Chapter 3: Living in the Environment

4 Major components of Earth’s life-support systems

• Atmosphere

• Hydrosphere

• Geosphere

• Bioshpere

Atmosphere

• The innermost layer is the troposphere

  • Contains the air we breathe

• The stratosphere contains the ozone layer

  • Filters sun’s harmful UV radiation

Hydrosphere

• All water vapor, liquid water, and ice

• Oceans contain 97% of the planet’s water

Geosphere

• Upper portion of crust contains nutrients organisms need to live, grow, and reproduce

• Contains nonrenewable fossil fuels

Biosphere

• Parts of atmosphere, hydrosphere, and geosphere where life is found

The 3 Factors that Sustain the Earth’s Life

• A one-way flow of high-quality energy from the sun

  • Supports plant growth and warms troposphere

• Cycling nutrients through parts of the biosphere

• Gravity holds the earth’s atmosphere

  • Enables movement and cycling of chemicals through air, water, soil, and organisms

The 5 Levels of Matter

• Biosphere

• Ecosystems

• Communities

• Populations

• Organisms

Trophic (feeding) level

Organisms classified as producers or consumers based on source of nutrients

Producers (autotropohs)

Organisms that make needed nutrients from their environment through photosynthesis

Biotic factors 

Living components of an environment

Abiotic factors

Nonliving components of an environment

Photosynthesis

• Used by autotrophs

• Plants generate energy and emit oxygen

  • carbon dioxide + water + solar energy —— glucose + oxygen

  • CO₂ + H₂O + solar energy —— C₆H₁₂O₆ + O₂

Consumers (heterotrophs)

• Cannot produce the nutrients they need

• Primary consumers (herbivores) only eat plants

• Carnivores feed on the flesh of other animals

  • Secondary and tertiary consumers

• Omnivores eat both plants and animals

Decomposers

• Consumers that release nutrients from wastes or remains of plants or animals

• Nutrients return to soil, water, and air for reuse

• Bacteria, fungi

• Detritivores (feed on the dead matter)

Aerobic respiration

• Used by producers, consumers, and decomposers

• Use the chemical energy that is stored in glucose and in other organic molecules

  • Use oxygen to turn glucose back into carbon dioxide and water

  • C₆H₁₂O₆ + O_{2 ——} CO₂ + H₂O + energy

• Some decomposers use anaerobic respiration or fermentation

  • Used in the absence of oxygen

  • Releases methane gas, ethyl alcohol, acetic acid, and hydrogen sulfide

Soil

Complex mixture of rocks, particles, mineral nutrients, organic matter, waste, air, and living organisms

• Soil formation begins with weathering of bedrock into small pieces

• Mature soils contain several layers (horizons)

  • Differ in texture, composition, and thickness

• Each horizon of soil is visible in a soil profile

• Most mature soils contain several horizontal layers

• A cross-sectional view of the horizons is called a soil profile

  • O (leaf litter)

  • A (topsoil)

  • B (subsoil)

  • C (weathered parent material)

• Soil forms faster in wet, warm climates

• The color of topsoil indicates how useful it is for growing crops

  • Black or dark brown topsoil is rich in nitrogen and organic matter

  • A gray, bright yellow or red topsoil is low in organic matter and needs the addition of nitrogen to support most crops

• The B and C horizons contain most of a soil’s inorganic matter

• Soils can include particles of three sizes

  • Very small clay, medium-sized silt, larger sized sand

• Soil is a renewable resource

  • Renewed very slowly

  • Formation of 1 inch of topsoil can take hundreds to thousands of years

  • Becomes nonrenewable if we deplete faster than it can be replenished

Energy in an ecosystem

• Energy flows through ecosystems in food chains and webs

• Food chain - movement of energy and nutrients from one trophic level to the next

• Food web - network of interconnected food chains

• Every use and transfer of energy involves energy loss as heat

• Pyramid of energy flow

  • 90% of energy lost with each transfer

  • Less chemical energy for higher trophic levels

• Biomass - total mass of organisms in a given trophic level

Gross primary productivity (GPP)

