Samacheer Kalvi Class 12 Bio Zoology Solutions Chapter 10 Organisms and Population

 

Question 1. All populations in a given physical area are defined as
(a) Biome
(b) Ecosystem
(c) Territory
(d) Biotic factors
Answer: (a) Biome
In simple words: A biome is a large area with a certain type of environment, and all the living things in it make up its populations. These populations are defined by the specific biome they live in.

🎯 Exam Tip: Remember that a biome is a large ecological area characterized by its climate, plants, and animals, encompassing many populations.

 

Question 2. Organisms which can survive a wide range of temperature are called
(a) Ectotherms
(b) Eurytherms
(c) Endotherms
(d) Stenotherms
Answer: (b) Eurytherms
In simple words: Eurytherms are creatures that can live comfortably in places where the temperature changes a lot. This means they are very adaptable to different heat levels.

🎯 Exam Tip: Distinguish between 'eurythermal' (wide range) and 'stenothermal' (narrow range) species based on their temperature tolerance.

 

Question 3. The interaction in nature, where one gets benefit on the expense of other is
(a) Predation
(b) Mutualism
(c) Amensalism
(d) Commensalism
Answer: (d) Commensalism
In simple words: In commensalism, one creature gets help or food, but the other creature is neither helped nor harmed. It's a one-sided benefit without causing any trouble to the other party.

🎯 Exam Tip: Understand the different types of ecological interactions: predation (harm, benefit), mutualism (benefit, benefit), amensalism (harm, no effect), and commensalism (benefit, no effect).

 

Question 4. Predation and parasitism are which type of interactions?
(a) (+,+)
(b) (-, -)
(c) (+, -)
Answer: (c) (+, -)
In simple words: In both predation and parasitism, one animal benefits (gets food or resources), and the other animal is harmed. This is why we use (+, -) to show this relationship.

🎯 Exam Tip: Remember that in the (+, -) interaction, the plus sign indicates benefit for one species, and the minus sign indicates harm for the other.

 

Question 5. Competition between species leads to
(a) Extinction
(b) Mutation
(c) Amensalism
(d) Symbiosis
Answer: (a) Extinction
In simple words: When different kinds of living things fight over the same limited resources, like food or space, it can make some of them disappear completely. This struggle for survival can sadly lead to their extinction.

🎯 Exam Tip: Competition is a powerful ecological force; intense competition can reduce population numbers and, in severe cases, cause local or global extinction of a species.

 

Question 6. Which of the following is an r-species?
(a) Human
(b) Insects
(c) Rhinoceros
(d) Whale
Answer: (b) Insects
In simple words: r-species, like insects, have many babies quickly and don't care much for them, hoping many will survive by chance. They usually live in places where resources might be scarce and unpredictable.

🎯 Exam Tip: r-selected species (like insects) are characterized by high growth rates, many small offspring, and short lifespans, thriving in unstable environments.

 

Question 7. Match the following and choose the correct combination from the options given below.

(a) A – 4, B – 5, C – 2, D – 3, Е – 1
(b) A – 3, B – 1, C – 4, D – 2, Е – 5
(c) A – 2, B -3, C – I,D – 5, E-4
(d) A – 5, B – 4, C – 2, D – 3, Е – 1
Answer: (a) A – 4, B – 5, C – 2, D – 3, Е – 1
In simple words: Mutualism is when both benefit, like a sea anemone and hermit crab. Commensalism is when one benefits and the other is not harmed, like barnacles on a whale. Parasitism is when one benefits and the other is harmed, like a roundworm in a person. Competition is when both are harmed by fighting for resources, like birds and squirrels. Predation is when one kills and eats the other, like a lion eating a deer.

🎯 Exam Tip: Thoroughly understand the definitions and classic examples for each type of ecological interaction to match them correctly.

 

Question 8. The figure given below is a diagrammatic representation of response of organisms to abiotic factors. What do A, B and C represent respectively.

(a) Conformer, Regulator, Partial Regulator
(b) Regulator, Partial Regulator, Conformer
(c) Partial Regulator, Regulator, Conformer
(d) Regulator, Conformer, Partial Regulator
Answer: (a) Conformer, Regulator, Partial Regulator
In simple words: This graph shows how living things react to changes in their surroundings. A conformer's inside conditions change along with the outside. A regulator keeps its inside conditions steady no matter what happens outside. A partial regulator tries to keep things steady for a while, then lets its inside conditions change.

🎯 Exam Tip: When analyzing such graphs, relate the shape of the curve to the organism's ability to maintain its internal environment (homeostasis) despite external fluctuations.

 

Question 9. The relationship between sucker fish and shark is
(a) Competition
(b) Commensalism
(c) Predation
(d) Parasitism
Answer: (b) Commensalism
In simple words: Sucker fish travel with sharks and eat leftover food, getting a free ride and meals. The shark doesn't get anything from this, and it also doesn't get hurt.

🎯 Exam Tip: Remember that commensalism is a relationship where one organism benefits, and the other is neither helped nor harmed.

 

Question 10. What type of human population is represented by the following age pyramid?

(a) Vanishing population
(b) Stable population
(c) Declining population
(d) Expanding population
Answer: (b) Stable population
In simple words: Age pyramids show how many people are in different age groups in a population. A stable population pyramid has a roughly equal number of young and middle-aged people, showing a balanced birth and death rate.

🎯 Exam Tip: Identify stable populations by their bell-shaped age pyramids, where pre-reproductive and reproductive age groups are relatively balanced, not expanding or contracting rapidly.

 

Question 11. Which of the following is correct for r-selected species?
(a) large number of progeny with small size
(b) large number of progeny with large size
(c) small number of progeny with small size
(d) small number of progeny with large size
Answer: (a) large number of progeny with small size
In simple words: r-selected species usually have many offspring that are small. They put a lot of energy into having many babies, but not much into caring for each one. This helps them quickly increase their numbers when conditions are good.

🎯 Exam Tip: The key traits of r-selected species include producing many small offspring with little parental care, leading to rapid population growth in unstable environments.

 

Question 12. Animals that can move from fresh water to sea called as
(a) Stenothermal
(b) Eurythermal
(c) Catadromous
(d) Anadromous
Answer: (c) Catadromous
In simple words: Catadromous animals, like some eels, are born in the sea, then live most of their lives in fresh water, and finally return to the sea to lay their eggs. It's like having a reverse migration journey compared to salmon.

🎯 Exam Tip: Distinguish between anadromous (sea to fresh for breeding) and catadromous (fresh to sea for breeding) migratory patterns in fish.

 

Question 13. Some organisms are able to maintain homeostasis by physical means
(a) Conform
(b) Regulate
(c) Migrate
(d) Suspend
Answer: (b) Regulate
In simple words: Regulating means that an organism can keep its internal body conditions steady, like temperature or water balance, even when the outside world changes. This helps them stay healthy.

🎯 Exam Tip: Homeostasis refers to the ability of an organism to maintain stable internal conditions; 'regulation' actively achieves this, while 'conformation' means internal conditions match external ones.

 

Question 14. What is a Habitat?
Answer: A habitat is like the home address of an organism, a specific place where it lives. In this habitat, organisms interact with each other and are part of food chains and webs, showing how they get food and energy.
In simple words: A habitat is the natural home of a plant or animal. It's where they find food, shelter, and everything they need to live.

🎯 Exam Tip: Clearly define habitat as the physical place an organism lives, emphasizing its role in providing resources and facilitating interactions.

