Chapter 15: Ecology

Select the correct answer:

1. Rhizobium is a group of nitrogen fixing bacteria found in the root nodules of;

A) Grasses

B) legume plants

C) ferns

D) all plants

Answer: B) legume plants

Explanation: Rhizobium bacteria form symbiotic relationships with leguminous plants (e.g., peas, beans, clover), living in root nodules where they convert atmospheric nitrogen into ammonia.

2. During succession process, with the passage of time the change in communities is;

A) Orderly and sequential

B) Parallel

C) Perpendicular

D) Random

Answer: A) Orderly and sequential

Explanation: Ecological succession is a predictable, orderly, and sequential process where communities change over time until a stable climax community is reached.

3. Producers of an ecosystem are;

A) Plants only

B) plants and algae only

C) plants, algae and autotrophic bacteria

D) plants, algae, fungi and autotrophic bacteria

Answer: C) plants, algae and autotrophic bacteria

Explanation: Producers (autotrophs) are organisms that can synthesize their own food. This includes plants, algae, and autotrophic bacteria (like cyanobacteria). Fungi are heterotrophs (decomposers).

4. What is the predictable and gradual change in the species composition of a given area called?

A) Environmental Issues

B) Climax community

C) Pioneer community

D) Ecological succession

Answer: D) Ecological succession

Explanation: Ecological succession is the gradual and predictable change in the species structure of an ecological community over time.

5. The sequence of organisms through which energy moves in an ecosystem is called.

A) trophic level

B) food web

C) biomass

D) food chain

Answer: D) food chain

Explanation: A food chain is a linear sequence of organisms through which nutrients and energy pass as one organism eats another.

6. The role of decomposers in nitrogen cycle is to;

A) fix atmospheric nitrogen to ammonia

B) release ammonia from organic compounds, thus returning it to the soil

C) denitrify ammonia, thus return nitrogen to the atmosphere

D) convert ammonia to nitrates for plant use

Answer: B) release ammonia from organic compounds, thus returning it to the soil

Explanation: Decomposers break down dead organic matter and waste, releasing ammonia (NH₃) back into the soil through a process called ammonification.

7. Which of these about ecological succession is incorrect?

A) food chain relationships become more complex

B) species diversity increases as succession proceeds

C) role of decomposers becomes all the more important

D) is a random process

Answer: D) is a random process

Explanation: Ecological succession is not random; it is an orderly, predictable, and directional process.

8. The nutrient cycle always involves;

A) Rocks as reservoir

B) Movement of nutrients through the biotic community

C) The atmosphere as an exchange pool

D) Loss of nutrients from the biosphere

Answer: B) Movement of nutrients through the biotic community

Explanation: Nutrient cycles (biogeochemical cycles) involve the movement and exchange of organic and inorganic matter through biotic (living) and abiotic (non-living) components of the ecosystem.

9. The ecosystems with very less annual rain and higher temperatures are;

A) Grass land ecosystems

B) deciduous forest ecosystems

C) Boreal forest ecosystems

D) desert ecosystems

Answer: D) desert ecosystems

Explanation: Deserts are characterized by very low annual rainfall (less than 25 cm) and extreme temperatures.

10. The main cause of ocean acidification is.

A) Excessive use of water

B) offshore oil exploration drilling

C) increasing level of carbon dioxide in the atmosphere

D) volcanic activity in the oceans.

Answer: C) increasing level of carbon dioxide in the atmosphere

Explanation: When atmospheric CO₂ dissolves in seawater, it forms carbonic acid, which lowers the ocean's pH, causing ocean acidification.

1. Describe water in 'basins'.

Answer: Water basins, also known as watersheds or drainage basins, are areas of land where all the precipitation (rain or snow) that falls drains into a common outlet, such as a river, lake, or ocean. They are defined by the topography of the land, with higher elevations (ridges) acting as boundaries. Water basins are crucial for collecting, storing, and supplying water to ecosystems and human communities. They are dynamic systems that interact with the atmosphere, land, and living organisms.

2. Describe the ways of nitrogen fixation.

Answer: Nitrogen fixation is the conversion of atmospheric nitrogen (N₂) into ammonia (NH₃). It occurs through three main ways:

1. Biological Fixation: Carried out by nitrogen-fixing bacteria (e.g., Rhizobium in root nodules of legumes, Azotobacter in soil, Frankia in actinorhizal plants) and cyanobacteria (e.g., Anabaena in water).

2. Atmospheric Fixation: Lightning provides enough energy to convert N₂ into nitrogen oxides (NOx), which dissolve in rain to form nitrates.

