Chapter 1 – Environment & Ecology Continued..,
Effect of Abiotic Components on Terrestrial Primary Producers (Plants)
- Extremely high intensity favours root growth than shoot growth which results in increased transpiration, short stem, smaller thicker leaves.
- On the other hand, low intensity of light re- tards growth, flowering and fruiting.
- When the Intensity of light is less than the mini- mum, the plants cease to grow due to the accumulation of CO2 and finally die.
- Of the visible part of the spectrum, only red and blue are effective in photosyn- thesis.
· Plants grown in blue light are small, red light results in elongation of cells (etiolated plants).
- Plants grown in ultraviolet and violet light are dwarf.
- Frost results in freezing the soil moisture.
· The plants are killed due to increased transpi- ration when their roots are unable to supply moisture.
- Water in the intercellular spaces of the plant gets
frozen into ice. This results in increasing con- centration of salts and dehydration of cells.
- Also, frost leads to the formation of canker (var- ious plant diseases with similar symptoms caused by a wide range of fungi, bacteria, and viruses).
- Snow acts as a blanket, prevents a further drop in temperature and protects seedlings from excessive cold and frost.
- Accumulation of snow on tree parts can break the branches or even uproot the tree.
- Snow shortens the period of vegetative growth.
- High-temperature results in the death of plant due to coagulation of protoplasmic proteins (some bacteria can survive high temperatures because of their protoplasmic proteins that don’t coagulate at normally high tempera- tures).
- High temperature disturbs the balance between respiration and photosynthesis.
- It also results in desiccation of plant tissues and depletion of moisture.
- Refers to the progressive dying usually backwards from the tip of any portion of the plant.
- This is one of the adaptive mechanisms to avoid adverse conditions like drought.
- In this mechanism, the root remains alive for years together, but the shoots die.
- E.g. sal, red sanders, silk cotton tree etc.
Primary producers or Autotrophs (self-nourish- ing)
- Primary producers are green plants, certain bac- teria and algae that carry out photosynthesis.
- In the aquatic ecosystem, microscopic algae (plankton) are the primary producers.
Consumers or Heterotrophs or Phagotrophs (other nourishing)
- Consumers are incapable of producing their own food.
- They depend on organic food derived from plants, animals or both.
- Consumers can be divided into two broad groups namely micro and macro consumers.
- Herbivores are primary consumers which feed mainly on plants. E.g. sheep, rabbit, etc.
- Secondary consumers feed on primary con- sumers. E.g. wolves, dogs, snake, etc.
- Carnivores which feed on both primary and sec- ondary consumers are called tertiary consum- ers. E.g. lion (can eat wolves), snakes etc.
- Omnivores are organisms which consume both plants and animals. E.g. man, bear, pig, etc.
Micro consumers or Saprotrophs (decomposers or osmotrophs)
- They are bacteria and fungi which obtain en- ergy and nutrients from dead organic substances (detritus).
- Earthworm and certain soil organisms (such as nematodes, and arthropods) are detritus feed- ers and help in the decomposition of organic matter and are called detrivores.
Ecology – Principles and Or- ganizations
- The term ecology was derived from two Greek words ‘Oikos’ meaning home and ‘logos’ mean- ing study.
- Ecology is the branch of biology concerned with the relations of organisms to one another (en- ergy flow and mineral cycling) and to their phys- ical surroundings (environment).
Levels of Organizations in Ecology
Ecology encompasses the study of individual, organisms, population, community, ecosys- tem, biome and biosphere which form the var- ious levels of ecological organisation
Individual and Species
- Organism is an individual living being that has the ability to act or function independently.
- Species are a group of living organisms consist- ing of similar individuals capable of exchang- ing genes or of interbreeding.
- They are considered as the basic unit of taxon- omy and are denoted by a Latin binomial,
e.g. Homo sapiens.
- Population is a community of interbreeding organisms (same species), occupying a defined area during a specific time.
- Population growth rate can be positive due to birth and/or immigration or negative due to death and/or emigration.