 

Question 15. Define ecological niche.
Answer: An ecological niche describes the complete role and position of an organism in its environment. This includes what it eats, where it lives, and how it interacts with other species. It's essentially the organism's unique job and address in the ecosystem.
In simple words: An ecological niche is an organism's special role in its environment. It's like its job, including what it eats and where it lives.

🎯 Exam Tip: Differentiate between habitat (where an organism lives) and niche (what an organism does and its role in the ecosystem).

 

Question 16. What is Acclimatisation? Explain with example.
Answer: Acclimatization is when animals change how they react to stress from the environment over a short time. For example, people who move from plains to high mountains start making more red blood cells within a few days. This helps them get enough oxygen even with less air pressure at high altitudes.
In simple words: Acclimatization is when living things adjust their bodies to new surroundings over a short period. It helps them deal with new stresses like different temperatures or less oxygen.

🎯 Exam Tip: Highlight that acclimatization is a physiological adjustment to changing environmental conditions, typically reversible and occurring over an individual's lifetime, unlike adaptation, which is genetic and occurs over generations.

 

Question 17. What is Pedogenesis?
Answer: Pedogenesis is the natural process through which soil is formed. It involves breaking down rocks into smaller pieces, which then mix with organic matter, leading to the creation of young soil.
In simple words: Pedogenesis is the way soil is made from rocks and other things over time.

🎯 Exam Tip: Remember pedogenesis as the process of soil formation, linking it to weathering and the breakdown of parent rock material.

 

Question 18. What is Stress?
Answer: Stress is any environmental factor that causes a harmful change in a living system. These factors can potentially cause injury or damage to the biological processes of an organism.
In simple words: Stress in nature means anything in the environment that can hurt a living thing or make it sick.

🎯 Exam Tip: Define stress in an ecological context as an environmental factor that negatively impacts an organism's normal functions or survival.

 

Question 19. What is soil permeability?
Answer: Soil permeability is a special feature of soil that allows water to move through its tiny holes. How easily water passes depends on the size of these holes, and soil's ability to hold water works in the opposite way to its porosity, meaning more porous soil allows faster water movement but might hold less if not balanced.
In simple words: Soil permeability is how well water can pass through the soil. Soil with bigger gaps lets water through faster.

🎯 Exam Tip: Understand that soil permeability is crucial for water drainage and availability to plants, and it is directly related to soil pore size.

 

Question 20. Differentiate between Eurytherms and Stenotherms.

In simple words: Eurytherms can live in many different temperatures, like humans. Stenotherms can only live in a small, steady temperature range, like most fish.

🎯 Exam Tip: Focus on the 'wide' vs. 'narrow' range of temperature tolerance when distinguishing between eurythermal and stenothermal organisms.

 

Question 21. Explain hibernation and aestivation with examples.
Answer: Sometimes, if living things cannot move to a better place, they become inactive to escape bad weather. This is common in bears, which go into a deep sleep called hibernation during winter to avoid the cold. Some snails and fish go into aestivation to avoid problems like too much heat and dryness in summer. Both are ways to survive difficult conditions by slowing down body functions.
In simple words: Hibernation is a winter sleep to avoid cold, like bears. Aestivation is a summer sleep to avoid heat and dryness, like some snails. Both help animals survive bad weather by becoming inactive.

🎯 Exam Tip: Clearly state that both hibernation and aestivation are forms of dormancy, but specify that hibernation is for cold/winter, and aestivation is for heat/drought in summer.

 

Question 22. Give the diagnostic characters features of a Biome.
Answer: Here are the main features that help identify a biome:

• Location and geographical position (its latitude and longitude).
• The climate and physical-chemical environment, like rainfall and soil type.
• The main types of plants and animals that live there.
• The borders between biomes are usually not sharp; there are often transition zones where different biomes meet.

In simple words: Biomes are known by their location, climate, the plants and animals living there, and their borders which are usually not very clear.

🎯 Exam Tip: When describing biome characteristics, always include geographical factors, climate, and the dominant forms of life (flora and fauna).

 

Question 23. Classify the aquatic biomes of Earth.
Answer: The aquatic biomes of Earth can be divided into a few main types:

• Freshwater: These include still bodies of water like lakes and ponds, and flowing water such as rivers.
• Brackish water: This is a mix of fresh and salt water, found in estuaries and wetlands.
• Marine: This covers vast ocean areas, including coral reefs, pelagic zones (open ocean), and abyssal zones (deep sea).

In simple words: Earth's water biomes are grouped into three types: freshwater (like rivers), brackish water (where fresh and salt water mix), and marine (like oceans and coral reefs).

🎯 Exam Tip: Ensure you include specific examples for each aquatic biome category to demonstrate a comprehensive understanding.

 

Question 24. What are the ways by which organisms respond to abiotic factors?
Answer: Organisms have several ways to deal with non-living environmental factors, such as temperature or water availability. These responses include regulating their internal conditions, conforming to external changes, migrating to new areas, or suspending their life processes, among others. Each method helps them survive harsh conditions.
In simple words: Living things react to their environment by controlling their bodies, changing with the environment, moving to new places, or pausing their activities.

🎯 Exam Tip: List and briefly explain the four main responses to abiotic factors: regulate, conform, migrate, and suspend (or hibernate/aestivate).

 

Question 25. Classify the adaptive traits found in organisms.
Answer: Living things show different types of special features that help them survive in their environment. These special traits can be structural, meaning changes in their body parts; behavioral, meaning changes in how they act; or physiological, meaning changes in how their body functions internally. All these traits help them adapt better.
In simple words: Organisms adapt in three main ways: by changing their body structure, by changing their behavior, or by changing how their body works inside.

🎯 Exam Tip: Remember the three broad categories of adaptations: structural (e.g., camouflage), behavioral (e.g., migration), and physiological (e.g., changes in metabolism).

 

Question 26. Differentiate Natality and Mortality?

In simple words: Natality is about how many new babies are born in a group over a certain time, showing population growth. Mortality is about how many individuals die in that group over the same time, showing population decrease.

🎯 Exam Tip: Remember that natality increases population size, while mortality decreases it; both are expressed as rates over a specific time period.

 

Question 27. Differentiate J and S shaped curve.

In simple words: A J-shaped curve shows fast growth that suddenly stops. An S-shaped curve shows growth that slows down over time as resources become limited, eventually becoming stable.

🎯 Exam Tip: Associate J-shaped growth with unlimited resources and rapid, unchecked growth followed by a crash, while S-shaped growth reflects growth limited by carrying capacity and environmental resistance.

 

Question 28. Give an account of population regulation.
Answer: All animal populations naturally tend to grow in number, but this growth does not go on forever. Once the environment can no longer support more individuals (its carrying capacity), the population size either stays the same or changes up and down depending on what's happening in the environment. Many different things control this, which are either extrinsic (outside factors) or intrinsic (inside factors).

• Density independent – Extrinsic factors: These include things like how much space is available, shelter, weather conditions, and food supply.
• Density dependent – Intrinsic factors: These are internal factors like competition for resources, animals hunting each other (predation), animals moving in (immigration) or out (emigration), and diseases.

In simple words: Population regulation means that many things stop animal numbers from growing too big. This includes outside factors like weather and food, and inside factors like how many animals compete or get sick.

🎯 Exam Tip: When discussing population regulation, always include both density-dependent factors (e.g., competition, predation) and density-independent factors (e.g., natural disasters, climate) that limit population growth.

 

Question 29. What is ecological density, crude density and population density?

In simple words: Population density is how many individuals are in a certain area. Crude density is about total space. Ecological density is about the space they actually use.

🎯 Exam Tip: Differentiate these terms by focusing on whether the 'area' or 'volume' refers to the total space or only the habitable, utilized space.

