Plus Two Botany Notes Chapter 6 Organisms and Populations is part of Plus Two Botany Notes. Here we have given Plus Two Botany Notes Chapter 6 Organisms and Populations.
|Text Book||NCERT Based|
|Chapter Name||Organisms and Populations|
|Category||Plus Two Kerala|
Kerala Plus Two Botany Notes Chapter 6 Organisms and Populations
Simplified Detailed Notes
Ecology is a subject which studies the interactions among organisms and between the organism and its physical (abiotic) environment. Ecology is basically concerned with four levels of biological organisation ie, organisms, populations, communities and biomes.
Organism and its Environment
The annual variations in the intensity and duration of temperature, resulting in distinct seasons. These variations together with annual variation in precipitation (both rain and snow) responsible for the formation of major biomes such as desert, rain forest and tundra. Regional and local variations within each biome lead to the formation of a wide variety of habitats.
Biome distribution w.r.t annual temperature and precipitation
Life exists in unfavourable habitats like desert, deep ocean, polar regions, thermal springs etc.
Environment: It is the sum of all external conditions which influence the organism in terms of survival and reproduction. These can be classifieds into two:
- Biotic Environment: All living things like pathogens, parasitism, predators, etc. and their interactions.
- Abiotic Environment: It include water, air, soil, temperature etc.
Major Abiotic Factors
1. Temperature: The average temperature on land varies seasonally, it decreases from the equator towards the poles and from plains 0to the mountain tops. The temperature influence the basal metabolism, activity and other physiological functions of the organism.
Eurythermal organism: It is an organism that can tolerate and thrive in a wide range of temperature.
Stenothermal organism: These are the organism which tolerate only a narrow range of temperature.
2. Water: Water supports life on the earth because:
- The productivity and distribution of plants is heavily dependent on water.
- For aquatic organisms the water quality (pH, chemical composition) is important.
- Many fresh water animals cannot live for long in sea water because of osmotic problems, they would face.
Euryhaline organism: It can tolerate a wide range of salinities.
Stenohaline organism: These are restricted to a narrow range of salinity.
3. Light: It is the main source of energy and used by the plants for photosynthesis.
- Some plants are dependent on sunlight to meet their photoperiodic requirement for flowering.
- For many animals too, diurnal and seasonal variations in light intensity and duration act as clues for timing their foraging, reproductive and migratory acivities.
4. Soil: The nature and properties of soil is dependent on the climate, the weathering process. whether soil is transported or sedimentary and how soil development occurred. Various characteristics of the soil such as soil composition, grain size and aggregation determine the percolation and water holding capacity of the soils. These characteristics along with parameters such as pH, mineral composition and topography determine to a large extent the vegetation in any area.
Responses to Abiotic Factors
During the course of millions of years many species would have evolved constant internal (within the body) environment that permits maximum efficiency of biological reactions and physiological functions that results overall fitness of the species.
Homeostasis: Some organism maintain the constant internal environment when the external environmental conditions changes. It is called homeostasis.
Living organism cope with stressful condition by any of the following methods:
1. Regulate: Homeostasis maintained by ensuring constant body temperature and constant osmotic concentration.
2. Conform: About 99% of animals and almost all plants cannot maintain a constant internal environment. Their body temperature changes with the ambient temperature.
Conformers: In aquatic animals, the osmotic concentration of the body fluids change with that of the surrounding osmotic concentration water. These animals and plants are conformers.
3. Migrate: If an organism moves away temporarily from a stressful habitat to a more hospitable area and returns, when a stressful period is over.
4. Suspend: Bacteria, fungi and lower plants make protective spores that help them survive in unfavourable conditions.
Hibernation: The winter sleep of animals like bears are called hibernation.
Aestivation: Summer sleep of certain animals like few snails and fish is called aestivation.
- During unfavourable condition many zooplanktons enter diapause (a stage of suspended) development.
It is an attribute of an organism (morphological, physiological and behavioural) that ertables
them to survive and reproduce in its habitat. Some examples are:
- Kangaroo rat in deserts uses water produced through internal fat oxidation.
- Desert plants have thick cuticle on their leaf surfaces, its stomata arranged in deep pits to minimize water loss.
- Mammals from colder climates have shorter ears and limbs to minimize heat loss.
- Aquatic mammal like seals have thick layer of fat (blubber) below their skin to reduce loss of body heat.
