GSEB Class 12 Biology Solutions Chapter 13 Organisms and Populations

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 1. How is diapause different from hibernation?
Answer: Hibernation is a natural process primarily observed in ectothermic (cold-blooded) animals, allowing them to escape cold conditions by seeking refuge in various shelters like caves, burrows, tree trunks, or mud. During this period, their physiological activity is significantly reduced. Some warm-blooded mammals also exhibit this behavior. In contrast, diapause is a developmental stage where insects endure unfavorable climatic conditions by suspending their growth and metabolic activity.
In simple words: Hibernation is a long winter sleep for animals to escape cold, reducing their body functions. Diapause is a similar inactive state, specifically for insects, to survive harsh environmental conditions during their development.

🎯 Exam Tip: Focus on the key differences: hibernation is generally for cold-blooded animals (and some mammals) against cold, while diapause is a developmental arrest in insects against various unfavorable conditions.

Question 2. If a marine fish is placed in a fresh water aquarium, will the fish be able to survive? Why or why not?
Answer: No, a marine fish would not survive if placed in a freshwater aquarium. This is because marine fish are physiologically adapted to live in saline environments. When moved to freshwater, they face severe osmoregulation challenges due to the hypotonic external environment, which they are unable to properly manage.
In simple words: Marine fish cannot survive in fresh water because their bodies are designed for salty water, and they can't balance the water and salt in their systems in a freshwater environment.

🎯 Exam Tip: Understanding osmoregulation is crucial. Mentioning the hypotonic environment and the specific problem of osmoregulation will earn full marks.

Question 3. Define phenotypic adaptation. Give one example.
Answer: Phenotypic adaptation refers to non-genetic alterations in an organism's physical and physiological characteristics that arise in response to environmental shifts. These changes help organisms adjust to prevalent conditions. For example:
- Individuals living in the Himalayas for generations do not suffer from mountain sickness, unlike normal people visiting high altitudes.
- The plant species *Euphorbia hirta*.
In simple words: Phenotypic adaptation means an organism changes its physical or functional traits to suit a new environment, but these changes are not passed down genetically. For instance, someone new to high altitude might get sick, but locals don't.

🎯 Exam Tip: Clearly state that these adaptations are non-genetic and provide a distinct, biological example to illustrate the concept.

Question 4. Most living organisms cannot survive at temperatures above 45°C. How are some microbes able to live in habitats with temperatures exceeding 100°C?
Answer: Certain microorganisms possess a minimal amount of free water within their cellular structure. The reduction or removal of this free water enhances their resistance, allowing them to withstand and survive extremely high temperatures, often exceeding 100°C.
In simple words: Some microbes survive very hot places, even over 100°C, because they have very little water inside them, which helps them resist heat damage.

🎯 Exam Tip: The key to their survival is the reduced free water content, which confers high-temperature resistance. Mentioning this specific physiological adaptation is important.

Question 5. List the attributes that populations but not individuals possess.
Answer: Populations exhibit several unique attributes that individual organisms do not. These include:
- Population density
- Birth rate
- Death rate
- Sex ratio
- Population growth
- Age distribution
- Population dispersal
In simple words: A group of the same species (a population) has characteristics like how dense it is, how many babies are born, how many die, and the male-to-female ratio, which individual organisms don't have.

🎯 Exam Tip: When listing attributes, ensure you include at least three to four distinct characteristics like density, birth rate, and sex ratio, emphasizing they are group-level properties.

Question 6. If a population growing exponentially doubles in size in 3 years, what is the intrinsic rate of increase (r) of the population?
Answer: If a population demonstrates exponential growth and doubles in size over a period of three years, its intrinsic rate of increase (r) will be approaching its maximum potential under those conditions.
In simple words: If a population grows very fast and doubles every three years, its natural growth rate (r) is at its highest possible level.

🎯 Exam Tip: For exponential growth scenarios, a population doubling in a specific time frame implies its intrinsic growth rate is maximized given the conditions. The question doesn't ask for calculation, but conceptual understanding.

Question 7. Name important defence mechanisms in plants against herbivory.
Answer: Plants employ two primary categories of defense mechanisms against herbivory: Morphological and Chemical Defenses.
Morphological defenses include:
- Thorns, spines, prickles, and bristles
- Stinging hairs, sticky hairs, and hairy coatings
- Harboring ants for protection
- Mimicking the appearance of dangerous animals
Chemical defenses involve:
- Latex
- Alkaloids
- Tannins
- Bitter taste or offensive smell
- Irritating substances
- Poisonous cardiac glycosides
In simple words: Plants protect themselves from animals eating them using physical features like thorns or hairs, and by producing harmful chemicals like latex, poisons, or foul-tasting compounds.

🎯 Exam Tip: Categorize defenses into morphological and chemical types and provide at least two examples for each category for a comprehensive answer.

Question 8. An orchid plant is growing on the branch of mango tree. How do you describe this interaction between the orchid and the mango tree?
Answer: The relationship between an orchid plant growing on a mango tree branch is known as commensalism. In this interaction, the orchid benefits by gaining support and access to sunlight, while the mango tree remains unaffected, experiencing neither benefit nor harm.
In simple words: An orchid growing on a mango tree is an example of commensalism; the orchid gets a place to live, but the mango tree isn't helped or hurt.

🎯 Exam Tip: Define commensalism clearly by stating that one species benefits and the other is neither helped nor harmed, then apply it directly to the given example.

