GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

   

Gujarat Board GSEB Textbook Solutions Class 12 Biology Chapter 13 Organisms and Populations Textbook Questions and Answers, Additional Important Questions, Notes Pdf.

Gujarat Board Textbook Solutions Class 12 Biology Chapter 13 Organisms and Populations

GSEB Class 12 Biology Organisms and Populations Text Book Questions and Answers

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 1.
How is diapause different from hibernation?
Answer:
Hibernation is the phenomenon commonly depicted by ectothermal (cold blopded) animals which escape cold by hiding them in shelters such as caves, burrows, crevices, hollow tree trunks, mud etc. revealing minimum physiological activity. This phenomenon is also shown by some warm blooded mammals.
Diapause is the phenomenon of spending unfavourable climatic conditions by insects during their development.

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 2.
If a marine fish is placed in a fresh water aquarium, will the fish be able to survive? Why or why not?
Answer:
No. Because marine fish is adapted to live in saline water. In fresh water, it will not be able to cope with the outside hypotonic environment because of osmoregulation problems.

Question 3.
Define phenotypic adaptation. Give one example.
Answer:
Phenotypic adaptation: It is a non-genetic change in physical and physiological characteristics which develops in response to changes in the environment and are useful to organisms in adjustment to prevailing Pvt. conditions.
eg:-

  • Mountain sickness in normal people in high attitudes but tribes living in the Himalayas do not have mountain sickness
  • Euphorbia hirta plant species.

Question 4.
Most living organisms cannot survive at temperatures above 45°C. How are some microbes able to live in habitats with temperatures exceeding 100°C?
Answer:
Such microorganisms have a minimum amount of free water in their bodies. Removal of water provides resistance to high temperatures.

Question 5.
List the attributes that populations but not individuals possess.
Answer:

  • Population density
  • Birth rate
  • Death rate
  • Sex ratio
  • Population growth
  • Age distribution
  • Population dispersal.

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 6.
If a population growing exponentially doubles in size in 3 years, what is the intrinsic rate of increase (r) of the population?
Answer:
The intrinsic rate of increase of this population will be towards the maximum.

Question 7.
Name important defence mechanisms in plants against herbivory.
Answer:
Defence is of 2 types Morphological and chemical Defences.
Morphological defence-

  • Thoms, spines, prickles, bristles
  • Stinging hair, sticky hair, hairy coating
  • Harboring ants
  • The resemblance to dreaded animals.

Chemical Defences:

  • Latex
  • Alkaloids
  • Tannins
  • Silica
  • Bitter taste, Offensive smell
  • Irritating substance
  • Poisonous cardiac glycosides.

Question 8.
An orchid plant is growing on the branch of mango tree. How do you describe this interaction between the orchid and the mango tree?
Answer:
The interaction between orchid and the mango tree is termed commensalism where in orchid derives benefit of interaction while mango tree is not affected.

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 9.
What is the ecological principle behind the biological control method of managing pest insects?
Answer:
The ecological principle behind the control of pest insects is controlling the growth of their population through natural enemies, predators, parasites.

Question 10.
Distinguish between the following:
a. Hibernation and Aestivation
b. Ectotherms and Endotherms
Answer:
a. The phenomenon of spending a cold period in an inactive stage by an animal is called hibernation.
Aestivation is a period of dormancy during the summer months to escape from the scorching heat of the sun.

b. Ectotherms are the cold-blooded animals having body temperature matching with the environmental temperature. They are affected by temperature variations.

Endotherms are warm-blooded animals who can regulate their body temperature by physiological means and maintain the more or less constant internal temperature.

