1. What are ecozones? [2]

Ecozones (also known as biogeographic realms) are the broadest biogeographic divisions of the Earth's land surface, based on the distributional patterns of terrestrial organisms. They represent large areas where organisms have evolved in relative isolation over long periods of time.

2. Define biosphere. [2]

The biosphere is the global sum of all ecosystems; it is the zone of life on Earth, integrating all living beings and their relationships, including their interaction with the elements of the lithosphere, geosphere, hydrosphere, and atmosphere.

3. What is synecology? Give one example. [2]

Synecology is the branch of ecology that deals with the study of groups of organisms (communities) associated together as a unit in relation to their environment.

Example: Studying the interactions and nutrient cycling within an entire forest community rather than focusing on a single tree species.

4. What are survivorship curves? [2]

A survivorship curve is a graph showing the number or proportion of individuals surviving to each age for a given species or group. It is used to visualize how a population changes over time.

5. What are r-selection species? Give one example. [2]

r-selection species are those that emphasize high growth rates, typically exploit less-crowded ecological niches, and produce many offspring, each of which has a relatively low probability of surviving to adulthood.

Example: Bacteria, insects, or weeds (dandelions).

6. What are K-selection species? Give one example. [2]

K-selection species possess relatively stable populations fluctuating near the carrying capacity (K) of the environment. They invest more heavily in fewer offspring, each of which has a higher probability of surviving to adulthood.

Example: Humans, elephants, or whales.

7. What is a keystone species? Give one example. [2]

A keystone species is a species that has a disproportionately large effect on its natural environment relative to its abundance, maintaining the structure of an ecological community.

Example: Sea otters in kelp forest ecosystems.

8. What is an ecotone? Give one example. [2]

An ecotone is a transition area between two biological communities, where two communities meet and integrate. It often has higher species diversity than either of the bordering communities.

Example: A marshland located between a river and a riverbank.

9. What do you mean by community? [2]

In ecology, a community (also known as a biocenosis) is an interacting group of various species in a common location. For example, a forest of trees and undergrowth plants, inhabited by animals and rooted in soil containing bacteria and fungi, constitutes a biological community.

10. What is food chain? Give one example. [2]

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

Example: Grass → Grasshopper → Frog → Snake → Hawk.

11. What is food web? Give one example. [2]

A food web is a complex network of interconnecting and overlapping food chains in an ecosystem, showing the multiple feeding relationships between different organisms.

Example: A forest food web where a single plant might be eaten by rabbits, mice, and insects, each of which has multiple predators.

12. What is ecosystem? [2]

An ecosystem is a structural and functional unit of biosphere consisting of a community of living organisms interacting with their physical environment (abiotic factors) through energy flow and nutrient cycling.

13. What is biogeochemical cycle? [2]

A biogeochemical cycle is the pathway by which a chemical substance (like Carbon, Nitrogen, or Phosphorus) moves through both the biotic (living) and abiotic (lithosphere, atmosphere, and hydrosphere) compartments of Earth.

14. What are the different forms of nitrogen available for plants? [2]

Plants primarily absorb nitrogen in the following forms:

• Nitrate (NO3-) - Most common form absorbed.
• Ammonium (NH4+) - Absorbed directly by some species.

15. What is the available form of phosphorus for plants? [2]

Phosphorus is mainly taken up by plant roots as orthophosphate ions, specifically H2PO4- and HPO4(2-), depending on the soil pH.

16. What do you mean by biomes? Describe briefly the characteristic features of any two terrestrial biomes. [2+4+4=10]

Biomes are large geographical areas characterized by specific climate, soil conditions, and distinctive plant and animal communities. They are categorized based on the dominant vegetation type and climate adaptation of organisms.

1. Tropical Rainforest Biome

• Climate: High temperatures (20-29°C) and heavy rainfall throughout the year (200-400 cm annually).
• Vegetation: Dense, multi-layered canopy. Includes epiphytes and lianas. Very high biodiversity.
• Soil: Nutrient-poor due to rapid leaching and high decomposition rates.

2. Desert Biome

• Climate: Extremely low precipitation (less than 30 cm per year). High daytime temperatures and cold nights.
• Vegetation: Sparse, specialized plants like cacti (succulents) with deep roots or water storage tissues.
• Adaptations: Nocturnal animals and drought-resistant seeds.

17. Write short notes on the following: (a) Liebig's law of minimum, (b) Shelford's law of tolerance. [5+5=10]

(a) Liebig's Law of Minimum

Proposed by Justus von Liebig, this law states that the growth of an organism or population is controlled not by the total amount of resources available, but by the scarcest resource (limiting factor).

Growth is dictated by the limiting factor, not the total resources available.

Example: Even if a plant has perfect sunlight and water, it will not grow if the soil lacks a specific micronutrient like Zinc.

