Class 12 Biology Chapter 11 Organisms and Populations

Key Concept:Interaction Dynamics

b) Only the orchid benefits, with no harm to the mango tree
[Solution Description] Orchids growing on mango trees represent a commensal relationship, where orchids gain support and access to sunlight without affecting the mango tree.

Key Concept:Basic Formula

d) Intrinsic rate of natural increase
[Solution Description] In the exponential growth model, the term ‘r’ is referred to as the intrinsic rate of natural increase. It indicates how fast the population grows when resources are unlimited.

Key Concept:Complex Interaction, Real-World Implication

d) Increased growth and dominance of the remaining tree species
[Solution Description] The loss of one tree species due to disease can lead to competitive release for the remaining species. Without competition for sunlight and nutrients, the other species may have increased growth opportunities. However, this change can also disturb the ecosystem balance leading to possible over-dominance by the surviving species.

Key Concept:Interaction Characteristics

b) One species benefits, the other is unaffected
[Solution Description] In commensalism, one species benefits and the other is neither helped nor harmed, unlike mutualism or parasitism where there are clear benefits or harm involved.

Key Concept:Breeding Frequency

c) Pacific salmon
[Solution Description] Semelparous organisms breed only once during their lifetime before they die. The Pacific salmon is a classic example as it breeds once and dies after spawning.

Key Concept:Concept Identification

d) Natality and mortality
[Solution Description] Under normal conditions, natality (birth rate) and mortality (death rate) are the primary factors that affect population growth.

Key Concept:Realistic Model

b) It accounts for resource limitations
[Solution Description] Logistic growth takes into account resource limitations by incorporating carrying capacity (K), unlike exponential growth, which assumes unlimited resources.

Key Concept:Interaction Dynamics

b) It decreases algal population by inhibiting growth
[Solution Description] If fish release substances that inhibit algal growth, the algae are directly harmed by these substances while the fish remain unaffected. This results in a decrease in the algal population since their growth is suppressed by the inhibitory substances.

Key Concept:Complex Interaction Evaluation, Scenario Analysis

b) Orchid populations may decline due to loss of potential habitats.
[Solution Description] The removal of trees would directly impact the orchids as they rely on them for physical support in growth. With fewer trees, there would be less habitat available for orchids, potentially leading to a decrease in their population as they have nowhere else to grow.

Key Concept:Offspring Size

c) Oysters
[Solution Description] Organisms like oysters are known to produce a vast number of small-sized offspring as part of their reproductive strategy. This increases the probability of offspring survival through sheer numbers.

Key Concept:Complex Scenario, Long-term Effects

c) Stable coexistence and enhanced ecosystem balance.
[Solution Description] Feeding at different tree heights is a form of vertical resource partitioning, which reduces direct competition between the species. Over time, this behavior stabilizes the population dynamics, contributing to a more diverse and balanced ecosystem.

Key Concept: Exponential Growth

b) Unlimited resources

[Solution Description] Exponential growth occurs when resources are unlimited, allowing the population to grow at a constant rate without limitations. Limited resources, high mortality rates, and low birth rates prevent this type of growth.

Key Concept:Predator Impact on Competition, Herbivores as Predators

c) Increased competition among herbivorous prey species
[Solution Description] The removal of a top predator often leads to increased competition among herbivorous prey species because the control that predators exert over prey population is reduced. Without predation pressures, prey populations can grow unchecked, leading to resource depletion and increased competition for those limited resources.

Key Concept: Ecological Roles

b) Consumer

[Solution Description] Parasites derive nourishment from their hosts and are considered consumers because they consume resources produced by or within another organism.

Key Concept:Evolutionary Adaptations, Coexistence Strategies

b) By promoting specialization
[Solution Description] Evolutionary adaptations such as morphological changes or behavioral shifts can allow multiple species to exploit different aspects of the environment or resources, thereby enabling their coexistence rather than elimination.

Key Concept: Per Capita Rates

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

[Solution Description] To determine the per capita rates, we need to consider both the formula for birth and death rates. – The per capita birth rate is indeed calculated as:

$$b = \frac{\text{Number of Births}}{\text{Initial Population Size}}$$

– Similarly, the per capita death rate is:

$$d = \frac{\text{Number of Deaths}}{\text{Initial Population Size}}$$

Since both statements are correct and describe how to calculate the respective per capita rates, but they do not explain each other directly, option b is correct.