 

Question 30. Give an account of the properties of soil.
Answer: Soil has several important properties that affect life. The soil's **texture** is determined by the size of its particles, such as sand, silt, and clay, which influences how it feels. **Porosity** refers to the empty spaces between soil particles, allowing air and water to exist. The percentage of soil volume taken up by these spaces is called soil porosity. **Permeability** is how easily water moves through these pore spaces; it depends directly on the size of the pores. Soil's ability to hold water is also affected, being lower in very porous soil. **Soil temperature** comes from the sun, decaying matter, and Earth's interior, and it impacts seed growth, root development, and the activity of tiny organisms in the soil. Finally, **soil water** is vital not just as a solvent and transporter of nutrients, but also for maintaining soil structure and keeping soil particles together, making it a suitable home for plants and animals.
In simple words: Soil has texture (how fine or coarse it is), porosity (how much empty space it has), and permeability (how easily water flows through it). Its temperature and the water it holds are also important for plants and animals living in it.

🎯 Exam Tip: When describing soil properties, always include texture, porosity, permeability, temperature, and water content, and briefly explain their ecological significance.

 

Question 31. Differentiate between Tundra and Taiga Biomes.

In simple words: Tundra is a cold, treeless plain with little rain, while Taiga is a forest of cone-bearing trees with more rainfall.

🎯 Exam Tip: Key differentiators for Tundra and Taiga are the presence of trees (Taiga has conifers, Tundra does not) and the amount of annual precipitation.

 

Question 32. List the adaptations seen in terrestrial animals.
Answer: Terrestrial animals show various adaptations to live on land:

• Earthworms and land planarians produce a slimy coating to stay moist, which helps them burrow, coil, and breathe.
• Arthropods have a tough outer covering and special breathing tubes (tracheal systems) to protect their respiratory surfaces from drying out.
• Vertebrate skin has many cell layers and protective surfaces to stop water loss.
• Some animals get all the water they need from their food, which partly replaces water lost through waste.
• Birds build nests and breed before the rainy season when food is plentiful, avoiding drought periods when they rarely reproduce.
• Camels can control their body water very well for cooling through their skin and breathing, and they produce very strong urine. They can also handle losing up to 25% of their body water without getting sick.

In simple words: Land animals adapt by having waterproof skin or coverings, special breathing systems, getting water from food, and controlling water loss. Some also change when they breed or go to sleep to survive bad weather.

🎯 Exam Tip: Focus on adaptations related to water conservation (e.g., skin, excretion), temperature regulation, and reproduction cycles in response to terrestrial challenges.

 

Question 33. Describe Population Age Distribution.
Answer: Population age distribution refers to how many individuals are in different age groups within a population. These groups are usually pre-reproductive (young), reproductive (adults), and post-reproductive (old). This distribution tells us about the population's ability to have babies at any given time and is a good sign of whether the population is growing, shrinking, or staying the same. A quickly growing population will have more young individuals. A stable population will have an even distribution across different age classes. A declining population tends to have a larger proportion of older individuals.
In simple words: Population age distribution shows how many young, adult, and old individuals are in a group. This helps us understand if the group is growing, shrinking, or staying steady.

🎯 Exam Tip: Illustrate age distribution using age pyramids (expanding, stable, declining) to clearly show the proportion of individuals in pre-reproductive, reproductive, and post-reproductive age groups.

 

Question 34. Describe Growth Models/Curves.
Answer: Populations show special patterns of growth, which can be plotted as J-shaped or S-shaped (also called Sigmoid) growth curves. These curves help us understand how populations change over time.

In simple words: J-shaped growth means quick growth then a sudden stop, while S-shaped growth shows a slow start, fast middle, and then levels off. Both describe how populations change in number.

🎯 Exam Tip: When describing growth curves, clearly mention the phases of each curve (lag, exponential, stationary) and provide relevant examples to score full marks.

12th Bio Zoology Guide Organisms and Population Additional Important Questions and Answers

12th Bio Zoology Guide Organisms and Population One Mark Questions and Answers

 

Question 1. The study dealing with animal behaviour is called as
(a) Euthenics
(b) Ethology
(c) Ecology
(d) Pedogenesis
Answer: (b) Ethology
In simple words: Ethology is the scientific study of how animals behave, especially in their natural environments. It helps us understand why animals act the way they do.

🎯 Exam Tip: Remember that 'ethology' focuses on natural behavior, differentiating it from other biological studies.

 

Question 2. Identify the proper sequence in increasing order of population
(a) Species \( \rightarrow \) Population \( \rightarrow \) Community \( \rightarrow \) biome
(b) Population \( \rightarrow \) Community \( \rightarrow \) Species \( \rightarrow \) biome
(c) Biome \( \rightarrow \) Species \( \rightarrow \) Community \( \rightarrow \) Population
(d) Community \( \rightarrow \) Population \( \rightarrow \) Biome \( \rightarrow \) Species
Answer: (a) Species \( \rightarrow \) Population \( \rightarrow \) Community \( \rightarrow \) biome
In simple words: The correct order from smallest to largest group is: one type of living thing (species), then all of those types in an area (population), then different types living together (community), and finally a very large natural area (biome).

🎯 Exam Tip: Understand the hierarchy of ecological organization: individual, population, community, ecosystem, biome, biosphere.

 

Question 3. Functional status of an organism in its community is
(a) Biome
(b) Niche
(c) Species
(d) Population
Answer: (b) Niche
In simple words: An organism's niche describes its specific role, job, and place within its community. It includes what it eats, where it lives, and how it interacts with others.

🎯 Exam Tip: Distinguish between habitat (where an organism lives) and niche (its role and all interactions within that habitat).

 

Question 4. Pick out the eurythermal organism
(a) Fish
(b) Frog
(c) Tiger
(d) Lizards
Answer: (c) Tiger
In simple words: A eurythermal organism can live in a wide range of temperatures. Tigers can adapt to different climates, from cold to warm.

🎯 Exam Tip: Remember that eurythermal species have a broad tolerance for temperature changes, unlike stenothermal species which tolerate only narrow ranges.

 

Question 5. Locomotary speed of an organism changes due to light. This phenomenon is referred as
(a) Photonasty
(b) Photokinesis
(c) Phototropism
(d) Phototaxis
Answer: (b) Photokinesis
In simple words: Photokinesis is when an animal changes how fast it moves or how often it turns because of changes in light intensity. It's an undirected movement related to light.

🎯 Exam Tip: Photokinesis is about the *rate* or *frequency* of movement changing with light intensity, while phototaxis is about *direction* towards or away from light.

 

Question 6. Identify the incorrect statement
(a) Water is a universal solvent
(b) Water has less surface tension
(c) Water is heavier than air
(d) When freezes water contracts
Answer: (d) When freezes water contracts
In simple words: The incorrect statement is that water contracts when it freezes. Actually, water expands when it freezes, which is why ice floats.

🎯 Exam Tip: Knowing the unique properties of water, like its expansion upon freezing and high surface tension, is crucial for understanding biological systems.

 

Question 7. The soil zone is known as
(a) Pedosphere
(b) Atmosphere
(c) Hydrosphere
(d) Stratosphere
Answer: (a) Pedosphere
In simple words: The pedosphere is the Earth's soil layer, which is where rock, water, air, and living things meet. It is a vital part of the Earth system where life thrives.

🎯 Exam Tip: Distinguish between the different "spheres" of the Earth: atmosphere (air), hydrosphere (water), lithosphere (rock), and pedosphere (soil).

