Natural Environment

Cheatsheet Content

### Introduction The natural environment encompasses all living and non-living things that occur naturally on Earth. All organisms depend on the environment for survival, regulating and influencing it. Understanding its components and their relationships is crucial for maintaining the delicate ecological balance. ### Ecosystem and Its Components An **ecosystem** is a biological environment comprising all organisms in a specific area and the non-living physical components they interact with. A.G. Tansley coined the term in 1935, derived from Greek "oikos" (home) and "systema" (system). Ecosystems can be: - **Natural Ecosystems:** Exist in nature. - **Terrestrial:** Grasslands, deserts. - **Aquatic:** Rivers, ponds, oceans. - **Human-designed (Artificial) Ecosystems:** Gardens, aquariums, crop fields. #### Biotic and Abiotic Components Ecosystems consist of: - **Abiotic Components:** Non-living physical and chemical factors. - Sunlight, Temperature, Precipitation, Water/Moisture, Soil, Air. - **Biotic Components:** Living organisms. - **Producers (Autotrophs):** Plants, phytoplankton. - **Consumers (Heterotrophs):** Herbivores, carnivores, omnivores. - **Decomposers (Saprotrophs):** Fungi, bacteria. Abiotic factors (e.g., temperature, soil, moisture) significantly influence the types of organisms found in different regions. Green plants use sunlight and CO2 to produce food, supporting all other life. ### Biotic Community A **biotic community** includes populations of various organisms living together and sharing the same habitat. An ecosystem hosts multiple interacting biotic communities. #### Classification by Nutrition Mode: - **Autotrophs (Producers):** "Self-feeders." Manufacture their own food. - **Photosynthesis:** Most plants (using sunlight). - **Chemosynthesis:** Certain bacteria (without sunlight). - Form the base of the food web. Examples: rooted plants, phytoplankton, macrophytes. - **Heterotrophs (Consumers):** "Other-feeders." Feed on other organisms. - **Herbivores:** Eat plants (primary consumers). - **Carnivores:** Eat other animals (secondary/tertiary consumers). - **Saprotrophs (Decomposers):** "Rotten-feeders." Feed on dead and decaying matter. - Break down complex organic compounds into simpler forms, returning nutrients to the environment. - Crucial link between living and non-living components. Examples: fungi, bacteria. ### Food Chain and Food Web #### Food Chain A **food chain** describes the succession of organisms where food energy is passed from one organism to another as each consumes a lower member and is preyed upon by a higher member. Each link represents a **trophic level**. - **Trophic Level I:** Producers (e.g., trees, shrubs, phytoplankton). - **Trophic Level II:** Primary Consumers (Herbivores, e.g., giraffes, small fish). - **Trophic Level III+:** Secondary/Tertiary Consumers (Carnivores, e.g., lions, bigger fish). **Types of Food Chains:** 1. **Grazing Food Chain:** Starts with producers. Common in terrestrial and aquatic ecosystems. - Terrestrial: Grass → Deer → Lion - Aquatic: Phytoplankton → Zooplankton → Fish 2. **Detritus Food Chain:** Starts with dead organic matter. - Dead organic matter → Microorganisms (fungi, bacteria) → Smaller carnivores → Larger carnivores. #### Food Web A **food web** consists of interconnected food chains, where most animals are part of multiple chains and eat more than one type of food. #### Significance: - Maintain ecological balance. - Illustrate feeding relationships. - Facilitate energy flow and nutrient cycling. ### Energy Flow in an Ecosystem Energy flow is **unidirectional**. Energy is transferred from one trophic level to the next, but it does not return. - Only a fraction of energy (e.g., from plant food) becomes new body mass; the rest is lost as heat or used for life processes (movement, digestion, respiration). - The amount of energy transferred decreases significantly at each successive trophic level. This is why food chains are typically limited to four or five trophic levels. ### Biogeochemical (Nutrient) Cycles These are cyclic pathways by which chemical elements (nutrients) move through the environment, unlike unidirectional energy flow. Nutrients are never lost; nature replenishes them. #### A. Carbon Cycle Exchanges carbon between soil, water, and atmosphere. Essential for all organisms. - **Human impact:** Deforestation, burning fossil fuels increase atmospheric CO2. #### B. Nitrogen Cycle Transforms nitrogen and nitrogen-containing compounds in nature. - **Atmospheric Nitrogen:** Biggest source. - **Steps:** 1. **Nitrogen Fixation:** Atmospheric N2 is converted into usable forms (nitrates, nitrites). - **Lightening:** Forms nitrogen oxides that dissolve in rain. - **Microorganisms:** Free-living bacteria (e.g., *Azotobacter*) and symbiotic bacteria (*Rhizobium* in leguminous plants) fix nitrogen. 2. **Nitrogen Assimilation:** Plants absorb nitrates/nitrites to make amino acids; animals get nitrogen by consuming plants. 3. **Ammonification:** Proteins break down into urea/ammonia; dead organisms return nitrogen to soil as ammonium compounds, converted to ammonia by ammonifying bacteria. 4. **Nitrification:** Ammonia converted to nitrites, then nitrates by nitrifying bacteria (*Nitrosobacter*, *Nitrosomonas*). 