Question 9. What is the ecological principle behind the biological control method of managing pest insects?
Answer: The ecological principle underlying biological control for managing pest insects involves regulating their population growth through the use of their natural enemies, which include predators, parasites, and pathogens.
In simple words: Biological control uses natural enemies like predators or parasites to limit the population of pest insects instead of using chemicals.

🎯 Exam Tip: The core principle is manipulating natural population control mechanisms (predation, parasitism) to reduce pest numbers. Focus on the 'natural enemies' aspect.

Question 10. Distinguish between the following: a. Hibernation and Aestivation b. Ectotherms and Endotherms
Answer: a. Hibernation is the process where an animal enters an inactive state during cold periods. Aestivation, conversely, is a period of dormancy that occurs during summer months, allowing animals to escape the sun's scorching heat.
b. Ectotherms are cold-blooded animals whose body temperature largely matches their environmental temperature, making them susceptible to external temperature fluctuations. In contrast, endotherms are warm-blooded animals that can physiologically regulate their internal body temperature, maintaining it at a relatively constant level.
In simple words: Hibernation is for surviving winter cold, while aestivation is for surviving summer heat. Ectotherms are cold-blooded and change temperature with their surroundings, but endotherms are warm-blooded and keep their internal temperature stable.

🎯 Exam Tip: Clearly differentiate based on the environmental condition they cope with (cold vs. heat) for hibernation/aestivation, and internal temperature regulation for ectotherms/endotherms.

Question 11. Write a short note on (a) Adaptations of desert plants and animals
Answer: Desert plants and animals exhibit specific adaptations to survive arid conditions.
(1) Desert vegetation is typically sparse, with growth primarily occurring during rain periods (drought-exiting).
(2) Many annual plants are drought evaders, completing their life cycle quickly after rains.
(3) Succulents (drought-resisting) store water, often with mucilage and latex.
(4) Non-succulent perennials (drought-enduring) have long roots and employ modifications to minimize transpiration.
(5) Plant modifications include:
- Leaves modified into spines and thorns
- Stems acting as water storage organs, often with thick bark
- Long, deep roots combined with a reduced shoot system
Animals in deserts also show adaptations:
- Many live in burrows to escape heat.
- They have very low water requirements and can store water in specialized body parts.
- Their urine is concentrated, and faeces are nearly solid, utilizing metabolic water.
- A nasal counter-current mechanism prevents water loss during breathing, aided by small nostril size.
- Some feed on dry seeds, rehydrating and storing water when available.
- A very small body surface area minimizes sweating and water loss.
(b) Adaptations of plants to water scarcity: This is covered in the plant adaptations mentioned above, specifically addressing drought conditions.
(c) Behavioural adaptations in animals:
- Snakes emerge from burrows in winter to bask in the sun, warming their bodies for activity.
- Desert lizards maintain a relatively constant body temperature through behavioral changes; they bask in the sun when their body temperature drops below their comfort zone and seek shade when ambient temperature rises.
(d) Importance of light to plants: Light is crucial for plants, influencing photosynthesis, growth, reproduction, height, flower induction, seed germination, and overall plant movement.
(e) Effect of temperature or water scarcity and the adaptations of animals: Animals in arid regions are specifically adapted to manage limited water availability and minimize water loss. For instance, the Kangaroo rat obtains all its water from dry seeds. Animals also protect themselves from extreme cold through hibernation, thick fur, and constriction of peripheral blood vessels.
In simple words: Desert plants adapt with deep roots, water-storing stems, or by only growing when it rains. Desert animals cope by living in burrows, needing little water, and concentrating their waste to conserve moisture. Light is vital for plant growth. Animals also adapt to temperature extremes and water scarcity through behaviors like basking or hibernation.

🎯 Exam Tip: Provide a balanced overview of both plant and animal adaptations. For plants, mention water storage, root systems, and leaf modifications. For animals, highlight behavioral responses, water conservation, and body surface area considerations.

Question 12. List the various abiotic environmental factors.
Answer: Abiotic environmental factors encompass non-living components that influence an ecosystem. These include:
- Climatic factors: temperature, light, air, atmospheric humidity, precipitation, and water.
- Edaphic factors: soil texture, substratum (underlying material), topography (land features), background (color/camouflage), minerals, and pH.
In simple words: Abiotic factors are non-living parts of the environment that affect life, like temperature, light, water, air, humidity, soil type, minerals, and land shape.

🎯 Exam Tip: Group abiotic factors into categories like climatic and edaphic for a structured answer, ensuring comprehensive coverage of relevant elements.

Question 13. Give an example for a. an endothermic animal. b. an ectothermic animal. c. an organism of benthic zone.
Answer: Here are examples for each category:
a. An endothermic animal: Human beings
b. An ectothermic animal: Frog
c. An organism of the benthic zone: Bacteria
In simple words: An endothermic animal maintains its own body heat (like humans), an ectothermic animal relies on external heat (like a frog), and an organism of the benthic zone lives at the bottom of a body of water (like certain bacteria).

🎯 Exam Tip: Provide clear and commonly known examples for each term. Ensure the examples are biologically accurate and distinct.

Question 14. Define population and community.
Answer: A population is defined as a collection of individuals from the same species who can interbreed to produce fertile offspring, living together within a specific geographical area at a particular time.
A community refers to various groups of organisms, each belonging to a different species, that coexist within the same area or habitat and interact with each other through trophic (feeding) and spatial relationships.
In simple words: A population is a group of the same species in one area that can have offspring. A community is all the different populations (different species) living and interacting together in the same area.

