UPCAT General Science (Extended) — Ecology, Biogeochemical Cycles & Species RelationshipsFlash Cards

A forest fire destroyed a mature woodland. After 5 years, grasses and small shrubs have started growing. What type of ecological succession is this?

Secondary succession. The area was previously colonized but damaged by the fire. Secondary succession occurs faster than primary succession because soil and nutrients are already present, allowing grasses and shrubs to quickly recolonize the area.

Why do nitrogen-fixing bacteria in root nodules have a mutualistic relationship with legume plants?

The bacteria convert atmospheric nitrogen into ammonia that plants can use for protein synthesis. In return, plants provide carbohydrates and shelter. Both organisms benefit: plants get essential nitrogen, bacteria get food and protection.

What happens to energy as it moves from producers to tertiary consumers in a food chain?

Energy decreases at each trophic level due to the 10% rule - only about 10% of energy is transferred to the next level. The rest is lost as heat during metabolism. This explains why there are fewer top predators than herbivores in ecosystems.

How does deforestation affect the water cycle?

Trees normally absorb groundwater and release it as water vapor through transpiration. Without trees: less transpiration occurs, reducing cloud formation and rainfall; more surface runoff causes flooding and soil erosion; groundwater recharge decreases.

Biosphere

The broadest level of ecological organization - the thin layer of Earth and its atmosphere that supports all life. It includes all ecosystems on Earth, from the deepest ocean trenches to the highest mountains.

A farmer notices that corn grows poorly in soil where previous crops removed most nitrogen. What biogeochemical process could help restore soil fertility?

Nitrogen fixation by planting legumes (beans, peas). Nitrogen-fixing bacteria in legume roots convert atmospheric nitrogen (N₂) into ammonia (NH₃), which plants can use. When legumes decompose, they add nitrogen back to the soil.

Why can't two species occupy exactly the same ecological niche in the same habitat?

According to the Competitive Exclusion Principle (Gause's Law), two species competing for the same limited resources cannot coexist permanently. The more efficient competitor will eventually eliminate the other, or the species must evolve to occupy different niches.

What is the difference between primary and secondary consumers in a food web?

Primary consumers are herbivores that eat producers (plants) - like rabbits eating grass. Secondary consumers are carnivores that eat primary consumers - like snakes eating rabbits. Each represents a different trophic level in energy transfer.

How does carbon move from the atmosphere into living organisms?

Through photosynthesis: plants absorb CO₂ from air and use sunlight energy to convert it into glucose (C₆H₁₂O₆). The process is: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂. Carbon becomes part of plant tissues and enters food chains.

A bird builds its nest in a tree without harming the tree. The tree provides shelter while the bird provides nothing in return. What type of relationship is this?

Commensalism. One species (bird) benefits by getting shelter and nesting space, while the other species (tree) is neither helped nor harmed. The relationship is neutral for the tree.

Why do decomposers play a crucial role in biogeochemical cycles?

Decomposers break down dead organisms and waste products, releasing essential nutrients (nitrogen, phosphorus, carbon) back into the environment. Without them, nutrients would remain locked in dead matter and become unavailable for new plant growth.

What happens during eutrophication of a lake ecosystem?

Excess nutrients (nitrogen, phosphorus) from fertilizers cause rapid algae growth. Algae block sunlight to underwater plants and consume oxygen when they decompose. Fish and other aquatic life die from lack of oxygen, disrupting the entire ecosystem.

Autotrophs vs Heterotrophs

Autotrophs make their own food using energy (photosynthesis or chemosynthesis) - like plants and algae. Heterotrophs cannot make their own food and must consume other organisms - like animals, fungi, and most bacteria.

How does resource partitioning allow competing species to coexist?

Species evolve to use different resources or the same resources at different times/places. Example: different bird species feeding at different heights in the same tree, or hunting at different times of day. This reduces direct competition.

What is the role of pioneer species in primary succession?

Pioneer species (like lichens and mosses) are the first to colonize bare rock or new land. They break down rock into soil, add organic matter when they die, and create conditions that allow other plants to establish, starting the succession process.

A tick feeds on human blood, potentially transmitting diseases. The human is harmed while the tick benefits. What type of relationship is this?

Parasitism. The parasite (tick) benefits by obtaining nutrients from the host's blood, while the host (human) is harmed through blood loss and potential disease transmission. The tick depends on the host for survival.

Why does phosphorus cycle differently from carbon and nitrogen cycles?

Phosphorus has no significant gaseous phase at normal temperatures. It cycles mainly through weathering of rocks, soil, water, and living organisms. Unlike carbon and nitrogen, phosphorus cannot cycle through the atmosphere, making it often the limiting nutrient in ecosystems.

What is an ecological niche?

An organism's ecological role in its environment - including what it eats, when it's active, where it lives, how it reproduces, and its interactions with other species. It's like the organism's 'profession' in the ecosystem community.

How do humans impact the carbon cycle through fossil fuel burning?

Burning fossil fuels releases stored carbon as CO₂ into the atmosphere faster than natural processes can absorb it. This increases atmospheric CO₂ levels, contributing to global warming and climate change by enhancing the greenhouse effect.

What is the difference between intraspecific and interspecific competition?

Intraspecific competition occurs between individuals of the same species (lions competing for territory). Interspecific competition occurs between different species (lions and cheetahs competing for prey). Both involve competition for limited resources.