Ecosystem - Class 12 Biology - Chapter 12 - Notes, NCERT Solutions & Extra Questions
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Extra Questions - Ecosystem | NCERT | Biology | Class 12
Consider the following statements: (a) The portion of the spectrum between $500 \mathrm{~nm}$ and $800 \mathrm{~nm}$ is also referred to as photosynthetically active radiation (PAR). (b) Magnesium, calcium, and chloride ions play prominent roles in the photolysis of water. (c) In cyclic photophosphorylation, oxygen is not released (as there is no photolysis of water) and NADPH is also not produced. Of these statements given above,
A. (a) and (c) are true, but (b) is false.
B. (a) is true, but (b) and (c) are false.
C. (a) and (b) are true, but (c) is false.
D. (a) and (b) are false, but (c) is true.
The correct answer is Option D: (a) and (b) are false, but (c) is true.
For statement (a): The wavelength range from $500 \mathrm{~nm}$ to $800 \mathrm{~nm}$ is not referred to as photosynthetically active radiation (PAR). PAR actually encompasses the spectrum between $400 \mathrm{~nm}$ and $700 \mathrm{~nm}$, where light is effectively absorbed by plants for photosynthesis.
For statement (b): The ions Magnesium, Calcium, and Chloride do not have significant roles in the photolysis of water during photosynthesis. Key ions involved in catalyzing the reaction, particularly in the oxygen-evolving complex of photosystem II, include Manganese and Calcium, but not Magnesium or Chloride directly in the photolysis process.
For statement (c): Cyclic photophosphorylation involves the synthesis of ATP without the production of NADPH and without the release of oxygen. This is because the electrons are cycled back to the photosystem and water is not split, confirming that this statement is true.
Hence, the correct choice based on the statements and their verification is (a) and (b) are false, but (c) is true, corresponding to Option D.
Match the following columns. Here is the table you requested, formatted to display the relationships between terms in Column I and their descriptions in Column II:
Column I | Column II | ||
---|---|---|---|
A. | Cuticle | 3. | Waxy layer |
B. | Bulliform cells | 4. | Empty, colourless cell |
C. | Stomata | 1. | Guard cells |
D. | Epidermis | 2. | Single layer |
This table matches each biological structure with its appropriate description, simplifying the learning and review process.
Codes: A B C D
(a) 3 4 1 2
(b) 1 2 3 4
(c) 3 2 4 1
(d) 3 2 1 4
The correct matches for each item in Column I to the corresponding description in Column II can be established based on their definitions:
A. Cuticle: This is described as a waxy layer that is present all over the plant body, except for the roots. Thus, A corresponds to 3.
B. Bulliform cells: These cells are characterized as empty, colorless cells. Their main function involves aiding in leaf movements to minimize water loss under stress. Hence, B matches with 4.
C. Stomata: Stomata are known for being apertures in the epidermis used for gas exchange. Each stomatal aperture is flanked by two kidney-shaped guard cells which regulate the opening and closing of the stomata. Therefore, C corresponds to 1.
D. Epidermis: Typically, the epidermis is a single layer of cells, protecting the underlying tissues. On some occasions, it could be multilayered, but usually, it consists of a single layer. Thus, D matches with 2.
Given these correspondences, the correct answer is option (d): 3, 4, 1, 2.
Match the Column I with the Column II and choose the correct option.
Column I | Column II |
---|---|
A. Mutualism | 1. Tiger and deer |
B. Commensalism | 2. Cuscuta on Citrus |
C. Parasitism | 3. Sucker fish and shark |
D. Predation | 4. Hermit Crab and sea anemone |
A | B | C | D | |
---|---|---|---|---|
(e) | 1 | 2 | 3 | 4 |
(f) | 4 | 3 | 2 | 1 |
(g) | 2 | 3 | 1 | 4 |
(h) | 4 | 2 | 1 | 3 |
The correct option is Option B: (f).
Let's analyze each ecological relationship and match it to its corresponding example:
Mutualism: In this symbiotic relationship, both organisms benefit. The example of Hermit Crab and Sea Anemone fits here since the hermit crab provides the sea anemone with movement which helps it catch prey while the anemone offers the crab protection.
Commensalism: Here, one organism benefits and the other is unaffected. The relationship between Sucker Fish and Shark is an example of this, where the sucker fish attaches to the shark, gaining mobility and protection without affecting the shark.
Parasitism: In this relationship, one organism benefits at the expense of the other, often causing harm. Cuscuta (a parasitic plant) on Citrus exemplifies this as Cuscuta derives nutrition from the citrus plant, negatively affecting its host.
Predation: This describes an interaction where one organism (predator) kills and consumes another (prey). The interaction between a Tiger and Deer, where the tiger hunts the deer for food, is a clear instance of predation.
Therefore, the matching according to the descriptions and examples provided would be:
Mutualism -> Hermit Crab and Sea Anemone,
Commensalism -> Sucker Fish and Shark,
Parasitism -> Cuscuta on Citrus,
Predation -> Tiger and Deer.
Which corresponds to Option B: (f) in the problem statement.
Slow-acting endogenic forces are known as forces.
A) trophic
B) diastrophic
C) ditrophic
The correct answer is B) diastrophic.
Diastrophic forces are a category of endogenic forces that manifest their effects over an extended period. These forces are essentially responsible for various large-scale deformations of the Earth's crust.
Vertical distribution of different species occupying different levels is called:
A) energy flow
B) productivity
C) food chain
D) stratification
The correct answer is D) stratification.
Stratification refers to the vertical layering of a habitat, specifically the arrangement of vegetation in distinct layers. A notable example of this can be seen in tropical forests, which typically exhibit between 5 to 7 strata. In these forests, tall trees form the uppermost layer, while herbs and grasses are found at the ground level. In contrast, stratification is seldom found or is absent in desert environments.
Lichens are a well-known combination of an alga and a fungus, where the fungus has:
A) An epiphytic relationship with the alga
B) A saprophytic relationship with the alga
C) A symbiotic relationship with the alga
D) A parasitic relationship with the alga
Correct Answer: C) A symbiotic relationship with the alga
Lichens represent a unique and enduring symbiotic association between two different organisms: a mycobiont (the fungal component) and a phycobiont (the algal component). This partnership allows both to survive in conditions where separately they might not thrive, showcasing a perfect example of symbiosis.
"The underwater Ghost nets are posing threats to the marine ecosystem of the Kerala coast. What are Ghost Nets?
A. It is a network system spread by underwater submarines.
B. These are large fishing nets used by fish pirates for fish theft.
C. These are the fishing nets that have been left or lost in the ocean by the fishermen.
D. These are networks of fibrous vegetation where fishes are trapped and get killed."
The correct answer is C: These are the fishing nets that have been left or lost in the ocean by the fishermen.
Ghost nets refer to fishing nets that have been abandoned, lost, or otherwise discarded in the ocean. These nets are often nearly invisible under the dim light of the deep sea. They can either become entangled on a rocky reef or drift in the open sea. Such nets pose a significant threat to the marine ecosystem, including off the coast of Kerala, as they can harm the natural habitat and breeding grounds of marine life.
Did you know?
There are four primary types of ghost nets found in marine environments:
Large fishing nets used by commercial vessels that unintentionally enter territorial waters and deploy extensive netting systems.
Smaller fishing nets cut off from their boats by passing vessels.
Nets caught in strong currents that tumble to the ocean floor, becoming stuck and creating hazards.
Abandoned nets that are discarded at sea after a few uses.
"Can the organisms of any trophic level be removed without causing any damage to the ecosystem? Will the impact of removing all the organisms in a trophic level be different for different trophic levels?"