 

Question 8. Assertion (A): Snake is a stenotherm. Reason (R): Organism can tolerate narrow temperature fluctuations.
(a) Both A and R are correct R explain A
(b) A is correct R is incorrect
(c) R does not explain A
(d) Both A and R are incorrect
Answer: (a) Both A and R are correct R explain A
In simple words: Both the statement that a snake is a stenotherm and the reason that stenotherms tolerate only small temperature changes are correct, and the reason explains why snakes are stenotherms. Snakes need stable temperatures to survive.

🎯 Exam Tip: For assertion-reason questions, first check if both statements are true, then see if the reason directly explains the assertion.

 

Question 9. Assertion (A): Diapause is carried out to overcome abiotic stress. Reason (R): Animals become inactive during winter.
(a) Both A and R are correct R explain A
(b) A is correct R is incorrect
(c) R does not explain A
(d) Both A and R are incorrect
Answer: (b) A is correct R is incorrect
In simple words: Diapause is a real way animals cope with harsh non-living conditions (abiotic stress). However, animals becoming inactive in winter is called hibernation, not diapause, so the reason is incorrect.

🎯 Exam Tip: Clearly differentiate between diapause (a suspended development state) and hibernation (winter inactivity) or aestivation (summer inactivity).

 

Question 10. Assertion (A): Movement of organism from one place to another and back is called migration. Reason (R): Eel is an example for aradromous migration.
(a) Both A and R are correct R explain A
(b) A is correct R is incorrect
(c) R does not explain A
(d) Both A and R are incorrect
Answer: (d) Both A and R are incorrect
In simple words: The first statement defines migration correctly. However, the second statement is incorrect because eels are known for catadromous migration (moving from freshwater to sea to breed), not anadromous migration.

🎯 Exam Tip: Understand the difference between anadromous (sea to freshwater for breeding) and catadromous (freshwater to sea for breeding) migration, using classic examples like salmon and eels.

 

Question 11. Which is not a feature of Tundra?
(a) Large population oscillation
(b) Short season of growth and reproduction
(c) Low biotic diversity
(d) Extremely hot climate
Answer: (d) Extremely hot climate
In simple words: The tundra is a very cold biome. Therefore, an extremely hot climate is not a characteristic of the tundra.

🎯 Exam Tip: Associate key climatic features (like temperature extremes) with specific biomes for accurate answers.

 

Question 12. Pick out the correct statement regarding K-selected species
(a) Produce many offsprings
(b) Only few reach adulthood
(c) Unstable environment
(d) Long life expectancy
Answer: (d) Long life expectancy
In simple words: K-selected species usually have long lives and invest a lot in a few offspring. This strategy helps them survive in stable environments.

🎯 Exam Tip: Remember that K-selected species typically live in stable environments, have few offspring, provide parental care, and have longer lifespans, contrasting with r-selected species.

 

Question 13. Maximum reproductive capacity of an organism under favourable condition is referred as
(a) Carrying capacity
(b) Biotic potential
(c) Natality
(d) Fecundity
Answer: (b) Biotic potential
In simple words: Biotic potential refers to the highest possible rate at which an organism can reproduce if conditions are perfect and there are no limits. It shows the species' maximum ability to multiply.

🎯 Exam Tip: Differentiate biotic potential (maximum possible growth) from carrying capacity (the maximum population size an environment can sustain).

 

Question 14. During breeding season, Salmon migrates from sea to fresh water. This is an example for.
Answer: Anadromous migration. Salmon fish are a classic example of this type of migration, where they travel against the current to breed.
In simple words: Salmon fish moving from the sea to freshwater to lay eggs is called anadromous migration.

🎯 Exam Tip: Be sure to use the specific term 'anadromous' for migration from sea to freshwater for breeding, and provide relevant examples.

 

Question 15. Exponential growth shows growth patterns.
Answer: J-shaped. This type of growth occurs when resources are unlimited, leading to a rapid increase in population.
In simple words: When a population grows very fast because there are no limits, it follows a J-shaped pattern.

🎯 Exam Tip: Remember that J-shaped growth implies ideal conditions with no limiting factors, leading to explosive population increase.

 

Question 16. Interaction between Ascaris in human gut is an example for.
Answer: Parasitism. In this relationship, the Ascaris worm benefits by living in the human gut, while the human (host) is harmed.
In simple words: Ascaris living in a human's gut is an example of parasitism, where the worm lives off the human and causes harm.

🎯 Exam Tip: Clearly define parasitism as one organism benefiting at the expense of another and provide common examples like Ascaris.

 

Question 17. If both the species of an interaction is benefitted then it is said to be.
Answer: Mutualism. This is a symbiotic relationship where both organisms involved gain a benefit from each other.
In simple words: When two different living things help each other, it is called mutualism.

🎯 Exam Tip: Define mutualism as a win-win interaction and contrast it with other types of species interactions like commensalism or parasitism.

 

Question 18. Match the following

(a) a – ii, b - i, c – iv, d – iii
(b) a – iii, b – ii, c – i, d – iv
(c) a – iv, b – iii, c – ii, d – i
(d) a – i, b -iv, c – iii, d – ii
Answer: (a) a – ii, b – i, c – iv, d – iii
In simple words: This match correctly pairs stenotherms with lizards (narrow temperature range), eurytherms with humans (wide temperature range), phototaxis with earthworms (movement in response to light), and anadromous migration with salmon (moving from sea to freshwater to breed).

🎯 Exam Tip: For matching questions, it's often helpful to match the most certain pairs first and then deduce the remaining ones.

 

Question 19. As altitude increases
(a) O2 density increases
(b) Precipitation decreases
(c) Temperature increases
(d) Snowing decreases
Answer: (b) Precipitation decreases
In simple words: As you go higher up a mountain, the amount of rain or snow generally decreases. This affects the types of plants and animals that can live there.

🎯 Exam Tip: Remember that higher altitudes usually mean lower temperatures, lower oxygen, and often less precipitation, creating unique ecological zones.

12th Bio Zoology Guide Organisms and Population Two Marks Questions and Answers

 

Question 1. What is ecosphere?
Answer: The ecosphere is often called the largest and most self-sufficient biological system. It includes all living organisms on Earth and their interactions with the physical environment. This interaction helps to control how these organisms are spread, how many there are, how they grow, and how they change over time.
In simple words: The ecosphere is like a giant, complete life system on Earth, including all living things and their surroundings.

🎯 Exam Tip: Define ecosphere as the global sum of all ecosystems, emphasizing its self-regulating nature and the interaction between living and non-living components.

 

Question 2. List out the adaptation of fish to survive in aquatic environment.
Answer: Fish have several adaptations to survive in water. They have fins for moving around and a streamlined body shape (aerodynamic) to swim easily. They also have a special lateral line system for sensing things in the water, gills for breathing underwater, and air sacs to help them float or sink.
In simple words: Fish have fins to swim, a smooth body, gills to breathe, and air sacs to float easily in water.

🎯 Exam Tip: When listing adaptations, group them by function (e.g., locomotion, respiration, buoyancy) for a clear and comprehensive answer.

 

Question 3. Define niche.
Answer: An organism's niche can be described as its complete role and function within its environment. It includes everything an organism needs and does, like its food, habitat, and interactions with other species.
In simple words: An organism's niche is its job and place in its environment.

🎯 Exam Tip: Emphasize that a niche is more than just a place; it's the organism's entire functional position, including all its interactions.

 

Question 4. Name few abiotic factors that influence organisms in an environment.
Answer: Some non-living factors that affect organisms in an environment include temperature, light, water, soil, humidity, and altitude. These factors play a crucial role in shaping where organisms can live and how they survive.
In simple words: Non-living factors like heat, light, water, and soil affect where living things can grow.

