Samacheer Class 12 Bio Botany - Principles of Ecology

Ecological hierarchy is the interaction of organisms with their environment results in the establishment of a grouping of organisms. Which is called ecological hierarchy (or) ecological levels of organisation.

Taxonomically different species occupying similar habitats (Niches) in different geographical regions are called Ecological equivalents.
E.g: Certain species of epiphytic orchids of Western Ghats of India differ from the epiphytic orchids of South America. But they are epiphytes.

Habitat
* A specific phsical space occupied bv an organism (species)
* The same habitat may be shared by many organisms (species)
* Habitat specificity is exhibited by organisms.
Niche
* A functional space occupied by an organism in the same ecosystem
* A single niche is occupied by a single species
* Organisms may change their niche with time and season.

* Eurythermal: Organisms which can tolerate a wide range of temperature fluctuations.
Example: Zostera.
* Stenothermal: Organisms that can tolerate only a small range of temperature variations.
Example: Mango.

• The deepest strata of the ocean is dark and sufficient light is not available for the photosynthesis of green algae.
• Algae need brackish water for its growth. Which is also not available in the deepest strata of the ocean.

• The albedo effect is due to greenhouse effect.
• Aerosols (suspension of fine solid (or) liquid particles in gas) with small particles is reflecting the solar radiation entering the atmosphere is known as Albedo effect.
• It reduces the temperature, photosynthesis and respiration
• The sulphur compounds present in the aerosol are responsible for acid rain due to acidification of rain water and destroy the ozone.

• Soil formation is initiated by the weathering process.
• Biological weathering takes place when organisms like bacteria, fungi, lichens and plants helps in the breakdown of rocks through the production of acids and certain chemical substances.

• Mutualism interaction exist between fig tree and wasp
• In fig tree there is a tight one to one relationship with a pollinator species of wasp and no other species.
• The wasp pollinates the fig while finding egg lav ing sites and in turn, the fig offers the wasp developing seeds, as food for the developing larvae.

• It is an interaction between two species of organisms in which both are benefitted from the obligate association.
• Lichens is a mutual association of algae and a fungus.
• The alga is usually green alga (or) blue green alga. The fungus is an ascomycete (or) basidiomycete.
• It is believed that alga contributes organic food from photosynthesis and the fungus is able to absorb water and mineral salts.
• The fungus can also conserver water and this enables lichens to grow in extremely dry conditions where no other plants can exist.

• Mutualism is an interaction between two species of organisms in which both are benefitted from their association.
• Eg: 1 – Water Fern (Azolla) and Nitrogen fixing Cyanobacterium (Anabaena)
• Eg: 2 – Roots of terrestrial plants and fungal hyphae – Mycorrhiza.

Holoparasites:
The organisms which are dependent upon the host plants for their entire nutrition are called Holoparasites. They are also called total parasites.
Examples:
* Cuscuta is a total stem parasite of the host plant Acacia, Duranta, and manv other plants. Cuscuta even gets flower inducing hormone from its host plant.
* Balanophora, orobanche, and refflesia are the total root parasites found on higher plants.
Hemiparasites:
The organisms which derive only water and minerals from their host plant while synthesizing their own food by photosynthesis are called Hemiparasites. They are also called partial parasites.
Examples:
Viscum and Loranthus are partial stem parasites.

Predation:
* It is an interaction between two species, one of which captures, kills, and eats up the other.
* The species which kills is called a predator and the species which is killed is called prey.
* The predator is benefitted while the prey is harmed.
Examples:
A number of plants like Drosera (Sundew Plant), Nepenthes (Pitcher Plant), Diaonaea (Venus flytrap), Utricularia (Bladderwort), and Sarracenia are predators
* which consume insects and other small animals for their food as a source of nitrogen.
* They are also called insectivorous plants.
* Many herbivores are predators. Cattles, Camels, Goats, etc., frequently browse on the tender shoots of herbs, shrubs, and trees.
* Generally, annuals suffer more than perennials.
* Grazing and browsing may cause remarkable changes in vegetation.
* Nearly 25 percent of all insects are known as phytophagous (feeds on plant sap and other parts of the plant)
Many defense mechanisms are envoloved to avoid their predations by plants.
Calotropis produces highly poisonous cardiac glycosides.
Tobacco: Produces nicotine.
Coffee: coffee plants produce coffeine.

