Concepts

•

The exponential growth of the human population increases the demand for food, leading to intensive farming practices such as the use of chemical fertilizers, pesticides, and herbicides.

•

Monoculture is the practice of growing a single crop species (e.g., wheat or corn) over a large area. While efficient for harvesting, it significantly reduces biodiversity and increases the risk of total crop failure due to specific pests or diseases.

•

Habitat destruction is primarily caused by deforestation for agricultural land, livestock grazing, and urban development, leading to the extinction of species and loss of genetic variation.

•

Deforestation impacts the carbon cycle by reducing the rate of photosynthesis, thereby increasing the concentration of atmospheric CO2CO_2 and contributing to global warming.

•

Soil erosion occurs when tree roots are removed; the soil is no longer held in place and is easily washed away by rain, often leading to the siltation of rivers and loss of fertile land.

•

Leaching occurs when inorganic fertilizers, containing high concentrations of nitrates (NO3−NO_3^-) and phosphates (PO43−PO_4^{3-}), are washed into water bodies, leading to eutrophication.

•

Eutrophication sequence: Nutrient runoff →\rightarrow Algal bloom →\rightarrow Death of submerged plants (lack of light) →\rightarrow Decomposition by aerobic bacteria →\rightarrow Depletion of dissolved O2O_2 →\rightarrow Death of fish and other aquatic organisms.

📐Formulae

6CO2+6H2O→light/chlorophyllC6H12O6+6O26CO_2 + 6H_2O \xrightarrow{\text{light/chlorophyll}} C_6H_{12}O_6 + 6O_2

Rate of Population Increase=(Birth Rate+Immigration)−(Death Rate+Emigration)\text{Rate of Population Increase} = (\text{Birth Rate} + \text{Immigration}) - (\text{Death Rate} + \text{Emigration})

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

NH4+→NO2−→NO3−NH_4^+ \rightarrow NO_2^- \rightarrow NO_3^-

💡Examples

Problem 1:

A farmer applies excessive amounts of ammonium nitrate (NH4NO3NH_4NO_3) fertilizer to a field adjacent to a lake. After a period of heavy rainfall, the fish in the lake begin to die. Explain the biological process that led to this event.

Solution:

The process is eutrophication. 1. The NO3−NO_3^- ions leach into the lake. 2. This causes an 'algal bloom' (rapid growth of algae). 3. The thick layer of algae blocks sunlight from reaching aquatic plants below. 4. These plants die as they cannot perform photosynthesis. 5. Aerobic bacteria decompose the dead organic matter. 6. The bacteria consume the dissolved O2O_2 for respiration. 7. The water becomes hypoxic, and fish die due to lack of oxygen.

Explanation:

This demonstrates the negative impact of intensive farming on aquatic ecosystems through the disruption of the oxygen balance.

Problem 2:

Calculate the impact of deforestation on the carbon cycle in a 100-hectare forest where each hectare absorbs 1515 tonnes of CO2CO_2 per year. If 40%40\% of the forest is cleared for palm oil plantations, how much less CO2CO_2 is absorbed annually?

Solution:

Total initial absorption = 100 ha×15 tonnes/ha=1500 tonnes of CO2100 \text{ ha} \times 15 \text{ tonnes/ha} = 1500 \text{ tonnes of } CO_2. Area cleared = 40%40\% of 100=40 ha100 = 40 \text{ ha}. Reduction in absorption = 40 ha×15 tonnes/ha=600 tonnes of CO240 \text{ ha} \times 15 \text{ tonnes/ha} = 600 \text{ tonnes of } CO_2.

Explanation:

Removal of producers reduces the 'carbon sink' capacity of the ecosystem, leading to higher net CO2CO_2 levels in the atmosphere.

Food supply and habitat destruction Revision - Grade 12 Biology IGCSE