🎯 Exam Tip: Provide a diverse list of abiotic factors (e.g., physical, chemical) to show a broad understanding of environmental influences.

 

Question 5. State Allen's rule and Bergmann's rule.
Answer: Allen's rule states that warm-blooded animals living in cold places tend to have shorter limbs, ears, and other body parts that stick out. This helps them lose less body heat. Bergmann's rule states that birds and mammals tend to have larger body sizes in colder regions compared to warmer ones. A larger body size has a smaller surface area to volume ratio, which helps conserve heat.
In simple words: Allen's rule says animals in cold places have shorter ears and limbs. Bergmann's rule says animals in cold places are usually bigger.

🎯 Exam Tip: Clearly state both rules and briefly explain the underlying biological principle (heat conservation) for each.

 

Question 6. What does Jordon's rule state?
Answer: Jordon's rule states that in some aquatic environments, there's an inverse relationship between water temperature and fish meristic characters. This means that if the water temperature is lower, fish tend to have more vertebrae. This adaptation helps fish thrive in different water temperatures.
In simple words: Jordon's rule says that colder water often makes fish have more backbone bones (vertebrae).

🎯 Exam Tip: Ensure you mention both elements of Jordon's rule: inverse relationship and fish meristic characters (like vertebrae count).

 

Question 7. State Van't Hoff's rule.
Answer: Van't Hoff's rule states that for every 10°C increase in temperature, the rate of metabolic activity in an organism doubles. Conversely, for every 10°C decrease, the metabolic rate is halved. This highlights the strong influence of temperature on biological processes.
In simple words: Van't Hoff's rule says that for every 10°C hotter it gets, living things work twice as fast; for every 10°C colder, they work half as fast.

🎯 Exam Tip: Clearly state the direct relationship between temperature change (in 10°C increments) and the doubling/halving of metabolic rates.

 

Question 8. What is Q10 value? How it is calculated?
Answer: The Q10 value, also known as the temperature coefficient, shows how much the rate of a reaction changes with temperature. It is calculated by dividing the reaction rate at a certain temperature (X°C) by the reaction rate at a temperature 10°C lower (X-10°C). This helps scientists understand how sensitive biological processes are to temperature changes.
In simple words: Q10 tells us how much faster a reaction goes when the temperature rises by 10°C. We find it by dividing the reaction speed at a temperature by its speed at 10°C lower.

🎯 Exam Tip: State the Q10 value's definition and its simple formula clearly: Rate at X°C / Rate at (X-10°C).

 

Question 9. Differentiate between Eurytherms and Stenotherm
Answer:

In simple words: Eurytherms can live in many different temperatures, while stenotherms need very specific, unchanging temperatures to survive.

🎯 Exam Tip: When differentiating, clearly state the definition for each term and provide a distinct example for both Eurytherms and Stenotherms.

 

Question 10. Snakes are stenotherms. Why?
Answer: Snakes are classified as stenotherms because they can only tolerate a narrow range of temperature fluctuations. This means they cannot survive large changes in temperature, often requiring specific environmental conditions to thrive.
In simple words: Snakes can only live in a small range of temperatures, so they are called stenotherms.

🎯 Exam Tip: Link the term 'stenotherm' directly to the organism's ability to tolerate only narrow temperature variations.

 

Question 11. Define phototaxis.
Answer: Phototaxis is the movement of a motile organism or cell either towards or away from a light source. For instance, moths show positive phototaxis by moving towards light, while earthworms show negative phototaxis by moving away from it.
In simple words: Phototaxis means a living thing moves towards or away from light.

🎯 Exam Tip: Specify that phototaxis is a *directional* movement in response to light, and give examples for both positive and negative responses.

 

Question 12. What is photokinesis?
Answer: Photokinesis is when the speed of movement (locomotion) or how often a motile organism or cell changes direction (frequency of turning) is altered in response to changes in light intensity. It involves random, undirected movement that is influenced by light levels.
In simple words: Photokinesis is when an organism changes how fast it moves or how much it turns based on how bright the light is.

🎯 Exam Tip: Differentiate photokinesis (change in speed/frequency of movement) from phototaxis (directional movement) in relation to light.

 

Question 13. What is pedosphere and soil profile?
Answer: The pedosphere refers to the outermost layer of the Earth, which is made up of soil. A soil profile is the vertical section of soil that shows its different horizontal layers, called horizons, which form over time. These layers show how soil develops and changes.
In simple words: The pedosphere is Earth's soil layer, and a soil profile shows the different layers of soil from top to bottom.

🎯 Exam Tip: Clearly define both terms, highlighting the 'outer soil zone' for pedosphere and 'horizontal layers' for soil profile.

 

Question 14. Point out the major functions of soil.
Answer: Soil has several major functions:

• It serves as a medium for plant growth, providing support and nutrients.
• It acts as a means for water storage and purification, filtering water as it passes through.
• It modifies Earth's atmosphere by exchanging gases and influencing climate.
• It provides a habitat for many organisms, which in turn help to modify the soil itself.

In simple words: Soil helps plants grow, stores and cleans water, affects the air, and is home to many small living things.

🎯 Exam Tip: When listing functions, provide concise explanations for each point to demonstrate understanding, rather than just naming them.

 

Question 15. What is humidity?
Answer: Humidity is the amount of invisible water vapor present in the atmosphere. It is typically measured and expressed as absolute humidity, relative humidity, or specific humidity. Understanding humidity is important because it impacts weather patterns and the survival of organisms.
In simple words: Humidity is simply how much water vapor is in the air around us.

🎯 Exam Tip: When defining humidity, mention it as water vapor in the atmosphere and briefly list the ways it's measured.

 

Question 16. What is a Biome?
Answer: A biome is a large area on Earth that has similar plants, animals, and climate conditions. Biomes are essential for life on Earth and are defined by factors like their soil, climate, and the types of plants and animals found there. Each biome has unique living communities that have adapted to its specific physical and chemical environment.
In simple words: A biome is a big natural area on Earth with its own kind of weather, plants, and animals.

🎯 Exam Tip: Emphasize that biomes are large-scale ecological units characterized by similar climate, flora, and fauna, not just geographic location.

 

Question 17. Enumerate the characters of a Biome.
Answer: The main characteristics of a biome include:

• Its location and geographical position, defined by latitude and longitude.
• The specific climate and physiochemical environment present.
• The predominant types of plant and animal life that thrive there.
• The fact that boundaries between biomes are usually not very sharp, with transition zones (ecotones) often found between them.

In simple words: Biomes are defined by where they are, their weather, the main plants and animals, and how they gradually change into other biomes.

🎯 Exam Tip: When enumerating, ensure each characteristic is distinct and accurately describes a key feature of biomes.

 

Question 18. Which is the largest biome on Earth? Classify it.
Answer: The aquatic biome is the largest biome on Earth, covering 71% of the biosphere. It can be classified into:
a) Freshwater biome (Lakes, ponds, and rivers)
b) Brackish water biome (Estuaries and Wetlands)
c) Marine biome (Coral reefs, pelagic zones, and abyssal zones)
This vast biome supports a huge diversity of life forms.
In simple words: The ocean and other water bodies make up the biggest biome on Earth. It is divided into freshwater, brackish water, and marine (saltwater) types.

🎯 Exam Tip: Identify the aquatic biome as the largest and correctly categorize its major subdivisions with examples for each.

 

Question 19. Define alpine zone.
Answer: The alpine zone is an ecological region found between the timberline (where trees stop growing due to cold) and the permanent snow zone. In descending order, it includes a sub-snow zone just below the snow, a meadow zone in the middle, and a shrub zone that gradually blends into the timber zone. This zone is characterized by its harsh, cold conditions.
In simple words: The alpine zone is the cold, treeless area on mountains between where trees can grow and where there's always snow.