The plant, Ophrys an orchid, the flower looks like a female insect to attract the male insect to get pollinated by the male insect and it is otherwise called ‘floral mimicry.’

* Xerophytes are the plants which are living in dry (or) xeric condition are known as xerophytes.
Adaptations of xerophytes:
* Root system is well developed and is greater than that of shoot system.
* In some xerophytes all the internodes in the stem are modified into a fleshy leaf structure called phvlloclades (Opuntia)
* In some the petiole is modified into a fleshy leaf like structure called phyllode (Acacia melanoxylon).

• Submerged plants which receive weak illumination because
• Submerged plants are completely immersed in water and not in contact with the atmosphere (or) surface of the water.
• The floating hydrophytes float freely (or) float their leaves and flowers on the surface of water do not allow light to pass inside the lake.
• So submerged plants receive weak illumination than exposed floating plants.

• Vivipary is the special type of seed germination
• During germination, the seed is till attached to the parent plant and nourished by it.
• Vivipary generally occurs in mangrove plants.
• The mangrove plants are medium sized trees which grow in salty marshes of sea coasts. (Eg.) Rhizophora, Sonneratia, Avicennia.
• The seeds of this plant cannot germinate on the marshy habitat because of the excessive salt concentration and lack of oxygen.
• The radicle of the plant elongates considerably and projects out of the fruit.
• Then dark like seedling breaks off from the parent plant.
• Then radicle immediately forms new roots and establishes the seedling as a new plant.

Thermal Stratification is usually found in aquatic habitats. The change in the temperature profile with increasing depth in a water body is called thermal stratification. There are three kinds of thermal stratifications.
* Epilimnion – The upper layer of warmer water.
* Metalimnion – The middle layer with a zone of a gradual decrease in temperature.
* Hypolimnion – The bottom layer of colder water.

• Rhytidome is the structural defense by plants against fire
• The outer bark of trees which extends to the last formed periderm is called Rhytidome.
• It is composed of multiple layers of suberized periderm, cortical and phloem tissues.
• It protects the stem against fire, water loss, invasion of insects and prevents infections by microorganisms.

Sometimes, ants take their shelter on some trees such as Mango, Litchi, Jamun, and Acacia, etc. These ants act as bodyguards of the plants against any disturbing agent and the plants, in turn, provide food and shelter to these ants. This phenomenon is known as Myrmecophily. Example: Acacia and its ants.

• It is a method of human aided seed dispersal r Seed ball is an ancient Japanese technique of encasing
• seeds in a mixture of clay and soil humus (also in cow dung) and scattering them on suitable ground, not planting of trees manually.
• This method is suitable for barren and degraded lands for tree regeneration and vegetation before the monsoon period where the suitable dispersal agents become rare.

Anemochory
Zoochory
1. Individual seeds (or) the whole fruit may be modified to help for the dispersal by wind, wind dispersal of fruits and seeds is quite common in tall trees.
1. Birds and mammals, including human beings play an efficient and important role in the dispersal of fruit and seeds.
2. Minute seeds are very small light and with inflated covering. (Eg.) Orchids.
2. The surface of the fruits (or) seeds have hooks (Xanthium) barbs (Andropogon) Spines (Aristida) by means of which they adhere to the body of animals (or) clothes of human beings and get disposed.
3. Seeds (or) whole fruits are flattened to form a wing.(Eg.) Maple, Gyrocarpus
3. Some fruits and seeds have sticky glandular hairs by which they adhere to the fur of grazing animals.
(Eg.) Boerhaavia and cleome
4. Seeds (or) fruits may have feathery appendages which greatly increase their buoyancy to disperse to high altitudes. (Eg.) Asclepias and vernonia.
4. Some fruits have viscid layers (sticky layer) which adhere to the beak of the bird which eats them and when they rub them on to the branch of the tree, they disperse and germinate. (Eg.) Cordia, Alangium
Censor mechanism
Fleshy fruit
The fruits of many plants open in such a way that the seeds can escape only when the fruits are violently shaken by a strong wind.
Some fleshy fruits with conspicuous colours are dispersed by a human being to distant places after consumption.
(Eg.) Mango and Papaya.

The interaction between organisms, when continues for generations, involves reciprocal changes in genetic and morphological characters of both organisms. This type of evolution is called Co-evolution. It is a kind of co-adaptation and mutual change among interactive species.
Examples:
* Corolla length and probosci’s length of butterflies and moths (Habenaria and Moth).
* Bird’s beak shape and flower shape and size.

