Biology Unit 6

The Carbon Cycle

The carbon cycle is a vital biogeochemical process that describes how carbon moves through both the living (biosphere) and non-living (atmosphere, geosphere, hydrosphere) components of the Earth. It is a dynamic system that regulates the amount of carbon in the atmosphere and other reservoirs, playing a crucial role in sustaining life and influencing the Earth's climate.

Overview of Biogeochemical Cycles

A biogeochemical cycle refers to the movement of essential elements through various environmental compartments. These cycles are key to maintaining the balance of elements necessary for life. Carbon is one of these essential elements, forming the backbone of all organic life forms.

Carbon: Carbon, with its atomic structure of 6 protons, 6 neutrons, and 6 electrons, is the most fundamental element for life. It forms a wide variety of molecules, such as carbohydrates, proteins, lipids, and nucleic acids (DNA, RNA). These compounds are the foundation of all living organisms and are involved in nearly every biological process.

Law of Conservation of Matter

The Law of Conservation of Matter states that matter cannot be created or destroyed; it can only change form. As a result, the total amount of carbon in the Earth's system remains constant over time. Carbon cycles between various forms—gaseous (CO₂), organic (glucose, proteins), and inorganic (carbonates, fossil fuels)—but is never lost. If carbon did not cycle, we would run out of carbon-based compounds, ultimately jeopardizing all life forms dependent on these compounds.

Key Processes in the Carbon Cycle

Several biological and geological processes transfer carbon throughout ecosystems:

1. Respiration: This process occurs in all living organisms, including plants, animals, fungi, and microorganisms. During respiration, glucose (C₆H₁₂O₆) is broken down in the presence of oxygen to release energy. This process produces carbon dioxide (CO₂) as a byproduct, which is then released into the atmosphere.

2. Consumption: When herbivores consume plants, they absorb the carbon stored in the plant tissues. This carbon is incorporated into the herbivore's own body. Similarly, when carnivores eat herbivores, carbon moves up the food chain, being passed along to higher trophic levels.

3. Decomposition: When organisms die, decomposers such as bacteria, fungi, and detritivores break down their organic matter, releasing carbon back into the soil and atmosphere. Some carbon is stored as organic material in the soil, while some is released as CO₂ during microbial respiration.

4. Photosynthesis: Plants, algae, and cyanobacteria use sunlight to convert carbon dioxide (CO₂) from the atmosphere into glucose (C₆H₁₂O₆) during photosynthesis. This process reduces the concentration of atmospheric CO₂ and stores carbon in plant tissues.

5. Combustion: The burning of fossil fuels (coal, oil, natural gas) and biomass (wood, plant material) releases stored carbon back into the atmosphere in the form of CO₂. Human activities, such as deforestation and industrial burning of fossil fuels, have significantly increased the rate of combustion, leading to higher CO₂ concentrations in the atmosphere.

6. Weathering: Weathering of carbon-rich rocks, such as limestone (CaCO₃), leads to the release of carbon into the environment. When these rocks break down, carbon is released into the soil and atmosphere, contributing to the cycling of carbon.

The Cycling of Carbon

1. Photosynthesis: Plants absorb carbon dioxide (CO₂) from the atmosphere during photosynthesis and convert it into glucose. This glucose is then used by plants for growth, energy storage, and reproduction, making it a major carbon sink in terrestrial ecosystems.

2. Herbivores and Carnivores: When herbivores eat plants, they ingest carbon in the form of carbohydrates, proteins, and fats. Carnivores, in turn, consume herbivores, passing the carbon up the food chain. This movement of carbon through the food web is essential for sustaining life.

3. Decomposition: After death, organisms are broken down by decomposers, such as bacteria and fungi. These decomposers release carbon back into the soil and atmosphere as CO₂, ensuring that carbon is recycled. In some cases, carbon may be trapped in the soil for long periods.

4. Fossil Fuel Formation: In rare instances, organisms do not fully decompose and are buried under sediments. Over millions of years, these organic remains transform into fossil fuels such as coal, oil, and natural gas. These fuels store carbon that is eventually released back into the atmosphere when burned.