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 11.
Write a short note on
(a) Adaptations of desert plants and animals
Answer:
(1) Plants vegetation is sparse, grows during rains only. (Drought exoping)
(2) Annuals (Drought evaders)
(3) Succulents (Drought resisting) – stores water with mucilage and latex.
(4) Nonsucculent perennials (Drought enduring) – long roots and avoids transpiration by modification.
(5) Modifications

  • leaves as spines and thorns
  • Stems as water storage body with thick bark
  • Long, deep roots with shoot system

Animals

  • Lives in burrows
  • Very little water requirement and can store water in modified body parts.
  • Urine is concentrated and faeces is nearly solid with very little water and metabolic water is also used by them as source of water.
  • Nasal counter- Current mechanism prevents loss of water during breathing with small nostril size.
  • Feeds on dry seeds and rehydrates and stores water when they reach a water body.
  • Very small body surface area so very less sweating so less water loss from body.

(b) Adaptations of plants to water scarcity
Answer:
same answer as above (drought/desert animals or plants).

(c) Behavioural adaptations in animals
Answer:
Snakes – in winter, the snakes will come out of their burrows and bask in the sun to warm their body for activity.

Desert lizards keep their body temperature fairly constant by their behaviour changes. When their body temperature drops below their comfort zone, they would come out of the burrow and bask in sun.

(d) Importance of light to plants
Answer:
In plants light influences photosynthesis growth and reproduction height influences flower induction, seed germination plant movement etc.

(e) Effect of temperature or water scarcity and the adaptations of animals.
Answer:
Animals living in arid areas are adapted to manage with scarcity of available water and reduce water loss to a minimum.

Eg: Kangaroo rat feeds on dry seeds. Animals protect themselves from the excessive cold by hibernation, thick for, constriction of peripheral blood vessel.

Question 12.
List the various abiotic environmental factors.
Answer:
Abiotic factors include climatic factors (temperature, light, air, atmospheric humidity, precipitation and water) and edaphic factors (soil texture, substratum, topography, background, minerals, and pH).

Question 13.
Give an example for
a. an endothermic animal.
b. an ectothermic animal.
c. an organism of benthic zone.
Answer:
a. Human beings b. Frog c. Bacteria

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 14.
Define population and community.
Answer:
A group of individuals of the same species, who interbreed to produce fertile young, living together in the same geographical area at a time is called population.

Community refers to groups of organisms belonging to several different species that live together in the same area or habitat and interact through trophic and spatial relationships.

Question 15.
Define the following terms and give one example for each:
(a) Commensalism
(b) Parasitism
(c) Camouflage
(d) Mutualism
(e) Interspecific competition
Answer:
(a) Commensalism:- Interaction where one species is benefitted and the other is neither benefitted nor harmed is called commensalism, eg: Clone Fish living in the company of sea Anemones.

(b) Parasitism:- It is interspecific interaction in which a small-sized organism of one species obtains nourishment and spends a part or whole Of its life on or inside the body of a large-sized organism of other species, eg: Plasmodium in human, liver fluke in snail and fish.

(c) Camouflage:- Phenomenon of blending with surroundings with similar colour, marking, shape etc. to escape from predators and preys eg: Stick insect, leaf insect.

(d) Mutualism:- Interaction confers benefits on both the interacting species, eg: Lichen (fungus + Algae); Rhizobium and legumes.

(e) Interspecific competition:- struggle against, members of different species for obtaining some resource (food, water etc) eg: roots of plant species in same area of a forest.
→ It is a potent force in organic evolution.

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 16.
With the help of suitable diagram describe the logistic population growth curve.
Answer:
GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations 1
S-shaped or Sigmoid growth curve is a type of growth curve which is otherwise known as Verhulst-Pearl logistic curve. It is shown by the populations of most organisms. It has five phases – lag phase, positive acceleration phase, exponential phase, negative acceleration phase and stationary phase.

Question 17.
Select the statement which explains best parasitism.
a. One organism is benefitted.
b. Both the organisms are benefitted.
c. One organism is benefitted, other is not affected.
d. One organism is benefitted, other is affected.
Answer:
a. One organism is benefitted.