Based on the temperature prevailing in an area, Raunkiaer classified the world’s vegetation into the following four types.
They are megatherms, mesotherms, microtherms, and hekistotherms.
In thermal springs and deep sea hydrothermal vents where average temperature exceed 100°c.
Based on the range of thermal tolerance, organisms are divided into two types.
* Eurythermal: Organisms which can tolerate a wide range of temperature fluctuations.
(Eg.) Zostera (A marine Angiosperm) and Artemisia tridentata.
* Stenothermal: Organisms which can tolerate only a small range of temperature variations.
(Eg.) Mango and Palm (Terrestrial Angiosperms).
Mango plants do not and cannot grow in temperate countries like Canada and Germany.
Thermal stratifications:
It is usually found in aquatic habitat.
The change in the temperature profile with increasing depth in a water body is called thermal stratification. There are three kinds of thermal stratification
* Epilimniotn The upper layer of warmer water
* Metalimnion The middle layer with a zone of gradual decrease in temperature.
* Hypolimnion The bottom layer of colder water.
Temperature based zonation:
Variations are latitude and altitude do affect the temperature of the vegetation on the earth’s surface.
Latitude: Latitude is an angle which ranges from 0° at the equator to 90° at the poles.
Altitude: How High a place is located above the sea level is called the altitude of the place.

Effects of fire:
* A fire has a direct lethal effect on plants
* Burning scars are suitable places for the entry of parasitic fungi and insects
* It brings out the alteration of light, rainfall, nutrient cycle, the fertility of the soil, pH, soil flora, and fauna
* Some fungi which grow in the soil of burnt areas called pyrophilous. (Eg.) Pyronema confluens.

Soil Profile:
* Soil is commonly stratified into horizons at different depth. These layers differ in their physical, chemical and biological properties.
* This succession of super-imposed horizons is called a soil profile.

(a) Parasitism: It is an interaction between two different species in which the smaller partner (parasite) obtains food from the larger partner (host or plant). So the parasitic species is benefitted while the host species is harmed. Based on the host-parasite relationship, parasitism is classified into two types they are holoparasite and hemiparasite.
(b) Holoparasites: The organisms which are dependent upon the host plants for their entire nutrition are called Holoparasites. They are also called total parasites.
Examples:
* Cuscuta is a total stem parasite of the host plant Acacia, Duranta and many other plants. Cuscuta even gets flower inducing hormone from its host plant.
* Balanophora, Orobanche and Rafflesia are the total root parasites found on higher plants.
(c) Hemiparasites: The organisms which derive only water and minerals from their host plant while synthesizing their own food by photosynthesis are called Hemiparasites. They are also called partial parasites.
Examples:
* Viscum and Loranthus are partial stem parasites.
* Santalum (Sandal Wood) is a partial root parasite.
The parasitic plants produce the haustorial roots inside the host plant to absorb nutrients from the vascular tissues of host plants.

The plants which are living in water or wet places are called hydrophytes. According to their relation to water and air, they are sub-divided into the following categories:
* Free floating hydrophytes: These plants float freely on the surface of the water. They remain in contact with water and air, but not with soil. Examples: Eichhornia, Pistia and Wolffia (smallest flowering plant).
* Rooted floating hydrophytes: In these plants, the roots are fixed in mud, but their leaves and flowers are floating on the surface of water. These plants are in contact with soil, water and air. Examples: Nelumbo, Nymphaea, Potomogeton, and Marsilea.
* Submerged floating hydrophytes: These plants are completely submerged in water and not in contact with soil and air. Examples: Ceratophyllum and Utricularia.
* Rooted- submerged hydrophytes: These plants are completely submerged in water and rooted in soil and not in contact with air. Examples: Hydrilla, Vallisneria, and Isoetes.
Amphibious hydrophytes (Rooted emergent hydrophytes): These plants are adapted to both aquatic and terrestrial modes of life. They grow in shallow water. Examples: Ranunculus, Typha and Sagittaria.
Hygrophytes: The plants which can grow in moist damp and shady places are called hygrophytes. (Eg.) Habenaria (Orchid), Mosses (Bryophytes), etc.