No, organisms from any trophic level cannot be removed without causing damage to the ecosystem. The removal of organisms from a trophic level results in disturbances to the food chain.
Furthermore, yes, the impact of removing all organisms from a particular trophic level will differ across various trophic levels. For example, if producers (occupying the first trophic level) are eliminated, then no organisms in the higher trophic levels would survive, as these producers supply the essential food and energy.
On the other hand, if a group of primary consumers like deer are removed, their predators (e.g., lions) would face a shortage of food, leading to a decline in their population. Conversely, removing top-level consumers such as lions would result in no predator regulation for species like deer. This absence would cause a spike in the deer population, which in turn would lead to overgrazing, affecting the vegetation adversely.
Based on the assertion and reason, choose the right option.
Assertion [A]: Different ecosystems have different species composition. Reason [R]: The type of species that can thrive in an ecosystem is dependent upon its geography, topography, and climate.
A) Both A and R are true, and R explains A.
B) Both A and R are true, but R does not explain A.
C) A is true, and R is false.
D) Both A and R are false.
The correct option is A) Both A and R are true, and R explains A.
Each ecosystem is characterized by a distinct species composition, which varies based on specific environmental conditions. This diversity is principally because the survival and flourishing of species in any given ecosystem are influenced by its geography, topography, and climate. For instance, desert ecosystems typically support species that can tolerate scant water availability and high temperatures, such as camels and cacti. Conversely, tundra ecosystems are home to species adapted to cold environments, like the polar bear, which possesses thick fur and substantial fat layers for insulation. This alignment between species traits and environmental conditions exemplifies how R effectively explains A.
Complete the food chain given below with the appropriate options.
A Primary Consumer; Secondary Consumer; Tertiary Consumer
B Tertiary Consumer; Secondary Consumer; Primary Consumer
C Tertiary Consumer; Primary Consumer; Secondary Consumer
D Primary Consumer; Tertiary Consumer; Secondary Consumer
The correct answer is Option A: Primary Consumer; Secondary Consumer; Tertiary Consumer.
In an ecological food chain:
Producers, such as photosynthetic plants and bacteria, synthesize food which forms the base of the chain.
Primary Consumers, like krill, consume these producers.
Secondary Consumers, such as small fish, prey on the primary consumers.
Finally, Tertiary Consumers, like large fish, feed on the secondary consumers.
In this sequence, the tertiary consumers might also be prey for other predators, including humans. This order illustrates the energy flow from producers to various levels of consumers, maintaining the ecosystem's balance.
Which of the following pairs is/are correctly matched?
Ecotone: Interaction of complex living organisms with their environment.
Niche: Zone of tension for species.
Biomes: Description of characteristics of different terrestrial parts of the biosphere.
Select the correct answer using the codes given below.
The correct option is C, i.e., option 3 only.
Explanation:
Pair 1 is incorrectly matched: An Ecotone is a transitional zone between two or more ecosystems, for example, a mangrove or an estuary. It's characterized by conditions intermediate to the adjoining ecosystems and is a zone of tension. It’s not about the interaction of complex living organisms with their physical environment, that describes an ecosystem.
Pair 2 is incorrectly matched: A niche specifies the conditions under which a particular species exists, including its use of resources and relationships with other species. It is not merely a zone of tension; rather, a well-suited niche aids a species in thriving and surviving. Conversely, an Ecotone acts as a tension zone because it lies between different ecosystems, leading to higher competition for resources among a variety of species.
Pair 3 is correctly matched: Biomes are large regions characterized by specific climatic features, soil types, and the living organisms adapted to them. Examples include evergreen forests, deciduous forests, taiga, and tundra. Each biome has a distinct set of environmental conditions and biological communities.
Therefore, only statement 3 about biomes correctly matches the description given.
In relation to energy transfer in ecosystems, explain the statement "10 kg of deer's meat is equivalent to $1 \mathrm{~kg}$ of lion's flesh."
The phrase "10 kg of deer's meat is equivalent to 1 kg of lion's flesh" demonstrates the 10% law of energy transfer in ecosystems. According to this rule, only 10% of energy from one trophic level is transferred to the next higher level. Therefore, if a lion consumes deer, it means that approximately 10 kg of deer meat would be required to produce 1 kg of lion's flesh. This is because the lion will assimilate only about 10% of the energy from the consumed deer meat into its own body mass.
Which of the following should be the SECOND sentence after rearrangement?
A) E
B) D
C) C
D) B
The correct answer is A) E.
E is the second sentence in the logical order of the paragraph. The correct sequence of sentences after rearranging would be DEABC, where D serves as the introductory sentence, followed by E, A, B, and finally C.
If we completely remove the decomposers from an ecosystem, its functioning will be adversely affected because:
A) the mineral movement will be blocked.
B) the rate of decomposition will be very high.
C) energy flow will be blocked.
D) herbivores will not receive solar energy.
The correct answer is A) the mineral movement will be blocked.
Decomposers are crucial in an ecosystem because they break down dead organic matter, releasing enzymes that help in decomposition. These organisms are sometimes referred to as mineralizers because they unlock minerals contained within organic remains. Without these decomposers, the minerals would remain trapped in the organic matter, thus halting the normal circulation of minerals throughout the ecosystem. As a result, other organisms dependent on these minerals for nutrition would be adversely affected.
Select the mismatched pair in the following and correct it.
Column I | ||
---|---|---|
(a) | Biomagnification | Accumulation of chemicals at the successive trophic levels of a food chain |
(b) | Ecosystem | Biotic components of the environment |
(c) | Aquarium | A man-made ecosystem |
(d) | Parasites | Organisms which obtain food from other living organisms |
The mismatched pair in the given options is:
(b) Ecosystem - Biotic components of the environment
An ecosystem encompasses not only the biotic components (living things) but also the abiotic components (non-living things such as water, air, and minerals) that interact within a system. Therefore, the corrected form should state:
(b) Ecosystem - The interdependent system of biotic and abiotic components.
All other pairs described in the options correctly define their terms.
Identify the correct option after reading the following information thereof.
It is a marine biome and a coastal water body. It is home to unique plant and animal communities that have adapted to brackish water. It serves as a natural filter for runoff and provides nursery grounds for many species of birds, fish, and other animals.
A) Lake
B) River
C) Estuary
D) Coastal reef
The correct option is C) Estuary
An estuary is characterized by where a freshwater river or stream meets the ocean. This confluence results in brackish water, which is notably less salty than seawater. Estuaries are crucial because their salinity levels fluctuate with the tides, making them a highly dynamic and productive ecosystem. These biomes serve as critical habitats for a wide array of wildlife, providing essential services such as natural filtration, breeding grounds, and migratory stopovers. Due to their ecological importance and productivity, estuaries are considered among the most vital ecosystems on the planet.
Which of the statements best describes Lindeman's Law?
A. There is 100 percent transfer of energy between trophic levels.
B. There is only 10 percent of the energy entering a particular trophic level.
C. At each trophic level, there is 20 percent of energy lost as heat.
D. There is 2-10 percent energy transfer at each trophic level.
Correct Answer: B. There is only 10 percent of the energy entering a particular trophic level.
Lindeman's Law, established in 1942, emphasizes the inefficiency in the transfer of energy between trophic levels within an ecosystem. It is widely known as the 10 percent law. This principle states that only about 10 percent of the energy entering a particular trophic level is available for transfer to the next higher trophic level. The remaining energy is mostly lost as heat or used in metabolic processes. Thus, each successive trophic level receives a smaller portion of energy, leading to a limit in the number of sustainable trophic levels in an ecological pyramid.