🎯 Exam Tip: For population, emphasize "same species" and "interbreeding." For community, highlight "different species" and "interactions" (trophic and spatial).

Question 15. Define the following terms and give one example for each: (a) Commensalism (b) Parasitism (c) Camouflage (d) Mutualism (e) Interspecific competition
Answer: (a) Commensalism: This is an interaction where one species gains a benefit, while the other species is neither benefited nor harmed. For instance, Clown Fish living among sea anemones.
(b) Parasitism: An interspecific interaction where a smaller organism of one species obtains sustenance and spends all or part of its life on or within the body of a larger organism from another species. Examples include *Plasmodium* in humans or liver fluke in snails and fish.
(c) Camouflage: This phenomenon involves an organism blending with its surroundings through similar color, markings, or shape, primarily to evade predators or ambush prey. Examples are stick insects or leaf insects.
(d) Mutualism: An interaction that provides benefits to both interacting species. Examples include lichens (a symbiotic relationship between fungus and algae) or the relationship between *Rhizobium* bacteria and legumes.
(e) Interspecific competition: This involves a struggle among members of different species for shared resources such as food, water, or other necessities. An example is the competition for resources among different plant species in a forest area. This interaction is a powerful driver in organic evolution.
In simple words: Commensalism benefits one species without affecting the other. Parasitism benefits one (the parasite) at the expense of the other (the host). Camouflage helps an organism hide by blending in. Mutualism benefits both interacting species. Interspecific competition is when different species fight over the same limited resources.

🎯 Exam Tip: For each term, provide a concise definition and a clear, biologically relevant example. Pay attention to whether one, both, or neither species are affected in the interactions.

Question 16. With the help of suitable diagram describe the logistic population growth curve.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह ग्राफ एक S-आकार का लॉजिस्टिक जनसंख्या वृद्धि वक्र (Verhulst-Pearl logistic curve) दर्शाता है, जो अधिकांश जीवों की आबादी में देखी जाती है। इसमें चार मुख्य चरण होते हैं: लैग चरण (धीमी शुरुआत), सकारात्मक त्वरण चरण (तेज वृद्धि), नकारात्मक त्वरण चरण (वृद्धि धीमी होना), और स्थिर चरण (जनसंख्या स्थिरता) जब यह अपनी वहन क्षमता तक पहुँच जाती है।
Answer: The S-shaped or Sigmoid growth curve, also known as the Verhulst-Pearl logistic curve, illustrates the typical population growth pattern for most organisms. This curve encompasses five distinct phases: the initial lag phase (slow growth), followed by a positive acceleration phase (rapid increase), an exponential phase (maximum growth rate), a negative acceleration phase (slowing growth), and finally, a stationary phase (population stabilization as it reaches carrying capacity).
In simple words: The logistic growth curve is an S-shaped graph showing how populations typically grow: slow start, then fast growth, then slowing down, and finally leveling off when resources limit further expansion.

🎯 Exam Tip: When describing the logistic curve, ensure you accurately name and explain each of the five phases and mention the concept of carrying capacity.

Question 17. Select the statement which explains best parasitism. a. One organism is benefitted. b. Both the organisms are benefitted. c. One organism is benefitted, other is not affected. d. One organism is benefitted, other is affected.
Answer: (a) One organism is benefitted.
In simple words: Parasitism is an interaction where one organism benefits at the expense of another.

🎯 Exam Tip: While the given answer is 'one organism is benefitted', for parasitism, it's crucial to also remember that the other organism (host) is harmed or adversely affected. The question asks what *best* explains it among the options, and option 'a' is the only one stating benefit to *one* organism. However, a more complete answer for parasitism would involve harm to the host, which is only indirectly implied by "other is affected" in option d.

Question 18. List any three important characteristics of a population and explain.
Answer: Populations exhibit unique characteristics that are not present in individual members. These include:
a. Natality (birth) rate: This refers to the average number of young individuals produced per unit time within a population, whether through birth or germination. The highest possible birth rate under ideal conditions is termed potential natality or biotic potential.
b. Mortality (death) rate: This indicates the average number of individuals dying per unit time within a population. It is expressed as a change in the number of deaths relative to the total population size.
c. Dispersal: Individuals within a population may spread out at different points in their life cycles. This phenomenon includes both immigration (movement into an area) and emigration (movement out of an area).
In simple words: Important population characteristics include birth rate (how many are born), death rate (how many die), and dispersal (how individuals move in or out of the area), all of which describe the group, not just one individual.

🎯 Exam Tip: When explaining population characteristics, define each term clearly and highlight how they are group-level properties rather than individual traits.

GSEB Class 12 Biology Organisms And Populations Additional Important Questions And Answers

Question 1. Study the relationship of the given pair and fill up the blanks a. Hibernation : Bears : : Aestivation : _______ b. Euryhaline : wide range of salinity : : Stenohaline : _______
Answer: The relationships are as follows:
a. Hibernation : Bears : : Aestivation : Snail
b. Euryhaline : wide range of salinity : : Stenohaline : narrow range of salinity
In simple words: Bears hibernate, so snails aestivate. Euryhaline species tolerate wide salinity, while stenohaline species tolerate narrow salinity.

