Chapter 13: Organisms and Populations

1. Figure 1 shows a single population (A). All individuals of the same species interact among themselves and their environment only.

2. Figure 2 shows three species which are A, B and These three species are interacting among themselves and their environment.

3. Figure 3 shows a biome. It has three communities. Each community has a different species. These three communities interact with each other and the environment forming a biome.

A) A population has birth rate (natality) and death rate (mortality) whereas an individual has birth and death.

B) Population density: The density is referred to as the individual per unit area and density changes with space and time

C) Population Growth: It is the growth rate seen in a population over time.

D) Natality: It is the rate of reproduction or birth rate per unit time.

E) Mortality: It is the rate of deaths per unit time. Increased mortality shows a decline in population.

The base is the pre-reproductive population. The mid part of the pyramid is the reproductive population and the top is the post-reproductive population. Figure ‘A’ is a pyramid-shaped figure. This structure has a larger base than the mid and the top.

Status: This shape indicates the population would grow rapidly.

Figure ‘B’ is an inverted bell-shaped pyramid. In this, both the pre-reproductive and reproductive population is the same.

Status: This shape indicates the population is stable.

Figure ‘is an urn-shaped pyramid. The pre-reproductive and reproductive population is lesser than the post-reproductive population.

Figure ‘B’ is an inverted bell-shaped pyramid. In this, both the pre-reproductive and reproductive population is the same.

Status: This shape indicates the population is stable.

The above graph shows a population growing in a habitat having limited resources. The graph shows an initial lag phase. After that, an increase in population takes place, known as acceleration, following which deceleration takes place and at last, asymptote occurs. A sigmoid curve plot is formed when the population reaches carrying capacity. This is called Verhulst-Pearl logistic growth. This is represented by an equation: dN/dT=rN(K-N/K)

dN/dT=rN(1-N/K)

Here, (1-N/K) is environmental resistance.

Sigmoid type of growth curve would be obtained. It shows a population growing in a habitat having limited resources.

The graph obtained is shown below:

The graph initially shows the lag phase. Due to acceleration, a sudden increase has taken place. After that it is followed by deceleration as the available nutrients got depleted because of excessive usage and growth of paramoecium stops. At last, asymptote occurs.

According to Gause’s principle, one of the species is to be eliminated, i.e., no two species can live in the same niche and hence one of them need to be eliminated. But in the given scenario, two herbivorous species are living in the same niche and feeding on phytoplankton may be due to sufficient availability of phytoplanktons.

The loss of unnecessary sense organs, for example, lice, mites and fleas don’t have wings, Presence of adhesive organs or suckers to cling on to the host in tapeworms and leeches. Loss of digestive system i.e., tapeworm. High reproductive capacity i.e., roundworm produces large progeny.

Yes, regional and local variations exist within each biome. A biome is a large community in the world. The main biome of the world does not show the boundary of any country. Regional and local variations lead to the formation of a wide variety of habitats. On earth, life exists even in extreme and harsh habitats – scorching Rajasthan desert, perpetually rain-soaked Meghalaya forest, deep ocean trenches, torrential streams, permafrost Polar Regions, high mountain tops, boiling thermal springs and stinking compost pits, etc.

The elements responsible for causing soil salinity are Na+, K+, Ca2+, Mg2+ and Cl-.

Soil salinity is the salt content in the soil, which is caused by improper irrigation. Causes of Soil Salinity are improper irrigation and human activities like fertilizing crops.