Organisms and Populations - Class 12 Biology - Chapter 11 - Notes, NCERT Solutions & Extra Questions
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Extra Questions - Organisms and Populations | NCERT | Biology | Class 12
To determine if a population will exist in Hardy-Weinberg equilibrium, we need to consider the following conditions:
Option A: the population is large
Option B: individuals mate selectively
Option C: there are no mutations
Option D: there is no migration
Therefore, a population will not exist in Hardy-Weinberg equilibrium if:
the population is large
individuals mate selectively
there are no mutations
there is no migration
The Hardy-Weinberg equilibrium model assumes certain conditions for a population to adhere to its predictions. These conditions include:
The population must be large to minimize the effects of genetic drift.
Mating must be random (non-selective); individuals do not choose mates based on genotype or phenotype.
There are no mutations affecting the gene pool.
There is no migration in or out of the population, which would alter allele frequencies.
No natural selection occurs, so all traits must equally affect survival.
Given the list in the question, the correct factor that will result in a population not being in Hardy-Weinberg equilibrium is:
individuals mate selectively
This selective mating disrupts the assumption of random mating, crucial for maintaining Hardy-Weinberg equilibrium.
How many of the following features mentioned below belong to Osteichthyes?
A) Five
B) Four
C) Three
D) Six
The correct answer is Option B: Four.
The class Osteichthyes includes bony fishes characterized by:
Two-chambered heart
Air bladder for regulating buoyancy.
Oviparous reproduction (laying eggs).
External fertilization that occurs in water.
Features not typical of Osteichthyes include:
Placoid scales, which are found in cartilaginous fishes like sharks. Bony fishes instead have cycloid or ctenoid scales. Cycloid scales are large, round, or oval and show growth rings, while ctenoid scales are similar but feature a comb-like edge.
Claspers, which are used by male sharks to hold onto females during mating and are not found in bony fishes.
A group of similar individuals living in a given area that have the potential to interbreed is called:
A. community
B. organism
C. population
The correct answer is C. population.
A population is defined as a group of individuals of the same species located in a specific area that are capable of interbreeding. This is distinct from a community, which refers to a group of various species that interact within a given location.
According to Neo-Darwinism, natural selection operates through:
A Variations
B Reduction in the population of weaker organisms
C Differential reproduction
D Natural selection operates on disputes among organisms.
The correct answer is C Differential reproduction.
Differential reproduction is the principle stating that organisms best adapted to their environment are more likely to survive and reproduce, thus passing on advantageous traits to their offspring. This concept is central to Neo-Darwinism, which integrates Mendel's genetic theories with Darwin's original evolutionary theory to provide a more comprehensive understanding of how natural selection works at the genetic level.
The blood group which is the universal acceptor is (i) _____ and the one that is universal donor is (ii).
A (i) $\mathrm{AB}$, (ii) $\mathrm{O}$
B (i) $\mathrm{O}$, (ii) $\mathrm{A B}$
C (i) $\mathrm{A}$, (ii) $\mathrm{B}$
D (i) $\mathrm{O}$, (ii) $\mathrm{A}$
The correct answer is A:
(i) $\mathrm{AB}$,
(ii) $\mathrm{O}$.
$\mathrm{AB}^+$ is regarded as the universal acceptor because this blood type contains A, B, and Rh antigens, but has no antibodies in its serum. Conversely, $\mathrm{O}^-$ is known as the universal donor due to its lack of A antigens, B antigens, and the Rh antigen, allowing its blood to be donated to any other group since it does not provoke immune responses typical of other antigens. This blood type contains A, B, and Rh antibodies in its serum.
A _______ refers to any animal that is being hunted by another animal.
A producer
B prey
C predators
D parasites
The correct answer is B - prey.
Prey refers to animals that are hunted and consumed by other animals, known as predators. For instance, a snake can prey on mice, making the snake a predator. In a situation where a hawk hunts a snake, the snake then becomes the prey. Thus, what constitutes a prey is dependent on the scenario and the relationship between the hunter and the hunted.
The following table shows the blood groups of 40 students of a class.