3. Industrial Fixation: The Haber-Bosch process converts N₂ and H₂ into ammonia for fertilizers.

3. Give the role of decomposers in the nutrient cycle.

Answer: Decomposers (bacteria and fungi) play a vital role in nutrient cycles by breaking down dead organic matter (plants, animals, and waste). They secrete enzymes that digest complex organic compounds into

simpler inorganic molecules. This process releases essential nutrients (e.g., carbon, nitrogen, phosphorus, sulfur) back into the soil, water, and atmosphere, making them available for uptake by producers. Without decomposers, nutrients would remain locked in dead matter, and life would cease.

4. What is productivity? Describe productivity in desert ecosystem.

Answer: Productivity is the rate at which an ecosystem generates biomass (organic matter). It is measured as energy per unit area per unit time (e.g., kcal/m²/year).

Desert Ecosystem: Deserts have very low primary productivity due to extreme temperatures, scarce water, and nutrient-poor soil. Plant growth is slow and limited to short periods after rainfall. Annual net primary productivity is typically less than 100 g/m²/year. The sparse vegetation supports a low diversity and density of consumers. Decomposition is also slow due to dryness.

5. Explain the pyramid of energy.

Answer: The pyramid of energy is a graphical representation of the flow of energy through trophic levels in an ecosystem. It shows that energy decreases at each successive trophic level. Producers (first trophic level) capture a large amount of solar energy. However, only about 10% of this energy is transferred to primary consumers (second trophic level) because most is used for respiration, lost as heat, or not consumed. This 10% rule continues up the food chain. Therefore, the pyramid is always upright, with the base representing the most energy and the apex the least.

6. Differentiate between primary and secondary succession.

Answer:

7. What is net primary productivity?

Answer: Net primary productivity (NPP) is the amount of biomass (organic matter) produced by producers (plants) after subtracting the energy used for their own respiration. It is the energy available to primary

consumers (herbivores). NPP is calculated as: NPP = GPP - R, where GPP is gross primary productivity (total energy captured by photosynthesis) and R is respiration. NPP is a measure of the rate at which an ecosystem accumulates biomass and is important for understanding ecosystem health and carbon cycling.

8. Explain the term 'biosphere'.

Answer: The biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere (land), hydrosphere (water), and atmosphere (air). It is the zone of life on Earth, extending from the deepest ocean trenches to the highest mountains. The biosphere is a complex, self-regulating system that includes all ecosystems. It is characterized by the presence of life and the continuous cycling of matter and flow of energy.

1. Describe greenhouse effect. Give the consequences of increase in greenhouse gases.

Answer: The greenhouse effect is a natural process that warms the Earth's surface. It is essential for life as we know it,

but human activities have enhanced it, leading to global warming.

Mechanism of the Greenhouse Effect:

1. Solar Radiation: The sun emits shortwave radiation (visible light and UV) that passes through the atmosphere and warms the Earth's surface.

2. Absorption and Re-radiation: The Earth absorbs this energy and re-emits it as longwave infrared radiation.

3. Greenhouse Gases: Greenhouse gases (carbon dioxide, methane, nitrous oxide, water vapor, ozone, CFCs) in the atmosphere absorb the outgoing infrared radiation.

4. Trapping Heat: These gases re-radiate the absorbed energy in all directions, including back towards the Earth's surface. This traps heat in the lower atmosphere, keeping the planet warmer than it would be otherwise.

Consequences of Increase in Greenhouse Gases:

Global Warming: An increase in greenhouse gases (especially CO₂ from burning fossil fuels) leads to an enhanced greenhouse effect, causing a rise in global temperatures. Rising Sea Levels: Thermal expansion of oceans and melting of glaciers and ice caps lead to rising sea levels, threatening coastal areas. Extreme Weather Events: More frequent and intense heatwaves, droughts, floods, and hurricanes. Melting Ice and Glaciers: Loss of polar ice and mountain glaciers, affecting freshwater supplies and ecosystems. Ocean Acidification: Increased CO₂ absorption by oceans lowers pH, harming coral reefs and shellfish. Disruption of Ecosystems: Shifts in habitats, migration patterns, and biodiversity loss. Impact on Agriculture: Changes in rainfall and temperature affect crop yields.

Human Health: Heat-related illnesses, spread of infectious diseases.

In summary, the greenhouse effect is a natural phenomenon, but its enhancement by human activities is causing severe environmental and socio-economic consequences. Mitigation efforts are essential to reduce greenhouse gas emissions.

2. What is succession? Give the stages of primary succession on a barren rock.

Answer: Ecological Succession is the gradual, directional, and predictable change in the species composition of an ecological community over time. It occurs after a disturbance or in newly formed habitats.

Primary Succession on a Barren Rock: Primary succession occurs in lifeless areas where no soil exists, such as a bare rock exposed by a retreating glacier or a new volcanic island.