🎯 Exam Tip: When defining the alpine zone, clearly specify its location relative to the timberline and snow zone, and briefly mention its typical sub-zones.

 

Question 20. What is a forest? Name the major forest biomes.
Answer: A forest is a broad term for areas with a large number of trees. Forests are crucial for the environment, providing habitats and regulating climate. The major forest biomes are:
Tropical forests
Temperate forests
In simple words: A forest is a place with many trees. The main types of forest biomes are tropical and temperate forests.

🎯 Exam Tip: Give a simple definition of a forest and name the two primary forest biome categories for clarity.

 

Question 21. What are the types of tropical forest?
Answer: The types of tropical forests include:
(a) Evergreen rain forest
(b) Seasonal rain forest
(c) Semi evergreen forest
(d) Dry deciduous forest
Each type is characterized by its rainfall patterns and how trees retain their leaves.
In simple words: Tropical forests come in different kinds like evergreen, seasonal, semi-evergreen, and dry deciduous forests.

🎯 Exam Tip: List the different types of tropical forests clearly, recognizing that their classification often depends on rainfall and leaf shedding patterns.

 

Question 22. How the cold deserts are characterized? Give an example.
Answer: Cold deserts are characterized by very cold winters with snowfall and usually high overall precipitation throughout the year, including winter snowfall and occasional summer rain. This creates a challenging environment for life. For example, the Ladakh region in India is a cold desert.
In simple words: Cold deserts have very cold, snowy winters and get a lot of rain or snow throughout the year. Ladakh in India is one example.

🎯 Exam Tip: When describing cold deserts, mention both cold temperatures and the precipitation patterns (snowfall, high overall precipitation) and provide a geographical example.

 

Question 23. Fishes are said to be conformers Justify.
Answer: Fishes are considered conformers because the osmotic concentration of their body fluids changes along with the osmotic concentration of the surrounding water. This means their internal body conditions match their external environment rather than actively regulating them.
In simple words: Fish are conformers because their body's salt-water balance changes to match the water around them.

🎯 Exam Tip: Justify 'conformers' by explaining that the organism's internal environment changes with the external, without active regulation, using osmotic concentration as a key detail.

 

Question 24. When and why do snails go into aestivation?
Answer: Snails go into aestivation during the summer months. They do this to avoid extreme heat and to protect themselves from dessication, which is the loss of water from their bodies. Aestivation is a state of dormancy that helps them survive harsh summer conditions.
In simple words: Snails aestivate in summer to escape heat and prevent drying out.

🎯 Exam Tip: Clearly state *when* (summer) and *why* (avoid heat, dessication) snails aestivate, defining aestivation as a survival strategy.

 

Question 25. How do animals like fishes and bears avoid unfavourable climatic conditions?
Answer: Animals like fishes and bears avoid bad weather conditions by entering a state of inactivity. Fishes undergo aestivation to avoid summer-related problems like heat and dryness. Bears, on the other hand, go into hibernation during winter to cope with cold temperatures and limited food. Both are forms of dormancy to conserve energy.
In simple words: Fish use aestivation to avoid hot, dry summers, while bears use hibernation to survive cold winters.

🎯 Exam Tip: Distinguish between aestivation (summer dormancy) and hibernation (winter dormancy) as different strategies for coping with unfavorable conditions.

 

Question 26. What are cryptic animals? How cryptic adaptation helps them?
Answer: Cryptic animals are those that can camouflage perfectly with their environment, making them very hard to see or detect. This cryptic adaptation helps them in two main ways: either to hide from predators or to sneak up on their prey. Examples include chameleons and stick insects, which blend in seamlessly.
In simple words: Cryptic animals hide by looking exactly like their surroundings. This helps them catch food or avoid being eaten.

🎯 Exam Tip: Define cryptic animals by their ability to camouflage and explain that this adaptation serves both predatory and defensive purposes.

 

Question 27. Explain two behavioral adaptations.
Answer: Two main types of behavioral adaptations are migration and courtship. Migration is when animals move from one place to another, usually to find better food or shelter, or to escape danger. Courtship involves specific actions and displays that animals use to attract a mate and reproduce. Both behaviors help ensure the survival of the species.
In simple words: Migration is when animals move to a new place for food or safety. Courtship is when animals do special things to find a partner to have babies.

🎯 Exam Tip: When explaining behavioral adaptations, choose two distinct examples and describe the purpose and benefit of each behavior clearly.

 

Question 28. Define population.
Answer: A population is any group of organisms of the same species that can breed with each other. They live in a specific area and act as a part of a larger living community. This group shares a common gene pool.
In simple words: A population is a group of the same kind of animals or plants living in one place and able to have babies together.

🎯 Exam Tip: Remember to include the idea of "same species" and "interbreeding" when defining population, as these are key biological concepts.

 

Question 29. What are the attributes of population?
Answer: The main characteristics of a population include its density, the birth rate (natality), the death rate (mortality), how individuals are spread across different ages (age distribution), and how individuals move in and out of the area (dispersion, which includes immigration and emigration). These attributes help scientists understand how a population changes over time.
In simple words: A population has features like how many individuals live in an area, how many are born, how many die, their ages, and if they move in or out.

🎯 Exam Tip: When listing attributes, always define each term briefly to show a deeper understanding of population dynamics.

 

Question 30. Camels are well adapted to xeric conditions, how?
Answer: Camels are good at managing water in dry, desert places. They can control their body temperature to save water through evaporative cooling from their skin and breathing system. They also produce very concentrated urine, which means less water is lost. Because of these adaptations, they can handle losing up to 25% of their body weight through dehydration. Their humps, rich in fat, also provide an energy and water source.
In simple words: Camels handle dry places by saving water with smart cooling, very concentrated urine, and can survive a lot of dehydration.

🎯 Exam Tip: Focus on the specific physiological adaptations (water regulation, concentrated urine, dehydration tolerance) that make camels suited to xeric environments.

 

Question 31. How natality and mortality can be calculated?
Answer: Natality (birth rate) and mortality (death rate) are calculated by looking at the number of births or deaths over a certain period compared to the total population. These calculations help us understand population changes. Here are the formulas:
Birth rate \( (b) = \frac{\text{number of births per unit time}}{\text{average population}} \)
Death rate \( (d) = \frac{\text{number of deaths per unit time}}{\text{average population}} \)
In simple words: You find the birth rate by dividing the number of babies born by the total population. You find the death rate by dividing the number of deaths by the total population.

🎯 Exam Tip: Remember to clearly state "per unit time" when explaining birth and death rates, as these are measures over a specific duration.

 

Question 32. Define biotic potential.
Answer: Biotic potential is the highest possible rate at which a species can reproduce under the best possible environmental conditions. It represents the maximum capacity of an organism to produce offspring if there are no limits from the environment. This theoretical maximum helps us understand a species' potential for growth.
In simple words: Biotic potential is how fast a species can reproduce if everything is perfect, with no problems getting in the way.

🎯 Exam Tip: Emphasize "maximum reproductive capacity" and "optimum environmental conditions" in your definition of biotic potential.

 

Question 33. Which type of species interaction is noticed between a) Cat and Rat (b) Crocodile and birds
Answer:
(a) Cat and Rat: Predation
(b) Crocodile and birds: Mutualism
In predation, one organism hunts and kills another for food. In mutualism, both species benefit from the interaction.
In simple words: A cat hunting a rat is predation. A crocodile letting birds clean its teeth is mutualism because both help each other.