5. **Denitrification:** Nitrates/nitrites reduced back to atmospheric nitrogen by denitrifying bacteria (*Pseudomonas*, *Clostridium*). - **Human impact:** Agriculture (fertilizers), industrial processes. #### C. Water Cycle The continuous movement of water on, above, and below the surface of the Earth. Essential for all life. ### Ecosystem Services Benefits humans receive from ecosystems, often free of charge. - **Air quality:** Production of oxygen (by plants), absorption of CO2. - **Climate regulation:** Forests, rivers, oceans influence climate. - **Pest control:** Natural predators and parasites regulate pest populations. - **Food and water:** Provided by plants, algae, and natural water sources. - **Resources:** Minerals, biomass fuels, wood (for fuel and construction). It is crucial to appreciate and judiciously utilize these services for future generations. ### Adaptations in Organisms **Adaptations** are special features that allow an organism to live in a particular habitat. Organisms adapt to: - Successfully compete for food. - Defend against predators. - Find favorable conditions for reproduction. - Respond efficiently to environmental changes. #### Aquatic Adaptations in Plants (Hydrophytes): - **Reduced root system:** Water is readily available. - **Leaves:** Floating leaves have stomata on the upper surface; submerged leaves have no stomata. Thin, narrow, or ribbon-shaped to resist water currents (e.g., *Hydrilla*, *Vallisneria*). - **Stem:** Long, slender, spongy (e.g., Lotus) to prevent being carried away. - **Floatation:** Flat leaves with waxy coating (e.g., Lotus, Water Lily) act as water repellent. #### Aquatic Adaptations in Animals: - **Streamlined body:** Reduces friction in water. - **Smooth, hairless body:** For aquatic mammals, reduces friction. - **Webbed feet:** (Ducks) Act as paddles. - **Flattened tail:** Serves as an oar. - **Fins/Flippers:** For swimming, steering, balance (fish, whales). - **Long legs/necks:** (Cranes) Keep body out of water, help reach food. - **Blubber:** Thick fat layer (whales) for insulation. - **Eyes:** Positioned on top of head (detect predators/prey above water). Transparent eyelids (underwater). - **Nostrils:** Positioned near top of head, close underwater (whales, dolphins). - **Swim bladder:** (Some fish) Filled with air for buoyancy. - **Gills:** For respiration (fish, prawns). #### Terrestrial Adaptations in Plants: - **Mesophytes:** Adapted to moderate environments. - **Leaves:** Large, thin, broad with many stomata on undersides. - **Roots:** Well-developed, branched, with root cap. - **Shoot system:** Well-organized. - **Xerophytes:** Desert plants, adapted to high temperature and water shortages. - **Leaves/Stems:** Succulent (cacti) for water storage. Few or no leaves to reduce transpiration. - **Protection:** Thorns (many desert trees/shrubs). - **Stomata:** Fewer stomata to reduce water loss. - **Root system:** Deep, widespread for maximum water uptake. #### Adaptations in Desert Animals: - **Behavioral:** Avoid sun during the day, burrow to escape heat, active at night. - **Body parts:** Long body parts to dissipate heat. - **Skin:** Scaly, resistant to drying. - **Water storage:** Hump (camel) stores fat. Can drink large amounts of water, excrete concentrated urine (reduce water loss). - **Waste excretion:** Excrete insoluble uric acid (reptiles) to minimize water loss. #### Adaptations to Extreme Cold: - **Fur/Feathers:** Thick fur (polar bear) or densely packed feathers (penguins) for insulation. - **Fat layer:** Stored fat under skin for additional insulation (blubber). - **Body shape:** Round, bulky with short legs, ears, tail (conserve heat). - **Flippers/Legs:** Adapted to reduce heat loss (penguins). #### Aerial Adaptations in Animals: - **Arboreal animals:** Dwell on trees, may glide (flying squirrel, tree frogs). - **True aerial animals (birds, bats):** - **Streamlined body:** For steering through air. - **Wings:** Forelimbs modified into wings. Feathers (birds) trap air and aid flight. Skin extension (bats) between fingers. - **Bones:** Hollow to reduce weight. - **Flight muscles:** Strong muscles attached to wings. ### Population Interaction **Population:** A group of similar individuals living in a particular geographical area. Populations interact within an ecosystem. #### Types of Interactions: 1. **Mutualism:** Both species benefit. - Example: Lichen (alga provides food, fungus provides water/minerals/shelter). Pollination (bees get nectar, plants get pollinated). 2. **Commensalism:** One species benefits, the other is unaffected. - Example: Hermit crab uses gastropod shell for protection. Sucker fish attaches to shark for transport and protection. 3. **Parasitism:** One organism lives in/on another (host), derives nourishment, and harms the host. - Example: Tapeworm in human intestine. 4. **Symbiosis:** A close interaction between two or more different organisms of different species living in close physical association. It's a broad term encompassing mutualism, commensalism, and parasitism when there's a close relationship. ### Population Growth Population size is dynamic, influenced by: - **Density:** Number of individuals per unit area. - **Natality (Birth Rate):** Number of live births per thousand per unit time. - **Mortality (Death Rate):** Number of individuals dying per thousand per unit time. - **Population Dispersal:** Movement of individuals. - **Environmental Resistance:** Factors limiting growth. #### Population Dispersal: 1. **Emigration:** Permanent outward movement from a population (decreases size). 2. **Immigration:** Permanent inward movement into a population (increases size). #### Environmental Resistance: Environmental conditions (abiotic like temperature/space, biotic like natural enemies) prevent species from reproducing at their maximum rate, thus limiting population growth. #### Carrying Capacity: The maximum population size that an environment can sustain indefinitely. #### Growth Curves: 1. **S-shaped (Sigmoidal) Growth Curve:** - **Lag Phase:** Slow initial growth as organisms adapt. - **Growth Phase:** Rapid increase due to abundant resources, low mortality. - **Stable Phase:** Population stabilizes as natality equals mortality, reaching carrying capacity. 2. **J-shaped Growth Curve:** - Exponential growth continues until environmental resistance becomes effective, leading to an abrupt stop and a sudden increase in mortality (population crash).