5. Ocean as a Carbon Sink: Oceans are significant carbon sinks. Marine organisms, such as corals and shellfish, absorb carbon in the form of calcium carbonate (CaCO₃) to form their shells. When these organisms die, their shells sink to the ocean floor, storing carbon in marine sediments. Additionally, the ocean itself absorbs large amounts of CO₂ directly from the atmosphere.

6. Carbon Release through Weathering: Carbon can be released into the atmosphere through the weathering of carbon-rich rocks like limestone. This process releases carbon compounds into the soil and water, contributing to the cycling of carbon.

The Role of Fire in Carbon Cycling

1. Wildfires and Combustion: Wildfires, which occur naturally or as a result of human activities, burn large amounts of vegetation and organic matter, releasing carbon dioxide into the atmosphere. Although wildfires are a natural part of some ecosystems, their frequency and intensity have increased due to climate change, resulting in higher carbon emissions.

2. Controlled Fires: Controlled or prescribed fires are used in some ecosystems to reduce excess biomass, recycle nutrients, and stimulate plant growth. These fires also release carbon into the atmosphere, but their role in the natural cycling of carbon is critical to ecosystem health.

Greenhouse Effect and Global Warming

Carbon is a greenhouse gas, meaning that it traps heat in the Earth’s atmosphere. This greenhouse effect keeps the Earth warm enough to support life. However, human activities, especially the burning of fossil fuels, have increased the concentration of carbon dioxide (CO₂) in the atmosphere. This enhanced greenhouse effect has led to global warming and climate change, disrupting ecosystems and weather patterns.

Conclusion: The Impact of Human Activities on the Carbon Cycle

The carbon cycle is vital for the continuation of life on Earth. It regulates the flow of carbon through various environmental compartments and sustains biological processes. However, human activities, particularly deforestation and the combustion of fossil fuels, have significantly altered the natural carbon cycle, resulting in an increase in atmospheric CO₂ levels. This contributes to climate change and the warming of the planet. Understanding and mitigating these impacts is crucial for preserving ecosystems and stabilizing the climate/

The Nitrogen Cycle

The nitrogen cycle is a crucial biogeochemical cycle that converts nitrogen from its inert atmospheric form (N₂) into biologically available compounds that can be used by living organisms. Nitrogen is vital for life as it is a key component of amino acids, proteins, and nucleic acids (DNA and RNA).

Key Processes in the Nitrogen Cycle

1. Nitrogen Fixation:

   • Biological Nitrogen Fixation: This process is carried out by specific bacteria, particularly diazotrophs, which include rhizobium (found in leguminous plant roots) and cyanobacteria (found in aquatic environments). These bacteria convert atmospheric nitrogen (N₂) into ammonia (NH₃) by using the enzyme nitrogenase. In the roots of legumes, these bacteria form a symbiotic relationship, providing the plants with ammonia, which they can use to form proteins and other nitrogen-containing compounds.

   • Abiotic Nitrogen Fixation: Nitrogen can also be fixed by non-biological processes, such as lightning, where high-energy conditions in the atmosphere convert nitrogen gas (N₂) into nitrogen oxides (NOx), which dissolve in rain to form nitrates (NO₃⁻). These nitrates are then available for plant uptake.

   • Industrial Nitrogen Fixation: The Haber-Bosch process is an industrial method where nitrogen gas is combined with hydrogen under high pressure and temperature to produce ammonia (NH₃), which is used in fertilizers.

2. Assimilation:

   • Once nitrogen is converted into ammonia (NH₃) or nitrate (NO₃⁻), plants absorb these compounds through their roots. The nitrogen is then incorporated into amino acids, nucleic acids, and chlorophyll. Herbivores obtain nitrogen by consuming plants, and carnivores obtain nitrogen by consuming herbivores or other carnivores. Nitrogen in organic form is then used to build proteins and enzymes, essential for cellular processes.

3. Ammonification (also called Mineralization):

   • When organisms die or excrete waste, the organic nitrogen contained in their bodies is broken down by decomposers (such as bacteria and fungi) into ammonia (NH₃) or ammonium ions (NH₄⁺). This process is called ammonification. Ammonia can then be re-assimilated by plants or can undergo nitrification.