Statement I: Pyramid of biomass is inverted for aquatic ecosystem. Statement II: Ecological pyramids consider simple food chains.
A) I and II are correct. B) I is correct and II is incorrect. C) I is incorrect and II is correct. D) Both are incorrect.
The correct answer is A) I and II are correct.
Explanation:
Statement I: The pyramid of biomass is indeed often inverted in aquatic ecosystems. In such ecosystems, the biomass of the producers (such as phytoplankton) is less than that of the consumers (like zooplankton and fish) above them in the food chain. This scenario leads to an inverted biomass pyramid because small-sized producers reproduce quickly and are consumed rapidly, maintaining a lower overall biomass compared to their consumers.
Statement II: Ecological pyramids do consider simple food chains. These pyramids represent the quantitative differences in trophic levels of a food chain and are usually drawn considering a simple, straight-line food chain, even though natural food webs can be more complex.
Thus, both statements are correct, making option A the valid choice.
Above graph shows the amount of $\mathrm{CO}_{2}$ produced by plant cells at various levels of atmospheric $\mathrm{O}_{2}$. In respiration at atmospheric oxygen below $1%$ level, the amount of $\mathrm{CO}^{\wedge}$ released is relatively high. This is due to:
A. TCA cycle is hyperactive.
B. There is insufficient amount of coenzyme A.
C. Alcoholic fermentation is occurring.
D. Pyruvic acid oxidation is incomplete.
The provided graph illustrates the amount of $\mathrm{CO}_2$ released by plant cells at varying concentrations of atmospheric $\mathrm{O}_2$. When the level of $\mathrm{O}_2$ drops below 1%, we see a notable increase in $\mathrm{CO}_2$ release. This phenomenon can be attributed to different physiological processes within the plant cells. Among the options given:
TCA (Tricarboxylic Acid) cycle being hyperactive
Insufficient amount of coenzyme A
Occurrence of alcoholic fermentation
Incomplete oxidation of pyruvic acid
It's clear that this increase in $\mathrm{CO}_2$ release is linked to alcoholic fermentation. Alcoholic fermentation is a biochemical process that occurs in the absence of oxygen (anaerobic conditions), where glucose is converted into ethanol and $\mathrm{CO}_2$. When oxygen levels are low, plants cannot perform aerobic respiration efficiently, which normally leads to the complete oxidation of pyruvate in the mitochondria with more ATP being produced. Instead, they rely on alcoholic fermentation in the cytoplasm to deal with low oxygen availability, resulting in the production and release of $\mathrm{CO}_2$ and ethanol, albeit with much less ATP yield compared to aerobic respiration.
Thus, the correct answer to why there's a relatively high amount of $\mathrm{CO}_2$ released in plant cells at atmospheric oxygen levels below $1%$ is:
C. Alcoholic fermentation is occurring.
When deciduous trees drop their leaves during fall, the color of leaves turns to various shades of red, orange, and yellow due to the presence of:
A. Chlorophyll A & B
B. Presence of Fungal growth
C. Presence of carotenoids
D. Insufficient ATP
During the fall, deciduous trees shed their leaves, which often change color to red, orange, and yellow. This change in color is not due to the pigment we typically associate with leaves' color, which is chlorophyll. Chlorophyll gives leaves their green color and is vital for photosynthesis.
In the fall, as the days get shorter and temperatures drop, chlorophyll in the leaves breaks down. When this happens, the green color fades, and the colors of other pigments present in the leaves become visible. These pigments, known as carotenoids, are responsible for the red, orange, and yellow hues that are characteristic of fall foliage.
Carotenoids are always present in the leaves but are usually masked by the dominant green color of chlorophyll. When chlorophyll degrades with the change in season—due to less light and cooler weather—the carotenoids' colors can show through.
Therefore, the correct answer to the question is: C. Presence of carotenoids
These pigments become visible as chlorophyll breaks down, accounting for the vivid fall colors in deciduous trees.
The decomposers in an ecosystem:
A. Inorganic substance into organic substance B. Simpler substance into complex substance C. Solar energy into chemical energy D. Organic substance into inorganic substance.
Decomposers play a crucial role in an ecosystem by breaking down dead plants and animals. They are involved in the process of decomposition, where organic material is converted into inorganic material. This transformation is essential for recycling nutrients in the ecosystem.
Among the options given:
Option A involves converting inorganic substances into organic substances, which is not applicable to decomposers.
Option B, where a simpler substance is made into a complex substance, is also incorrect.
Option C discusses the conversion of solar energy into chemical energy, which is a function of producers like plants, not decomposers.
Option D is correct as it states that decomposers convert organic substances into inorganic substances. This reflects their role in breaking down complex organic matter into simpler inorganic compounds that can be reused by other organisms in the ecosystem.
Therefore, the correct answer is: D. Organic substance into inorganic substance.
Which of the following reactions takes place during breakdown of molecules in the respiration in our body?
A. Oxidation
B. Reduction
C. Oxidation-reduction
D. Photo-oxidation
During the process of respiration in our bodies, molecules, particularly carbohydrates like glucose, undergo a breakdown. This is primarily in the presence of oxygen, where glucose is decomposed into carbon dioxide and water. In this reaction, the oxygen is not just present but is actively participating in breaking down the glucose.
The phenomenon where oxygen molecules are gained or where a reaction takes place in the presence of oxygen is termed as an oxidation reaction. On the other hand, reduction reactions involve the gain of hydrogen ions or atoms.
In the context of cellular respiration, the breakdown of glucose involves the addition of oxygen, making it an oxidation process. Additionally, since this reaction releases a significant amount of heat and ATP (adenosine triphosphate), it is considered an exothermic reaction as well.
Out of the given options:
A. Oxidation
B. Reduction
C. Oxidation-reduction
D. Photo-oxidation
The correct answer to the question is: A. Oxidation
The thick stem of trees respire through:
A. Trachea
B. Stomata
C. Lenticel
D. Gills
To address the question on how the thick stem of trees respire, let's discuss the role of different structures mentioned in the options:
Option Analysis:
The Trachea is an organ found in animals, not plants; hence, it is incorrect.
Stomata are primarily located in the leaves of plants. They play a crucial role in gas exchange, which includes both respiration and the transpiration process. However, they are not found in thick tree stems, so this choice is incorrect.
Gills are structures found in animals (particularly aquatic), used for breathing under water and not applicable to trees.
Correct Answer:
The correct answer is Lenticels. These are small structures scattered throughout the bark of a tree. They facilitate the exchange of gases in and out of the tree bark. These structures are especially crucial in older trees and those with thick barks where internal gas exchange is vital for respiration but the outer surface area is vast and impermeable.
Thus, for trees with thick stems, the respiratory process occurs through Lenticels. The answer is option:
C. Lenticel.
Which of the following products of light-dependent phase are used during the light-independent phase of photosynthesis?
A. RUBP and ATP
B. $\mathrm{H}_{2} \mathrm{O}$ and $\mathrm{O}_{2}$
C. NADPH and ATP
D. ATP and $O_{2}$
The process of photosynthesis is divided into two primary phases: light-dependent and light-independent phases. In the light-dependent phase, sunlight is utilized in the presence of chlorophyll to drive the reactions that produce chemical energy, specifically in the form of NADPH and ATP. These are essential molecules that act as energy carriers.
During the light-independent phase, also referred to as the Calvin cycle or dark phase, the energy stored in ATP and the reducing power of NADPH are used to convert carbon dioxide (CO2) into glucose. This phase doesn't require light and focuses more on using the chemical energy generated previously to synthesize food for the plant.