🎯 Exam Tip: For analogy questions, identify the relationship between the first pair (e.g., phenomenon and example) and apply it consistently to complete the second pair.

Question 2. An individual may have births and deaths, but a population has ...............(a) ...... .(b). An individual is either a male or a female but a population has a ...(c).
Answer: The blanks should be filled as follows:
a. birth rate
b. death rate
c. sex ratio
In simple words: While individuals are born and die, populations are characterized by their overall birth rate, death rate, and sex ratio.

🎯 Exam Tip: Remember that "rates" and "ratios" are population-level attributes, distinguishing them from individual events like a single birth or death.

Question 3. Temperature of the earth ...............(a) (decreases/increases) progressively from the .(b) (poles/equator) towards the ...............(c) (poles/equator) and from ...............(d) (plains/mountain tops) to the ...............(e) (plains/mountain tops).
Answer: Filling the blanks, the statements are:
a. decreases
b. equator
c. poles
d. plains
e. mountain tops
In simple words: Earth's temperature generally decreases from the equator towards the poles and from plains to mountain tops.

🎯 Exam Tip: This question tests geographical and ecological understanding of temperature gradients. Remember the general patterns: temperature decreases with increasing latitude (towards poles) and increasing altitude (towards mountain tops).

Question 4. Organisms that can tolerate and thrive in a wide range of temperature are called (a) and organisms restricted to a narrow range of temperature are called (b)
Answer: The correct terms are:
a. eurythermal
b. stenothermal
In simple words: Organisms tolerant to wide temperature changes are eurythermal, while those needing a narrow temperature range are stenothermal.

🎯 Exam Tip: Distinguish between 'eury-' (wide) and 'steno-' (narrow) prefixes when defining tolerance ranges for environmental factors like temperature or salinity.

Question 5. The spectral quality of solar radiation is important to life. Justify this statement.
Answer: The spectral quality of solar radiation is indeed vital for life. For instance, the UV component of the spectrum is detrimental to many organisms. Marine plants, in particular, have evolved to utilize specific colors within the visible spectrum because only certain wavelengths of light can penetrate and reach them at various depths in the oceans.
In simple words: Different parts of sunlight affect life uniquely; UV light is harmful, while underwater plants adapt to use only specific colors of light that reach them.

🎯 Exam Tip: Emphasize both the harmful aspects (UV) and the selective utilization (marine plants using specific visible spectrum colors) to justify the statement's importance.

Question 6. The vegetation in an area is determined by different characteristics and parameters of soil. Comment on this statement.
Answer: The statement is accurate; the vegetation in any given area is significantly influenced by various characteristics and parameters of the soil. Factors such as soil composition, grain size, and aggregation directly impact the soil's percolation rate and water-holding capacity. Additionally, parameters like pH, mineral composition, and topography of the land, along with the aforementioned characteristics, collectively determine the extent and type of vegetation that can thrive in that area.
In simple words: Soil properties like its texture, ability to hold water, pH, and minerals strongly influence what kind of plants can grow in a particular area.

🎯 Exam Tip: Provide a comprehensive explanation by listing key soil characteristics (composition, grain size, pH, minerals) and linking them directly to their impact on vegetation, such as water retention and nutrient availability.

Question 7. Briefly explain the need for a constant internal environment for organisms. What do you mean by homeostasis?
Answer: Organisms require a stable internal environment to ensure that all biochemical reactions and physiological functions can proceed with maximum efficiency. Homeostasis refers to the dynamic process by which organisms maintain this constant internal environment, despite fluctuations in external conditions.
In simple words: Organisms need a steady internal environment for their body processes to work best. Homeostasis is the ability to keep this internal environment stable.

🎯 Exam Tip: Clearly state the reason for needing a constant internal environment (optimal physiological function) and provide a precise definition of homeostasis.

Question 8. Observe the graph and differentiate the characters of conformers and regulators.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक ग्राफ दर्शाता है जो बाहरी पर्यावरण स्तरों के सापेक्ष जीवों के आंतरिक स्तरों में भिन्नता दिखाता है। इसमें तीन प्रकार के जीव शामिल हैं: कन्फॉर्मर (जिनका आंतरिक स्तर बाहरी स्तर के साथ बदलता है), रेगुलेटर (जो बाहरी बदलावों के बावजूद आंतरिक स्तर को स्थिर रखते हैं), और आंशिक रेगुलेटर (जो एक सीमा तक आंतरिक स्तर को स्थिर रखते हैं और फिर बाहरी स्तर के अनुरूप हो जाते हैं)।
Answer: Based on the graph:
Regulators are organisms capable of maintaining a constant internal environment, regardless of external environmental fluctuations. They actively regulate their internal conditions.
Conformers are organisms whose internal environment changes and aligns with the external environmental changes. They do not actively regulate their internal conditions.
In simple words: Regulators keep their internal body conditions stable regardless of outside changes, while conformers allow their internal conditions to change along with the external environment.

🎯 Exam Tip: Clearly define both regulators and conformers, emphasizing the presence or absence of internal regulation mechanisms, and relate it to maintaining a constant internal environment.

Question 9. Small animals are rarely found in polar regions. Comment.
Answer: Small animals are seldom encountered in polar regions due to their relatively large surface area-to-volume ratio. This characteristic causes them to lose body heat very rapidly in cold external conditions. Consequently, they would need to expend a considerable amount of energy through metabolism to generate and maintain sufficient body heat. This high energy demand makes it energetically unfavorable for them to thrive in such frigid environments.
In simple words: Small animals struggle in polar regions because their large surface area causes them to lose body heat quickly, requiring too much energy to stay warm.

