Class 12 biology chapter 13 Organisms and Populations solutions

Class 12 biology chapter 13 Organisms and Populations textbook solutions


Maharashtra Biology Textbook Solutions for Class 12 are very important and crusial that helps the students in understanding the complex topics and helps them in the preparation of class 12 board examination as well as verious compititive entrance examinations also. Studying the answers to the questions in the biology textbook will check your understanding of a particular topic and helps you determine your strengths and weaknesses.

Class 12 biology textbook Solutions for Class 12,  Biology  Chapter 13 Organisms and Populations maharashtra state board are provided here with simple step-by-step  detailed explanations. These solutions for Organisms and Populations  are very popular among Class 12 students for biology chapter 13  Organisms and Populations Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the biology textbook Solutions Book of Class 12 biology Chapter 13 are provided here for you for free. You will also love the experience on ybstudy class 12 Solutions. All biology textbook Solutions. Solutions for class 12, These biology textbook solutions are prepared by biology experts and are 100% accurate.


Q. 1 Multiple choice questions.
1. Which factor of an ecosystem includes 
plants, animals and microorganisms?
a. Biotic factor
b. Abiotic factor
c. Direct factor
d. Indirect factor

2. An assembladge of individuals of 
different species living in the same habitat and having functional interactions is
................
 a. Biotic community
 b. Ecological niche
 c. Population
 d. Ecosystem

3. Association between sea anemone and 
Hermit crab in gastropod shell is that of 
................
 a. Mutualism
b. Commensalism
c. Parasitism
d. Amensalism

4. Select the statement which explains best parasitism.
 a. One species is benefited.
 b. Both the species are benefited.
c. One species is benefited, other is not
affected.
d. One species is benefited, other is 
harmed.

5. Growth of bacteria in a newlly 
innoculated agar plate shows ................ 
 a. exponential growth
 b. logistic growth
 c. Verhulst-Pearl logistic growth
 d. zero growth


Q. 2 Very short answer questions.
1. Define the following terms : 
a. Commensalism :  an association between two organisms in which one benefits and the other derives neither benefit nor harm.

b. Parasitism :
Parasitism describes a relationship between two organisms where one benefits, and the other is harmed.

c. Camouflage :
Camouflage, also called cryptic coloration, is a defense or tactic that organisms use to disguise their appearance, usually to blend in with their surroundings.

2. Give one example for each :
 a. Mutualism : Sharks and Remora Fish.
Lichens, Nitrogen-Fixing Bacteria and Legumes

 b. Interspecific competition:
interspecific competition is between lions and tigers that vie for similar prey. Another example is a farm of rice paddies with weeds growing in the field.

3. Name the type of association:
 a. Clown fish and sea anemone
- mutualism

 b. Crow feeding the hatchling of Koel
- Brood parasitism

c. Humming birds and host flowering
plants - mutualism

4. What is the ecological process behind the biological control method of managing with pest insects? 
Answer : The basis of various biological control methods is on the concept of predation. Predation is a biological interaction between the predator and the prey, whereby the predator feeds on the prey. Hence, the predators regulate the population of preys in a habitat, thereby helping in the management of pest insects.


Q. 3 Short answer questions.
1. How is the dormancy of seeds different from hibernation in animals?
Answer : Dormancy is a period of inactivity, either in winter or summer. Both plants and animals have dormant periods. ... Hibernation is a unique form of dormancy.

2. If a marine fish is placed in a fresh water aquarium, will it be able to survive? Give reason.
Answer : If a marine fish is placed in a fresh water aquarium, then its chances of survival will diminish. This is because their bodies are adapted to high salt concentrations of the marine environment. In fresh water conditions, they are unable to regulate the water entering their body (through osmosis)

3. Name important defense mechanisms in plants against herbivores.
Answer : The first line of defense in plants is an intact and impenetrable barrier composed of bark and a waxy cuticle. Both protect plants against herbivores. Other adaptations against herbivores include hard shells, thorns (modified branches), and spines (modified leaves).

4. 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 orchid grows as an epiphyte on branch of mango tree. The interaction between orchid and the mango tree is termed commensalism where in orchid derives benefit of interaction while mango tree is neither harmed nor benefited.


5. Distinguish between the following:
 a. Hibernation and Aestivation
Answer :  The state of inactivity and a low metabolic process performed by the animals during the winters is known as Hibernation. It is also known as winter sleep. On the contrary, when animals take rest in shady and moist place during summer, it is called Aestivation or Estivation. Aestivation is also known as summer sleep.

 b. Ectotherms and Endotherms
Answer : Ectotherms, including reptiles and amphibians, are organisms that don't possess the ability to generate sufficient heat to keep themselves warm. As such, they are dependent on environmental sources of heat, such as sunlight. This explains why most ectotherms are confined to warmer parts of the world, and why snakes in particular can often be seen basking on roadsides in many countries.

Endotherms, in contrast, do possess the ability to generate their own body heat. Mammals and birds are the only endothermic classes of organisms. Because of this trait, many mammal and bird species have been able to colonise some of the coldest parts of the planet.

 c. Parasitism and Mutualism
Answer : 
Mutualism is a symbiotic relationship in which both species benefit. Commensalism is a symbiotic relationship in which one species benefits while the other species is not affected. Parasitism is a symbiotic relationship in which one species (the parasite) benefits while the other species (the host) is harmed.


6. Write a short note on
 a. Adaptations of desert animals 
Answer : Mammals from colder climates generally have shorter snout, ears, tail and limbs to minimize the loss of body heat (Allen’s Rule.) In the polar seas, aquatic mammals like seals have a thick layer of fat (blubber) below their skin acting as an insulator to reduce loss of body heat.

b. Adaptations of plants to water scarcity
Answer : Many desert plants have a thick cuticle on their leaf surfaces and have their stomata in deep pits to minimize loss of water through transpiration. They also have a special photosynthetic pathway (CAM - Crassulacean acid metabolism) that enables their stomata to remain closed during daytime. Some desert plants like Opuntia, have their leaves reduced
(modified) to spines and the photosynthetic
function is taken over by the flattened stems.

c. Behavioural adaptations in animals
Answer : Some organisms show behavioural responses to cope with variations in their environment. Desert lizards manage to keep their body temperature fairly constant by behavioural adaptations. 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 burrow into the sand to hide and escape from the heat.

7. Define Population and Community.
Answer : Population - a group of organisms of the same species who live in the same area at the same time.

Community - a group of populations living and interacting with each other in an area.



Q. 4 Long answer questions.

1. With the help of suitable diagram describe the logistic population growth curve.
Answer :

 Logistic growth: competition between individuals for limited resources will weed out the ‘weaker’ ones. Only the ‘fittest’ individuals will survive and reproduce. In nature, a given habitat has enough resources to support a maximum possible number, beyond which no further growth is possible. Let us call this limit as nature’s carrying capacity (K) for that
species in that habitat.

A population growing in a habitat with
limited resources show initially a lag phase, followed by phases of acceleration and
deceleration and finally an asymptote, when the population density reaches the carrying capacity. A plot of population density (N) in relation to time (t) results in a sigmoid curve. This type of population growth is called Verhulst-Pearl Logistic Growth. Since resources for growth for most animal populations, are finite and become limiting sooner or later, the logistic growth model is considered a more realistic one.

2. Enlist and explain the important characteristics of a population.
Answer : The population has the following characteristics:

  1. Population Size and Density:
  2. Population dispersion or spatial distribution:
  3. Age structure:
  4. Natality (birth rate):
  5. Mortality (death rate):
  6. Vital index and survivorship curves:
  7. Biotic Potential:
  8. Life tables: