Chapter 11: Organisms and Populations

Ans: Diapause could be a stage of suspended development to cope with unfavorable conditions. Diapause is a coping mechanism used by many species of Zooplankton and insects to survive adverse climatic conditions. Hibernation is the period of dormancy during winter months so is also called winter sleep. Their metabolism slows during the winter so they can escape the cold weather. The development of hibernation is exhibited by bats, squirrels, and other rodents.

Ans: If a marine fish is placed in a freshwater aquarium, then its possibilities of survival will diminish. This is often because their bodies are adapted to high salt concentrations of the marine environment. In  water conditions, they are unable to control the water entering their body (through osmosis). Water enters their body due to the hypotonic environment outside. This ends up in the swelling up of the body, eventually resulting in the death of the marine fish.

Ans: In hot water springs and deep sea hydrothermal vents, archaebacteria (thermophiles) grow. They are able to survive in high temperatures (which far exceed 100°C) because their bodies have adapted to such environmental conditions. Organisms that withstand high temperatures contain enzymes with specialized thermal-resistance in order to perform metabolic functions.

Ans: A population is defined as a group of individuals belonging to the same species living together in a particular geographic area at the same time. For example, all individuals living at a particular place at a particular time represent the population of humans. The most attributes or characteristics of a population residing during a given area are: 

• Birth Rate (Natality): It is the ratio of live births per thousand people in an area. It is expressed because the range of number of individuals added to the population with respect to the members of the population.

• Death Rate (Mortality): This is a measure of the percentage of deaths in an area to the total population. It is expressed as the loss of individuals with respect to the members of the population age groups. The age distribution pattern is usually represented through age pyramids.

• Population Density: It is defined as the number of individuals of a population present per unit space at a given time.

Ans: If there are sufficient amounts of food resources available to an individual population, it will grow exponentially. The exponential growth equation can be expressed as the following integral form:

Where,

N Population density after time t

No-Population density at time zero

r-Intrinsic rate of natural increase

e=Base of natural logarithms (2.71828)

From the above equation, we can calculate the intrinsic rate of increase (r) of a population.

Now, as per the question,

Present population density=x

Then,

Population density after two years = 2x

t = 3 years

Substituting these values in the formula, we get:

$\Rightarrow 2x = xe^3r$

$\Rightarrow 2 = e^3r$

Applying log on both sides:

$\log 2 = 3 r \log (e)$

$\log \dfrac{2}{3} \log e = r$

$r = \dfrac{\log 2}{3 \times 0.434}$

$\Rightarrow 0.301$

$3 \times 0.434$

$\dfrac{0.301}{1.302} = r$

$r = 0.2311$

Hence, the intrinsic rate of increase for the above illustrated population is 0.2311.

Ans: The presence of morphological and chemical shielding mechanisms is present in several plants in order to defend themselves against herbivores.

(1) Morphological Defense Mechanisms:

• Cactus leaves (Opuntia) are modified into sharp spines (thorns) to deter herbivores from feeding on them.

• Besides leaves, Acacia has sharp thorns to deter herbivores. 

• Some plants have margins of their leaves that are spiny or have sharp edges that stop insects from eating them.

(2) Chemical Defense Mechanisms:

• A herbivore might be fatally affected if they eat any part of a Calotropis weed.

•  Several chemicals are produced in plants as a part of self-defense, including nicotine, caffeine, quinine, and opium.

Ans: An orchid growing on a mango tree branch is an epiphyte. Epiphytes are plants growing on other plants which however, do not derive nutrition from them. This relationship therefore exists as commensalism . There is a commensalism between a mango tree and an orchid, where one species benefits from the other while the other remains unaffected. The orchid is benefited by the above interaction because it receives support, while the mango tree remains unaffected.

Ans: Variable biological control methods are based on a concept known as predation. In predation, the predator feeds on the prey. Hence, predators regulate the population of prey in a habitat, helping in the control of pest insects.