🎯 Exam Tip: For interaction questions, identify which organism benefits, which is harmed, or if both benefit, to correctly classify the relationship.

 

Question 34. Define Commensalism.
Answer: Commensalism is a type of relationship between two different species where one species benefits, but the other species is neither helped nor harmed. For example, a sucker fish attaches to a shark; the sucker fish gets food and protection, while the shark is unaffected. This shows a one-sided benefit without causing damage.
In simple words: Commensalism is when one living thing gets help from another, but the other living thing doesn't get anything or lose anything.

🎯 Exam Tip: Always remember that in commensalism, one species benefits (+), and the other is neither helped nor harmed (0). Providing a clear example strengthens your answer.

 

12th Bio Zoology Guide Organisms and Population Three Marks Questions and Answers

 

Question 35. Define the terms (a) guilds (b) ecological equivalents
Answer:
(a) Guilds: Groups of different species that have a similar role and use resources in a similar way within a community are called guilds. They might eat the same type of food or live in the same kind of space. For example, different bird species that all feed on nectar form a guild.
(b) Ecological equivalents: Species that live in different places but occupy the same type of niche and perform similar ecological roles are called ecological equivalents. They have adapted similarly to similar environmental pressures. For instance, kangaroos in Australia and bison in North America both fill the role of large grazing herbivores in their respective ecosystems.
In simple words: Guilds are different species in one place doing the same job, like many types of birds eating seeds. Ecological equivalents are different species in different places that do the same job, like kangaroos and bison both eating grass in different countries.

🎯 Exam Tip: When differentiating, emphasize "within a community" for guilds and "different geographical regions" for ecological equivalents, clearly illustrating the spatial aspect.

 

Question 36. Define temperature. How it impacts the life of an organism?
Answer: Temperature is a measure of how hot or cold something is; it is a key and changing factor in any environment. Temperature affects all forms of life by influencing important activities such as metabolism (how the body works), behavior, reproduction, and overall development, and can even cause death. Organisms have adapted various strategies to cope with temperature variations. For example, cold temperatures can slow down metabolic rates.
In simple words: Temperature is how hot or cold it is, and it deeply affects how living things grow, act, and reproduce.

🎯 Exam Tip: When discussing temperature's impact, link it to fundamental biological processes like metabolism, reproduction, and behavior to show a comprehensive understanding.

 

Question 37. Light is essential for life. Why?
Answer: Light is crucial for life because it affects many biological processes. It influences growth, skin color (pigmentation), migration, and reproduction in organisms. The brightness and duration of light also impact metabolic activity and can even cause changes in genes (mutations) through UV or X-rays. Light is also vital for sight, as seen in how cave-dwelling organisms often have poorly developed or absent eyes. Additionally, light can influence diapause (a resting state) in animals and guide the movement and locomotion of smaller animals. For instance, birds' reproductive glands become more active when there's more light in summer.
In simple words: Light is very important because it helps living things grow, change color, move, reproduce, and even see. It also affects their body's processes.

🎯 Exam Tip: When explaining the importance of light, cover its diverse effects on both physiological processes (metabolism, reproduction) and behavioral aspects (migration, locomotion).

 

Question 38. What is Acclimatization? Explain with example.
Answer: Acclimatization is when animals change their body's response to environmental stress over a short period. It's a natural way for them to adjust to new conditions. For example, when people move from low plains to high altitudes, their bodies produce more red blood cells within a few days. This helps them manage with less oxygen in the air and meet their body's higher oxygen needs. This adjustment allows them to live comfortably in the new environment.
In simple words: Acclimatization is when an animal's body quickly changes to handle a new environment, like people making more red blood cells when they go to mountains.

🎯 Exam Tip: Use a clear, relatable example like people moving to high altitudes to illustrate acclimatization, showing the physiological change and its benefit.

 

Question 39. Enlist the characteristics of Tundra.
Answer: The Tundra biome has several distinct characteristics:

• It has an extremely cold climate.
• There is low biodiversity, meaning fewer types of plants and animals.
• The vegetation structure is simple, with mostly small plants.
• Drainage is limited, leading to waterlogged soil in some areas.
• It has a very short growing and reproduction season for plants and animals.
• Energy and nutrients are stored in dead organic material in the soil.
• Populations of animals often show large fluctuations, meaning their numbers go up and down greatly.

This harsh environment demands unique adaptations from its inhabitants.
In simple words: Tundra is very cold, has few different kinds of life, simple plants, poor water drainage, a short summer, and animal numbers that change a lot.

🎯 Exam Tip: When listing characteristics of a biome, categorize them (climate, biodiversity, vegetation, etc.) for a structured and comprehensive answer.

 

Question 40. Name the major biomes of the Earth.
Answer: The Earth has several major biomes, each defined by its climate and dominant plant and animal life. These include the Tundra biome, the Taiga biome (or Boreal Forest), Grassland biome, Alpine biome, Forest biome, and Desert biome. These large ecological areas cover vast regions and are crucial for global biodiversity.
In simple words: The main biomes on Earth are Tundra, Taiga, Grassland, Alpine, Forest, and Desert.

🎯 Exam Tip: List the major biomes clearly and concisely, focusing on their names rather than detailed descriptions for this type of question.

 

Question 41. Why do organisms migrate? Give example.
Answer: Organisms migrate to temporarily move away from a stressful or difficult habitat to a new, more suitable one until the harsh period is over. This movement helps them find better resources, avoid predators, or find breeding grounds. For example, many birds migrate from Siberia to Vedanthangal in Tamil Nadu to escape the severe winter periods and find warmer places with more food.
In simple words: Animals migrate to escape bad weather or find food, like birds flying south for winter.

🎯 Exam Tip: When explaining migration, always provide both the "why" (avoid stress, find resources) and a concrete example to illustrate the concept.

 

Question 42. Define (a) Diapause (b) Ethology
Answer:
(a) Diapause: Diapause is a special period when some lower animals pause a certain stage of their life cycle. They do this to survive unfavorable conditions, like very cold or very dry seasons. It's like a temporary halt in development or activity.
(b) Ethology: Ethology is the scientific study of animal behavior. It focuses on understanding how animals act in their natural environments, including their communication, mating rituals, and social structures.
In simple words: Diapause is when some animals stop their life cycle for a while to survive bad weather. Ethology is the study of how animals behave in nature.

🎯 Exam Tip: For definitions, ensure clarity and conciseness. For Diapause, mention "suspending a phase of their life cycle" and for Ethology, "study of animal behavior in natural conditions."

 

Question 43. Comment on the J-shaped growth form.
Answer: A J-shaped growth form happens when a population grows very quickly, almost exponentially, and then suddenly stops. This rapid increase occurs because there are plenty of resources and no limiting factors. However, growth stops abruptly when environmental resistance appears, or a sudden limiting factor is introduced, causing a sharp decline or halt. For example, many insect populations grow explosively during the rainy season and then disappear when the season ends. This rapid increase is possible when resources are abundant.
In simple words: J-shaped growth is when a population grows very fast, then suddenly stops when something in the environment limits it.

🎯 Exam Tip: When describing J-shaped growth, highlight the initial exponential rise and the sudden, abrupt halt due to environmental limits, contrasting it with gradual changes.

 

Question 44. Explain sigmoid growth.
Answer: Sigmoid growth, also known as S-shaped growth, describes how some populations, like small mammals, grow. It starts slowly, then speeds up rapidly, and finally slows down gradually as environmental resistance increases. Eventually, the population reaches a stable level, or equilibrium, which is called the carrying capacity. This type of growth curve shows a more realistic population trend in most natural environments. The S-shaped curve is often observed when resources become limited.
In simple words: S-shaped growth means a population grows slowly, then fast, and then slows down again as it reaches a stable number in its environment.