Anatomical adaptations:
* Presence of multilayered epidermis with heavy cuticle to prevent water loss due to transpiration.
* The hypodermis is well developed with sclerenchymatous tissues.
* Sunken shaped stomata are present only in the lower epidermis with hairs in the sunken pits.
* Scotoactive type of stomata found in succulent plants.
* Vascular bundles are well developed with several layered bundle sheath.
* Mesophyll is well differentiated into palisade and spongy parenchyma.
* In succulents the stem possesses a water storage region.

Morphological adaptations:
* The temperate halophytes are herbaceous but the tropical halophytes are mostly bushy
* In addition to the normal roots, many stilt roots are developed
* A special type of negatively geotropic roots called pneumatophores with pneumathodes to get sufficient aeration are also present. They are called breathing roots.
Example: Avicennia
* Presence of thick cuticle on the aerial parts of the plant body
* Leaves are thick, entire, succulent and glossy. Some species are aphyllous (without leaves).
* Vivipary mode of seed germination is found in halophytes

Advantages of seed dispersal:
* Seeds escape from mortality near the parent plants due to predation by animals or getting diseases and also avoiding competition.
* Dispersal also gives a chance to occupy favourable sites for growth.
* It is an important process in the movement of plant genes, particularly this is the only method available for self-fertilized flowers and maternally transmitted genes in outcrossing plants.
* Seed dispersal by animals helps in conservation of many species even in human-altered ecosystems.
* Understanding of fruits and seed dispersal acts as a key for proper functioning and establishment of many ecosystems from deserts to evergreen forests and also for the maintenance of biodiversity conservation and restoration of ecosystems.

Birds and mammals, including human beings, play an efficient and important role in the dispersal of fruit and seeds. They have the following devices,
i. Hooked fruit: The surface of the fruit or seeds have hooks,(Xanthium), barbs (Andropogon), spines (Aristida) by means of which they adhere to the body of animals or clothes of human beings and get dispersed.
ii. Sticky fruits and seeds:
* Some fruits have sticky glandular hairs by which they adhere to the fur of grazing animals. Example: Boerhaavia and Cleome.
* Some fruits have a viscid layer which adheres to the beak of the bird which eats them and when they rub them on to the branch of the tree, they disperse and germinate. Example: Cordia and Alangium
iii. Fleshy fruits: Some fleshy fruits with conspicuous colours are dispersed by human beings to distant places after consumption. Example: Mango and Diplocyclos
12th Bio Botany Guide Principles of Ecology Additional Important Questions and Answers
I. Match the following

C) T, T, F, T
IX. Fill in the blanks Answers
1. Roots and hulls of Black Walnut Juglans nigra secretes an alkaloid……………………………………….
Juglone
2. The plants which behave as xerophytes at summer and behave as mesophvtes during rainv season is……………………………….
tropophytes
3. The ……………………………….wave length of spectrum is less strongly absorbed by plants.
green (500 – 600 nm)
4. The rate of photosynthesis is maximum at blue (400 – 500 nm) and……………………………….
red (600 – 700 nm)
5. ……………………………….is well known factor needed for the physiological process of plants.
Light
6. In climatology diurnal cycle is the basic form of climatic pattern in every ………………………………..
24 hrs.
7. The altitudinal limit of normal tree growth is about ………………………………..
3000 to 4000
8. ……………………………….are organisms, which derive onlv water and minerals from their host plant for synthesizing their own food.
Hemiparasites
9. ……………………………….is the smallest free floating hvdrophvtes.
Wolffia
10. Scotoactive tvpe of stomata found in ……………………………….plants.
succulent
11. ……………………………….are plants which grow perched on other plants.
Epiphytes
12. The plants which are living in moderate conditions (neither too wet nor too drv) are known as……………………………….
Mesophytes
13. ……………………………….is the world forest dav.
March – 21
14. Earth dav falls on……………………………….
April – 22
15. International ozone dav is celebrated on……………………………….
September -16
X. Choose the correct answer

Evergreen forest
It is found where heavy rainfall occurs throughout the year.
Sclerophyllous forest
It is found where heavy rainfall occurs during winter and low rainfall during summer.
Give reason for the following
* Species of the grass lands of western ghats of India differ from the grass species of temperate grass lands of steppe in North America. But they are all ecologically primary producers.
* Taxonomically different species occupying similar habitats (Niche) in different geographical regions are called ecological equivalents.