Given the options: A. RUBP and ATP
B. $\mathrm{H}_{2} \mathrm{O}$ and $\mathrm{O}_{2}$
C. NADPH and ATP
D. ATP and $O_{2}$
The correct answer is Option C (NADPH and ATP), as these are the products of the light-dependent reactions utilized in the light-independent phase for the synthesis of glucose.
The structural and functional units of the kidney are called:
A) Nephron
B) Nephridia
C) Ureter
D) Urethra
The structural and functional units of the kidney are referred to as the nephrons. Nephrons play a critical role in the kidneys by removing waste and excess substances from the blood. This process is fundamental for producing urine, which helps in detoxifying the body.
In summary, the correct answer to the question regarding the structural and functional units of the kidney is:
A) Nephron
The other options provided, such as neurons, medulla, and cortex, do not correctly describe the main functional unit of the kidney. Only the nephrons fulfill this role, making them essential for the kidney's overall function and effectively supporting the body's urinary system.
Which one of the following is a renewable resource?
A. Coal
B. Oil
C. Forest
D. Petrol
When evaluating whether a resource is renewable or not, the main criterion is whether it can be replenished naturally in a relatively short timeframe. Renewable resources can be regenerated and are typically sustainable, as they are not depleted by human consumption. Comparatively, nonrenewable resources are those which take millions of years to form and are exhausted much faster than they can be replaced.
From the options provided:
Coal, Oil, and Petrol are all derived from fossils that formed over millions of years. They are considered nonrenewable because they cannot be quickly replenished once consumed.
Forests, on the other hand, are capable of regenerating naturally through the process of seeding and growth. This regeneration can occur over a much shorter period compared to geological processes. Therefore, as long as forests are managed correctly and not depleted faster than they can regenerate, they can be considered a renewable resource.
Therefore, the correct answer here is C. Forest, as it is the only renewable resource among the options listed.
The study of interaction between living organisms and environment is called:
A. Ecology
B. Phytogeography
C. Psychology
D. Mycology
The correct answer is A. Ecology.
Ecology is the branch of biology that deals with the interactions between living organisms and their physical environment. It involves studying how different living organisms such as plants and animals relate with both the biotic (living) and abiotic (non-living) components of their environment. These non-living components can include things like temperature, light, and water.
Other terms mentioned in the options have distinct meanings:
Ecosystem refers to a specific area where biotic and abiotic components interact, such as ponds, lakes, or forests. It's more about the system or a particular location rather than the broad science studying these interactions.
Phytology, also known as Botany, is the study of plants.
Phytogeography concerns the geographical distribution of plant species.
Thus, the study of interaction between living organisms and their environment, focusing on both biotic and abiotic components, is widely recognized and accurately described by Ecology (Option A).
Energy flow in an ecosystem is:
A. Unidirectional
B. Bidirectional
C. Multidirectional
D. None of these.
In ecosystems, the flow of energy is characterized by its pathway from producers to various consumer levels. The process can be unpacked by examining the role of different organisms within the system.
Initially, producers, mainly green plants, utilize photosynthesis to convert solar energy into chemical energy. They form the base of the food chain or the first trophic level.
Then, the energy is transferred to herbivores (second trophic level), who consume the producers. Following this, carnivores, who prey on herbivores, represent the third trophic level, and when there are carnivores that prey on other carnivores, they constitute the fourth trophic level.
Importantly, this energy flow is strictly from producers to various consumer levels and does not reverse. Thus, the flow of energy never goes from carnivores back to producers or from higher trophic levels to lower. This unidirectional energy path underscores a fundamental principle in ecology.
Given this understanding, the answer to the question regarding the nature of energy flow in an ecosystem is: A. Unidirectional.
Energy flow in an ecosystem is:
A. Tetra-directional
B. Tri-directional
C. Bi-directional
D. Uni-directional
Energy flow in an ecosystem is characterized as being uni-directional, and here's a step-by-step explanation of why this is the case:
Producers: The base of an ecosystem's energy flow starts with the producers, typically green plants. These organisms synthesize energy through the process of photosynthesis, converting sunlight into usable chemical energy.
Consumers: This energy is then transferred upwards through the ecosystem. First, it moves to the primary consumers or herbivores, which feed directly on the plants. From the herbivores, the energy moves to secondary consumers or carnivores, which eat the herbivores.
Trophic Levels: This sequence may progress even further to tertiary consumers or top carnivores, depending on the complexity of the ecosystem.
One-Way Flow: It’s crucial to note that the energy flow does not reverse; energy does not move back from carnivores to herbivores or from herbivores to producers. Once consumed, the energy flows from one group to the next without reversing direction.
This unidirectional flow of energy emphasizes the existence of a straightforward pathway from producers through various levels of consumers. This concept firmly supports that energy flow in an ecosystem is uni-directional (Option D). Therefore, energy cannot be recycled between the trophic levels and always flows from the producers to various consumers, supporting the complex structure of the ecosystem.
$\mathrm{pH}$ of which of the following is acidic in nature?
A. Gastric Juice
B. Bile Juice
C. Pancreatic Juice
D. Intestinal Juice
To determine which of the listed juices has acidic nature, we need to consider their respective $\text{pH}$ values:
Gastric Juice: This juice is secreted in the stomach, which is part of the elementary canal. Gastric juice is highly acidic, mainly due to the presence of hydrochloric acid (HCl), and it plays a significant role in the digestion of proteins. The typical $\text{pH}$ range of gastric juice is between 1.5 and 2.5, categorizing it as strongly acidic.
Bile Juice: Secreted by the liver and stored in the gallbladder, bile juice is involved in the digestion and absorption of fats. It has a generally alkaline or neutral $\text{pH}$, generally above 7.
Pancreatic Juice: Produced by the pancreas, this juice contains enzymes that aid in the digestion of carbohydrates, proteins, and fats. Its $\text{pH}$ is usually neutral to slightly alkaline.
Intestinal Juice: Secreted by the glands in the intestine, this juice plays a role in the final stages of digestion. It has a neutral or slightly alkaline $\text{pH}$.
Given the information and the roles of these digestive juices, it is clear that Gastric Juice (Option A) is the only one among the options listed that is acidic in nature, with a $\text{pH}$ well below 7. This is essential for the digestion of food, particularly proteins, in the stomach. Thus, option A (Gastric Juice) is the correct answer for the juice that is acidic in nature.
Which of the following groups constitutes a correct food chain?
A. Grass $\rightarrow$ Rabbit $\rightarrow$ Snake $\rightarrow$ Eagle
B. Grass $\rightarrow$ Goat $\rightarrow$ Fox $\rightarrow$ Lion
C. Goat $\rightarrow$ Grass $\rightarrow$ Elephant $\rightarrow$ Snake
D. Grass $\rightarrow$ Wheat $\rightarrow$ Frog $\rightarrow$ Goat.
A correct food chain correctly represents the flow of energy from one organism to another in an ecosystem. The energy begins with producers and moves through various levels of consumers. Let's explore the given options to find the correct food chain:
Option A: Grass $\rightarrow$ Rabbit $\rightarrow$ Snake $\rightarrow$ Eagle. This appears to be a feasible chain as it starts with a producer (grass), followed by an herbivore (rabbit), then a carnivore (snake), and finally a higher-level predator (eagle).
Option B: Grass $\rightarrow$ Goat $\rightarrow$ Fox $\rightarrow$ Lion. This chain also starts with a producer, followed by an herbivore (goat). However, while a fox might prey on goats, lions do not typically prey on foxes, which breaks the chain's logical progression.