Blood Group | A | B | O | |
---|---|---|---|---|
Number of students | 11 | 9 | 14 | 6 |
One student of the class is chosen at random. What is the probability that the chosen student has blood group (i) O? (ii) AB?
Total number of students: $40$
(i) Number of students with blood group O: $14$
Let $E1$ represent the event where the chosen student has blood group O.
Probability of selecting a student with blood group O ($P(E1)$) is calculated as: $$ P(E1) = \frac{14}{40} = 0.35 $$
(ii) Number of students with blood group AB: $6$
Let $E2$ represent the event where the chosen student has blood group AB.
Probability of selecting a student with blood group AB ($P(E2)$) is calculated as: $$ P(E2) = \frac{6}{40} = 0.15 $$
These calculations represent the likelihood of selecting a student with a specific blood group from the group.
When the concentration of solutes differs on the two sides of a membrane permeable only to water, then:
Water will move across the membrane by the process of osmosis.
When the concentration of solutes differs on the two sides of a membrane that is only permeable to water, osmosis occurs. Osmosis is a critical biological process where water moves across a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration. This process doesn't require energy in the form of ATP but happens spontaneously due to the concentration gradient across the membrane.
Here's a breakdown of the process:
Semi-permeable membrane: This type of membrane allows some substances (such as water) to pass through, but blocks others (such as certain solutes).
Concentration gradient: This is the difference in solute concentration from one side of the membrane to the other. Water moves to balance these concentrations.
Direction of water movement: Water moves from the side where it is in higher concentration (lower solute concentration) to the side where it is in lower concentration (higher solute concentration).
This movement of water aims to equalize the solute concentration on both sides of the membrane, characterizing a fundamental aspect of osmosis. The options given might confuse osmosis with active transport or plasmolysis, but these processes are distinct:
Active transport requires energy (ATP) and moves substances against the concentration gradient.
Plasmolysis refers to the contraction of the protoplasm in cells due to the loss of water through osmosis but is not the movement of water itself.
Therefore, the correct understanding is that water will move across the membrane by osmosis, not by active transport or plasmolysis. Osmosis emphasizes water's movement following the passive transport principle, moving naturally with the concentration gradient without the requirement of external energy.
Secondary consumer in the following is: A. Cat B. Rat C. Food grains (Crops) D. Tiger
In ecosystems, organisms are categorized based on their roles in the food chain. Producers, such as green plants, form the base as they produce food through photosynthesis. The next level includes the primary consumers, which are usually herbivores that consume the producers. Animals that eat these herbivores are called secondary consumers.
Option A - Cat: A cat generally consumes small animals like rats or birds. Here, the rat, a primary consumer, serves as food for the cat. Thus, the cat acts as a secondary consumer.
Option B - Rat: Rats primarily eat grains and seeds, which are produced by plants. This categorizes rats as primary consumers.
Option C - Food grains (Crops): These are producers as they are capable of producing their own food through photosynthesis.
Option D - Tiger: Tigers typically eat other animals, including those that are secondary consumers. This positions the tiger higher up in the food chain, making it a tertiary consumer.
Given the context, the correct choice for a secondary consumer among the options provided is Option A - Cat, as it consumes primary consumers like rats.
Kingdom | Example |
---|---|
(A) Protista | Amoeba |
(B) Fungi | Yeast |
(C) Plantae | Cuscuta |
(D) Monera | Euglena |
In the table provided, we need to identify the mismatched pair between kingdoms and their representative examples:
Kingdom Protista - Example: Amoeba
Protista generally includes unicellular eukaryotic organisms. This category fits Amoeba well, along with other protists like Paramecium and Euglena. Hence, this pairing is correct.
Kingdom Fungi - Example: Yeast
While most fungi are multicellular eukaryotic and saprophytic organisms, yeast stands out as a unicellular fungus. Despite this, it is still a proper representative of the fungal kingdom. This pairing is therefore considered correct.
Kingdom Plantae - Example: Cuscuta
Cuscuta, or dodder, is a parasitic plant, but it still retains the fundamental characteristics of multicellular eukaryotic plants. Thus, it correctly matches the Plantae kingdom.
Kingdom Monera - Example: Euglena
Monera primarily comprises unicellular prokaryotic organisms (bacteria). Euglena, however, is a unicellular eukaryotic organism and is actually a member of the Protista kingdom. Therefore, this is a mismatch.