- In the case of large, mobile animals like tigers, leopards, lions, deer etc., the population den- sity may be determined by counting the pug- marks (foot imprints) left by the animals in a defined area.
- Study of pug marks can provide the following information reliably:
- Presence of different species in the area of study.
- Identification of individual animals.
- Population of large cats (tigers, lions etc.).
Sex ratio and age (young or adult) of large cats. (sex of tigers can be determined from pugmarks)
- Communities in most instances are named after the dominant plant form.
- For example, a grassland community is domi- nated by grasses, though it may contain herbs, trees, etc.
- These are large sized and relatively independent.
- They depend only on the sun’s energy from out-
side. E.g. Tropical evergreen forests.
- These are dependent on neighbouring commu- nities and are often called societies.
They are secondary aggregations within a major community. E.g. A mat of lichen on a cow dung pad
An ecosystem is a community of organisms in- teracting with each other and each other and with their environ- ment such that energy is exchanged and system- level processes, such as the cycling of elements, emerge.
- A biome is a large naturally occurring commu- nity of flora and fauna occupying a major habitat. E.g. Rainforest biome or tundra biome.
- Plants and animals in a biome have common
characteristics due to similar climates and can be found over a range of continents.
- Biomes are distinct from habitats because any biome can comprise a variety of habitats.
- The biosphere includes all living organisms on earth, together with the dead organic matter produced by them.
Principles of Ecology
- An adaptation is, “the appearance or behaviour or structure or mode of life of an organism that allows it to survive in a particular environment”.
Adaptation may be:
- Morphological – when trees grew higher, the giraffe’s neck got longer;
- Physiological – in the absence of an external source of water, the kangaroo rat in North Amer- ican deserts is capable of meeting all its water requirements through its internal fat oxidation (in which water is a by-product). It also has the ability to concentrate its urine so that minimal volume of water is used to remove excretory products;
- Behavioural – animals migrating temporarily to a less stressful habitat.
Examples of Adaptation
- Many desert plants have a thick cuticle on their leaf surfaces and have their stomata arranged in deep pits to minimise water loss through transpiration.
- Some desert plants like Opuntia, have no leaves – they are reduced to spines, and the photosynthetic function is taken over by the flat- tened stems (few leaves mean less area is availa- ble for transpiration).
- Mammals from colder climates generally have shorter ears and limbs to minimise heat loss. (This is called Allen’s Rule.) Guess why an elephant has huge ears?
- We need to breathe faster when we are on high mountains. After some days, our body adjusts to the changed conditions on the high mountain.
- Such small changes that take place in the body of a single organism over short periods, to over- come small problems due to changes in the sur- roundings, are called acclimatisation.
- The body compensates low oxygen availability by increasing red blood cell production, de- creasing the binding capacity of haemoglo- bin and by increasing breathing rate.
- A hyperthermophile is an organism that thrives in extremely hot environments — from 60 °C. E.g. Archaebacteria flourish in hot springs and deep- sea hydrothermal vents.
- Desert lizards lack the physiological ability that mammals have. They bask in the sun and absorb heat when their body temperature drops but move into the shade when the ambient temper- ature starts increasing.
- Some species are capable of burrowing into the soil to hide and escape from the above-ground heat.
- Variations are induced by changes in genetic makeup due to addition or deletion of certain genes.
- Mutations, change in climate, geographical barriers etc. induce variations over a period of time.
- The difference in the colour of skin, type of hair; curly or straight, eye colour, blood type among different ethnic groups represents variation within human species.
- Adaptive radiation is a process in which organ- isms diversify from an ancestral species into a multitude of new forms when the environment creates new challenges or opens new environ- mental niches.
- Speciation is the process by which new species are formed, and evolution is the mechanism by which speciation is brought about.
- A species comprises of many populations. Often different populations of a species remain iso- lated due to some geographic barrier such as mountain, ocean, river, etc.
- Geographic isolation leads to speciation (allo- patric speciation or geographic speciation).
- After a long period of time, the sub-populations become very different (genetic drift) and get isolated, reproductively, i.e. they no longer inter- breed.