Option C: Goat $\rightarrow$ Grass $\rightarrow$ Elephant $\rightarrow$ Snake. This order is incorrect as it implies animals (goat) consuming plants (grass) out of the traditional flow, and an elephant being prey for a snake, which is ecologically inaccurate.
Option D: Grass $\rightarrow$ Wheat $\rightarrow$ Frog $\rightarrow$ Goat. This chain is flawed as both grass and wheat are producers (plants) and do not consume one another. Additionally, goats do not typically prey on frogs.
Based on the correct progression of energy transfer from a producer to higher levels of consumers, Option A correctly represents a viable food chain: $$ \text{Grass} \rightarrow \text{Rabbit} \rightarrow \text{Snake} \rightarrow \text{Eagle} $$ This sequence accurately follows the ecosystem's natural order: starting with a primary producer (grass) and moving up through various consumer levels — from primary consumer (rabbit) to secondary (snake) and finally a tertiary consumer (eagle), maintaining ecological accuracy and energy flow continuity.
Lack of which element occurs when Algal Bloom is formed in a water body.
A. Oxygen
B. Nitrogen
C. Hydrogen
D. Calcium
When an algal bloom forms in a water body, it indicates an excessive growth of small plant-like organisms known as phytoplans in the water. This rapid proliferation of algae turns the water green and leads to significant ecological consequences. One of the primary issues caused by algal blooms is the consumption of oxygen by these plants as they grow and decompose. This excessive use of oxygen reduces its availability for other aquatic organisms, such as fish, leading to a condition often referred to as hypoxia or low oxygen levels. As a result, aquatic organisms that rely on dissolved oxygen struggle to survive, often leading to die-offs of these populations.
Therefore, the element that tends to be lacking when an algal bloom is formed in a water body is oxygen. The correct answer is: A. Oxygen.
Which one of the following animals is different from others in not having the paired gill pouches?
A. Whale
B. Water snake
C. Starfish
D. Seahorse
. The importance of gill pouches mainly lies in their role in respiration. To understand this better, let's briefly look at the anatomy related to gills in different animals, including humans at their fetal stage, where such structures are also observed aiding in gas exchange.
Among the animals listed:
Whales are mammals and do not have gill pouches as they breathe air through lungs.
Water snakes are reptiles and also breathe using lungs, hence they don't possess gill pouches.
Seahorses are fish, and they do possess gills that assist in breathing underwater.
Starfish, on the other hand, differ significantly as they belong to a group known as echinoderms and do not have gills in the form of pouches. Instead, they breathe through their tube feet and skin, using a water vascular system, which is unique to their group.
Therefore, the correct answer to which animal is different in not having paired gill pouches is: C. Starfish. This choice stands out because it utilizes a completely different respiratory system.
A taxonomist, during his voyage, found a solitary marine animal with spines on skin made of calcium carbonate. However, its coelom was made of pouches pinched off from endoderm. Assign the specimen to the most appropriate phylum.
A. Chordata
B. Nematoda
C. Coelenterata
D. Echinodermata
The correct answer is Phylum Echinodermata. Here are the reasons supporting this classification:
The animal has a skin with spines made of calcium carbonate, which is characteristic of echinoderms. Echinoderms, like sea urchins and starfish, often possess external structures or ossicles formed from calcium carbonate, providing them with a spiny appearance.
The mention of the animal's coelom being made of pouches pinched off from the endoderm aligns with the development process found in echinoderms, where the coelom forms through enterocoely (the formation of the coelom as out-pocketings from the primitive gut in the embryo).
Furthermore, echinoderms are wholly marine organisms, which corresponds to the animal being described as 'solitary marine.' They have a unique water vascular system used for locomotion, feeding, and respiration, which matches the specialized systems referred to in the discussion.
Given these details, the specimen does not fit with the characteristics of Chordata, Nematoda, or Coelenterata, solidifying Option D (Echinodermata) as the most suitable classification based on the described physical and anatomical features.
Which factor is responsible for the Greenhouse Effect?
A. $\mathrm{H}{2} \mathrm{O}$
B. $\mathrm{CO}$
C. $\mathrm{SO}{2}$
D. $\mathrm{CO}_{2}$
Correct Answer: D. $\mathrm{CO}_2$
The Greenhouse Effect is a crucial environmental phenomenon where certain gases in Earth's atmosphere trap sunlight, which has been converted into heat. This trapping of heat helps maintain Earth's average temperature, but excessive trapping can lead to global warming. Among the provided options, carbon dioxide ($\mathrm{CO}_2$) is a significant greenhouse gas that contributes to this effect.
Here's a detailed breakdown:
$\mathrm{H}_2\mathrm{O}$ (water) does contribute to the greenhouse effect, but in this context, we are focusing on gases where human activity has a direct impact on atmospheric concentrations.
$\mathrm{CO}$ (carbon monoxide) and $\mathrm{SO}_2$ (sulfur dioxide), although pollutants, are less significant in direct contributions to the greenhouse effect compared to $\mathrm{CO}_2$.
$\mathrm{CO}_2$, on the other hand, is a major greenhouse gas which is primarily released through activities like fossil fuel combustion and deforestation. It has a direct and substantial impact on the warming of the planet.
Thus, option D. $\mathrm{CO}_2$ is the primary factor responsible for the Greenhouse Effect among the choices given.
Biotic components of the ecosystem among the following are:
A Producers
B Consumers
C Decomposers
D All of the above
In an ecosystem, we differentiate between two major types of components: biotic and abiotic. Biotic components refer to the living elements of the ecosystem, such as organisms, while abiotic components include non-living environmental factors like sunlight, wind, and water.
The primary biotic components can be categorized into:
Producers (Option A): These are organisms, mainly plants and algae, that produce their own food through photosynthesis.
Consumers (Option B): These are organisms that consume other organisms for energy. Examples include animals such as deer and lions.
Decomposers (Option C): These include organisms like bacteria and fungi that break down dead material and waste, recycling nutrients back into the ecosystem.
Given the options provided:
A (Producers)
B (Consumers)
C (Decomposers)
Since all these options represent living components involved in the ecosystem's food web and nutrient cycles, the correct answer would be:
D (All of the above).
Which organelle of a cell is called the powerhouse of the cell?
A. Mitochondria
B. Chloroplast
C. Ribosome
D. Lysosome
The organelle known as the powerhouse of the cell is the Mitochondria. The primary reason it's termed the powerhouse is due to its role in the production of ATP (adenosine triphosphate), which is the main energy currency in cells. This process is crucial because ATP is what provides the energy for various functions within the cell.
Mitochondria are unique because they have their own DNA and ribosomes, which allows them to replicate independently within the cell. These features contribute to their ability to efficiently produce ATP through the process of ATP synthesis. Essentially, mitochondria facilitate the conversion of nutrients into energy, which is why they are referred to as the powerhouse of cells, heavily involved in energy production, especially in plant cells where they are prominent. This organelle is vital not only in energy production but also for other cellular processes that require energy input derived from ATP.
Which of the following is known as the 'suicide bag' of the cell?
A. Plastid
B. Mitochondria
C. Ribosome
D. Lysosome
The correct answer is D. Lysosome.
Here's why:
Lysosomes are referred to as the "suicide bags" of the cell due to their critical role in autolysis, which involves breaking down cellular components. They contain hydrolytic enzymes, which are capable of degrading all types of biological polymers including proteins, nucleic acids, carbohydrates, and lipids. These enzymes are vital for digestion and waste handling, helping to break down excess or worn-out organelles, food particles, and engulfed viruses or bacteria.