Question 18.
List any three important characteristics of a population and explain.
Answer:
A population has characteristics not shown by its individual members. Each population has natality, mortality, dispersal, biotic potential, sex ratio, pattern of distribution, variation in numbers etc.

a. Natality (birth) rate
The birth rate of population refers to the average number of young ones produced by birth or germination per unit time. The maximum birth rate, a species can achieve under ideal environmental conditions is called potential natality, also called biotic potential.

b. Mortality (death) rate
The death rate of a population is the average number of individuals that die per unit time. The death rate is expressed as change in numbers with respect to members of the population.

c. Dispersal
Individuals in a population disperse at one time or the other during their life. These reveal immigration or emigration.

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

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

Question 1.
Study the relationship of the given pair and fill up the blanks
a. Hibernation : Bears: : Aestivation: ………………….
b. Wide range of salinity: Euryhaline:: Narrow range of salinity: ……………………
Answer:
a. Snail
b. Stenohaline

Question 2.
An individual may have births and deaths, but a population has ……………(a) ………….. and …………..(b)………….. . An individual is either a male or a female but a ………….(c)……………..
population has a
Answer:
a. birth rate
b. death care
c. sex ratio

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 3.
Temperature of the earth ……………(a) ………….. (decreases/increases) progressively from the ……………(b) ………….. (poles/equator) towards the ……………(c) ………….. (poles/equator) and from ……………(d) ………….. (plains/mountain tops) to the ……………(e) ………….. (plains/mountain tops).
Answer:
a. decreases
b. equator
c. poles
d. plains
e. mountain tops

Question 4.
Organisms that can tolerate and thrive in a wide range of temperature are called ……………(a) ………….. and organisms restricted to a narrow range of temperature are called ……………(b) …………..
Answer:
a. eurythermal
b. stenothermal

Question 5.
The spectral quality of solar radiation is important to life. Justify this statement.
Answer:
The UV component of the spectrum is harmful to many organisms. The marine plants are adapted to use the selected colour of visible spectrum because they receive only certain colours at various depth of the oceans.

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 6.
The vegetation in an area is determined by different characteristics and parameters of soil. Comment on this statement.
Answer:
The soil composition, grain size and aggregation are the characteristics of the soil which determine the percolation and water holding capacity of soils. Parameters such as pH, mineral composition and topography and the above characteristic determine to a large extent, the vegetation in any area.

Question 7.
Briefly explain the need for a constant internal environment for organisms. What do you mean by homeostasis?
Answer:
A constant internal environment is needed to permit all biochemical reactions and physiological functions to proceed with maximum efficiency.
The maintenance of a constant internal environment by organisms is called homeostasis.

Question 8.
Observe the graph and differentiate the characters of conformers and regulators.
Answer:
GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations 4
Answer:
Regulators are organisms which are able to maintain a constant internal environment irrespective of external factors.
Conformers are organisms which change the internal environment according to the external changes.

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 9.
Small animals are rarely found in polar regions. Comment.
b. Which of these cause a decline and which cause an increase in population?
Answer:
Since small animals have a larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside. They have to expend much energy to generate body heat through metabolism. So they are rarely found in polar regions.

Question 10.
Most organisms usually maintain their internal environment in a constant condition irrespective of external factors. But if the external conditions are stressfull and are localised or remain only for a short duration, what are the alternatives for the organisms to cope up with such condition?
Answer:
Organisms have many alternatives.
a. The organisms can migrate i.e., they can move away temporarily from the stressfull habitat to a more hospitable area and return when stressfull period is over. e.g. Birds

b. The organisms can suspend, organism like bacteria and fungi produce thick walled spores and tide over unfavourable conditions. Plants produce seeds and some other vegetative reproductive structures. These protective structures of organisms germinate on availability of suitable environment.

c. Hibernation/aestivation are other alternatives for animals.

d. Many zoo planktons species in lakes and ponds enter into a stage of
suspended development called diapause.

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 11.
Organisms are adapted to live in their habitat. Briefly give explanation for adaptation with example of Kangaroo rat.
Answer:
Adaptation is any attribute of the organism that enables the organism to survive and reproduce in its habitat.
The Kangaroo rat in North American deserts is capable of meeting all its water requirements through its internal fat oxidation. It also has the ability to concentrate its urine so that minimal volume of water is used to remove excretory products.

