Chapter 5 Environment And Its Resources Ecology And Ecological Organization Long Answer Type Questions
WBBSE Life Science And Environment Class 9 Solutions
Question 1. Briefly explain the impact of light on living organisms.
Answer:
Effect of Light on living organisms:
1. In green plants, chloroplasts tend to concentrate on the surface of a leaf which gets more light.
2. In some plants, a span of daylight affects their flowering and other physiological activities. This phenomenon is known as photoperiodism. The plants, such as dahlia, sugarcane, strawberry, etc., flowers bloom during shorter daylight periods and are called Short Day Plants (SDP). The plants, such as peas, radishes, spinach, etc., flowers bloom during longer daylight periods and are called Long Day Plants (LDP).
In some plants, such as tomatoes, cucumbers, cotton, etc., a span of daylight does not have any significant impact on blooming. These are known as Day Neutral Plants (DNP).
WBBSE Class 9 Ecology Long Answer Questions
3. Light enhances the pigmentation of the skin. Animals living in hot and humid climates have darker body colours. Animals living in polar regions have pale body colours. Similarly, the human population living in strongly sunlit regions have darker body colour.
4. Photoperiod is the controlling factor for the breeding features of different animals. The animals, such as sheep, goats, deer, etc., breed during decreasing day length of autumn, known as Short Day Breeders (SDB).
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On the other hand, lemurs, horses, hamsters, etc., breed during increasing day length of spring and are known as Long Day Breeders (LDB). Also, there are certain animals, whose breeding is not affected by day length. These animals include guinea pigs, cats, rabbits, etc.
Important Long Answer Questions for Chapter 5 Life Science
Question 2 Explain the effect of temperature on the living world.
Answer:
Effect of temperature on living organisms:
1. Plants growing in desert regions have light-coloured body hairs, that act as heat reflectors. Their leaves are modified into spines and they have fewer stomata to reduce transpiration.
The overall surface area of these plants is less, compared to other plants. As a result, the area exposed to air is reduced, thereby reducing the rate of transpiration.
2. Plants growing in the hot but humid climate of the tropical region, have broad flat and thick green leaves to increase the rate of transpiration.
3. In amphibians, reptiles and fishes, body temperature varies with environmental temperature. These animals are, therefore, known as poikilothermic animals. On the other hand, birds and mammals maintain constant body temperature in any environment. These are known as homeothermic animals.
4. Some animals, such as toads, house lizards, ants, etc., can withstand a wide range of temperature variations in the environment. These are called eurythermal animals. Some animals, such as fishes and cnidarians cannot tolerate wide temperature fluctuation. These are called stenothermal animals.
WBBSE Life Science And Environment Class 9 Solutions
Question 3. Explain the effect of relative humidity on living organisms.
Answer:
Effect of relative humidity on living organisms:
1. Plants growing in moist environments have wider leaves with many stomata to dispose of excess water and these plants perform transpiration at a higher rate.
Certain plants like tomatoes and a few types of grass dispose of excess water as tiny droplets through special water pores, called hydathodes, situated along the edge of the leaves to get rid of excess water.
2. Animals living in desert regions have few sweat glands and discharge scanty urine and dry faeces. A desert reptile, Moloch horridus have uniquely designed spiny skin to reduce water loss and maintain body humidity. Insects living in desert regions bear a layer of waxy cuticles over their body to reduce water loss.
3. Plants growing in arid climates develop features that help them to resist atmospheric dryness. They have elaborate root systems, few leaves, fewer stomata, waxy leaf and stem surfaces, elaborate tap root systems, etc. to conserve and collect more water.
4. Excessive relative humidity is favourable for the growth of the fungal population. In moist weather, different pathogenic and non-pathogenic fungi grow. In moist weather, the population of bryophytes and pteridophytes also increase significantly.
Question 4. Explain the role of different factors regulating population size.
Answer:
Factors regulating population size:
Four factors play a significant role in regulating the population size.
These are:
1. Natality
2. Mortality
3. Immigration
4. Emigration.
1. Natality:
Natality can be defined as the ratio of total live births to a population in a specified community or area, over a specific period of time. We may express natality or birth rate as the number of live births per 1000 of the population per year. It can be represented as the following equation-
B = \(\frac{nb}{N} x 1000, where, B = natality or birth rate, N = total number of individuals in a population, nb number of live births.