The mismatched pair in the table is:
Option D (Kingdom Monera & Euglena): Euglena should be classified under Protista instead of Monera.
Thus, the correct answer is Option D, which is the unmatched pair.
The wings of a housefly and the wings of a sparrow are an example of:
A. Analogous organ
B. Vestigial Organs
C. Respiratory Organs
D. Homologous Organs
The given question asks about the nature of housefly wings and sparrow wings. These two wings serve the primary purpose of flight. Let's break down the properties and functions of each:
Houseflies belong to the insect group. Their wings are typically thin and delicate and are not composed of bones.
Sparrows are birds. Their wings are built with bones and feathers, providing robustness and further functions like body protection and heat retention.
Despite serving the same primary function of flying, housefly wings and sparrow wings do not share a common ancestor that also had wings. Instead, their wings have evolved separately to perform the same function (flight). This situation is typical of analogous organs, which are structures in different species having similar functions but not derived from a common ancestral structure.
Therefore, the wings of a housefly and the wings of a sparrow are examples of:
Analogous organs (Option A).
Identify the unmatched pairs:
(A) Cuscuta - Autotrophic
(B) Plantae - Autotrophic
(C) Fungi - Saprophytic
(D) Animalia - Heterotrophic.
The question presented here is about identifying which pair among the listed options incorrectly matches a group or species with its nutritional method. Let's analyze each pair:
(A) Cuscuta - Autotrophic:
Cuscuta, commonly known as dodder, is incorrectly described here as autotrophic. Cuscuta is a parasitic plant; it obtains its nutrients by attaching to other plants rather than synthesizing its own food through photosynthesis. This makes it heterotrophic, not autotrophic. Therefore, this pair is unmatched.
(B) Plantae - Autotrophic:
This is correct. Most members of the kingdom Plantae are autotrophic, meaning they can synthesize their own food through the process of photosynthesis, facilitated by chlorophyll.
(C) Fungi - Saprophytic:
This pairing is appropriate. Many fungi are saprophytic, meaning they derive nutrients by decomposing dead organic matter. Not all fungi strictly fit this category, but it is a predominant nutritional method in this kingdom.
(D) Animalia - Heterotrophic:
This description is accurate. All animals in the kingdom Animalia are heterotrophic, which means they must consume other organisms or organic substrates to obtain their nutrients, as they cannot produce food internally.
In conclusion, the incorrect or unmatched pair in this set is (A) Cuscuta - Autotrophic.
The plant group called "pollution indicator" is:
A. Bryophyta B. Lichen C. Gymnosperm D. Pteridophyta
The correct answer to the question "The plant group called 'pollution indicator' is" is option B: Lichen. Lichens are known as pollution indicators because they are particularly sensitive to air pollution. Lichens are not a single organism but a symbiotic association between a fungus and photosynthetic algae or bacteria.
These organisms are exceptionally sensitive to environmental changes, especially to the presence of airborne pollutants. In areas where the air is clean and free from pollutants, lichens can thrive and grow well. Conversely, in polluted areas, lichens often struggle to survive or may not be present at all. This unique characteristic makes lichens effective and natural indicators of air quality and pollution levels.
You are observing a non-chlorophyllous, eukaryotic organism with a chitinous cell wall under a microscope. You shall describe the organism as a:
A. fungus
B. alga
C. protozoan
D. bacterium
The organism you are studying is identified by several key characteristics from the provided description:
Non-chlorophyllous - This indicates that the organism does not contain chlorophyll, meaning it cannot perform photosynthesis and has to obtain its nutrients from other sources.
Eukaryotic - This classifies the organism as having a cell nucleus and other organelles enclosed within membranes, unlike prokaryotes like bacteria.
Chitinous cell wall - The presence of chitin in the cell wall is a distinctive feature of fungi, as opposed to plants which typically have cellulose-based cell walls.
Combining these traits, the correct classification of the organism is:
A fungus, as fungi are eukaryotic, non-chlorophyllous organisms that have chitinous cell walls. They are heterotrophs, meaning they rely on other organisms for nutrition, typically through a saprophytic lifestyle where they feed on decaying organic matter. Also, fungi typically reproduce through spores, often via asexual reproduction methods.
