Biology

Learninsta presents the core concepts of Biology with high-quality research papers and topical review articles.

Definition Of Populations

Population is defined as any group of organisms of the same species which can interbreed among themselves, and occupy a particular space and function as part of a biotic community. A population has various properties like population density, natality (birth rate), mortality (death rate), age distribution, biotic
potential, dispersion and ‘r’, ‘K’ selected growth forms.

A population possesses genetic characteristics that are directly related to their adaptiveness, reproductive success, and persistence in their habitats over time. Life history of an organism is an important part of this attribute. The population has a definite structure and function that can be described with reference to time.

A population is a distinct group of individuals, whether that group comprises a nation or a group of people with a common characteristic. Thus, any selection of individuals grouped together by a common feature can be said to be a population.

The top 10 most populous countries are: China, India, United States, Indonesia, Brazil, Pakistan, Nigeria, Bangladesh, Russia, and Mexico.

Three kinds of populations used in the history and philosophy of population genetics, population biology, and evolutionary ecology can be distinguished: theoretical, laboratory, and natural.

There are three types of population pyramids: expansive, constrictive, and stationary. Expansive population pyramids depict populations that have a larger percentage of people in younger age groups. Populations with this shape usually have high fertility rates with lower life expectancies.

Learninsta presents the core concepts of Biology with high-quality research papers and topical review articles.

Adaptations | Definition, Importance and Its Types

In biology, adaptation is a dynamic evolutionary process that fits organisms to their environment and enhancing their evolutionary fitness. Adaptations can be a phenotypic or adaptive trait with a functional role in each individual organism that is maintained and has been evolved by natural selection. The adaptive traits may be structural adaptation, behavioural adaptation and physiological adaptation.

(a) Structural adaptations

The external and internal structures of animals can help them to adapt better to their environment. Some of the most common examples are mammals growing thicker fur to survive freezing climates. Some of the most attractive adaptations in nature occur for reasons of crypsis (e.g. camouflage) and mimicry.

Cryptic animals are those which camouflage perfectly with their environment and are almost impossible to detect. Certain reptiles and insects such as chameleons and stick insects show this type of adaptation, which helps in prey capture or to evade from predators. Likewise, horse legs are suitable for fast running and adapted for grasslands and similar terrestrial environments.

(b) Behavioural adaptations

Action and behaviour of animals are instinctive or learned. Animals develop certain behavioural traits or adaptations for survival. Fleeing from a predator, hiding during sleep, seeking refuge from climate change or moving to find different food sources are all behavioral adaptations.

The two most characteristic forms of behavioral adaptations are migration and courtship. Migration allows the animals to find better resources or evade threat. Courtship is a set of behavioral patterns to find a mate to reproduce. Most nocturnal animals remain underground or inactive during daytime. This is a modifiation of their feeding and activity pattern or habit or behaviour.

(c) Physiological adaptations

These are adaptations of organisms that help them to live and survive in their environment with unique niches. Example: Lions have sharp canines to hunt and tear meat and a digestive system suitable for digesting raw meat.

The two most well-known physiological adaptations are hibernation and aestivation. These are two different types of inactivity where the metabolic rate slows down so much that the animal can survive without eating or drinking. Aquatic medium and terrestrial habitats have their own respective environmental conditions. Hence organisms have to evolve appropriate adaptations to select suitable habitats and niches.

Adaptations of aquatic animals

1. The pectoral fins and dorsal fins act as stabilizers or balancers and the caudal fin helps in changing the direction as a rudder.
2. Arrangement of body muscles in the form of bundles (myotomes) help in locomotion.
3. Stream lined structure helps in the swift movement of the animals in water.
4. Respiration by gills making use of gases dissolved in water.
5. Presence of air-bladders filled with air for buoyancy.
6. Presence of lateral-line system. They function as rheoreceptors which is helpful in echolocating objects in water.
7. Integuments rich in mucous glands are protected by scales.
8. Maintain water and ionic balance in its body with excretory structures.

Adaptions of terrestrial animals

1. Earthworms, land Planarians secrete a mucus coating to maintain a moist situation for burrowing, coiling, respiration, etc.,
2. Arthropods have an external covering over the respiratory surfaces and welldeveloped tracheal systems.
3. In vertebrate skin, there are many cellular layers besides the well protected respiratory surfaces that help in preventing loss of water.
4. Some animals obtain their water requirement from food as partial replacement of water lost through excretion.
5. Birds make nests and breed before the rainy season as there is availability of abundant food. But during drought birds rarely reproduce.
6. Camels are able to regulate water effectively for evaporative cooling through the skin and respiratory system and excrete highly concentrated urine, and can also withstand dehydration up to 25% of their body weight.