However, if a lysosome's enzymes are released into the cytosol, they can also cause destruction of the cell's own components, potentially leading to cell death. This capability is crucial for controlling cell quality and health, but it also means that a lysosome can essentially cause the cell to digest itself, hence the nickname "suicide bag."
In terms of the other options:
A. Plastid primarily relates to functions like photosynthesis in plant cells and is involved in food production and storage.
B. Mitochondria are known for cellular respiration and energy production but not for digesting cell components.
C. Ribosome is responsible for protein synthesis, not cellular digestion.
Thus, the label "suicide bag" fittingly applies to the lysosome due to its potent enzyme content and role in cell breakdown and turnover, making option D correct.
Where does glycolysis occur in a cell? A) In Mitochondria B) In Chloroplast C) In Cytoplasm D) In Nucleus
Glycolysis, a key process in cellular respiration responsible for the synthesis of energy, occurs in the cytoplasm of the cell. This process involves the breakdown of glucose into pyruvic acid. Answering the multiple-choice question provided, option C) In Cytoplasm is the correct answer.
Further details about other components mentioned:
Mitochondria are involved in later stages of cellular respiration, such as the Krebs cycle, which occurs in the mitochondrial matrix.
Chloroplasts are known as the 'kitchen of the cell', where photosynthesis happens.
Nucleus acts as the 'brain of the cell' containing all the genetic material or DNA.
Thus, for the process of glycolysis, the cytoplasm is where it primarily takes place.
What is the Ecosystem pyramid?
The ecosystem pyramid (also known as the ecological pyramid, energy pyramid, or trophic pyramid) is a graphical representation that shows the biomass or biomass productivity at each trophic level in a given ecosystem.
The bottom of the pyramid represents the primary producers (like plants), the next level up represents the primary consumers (herbivores), then comes the secondary consumers (predators or omnivores), and so on. Each succeeding level represents a decrease in energy, biomass, and population size as you move up the pyramid. This is because, as per the 10% law, only about 10% of the energy at each trophic level is available to the next.
In addition to illustrating the trophic structure of an ecosystem, the pyramid also represents the flow of energy in the ecosystem, from the most energy-dense level (the bottom) to the least energy-dense level (the top). It expresses the concept of energy flow and the loss of energy through respiration, exertion, and waste production at each level.
Match the following organisms with their respective types:
Column I | Column II |
---|---|
Grass | Primary Consumers |
Deer | Producers |
Lion | Decomposers |
Fungi | Secondary Consumers |
In an ecosystem, the biotic components are interconnected through the flow of food and energy. These components are categorized into three main types based on their method of acquiring food:
Producers:
Definition: Producers are photosynthetic organisms that can synthesize organic food from inorganic substances using solar energy through photosynthesis.
Examples: Green plants, photosynthetic bacteria, and some protists.
Consumers:
Definition: Consumers are organisms that cannot produce their own food and rely on consuming other organisms to obtain energy and nutrients.
Types:
Primary Consumers (Herbivores): These organisms eat producers. For example, deer feed on grass.
Secondary Consumers (Carnivores): These organisms eat primary consumers. For example, lions feed on deer.
Decomposers:
Definition: Decomposers obtain their nutrients by breaking down the organic materials of dead producers and consumers, as well as waste products.
Examples: Fungi and bacteria that decompose dead matter and waste.
Therefore, the options can be categorized as follows:
Grass: Producer (Option 1)
Deer: Primary Consumer (Option 2)
Lion: Secondary Consumer (Option 3)
Fungi: Decomposer (Option 4)
In summary, each component plays a crucial role in the ecosystem by participating in the cycle of food and energy transfer.
Two important steps of aerobic respiration, namely oxidative decarboxylation and oxidative phosphorylation, occur respectively in:
A. Cytoplasm and mitochondrial cristae
B. Mitochondrial matrix and mitochondrial cristae
C. Mitochondrial cristae and cytoplasm
D. Mitochondrial matrix and cytoplasm
To determine where the key steps of aerobic respiration, oxidative decarboxylation and oxidative phosphorylation, occur, let's first recall the structure of the eukaryotic mitochondrion.
Aerobic respiration consists of multiple phases, some of which take place in specific parts of the mitochondrion:
Mitochondrial Matrix: This is the innermost space of the mitochondrion. Here, the Krebs cycle (also known as the citric acid cycle) occurs, which includes the step of oxidative decarboxylation. This is where a carboxyl group is removed and carbon dioxide is released.
Mitochondrial Cristae: These are the intricate folds of the inner mitochondrial membrane. The electron transport chain, crucial for oxidative phosphorylation, takes place here. During oxidative phosphorylation, ATP is produced as electrons are transferred through a series of proteins embedded in these cristae.
Given this understanding, the two steps, oxidative decarboxylation and oxidative phosphorylation, occur respectively in:
The mitochondrial matrix for oxidative decarboxylation.
The mitochondrial cristae for oxidative phosphorylation.
Thus, the correct answer is:
B. Mitochondrial matrix and mitochondrial cristae
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Fill in the blanks.
(a) Plants are called as ............................. because they fix carbon dioxide.
(b) In an ecosystem dominated by trees, the pyramid (of numbers) is ............................. type.
(c) In aquatic ecosystems, the limiting factor for the productivity is .............................
(d) Common detritivores in our ecosystem are
(e) The major reservoir of carbon on earth is ..............................
(a) Plants are called as producers because they fix carbon dioxide.
(b) In an ecosystem dominated by trees, the pyramid (of numbers) is inverted type.
(c) In aquatic ecosystems, the limiting factor for the productivity is nutrients.
(d) Common detritivores in our ecosystem are earthworms.
(e) The major reservoir of carbon on earth is earth's crust.
Which one of the following has the largest population in a food chain?
(a) Producers
(b) Primary consumers
(c) Secondary consumers
(d) Decomposers
In a food chain, the largest population is typically found in the producers. Producers form the base of the ecological pyramid and have the highest amount of biomass and energy available in the ecosystem. As you move up the trophic levels to primary consumers, secondary consumers, and so on, the population typically decreases because each subsequent level has less energy available due to energy losses at each trophic transfer.
Thus, the correct answer is:
(a) Producers
The second trophic level in a lake is
(a) Phytoplankton
(b) Zooplankton
(c) Benthos
(d) Fishes
The second trophic level consists of primary consumers, which consume the primary producers.
In a lake ecosystem:
Phytoplankton are the primary producers (first trophic level).
Zooplankton consume the phytoplankton.
Therefore, the second trophic level in a lake is:
(b) Zooplankton.
Secondary producers are
(a) Herbivores
(b) Producers
(c) Carnivores
(d) None of the above
The correct answer is:
(c) Carnivores
Explanation:Secondary producers are organisms that occupy the second level of secondary productivity, which involves forming new organic matter by consuming herbivores. In ecological terms, these are typically carnivores that feed on herbivores (primary consumers). Herbivores are primary consumers, and producers are plants or autotrophs that generate organic matter from inorganic substances through photosynthesis.
What is the percentage of photosynthetically active radiation (PAR) in the incident solar radiation?
(a) $100 \%$
(b) $50 \%$
(c) $1-5 \%$
(d) $2-10 \%$
The percentage of photosynthetically active radiation (PAR) in the incident solar radiation is less than 50 percent.
Therefore, the correct answer is:
(b) $50 %$
Distinguish between
(a) Grazing food chain and detritus food chain
(b) Production and decomposition
(c) Upright and inverted pyramid
(d) Food chain and Food web
(e) Litter and detritus
(f) Primary and secondary productivity
(a) Grazing Food Chain and Detritus Food Chain
Grazing Food Chain (GFC):
Starts with: Primary producers like plants.