Therefore, the correct answer to describing the organism is: A. fungus
Which of the following are characteristic features of cells of meristematic tissue?
Actively dividing cells with dense cytoplasm, thick cell wall, and prominent nuclei
Actively dividing cells with little cytoplasm, thin cell wall, and prominent nuclei.
Actively dividing cells with dense cytoplasm, thin cell wall, and no vacuoles.
Actively dividing cells with thin cytoplasm, thin cell wall, and no vacuoles.
Meristematic tissues in plants are characterized by their rapid growth and cell division. Given the nature of these tissues, let’s analyze the offered options based on the structure and features unique to meristematic cells:
The first option mentions the cells having thick cell wall along with dense cytoplasm and prominent nuclei. Meristematic cells actually need to have a thin cell wall to facilitate easier and flexible division, thereby making this description incorrect.
The second option describes the cells as having dense cytoplasm, a thin cell wall, and no vacuoles, in addition to a prominent nucleus. This description aligns perfectly with the characteristics of meristematic cells. Dense cytoplasm provides necessary resources for cell activities, a thin wall supports frequent divisions, and the lack of vacuoles indicates that these cells are more focused on division rather than storage functions.
The presence of little to no cytoplasm and/or thin cytoplasm, mentioned in other options, would not support the active division and growth due to insufficient resources and structural components necessary for the cell functions.
Therefore, the correct characteristics for cells of meristematic tissue are:
Actively dividing cells
Dense cytoplasm
Thin cell wall
Prominent nuclei
No vacuoles
Based on this information, the second option is the most accurate description of the cells in meristematic tissue.
Hormones produced in one part of the organism reach the distantly located target via:
A) muscles
B) bone
C) cartilage
D) blood
Hormones are special chemical substances produced in one part of an organism that need to travel to another part to exert their effects. These hormones are typically released into the bloodstream from their origin, such as the adrenal glands or the pancreas. Once released, they travel through the bloodstream to reach their target organs or cells. This transportation is crucial because it allows the hormone to affect different parts of the body, even if those parts are far from where the hormone was initially produced.
Other answer choices in the question, such as muscles, bone, and cartilage, are more structurally oriented and do not function primarily as transport mediums for hormones. They form solid structures and are not involved directly in the wide distribution of hormones throughout the organism. Blood, being a fluid connective tissue, facilitates this distribution effectively.
Thus, the correct answer to how hormones reach distant target organs in the body is through the:
D) blood
An animal kept in a jar has the following features:
I. It is bilaterally symmetrical. II. It has a coelomic cavity. III. The body is segmented. IV. It has jointed appendages.
A. Arthropoda B. Annelida C. Platyhelminthes D. Mollusca
To determine the phylum of an animal with the given features, let's analyze each of those features in context with the options provided:
Bilaterally symmetrical - The body can be divided into mirror-image halves along one plane.
Coelomic cavity - A true body cavity that is fully lined by tissue derived from mesoderm.
Segmented body - The body is divided into repeated segments.
Jointed appendages - Limbs or other outgrowths that articulate at joints.
Options Analysis:
A. Arthropoda:
Bilaterally symmetrical? Yes.
Coelomic cavity? Yes, arthropods have a hemocoel, a blood-filled cavity derived from the coelom.
Segmented body? Yes, clearly seen in insects, crustaceans, etc.
Jointed appendages? Yes, a defining characteristic of arthropods.
B. Annelida:
Lack of jointed appendages makes this incorrect.
C. Platyhelminthes:
Lack of a coelomic cavity disqualifies this option.
D. Mollusca:
These often do not show clear segmentation.
Given these points, the animal described fits all the unique characteristics of the Arthropoda phylum, which includes insects like spiders, crabs, and other similar creatures. This phylum is known for its jointed limbs and segmented bodies, making it the largest and most diverse in the animal kingdom. Therefore, the correct choice is:
Option A: Arthropoda
Photosynthesis occurs in which cellular organelles?