Learninsta presents the core concepts of Biology with high-quality research papers and topical review articles.

Responses To Abiotic Factors

Every living organism responds to its environment. There are various ways by which organisms respond to abiotic conditions. Some organisms can maintain constant physiological and morphological conditions or undertake steps to overcome the environmental condition, which in itself is a response (Fig. 10.9).

The types of responses observed are

Regulate:

Some organisms are able to maintain homeostasis by physiological means which ensures constant body temperature, ionic / osmotic balance. Birds, mammals and a few lower vertebrate and invertebrate species are capable of such regulation.

Conform:

Most animals cannot maintain a constant internal environment. Their body temperature changes with the ambient temperature. In aquatic animals like fishes, the osmotic concentration of the body fluids changes with that of the ambient water osmotic concentration. Such animals are called Conformers. In case of extreme condition, the inhabitants relocate themselves as in migration.

Migrate:

Organisms tend to move away temporarily from a stressful habitat to a new, hospitable area and return when the stressful period is over. Birds migrate from Siberia to Vedanthangal in Tamilnadu to escape from the severe winter periods.

Suspend:

In certain conditions, if the organisms is unable to migrate, it may avoid the stress by becoming inactive. This is seen commonly in bears going into hibernation during winter. Some snails and fish go into aestivation to avoid summer related problems like heat and desiccation. Some lower animals suspend a certain phase of their life cycle, which is referred to as diapause.

Learninsta presents the core concepts of Biology with high-quality research papers and topical review articles.

Concept of Biome and Their Distribution

Biomes are large regions of earth that have similar or common vegetation and climatic conditions. They play a crucial role in sustaining life on Earth. They are defined by their soil, climate, flora and fauna. Biomes have distinct biological communities that have been formed in response to a shared physio-chemical climate. Biomes are seen to even spread across continents. Thus, it can be observed that a biome is a broader term than habitat.

Any biome can comprise a variety of habitats. Factors such as temperature, light, water availability determine what type of organisms and adaptations are observed in a biome (Fig. 10.4).

Characters of a biome

• Location, Geographical position (Latitude, Longitude)
• Climate and physiochemical environment.
• Predominant plant and animal life.
• Boundaries between biomes are not always sharply defined. Transition or transient zones are seen as in case of grassland and forest biomes (Fig. 10.5).

Aquatic Biomes

They occupy about 71% of the biosphere. The aquatic biome is home to millions of aquatic organisms like fishes. The climate of coastal zones are inflenced by aquatic bodies.

Aquatic biomes of earth

1. Freshwater (Lakes, ponds, rivers)
2. Brackish water (Estuaries / Wetlands)
3. Marine (Coral reefs, pelagic zones and abyssal zones)

Terrestrial biomes

These are large communities of plants and animals that occupy a distinct region. They include grassland, tundra, desert, tropical rainforest, and deciduous and coniferous forests. Terrestrial biomes are distinguished primarily by their predominant vegetation, and are mainly determined by climate, which in turn, determines the organisms inhabiting them.

These include the keystone species and indicator species which are unique to their respective biomes. The terrestrial biomes are a source of food, O₂ and act as CO₂ sink, apart from the climate regulatory role.

Major Biomes of the Earth

Tundra biome, Taiga biome, Grassland biome, Alpine biome, Forest biome and Desert biome.

TUNDRA BIOME

• This is the almost treeless plain in the northern parts of Asia, Europe and North America.
• Winters are long with little daylight, Summers are short, with long daylight hours.
• Precipitation is less than 250 mm per year. It is a zone of permafrost.
• Dwarf willows, birches, mosses, grasses, sedges are the flora here.
• Reindeer, arctic hare, musk ox, lemmings are important Tundra herbivores. Some important carnivores are the arctic fox, arctic wolf, bobcat and snowy owl. Polar bears live along coastal areas.
• Because of the severe winters, many of the animals are migratory. For example, the many shore birds and waterfowl such as ducks and geese, nest in the Tundra during the summer and migrate south for the winter.