Key Concept: Growth Model Understanding

b) Logistic growth

[Solution Description] The logistic growth model starts with exponential growth when resources are abundant but slows down as resources become limited, eventually stabilizing at the carrying capacity of the environment.

Key Concept:Advanced Interpretation, Impact of External Factors

a) The base remains the same but the middle portion widens significantly, indicating a balanced growth.
[Solution Description] The current age pyramid shows a high birth rate with many young people, indicative of a growing population. Introducing a large number of middle-aged immigrants will widen the middle section of the pyramid, balancing it more toward a stable growth model where there is a significant working-age population. This influx might reduce the relative percentage of younger individuals in comparison to other groups, leading to potential economic advantages due to an increased workforce.

Key Concept:Endoparasite Complexity

c) Complex life cycles
[Solution Description] Endoparasites often have complex life cycles involving multiple stages and sometimes different hosts or vectors, unlike many ectoparasites which usually have simpler life requirements.

Key Concept:Basic Concept Application

a) Mutualism
[Solution Description] This scenario describes mutualism since both the bee and the flower benefit from the relationship.

Key Concept:Basic Concept

c) Oysters
[Solution Description] According to the syllabus, oysters and pelagic fishes are examples of organisms that produce many small offspring. For this question, oysters typically fit this category.

Key Concept:Species Diversity, Predator-Prey Dynamics

b) To prevent the overexploitation of prey resources
[Solution Description] Prudent behavior ensures that predators do not overexploit their prey populations, which would otherwise lead to prey extinction and subsequently harm the predator’s survival. It maintains balance and supports species diversity.

Key Concept:Predator-Prey Co-evolution, Ecological Impact

c) Decline of native prey and predator species leading to reduced biodiversity
[Solution Description] The introduction of an invasive predator can disrupt existing predator-prey dynamics by preying more heavily on native prey and outcompeting or preying on native predators. In the long term, this may lead to the decline in populations of native prey due to overexploitation and possible extinction of native predators. This disruption reduces biodiversity and ecosystem stability.

Key Concept: Real-World Applications, Advanced Research Implications

a) By predicting resource availability and planning forest management accordingly

[Solution Description] Understanding the synchronous flowering and subsequent death of bamboo can aid conservation efforts by planning harvests and ensuring sustainable use, while considering the ecological impact on dependent species and biodiversity. In agriculture, it helps in synchronizing planting cycles with natural flowering patterns to optimize yield and manage resources effectively.

Key Concept:Population Ecology Importance

c) It bridges ecology with genetics and evolution
[Solution Description] Population ecology is crucial because it links the study of ecology with genetics and evolution. It helps us understand how populations interact with environmental factors and evolve over time due to natural selection.

Key Concept:Basic Formula

c) $\frac{dN}{dt} = rN$
[Solution Description] The formula for exponential growth is given by $\frac{dN}{dt} = rN$, where $r$ represents the intrinsic rate of natural increase, and $N$ is the population size.

Key Concept:Co-evolution Impact

b) Pollination success decreases
[Solution Description] If a pollinator changes its behavior significantly, it may affect pollination success, leading to reduced reproductive success for the orchid until it adapts or finds alternative solutions.

Key Concept:Evolutionary Significance, Mutualism and Biodiversity

b) By enabling plants to colonize new habitats, thus increasing plant diversity.
[Solution Description] Mycorrhizal fungi form symbiotic associations with plant roots, enhancing water and nutrient absorption for plants while receiving carbohydrates in return. This interaction enables plants to inhabit diverse ecological niches, increasing plant diversity which indirectly supports greater biodiversity by providing varied habitats and food sources for other organisms.

Key Concept:Basic Concept

b) J-shaped
[Solution Description] When resources are unlimited, populations grow in a geometric fashion resulting in a J-shaped curve.

Key Concept:Evolutionary Implications, Predictive Modeling

b) Sexual selection drives evolution of exaggerated male traits
[Solution Description] A consistently male-biased sex ratio may enhance sexual selection, where males compete fiercely for mating opportunities. Over time, this could intensify the evolution of secondary sexual characteristics, potentially influencing mate choice dynamics and altering population structure.