Understanding Ecosystems and Evolutionary Processes
Nitrogen and Carbon Cycles
Nitrogen Cycle
Nitrogen is a major compound, comprising 78% of the Earth’s atmosphere. The nitrogen cycle involves several key processes:
- Nitrogen Fixation: Nitrogen gas (N2) is converted into ammonium (NH4) by cyanobacteria and other bacteria in the soil, or into organic compounds by nitrogen-fixing bacteria in the roots of legumes. Plants utilize these compounds to form proteins and amino acids.
- Nitrification: Nitrates are produced in two ways. Firstly, nitrogen gas is converted into nitrate through energy provided by cosmic radiation, meteor trails, and lightning. Secondly, ammonium ions from decomposition in the soil are converted into nitrite by nitrite-producing bacteria, and then into nitrate by nitrate-producing bacteria.
- Denitrification: Bacteria convert nitrate back into nitrogen gas, counterbalancing nitrogen fixation, except for human activities.
Human Impact on the Nitrogen Cycle
Fertilizers produced from nitrogen gas, often containing phosphate, contribute to algal overgrowth and fish kill in lakes and rivers. They also release nitrogen oxide, contributing to the greenhouse effect, acid rain, and ozone shield depletion.
Carbon Cycle
Carbon dioxide (CO2) is essential for photosynthesis in terrestrial and aquatic ecosystems. It’s incorporated into food for both heterotrophs and autotrophs. Respiration releases some CO2 back into the atmosphere.
In aquatic ecosystems, CO2 primarily exists as bicarbonate ions, a crucial carbon source for algae. During respiration, CO2 transforms into bicarbonate ions, maintaining equilibrium with atmospheric CO2.
Fossil fuels and inorganic carbonates like limestone and shells serve as carbon reservoirs. Human activities, such as burning fossil fuels and deforestation, release excess CO2, contributing to the greenhouse effect, global warming, and climate change.
Evolution and Adaptation
Darwin’s Theory of Evolution
Organisms exhibit heritable variations. Within a population, individuals compete for limited resources, leading to differential reproductive success. Those with advantageous traits are more likely to survive and reproduce, passing those traits to their offspring. This process of natural selection drives adaptation to changing environments.
Evidence for Evolution
- Fossil Evidence: Remains of past life, often hard parts like shells, bones, or teeth, embedded in sedimentary rock. Paleontologists seek transitional links between species.
- Biogeography: The study of the distribution of plants and animals globally, providing insights into continental drift and evolutionary history.
- Biochemical Evidence: Similarities in DNA and protein sequences indicate evolutionary relationships.
- Anatomical Evidence: Homologous structures, like forelimbs adapted for flight or swimming, suggest common ancestry. Vestigial structures, like the ostrich’s wings, are remnants of features that served a purpose in ancestors.
Coastal and Freshwater Ecosystems
Coastal Ecosystems: Estuaries and Seashores
Estuaries, where freshwater and saltwater mix, are highly productive ecosystems. Organisms here must tolerate fluctuating salinity levels. These nutrient-rich environments serve as nurseries for many marine species.
Seashores, whether rocky or sandy, are shaped by tides. The littoral zone, between high and low tide, supports diverse life adapted to harsh conditions.
Lakes: Oligotrophic and Eutrophic
Lakes are classified by nutrient content. Oligotrophic lakes are nutrient-poor, while eutrophic lakes are nutrient-rich. Eutrophication can transform oligotrophic lakes into eutrophic ones.
Lakes have distinct life zones: the littoral zone with rooted plants, the limnetic zone with plankton and fish, and the profundal zone where organisms feed on falling debris.