Question 12.
What do you mean by Allen’s rule?
Answer:
Mammals from colder climates generally have shorter ears and limbs to minimise heat loss.

Question 13.
While going to a high altitude area, many people experience altitude sickness which include nausea, fatigue and heart palpitations. How do your body adjust physiologically to such conditions?
Answer:
The body compensates low oxygen availability by increasing red blood cell production, decreasing the binding affinity of haemoglobin and by increasing breathing rate.

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 14.
Some organisms like desert lizards lack the physiological abilities to cope with variations in their environment, but show some behavioural responses. Comment on.
Answer:
They bask in the sun and absorb heat when their body temperature drops below the comfort zone, but move into shade when the ambient temperature starts increasing: Some species are capable of-burrowing into the soil to hide and escape from the above ground heat.

Question 15.
The density of a population in a given habitat during a given period, fluctuates due to changes in four basic processes. Two of them contribute to increase in population and two of them contribute to a decrease in population.
a. Name the four basic process.
b. Which of these cause a decline and which cause an increase in population?
Answer:
a. Natality, Mortality, Immigration and Emigration.
b. Natality and immigration cause an increase in population.
Mortality and emigration cause a decrease in population.

Question 16.
Differentiate exponential growth and logistic growth.
Answer:
When resources in the habitat are unlimited, each species has the ability to realise fully its innate potential to grow in number. Then the population grows in an exponential or geometric fashion within short period. This is called exponential growth.

A population growing in a habitat with limited resources show initially a lag phase, followed by phases of accelerated growth (lag phase) and finally a stationary phase, when the population density reaches the carrying capacity. This type of population growth is called logistic growth.

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 17.
Fill up the blanks with suitable examples.
a. Organisms breed only once in their life time – …………. (oyster/ Pacific salmon/birds)
b. Organism which produces a large number of small sized offspring. (Birds/Mammals/Oyster)
c. Organisms which produce small number of large sized offsprings. (Bamboo / Oyster /Mammals)
Answer:
a. Pacific salmon
b. Oyster
c. Mammals

Question 18.
Observe the figures and identify
i. stable population
ii. expanding population
iii. What is the name of the remaining figure?
GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations 2
Answer:
i. Figure B represents stable population.
ii. Figure A represents expanding population. .
iii. The remaining figure (C) represents declining population.

Question 19.
What is meant by competitive release?
Answer:
A species whose distribution is restricted to a small geographical area because of the presence of a completely superior species, is found to expand its distributional range dramatically when the competing species is experimentally removed.

Question 20.
Briefly explain Gause’s competitive exclusion principle.
Answer:
This principle states that two closely related species competing for the same resources cannot coexist indefinitely and the competitively inferior one will be eliminated eventually.

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 21.
According to recent studies on competition, it is stated that species facing competition might evolve mechanisms that promote coexistence rather than exclusion. Explain this with the example of resource partitioning
Answer:
If two species compete for the same resource, they could avoid competition •by choosing, for instance different times for feeding a different foraging patterns.

Question 22.
Briefly explain the special adaptations evolved by parasites in accordance with their life styles.
Answer:
a. Loss of unnecessary sense organs.
b. Presence of adhesive organs or suckers.
c. Loss of digestive system.
d. High reproductive capacity.

Question 23.
Explain the effects of parasite on the host.
Answer:
a. They may reduce the survival, growth and reproduction of the host.
b. Reduces its population density.
c. They might render the host more vulnerable to predation by making it physically weak.