Euryhaline Stenohaline
* Organisms which can live in water with wide range of salinity.
* (Eg.) Marine algae and marine angiosperms
stenohaline.
* Organisms which can withstand only small range of salinity.
* (Eg.) Plants of estuaries

• Some pteris are well adapted to grow in burnt and highly disturbed area
• Pteris (fern) and pyronema (fungus) indicates the burnt up and fire disturbed areas.
• So they are called indicators of fire.

• Some species are found in the ecotone areas border between forest and grassland due to the effect of the environment of the two habitats. This is called the edge effect.
• (Eg.) Owl in the ecotone area between forest and grassland.

• The steepness of the mountain (or) hill allows the rain to run off.
• Asa result the loss of water causes water deficit and quick erosion of the top soil resulting in poor vegetation.
• On the other hand the plains and valley are rich in vegetation due to the slow drain of surface water and retention of water in the soil.

Roots and hulls of black walnut junglone nigra secretes an alkaloid junglone.
* Which inhibits the growth of seedlings of apple,tomato and alfalfa around it.
* It is an example for amensalism type of interspecific interaction.

• Many orchids ferns, lianas, money plant usnea (lichen) are some of examples of epiphytes.
• These plants which are found on other plants and growing without harming them are called epiphytes.

• Caruncle is a structure found in micropylar region of euphorbiaceae seeds, that attract ants. Which feed the caruncle to their larvae.
• Then ants leave the seed to their waste disposal area. Where the seeds germinate.
• This type of seed dispersal called myrmecophily.

• It is called physiological dryness.
• In these habitats, water is sufficiently present but plants are unable to absorb it because of the absence of capillary spaces.
• (Eg.) Plants in salty and acidic soil.

• Helps to reconstruct past climates of our planet and flora, fauna and ecosystem in which they lived.
• Example: Air bubbles trapped in ice for tens of thousands of years with fossilized pollen, coral, plant and animal debris.

• Air in motion is called wind.
• It is also a vital ecdogical factor.
• The atmospheric air contains a number of gases, particles and other constituents.
• Anemometer is the instrument used to measure the speed of wind.

Rhizoblum (Bacterium) forms nodules in the roots of leguminous plants and lives symbiotically.
The Rhizobium obrains food from leguminous plant and in turn fixes atmospheric nitrogen in to nitrate, making it available to host plants.
XII. Three Marks

* Timberline (or) tree line is an imaginary line in a mountain (or) higher areas of land that marks the level above which trees do not
grow.
* The altitudinal limit of normal tree growth is about 3000 to 4000 m.

• It is the structural defense by plant against.
• The outer bark of trees which extends to the last formed periderm is called Rhytidome.
• It is composed of multiple layers of suberized periderm cortical and phloem tissue. It protects the stem against fire, water loss, invasion of insects and prevents infections by microorganism

Applied ecology (or) environmental technology helps us to manage and conserve natural resource particularly ecosystems, forest and wild life conservative management.
Environmental management involves bio-diversity, conservation, ecosystem restoration, habitat management, invasive SPS management protected areas management and also help us plan landscapes and environmental impact designing for the futuristic ecology.

• Many organisms co-exist in an environment.
• The environment includes physical, chemical biological component.
• When a component surrounding an organism affects the life of an organism called factor.
• These factors may be biotic and abiotic.

• Climatic factors: Sunlight, precipitation wind, carbon dioxide and water vapour.
• Biotic factors: Birds, insects, man, grazing animals, rodents, plant pathogens and epiphytes.
• Edaphic factors: Soil slope, soil water, physical nature of soil, minerals, soil air.

Some plants are used to remove cadmium from contaminated soil is known as phyto remediation. tM.-fTiVM
(Eg.) Rice and eichhornia tolerate cadmium by binding it to their proteins.
Soybean and tomato manage to tolerate cadmium by storing into few group of cells.

• Loamy soil is ideal for cultivation. It consist of 70% sand and 30% clay (or) silt.
• It ensures good retention and proper drainage of water.
• The porosity of soil provides adequate aeration and allows the penetration of roots.

• Soil is commonly stratified into horizons at different depth.
• These layers differ in their physical, chemical and biological properties.
• This succession of super-imposed horizons is called soil profile.