- Desert lizards bask in the sun and absorb heat when their body temperature drops, but move into shade when the surrounding temperature starts increasing.
Populations Representation age pyramids for human population
It is a set of individuals of a particular species which are found in a particular geographical area.
Population ecology: It is an important area of ecology because it links to the population genetics and evolution.
Population attributes: A population has certain attributes that an individual organism does not have.
A population at any given time is composed of individuals of different ages. If the age distribution is plotted for the population, the resulting structure is called age pyramid. The shape age pyramid reflects the growth status of the population, whether it is
Some population attributes are:
1. Population size or density: It is number of species per unit area. Population density, PD = N/S; where N = number of individual in a region, S = number of unit area in the region.
2. Population growth: It is the size of population which keeps changing with time and depending on food availability, predation pressure, weather conditions. The changes include many processes. These are:
- Natality refers to the number of births during a given period in the population that are added to the initial density .
- Mortality is the number of deaths in the population during a given period.
- Immigration is the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration.
- Emigration is the number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration.
Equation of population density
Nt+1 = Nt + [(B+l) – (D+E)]
where Nt+1 = population density at a time t+1
B = birth rate
I = immigration
D = death rate
E = emigration
Nt = population at the time t.
This equation shows that the population density will increase if the number of births plus the number of immigrants (B + I) is more than the number of deaths plus the number of emigrants (D + E), otherwise it will decrease.
Growth models: It tells about the patterns of growth of a population with time.
1. Exponential growth: Availability of resources (food and space) is essential for the growth of population.
The unlimited availability of results in population exponential. The increase or decrease in population density (N) at a unit time t is calculated as,
Let (b-d) = r, then = rN
where N = population density or size, b = birth per capita, d = death per capita, t = time period, r = intrinsic rate of natural increase.
It is an important parameter that assess the effects of biotic and abiotic factors of population growth. It is different for different organism.
2. Logistic growth:
Practically no population of any species in nature has unlimited resources at its disposal. This leads to competition among the individuals and the survival of the fittest.
The logistic growth show sigmoid curve and it is’called Verhulst-Pearl Logistic Growth. It can be calculated as,
where K = carrying capacity for that species in that habitat.
Life History Variation
Populations evolve to maximise their reproductive fitness, called as Darwinian fitness. Some organisms breed only once in their lifetime while others breed many times during their lifetime. Some produce a large number of small sized offspring while others produce a small number of large sized offspring.
It occurs between species. Interspecific interactions arise from the interaction of populations of two different species. It is beneficial, detrimental or neutral to one of the species or both. Assigning a ‘ + ’ sign for beneficial interaction, ‘-‘ sign for detrimental and 0 for neutral interaction.
Interactions with beneficial effects are:
1. Commensalism: This is the interaction in which one species benefits and the other is neither harmed nor benefited.
eg., An epiphytic orchid on a mango tree, the cattle egret and grazing cattle, the interaction between sea anemone with stinging tentacles and the clown fish.
2. Mutualism: In which both the species benefit. eg., Lichens (between a fungus and algae), mycorrhizae (between fungi and the roots of higher plants). The fungi help the plant in the absorption of essential nutrients from the soil while the plant in turn provides the energy-yielding carbohydrates.
Interactions with harmful effects are:
1. Competition: In which both lose in their interactions with each other.
These are two types:
- Intraspecific: Competition occuring between the individuals of the same species.
- Interspecific: Competition occuring between the individuals of two different species.
eg., the plants compete with each other to obtain an adequate amount of light, water, nutrients etc.
Gause’s ‘Competitive Exclusion Principle’ or Gause’s hypothesis states that two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually. This may be true if resources are limiting, but not otherwise.
Species facing competition might evolve mechanisms that promote co-existence rather than exclusion. One such mechanism is ‘resource partitioning’. If two species compete for the same resource, they could avoid competition by choosing, for instance, different times for feeding or different foraging patterns.
2. Predation: It is a kind of interaction between species in which one individual kills another for food.
eg., prey is deer and predator is tiger.
If a predator is too efficient and overexploits its prey, then the prey might become extinct and following it, the predator will also become extinct for lack of food. This is the reason why predators in nature are ‘prudent’. Prey species have evolved various defenses to lessen the impact of predation.
3. Amensalism: In this, one population inhibits the growth and development of other population. eg., antibiotics produced by bacteria, fungi etc are widespread in nature and that is why bacteria, pathogenic to man cannot multiply well in soil.
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