- Later even when the barrier is removed, the sub- populations are unable to interbreed, and thus subsequently the sub-populations become two different species.
- Mutation (a change in genetic material that re- sults from an error in replication of DNA) causes new genes to arise in a population.
- Further, in a sexually reproducing popula- tion, meiosis and fertilisation produce a new combination of genes every generation, which is termed recombination.
- Thus, members of the same species show ‘varia- tion’ and are not identical.
- Natural Selection is the mechanism proposed by Darwin and Wallace.
- Natural selection is the process by which spe- cies adapt to their environment.
- It is an evolutionary force that selects among variations, i.e. genes that help the organism to better adapt to its environment. Such genes are reproduced more in a population due to nat- ural selection.
- Those offsprings which are suited to their immediate environment have a better chance of sur- viving, reaching reproductive age and passing on the suitable adaptations to their progeny.
- Evolution is the change which gives rise to new species.
- It happens in order to make the organism better suitable to the present environment.
- Evolution involves the processes of natural selec- tion, adaptation, variation etc.
- A valid theory of evolution was propounded by Charles Darwin and Alfred Wallace in 1859.
- This theory has been extended in the light of progress in genetics and is known as Neo-Dar- winism.
- The primary reason behind extinctions is envi- ronmental change or biological competition.
- Extinction occurs when species cannot evolve fast enough to cope with the changing environ- ment.
- At present, the 6th Mass Extinction (Anthropo- genic Extinction – human induced) is in progress.
Q. The term “sixth mass extinction/sixth extinc- tion” is often mentioned in the news in the con- text of the discussion of (2018)
- Widespread monoculture practices in agri- culture and large-scale commercial farming with indiscriminate use of chemicals in many parts of the world that may result in the loss of good native ecosystems.
- Fears of a possible collision of a meteorite with the Earth in the near future in the man- ner it happened 65 million years ago that caused the mass extinction of many species including those of dinosaurs. .
- Large scale cultivation of genetically modi- fied crops in many parts of the world and promoting their cultivation in other parts of the world which may cause the disappear- ance of good native crop plants and the loss of food biodiversity.
- Mankind’s over-exploitation/misuse of natu- ral resources, fragmentation/loss of natural habitats, destruction of ecosystems, pollu- tion and global climate change.
Q. Which of the following are true?
- The presence of specific features or certain habits, which enable a plant or an animal to live in its surroundings, is called evolution.
- The surroundings where an organism lives is called its habitat.
- Small changes that take place in the body of a single organism over short periods, to over- come small problems due to changes in the surroundings, is called acclimatization
- Gradual changes in an organism to survive in an environment is call adaptation
- 2,3 only
- 1,2,4 only
- 1,2,3 only Explanation
- The presence of specific features or certain hab- its, which enable a plant or an animal to live in its surroundings, is called adaptation and not evo- lution. E.g. Hibernation.
- The surroundings where an organism lives is called its habitat. (True)
- Small changes that take place in the body of a single organism over short periods, to overcome small problems due to changes in the surround- ings, is called acclimatization (True). E.g. Sol- diers undergo rigorous acclimatization training before they can serve in harsh climatic regions like Siachen Glacier.
- Gradual changes in an organism to survive in an environment is call evolution and not Adapta- tion. E.g. The evolution of Giraffes neck over a period of time.
Answer: b) 2,3 only
Q. Choose the incorrect pairs
|1. Sloping branches and needle-like leaves||Desert vegetation|
|2. Deep roots||Taiga vegetation|
|3. Waxy stem, thick leaves or no leaves||Tundra vegetation|
|4. Canopy||Tropical vegetation|
- 4 only
- 1,2,3 only
- 2,3 only Explanation:
- Sloping branches (prevent accumulation of snow) and needle-like leaves (reduce transpira- tion) – Taiga vegetation.
- Deep roots – Desert vegetation
- Waxy stem, thick leaves or no leaves – Desert vegetation
- Canopy – the characteristic feature of tropical forests – rainforests, deciduous forests etc.
Answer: c) 1,2,3 only (incorrect pairs)