🎯 Exam Tip: The key concept here is the surface area-to-volume ratio. Explain how a higher ratio in small animals leads to greater heat loss and thus a higher metabolic cost for thermoregulation.

Question 10. Most organisms usually maintain their internal environment in a constant condition irrespective of external factors. But if the external conditions are stressfull and are localised or remain only for a short duration, what are the alternatives for the organisms to cope up with such condition?
Answer: When external conditions are stressful, localized, or short-lived, organisms employ several alternatives to cope instead of maintaining constant internal environments:
a. Migration: Organisms can temporarily move away from the stressful habitat to a more hospitable area and return once the challenging period concludes. Birds are a common example of this behavior.
b. Suspension: Organisms like bacteria and fungi can produce thick-walled spores to endure unfavorable conditions. Plants develop seeds and other vegetative reproductive structures for survival, germinating when suitable environmental conditions return.
c. Hibernation/Aestivation: These are alternative strategies for animals to survive extreme cold (hibernation) or intense heat and drought (aestivation).
d. Diapause: Many zooplankton species in lakes and ponds enter a stage of suspended development called diapause to survive adverse conditions.
In simple words: When conditions are bad but temporary, organisms can cope by migrating to better places, suspending their activities (like seeds or spores), entering dormancy like hibernation or aestivation, or undergoing a developmental pause called diapause.

🎯 Exam Tip: List and briefly describe each coping mechanism (migration, suspension, hibernation/aestivation, diapause) and provide an example for clarity.

Question 11. Organisms are adapted to live in their habitat. Briefly give explanation for adaptation with example of Kangaroo rat.
Answer: Adaptation refers to any inheritable trait or attribute of an organism that enhances its ability to survive and reproduce successfully within its specific habitat.
A classic example is the Kangaroo rat found in North American deserts. This rodent is remarkably adapted to arid conditions:
- It can fulfill all its water requirements through internal fat oxidation, producing metabolic water.
- The Kangaroo rat also has a specialized ability to concentrate its urine, minimizing the volume of water lost through excretory products.
In simple words: Adaptation means an organism has traits that help it survive and reproduce in its home. The Kangaroo rat, for example, makes its own water from food and has very concentrated urine to save water in the desert.

🎯 Exam Tip: Define adaptation first, then provide a detailed explanation of the Kangaroo rat's specific physiological adaptations for water conservation (metabolic water production, concentrated urine) in its desert habitat.

Question 12. What do you mean by Allen's rule?
Answer: Allen's rule states that mammals residing in colder climates generally possess shorter ears and limbs. This anatomical adaptation serves to minimize the surface area exposed to the environment, thereby reducing heat loss and conserving body warmth.
In simple words: Allen's rule says that animals in cold places tend to have smaller ears and limbs to reduce heat loss and stay warm.

🎯 Exam Tip: State Allen's rule precisely and explain the physiological reason behind it (reduced surface area for heat conservation) for full understanding.

Question 13. While going to a high altitude area, many people experience altitude sickness which include nausea, fatigue and heart palpitations. How do your body adjust physiologically to such conditions?
Answer: When individuals ascend to high-altitude areas, the body physiologically adjusts to the lower oxygen availability through several mechanisms:
- It increases the production of red blood cells to enhance oxygen carrying capacity.
- The binding affinity of hemoglobin to oxygen is decreased, allowing for more efficient oxygen release to tissues.
- The breathing rate is increased to take in more oxygen.
In simple words: To adjust to high altitudes and less oxygen, your body makes more red blood cells, makes hemoglobin release oxygen more easily, and increases your breathing rate.

🎯 Exam Tip: Focus on the three main physiological responses: increased RBCs, altered hemoglobin affinity, and increased breathing rate, as these are critical for coping with hypoxia at high altitudes.

Question 14. Some organisms like desert lizards lack the physiological abilities to cope with variations in their environment, but show some behavioural responses. Comment on.
Answer: Desert lizards, despite lacking advanced physiological mechanisms to maintain a constant internal temperature, exhibit effective behavioral adaptations to manage environmental variations. They typically bask in the sun to absorb heat when their body temperature falls below their optimal comfort zone. Conversely, when the ambient temperature begins to rise excessively, they move into the shade to cool down. Furthermore, some species possess the ability to burrow into the soil, allowing them to hide and escape the intense ground heat.
In simple words: Desert lizards use behaviors like basking in the sun to warm up or moving into the shade to cool down, or even burrowing, because they can't control their body temperature internally like some other animals.

🎯 Exam Tip: Emphasize that behavioral adaptations are a compensatory mechanism when physiological regulation is limited. Provide clear examples of these behaviors in desert lizards.

Question 15. The density of a population in a given habitat during a given period, fluctuates due to changes in four basic processes. Two of them contribute to increase in population and two of them contribute to a decrease in population. a. Name the four basic process. b. Which of these cause a decline and which cause an increase in population?
Answer: a. The four basic processes that influence population density are Natality, Mortality, Immigration, and Emigration.
b. Natality (births) and Immigration (arrival of individuals) cause an increase in population.
Mortality (deaths) and Emigration (departure of individuals) cause a decrease in population.
In simple words: Population size changes due to four processes: births (natality) and new arrivals (immigration) increase it, while deaths (mortality) and individuals leaving (emigration) decrease it.