4. Nitrification:

   • First Step (Ammonia to Nitrite): In this process, nitrifying bacteria such as Nitrosomonas oxidize ammonia (NH₃) or ammonium (NH₄⁺) into nitrites (NO₂⁻), which are toxic to plants at high concentrations.

   • Second Step (Nitrite to Nitrate): Another group of nitrifying bacteria, such as Nitrobacter, further oxidizes nitrites (NO₂⁻) into nitrates (NO₃⁻), which are the most readily absorbed form of nitrogen by plants. Nitrate is essential for plant growth as it is used in the synthesis of proteins, chlorophyll, and other critical compounds.

5. Denitrification:

   • In oxygen-deprived environments, such as waterlogged soils or deep sediments, denitrifying bacteria (e.g., Pseudomonas and Clostridium) convert nitrates (NO₃⁻) back into nitrogen gas (N₂) or nitrous oxide (N₂O). This process completes the nitrogen cycle, returning nitrogen to the atmosphere.

   • Denitrification is vital in preventing excess nitrogen build-up in the environment, particularly in agricultural soils where nitrate levels may become too high due to fertilizer application.

6. Human Impacts on the Nitrogen Cycle:

   • Fertilizer Runoff: The widespread use of nitrogen-based fertilizers has increased the amount of available nitrogen in the environment, leading to eutrophication in aquatic ecosystems. Excess nitrates from fertilizers can run off into rivers and lakes, causing algal blooms and the creation of "dead zones" with low oxygen levels, which harm aquatic life.

   • Burning Fossil Fuels: Burning fossil fuels releases nitrogen oxides (NOx) into the atmosphere, contributing to air pollution and acid rain. NOx also interacts with sunlight to form ground-level ozone, a harmful air pollutant.

   • Industrial Agriculture: The intensive farming practices that rely on nitrogen fertilizer have disrupted natural nitrogen cycling by adding large quantities of nitrogen to the environment, leading to soil acidification and loss of biodiversity.

The Phosphorus Cycle

The phosphorus cycle is another essential biogeochemical cycle, focusing on the movement of phosphorus through the Earth’s systems. Phosphorus is crucial for all living organisms, as it is a key component of nucleic acids (DNA, RNA), ATP (adenosine triphosphate), and phospholipids that make up cell membranes.

Key Aspects of the Phosphorus Cycle

1. Phosphorus Sources:

   • Phosphorus primarily originates from rocks that contain phosphate minerals, such as apatite. These rocks are weathered over time by physical, chemical, and biological processes.

   • Unlike carbon and nitrogen, phosphorus does not have a gaseous phase in the atmosphere. It is mainly present in the form of phosphate ions (PO₄³⁻) in soils, rocks, water, and sediments.

2. Weathering and Erosion:

   • Weathering of phosphate-rich rocks releases phosphates into the soil and water, where they can be taken up by plants. The rate of weathering is slow, making the phosphorus cycle one of the slowest of the biogeochemical cycles.

   • As rainwater carries phosphates into rivers and oceans, it becomes available for aquatic organisms. In marine environments, organisms like corals and shellfish use phosphate to build calcium phosphate structures (e.g., shells and skeletons).

3. Assimilation:

   • Plants absorb phosphate from the soil, incorporating it into organic molecules like DNA, RNA, ATP, and phospholipids. Herbivores consume plants and obtain the phosphorus in the plant tissue, and this phosphorus moves up the food chain as carnivores eat herbivores.

   • Decomposers (bacteria and fungi) break down dead organisms and return phosphorus to the soil or water, making it available again for plant uptake.

4. Sedimentation and Formation of Phosphate Rocks:

   • Phosphates that are not taken up by organisms are washed into water bodies and can become part of marine sediments. Over geological timescales, these sediments can form new phosphate rocks.

   • Phosphorus in the ocean can also precipitate as insoluble phosphate compounds (e.g., calcium phosphate), becoming part of the ocean floor's sediment.

5. Return to the Cycle:

   • Over millions of years, some of the phosphates in marine sediments may be exposed by tectonic activity, where they can undergo weathering and return to the terrestrial system, starting the cycle anew.