TAIGA BIOME

• The Taiga is 1300-1450 km wide zone south of the Tundra.
• This area has long and cold winters.
• Summer temperature ranges from 10°C to 21°C.
• Precipitation ranges about 380-1000 mm annually.
• The Taiga is a forest of coniferous trees such as spruce, fir and pine. This is a major source for the logging industry.
• Important migratory herbivores include moose, elk, deer and reindeer. Moose and reindeer migrate to the Taiga for winter and to the Tundra for summers.
• The common smaller mammals are herbivorous squirrels, snowshoe hare and predatory pine martens. Important predators include the timber wolf, grizzly bear, black bear, bobcat and wolverines. (Fig. 10.6)

GRASSLAND BIOME

• Grasslands occur in temperate and in the tropical regions.
• They have hot summers, cold winters, and irregular rainfall.
• Often they are characterized by high winds.
• The low irregular rainfall is the factor which makes the difference between a temperate deciduous forest and a temperate grassland.
• Herbivores like antelope, bison, wild horse, jack rabbit, ground squirrel and prairie dogs are abundant.
• Predators include coyotes, foxes, hawks and snakes.
• In India, fauna of grasslands includes Elephant, Gaur, Rhino, Antelope.
• Flora of grasslands include purple needle grass, wild oats, foxtail, ryegrass and buffalo grass (Fig. 10.7).

Alpine biome

1. The alpine zone (zone between timber line and snow zone) includes in the descending order, a sub-snow zone immediately below the snow zone, a meadow zone in the centre and a shrub zone which gradually merges into the timber zone.
2. The snow zone of Himalayas lies over 5100m above mean sea level and alpine zone exists at a height of 3600m. From an ecological view point, the zone above the limits of tree growth (timber line) exhibits extreme environmental conditions which greatly influence the biota of this region.
3. Alpine zone of Himalayas is characterized by sparseness of animal groups. Many invertebrates of alpine zone are predatory and occur in lakes, streams and ponds. Among fishes, amphibians and vertebrates are totally lacking and reptilian fauna is greatly impoverished.
4. Flora of alpines includes alpine phacelia, bear grass, bristlecone pine, moss campion, polylepis forest, pygmy bitterroot, and wild potato.

Forest biomes

Forest is a broad term used to describe areas where there are a large number of trees (Fig. 10.8). The forest biomes include a complex assemblage of diffrent kinds of biotic communities. The major forest biomes are the Tropical forests and the Temperate forests.

Tropical forest

• They occur near the equator (between latitudes 23.5° at north and 23.5° at south).
• The major characteristic of tropical forests is their distinct seasons. Only two seasons are present (rainy and dry). Winter is absent. The length of daylight is about 12 hours and varies little.
• The average annual temperature ranges between 20°C and 25°C.
• Precipitation is evenly distributed throughout the year with annual rainfall exceeding 2000 mm.
• Soil is nutrient-poor and acidic. Decomposition is rapid and soils are subject to heavy leaching.
• Tree canopy is multilayered and continuous, allowing little light penetration.
• Flora is highly diverse: one square kilometer may contain as many as 100 different tree species. Trees are 25-35 m tall, with buttressed trunks and shallow roots, mostly evergreen, with large dark green leaves. Common vegetation are orchids, bromeliads, vines (lianas), ferns, mosses, and palms.
• They are characterized by the greatest diversity of fauna which includes birds, bats, small mammals, and insects.

Temperate forest

• These forests occur in eastern North America, northeastern Asia and western and central Europe.
• Have well-defined seasons with a distinct winter. Moderate climate and a growing season of 140-200 days during 4-6 frostfree months distinguish temperate forests.
• Annual temperature varies from – 30° C to 30° C.
• Precipitation (750-1500 mm) is distributed evenly throughout the year.
• Soil is fertile, enriched with decaying litter.
• Canopy is moderately dense and allows light to penetrate, resulting in well-developed and richly diversified understorey vegetation and stratification of animals.
• Flora is characterized by 3-4 tree species per km². Trees have broad leaves that are lost annually such as oak, hickory, beech, hemlock, maple, basswood, cottonwood, elm, willow, and spring-flowering herbs.
• Fauna consists of squirrels, rabbits, skunks, birds, deer, mountain lion, bobcat, timber wolf, fox, and black bear.