2 Mortality:
Mortality can be defined as the ratio of total deaths to a population in a specified community or area, over a specific period of time. Population size decreases with the increase in mortality of the individuals.
Death rate or mortality is often expressed as the number of deaths per 1000 of the population per year. It can be represented as the following equation.
D = [latex]\frac{nd}{N}\) x 1000, where, D = mortality or death rate, N = total number of individuals in a population, nd = number of deaths
3 Immigration: Immigration is the mass entry of individuals in a population in a given area, from some other place. Therefore, immigration increases the population size very quickly.
4 Emigration: Emigration, on the other hand, means the mass departure of individuals from a population in a given area, to some other place. By emigration, population size goes down abruptly.
Concepts Related to Ecosystems for Long Answers
Question 5. Discuss different levels of positive interspecific interactions in the living world.
Answer:
Positive interspecific interactions in the living world:
Positive interactions in the living world are collectively known as cooperation. In nature, several species live together in cooperation. Here, both or at least one of the species, involved in the relation, is benefited, but neither of them is harmed. This cooperative relationship between different species helps in better growth, reproduction and survival.
Cooperation may be of different types:
1. Symbiosis
2. Mutualism
3. Protocooperation
4. Commensalism.
These are described below:
1. Symbiosis:
Symbiosis is an interspecific cooperation, in which two species live in a close physical association and both are benefited some way or the other. Symbiosis may be obligate (both species entirely depend upon one another for survival) or facultative (both species do not depend on their partner for survival).
Example:
In lichens, algae and fungi develop symbiotic associations. Here, the fungus acts as a settling platform and provides water and mineral to the alga. In return, the alga synthesises food for both.
2. Mutualism:
Mutualism is the cooperation between two species, in which both are benefited but close physical association and nutritional interdependence between them is not evident. Example-Insects collect nectar and pollen from flowers. In exchange, they help in spreading pollen grains from one place to another that help in plant reproduction.
3. Protocooperation:
Protocooperation is a positive interspecific interaction, where both members are benefited but, they do not depend on one another for survival. Growth and survival of both species is possible even in the absence of this interaction. Mutualism between insect and flower.
Example:
Sea-anemone often rides on the shell of a hermit crab. Here sea anemone intakes discarded food of the hermit crab and in return protects it from the predators by its stinging cells. This relation is not obligatory because both can live independently.
4. Commensalism:
Commensalism is the cooperation between two species, where one of the members is benefits, but the other member is neither benefited nor harmed. In this relation, close association occurs between the two species, but nutritional interdependence is not developed.
Example:
Epiphytic orchids grow on the branches of big trees, but carry out photosynthesis independently. By this process, orchids escape predation, but the host tree is neither harmed nor benefited.
WBBSE Life Science And Environment Class 9 Solutions
Question 6. Discuss competition, predation and parasitism in the living world.
Answer:
Interactions in the living world:
In the living world, intraspecific and interspecific interactions involve two individuals, of which either both or one of the members is benefited and the other member sustains a loss, gets injured or dies. Among these interactions competition, predation and parasitism are important.
Study Guide for Class 9 Life Science Ecology Questions
These are described below:
1. Parasitism:
Parasitism is the most advanced type of interspecific interaction, in which one species depends upon other species for food or shelter or both. Here, the dependent member (parasite) is benefited, but the other member (host) is deprived.
Example:
Tapeworms (Taenia sp.), roundworms (Ascaris sp.), etc. are parasitic worms that draw nutrients from humans (host). Dodder plants (Cuscuta sp.) suck nutrients from the phloem of the host plants.
2 Competition:
Competition can be defined as a negative interaction, where members of the same or other species fight with each other to acquire a limited supply of environmental resources food, water, shelter and mates.
Competition is mainly of two types:
1. Intraspecific competition
2. Interspecific competition.
1. Intraspecific competition: In this competition, members of the same species fight among themselves for food and mate.
Example: Fighting among dogs or fighting among cats.
2. Interspecific competition: This competition takes place between members of two or more different species, for food and shelter.
Example: Sparrows quarrelling with common maina or dogs fighting with cats.
3. Predation:
Predation is another type of interspecific interaction, in which one species attacks another species to kill and consume it. Here, the attacker is known as the predator and the one, which is attacked, is called the prey. The predator obtains nutrition and energy from the prey.
Example:
Tigers kill deer, praying mantis kills other insects, pitcher plants trap insects, etc. In all the above examples, the former ones are the predators and the latter ones are the prey.