   • In the short term, phosphorus can be re-released into the environment when organisms die and decompose, or when phosphates from agricultural fertilizers run off into water bodies.

6. Human Impact on the Phosphorus Cycle:

   • Fertilizer Use: The use of phosphorus-rich fertilizers in agriculture significantly accelerates the cycling of phosphorus through ecosystems. Excess phosphorus from fertilizers often runs off into rivers and lakes, contributing to nutrient pollution and the formation of eutrophic conditions, which lead to algal blooms and reduced oxygen levels in aquatic ecosystems.

   • Eutrophication: The introduction of excess phosphorus into aquatic ecosystems can cause cultural eutrophication, a process in which nutrient overload leads to rapid algal growth. When the algae die, their decomposition consumes oxygen in the water, creating hypoxic conditions that can result in "dead zones," where oxygen levels are too low to support most marine life.

   • Phosphorus Mining: The demand for phosphorus in fertilizers has led to the extensive mining of phosphate rock. As phosphate rock reserves are depleted, there are concerns about future phosphorus shortages and the environmental impact of mining.

The Water Cycle

The water cycle, also known as the hydrological cycle, is a continuous process that moves water throughout the Earth's atmosphere, surface, and underground systems. It is essential for maintaining the Earth's water balance and supporting life.

Key Processes in the Water Cycle

1. Evaporation:

   • Definition: Evaporation occurs when liquid water is converted into water vapor (gas) due to heat from the sun. It is the primary mechanism by which water enters the atmosphere.

   • Climatic Influence: In humid climates, there is a high amount of water vapor in the air due to frequent evaporation, while arid climates have less water in the atmosphere. During the rainy season, evaporation rates are higher because of increased temperatures and more available water.

   • Purification: When water evaporates, impurities such as salts, minerals, and pollutants are left behind, resulting in purified water vapor. This is especially important in the natural filtration of water sources.

   • Transpiration: A specific type of evaporation occurs through transpiration, where water is absorbed by plant roots from the soil and evaporates from plant leaves. Transpiration plays a significant role in the water cycle and is a key process in regulating atmospheric moisture.

2. Condensation:

   • Definition: Condensation is the process where water vapor cools and changes back into liquid water. This is how clouds and fog are formed.

   • Cloud Formation: As water vapor rises and cools, it condenses into tiny droplets around dust particles in the air, forming clouds. These clouds eventually lead to precipitation.

   • Fog: Fog is a form of condensation near the Earth's surface, where water vapor cools and condenses into liquid droplets suspended in the air, reducing visibility.

3. Precipitation:

   • Definition: Precipitation is any form of water (liquid or solid) that falls from the atmosphere to the Earth's surface. Precipitation includes rain, snow, sleet, and hail.

   • Forms of Precipitation:

     • Rain: Liquid water droplets fall when they reach a size too large to be suspended in the air.

     • Snow: Frozen water vapor that falls in cold temperatures, forming crystalline flakes.

     • Sleet and Hail: Small pellets of ice formed under specific conditions during storms.

   • Return to Earth: Precipitation is the mechanism through which water in the atmosphere returns to the Earth's surface, replenishing rivers, lakes, and groundwater.

4. Runoff:

   • Definition: Runoff refers to the flow of water across the Earth's surface when precipitation exceeds the ground's ability to absorb it. It includes water flowing over the ground to rivers, lakes, and oceans.

   • Pollutant Transport: As water moves across the land, it can pick up pollutants, such as oils, pesticides, and chemicals, from the surface, carrying them to water bodies and contributing to water pollution.

   • Surface Water Movement: Runoff can affect ecosystems by carrying nutrients and organic material into lakes and rivers, sometimes leading to eutrophication if the nutrient levels are too high.

5. Percolation and Infiltration:

   • Infiltration: This is the process by which water soaks into the soil from the surface. The rate of infiltration depends on factors like soil type, vegetation, and land slope.

   • Percolation: Percolation occurs when water moves deeper through the soil layers, reaching the aquifer or underground water storage. This process ensures that groundwater supplies are replenished.

   • Groundwater Storage: Water that infiltrates and percolates through the soil enters aquifers, which are natural underground water reservoirs. These aquifers supply water for wells, springs, and other sources.