Desert biomes

• Deserts cover about one fit of the earth’s surface and occur where rainfall is >500 mm/year.
• Rainfall is usually very low and/or concentrated in short bursts between long rainless periods. Evaporation rates regularly exceed rainfall rates.
• Soils are course-textured, shallow, rocky or gravely with good drainage and have no subsurface water. The finer dust and sand particles are blown elsewhere, leaving heavier pieces behind. Sand dunes are common.
• Mean annual temperatures range from 20-25°C. The extreme maximum ranges from 43.5 – 49° C. Minimum temperatures sometimes drop to -18°C. Based on the temperature range, deserts can be Hot deserts and Cold deserts.
• Hot deserts such as the Sahara of North Africa and the deserts of the southwestern U.S., Mexico, Australia and India (Thar desert) occur at low latitudes.
• Hot deserts have a considerable amount of specialized vegetation (xerophytes), aloe, agave, Opuntia species, Euphorbia royleana as well as specialized vertebrate and invertebrate animals.
• The dominant animals of warm deserts are reptiles and small mammals. The Indian Spiny-tailed lizard, the blackbuck, the white-footed fox are the common fauna of the Thar deserts. There are also insects, arachnids and birds.
• Cold deserts occur in Antarctic, Greenland and the Nearctic realm, parts of USA and in parts of western Asia and the Ladakh region in India.
• Widely distributed animals are jack rabbits, kangaroo rats, kangaroo mice, pocket mice, grasshopper mice, antelope and ground squirrels.

Learninsta presents the core concepts of Biology with high-quality research papers and topical review articles.

Major Abiotic Components or Factors

The abiotic factors include the chemical and physical factors which influence or affect organisms and their functioning in their environment. The common abiotic factors are:

Temperature

Temperature or degree of hotness and coldness is an essential and variable factor in any environment. It influences all forms of life by affecting many vital activities of organisms like metabolism, behaviour, reproduction, development and even death in the Biosphere. The minimum and maximum temperature of an environment regulates the survival of a cell.

The metabolism of organisms is regulated by enzymes which are temperature sensitive. In many organisms, determination of sex and sex ratio, maturation of gonads, gametogenesis and reproduction is influenced by temperature. In certain environments, the size and colouration of animals are inflenced by temperature. Birds and mammals attain greater body size in colder regions than warmer regions (Bergmann’s rule).

Warm blooded animals, living in colder climates, tend to have shorter limbs, ears and their appendages when compared to the members of the same species in warmer climates (Allen’s rule). In some aquatic environments, an inverse relationship between water temperature and fish meristic characters is observed lower the temperature, more the vertebrae (Jordon’s rule).

Temperature influences the distribution of organisms. The tropics have higher diversity and density of populations, when compared to temperate and polar regions.

Adaptations to temperature

Adaptation to temperature is essential for the survival of the species/organisms. Organisms which can survive a wide range of temperature are referred to as Eurytherms (cat, dog, tiger, human). Eurythermy can be an evolutionary advantage: adaptations to cold temperatures (cold-eurythemy) are seen as essential for the survival of species during ice ages.

In addition, the ability to survive in a wide range of temperatures increases a species ability to inhabit other areas, an advantage for natural selection. Eurythermy is an aspect of thermoregulation in organisms. These organisms which can tolerate only a narrow range of temperature are Stenotherms (Fish, Frogs, Lizards and Snakes).

Over the course of time, by evolution, animals of different ecological habitats have developed different variations and adaptations to temperature changes. It enabled them to survive in different habitats and develop niches. In case of extreme temperatures, organisms have adapted by forming heat resistant spores, cysts (Entamoeba), antifreeze proteins (Arctic fihes).

Hibernation (winter sleep) and Aestivation (Summer sleep) are useful adaptations to overcome extreme winters and summers. In certain conditions, migration is an appropriate adaptation to overcome extreme temperatures and resultant water and food scarcity. (Fig 10.2).

Light

It is an important and essential abiotic factor. Ecologically, the quality (wavelength or colour), the intensity (actual energy in gram calories) and duration (length of day) of light are considered signifiant for organisms.

Light influences growth, pigmentation, migration and reproduction. The intensity and frequency of light influences metabolic activity, induce gene mutations (UV, X – rays). Light is essential for vision. This is proved by the poorly developed or absence of eyes in cave dwelling organisms. Diapause is also influenced by light in animals. Gonads of birds become more active with increasing light in summer. Light inflences the locomotion and movement of lower animals.