Species Ecology:
It is the study of a group of individual of particular species, (population)
Community Ecology:
It is the study of several species that are living together as a community (made up of several populations)

Height above the sea level forms the altitude.
At high altitudes
* The velocity of wind remains high.
* Temperature and air pressure-decreases.
* While humidity and intensity of light increases.
Due to these factors vegetation at different altitudes varies showing distinct zonation.

• They were epiphytes showing commensalism type of positive interaction.
• In which one is benefitted and other is neither benefitted nor harmed.
• The species that derives benefit is called the commensal, while the other species is called the host.

• The epiphytic higher plant gets its nutrients and water from the atmosphere with the help of their hygroscopic roots.
• These roots contain special type of spongy tissue called velamen.

An interaction between organisms of different species in which both organisms benefit but neither is dependent on the relationship.
(Eg.) Soil bacteria, fungi and plants growing in the soil.

• It is an inter specific interaction in which one species is inhibited while the other species is neither benefitted nor harmed.
• The inhibition is achieved by secretion of chemicals called allelopathic substances.

• It exhibits mimicry of inter specific interactions (or) mimicry of co-evolutionary dynamics.
• Mimicry is a phenomenon in which living organism modifies its form appearance structure (or) behaviour and looks like another living organism as a self defence and increases the chance of their survival.

kairomone is a chemical substance emitted by pieris rapae caterpillar (butterfly) exposed to wild radish gets the capacity to transmit defence induced by predator (butterfly) to progeny of wild radish.

• Sometimes, ants take their shelter on some trees such as Mango, Litchi, Jamun, Acacia etc.
• These ants act as body guards of the plants against any disturbing agent and the plants in turn provide food and shelter to these ants.
• This phenomenon is known as Myrmecophily. Example: Acacia and acacia ants.

• Mangroves protect vulnerable coastal areas from wave action by holding the soil together and prevent coastal erosion.
• Out of three districts of Tamil Nadu (Nagapattinam, Thanjavur and Thiruvarur), Muthupet (Thiruvarur district) was less damaged by Gaja Cyclone (Nov-2018) due to the presence of mangrove forest.

• In deep sea (>500 m) the environment is dark and its inhabitants are not aware of the existence of celestial source of energy called sun.
• Dead sea organisms use chemical energy rather than energy from sunlight.
• Chemosynthesis is a process, special bacteria use this process to produce energy without using sunlight.

Temperature based zonation:
* Variations in latitude and altitude do affect the temperature and the vegetation on the earth surface.
* Timber line / Tree line: It is an imaginary line in a mountain or higher areas of land that marks the level above which trees do not grow. The altitudinal limit of normal tree growth is about 3000 to 4000m.
Effects of temperature:
* The following physiological processes are influenced by temperature:
* Temperature affects the enzymatic action of all the bio-chemical reactions in a plant body.
* It influences CO2 and O2 solubility in the biological systems. Increases respiration and stimulates growth of seedlings.
* Low temperature with high humidity can spread diseases to plants
* The varying temperature with moisture determines the distribution of the vegetation types.

Effects of wind:
* Wind is an important factor for the formation of rain
* Causes wave formation in lakes and ocean, which promotes aeration of water
* Strong wind causes soil erosion and reduces soil fertility
* Increases the rate of transpiration
* Helps in pollination in anemophilous plants
* It also helps in dispersal of many fruits, seeds, spores, etc.
* Strong wind may cause up-rooting of big trees
* Unidirectional wind stimulates the development of flag forms in trees.

The important edaphic factors which affect vegetation are as follows:
1. Soil moisture:
Plants absorbs rain water and moisture directly from the air.
2. Soil water:
Soil water is more important than any other ecological factors affecting the distribution of plants. Rain is the main source of soil water. Capillary water held between pore spaces of soil particles and angles between them is the most important form of water available to the plants.
3. Soil reactions:
Soil may be acidic or alkaline or neutral in their reaction. pH value of the soil solution determines the availability of plant nutrients. The best pH range of the soil for cultivation of crop plants is 5.5 to 6.8.
4. Soil nutrients:
Soil fertility and productivity is the ability of soil to provide all essential plant nutrients such as minerals and organic nutrients in the form of ions.
5. Soil temperature:
Soil temperature of an area plays an important role in determining the geographical distribution of plants. Low temperature reduces use of water and solute absorption by roots.
6. Soil temperature:
The spaces left between soil particles are called pore spaces which contains oxygen and carbon-di-oxide.
7. Soil organisms:
Many organisms existing in the soil like bacteria, fungi, algae, protozoans, nematodes, insects, earthworms, etc. are called soil organisms.

