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Ecology
TOPIC: Biotic and Abiotic Factors (13.2)
KEY CONCEPT: Every ecosystem includes both living and nonliving factors
All ecosystems are made up of living and nonliving parts.
• The living parts are called biotic factors, such as plants, animals, fungi, and bacteria.
• The nonliving parts are called abiotic factors, such as moisture, temperature, wind, sunlight, and soil.
An ecosystem is formed from a complex web of connected biotic and abiotic factors. Biodiversity refers to the variety of
living things in an ecosystem. The amount of biodiversity found within an ecosystem depends on many abiotic factors, such
as moisture and temperature. A change in a single biotic or abiotic factor can have a significant impact on an ecosystem.
One biotic factor that greatly impacts an area’s biodiversity is the presence of a keystone species. A keystone species is a
species that has an unusually large effect on its ecosystem.
1. What is a biotic factor? List two examples.
2. What is an abiotic factor? List two examples.
3. What is biodiversity? Why might it be important to preserve areas with high biodiversity?
TOPIC: Energy in Ecosystems (13.3)
KEY CONCEPT: Life in an ecosystem requires a source of energy.
All organisms must have a source of energy in order to survive.
• Producers get their energy from nonliving resources, meaning they make their own food. Producers are also called
autotrophs.
• Consumers get their energy by eating other living or once-living resources.
Consumers are also called heterotrophs.
Photosynthesis is the two-stage process that green plants, cyanobacteria, and some protists use to produce energy in the
form of carbohydrates. These chemical reactions form carbohydrates from carbon dioxide and water.
Other producers use chemicals to form carbohydrates in a process called chemosynthesis. Chemosynthetic producers are
found in deep-sea vent communities as well as in sulfur-rich salt marsh flats and hydrothermal pools.
1. What is the difference between a producer and a consumer?
2. Why do all ecosystems depend on producers?
3. How are consumers dependent on the sun?
TOPIC: Food chains and food webs (13.4)
KEY CONCEPT: Food chains and food webs model the flow of energy in an ecosystem.
A food chain is a model that shows a sequence of feeding relationships between a producer and consumers. There are
several types of consumers.
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Herbivores eat only plants.
Carnivores eat only animals.
Omnivores eat both plants and animals.
Detritivores eat detritus, or dead organic matter.
Decomposers are detritivores that break down organic matter into simpler compounds.
Food chains are very helpful to explain the feeding relationships of very selective eaters. Specialists are consumers that mainly
eat only one specific organism or a very small number of organisms. In contrast, generalists are consumers that have a varying
diet. Trophic levels are the levels of nourishment in a food chain. Energy flows up the food chain from the lowest trophic level to
the highest.
• Primary consumers (herbivores) are the first consumer above the producer trophic level.
• Secondary consumers (carnivores) eat primary consumers.
• Tertiary consumers (carnivores) eat secondary consumers.
A food web is a model that shows the complex network of feeding relationships and the flow of energy within and sometimes
beyond an ecosystem. At each link in a food web, some energy is stored within an organism, and some energy is dissipated
into the environment.
1. What are the four main types of consumers?
2. What is the difference between a specialist and a generalist?
3. What are the trophic levels in a food chain?
4. What is the difference between a food chain and a food web?
5. What happens to energy at each link in a food web?