A. Mitochondria
B. Ribosome
C. Golgi body
D. Chloroplast
Photosynthesis, the process through which plants convert solar energy into chemical energy or glucose, occurs primarily in the chloroplast. This glucose serves as food for the plant and other organisms, making plants autotrophs (self-feeding organisms). The key pigment involved in photosynthesis is chlorophyll, which is present within the chloroplasts. These organelles are specialized components of the cell responsible for capturing light energy and converting it into chemical energy through photosynthesis.
Considering the other options provided:
Mitochondria are known as the powerhouse of the cell, primarily involved in energy production through respiration, not photosynthesis.
Ribosomes are involved in protein synthesis.
Golgi bodies are responsible for packaging and processing of proteins and lipid molecules within the cell.
Therefore, the correct answer to the question is: D. Chloroplast
In which animal, open blood vascular system is found?
A. In Earthworm
B. In Periplaneta
C. In Man
D. In Fish
The question posed is about identifying which animal has an open blood vascular system. There are two types of circulatory systems in animals: closed circulatory system and open circulatory system.
In a closed circulatory system, the blood flows through enclosed blood vessels, without coming in direct contact with the body tissues. This system is seen in animals such as earthworms, humans, and fishes.
Conversely, in an open circulatory system, the blood flows freely into the body cavity, directly bathing the cells and organs. This kind of circulatory system allows the blood to be in direct contact with tissues and is commonly found in insects.
The correct answer to the question is B. In Periplaneta (or cockroach), as they exhibit an open circulatory system. Earthworms, humans, and fishes all have a closed circulatory system. Therefore, the most accurate response is Option B.
Which group of organisms are heterotrophic?
A. Algae
B. Fungi
C. Bryophyta
D. Pteridophyta
Heterotrophic organisms are those that cannot synthesize their own food and depend on other sources of organic carbon, mostly plant or animal matter. In the context of the options provided:
Algae, Bryophyta (mosses and liverworts), and Pteridophyta (ferns) belong to the Kingdom Plantae. They are capable of photosynthesis due to the presence of chlorophyll pigments, which convert solar energy into chemical energy (glucose). Thus, they are known as autotrophs, meaning they produce their own food and are referred to as producers.
Fungi, unlike the other options, do not perform photosynthesis and do not have chlorophyll. Instead, they are saprotrophic, feeding on dead and decaying matter. This makes them heterotrophic as they rely on external sources of organic carbon for nourishment.
Therefore, the correct answer is:
B. Fungi
Choose the correct statement regarding the partial pressures of respiratory gases: A. $p \mathrm{CO}{2}$ is more than that of $\mathrm{O}{2}$ in atmosphere. B. $p \mathrm{CO}{2}$ in oxygenated blood is equal to the partial pressure of $\mathrm{O}{2}$ in deoxygenated blood. C. Solubility of $\mathrm{CO}{2}$ is 20-25 times lesser than $\mathrm{O}{2}$. D. $p \mathrm{CO}{2}$ in tissues is equal to the partial pressure of $\mathrm{O}{2}$ in oxygenated blood.
The correct statement regarding the partial pressures of respiratory gases is option B. Let's carefully analyze why this is the case by examining each option:
Option A:
Statement: Partial pressure of carbon dioxide ($p \text{CO}_2$) is more than that of oxygen ($O_2$) in the atmosphere.
Analysis: This statement is incorrect because the partial pressure of oxygen ($\text{O}_2$) in the atmosphere is significantly higher than that of carbon dioxide ($\text{CO}_2$). Oxygen constitutes about 21% of the atmospheric gases, whereas carbon dioxide makes up only about 0.04%.
Option B:
Statement: Partial pressure of carbon dioxide ($p \text{CO}_2$) in oxygenated blood is equal to the partial pressure of oxygen ($\text{O}_2$) in deoxygenated blood.
Analysis: This statement is correct. The partial pressure of carbon dioxide in oxygenated blood is typically around 40 mmHg, which is approximately equal to the partial pressure of oxygen in deoxygenated blood, also around 40 mmHg.
Option C:
Statement: Solubility of carbon dioxide ($\text{CO}_2$) is 20-25 times lesser than that of oxygen ($\text{O}_2$).