The surface features of earth are called topography. Its factors include, latitude, altitude, direction of mountain, steepness of mountain.
a. Latitudes and altitudes:
* Latitudes represent distance from the equator. Temperature values are maximum at the equator and decrease gradually towards poles.
* So different types of vegetation occur in latitude.
* Height above the sea level forms the altitude. At high altitudes
* The velocity of wind remains high. Temperature and are pressure – decrease While humidity and intensely of light increases.
* Due to these factors vegetation at difference altitudes varies showing distinct zonation.
b. Direction of mountain:
North and south faces of mountain (or) hill possess different types of flora and fauna because thev differ in their humidity, rainfall light intensity, light duration and temperature regions.
c. Steepness of the mountain:
* The steepness of the mountain (or) hill allows the rain to run off.
* As a result the loss of water causes water deficit and quick erosion of the top soil resulting in poor vegetation.
* On the other hand the plains and valley are rich in vegetation due to the slow drain of surface water and retention of water in the soil.

The interactions among living organisms such as plants and animals are called biotic factors.
Positive interactions:
When both (or) one the participating species are benefited. (Eg.) Mutualism and commen¬salism.
Mutualism:
* It is an interaction between two species of organisms in which both are benefitted from the obligate association.
* Lichens is a mutual association of an algae and a fungus.
* The alga is usually green alga (or) blue green alga. The fungus is an ascomycete (or) basidiomycetes.
* It is believed that alga contributes organic food from photosynthesis and the fungus is able to absorb water and mineral salts.
* The fungus can also conserve water and this enables lichens to grow in extreme dry conditions where no other plants can exist.
Nitrogen fixation:
* Rhizobium (Bacterium) forms nodules in the roots of leguminous plants and lives symbiotically.
* The Rhizobium obtains food from leguminous plant and in turn fixes atmospheric nitrogen into nitrate, making it available to host plants.
* Example: Water fern (Azolla) and Nitrogen fixing cyanobacterium (Anabaena)
* Anabaena present in coralloid roots of cycas
Commensalism:
Many orchids ferns, lianas, money plant usnea (lichen) are some of the examples of epiphytes.
These plants which are found on other plant and growing without harming them are called epiphytes.
Negative interactions:
a. Predation:
It is an interaction between two species, one of which captures, kills and eats up the other. The species which kills is called a predator and the species which is killed is called a prey. The predator is benefitted while the prey is harmed.
Examples:
A number of plants like Drosera (Sun dew Plant), Nepenthes (Pitcher Plant), Dionaea (Venus fly trap), Utricularia (Bladder wort) and Sarracenia are predators which consume insects and other small animals for their food as a source of nitrogen. They are also called as insectivorous plants.
Many herbivores are predators. Cattles, Camels, Goats etc., frequently browse on the tender shoots of herbs, shrubs and trees. Generally annuals suffer more than the perennials. Grazing and browsing may cause remarkable changes in vegetation. Nearly 25 percent of all insects are known as phytophagous(feeds on plant sap and other parts of plant)

Morphological Adaptations:
In root:
* Root system is well developed and is greater than that of shoot system.
* Root hairs and root caps are also well developed.
* In Xerophytic plants with the leaves and stem are covered with hairs are called tricho- phyllous plants.
* Eg: Cucubits (Melothria andMukia)
In stem:
* Stems are mostly hard and woody. They may be aerial or underground.
* The stems and leaves are covered with wax coating or covered with dense hairs.
* In some xerophytes all the internodes in the stem are modified into a fleshy leaf structure called phylloclades (Opuntia)
* In some of the others single or occasionally two internodes modified into fleshy green structure called cladode (Asparagus)
* In some the petiole is modified into a fleshy leaf like structure called phyllode (Acacia melanoxylon)
a) A succulent xerophyte: Phylloclade – opuntia
b) Non succulent: Perennial – Capparis
c) Cladode of Asparagus
d) Phyllode – Acacia
aquatic and terrestrial modes of life. They grow in shallow water.
Examples: Ranunculus, Typha and Sagittaria.

