bio tudy guide

Ecological Levels (Smallest to Largest)

Organism → Population → Community → Ecosystem → Biosphere

Organism

A single living thing

Population

All of the organisms of the same species in one area

Community

All the different populations in an area

Ecosystem

Living and non-living things interacting in an area

Biosphere

All ecosystems on Earth combined

Biodiversity and Survival

More variety = more chances to survive changes

Natural Selection

Best traits get passed on to help survival

Biodiversity and Ecosystem Health

Higher diversity = stronger and more adaptable ecosystem

Population Density

Number of individuals per unit area

Factors Affecting Population Density

Weather, predators, human impact, food availability

Biotic Factor

Living parts of an ecosystem (ex: plants, animals, bacteria)

Abiotic Factor

Non-living parts of an ecosystem (ex: water, sunlight, temp)

Exponential Growth

Population grows fast with no limits

Logistic Growth

Population slows or stops at carrying capacity

Carrying Capacity

Max number of individuals an area can support

Limiting Factor

Something that reduces or controls population growth

Density-Dependent Limiting Factor

Affects large populations (ex: disease, competition)

Density-Independent Limiting Factor

Affects all sizes (ex: storms, fires)

Food Chain

Shows one path of energy flow

Food Web

Shows many connected food chains in an ecosystem

Producer (Autotroph)

Makes own food using sunlight (ex: plants)

Consumer (Heterotroph)

Gets energy by eating other organisms

Ultimate Energy Source

The sun

Herbivore

Eats only plants

Carnivore

Eats only animals

Omnivore

Eats plants and animals

Primary Consumer

Eats producers

Secondary Consumer

Eats primary consumers

Tertiary Consumer

Eats secondary consumers

Quaternary Consumer

Top predator, eats tertiary consumers

Decomposer

Breaks down dead organisms (ex: fungi)

Scavenger

Eats dead animals but doesn’t break them down chemically

Energy Flow in Ecosystems

Only 10% of energy is passed on to the next level

Energy Pyramid (Example)

Grass → Grasshopper → Frog → Snake → Hawk (10% rule applies)

Energy Pyramid (Numbers)

100,000 → 10,000 → 1,000 → 100 → 10 kcal

Water Cycle

Water moves through evaporation, condensation, precipitation, collection

Why Water Cycle Matters

All organisms need water to live

Nutrient Cycles

Four types: water, carbon, nitrogen, phosphorus

Why Nitrogen Matters

Used to build proteins and DNA

Nitrogen Fixation

Bacteria change N2 gas into usable compounds (like nitrates)

Nitrogen-Fixing Organisms

Nitrogen-fixing bacteria in soil or plant roots

Carbon Removed by

Photosynthesis, ocean absorption

Carbon Added by

Respiration, burning fossil fuels, deforestation

Oxygen Cycle (Plant Role)

Plants take in CO2 and release O2 during photosynthesis

Human Impact on Carbon/Oxygen Cycles

Burning fossil fuels adds CO2, deforestation removes carbon-absorbing plants

Ecological Succession

Ecosystem rebuilding process

Primary Succession

Starts from bare land with no soil (ex: volcanic island)

Secondary Succession

Occurs where an ecosystem existed before (ex: after a fire)

Pioneer Species

First organisms in succession (ex: mosses, lichens)

Climax Community

Stable, mature ecosystem

Keystone Species

A species with a big impact on its environment

Keystone Species Examples

Sea otters, wolves

Human Impact: Climate Change

Long-term changes in temp and weather from human activity

Human Impact: Biomagnification

Toxins build up in animals as you go up the food chain

Human Impact: Invasive Species

Non-native species that hurt local ecosystems

Human Impact: Habitat Fragmentation

Breaking up ecosystems into smaller, isolated parts

Human Impact: Deforestation

Clearing forests, reduces biodiversity

Water Pollution

Contaminants harm aquatic ecosystems

Air Pollution

Caused by emissions; leads to smog, acid rain, health problems

BONUS: What happens if a keystone species is removed?

It can collapse or dramatically change the whole ecosystem

BONUS: What happens if a species is removed from a food web?

It affects every species connected to it (ripple effect)

BONUS: What is a trophic level?

A level in a food chain or pyramid (like producer, primary consumer, etc.)

BONUS: Why is only 10% of energy transferred?

Most energy is lost as heat during life processes