Ans: (a) 

Ans: 

Ans : 

(a) Adaptations of desert plants and animals:

(i) Adaptations of desert plants:

Many desert plants have been well adapted to cope with harsh conditions in the desert, including water adequate  and hot. Plants have an extensive root system to tap underground water. There are thick cuticles and sunken stomata on the surface of their leaves to reduce transpiration. Opuntia is a species of plant that has spines entirely as parts of its leaves, Photosynthesis is carried out by green stems. Plants in the desert have special pathways. It is the CAM (C4 pathway) pathway that synthesizes food. To reduce water loss through transpiration, the stomata can remain closed during the day.

(ii) Adaptations of desert animals:

Desert animals such as desert kangaroo rats, lizards, snakes, etc. are well adapted to their habitat. In Arizona, kangaroo rats do not drink water. In order to conserve water, it is capable of concentrating its urine. Desert lizards and snakes bask in the sun throughout the early morning and burrow themselves in the sand during afternoons to escape the heat of the day. Desert animals have developed these adaptations to stop the loss of water.

(b) Adaptations of plants to water scarcity:

Due to water scarcity and heat, desert plants are well adapted to survive in deserts. To obtain water from underground, plants have extensive root systems. They bear thick cuticles and sunken stomata on the surface of their leaves to reduce transpiration. In Opuntia, the leaves form spines, while the green stems are responsible for photosynthesis. Desert plants have special pathways to synthesize food, called CAM (C4 pathway). It enables their stomata to remain closed during the day to reduce water loss by transpiration.

(c) Behavioral adaptations in animals:

There are some organisms that are affected by temperature changes. To cope with environmental stress, these organisms undergo adaptations such as hibernation, aestivation, migration, etc. These adaptations in behavior of an organism are referred to as behavioral adaptations. Some ectothermic animals and certain endotherms exhibit behavioral adaptations. Ectotherms are cold blooded animals such as fish, amphibians, reptiles, etc. Depending on their environment, they have different body temperatures. During the early hours of the day when the temperatures are quite low, desert lizards bask in the sun. As the temperature rises, the lizard burrows into the sand to avoid the scorching sun. Similar burrowing strategies are exhibited by other desert animals. Certain endotherms (warm-blooded animals) such as birds and mammals escape cold and hot weather conditions by hibernating during winters and aestivating during summers. They hide themselves in shelters like  caves, burrows, etc. to protect against temperature variations.

(d) Importance of light to plants

Sunlight acts as the ultimate source of energy for plants. Plants are autotrophic organisms, which need light for carrying out the process of photosynthesis. Light also plays an important role in generating photoperiodic responses occurring in plants. Plants respond to changes in intensity of light during various seasons to fulfill  their photoperiodic changes in intensity of light during various seasons to meet their photoperiodic requirements for flowering. Light also plays an important role in aquatic habitats for vertical distribution of plants in the sea.

(e) Effects of temperature or water scarcity and the adaptations of animals.

Temperature is the most vital ecological factor. Average temperature on the Earth varies from one place to another. These variations in temperature affect the distribution of animals on the Earth. Animals that can tolerate a wide range of temperatures can be referred to as eurythermals. Those which can tolerate a narrow range of temperature are called stenothermal animals. Animals also undergo adaptations to suit their natural habitats. For example, animals found in colder areas have shorter ears and limbs that prevent the loss of heat from their body. Also, animals found in Polar regions have thick layers of fat below their skin and thick coats of fur to prevent the loss of heat. Some organisms exhibit various behavioral changes to suit their natural habitat. These adaptations present in the behavior of an organism to escape environmental stresses are called behavioral adaptations. For example, desert lizards are ectotherms. This means that they do not have a temperature: regulatory mechanism to escape temperature variations. These lizards bask in the sun during early hours when the temperature is quite low. As the temperature begins to increase, the lizard burrows itself inside the sand to escape the scorching sun. Similar burrowing strategy is seen in other desert animals.

Water deficiency is another factor that forces animals to undergo certain adaptations to suit their natural habitat. Animals found in deserts such as desert kangaroo rats, lizards, snakes, etc. are well adapted to stay in their habitat. The kangaroo rat found in the deserts of Arizona never drinks water in its life. It has the ability to concentrate its urine to conserve water. Desert lizards and snakes bask in the sun during early morning and burrow in the sand as the temperature rises to escape the heat of the day. Such adaptations can be used to stop the loss of water.