   • Filtration: As water percolates through soil, it is naturally filtered, removing impurities like sediments and pollutants before reaching groundwater.

Marine Biomes

Marine biomes are aquatic ecosystems found in the world's oceans. They play a vital role in regulating climate, supporting biodiversity, and providing food and resources for humans.

General Information:

• Salinity: Marine biomes typically have a salt concentration of about 3% (salt to water ratio). This salt concentration distinguishes marine biomes from freshwater ecosystems.

• Coverage: Oceans cover approximately 71% of Earth's surface and hold more than 97% of Earth's total water. The vastness and complexity of the oceans contribute significantly to Earth's climate, nutrient cycling, and atmospheric processes.

• Organisms and Depth: The types of organisms found in marine ecosystems depend on factors like depth, temperature, and the amount of light reaching the ocean. The distribution of light in the ocean is critical in determining where photosynthesis can occur and where various species can survive.

Ocean Zones:

1. Photic Zone: The upper layer of the ocean, where light can penetrate, allowing photosynthesis. The depth of the photic zone varies but typically extends to about 200 meters deep. This zone supports most marine life, as it provides the energy needed for primary producers (like phytoplankton) to thrive.

2. Aphotic Zone: The deeper part of the ocean where sunlight cannot penetrate. In this zone, photosynthesis does not occur, and organisms must rely on other food sources like detritus or other organisms.

3. Epipelagic Zone (Surface to 200 meters): This zone is the most productive and contains the greatest biodiversity. It is where most marine organisms live, including sponges, worms, sea anemones, crabs, turtles, and fish. The organisms here often display countershading, a camouflage adaptation where they are darker on top and lighter on the bottom to blend in with the ocean surface and the deeper waters.

4. Mesopelagic Zone (200 to 1000 meters): The "twilight zone" where there is some light, but not enough for photosynthesis. Organisms in this zone are adapted to low-light conditions and have developed specialized features, such as bioluminescence, to attract prey or mates.

5. Bathypelagic Zone (1000 to 4000 meters): This deep ocean zone has no light. Only a few species, like bioluminescent organisms, can survive here. The organisms are adapted to high pressure, low temperatures, and the absence of sunlight.

6. Abyssopelagic Zone (4000 to 6000 meters): The ocean floor, where it is dark, cold, and under immense pressure. Organisms in this zone are specially adapted to survive in extreme conditions, including deep-sea fish, giant squids, and unique species of crustaceans.

7. Hadalpelagic Zone (6000 meters and beyond): Found in ocean trenches, this zone experiences extreme pressure and cold temperatures. It is home to specialized organisms that can withstand the crushing depths, including certain species of fish, tube worms, and bacteria.

Coastal Zones:

• Upwelling: In coastal areas, upwelling occurs when cold, nutrient-rich water rises from the deep ocean to the surface, often due to surface winds pushing warm water away from the shore. This process brings nutrients to the surface, supporting high biological productivity and forming the basis of marine food webs.

Specific Marine Biomes:

1. Coral Reefs:

   • Coral reefs are found in the warm, shallow waters of the photic zone, typically in tropical regions. They are among the most productive ecosystems on Earth. Corals have a mutualistic relationship with zooxanthellae, algae that live within coral tissues and provide energy through photosynthesis.

   • Coral Bleaching: Coral bleaching occurs when corals expel their symbiotic zooxanthellae due to stress factors such as rising sea temperatures, pollution, or changes in light levels, leading to the loss of their vibrant colors.

2. Estuaries:

   • Brackish Water: Estuaries are areas where freshwater from rivers meets saltwater from the ocean, creating a mix of saline water known as brackish water. These areas are highly productive and provide vital ecosystems for breeding and nurseries for many marine species.

   • Estuaries are home to fish, crabs, birds, and other species and serve as vital habitats for many migratory species.

3. Mangroves:

   • Mangrove forests are salt-tolerant trees that thrive in calm, shallow waters of tropical and subtropical coastal regions. These forests protect coastlines from erosion, filter pollutants, and provide habitats for a diverse range of marine life.