WBBSE Life Science And Environment Class 9 Solutions
Question 7. Write down a brief note on different types of parasites in living world.
Answer:
Different types of parasites:
From an evolutionary point of view, parasitism is the most advanced type of interspecific interaction, in which one species depends upon other species for food or shelter or both. Here, the dependent member (parasite) is benefits, but the other member (host) is deprived. Different types of parasites are described below.
Based on their position in the host body, parasites are classified into two types:
1. Ectoparasites: These parasites draw nutrients from outside the body of the host.
Example:
Lice, ticks, and bedbugs live on the body surface of mammals. In the case of parasitism in plants, the Dodder plant needs special mention. Dodder plant
(Cuscuta sp.) produces root-like structures, called haustoria, which penetrate the vascular bundle of the host and derive nutrition directly.
2. Endoparasites: These parasites live inside the body of the host and collect nutrients from them.
Examples: Tapeworms, roundworms, Plasmodium (malarial parasite), liver fluke, etc. live inside the human body.
On the basis of the dependence of parasitism, they may be of two types-
3. Obligatory parasites: These species completely depend upon a host to complete their life cycle.
Example: Tapeworms, roundworms, Plasmodium, etc. spend their life permanently as parasites.
4. Facultative parasites: These species can survive without the parasitic mode of life but can also adapt a parasitic life.
Example: The parasitic nematode Strongyloides stercoralis can also be free living.
Sample Long Answer Questions from WBBSE Class 9 Life Science
Question 8. Briefly describe the general structural aspects of an ecosystem.
Answer:
The structural aspect of the ecosystem:
An ecosystem constitutes two types of components or factors:
1. Abiotic factors
2. Biotic factors.
1. Abiotic factors:
Abiotic factors include the non-living components of the ecosystem. They have a direct impact on the life process of living organisms.
Various abiotic components of the ecosystem are:
1. Organic component,
2. Inorganic component
3. Physical component.
1. Organic component:
Different organic matters, such as carbohydrates, proteins, fat, etc. are obtained from the dead and decaying organic remains of plants and animals. These organic matter mix with the soil and produce humus, which plays a significant role in regulating soil fertility.
2. Inorganic component:
It includes various mineral elements (such as calcium, magnesium, salts of sodium, potassium, sulphur, etc.) and gases (such as oxygen, nitrogen, carbon dioxide, etc.). Green plants use these elements for synthesizing their own food.
3. Physical component:
The physical component of the ecosystem includes various factors, such as light, temperature, humidity, altitude, steepness of slope, and firmness of soil. Of these, the most important physical factor is light, more specifically sunlight. Green plants trap solar energy and convert it to chemical energy to prepare their own food by the process of photosynthesis.
2 Biotic factors: The living organisms constitute the biotic factors of an ecosystem.
Various components of biotic factors are:
1. Autotrophs
2. Heterotrophs.
1. Autotrophs:
All those organisms, capable of synthesizing their own food by photosynthesis or chemosynthesis, are known as autotrophs. All green plants, photosynthetic and chemosynthetic microorganisms are examples of autotrophs.
2. Heterotrophs:
The living organisms, which depend directly or indirectly on autotrophs for their nutrition are known as heterotrophs.
Heterotrophs may be classified into three types:
1. Consumers
2. Decomposers
3. Transformers
1. Consumers:
These organisms directly or indirectly consume autotrophs, especially green plants and plant products, to gain nutrition and energy. So, they are called consumers. Depending upon the nature of food they eat, consumers are classified into three types- (a) Primary consumers: These animals directly consume green plants or plant products for nutrient and energy. Example-Deer, cow, grasshopper, etc. (all herbivores).
2. Secondary consumers: These animals directly consume herbivores for nutrition. Example-Frogs, small birds, rat, lizards, etc.
3. Tertiary consumers: These are larger consumers, which feed on both primary and secondary consumers.
Example: Owl, tiger, lion, falcon, king cobra, etc.
2. Decomposers and transformers:
The organisms, which get their nutrients from dead organisms and decaying organic matter and in this process break the larger organic compounds into smaller molecules, are called decomposers. Different microorganisms (such as bacteria) and some fungi (such as Agaricus) belong to this group.
Some bacteria act upon those small organic molecules, that are the end products of decomposition. These bacteria completely break those organic molecules and return the elementary components in nature. They are called transformers.