WATER

Life on earth began in the seas and water is essential for the survival of all forms of life. About three-fourth of the earth’s surface is covered with water (hydrosphere). Water is found in three states: gaseous, liquid, and solid.

There are two types of water on Earth. They are the Fresh water (rivers, lakes, ponds) and the Salt water (seas and oceans). Based on the dissolved salts, water can be hard water (sulphates/nitrates of Calcium/Magnesium) or soft water. If hardness can be removed by boiling, it is temporary hard water, and if boiling does not help, it is permanent hard water.

Essential properties of water

• Water is one of the main agents in Pedogenesis (soil formation).
• It is the medium for several different ecosystems.
• It is present as moisture in the atmosphere and the outer layers of the lithosphere and is uneven in distribution on the earth.
• Water is heavier than air and imparts greater buoyancy to the aquatic medium. This enables organism to flat at variable levels.
• Water has high heat capacity and latent heat, due to which it can withhold large amounts of heat. This, oceans and lakes tend to maintain a relatively constant temperature, and the biosphere is relatively thermostable.
• Water is physically unique because it is less dense as a solid (ice) than as a liquid.
• When water freezes (0oC), it contracts. The maximum density of liquid water occurs at 4oC. Below that, it expands markedly.
• This enables ice to flat on the top of water bodies. Hence, only the surface of water bodies will freeze, while below the surface, water will be in liquid form, sustaining life (Fig. 10.3).
• Water is considered as the Universal solvent. It is the main medium by which chemical constituents are transported from abiotic components to the living components of an ecosystem.
• Water has high surface tension. This allows pollen, dust, and even water striders to remain at the surface of a water body even though they are denser than the water.

Soil

It is a mixture of organic matter, minerals, gases, liquids and organisms that together support life. The soil zone is known as Pedosphere. Soil is formed from rocks which are the parent materials of soil, by weathering and is called embryonic soil (Pedogenesis).

It has four major functions:-

• Medium for plant growth
• Means for water storage and purification
• Modifier of earth’s atmosphere
• Habitat for many organisms, which in turn modify the soil.

Soil is formed of many horizontal layers called as Soil Profile.

Properties of Soil

1. Texture of soil:

The texture of soil is determined by the size of the soil particles. The types of soil include sand, silt and clay on the basis of their size differences.

2. Porosity:

The space present between soil particles in a given volume of soil are called pore spaces. The percentage of soil volume occupied by pore space or by the interstitial spaces is called porosity of the soil.

3. Permeability of soil:

The characteristic of soil that determines the movement of water through pore spaces is known as soil permeability. Soil permeability is directly dependent on the pore size. Water holding capacity of the soil is inversely dependent on soil porosity.

4. Soil Temperature:

Soil gets its heat energy from solar radiation, decomposing organic matter, and heat from the interior of earth. Soil temperature effects the germination of seeds, growth of roots and biological activity of soil-inhabiting micro-and macroorganisms.

5. Soil water:

In soil, water is not only important as a solvent and transporting agent, but also maintains soil texture, arrangement and compactness of soil particles, making soil habitable for plants and animals.

Wind

Wind is the natural movement of air of any velocity from a particular direction. The two main causes are differential heating between the equator and the poles and the rotation of the planet (Coriolis effect). Wind helps to transport pollen grains, seeds, and even flight of birds. While it is the source of wind energy, it also causes erosion. Wind speed is measured with an Anemometer.

Humidity

Moisture in the form of invisible vapor in the atmosphere is called humidity. which is generally expressed in terms of absolute humidity, relative humidity or specific humidity. Absolute humidity is the total mass of water vapour present in a given volume or mass of air. It does not take temperature into consideration.

Relative humidity is the amount of water vapour present in air and is expressed as a percentage of the amount needed for saturation at the same temperature Relative humidity is expressed as a percentage; a high percentage means that the air-water mixture is more humid at a given temperature. Humidity is measured with a Hygrometer.

Altitude

This factor is mainly the elevation or gradient and it affects temperature and precipitation in an ecosystem or biome. As altitude increases, temperature and density of oxygen decreases.

Higher altitudes usually receive snow instead of rain because of low temperature. Animals are known to modify their response to environmental changes (stress) in reasonably short time spans. This is known as Acclimatization. This is observed when people who have moved from the plains to higher altitudes show enhanced RBC count within a few days of settling in their new habitat. This helps them cope with
lower atmospheric oxygen and higher oxygen demand.