Food Webs and Biogeochemical Cycles

Study Notes

Food Webs and Relationships

A food chain shows how energy and nutrients flow between organisms.
A food chain starts with producers (plants) and proceeds to consumers.
A food web is more complex than a food chain, showing interconnected food chains.
Organisms in a food web can be part of multiple food chains.
Predation is when one organism kills and eats another.
Competition occurs when two organisms compete for the same resources.
Mutualism occurs when both organisms benefit from the relationship.
Commensalism occurs when one organism benefits, and the other is unaffected.
Parasitism occurs when one organism benefits at the expense of another.
A food chain is a simple, straight line showing energy flow.
A food web is a complex network of interconnected food chains.
Relationships describe how organisms interact (helping, harming, or having no effect).

Biogeochemical Cycles

Biogeochemical cycles describe the movement of elements and compounds (biological, geological, and chemical).
Cycles ensure essential elements (carbon, nitrogen, oxygen, and water) recycle in the environment.
The water cycle describes the continuous movement of water.
- Evaporation: Water turns into vapor.
- Condensation: Water vapor cools and forms clouds.
- Precipitation: Water falls from the clouds as rain, snow, or hail.
- Infiltration: Water soaks into the ground.
- Transpiration: Plants release water vapor.
- Runoff: Water flows across the land.
The carbon cycle describes how carbon moves between the atmosphere, organisms, and Earth's surface.
- Photosynthesis: Plants convert CO2 into glucose.
- Respiration: Organisms release CO2.
- Decomposition: Dead organisms break down, releasing carbon.
- Fossil fuels: Carbon stores in the Earth.
The nitrogen cycle describes the movement of nitrogen through the atmosphere, soil, and organisms.
- Nitrogen fixation: Bacteria convert atmospheric nitrogen into ammonia.
- Nitrification: Bacteria convert ammonia into nitrites, then nitrates.
- Assimilation: Plants absorb nitrates.
- Ammonification: Decomposers release ammonia.
- Denitrification: Bacteria convert nitrates back to nitrogen gas.
The phosphorus cycle describes the movement of phosphorus through the Earth's systems.
- Weathering: Phosphorus is released from rocks.
- Absorption: Plants absorb phosphorus.
- Decomposition: Decomposers return phosphorus to the soil.
- Sedimentation: Phosphorus settles into the ocean and forms new rocks.

Ecological Succession

Ecological succession is the gradual replacement of one community of organisms by another over time.
Two types of ecological succession:
- Primary succession: Occurs in areas with no soil (volcanic eruptions, glaciers).
- Pioneer species: First organisms to colonize
- Secondary succession: Occurs in areas where soil remains (fires, floods).
  - Early growth: Grasses and small plants.
  - Intermediate species: Shrubs and small trees.
  - Climax community: Mature ecosystem.

Photosynthesis

Photosynthesis is the process by which plants use sunlight to make food (glucose) from carbon dioxide and water.
It uses chlorophyll (green pigment).
The formula is 6CO2 + 6H2O + light energy → C6H12O6 + 6O2.

Population and Population Curves

A population is a group of individuals of the same species in the same area at the same time.
Population curves show how population size changes over time.
There are different types of population growth curves:
- Exponential growth: Rapid growth when resources are unlimited.
- Logistic growth: Growth slows as the population approaches the carrying capacity (the maximum population size the environment can support).
- Constant growth: Overshoots and dieback, crashing after exceeding carrying capacity.
Factors affecting population size:
- Biotic factors (birth rate, death rate, competition, predation).
- Abiotic factors (climate, food availability, space).
- Density-dependent factors (affect population based on size, disease, competition).
- Density-independent factors (affect populations regardless of size, natural disasters).

Water Pollution

Water pollution is the contamination of water bodies by harmful substances.
Types of water pollution:
- Chemical pollution (pesticides, fertilizers, heavy metals).
- Biological pollution (bacteria, viruses).
- Nutrient pollution (nitrogen, phosphorus).
- Physical pollution (sediment, plastics).
- Thermal pollution (high water temperatures).
Effects: Harm to aquatic life, human health risks, ecosystem damage, and economic impacts.