4. Salt Marshes:

   • Salt marshes are coastal wetlands dominated by salt-tolerant grasses. They are regularly flooded by tides and act as buffers to coastal erosion, filtering water before it reaches the ocean and providing habitat for fish, birds, and other wildlife.

5. Kelp Forests:

   • Kelp forests are underwater ecosystems found in shallow temperate waters. These forests are formed by large, fast-growing seaweeds known as kelp. They provide shelter and food for many marine organisms, including fish, sea otters, and invertebrates.

6. Intertidal Zones:

   • The intertidal zone is the area where land meets the sea, and it is characterized by extreme fluctuations in temperature, salinity, and exposure to air. Organisms in this zone must be adapted to survive in both wet conditions during high tide and dry conditions during low tide.

7. Open Ocean:

   • The open ocean is a large, nutrient-poor ecosystem with a low density of animals

Freshwater Biomes

Basic Information

• Freshwater biomes contain water with a salt concentration of less than 1%.

• They account for only 2.5% of Earth's total water supply, yet they are crucial for life on land.

• About ⅔ of freshwater is locked in ice caps and glaciers, leaving only a small fraction available in lakes, rivers, wetlands, and groundwater.

• These ecosystems provide essential habitats for a variety of organisms, regulate local climates, and play a significant role in the global water cycle.

Abiotic Factors Influencing Freshwater Biomes

Light

• Light penetration determines the types of organisms that can thrive in different parts of a freshwater biome.

• The photic zone is the upper layer where sunlight can penetrate, allowing photosynthesis to occur, supporting phytoplankton, aquatic plants, and algae.

• The aphotic zone is the deeper, darker layer where sunlight cannot reach, limiting photosynthesis and favoring organisms that rely on detritus and other energy sources.

Temperature

• Water has a high specific heat capacity, meaning it absorbs and retains heat well, creating a stable thermal environment for aquatic organisms.

• Temperature varies with depth; the surface layer is usually the warmest due to direct sunlight, while the bottom layers remain cold.

• Seasonal turnover occurs in lakes, where cool, oxygen-rich water from the surface sinks, mixing with warmer, nutrient-rich water from the bottom, supporting life by redistributing nutrients and oxygen.

Nutrients

• Essential nutrients like nitrogen and phosphorus are often limiting factors in freshwater ecosystems, regulating primary production.

• When excessive nitrogen and phosphorus enter freshwater ecosystems (from fertilizers, sewage, and industrial waste), they can trigger eutrophication.

• Cultural eutrophication occurs when excess nutrients cause explosive algal growth, depleting oxygen levels, which leads to the formation of dead zones—areas where aquatic life cannot survive due to low oxygen concentration.

Types of Freshwater Biomes

Flowing Water Ecosystems (Lotic Systems)

• Rivers and streams are examples of lotic ecosystems where water is constantly moving.

• Fast-moving rivers have higher oxygen levels, supporting organisms like trout and other fish adapted to strong currents.

• Downstream water tends to be slower-moving and murkier, allowing phytoplankton and plant life to thrive.

Standing Water Ecosystems (Lentic Systems)

• Lakes and ponds are lentic ecosystems where water remains mostly still.

• They have distinct zones based on depth and light availability:

  • Littoral zone – Shallow area near the shore with abundant sunlight and vegetation.

  • Limnetic zone – Open water area where sunlight supports plankton and fish.

  • Profundal zone – Deeper, colder, and darker area with little plant life.

  • Benthic zone – The lakebed, home to decomposers and bottom-dwelling organisms.

Wetlands

• Wetlands are transition zones between terrestrial and aquatic ecosystems, often saturated with water for most or all of the year.

• Swamps, marshes, and bogs are examples of wetlands, each supporting unique plant and animal species.

• Wetlands serve as natural water filters, flood buffers, and carbon sinks, making them critical for maintaining biodiversity.

Terrestrial Biomes

Savanna

• Characterized by low annual rainfall and warm temperatures year-round.

• Dominated by grasses with scattered trees adapted to drought conditions.

• Many herbivores, such as zebras, antelopes, and elephants, migrate seasonally in search of water.

• Fires are a natural part of the savanna ecosystem, clearing dead vegetation and promoting new growth.

