Attempt any ten questions. (2 x 10 = 20 Marks)
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.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
Plants primarily absorb nitrogen in the following forms:
Phosphorus is mainly taken up by plant roots as orthophosphate ions, specifically H2PO4- and HPO4(2-), depending on the soil pH.
Answer any five questions. (10 x 5 = 50 Marks)
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.
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.
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.
Population growth patterns generally follow two main models based on resource availability:
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.
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:
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.
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).
| Interaction Type | Species A | Species B | Description |
|---|---|---|---|
| Mutualism | (+) | (+) | Both species benefit (e.g., Lichens). |
| Commensalism | (+) | (0) | One benefits, the other is unaffected (e.g., Orchids on trees). |
| Parasitism | (+) | (-) | One benefits at the expense of the host (e.g., Ticks on dogs). |
| Predation | (+) | (-) | One captures and feeds on the other (e.g., Lion and Zebra). |
| Competition | (-) | (-) | Both are harmed as they struggle for same resource. |
| Amensalism | (-) | (0) | One is harmed, the other is unaffected (e.g., Antibiotic production by fungi). |
Succession is the process of change in the species structure of an ecological community over time.
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).
An ecosystem consists of two main components:
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
Graphic representations of trophic levels in an ecosystem.
The **Hydrological Cycle** (Water Cycle) describes the continuous movement of water on, above, and below the surface of the Earth.
Significance: It regulates Earth's temperature and distributes fresh water to all living organisms.