Pathway: Producer → Herbivore → Carnivore
Example: Grass → Grasshopper → Frog → Snake → Hawk
Major Conduit: More prominent in aquatic ecosystems.
Detritus Food Chain (DFC):
Starts with: Dead organic matter (detritus).
Pathway: Detritus → Decomposer → Detritus feeder
Example: Dead leaves → Fungi/Bacteria → Earthworms → Birds
Major Conduit: More prominent in terrestrial ecosystems.
(b) Production and Decomposition
Production:
Definition: The process of biomass or organic matter production by plants through photosynthesis.
Measure: Typically expressed in terms of weight ($\text{g m}^{-2}$) or energy ($\text{kcal m}^{-2}$).
Decomposition:
Definition: The breakdown of complex organic matter into simpler inorganic substances by decomposers.
Process: Involves fragmentation, leaching, catabolism, humification, and mineralization.
(c) Upright and Inverted Pyramid
Upright Pyramid:
Shape: Broad at the base and narrows toward the apex.
Energy Flow: Energy decreases at higher trophic levels.
Common Form: Most biomass and energy pyramids in terrestrial ecosystems.
Inverted Pyramid:
Shape: Narrow at the base and broad at the apex.
Energy Flow: Inverted typically in biomass pyramids of aquatic ecosystems where a small biomass of producers (phytoplankton) supports a larger biomass of consumers.
(d) Food Chain and Food Web
Food Chain:
Definition: A linear sequence of organisms where each is eaten by the next member in the chain.
Simplicity: Simplistic model with a single pathway of energy flow.
Food Web:
Definition: A network of interconnected food chains in an ecosystem.
Complexity: More complex and shows multiple pathways of energy flow.
(e) Litter and Detritus
Litter:
Definition: Freshly fallen, undecomposed organic matter like leaves, twigs, and other plant parts.
Position: Typically, found on the surface of the soil.
Detritus:
Definition: Partially decomposed organic matter including dead plant and animal remains.
Further Processed: Forms the raw material for decomposers.
(f) Primary and Secondary Productivity
Primary Productivity:
Definition: Rate at which energy is captured by producers through photosynthesis.
Types: Gross Primary Productivity (GPP) and Net Primary Productivity (NPP).
Secondary Productivity:
Definition: Rate of biomass formation by consumers (herbivores, carnivores).
Source: Depends on primary productivity for energy supply.
Describe the components of an ecosystem.
An ecosystem is made up of two main components: abiotic and biotic. These components interact with each other to form a functional unit.
Abiotic Components
These are the non-living chemical and physical parts of the environment:
Inorganic Materials - These include air, water, soil, and minerals.
Climate - Factors like temperature, light, and moisture.
Physical Factors - Elements such as the solar input, cycles of temperature, day-length, and climatic conditions that regulate the rate of functions in the ecosystem.
Biotic Components
These are the living parts of the ecosystem:
Producers (Autotrophs):
Examples: Phytoplankton, algae, plants.
Function: They capture solar energy and convert it into biomass through photosynthesis.
Consumers (Heterotrophs):
Primary Consumers (Herbivores): These feed directly on producers.
Examples: Insects, birds, mammals, molluscs.
Secondary Consumers (Primary Carnivores): These feed on primary consumers.
Examples: Frogs, small fish.
Tertiary Consumers (Secondary Carnivores): These feed on secondary consumers.
Examples: Larger fish, birds of prey.
Decomposers (Saprotrophs):
Examples: Fungi, bacteria, flagellates.
Function: They break down dead organic matter into simpler inorganic substances, thus recycling nutrients back into the ecosystem.
Key Processes
Productivity: The rate of biomass production, which includes processes like photosynthesis.
Decomposition: The breakdown of dead organic matter, making nutrients available for reuse.
Energy Flow: The unidirectional flow of energy from the sun to producers and then through various trophic levels to consumers and decomposers.
Nutrient Cycling: The recycling of nutrients through the biotic and abiotic components of an ecosystem.
Together, these components and processes ensure the structure, function, and sustainability of the ecosystem.
Define ecological pyramids and describe with examples, pyramids of number and biomass.
Ecological pyramids are graphical representations that show the relationship between different trophic levels in an ecosystem. They can illustrate the number of organisms, biomass, or energy at each trophic level. Generally, these pyramids are in three types:
Pyramid of Number
Pyramid of Biomass
Pyramid of Energy
Pyramid of Number
The Pyramid of Number depicts the number of individual organisms at each trophic level in an ecosystem.
Example: In a grassland ecosystem, the producers (grass) form the broad base of the pyramid with a large number of individuals. Primary consumers (herbivores such as rabbits) form a smaller layer above, followed by secondary consumers (such as snakes) with even fewer individuals. Finally, tertiary consumers (such as hawks) form the apex of the pyramid with the smallest number of individuals.
Diagram:
Pyramid of Biomass
The Pyramid of Biomass shows the total mass of organisms at each trophic level.
Example: In a terrestrial ecosystem, producers (plants) occupy the broad base of the pyramid with the highest biomass. Herbivores (like deer) come next with less biomass, followed by carnivores (like wolves) with even lesser biomass. This pyramid shows a considerable decrease in biomass at higher trophic levels.
Diagram:
However, in some ecosystems like the ocean, the pyramid of biomass can be inverted. For instance, the biomass of phytoplankton (producers) is much less than the biomass of zooplankton (primary consumers) and the fish that feed on them.
Diagram:
What is primary productivity? Give brief description of factors that affect primary productivity.
Primary Productivity
Primary productivity is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It is expressed in terms of weight ($\mathrm{gm}^{-2}$) or energy ($\mathrm{kcal} \mathrm{m}^{-2}$). The rate of biomass production is called productivity.
Types of Primary Productivity:
Gross Primary Productivity (GPP): The total rate of production of organic matter during photosynthesis.
Net Primary Productivity (NPP): The rate of storage of organic matter in plants after accounting for the energy used in respiration (R). It is given by: $$ \mathrm{GPP} - \mathrm{R} = \mathrm{NPP} $$
Factors Affecting Primary Productivity
Primary productivity depends on several factors:
Plant Species: Different plant species have varying capacities for photosynthesis and biomass production.
Environmental Factors: These include sunlight, temperature, water availability, and climatic conditions. For example, higher sunlight and optimal temperatures enhance photosynthesis.
Nutrient Availability: Essential nutrients, particularly nitrogen and phosphorus, play a critical role in plant growth and productivity.
Photosynthetic Capacity: The efficiency of a plant’s photosynthetic machinery, particularly chlorophyll content and leaf structure, impacts biomass production.
Summary
Primary Productivity is a measure of biomass/organic matter produced by plants.
It involves both Gross Primary Productivity (GPP) and Net Primary Productivity (NPP).
Major factors include plant species, environmental conditions, nutrient availability, and photosynthetic capacity.
These factors determine the productivity levels of different ecosystems, leading to substantial variation in biomass production across the planet.
Define decomposition and describe the processes and products of decomposition.
Decomposition is the process by which complex organic matter is broken down into simpler inorganic substances such as carbon dioxide, water, and nutrients. This process is essential for the recycling of nutrients in ecosystems, allowing the inorganic substances to be reused by autotrophs (producers).
Processes of Decomposition
Fragmentation: Detritivores, such as earthworms, break down detritus (dead plant and animal matter) into smaller particles.
Leaching: Water percolates through the soil, dissolving water-soluble inorganic nutrients that then move into the soil horizon and get precipitated as unavailable salts.
Catabolism: Microbial enzymes (mainly from bacteria and fungi) further degrade detritus into simpler inorganic substances.