🎯 Exam Tip: Clearly list all four processes and then specify which two increase the population and which two decrease it for a complete answer.

Question 16. Differentiate exponential growth and logistic growth.
Answer: Exponential growth occurs when resources within a habitat are unlimited, allowing each species to fully realize its intrinsic potential to increase in number. This results in a population growing in an exponential or geometric pattern over a short period.
In contrast, logistic growth describes a population pattern in a habitat with limited resources. It typically begins with a lag phase, followed by a phase of accelerated growth, then a deceleration phase, and finally reaches a stationary phase where the population density stabilizes at the carrying capacity of the environment.
In simple words: Exponential growth is rapid, unchecked growth when resources are unlimited, forming a J-shaped curve. Logistic growth is more realistic, showing an S-shaped curve where growth slows down and levels off as resources become limited and the population reaches its maximum sustainable size.

🎯 Exam Tip: Highlight the key difference: unlimited resources for exponential growth (J-shaped curve) versus limited resources leading to carrying capacity for logistic growth (S-shaped curve). Mentioning the phases of logistic growth is also important.

Question 17. Fill up the blanks with suitable examples. a. Organisms breed only once in their life time - (oyster/ Pacific salmon/birds) b. Organism which produces a large number of small sized offspring. (Birds/Mammals/Oyster) c. Organisms which produce small number of large sized offsprings. (Bamboo / Oyster /Mammals)
Answer: The blanks are filled with the following examples:
a. Pacific salmon
b. Oyster
c. Mammals
In simple words: Pacific salmon breed once then die. Oysters produce many small offspring. Mammals have fewer, larger offspring.

🎯 Exam Tip: This question tests knowledge of life history strategies. Connect the reproductive patterns (semelparity vs. iteroparity, r- vs. K-selected species characteristics) with the given examples.

Question 18. Observe the figures and identify i. stable population ii. expanding population iii. What is the name of the remaining figure?
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र तीन प्रकार के जनसंख्या आयु पिरामिड (A, B, C) दर्शाता है, जो विभिन्न आयु समूहों (पूर्व-प्रजनन, प्रजनन, और पश्च-प्रजनन) में व्यक्तियों की संख्या को दिखाते हैं। आकृति A एक विस्तृत आधार के साथ एक बढ़ती हुई जनसंख्या को इंगित करती है, आकृति B एक स्थिर जनसंख्या को दर्शाती है जिसका आधार प्रजनन आयु वर्ग के समान है, और आकृति C एक घटती हुई जनसंख्या को दर्शाती है जिसका आधार संकरा है।
Answer: Based on the figures:
i. Figure B represents a stable population (where pre-reproductive and reproductive age groups are roughly equal).
ii. Figure A represents an expanding population (characterized by a broad base of pre-reproductive individuals).
iii. The remaining figure (C) represents a declining population (identified by a narrower base of pre-reproductive individuals compared to reproductive ones).
In simple words: Figure A shows a growing population, Figure B shows a stable population, and Figure C shows a shrinking population, based on their age structures.

🎯 Exam Tip: Understand how the shape of an age pyramid (especially the base) correlates with population growth status: a wide base indicates expansion, a relatively even base indicates stability, and a narrow base indicates decline.

Question 20. Briefly explain Gause's competitive exclusion principle.
Answer: According to Gause's competitive exclusion principle, two closely related species that compete for the same limited resources cannot indefinitely coexist in the same niche. Ultimately, the species that is competitively inferior will be eliminated from the habitat.
In simple words: When two species compete for the exact same resources, one species will eventually outcompete and eliminate the other because they cannot both thrive in the same ecological role.

🎯 Exam Tip: Remember to clearly state the core idea of "exclusion" and the condition of "same resources" when explaining Gause's principle.

Question 21. According to recent studies on competition, it is stated that species facing competition might evolve mechanisms that promote coexistence rather than exclusion. Explain this with the example of resource partitioning.
Answer: Contemporary research on competition suggests that instead of leading to exclusion, competing species can develop strategies that facilitate their coexistence. Resource partitioning is one such mechanism, where species competing for similar resources avoid direct confrontation by opting for different foraging times or by adopting distinct foraging patterns. This allows them to utilize the same overall resource base without intense rivalry.
In simple words: Species that would normally compete can learn to share resources by using them at different times or in different ways, allowing them to live together without one species driving the other out.

🎯 Exam Tip: Emphasize "resource partitioning" as a key strategy for coexistence, moving beyond Gause's exclusion principle. Provide a simple scenario where this strategy might be observed.

Question 22. Briefly explain the special adaptations evolved by parasites in accordance with their life styles.
Answer: Parasites have evolved several distinct adaptations to suit their parasitic lifestyle:
(a) They often exhibit a loss of unnecessary sense organs, as their hosts provide a relatively stable environment.
(b) The presence of specialized adhesive organs or suckers is common, enabling them to attach securely to their host.
(c) Many parasites have lost their digestive system, relying on the host to pre-digest nutrients.
(d) A high reproductive capacity is typical, compensating for the risks associated with finding and infecting new hosts.
In simple words: Parasites develop specific traits like strong attachments, simplified sensory and digestive systems, and high reproduction rates to survive and thrive by depending on a host organism.