Analysis: This statement is incorrect. The solubility of carbon dioxide in water (and thus in blood) is actually 20-25 times higher than that of oxygen.
Option D:
Statement: Partial pressure of carbon dioxide ($p \text{CO}_2$) in tissues is equal to the partial pressure of oxygen ($\text{O}_2$) in oxygenated blood.
Analysis: This statement is incorrect. There is no such direct relationship between the partial pressures of carbon dioxide in tissues and oxygen in oxygenated blood. The partial pressures in tissues and blood depend on various factors including metabolic activity and gas exchange efficiency.
Conclusion
Thus, the correct statement about the partial pressures of respiratory gases is option B: The partial pressure of carbon dioxide in oxygenated blood is equal to the partial pressure of oxygen in deoxygenated blood.
A community is ______________________________.
A. A group of individuals of the same species that occupies the same geographical area and who interact with each other.
B. A community is a hierarchy that includes populations and the physical environment in which they live.
C. A community is organisms and the physical environment in which they live.
D. A community is organisms and the physical environment in which they live.
The correct option is C: organisms and the physical environment in which they live.
An ecological community refers to a group of species that live in the same location and have the potential to interact with one another. This definition encompasses both the living organisms and the physical environment they inhabit.
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Ask Chatterbot AINCERT Solutions - Organisms and Populations | NCERT | Biology | Class 12
List the attributes that populations possess but not individuals.
Populations possess certain attributes that individual organisms do not. These attributes include:
Birth rates: Refers to the number of births per capita in the population.
Death rates: Refers to the number of deaths per capita in the population.
Sex ratio: The proportion of males to females within a population.
Age distribution: The proportion of individuals of different ages within a population.
Population density (N): The number of individuals per unit area or volume.
These attributes are essential for studying population dynamics, understanding ecological interactions, and predicting changes in population size and structure.
If a population growing exponentially double in size in 3 years, what is the intrinsic rate of increase ( $\mathrm{r}$ ) of the population?
The intrinsic rate of increase ( $\mathrm{r}$ ) for a population that doubles in size in 3 years is:
$$ \mathrm{r} = \frac{\log(2)}{3} $$
Name important defence mechanisms in plants against herbivory.
Plants have evolved a variety of defence mechanisms against herbivory to protect themselves from being consumed by herbivores. Here are some important defence mechanisms:
Morphological Defences:
Thorns: Present in plants like Acacia and Cactus, thorns deter animals from eating them.
Spines: Sharp extensions that can injure herbivores.
Trichomes: Hair-like structures on the epidermis that can be sticky or irritating.
Chemical Defences:
Toxins: Compounds that can be poisonous or lethal to herbivores. An example is the cardiac glycosides produced by the Calotropis plant.
Secondary Metabolites: Including chemicals such as nicotine, caffeine, quinine, strychnine, and opium, which can have toxic, growth-inhibiting, or digestive-disruptive effects on herbivores.
Biochemical Defences:
Digestibility Reducers: Metabolic inhibitors such as tannins and lignins that make plant tissues less digestible by herbivores.
Anti-nutritional Compounds: Chemicals that interfere with the herbivore's ability to absorb nutrients. Examples include lectins and protease inhibitors.
In summary, thorns, toxic chemicals, and various metabolites are common defence strategies in plants to protect against herbivory.
An orchid plant is growing on the branch of mango tree. How do you describe this interaction between the orchid and the mango tree?
The interaction between the orchid plant and the mango tree can be described as commensalism. In this relationship, the orchid benefits by gaining a place to grow, while the mango tree is neither harmed nor benefited. This form of interaction demonstrates how one organism can obtain resources without affecting the other.
What is the ecological principle behind the biological control method of managing with pest insects?
The ecological principle behind the biological control method of managing pest insects is predation (or sometimes parasitism).
In biological control, a natural predator or parasite of the pest insect is introduced to control the pest population. Predators keep the prey populations under control by feeding on them, while parasites feed on or within the host, often leading to the host's death. This helps to maintain the balance in the ecosystem and prevents the pest population from reaching levels that can cause significant damage to crops or other plants. An example mentioned in the chapter is controlling the prickly pear cactus in Australia with a moth that feeds on it.
Define population and community.