WBBSE Class 9 Life Science Solutions
Question 9. How does energy flow through an ecosystem?
Answer:
Energy flow in the ecosystem:
Energy flow can be defined as the unidirectional transfer of solar energy, in the form of organic matter, from producers to the highest level of consumers, through different trophic levels via food chains.
Sun is the ultimate source of energy in all ecosystems. Only photosynthetic organisms are capable of trapping and transforming the light energy form the sun into chemical energy in the form of food.
This energy is transferred from producers to consumers through food chain, which is called flow of energy. Energy flow in an ecosystem occurs through the following three steps.
1. Acquiring energy:
All green plants and other photosynthetic microorganisms can trap radiant energy from the sun. Only 0.02% of the total energy of sun comes to the earth as light. Of this, only 0.1% is trapped by means of photosynthesis. This process is called acquiring energy.
2. Utilizing energy:
The light energy from the sun, trapped by the green plants, is oxidized during respiration to produce chemical energy. This energy is necessary to carry out different metabolic activities. This process is called utilization of energy.
3. Transfer of energy:
From the green plants, net primary production passes to different level of consumers through food chain. The herbivores or primary consumers directly get their share of energy from producers.
By respiration, primary consumers utilize a greater portion of the transferred energy. the remaining portion of the energy is then transferred to the higher level of consumers in the same way.
When energy flow occurs from one trophic level to another, subsequently an amount of energy is lost in the process which cannot be regained further.
Moreover, the energy that follows from producer to consumer, can never be returned to the producer. Hence, the flow of energy is always unidirectional.
According to famous scientist, Lindeman, out of the total energy produced or received in a particular trophic level, only 10% of it is transferred to the next trophic level.
This is known as Lindeman’s 10% law. As a result, a very less amount of energy is received by the members of the highest trophic level.
Question 10. With an example, describe how the biogeochemical cycle of a nutrient operates in nature.
Answer:
Biogeochemical cycle of a nutrient:
Living organisms obtain different nutrients (such as C, H2, O2, N2, S, P, Ca, etc.) from the environment through food and as respiratory gases. These elements act as structural components of a living body.
These elements are returned to the environment by excretion, respiration and decomposition of dead or decaying organic matter. Within the biosphere, several are structurally and metabolically important. elements are exchanged between the biotic and the abiotic components of the ecosystem.
This exchange of elements occurs through a cyclic path, known as the nutrient cycle or biogeochemical cycle. Here, the carbon cycle is discussed below as an example.
The carbon cycle refers to the cyclic exchange of carbon in the physical and biological systems:
1. Reservoir Pool: Carbon bed of the lithosphere act as a reservoir pool for carbon.
2. Cyclical Pool: The cyclic pool of carbon involves the atmosphere and the sea water.
3. Utilisation of carbon from nature: It involves two pathways
1. Biological path:
The biological path of carbon utilization involves activities of green plants and shelled molluscs. Green plants trap carbon within cellular compounds by photosynthesis. Shelled molluscs utilize carbon of CO2 to prepare their shell. The echinoderms from air to form the spinous body surface with ossicles, which is made up of calcium carbonate.
2. Physiochemical path: The physiochemical path of carbon utilization involves certain marine deposits, such as limestone, dolomite, feldspar, etc. absorb carbon (CO2) to prepare calcium carbonate (CaCO3).
4 Return of carbon to nature:
Carbon is returned to the environment by two pathways:
1. Biological path:
All living forms (except a few anaerobes) release CO2 by respiration. CO2 is released into the nature by decomposition of organic matters. After the death of molluscs and sea corals, their calcium carbonate rich shells are decomposed to produce CO2.
2. Physiochemical path:
Combustion of fossil fuel, wood, etc., forest fire and volcanic eruption produce huge quantity of CO2. This cyclic process of utilization and return of carbon to nature occurs at the same rate. This helps to maintain constant carbon content in the environment.
WBBSE Class 9 Life Science Solutions
Question 11. What are the features of energy flow in an ecosystem.
Answer:
The characteristics of energy flow:
1. Solar energy is the main source of energy in all ecosystem.
2. Energy flow is unidirectional.
3. Amount of energy gradually decreases along the trophic level.
4. Energy flow in an ecosystem occurs through three steps-acquiring of energy, utilisation of energy and transfer of energy.
5. Energy flow in an ecosystem obeys the first and second laws of thermodynamics.
6. In the year 1942, Lindemann formulated 10% law of energy flow. According to this law, only 10% of total energy of any trophic level is transmitted to next trophic level during energy flow through several trophic levels.