Anatomical adaptations:
* Cuticle is either completely absent or if present it is thin and poorly developed
* Single layer of epidermis is present
* Cortex is well developed with aerenchyma
* Vascular tissues are poorly developed. In emergent forms vascular elements are well developed.
* Mechanical tissues are generally absent except in some emergent forms. Pith cells are sclerenchymatous.
Physiological adaptations of hydrophytes:
* Hydrophytes have the ability to withstand anaerobic conditions.
* They possess special aerating organs.

Epiphytes:
Epiphytes are plants which grow perched on other plants (Supporting plants). They use the supporting plants only as shelter and not for water or food supply.
Orchids, Lianas, Hanging Mosses and Money plant.
Morphological adaptations:
* Root system is extensively developed. These roots may be of two types. They are Clinging roots and Aerial roots.
* Clinging roots fix the epiphytes firmly on the surface of the supporting objects.
* Aerial roots are green coloured roots which may hang downwardly and absorb moisture from the atmosphere with the help of a spongy tissue called velamen.
* Stem of some epiphytes are succulent and develop pseudo bulb or tuber.
* Generally the leaves are lesser in number and may be fleshy and leathery Myrmecophily is a common occurrence in the epiphytic vegetation to prevent the predators.

Anatomical adaptations:
* Multilayered epidermis is present. Inner to the velamen tissue, the peculiar exodermis layer is present.
* Presence of thick cuticle and sunken stomata greatly reduces transpiration.
* Succulent epiphytes contain well developed parenchymatous cells to store water.
Physiological adaptations:
Special absorption processes of water by velamen tissue.

Anatomical adaptations:
* Epidermal cells of stem is heavy cutinized, almost squarish and are filled with oil and tannins.
* Star’ shaped sclereids and ‘H’ shaped heavy thickened spicules that provide mechanical strength to cortex are present in the stem.
* The leaves may be dorsiventral or isobilateral with salt secreting glands. Physiological adaptations:
* High osmotic pressure exists in some plants
* Seeds germinate in the fruits of mother plant itself (Vivipary).

Dispersal of seeds and fruits by water usually occurs in those plants which grow in or near water bodies. Adaptation of hy drochory are
* Obconical receptacle with prominent air spaces. Example: Neliimbo.
* Presence of fibrous mesocarp and light pericarp. Example: Coconut.
* Seeds are light, small, provided with aril which encloses air. Example: Nymphaea.
* The fruit may be inflated. Examples:
Heritiera littoralis.
* Seeds by themselves would not float may be carried by water current.
Example: Coconut.

The individual seeds or the whole fruit may be modified to help for the dispersal by wind. Wind dispersal of fruits and seeds is quite common in tall trees.
* Minute seeds: Seeds are minute, very small, light and with inflated covering. Example: Orchids.
Wings: Seeds or whole fruits are flattened to form a wing. Examples: Maple, Gyrocarpus, Dipterocarpus and Terminalia
* Feathery Appendages: Seeds or fruits may have feathery appendages which greatly increase their buoyancy to disperse to high altitudes. Examples: Vernonia and Asclepias.
* Censor mechanisms: The fruits of many plants open in such a way that the seeds can escape only when the fruit is violently shaken by a strong wind. Examples: Aristolochia and Poppy.

* Some fruits burst suddenly with a force enabling to throw seeds to a little distance away from the plant. Autochory shows the following adaptations.
* Mere touch of some plants causes the ripened
fruit to explode suddenly and seeds are thrown out with great force. Example: Impatiens (Balsam), Hura.
* Some fruits when they come in contact with water particularly after a shower of rain, burst suddenly with a noise and scatter the seeds. Examples: Ruellia and Crossandra.
* Certain long pods explode with a loud noise like cracker, scattering the seeds in all directions. Example: Bauhinia vahlii (Camel’s foot climber)
* As the fruit matures, tissues around seeds are converted into a mucilaginous fluid, due to which a high turgor pressure develops inside the fruit which leads to the dispersal of seeds.
* Example: Ecballium elaterium (Squirting cucumber) Gyrocarpus and Dipterocarpus.

• Air in motion is called wind. It is also vitral ecological factor.
• The atmospheric air contains a number of gases, particles and other constituents.
• The composition of gases in atmosphere is as follows
• Nitrogen – 78%, Oxygen – 21%., Carbon-di¬oxide – 0.03%., Argon and other gases – 0.93%.
• The other components of wind are water vapour, gaseous pollutants, dust, smoke particles, microorganisms pollen grains, spores etc.
• Anemometer is the instrument used to measure the speed of wind.