Rate at which an ecosystem’s producers convert solar energy to stored chemical energy

• Measured in units such as kcal/m²/year

Net primary productivity (NPP)

The rate at which an ecosystem’s producers convert solar energy to chemical energy minus the rate at which they use the stored energy for aerobic respiration

• Terrestrial ecosystems and aquatic life zones differ in their NPP

• The planet’s NPP ultimately limits the number of consumers (including humans) that can survive on the earth

Nutrient cycles

• Nutrients cycle within and among ecosystems

• Cycles are driven by incoming solar energy and gravity

• Can be altered by human activity

  • Water

  • Carbon

  • Phosphorus

  • Nitrogen

The Water Cycle

• The water cycle collects, purifies, and distributes earth’s fixed supply of water

• Incoming solar energy causes evaporation

• Gravity draws water back as precipitation

  • Surface runoff evaporates to complete the cycle

  • Some precipitation stored as groundwater

• Ways humans alter the water cycle:

  • Withdrawing large amounts of freshwater at rates faster than nature can replace it

  • Clearing vegetation

    • Increases runoff and decreases infiltration

  • Draining and filling wetlands for farming and urban development

    • Wetlands provide flood control

    • Absorb and hold overflows of water

• Properties of water:

  • Liquid over large temperature range

  • Changes temperature slowly because it can store a large amount of heat

  • Takes lots of energy to evaporate

  • Can dissolve a variety of compounds

  • Filters out wavelengths of UV radiation

    • Protects aquatic organisms

  • Expands when it freezes

The Carbon Cycle

• Carbon is the basic building block of carbohydrates, fats, proteins, DNA and other organic compounds

• Photosynthesis from producers removes CO₂ from the atmosphere

  • Aerobic respiration by producers, consumers, and decomposers adds CO₂

  • Over millions of years, carbon in dead plant matter and algae may be converted to fossil fuels

• Some CO₂ dissolves in the ocean

  • Stores in marine sediments

• Humans have added large quantities of CO₂ to the atmosphere

  • Faster rate than natural processes can remove

    • Levels have been increasing sharply since about 1960

    • Result: warming atmosphere and changing climate

• Clearing vegetation reduces ability to remove excess CO₂ from the atmosphere

The Nitrogen Cycle

• Most nitrogen is in the atmosphere (N₂) but is not directly usable by most organisms

• Useful forms of nitrogen:

  • Created by lightning and specialized bacteria in topsoil and bottom sediment of aquatic systems

  • Used by plants to produce proteins, nucleic acids, and vitamins

• Bacteria convert nitrogen compounds back into nitrogen gas

• Human alteration of the nitrogen cycle:

  • Burning gasoline and other fuels create nitric oxide, which can return as acid rain

  • Removing large amounts of nitrogen from the atmosphere to make fertilizers

  • Adding excess nitrates in aquatic ecosystems

• Human nitrogen inputs to the environment have risen sharply and are expected to continue rising

The Phosphorus Cycle

• Phosphorus cycles through water, the earth’s crust, and living organisms

  • Major reservoir is phosphate rocks

  • Cycles slowly

• Human activities and impacts:

  • Clearing forests

  • Removing large amounts of phosphate from the earth to make fertilizers

  • Erosion leaches phosphate into streams

Methods used to study ecosystems

• Field research

  • Going into forests and natural settings

• Laboratory research

  • Simplified systems with controlled temperature, light, humidity, and other variables

  • Supported by field research

• Mathematical and other models

  • Way to study large and complex systems

• Aircraft, satellites, GIS software, GPS systems to track where animals go

4 Laws of Ecology

• Proposed by Commoner in 1971

  • Everything is connected to everything else

  • Everything must go somewhere

  • There is no free lunch

  • Nature knows best

• Observing these laws helps avoid going beyond ecological tipping points

  • Disruption of cycles, reduction of biodiversity, climate change, ocean acidification, ozone depletion, overconsumption of water, and pollution