A population refers to a group of individuals of the same species that live in a specific geographic area, share or compete for similar resources, and have the potential to interbreed. Populations possess certain attributes such as birth rates, death rates, sex ratios, and age distributions which are not applicable to individual organisms. In terms of ecology, populations are essential because natural selection operates at this level to evolve desired traits.
A community consists of all the different populations of various species living together in a specific area and interacting with one another. These interactions can be beneficial, detrimental, or neutral and include processes like predation, competition, mutualism, and commensalism. Communities form biological units and their structure and composition are characterized by these interspecific interactions.
Define the following terms and give one example for each:
(a) Commensalism
(b) Parasitism
(c) Camouflage
(d) Mutualism
(e) Interspecific competition
(a) Commensalism
Definition: Commensalism is an interaction between two species where one species benefits, and the other is neither harmed nor benefited. Example: The cattle egret and grazing cattle relationship is a classic example. The egrets feed on insects that are stirred up by cattle as they move through the grass, but the cattle are neither helped nor harmed by the egrets.
(b) Parasitism
Definition: Parasitism is a relationship between two species in which one species (the parasite) benefits at the expense of the other (the host). Example: The human liver fluke (_Fasciola hepatica_) is a parasite that affects the liver of its host, often causing significant harm and disease.
(c) Camouflage
Definition: Camouflage is an adaptation that allows organisms to blend in with their environments to avoid detection by predators or prey. Example: The praying mantis uses camouflage to blend in with its surroundings, making it difficult for predators to spot it and for its prey to see it before it strikes.
(d) Mutualism
Definition: Mutualism is a type of interaction between two species that benefits both parties. Example: The relationship between bees and flowering plants. Bees get nectar from the flowers, which they use as food, while helping the plants with pollination.
(e) Interspecific Competition
Definition: Interspecific competition occurs when individuals of different species compete for the same resources in an ecosystem (e.g., food, space). Example: In some shallow South American lakes, visiting flamingos and resident fish both compete for the same food resource, the zooplankton.
With the help of suitable diagram describe the logistic population growth curve.
The logistic population growth curve is often depicted as a sigmoid (S-shaped) curve and is represented by the Verhulst-Pearl logistic equation. This type of growth occurs when resources are limited, leading to an initial period of exponential growth, followed by a slowdown as the population approaches the environment's carrying capacity ((K)).
Here is the logistic growth equation:
[ \frac{dN}{dt} = rN \left( \frac{K-N}{K} \right) ]
(N) = Population size
(r) = Intrinsic rate of natural increase
(K) = Carrying capacity of the environment
Diagram and Explanation
Below is a graphical representation of the logistic growth curve.
Explanation:
Lag Phase: At the beginning (near zero time), population growth is slow because the population size (N) is small.
Exponential Growth Phase: As resources are still abundant, the population grows rapidly, showing an exponential growth pattern.
Deceleration Phase: The growth rate begins to slow as resources become limited and competition increases.
Stationary Phase (Plateau): The population size (N) approaches the carrying capacity (K), and the growth rate stabilizes around zero. At this point, the population size fluctuates around (K).
In summary, logistic growth is characterized by an initial period of exponential growth, which tapers off as the population size approaches the carrying capacity of the environment, resulting in an S-shaped curve.
Select the statement which explains best parasitism.
(a) One organism is benefited.
(b) Both the organisms are benefited.
(c) One organism is benefited, other is not affected.
(d) One organism is benefited, other is affected.
The best statement that explains parasitism from the given options is:
(d) One organism is benefited, other is affected.
List any three important characteristics of a population and explain.
1. Population Size (Population Density)
The size of the population, often referred to as population density (denoted as $N$), is a key characteristic. It indicates how many individuals of a species are present in a specific area at a given time. This measure can be given as total number, biomass, percent cover, etc.
Example: The number of Chlamydomonas in a pond can go into millions, whereas the population size of Siberian cranes at Bharatpur wetlands in any year could be less than 10.
2. Birth and Death Rates
These rates refer to the number of births and deaths per capita in the population.
Birth Rate: The number of new individuals added to the population through reproduction over a specific period. For example, if 8 new lotus plants are added to an initial population of 20, the birth rate is $\frac{8}{20} = 0.4$ offspring per lotus per year.