Question 24.
Comment on Brood parasitism.
Answer:
Here parasitic bird lays its eggs in the nest of its host and lets the host incubate them. e.g. Cuckoo

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 25.
Given below are some of the common examples of species interactions. Catagorise them into predation, commensalism, mutualism, parasitism or competition.
a. Egret foraging close to grazing cattle.
b. Fig flowers pollinated by wasp.
c. Cuckoo laying egg in crow’s nest.
d. Phytophagous insects feeding on a plant.
e. Clown fishes living among sea anemone.
f. Abingdon tortoise in Galapagos islands became extinct within a decade after goats were introduced on the island.
Answer:
a, e – Commensalism
b – Mutualism
c – Parasitism
d – Predation

Question 26.
GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations 3
Figure (i) and (ii) show a kind of ecological interaction.
a. Identify the type of interactions.
b. List out some adaptations for these interactions.
Answer:
a. i. Parasite ii. Epiphyte
b. Parasites have speacilised sucking roots called haustoria, which are used for stealing purpose. Epiphytes possess two types of roots-clinging roots and velamen roots. Clinging roots help to fix the epiphyte on host and velamen roots absorb water with the help of a special type of tissue called velamen.

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 27.
Differentiate between commensalism and symbiosis.
Answer:
Commensalism is the mutual interaction which is beneficial for one species, while the other neither gets benefit nor harmed. Symbiosis is a strong beneficial association between two species. The term symbiosis has often been applied to this relationship but symbiosis properly refers to intimate association of two or more dissimilar organisms regardless of benefits and hence includes mutualism, commensalism and parasitism.

Question 28.
Study the three representative figures of age pyramid relating to human population given below and answer the following questions.
GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations 5
a. Mention the names given to three kinds of age profiles (i), (ii) and (iii).
b. Which one of them is ideal for a population and why?
c. How do such age profile studies help policy makers get concerned about our growing population and prepare for future planning? (Say for example for the year 2022)
Answer:
a. (i) Expanding (ii) Stable (iii) Declining
b. Declining is ideal for population because changes in population density gives us some idea of what is happening to the population, whether it is flourishing or declining.
c. The age pyramids generally show age distribution of males and females in a combined diagram. The shape of pyramids reflects the growth status of the population. The size of the population tells us a lot about its status in the habitat.

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 28.
In the following table the ecological units are mentioned in the first column vertically and their attributes are mentioned horizontally. Match the ecological units and their attribute and put a tick in the blanks within the table.
GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations 6
Answer:
GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations 7

GSEB Solutions Class 12 Biology Chapter 13 Organisms and Populations

Question 29.
List the attributes that populations but not the individuals possess.
Answer:
Populations have attributes that an individual organism does not. An individual may have births and deaths but a population has birth rates and death rates. In a population these refer to per capita birth and deaths respectively.
An individual is either a male or a female but a population has sex ratio. The size of population tells us a lot about its status in the habitat.

Question 30.
What is an ecosystem? How energy transformation occurs in an ecosystem?
Answer:
An ecosystem is a structural and functional unit of the biosphere
which consists of living organisms and their nonliving environment. Sun is the ultimate source of energy. Organisms except plants are not able to trap the solar energy directly. So other organisms depend on plants for their own energy. In short, energy is transferred from solar system to autotrophic plants and from these producers to different level consumers and at last it reaches the decomposers. This unidirectional flow of energy is known as energy flow.

Plants are considered as the primary producers and they prepare organic compounds like carbohydrates, proteins and fats. When primary consumers like herbivore animals consume the plant, these organic compounds reach these animals and liberate energy. When the herbivore is eaten by secondary consumer (carnivore), energy is transferred to carnivore and a further decrease in energy takes place. Each trophic level receives 10% of energy of what is obtained in its first trophic levels. This process is known as law of 10%.

Question 31.
Which one of the two, stenothermals or eurythermals shows wide range of distribution on earth and why?
Answer:
A few organisms can tolerate and thrive in a wide range of temperatures. They are called eurythermal. But a majority of organisms are restricted to a narrow range of temperatures. Such organisms are called stenothermals. The levels of thermal tolerance of different species determine to large extent their geographical distribution.

Question 32.
Certain species of wasps are seen to frequently visit flowering fig trees. What type of interaction is seen between them and why?
Answer:
The interaction is mutualism. The female wasp uses the fruit not only as an oviposition (egg laying) site but uses the developing seeds within the fruit for nourishing its larvae. The favour of pollination the fig offers the wasp is its developing seeds.

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