(b) Shelford's Law of Tolerance

Victor Shelford expanded on the law of minimum by stating that an organism's success is based on a complex set of conditions and that each organism has a certain minimum, maximum, and optimum environmental factor limit or tolerance range.

• Zone of Optimum: Condition where the population is most abundant.
• Zone of Stress: Conditions where organisms can survive but are under physiological stress.
• Zone of Intolerance: Conditions beyond which the species cannot survive.

18. Describe the various growth patterns of population of different organisms in our ecosystems. [10]

Population growth patterns generally follow two main models based on resource availability:

1. Exponential Growth (J-shaped curve)

Occurs when resources are unlimited. The population increases at a constant rate per unit of time. It is represented by the equation:

dN / dt = rN

Where N is population size, t is time, and r is the intrinsic rate of increase.

2. Logistic Growth (S-shaped or Sigmoid curve)

Occurs when resources are limited. Growth slows down as the population reaches the Carrying Capacity (K), which is the maximum number of individuals the environment can sustain. The equation is:

dN / dt = rN [ (K - N) / K ]

Stages of Logistic Growth:

1. Lag Phase: Initial slow growth as individuals adapt.
2. Log Phase: Rapid exponential growth.
3. Deceleration Phase: Growth slows due to environmental resistance.
4. Stationary Phase: Population stabilizes at Carrying Capacity.

19. Write short notes on the following: (a) Density-dependent factors, (b) Life table. [5+5=10]

(a) Density-dependent factors of population growth

These are biological factors whose effect on the size or growth of the population vary with the population density. As density increases, these factors limit growth more severely.

• Competition: For food, space, or mates.
• Predation: Predators may focus on prey species that are more abundant.
• Disease: Pathogens spread more easily in crowded populations.
• Waste Accumulation: High density leads to toxic byproduct buildup.

(b) Life table

A life table is a table which shows, for each age, what the probability is that a member of a given population will die before their next birthday. It summarizes the mortality and survival data of a population.

Components: Age intervals (x), number surviving (nx), mortality rate (qx), and life expectancy (ex).

20. Describe briefly the various types of species interactions which are constantly occurring in our ecosystems. [10]

21. Write short notes on the following: (a) Ecological succession, (b) Edge effect. [5+5=10]

(a) Ecological succession

Succession is the process of change in the species structure of an ecological community over time.

• Primary Succession: Starts in lifeless areas (e.g., bare rock, lava flows).
• Secondary Succession: Starts in areas where a community has been removed but the soil remains (e.g., after a forest fire).
• Climax Community: The final stable stage of succession.

(b) Edge effect

The edge effect refers to the changes in population or community structures that occur at the boundary of two or more habitats. Areas with small habitat fragments exhibit especially pronounced edge effects. Often, edges support higher species richness and density than either habitat alone (e.g., a forest-grassland edge).

22. Discuss briefly the various components of ecosystem. [10]

An ecosystem consists of two main components:

1. Abiotic Components (Non-living)

• Climatic factors: Light, temperature, rainfall, wind.
• Edaphic factors: Soil texture, pH, minerals.
• Inorganic/Organic substances: C, N, H2O, proteins, lipids.

2. Biotic Components (Living)

• Producers (Autotrophs): Green plants that synthesize food via photosynthesis.
• Consumers (Heterotrophs):
  • Primary: Herbivores (e.g., Deer).
  • Secondary: Carnivores (e.g., Fox).
  • Tertiary: Top carnivores (e.g., Tiger).
• Decomposers (Saprotrophs): Fungi and bacteria that break down dead organic matter and recycle nutrients back to the soil.

23. Write short notes on the following: (a) Ecological efficiencies, (b) Ecological pyramids. [5+5=10]

(a) Ecological efficiencies

This refers to the efficiency with which energy is transferred from one trophic level to the next. According to **Lindeman's 10% Law**, only about 10% of the energy available at one trophic level is transferred to the next.

Energy Transferred = (Energy at Trophic Level n / Energy at Trophic Level n-1) x 100

(b) Ecological pyramids

Graphic representations of trophic levels in an ecosystem.

• Pyramid of Number: Shows the number of individuals at each level.
• Pyramid of Biomass: Shows total living organic matter at each level.
• Pyramid of Energy: Always upright, showing the total energy available at each level.

24. Describe the hydrological cycle with suitable diagrammatic illustration. [7+3=10]

The **Hydrological Cycle** (Water Cycle) describes the continuous movement of water on, above, and below the surface of the Earth.

Key Processes:

1. Evaporation: Solar energy turns surface water (oceans, lakes) into water vapor.
2. Transpiration: Loss of water vapor from plant leaves into the atmosphere.
3. Condensation: Water vapor cools and forms clouds.
4. Precipitation: Water falls back to Earth as rain, snow, or hail.
5. Infiltration and Runoff: Water enters the soil or flows over the land into water bodies.

Significance: It regulates Earth's temperature and distributes fresh water to all living organisms.