Death Rate: The number of individuals dying over a specified period. For instance, if 4 fruitflies die in a laboratory population of 40 during a week, the death rate is $\frac{4}{40} = 0.1$ individuals per fruitfly per week.
3. Sex Ratio
The sex ratio of a population refers to the proportion of males to females. It is important for understanding the reproductive potential and dynamics of the population.
Example: A population might have a sex ratio where 60% of the individuals are females and 40% are males.
Understanding these characteristics helps in analyzing, managing, and conserving species and their habitats.
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Introduction to Ecology for Class 12: Organisms and Populations
Ecology is a vital branch of biology that studies the relationships of living organisms with their environment, including both abiotic (physico-chemical factors) and biotic (other species) components. This chapter focuses on understanding ecology at the population level, linking it to genetics and evolution.
Levels of Biological Organisation in Ecology
Ecology is concerned with various levels of biological organisation, from macromolecules to biomes. Understanding these levels helps comprehend the complex interactions occurring in nature.
Levels of Biological Organisation:
- Macromolecules
- Cells
- Tissues
- Organs
- Individual Organisms
- Populations
- Communities
- Ecosystems
- Biomes
Population Ecology: An Intersection with Genetics and Evolution
Population ecology examines the factors affecting population sizes and their changes over time. It merges ecology with population genetics and evolution, emphasising natural selection and adaptation.
Population Attributes
Populations display attributes that individual organisms do not, such as birth rates, death rates, sex ratios, and age distribution.
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Birth and Death Rates: Birth rates and death rates in populations are calculated per capita. For example, if a pond had 20 lotus plants last year and 8 new plants were added, the birth rate is (8 / 20 = 0.4) offspring per lotus per year.
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Sex Ratio: The sex ratio in a population, such as 60% females and 40% males, is essential for understanding reproductive dynamics.
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Age Distribution: Age distribution, often represented as age pyramids, indicates the growth status of the population (growing, stable, or declining).
Measuring Population Density
Population density, the number of individuals per unit area, can be gauged using various methods depending on the species and context. It is crucial for assessing ecological processes.
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Methods of Measurement:
- Total Number
- Percent Cover
- Biomass
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Importance of Population Size: Changes in population size help understand the impacts of factors like competition, predation, and environmental changes.
Population Growth: Analysing Models
Population growth is dynamic and influenced by factors such as food availability, predation, and weather. The two main growth models are:
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Exponential Growth: When resources are unlimited, populations grow exponentially or geometrically, represented by a J-shaped curve.
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Logistic Growth: With limited resources, populations grow logistically, stabilising at the carrying capacity, depicted by an S-shaped or sigmoid curve.
Exponential and Logistic Growth Curves:
Reproductive Strategies and Darwinian Fitness
Populations evolve to maximise their Darwinian fitness (reproductive success). Different reproductive strategies have evolved to adapt to various environmental pressures.
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Single Breeding vs. Multiple Breeding:
- Some organisms breed once (e.g., Pacific salmon fish).
- Others breed multiple times (e.g., birds, mammals).
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Offspring Size and Number:
- Some produce many small-sized offspring (e.g., Oysters).
- Others produce fewer but larger-sized offspring (e.g., birds, mammals).
Population Interactions in Ecosystems
In nature, species interact in various ways, forming a biological community. These interactions can be beneficial, detrimental, or neutral.
Types of Interspecific Interactions:
- Mutualism: Both species benefit.
- Competition: Both species suffer.
- Predation: One species benefits, the other suffers.
- Parasitism: One benefits, the other suffers.
- Commensalism: One benefits, the other is unaffected.
- Amensalism: One is harmed, the other is unaffected.
Plant Defenses Against Herbivory
Plants have evolved diverse defences to protect against herbivores, including morphological (e.g., thorns) and chemical defences (e.g., toxins like nicotine).
Conclusion
Understanding the relationships between organisms and populations is fundamental in ecology. Populations grow and evolve under various pressures, and the intricate web of interactions forms the basis of ecological communities. This chapter provides a solid foundation for comprehending these dynamic processes essential for Class 12 Biology students.
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