Temperate Grasslands

• Experience seasonal variations, with cold winters and hot summers.

• Deep, nutrient-rich soils make them ideal for agriculture and grazing animals.

• Bison, prairie dogs, and burrowing owls are common inhabitants.

Temperate Woodland/Chaparral

• Characterized by hot, dry summers and mild, wet winters.

• Fire-adapted shrubs and small trees dominate the landscape.

• Found in regions like California, the Mediterranean, and Australia.

Tundra

• Extremely cold and dry, with long, harsh winters.

• Permafrost (permanently frozen soil) prevents deep-rooted plant growth.

• Low-growing plants like mosses and lichens dominate the landscape.

• Animals such as arctic foxes and caribou have thick fur for insulation.

• Climate change is rapidly melting permafrost, altering the tundra ecosystem.

Deserts

• Low precipitation levels make them one of the driest biomes.

• Extreme temperature fluctuations occur between day and night.

• Cacti and other drought-resistant plants have adaptations to conserve water.

• Nocturnal animals like kangaroo rats and desert foxes avoid daytime heat.

Forest Biomes

Temperate Forests

• Experience four distinct seasons with moderate temperatures.

• Trees like oak, maple, and beech lose their leaves in the fall (deciduous forests).

• Home to diverse wildlife, including deer, bears, and birds.

Coniferous Forests (Taiga/Boreal Forests)

• Found in northern latitudes, with long, cold winters and short summers.

• Dominated by evergreen trees (pines, spruces, firs) that retain their needles year-round.

• Wolves, moose, and lynx thrive in these forests.

Tropical Rainforests

• Located near the equator, with high temperatures and heavy rainfall year-round.

• Support an incredible diversity of life, with over 50% of Earth's species residing here.

• Rapid decomposition due to warmth and moisture creates nutrient-poor soils.

• Deforestation for agriculture and logging threatens these ecosystems.

Tropical Dry Forests

• Found in warm climates but experience seasonal droughts.

• Trees have adaptations like thicker bark and deep roots to conserve water.

Earth’s Atmosphere and Climates

Atmospheric Layers

1. Troposphere – Closest to Earth's surface, where weather occurs.

2. Stratosphere – Contains the ozone layer, which absorbs UV radiation.

3. Mesosphere – Coldest layer, where meteors burn up.

4. Thermosphere – Very thin air, home to auroras and the International Space Station.

5. Exosphere – The outermost layer, gradually fading into space.

Climate and Weather

• Solar radiation and ocean currents drive Earth's weather patterns.

• The Gulf Stream brings warm waters to Europe, moderating its climate.

• Greenhouse gases like CO₂ and methane trap heat, affecting global temperatures.

Atmospheric Composition

• The largest component of Earth's atmosphere is nitrogen (N₂), making up approximately 78% of the air we breathe.

• Oxygen (O₂) comprises about 21% of the atmosphere and is essential for respiration in most living organisms.

• Argon (Ar) makes up roughly 0.93%, while carbon dioxide (CO₂) and trace gases constitute the remainder.

• Carbon dioxide (CO₂) and methane (CH₄) are greenhouse gases, meaning they trap heat in the Earth's atmosphere and contribute to global warming.

• Water vapor is also an important greenhouse gas that plays a role in regulating temperature and weather patterns.

Earth’s Climate and Seasons

• Earth’s tilt (23.5°) on its axis is responsible for the changing seasons as the planet orbits the Sun.

• When the Northern Hemisphere tilts toward the Sun, it experiences summer, while the Southern Hemisphere experiences winter, and vice versa.

• Carbon dioxide and methane influence Earth's climate by trapping heat in the atmosphere, leading to long-term climate changes such as global warming and shifts in weather patterns.

Earth’s Winds and Ocean Currents

• Solar radiation and moisture drive global wind patterns, influencing climate and weather systems.

• Wind currents help distribute heat and moisture around the planet, affecting regional climates.

• The Gulf Stream is a powerful ocean current that carries warm water from the Gulf of Mexico across the Atlantic, moderating temperatures in Western Europe, particularly in Great Britain.

• Other ocean currents, such as the Jet Stream and Trade Winds, also influence global weather patterns, storms, and precipitation.