🎯 Exam Tip: When describing parasite adaptations, focus on how each adaptation directly benefits their survival within or on a host, especially the trade-offs (loss of organs vs. high reproductive output).

Question 23. Explain the effects of parasite on the host.
Answer: Parasites significantly impact their hosts in several ways:
(a) They can diminish the host's survival rates, impede its growth, and reduce its reproductive capabilities.
(b) Parasitic infections often lead to a reduction in the host's population density.
(c) Parasites may render the host more susceptible to predation by weakening it physically or compromising its immune system.
In simple words: Parasites harm their hosts by reducing their lifespan, growth, and ability to reproduce, making them weaker and more vulnerable to other threats.

🎯 Exam Tip: Highlight the direct negative consequences a parasite has on its host's fitness and overall population health.

Question 24. Comment on Brood parasitism.
Answer: Brood parasitism is an ecological strategy where a parasitic bird lays its eggs in the nest of another species, known as the host. The host bird then incubates the parasitic bird's eggs and raises the young as its own, often at the expense of its own offspring. A classic example of this phenomenon is observed with the cuckoo bird.
In simple words: Brood parasitism is when one bird species, like a cuckoo, lays its eggs in another bird's nest, tricking the host into raising the parasitic bird's young instead of its own.

🎯 Exam Tip: Ensure you mention both the parasitic bird and the host bird, and the key action of laying eggs in another's nest, with the cuckoo as a common example.

Question 25. Given below are some of the common examples of species interactions. Categorise them into predation, commensalism, mutualism, parasitism or competition.
a. Egret foraging close to grazing cattle.
b. Fig flowers pollinated by wasp.
c. Cuckoo laying egg in crow's nest.
d. Phytophagous insects feeding on a plant.
e. Clown fishes living among sea anemone.
f. Abingdon tortoise in Galapagos islands became extinct within a decade after goats were introduced on the island.
Answer:
a, e - Commensalism
b - Mutualism
c - Parasitism
d - Predation
f - Competition
In simple words: These examples illustrate how different species interact, either helping each other (mutualism), one benefiting without harming the other (commensalism), one benefiting at the expense of the other (parasitism/predation), or both being negatively affected (competition).

🎯 Exam Tip: For interaction-based questions, identify whether each organism benefits (+), is harmed (-), or is unaffected (0) to correctly categorize the relationship.

Question 26. Figure (i) and (ii) show a kind of ecological interaction.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र दो प्रकार की पौधों की अंतःक्रियाओं को दर्शाता है। चित्र (i) में, एक पौधा (परजीवी) दूसरे बड़े पौधे (मेजबान) से जुड़ा हुआ है, जिससे यह मेजबान से पोषण प्राप्त कर रहा है। चित्र (ii) में, एक दूसरा पौधा (अधिपादप) एक बड़े पेड़ की शाखा पर उग रहा है, लेकिन यह केवल समर्थन के लिए जुड़ा हुआ है और मेजबान से पोषण नहीं लेता है, बल्कि हवा और बारिश से नमी प्राप्त करता है।
a. Identify the type of interactions.
b. List out some adaptations for these interactions.
Answer:
a. i. Interaction (i) represents Parasitism.
ii. Interaction (ii) represents Epiphytism.
b. For Parasitism:
- Specialized sucking roots (haustoria) to absorb nutrients from the host.
- Reduced or absent photosynthetic ability, relying entirely on the host for food.
For Epiphytism:
- Clinging roots for attachment to the host plant.
- Velamen roots, which are spongy tissues, to absorb atmospheric moisture and nutrients.
In simple words: The first image shows a plant getting nutrients from another (parasitism), while the second shows a plant growing on another simply for support, getting its own water and food from the air (epiphytism). These plants have special roots adapted for their specific ways of living.

🎯 Exam Tip: Clearly distinguish between parasitism (one organism benefits by harming the other) and epiphytism (one benefits for support, the other is unaffected).

Question 27. Differentiate between commensalism and symbiosis.
Answer: Commensalism describes a mutual interaction where one species receives benefits, while the other species is neither advantaged nor disadvantaged. In contrast, symbiosis refers to a close and often long-term interaction between two or more different biological species. While symbiosis broadly encompasses relationships like mutualism, commensalism, and parasitism, it generally implies a more intimate and often reciprocal association between organisms.
In simple words: Commensalism is when one organism benefits and the other is not affected, but symbiosis is a broader term for any close relationship between different species, which can include mutual benefit, one-sided benefit, or even one-sided harm.

🎯 Exam Tip: Remember that symbiosis is a broad term for living together, while commensalism is a specific type of symbiotic relationship where only one species benefits and the other is neutral.