Stages:

1. Pioneer Stage: The first organisms to colonize the bare rock are pioneer species, such as lichens and mosses. Lichens secrete acids that break down the rock surface, initiating soil formation. When they die, their organic matter mixes with the rock particles to form a thin layer of soil.

2. Intermediate Stage (Seral Stage): As soil accumulates, small plants like grasses, herbs, and ferns can grow. Their roots further break up the rock and add organic matter. This creates a more suitable environment for larger plants.

3. Late Seral Stage: Shrubs and small trees begin to grow. The increasing vegetation provides shade

and modifies the microclimate, allowing more species to establish.

4. Climax Community: Eventually, a stable, self-sustaining climax community develops. This is typically a mature forest ecosystem (e.g., deciduous or coniferous forest) that is in equilibrium with the climate and soil conditions. The climax community has the highest species diversity and biomass.

Examples: Succession on volcanic lava flows (e.g., Krakatoa), retreating glaciers (e.g., Glacier Bay, Alaska).

In summary, primary succession on barren rock is a slow process that transforms a lifeless surface into a complex, stable ecosystem through the sequential colonization and replacement of species.

3. Give the significance of coral reefs. Explain the effects of ocean acidification on coral reef ecosystem.

Answer: Significance of Coral Reefs: Coral reefs are among the most diverse and valuable ecosystems on Earth.

Biodiversity: They support an estimated 25% of all marine species, despite covering less than 1% of the ocean floor. They are often called the "rainforests of the sea." Coastal Protection: Reefs act as natural barriers, protecting coastlines from erosion, storms, and wave damage. Economic Value: They provide food, income, and livelihoods for millions of people through fishing, tourism, and recreation. Medicine: Many marine organisms found in reefs produce compounds used in pharmaceuticals. Nutrient Cycling: They play a role in nutrient cycling and carbon fixation.

Effects of Ocean Acidification on Coral Reefs: Ocean acidification, caused by increased absorption of atmospheric CO₂, has severe effects on coral reefs.

Reduced Calcification: Corals build their skeletons from calcium carbonate (CaCO₃). Acidic water reduces the availability of carbonate ions, making it harder for corals to build and maintain their skeletons. Coral Bleaching: Acidification can stress corals, causing them to expel their symbiotic algae (zooxanthellae), leading to bleaching and death. Weakened Skeletons: Even if corals survive, their skeletons may become brittle and more susceptible to damage from storms and erosion. Ecosystem Collapse: Loss of corals leads to the collapse of the entire reef ecosystem, affecting all the species that depend on it. Reduced Biodiversity: Many fish and invertebrates that rely on reefs for food and shelter decline.

In summary, coral reefs are vital ecosystems, but ocean acidification poses a major threat to their survival. Urgent action to reduce CO₂ emissions is essential to protect these valuable resources.

4. Describe grassland ecosystems in Pakistan.

Answer: Grassland ecosystems in Pakistan are diverse and cover a significant portion of the country's land area. They are characterized by dominance of grasses, with few or no trees, and are adapted to specific climatic and soil conditions.

Types of Grasslands in Pakistan:

1. Tropical Thorn Forests and Grasslands: Found in the plains of Punjab and Sindh, with low rainfall (less than 50 cm). Dominated by thorny trees like Acacia and Prosopis, along with grasses.

2. Subtropical Dry Evergreen Forests: Found in the foothills of the Himalayas and Karakoram ranges, with moderate rainfall. Includes grasses and shrubs.

3. Temperate Grasslands: Found in the northern highlands of Pakistan (e.g., Balochistan, Khyber Pakhtunkhwa), with cold winters and moderate rainfall. Dominated by grasses like Poa, Festuca, and Stipa.

4. Alpine and Sub-alpine Grasslands: Found at high altitudes in the Himalayas, Karakoram, and Hindu Kush ranges. Short growing season, dominated by hardy grasses and sedges.

5. Desert Grasslands: Found in the Thar Desert and Cholistan, with very low rainfall. Sparse grasses and xerophytic plants.

Ecological Importance:

Grazing: Support livestock (sheep, goats, cattle) which are a major source of livelihood. Wildlife Habitat: Home to diverse fauna (e.g., deer, antelope, partridges). Soil Conservation: Grass roots bind soil, preventing erosion. Carbon Sequestration: Grasslands store carbon in soil.

Threats:

Overgrazing: Leading to degradation and desertification. Deforestation: For fuel and agriculture. Climate Change: Droughts and changing rainfall patterns. Urbanization: Encroachment on grassland.

In summary, grassland ecosystems in Pakistan are vital for biodiversity, livelihoods, and ecosystem services.

Sustainable management is essential to combat degradation and ensure their long-term survival.