🎯 Exam Tip: For sigmoid growth, explain the three phases (lag, exponential, stationary) and link the slowing growth to increasing environmental resistance and carrying capacity.

 

12th Bio Zoology Guide Organisms and Population Five Marks Questions and Answers

 

Question 45. Enumerate the properties of water.
Answer: Water has several unique properties that make it vital for life and ecosystems:

• It is a primary agent in pedogenesis, which is the process of soil formation.
• Water acts as the medium for many different ecosystems.
• It exists as moisture in the atmosphere and in the outer layers of the Earth, but its distribution is not even globally.
• Water is denser than air and provides greater buoyancy in aquatic environments, helping organisms float at various depths.
• It has a high heat capacity and latent heat, meaning it can store large amounts of heat. This helps oceans and lakes maintain a steady temperature, making the biosphere more stable.
• Water is unique because its solid form (ice) is less dense than its liquid form.
• When water freezes at \( 0^\circ C \), it contracts initially. However, it reaches its maximum density at \( 4^\circ C \). Below this temperature, it expands significantly. This property allows ice to float on the surface of water bodies, ensuring that aquatic life can survive below the frozen surface.

These properties collectively support diverse life forms.
In simple words: Water helps make soil, creates many homes for life, keeps temperatures steady because it can hold a lot of heat, and ice floats on it, which protects water animals.

🎯 Exam Tip: When listing properties of water, focus on those directly relevant to its role in sustaining life and shaping ecosystems, such as heat capacity, density anomaly, and solvent properties.

 

Question 46. Give an account of grass land biome.
Answer: Grassland biomes are found in both temperate and tropical regions around the world. They are characterized by hot summers, cold winters, and rainfall that is often irregular. High winds are also a common feature of these areas. The main difference between grasslands and temperate deciduous forests is the low, inconsistent rainfall. Grasslands are home to many herbivores like antelope, bison, wild horses, jack rabbits, ground squirrels, and prairie dogs. Predators such as coyotes, foxes, hawks, and snakes also live there. In India, grassland animals include elephants, gaur, rhinos, and antelopes. The flora consists of grasses like purple needle grass, wild oats, foxtail, ryegrass, and buffalo grass. These areas support a rich web of life adapted to open, grassy expanses.
In simple words: Grasslands have hot summers, cold winters, and uneven rain. They have many grass-eating animals and predators, with grasses like wild oats growing there.

🎯 Exam Tip: When describing biomes, always cover key aspects such as climate, dominant vegetation, and characteristic animal life to provide a complete picture.

 

Question 47. Write in detail about Temperate forest and its types.
Answer: Temperate forests are found in specific regions like eastern North America, northeastern Asia, and western and central Europe. They have distinct seasons, including a clear winter, and a moderate climate with a growing season of 140-200 frost-free days, which sets them apart. The yearly temperature usually ranges from \( -30^\circ C \) to \( 30^\circ C \), and rainfall is evenly distributed throughout the year, typically between 750-1500 mm. The soil in these forests is fertile and rich in decaying organic matter. The tree canopy is moderately dense, allowing sunlight to reach the forest floor, supporting a diverse understory of plants and various animal species. Typically, the flora includes 3-4 tree species per square kilometer, mostly broad-leaved trees that lose their leaves annually, such as oak, hickory, beech, and maple. Fauna consists of animals like squirrels, rabbits, skunks, birds, deer, mountain lions, bobcats, timber wolves, foxes, and black bears. Based on how rainfall is distributed seasonally, temperate forests can be categorized into:

• **Mediterranean forests:** These have rainfall concentrated in winter, usually less than 1000 mm per year.
• **Temperate coniferous forests:** They experience mild winters and high annual precipitation, often more than 2000 mm per year.
• **Temperate broad-leaved rainforests:** These have mild, frost-free winters and very high precipitation, exceeding 1500 mm per year, distributed evenly.

These different types highlight the varied conditions within temperate regions.
In simple words: Temperate forests have four seasons, moderate weather, fertile soil, and trees that lose leaves. Types depend on rain: Mediterranean (winter rain), Coniferous (lots of yearly rain), and Broad-leaved Rainforests (mild, very wet).

🎯 Exam Tip: For detailed descriptions of biomes, structure your answer by covering geographic location, climate, soil, vegetation, and fauna, then elaborate on the sub-types with their distinguishing rainfall patterns.

 

Question 48. Point out the adaptive traits of aquatic animals.
Answer: Aquatic animals have developed several adaptations to survive in water environments:

• Their pectoral and dorsal fins help them balance and stabilize, while the caudal fin (tail fin) is used for changing direction during swimming.
• Body muscles are arranged in segments called myotomes, which aid in efficient locomotion.
• They have a streamlined body shape, which reduces drag and helps them move swiftly through water.
• Respiration occurs through gills, which are specialized organs that extract dissolved oxygen from water.
• Many possess air-bladders filled with air to control buoyancy, allowing them to remain at different depths.
• They have a lateral-line system, which consists of sensory organs that act as rheoreceptors, helping them detect water movement and locate objects.
• Their integuments (outer coverings) are rich in mucous glands and are protected by scales, which help reduce friction and protect against pathogens.
• They have specialized excretory structures to maintain the balance of water and ions in their bodies, which is crucial for osmotic regulation.

These adaptations allow them to thrive in various aquatic habitats.
In simple words: Aquatic animals have fins for moving, streamlined bodies for fast swimming, gills for breathing underwater, and air bladders to float. They also have special lines on their bodies to feel water movement.

🎯 Exam Tip: When listing adaptations, group them by function (e.g., movement, respiration, buoyancy) to show a clear understanding of how each trait benefits the animal.

 

Question 49. Differentiate between r-selected species and k-selected species.
Answer: Here is a comparison between r-selected and k-selected species:

These two strategies represent different approaches to maximizing survival and reproduction in varying environmental conditions.
In simple words: r-selected species are small, have many babies early, and live short lives in changing places. k-selected species are big, have few babies later with care, and live long lives in stable places.

🎯 Exam Tip: When differentiating, create a clear table format and ensure each point of comparison highlights a distinct difference between the two strategies.

 

Question 50. Describe in detail on population interaction.
Answer: Organisms from different populations in an ecosystem often interact with each other for various reasons, such as food, shelter, mating, or protection. These interactions can significantly influence the population sizes and distribution of the species involved. Common types of population interactions include:

• **Mutualism (+,+):** Both species benefit from the interaction (e.g., bees pollinating flowers while getting nectar).
• **Commensalism (+,0):** One species benefits, and the other is neither helped nor harmed (e.g., barnacles on whales).
• **Predation (+,-):** One species (predator) benefits by killing and consuming another (prey) (e.g., lion hunting a deer).
• **Parasitism (+,-):** One species (parasite) benefits by living on or in another species (host) and deriving nutrients, usually harming the host (e.g., tapeworms in humans).
• **Competition (-,-):** Both species are harmed because they vie for the same limited resources (e.g., two different species of birds competing for the same type of seeds).
• **Amensalism (-,0):** One species is harmed, while the other is unaffected (e.g., a large tree shading out smaller plants below, hindering their growth).

These interactions are fundamental to the structure and function of ecological communities.
In simple words: Different kinds of living things often interact to find food, shelter, or mates. Some help each other, some harm each other, and some don't affect each other at all.

🎯 Exam Tip: To describe population interactions effectively, name each type, explain the impact on both species using a plus/minus/zero notation, and provide a clear example for each.