It is one of the most significant factors which varies seasonally on land, progressively decreases from the equator towards the poles, from plains to the mountain tops. From sub-zero levels in polar areas to temperatures greater than 50 degree Celsius in tropical deserts in summers, their range is wide. Some unique habitats such as deep sea hydrothermal vents, thermal springs sees average temperature exceeding more than 100 degree Celsius. Entities who can withstand a range of temperatures are termed as eurythermals example – birds and mammals whereas stenothermals are entities who can bear a narrow range of temperature, example – polar bears.

• Water –

Life cannot sustain without water. For marine entities, pH, water temperature, chemical composition etc is significant. It is also affected by water salinity that is less than 5 parts per thousand in inland water, 30-35 parts per thousand in sea etc

Euryhaline are entities which can bear a wide salinity range whereas stenohaline are entities that can tolerate a narrow range of salinity. Most of the fresh water animals cannot sustain in sea water for long due to osmotic issues that arise due to high salinity and vice-versa

• Soil –

Properties and nature of soil varies from place to place, depending on the following factors

-climate

-soil development process

-Weathering process

Characteristics such as grain size, aggregation, soil composition determine the water holding capacity and percolation of soil. Along with these, some other features such as pH, topography, mineral composition etc determine the type of type of plant that can grow in a specific habitat.

• Light –

All autotrophs depend on light to carry out photosynthesis, releasing oxygen during the process. In forests, small herbs and shrubs are adapted to photosynthesis under very low light intensities as they are overshadowed by tall trees. Also, most plants depend on sunlight to meet their photoperiodic necessities for flowering. Several animals are dependent on diurnal and seasonal differences in light intensity as prompts for timing their reproductive, foraging and migratory activities. Light availability on land is closely associated with that of temperature, as Sun is the ultimate source. In deep oceans, it is dark perpetually. Spectral quality of solar radiation is necessary for life. For many entities, UV component of light is harmful. Different components of visible spectrum is available for marine plants active at different oceanic depths. Hence, different algae types such as brown, green and red algae occur at various depths in the middle, upper and lowest levels of water respectively.

Question - 12 : -
Give an example for:
(a) An endothermic animal (b) An ectothermic animal (c) An organism of benthic zone

Answer - 12 : -

(a) An endothermic animal – Crows, sparrows, cranes, cows, rabbits, rats etc

(b) An ectothermic animal – Fish such as amphibians, sharks, frogs, snakes, tortoise, lizards

Question - 13 : - Define population and community.

Answer - 13 : -

Population – it can be defined as a group of individuals of the same species inhabiting a particular geographical area at a given time, functioning as a unit.

Community – it can be defined as a group of individuals of various species, living in a certain geographical region. These individuals can be dissimilar or similar, but cannot reproduce with members of other species.

Question - 14 : -
Define the following terms and give one example for each:

Answer - 14 : -

(a) Commensalism

(b) Parasitism

(d) Mutualism

(e) Interspecific competition

Answer

(a) Commensalism

The interaction between two species wherein one species is benefited and the other remains unaffected in known as commensalism. Examples – Barnacles attached to a whale’s body and an orchid growing on the branches of a mango tree

(b) Parasitism

The interaction between two species wherein one species is positively affected (typically the smaller one) and the other is negatively affected (typically the larger one) is known as Parasitism. Example – Liver fluke is a parasite living within the body of the host and deriving nutrition from it. Here, the parasite benefits from the host, as it derives nutrition from it while the host is affected negatively as the parasite reduces the host fitness causing its body to get weak.

(c) Camouflage

It is a tactic taken up by the prey to escape from predators. Intrinsically, organisms are colored to easily blend with their surroundings and escape from their predators. Several insects and frog species camouflage to escape their predators.

(d) Mutualism

An interaction between two species wherein both species involved are benefited is Mutualism. Example – lichens exhibit a mutual symbiotic relationship between blue green algae and fungi. Here, both are equally benefited from each other.

(e) Interspecific competition

An interaction between individuals of different species wherein both are negatively affected is interspecific competition. Example – The competition between resident fishes and flamingoes in South American lakes for shared food resources, that is, zooplankton

Question - 15 : - With the help of suitable diagram describe the logistic population growth curve.

Answer - 15 : -

The logistic population growth curve is usually observed in yeast cells cultivated in laboratory conditions and includes five phases, namely:

• The lag phase – the population of yeast cell is small initially as resources are limited in the habitat

• Exponential phase – in this stage, the population of the yeast cell suddenly rises as a result of rapid growth leading to an exponential population growth due to availability of enough food resources, consistent favorable environmental conditions without any interspecific competition. This results in the curve rising upwards steeply.

• Positive acceleration phase – at the start of this phase, the cell growth is limited. The yeast cell adjusts to the new environment and grows its population

• Negative acceleration phase – the environmental resistance increases and the growth rate of the population declines as a result of an increased competition between the yeast cells for shelter and food.

• Stationary phase – The population is stable in this phase. The count of cells generated in a population is equivalent to the number of cells that die out. Additionally, the species’ population is said to have touched nature’s carrying-capacity in its habitat. S-shaped growth curve is also referred to as the Verhulst- pearl logistic curve.

Question - 16 : -
Select the statement which explains best parasitism.

Answer - 16 : -

(a) One organism is benefited.

(b) Both the organisms are benefited.

(d) One organism is benefited, other is affected.

Answer

(d) One organism is benefited, other is affected

Parasitism is a type of interaction between two species wherein one species (parasite) gets benefited while the other species or the host is negatively affected/harmed. Example – Lice or ticks(parasites) found on human body(host) is an example wherein lice derives its nutrition by feeding on the humans’ blood causing the fitness of the individual(host) to reduce, harming the human body.

Question - 17 : - List any three important characteristics of a population and explain.

Answer - 17 : -

A group of entities belonging to the same species, residing in a specific geographical area at a particular time, together functioning as a unit can be termed as a population. Example – All humans living in a particular area at a specific time comprise the population of humans.

Listed below are the attributes that a population exhibits:

• Natality or Birth rate

It can be given by the ratio of live births in a particular area to the population of that area. Birth rate can be expressed as the number of individuals added to the population in terms of members of the population

• Mortality or Death rate

It is the ratio of deaths in a region to the population of a region. Death rate can be expressed as the loss of individuals in terms of members of the population

• Age distribution

It can be given by the percentage of individuals of various ages in a given population. A population consists of individuals at any given time, and are present in different age groups. Typically, an age pyramid can be used to depict the age distribution pattern.

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