Question 28. Study the three representative figures of age pyramid relating to human population given below and answer the following questions.
ℹ️ चित्र व्याख्या (Diagram Explanation): ये चित्र मानव जनसंख्या के लिए तीन विभिन्न आयु पिरामिडों को दर्शाते हैं। प्रत्येक पिरामिड की निचली परतें (15 वर्ष तक) पूर्व-प्रजनन आयु समूह को, मध्य परतें (15-45 वर्ष और 45-60 वर्ष) प्रजनन आयु समूह को, और ऊपरी परतें (60-75 वर्ष और 75 वर्ष से ऊपर) पश्च-प्रजनन आयु समूह को दर्शाती हैं। पिरामिड (i) का आधार चौड़ा है जो बढ़ती जनसंख्या को दर्शाता है, पिरामिड (ii) का आधार और मध्य लगभग बराबर है जो स्थिर जनसंख्या को दर्शाता है, जबकि पिरामिड (iii) का आधार संकीर्ण है जो घटती जनसंख्या को दर्शाता है।
a. Mention the names given to three kinds of age profiles (i), (ii) and (iii).
b. Which one of them is ideal for a population and why?
c. How do such age profile studies help policy makers get concerned about our growing population and prepare for future planning? (Say for example for the year 2022)
Answer:
a. (i) Expanding population (pyramid with a broad base)
(ii) Stable population (bell-shaped pyramid with a relatively uniform base and middle)
(iii) Declining population (urn-shaped pyramid with a narrow base)
b. A stable population (ii) is often considered ideal because it indicates a balance between birth and death rates, leading to minimal fluctuations in population size. A declining population can lead to labor shortages and economic challenges, while an expanding population can strain resources.
c. Age profile studies provide crucial insights for policymakers by revealing the current and projected growth status of a population. For instance, if an age pyramid shows an expanding population, policymakers can anticipate future demands for resources like education, employment, and infrastructure, allowing them to formulate policies for sustainable development and resource allocation. Conversely, a declining population might prompt policies aimed at increasing birth rates or managing an aging workforce. These insights are essential for long-term strategic planning.
In simple words: The three pyramids show populations that are growing, stable, or shrinking. A stable population is usually best as it avoids problems of too many or too few people. Governments use these population shapes to plan for things like schools, jobs, and healthcare in the future.

🎯 Exam Tip: When analyzing age pyramids, focus on the relative sizes of the pre-reproductive, reproductive, and post-reproductive age groups to determine the population's growth trend. Connect these trends to practical implications for society and policy.

🎯 Exam Tip: Understand the distinct attributes that apply to different levels of ecological organization. For example, individuals have age, but populations have birth rates (natality) and age distribution, while ecosystems involve energy flow.

Question 29. List the attributes that populations but not the individuals possess.
Answer: Populations exhibit unique characteristics that are not found in individual organisms. While an individual may experience birth and death, a population possesses birth rates and death rates, which are per capita measures of these events. Furthermore, an individual is either male or female, but a population is characterized by a sex ratio. The overall size and distribution pattern are also attributes solely of a population, providing insights into its status within a habitat.
In simple words: Populations have group traits like birth rates, death rates, and sex ratios, which are averages or proportions that don't apply to a single individual.

🎯 Exam Tip: When differentiating between individual and population attributes, remember that population attributes are statistical properties (rates, ratios, distributions) that emerge from the collective behavior of individuals.

Question 30. What is an ecosystem? How energy transformation occurs in an ecosystem?
Answer: An ecosystem represents a structural and functional unit of the biosphere, comprising living organisms interacting with their non-living environment. The sun serves as the ultimate source of energy for most ecosystems. Organisms, excluding photosynthetic plants, cannot directly capture solar energy. Consequently, other organisms depend on plants for their energy. Energy is transferred unidirectionally from the solar system to autotrophic plants (producers), then to various levels of consumers, and eventually to decomposers. This one-way movement of energy is termed energy flow.
Plants act as primary producers, synthesizing organic compounds such as carbohydrates, proteins, and fats. When primary consumers (herbivores) consume plants, these organic compounds transfer to them, liberating energy. As secondary consumers (carnivores) eat herbivores, energy is further transferred, with a significant reduction at each trophic level. The "Law of 10%" states that approximately 10% of the energy from one trophic level is transferred to the next.
In simple words: An ecosystem is where living things and their non-living environment interact. Energy flows through it, starting from the sun, captured by plants, then passed to animals that eat plants, and then to animals that eat other animals, with about 10% of energy transferred at each step.

🎯 Exam Tip: Define an ecosystem by its components (biotic and abiotic) and illustrate energy flow using the concepts of producers, consumers, decomposers, and the 10% law.

Question 31. Which one of the two, stenothermals or eurythermals shows wide range of distribution on earth and why?
Answer: Eurythermal organisms exhibit a wide range of distribution on Earth. This is because eurythermals are adapted to tolerate and thrive across a broad spectrum of temperatures. In contrast, stenothermals are organisms restricted to a narrow temperature range. The capacity for thermal tolerance in different species significantly determines their geographical spread.
In simple words: Eurythermal organisms are found in many places on Earth because they can live in a wide range of temperatures, unlike stenothermal organisms that can only survive in a narrow temperature range.

🎯 Exam Tip: Clearly define eurythermal and stenothermal, then directly link the ability to tolerate a broad temperature range (eurythermal) to a wider geographical distribution.

Question 32. Certain species of wasps are seen to frequently visit flowering fig trees. What type of interaction is seen between them and why?
Answer: The interaction observed between certain wasp species and flowering fig trees is mutualism. This relationship is mutually beneficial: the female wasp uses the fig fruit not only as a site for laying her eggs (oviposition) but also utilizes the developing seeds within the fruit to nourish her larvae. In return, the fig tree benefits from the wasp facilitating its pollination process.
In simple words: Wasps and fig trees have a mutualistic relationship because the wasp lays eggs and feeds its young inside the fig, while simultaneously pollinating the fig, benefiting both organisms.

🎯 Exam Tip: Identify mutualism by showing how both interacting species (wasp and fig tree) gain a clear benefit from the relationship.