Humification: This results in the accumulation of *humus*, a dark-colored amorphous substance that is highly resistant to microbial action and decomposes at an extremely slow rate.
Mineralisation: Microbes further degrade humus, releasing inorganic nutrients back into the soil.
Products of Decomposition
Humus: A dark, amorphous, colloidal substance that serves as a nutrient reservoir.
Inorganic Nutrients: Elements such as nitrogen, phosphorus, and other minerals that become available for uptake by plants.
Carbon Dioxide and Water: Byproducts of organic matter breakdown that are released into the environment.
Decomposition is largely an oxygen-requiring process, and its rate is influenced by the chemical composition of detritus and climatic factors like temperature and soil moisture. Warm, moist conditions generally favor decomposition, while low temperatures and anaerobic conditions inhibit it.
Give an account of energy flow in an ecosystem.
Energy flow in an ecosystem follows a unidirectional path: from the sun to producers, then to consumers, and finally to decomposers. Here is a step-by-step account of the energy flow in an ecosystem:
1. Solar Energy Capture
Producers (plants, algae, and photosynthetic bacteria) capture solar energy using chlorophyll and convert it into chemical energy via photosynthesis.
2. Primary Productivity
The total energy captured by producers is called Gross Primary Productivity (GPP). A portion of this energy is consumed by plants for respiration. The remaining energy, known as Net Primary Productivity (NPP), is available to the next trophic level - primary consumers.
3. Energy Transfer to Consumers
Primary consumers (herbivores) feed on producers and obtain energy. This energy is used for growth, reproduction, and metabolic activities. The energy transferred to herbivores is variable but follows the 10% law, where approximately 10% of the energy is transferred from one trophic level to the next.
For example: $$ \text{NPP} \quad \rightarrow \quad \text{Mainly used by primary consumers} $$
4. Secondary and Tertiary Consumers
Secondary consumers (primary carnivores) feed on primary consumers, while tertiary consumers (secondary carnivores) feed on primary carnivores. At each trophic level, energy is further reduced, following the 10% law.
5. Detritus Food Chain
Dead organisms and waste materials form the detritus, which is broken down by decomposers (fungi, bacteria). Decomposers play an essential role in converting organic matter into simpler inorganic substances, which are reused by producers.
6. Energy Loss
At every stage, a significant portion of energy is lost as heat due to metabolic processes, in line with the Second Law of Thermodynamics, which states that energy conversion includes energy loss as heat.
Representation of Energy Flow
The above diagram illustrates energy flow in an ecosystem through different trophic levels, emphasizing the decrease in energy at each successive trophic level.
Summary
Unidirectional flow from sunlight to producers → consumers → decomposers.
Decreasing energy at each trophic level due to 10% transfer efficiency.
Significant energy loss as heat.
Understanding this energy flow is crucial because it highlights the connections and dependencies within an ecosystem, emphasizing the importance of producers in sustaining all life forms.
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Ultimate Guide to Ecosystem Class 12 Notes: Structure, Function, and Energy Flow
Introduction to Ecosystems
An ecosystem can be visualised as a functional unit of nature where living organisms interact with each other and with their physical surroundings. Ecosystems vary widely in size, from a small pond to a vast forest or sea. They can be broadly classified into terrestrial ecosystems (like forests, grasslands, and deserts) and aquatic ecosystems (such as ponds, lakes, and rivers).
Structure and Function of Ecosystems
Components of Ecosystems
Ecosystems consist of both biotic (living) and abiotic (non-living) components. Biotic components include:
- Producers: Plants and algae that produce their own food through photosynthesis.
- Consumers: Herbivores, carnivores, and omnivores that depend on other organisms for food.
- Decomposers: Bacteria and fungi that break down dead organic matter.
Abiotic components encompass elements like water, air, soil, and sunlight.
Example of a Pond Ecosystem
A pond is an excellent example of an ecosystem where biotic and abiotic components interact seamlessly.
- Abiotic Factors: Water with dissolved substances and soil at the bottom.
- Autotrophic Components: Phytoplankton, algae, and edge plants.
- Consumers: Zooplankton, free-swimming organisms, and bottom dwellers.
- Decomposers: Fungi and bacteria at the pond’s bottom.
Productivity in Ecosystems
Understanding Primary Productivity
Primary productivity is essential for ecosystem functioning. It refers to the amount of biomass produced by plants through photosynthesis within a specific area and time. This can be measured in terms of weight or energy.
- Gross Primary Productivity (GPP): Total production of organic matter.
- Net Primary Productivity (NPP): GPP minus the energy used in plant respiration. This is the biomass available to consumers.
Factors Affecting Productivity
- Plant Species: Different species have varying photosynthetic capacities.
- Environmental Factors: Light, temperature, and nutrient availability all play crucial roles.
Decomposition Processes
Steps in Decomposition
Decomposition breaks down complex organic matter into simpler substances through five main steps:
- Fragmentation: Detritivores like earthworms break detritus into smaller particles.
- Leaching: Water-soluble nutrients from detritus sink into the soil.
- Catabolism: Microbial enzymes degrade detritus into simpler inorganic substances.
- Humification: Formation of dark, nutrient-rich humus.
- Mineralisation: Breakdown of humus to release inorganic nutrients.
Role of Decomposers
Decomposers like fungi and bacteria play a vital role in recycling nutrients, ensuring ongoing ecosystem productivity.
Energy Flow in Ecosystems
Food Chains and Food Webs
Energy flow in ecosystems can be understood through food chains and webs which illustrate the feeding relationships.
- Grazing Food Chain: Begins with producers and moves to herbivores and then carnivores.
- Detritus Food Chain: Starts with dead organic matter decomposed by fungi and bacteria.
graph LR
A[Sun] --> B[Producers]
B --> C[Primary Consumers]
C --> D[Secondary Consumers]
D --> E[Tertiary Consumers]
E --> F[Decomposers]
Trophic Levels and Energy Transfer
- Primary Consumers: Herbivores feeding on producers.
- Secondary Consumers: Carnivores feeding on herbivores.
- Tertiary Consumers: Higher-level carnivores.
Organisms at each trophic level rely on those at lower levels for energy. However, energy decreases with each trophic level due to energy loss as heat.
Ecological Pyramids
Types of Ecological Pyramids
Ecological pyramids depict the relationship between different trophic levels:
-
Pyramid of Numbers: Shows the number of organisms at each level.
-
Pyramid of Biomass: Illustrates the biomass at each level.
-
Pyramid of Energy: Demonstrates the energy content.
Characteristics of Ecological Pyramids
Most pyramids are upright, but some, like the pyramid of biomass in aquatic ecosystems, can be inverted due to high primary consumer biomass supported by a small producer biomass.
graph TB
A(Producers) -->|10% Energy Transfer| B(Herbivores)
B -->|10% Energy Transfer| C(Carnivores)
C -->|10% Energy Transfer| D(Top Carnivores)
Nutrient Cycling
Types of Nutrient Cycles
- Gaseous Cycles: Carbon and nitrogen cycles involve atmospheric exchanges.
- Sedimentary Cycles: Phosphorus cycle involves Earth’s crust as the main reservoir.
Importance of Nutrient Cycling
Nutrient cycling is essential for sustaining ecosystems by ensuring the reuse of nutrients.
Ecosystem Services
Ecosystems provide various services that are essential for human survival and well-being. For instance, forests purify air and water, while wetlands mitigate flooding.
Conclusion
Understanding the components, energy flow, and productivity of ecosystems helps us appreciate their complexity and significance. Ecosystems play a crucial role in sustaining life on Earth, making it imperative to study and conserve them.
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