Question 12. Deseribe about the different levels of ecological organisation.
Answer:
Different levels of ecological organisation:
The various levels of ecological organisations are:
1. Organism:
It is the lowest level of organisation, which includes both unicellular and multicellular organisms. All the living species in this level exhibits all the characteristics required for the existence of life.
2. Population:
A population is a group of individuals of a single species living together within a particular geographic area. They inter breed and complete with each other for resources.
3. Community:
It refers to the several populations that interact and inhabit a common environment and are inter dependent.
4. Ecosystem:
It is a set of all living species and abiotic components existing and interacting in a given area. There is an interaction with both living and non-living components of the environment.
5. Biosphere:
It is highest level of organisation. It is the global ecological system which consists of all the living organism and other factors which supports life. Biosphere mainly refers to the part of the earth’s crust.
WBBSE Class 9 Life Science Solutions
Question 13 How do you build a pond ecosystem?
Answer:
Pond Ecosystem:
The pond ecosystem contains two main components i.e.,
1. Abiotic.
2. Biotic.
1. Abiotic components:
They are formed as a result of the mixture of some organic and inorganic materials. They have direct or indirectly effects in aquatic organisms in the pond. These includes-light, temperature, dissolved oxygen, carbon dioxide, other gases, pH of water, turbidity, and dissolved minerals.
2. Biotic components:
They are the living components which consist of:
1. Producers:
They are the aquatic green plants, which may be divided into two groups:
1. Microphytes (Phytoplanktons): They are microscopic autotrophs, which fix solar energy. Example-Spirogyra, Zygonema, Volvox, Oedogonium, etc.
2. Macrophytes: They are large plants, which manufacture complex food. Example-Pistea, Hydrilla, etc.
2. Consumers:
They are those heterotrophic organisms, which consume producers as food.
Their types are:
1. Primary consumers: These herbivorous animals depend on autotrophic organisms such as microscopic plant eaters or zooplanktons, molluscs, beetles, Cyclops, Daphnia, etc.
2. Secondary consumers: These are primary carnivores, which depend on herbivorous animals for food.
Example: Insects, fish, frogs, crab, etc.
3. Tertiary consumers: These are the second grade of carnivores. They feed upon plants and animals (secondary consumers), therefore are called carnivores.
Example: Large fishes, frogs.
3. Decomposers:
Most of the decomposers of the pond ecosystem are saprophytes but some parasites are also found. Bacteria, and fungi, like Aspergillus, Cladosporium, Rhizopus, Alternaria, Fusarium, Saprolegnia, etc. are decomposers.
Generally, the decomposers either live in the soil layer beneath water or in the mud. They act on the dead and decayed organic matter of plants and animals and supply raw materials to the producers.
Understanding Ecosystem Dynamics for Long Answers
Question 14. Describe the structure of the forest ecosystem.
Answer:
Forest ecosystem:
The forest ecosystem contains two main components i.e.,
1. Biotic
2. Abiotic.
1 Biotic component:
1. Producer organisms: In a forest, the producers are mainly trees. Apart from trees, climbers, epiphytes, shrubs and ground vegetation. Dominant species of trees in major types of forest ecosystems are-Tectona grandis, acer, betula, picea, pine, cedrus.
2. Consumers:
In a forest, consumers are of three main types:
1. Primary consumers: These are herbivores which feed directly on producers.
Example: Ants, beetles, bugs, spiders, etc. feeding on tree leaves. Larger animals like elephants, deer, giraffe, etc. grazing on shoots and/or fruits of trees.
2. Secondary consumers: These are carnivores and feed on primary consumers.
Examples: Birds, lizards, frogs, snakes and foxes.
3. Tertiary consumers: These are secondary carnivores and feed on secondary consumers. These include top carnivores like lions, tigers, etc.
3. Decomposers:
These include a wide variety of saprotrophic microorganisms, like bacteria (Bacillus sp., Clostridium sp.), fungi (Aspergillus sp., Ganoderma sp., Fusarium sp.), actinomycetes (Streptomyces sp.). They attract dead or decayed bodies of organisms and thus decomposition takes place. Therefore, nutrients are released for reuse.
2 Abiotic components: These include basic inorganic and organic compounds present in the soil and atmosphere. In addition, dead organic debris is also found littered in forests.
