Biological Cylcle

8/8/2019 Biological Cylcle

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Biological cycles ranging from minutes to years occur

throughout the animal kingdom. Cycles involve hibernation,

mating behavior, body temperature and many other physiological

processes.

Rhythms or cycles that show cyclic changes on a daily (oreven a few hours) basis are known as circadian rhythms. Many

hormones, such as ACTH-cortisol, TSH, and GH show circadian

rhythms.

The menstrual cycle is controlled by a number of hormones

secreted in a cyclical fashion. Thyroid secretion is usually higher in

winter than in summer. Childbirth is hormonally controlled, and is

highest between 2 and 7 AM.

Internal cycles of hormone production are controlled by the

hypothalamus, specifically the suprachiasmic nucleus (SCN).

According to one model, the SCN is signaled by messages from the

light-detecting retina of the eyes.The SCN signals the pineal gland

in the brain to signal the hypothalamus, etc.


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Carbon Cycle

The carbon cyclei the bi eochemical cycle by

which carbon i exchanged among the biosphere, pedosphere,geosphere, hydrosphere, and atmosphere of the Earth. It is one of

the most important cycles ofthe earth and allows for carbon to be

recycled and reused throughout the biosphere and all of its

organisms

The carbon cycle was initially discovered by Joseph

Priestley and Antoine Lavoisier, and popularized byHumphry

Davy. It is now usually thought of as five major reservoirs of

carbon interconnected by pathways of exchange. These reservoirs

are:


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The atmosphere The terrestrial biosphere, which is usually defined to include

fresh water systems and non-living organic material, such as

soil carbon.

The oceans, including dissolved inorganic carbon and livingand non-living marine biota,

The sediments including fossil fuels. The Earth's interior, carbon from the Earth's mantle and crust

is released to the atmosphere and hydrosphere by volcanoes

and geothermal systems.

The annual movements of carbon, the carbon exchanges

between reservoirs, occur because of various chemical, physical,

geological, and biological processes. The ocean contains the largest

active pool of carbon near the surface of the Earth, but the deep

ocean part of this pool does not rapidly exchange with the

atmosphere in the absence of an external influence, such as a black

smoker or an uncontrolled deep-water oil well leak.

The gl l udget is the balance of the exchanges

(incomes and losses) of carbon between the carbon reservoirs or

between one specific loop (e.g., atmosphere biosphere) of the

carbon cycle. An examination of the carbon budget of a pool or

reservoir can provide information about whether the pool or

reservoir is functioning as a source or sink for carbon dioxide.


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In the atmosphere

Carbon exists in the Earth's atmosphere primarily as the gas carbon

dioxide (CO . Although itis a small percentage ofthe atmosphere

(approximately 0.04% on a molar basis), it plays a vital role in

supporting life. Other gases containing carbon in the atmosphere

are methane and chlorofluorocarbons (the latter is entirely

anthropogenic). Trees convert carbon dioxide into carbohydrates

during photosynthesis, releasing oxygen in the process. This

process is most prolific in relatively new forests where tree growth

is still rapid. The effect is strongest in deciduous forests during

spring leafing out. This is visible as an annual signalin the Keeling

curve of measured CO concentration. Northern hemisphere spring

predominates, as there is far more land in temperate latitudes inthat hemisphere than in the southern.


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Forests store 86% of the planet's above-ground carbon and73% of the planet's soil carbon.

At the surface of the oceans towards the poles, seawater becomes cooler and more carbonic acid is formed as C 2

becomes more soluble. This is coupled to the ocean's

thermohaline circulation which transports dense surface water

into the ocean's interior (see the entry on the solubility

pump).

In upper ocean areas of high biological productivity,organisms convert reduced carbon to tissues, or carbonates to

hard body parts such as shells and tests. These are,

respectively, oxidi ed (soft-tissue pump) and redissolved

(carbonate pump) at lower average levels of the ocean than

those at which they formed, resulting in a downward flow of

carbon (see entry on the biological pump).

The weathering of silicate rock (see Carbonate-SilicateCycle). Carbonic acid reacts with weathered rock to produce

bicarbonate ions. The bicarbonate ions produced are carried

to the ocean, where they are used to make marine carbonates.

Unlike dissolved C 2 in equilibrium or tissues which decay,

weathering does not move the carbon into a reservoir from

which it can readily return to the atmosphere.

In 1958, atmospheric carbon dioxide at Mauna Loa was about320 parts per million (ppm), and in 2010 it is about 385ppm.

Future C 2 emission can be calculated by the kaya identity


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Carbon is released into the atmosphere in several ways:

Through the respiration performed by plants and animals.This is an exothermic reaction and it involves the breaking

down of glucose (or other organic molecules) into carbon

dioxide and water.

Through the decay of animal and plant matter. Fungi andbacteria break down the carbon compounds in dead animals

and plants and convert the carbon to carbon dioxide if oxygen

is present, ormethane if not.

Through combustion of organic material which oxidi es thecarbon it contains, producing carbon dioxide (and other

things, like water vapor). Burning fossil fuels such as coal,

petroleum products, and natural gas releases carbon that has

been stored in the geosphere for millions of years. Burning

agrofuels also releases carbon dioxide which has been stored

for only a few years or less.

Production of cement. Carbon dioxide is released whenlimestone (calcium carbonate) is heated to produce lime

(calcium oxide), a component of cement.

At the surface of the oceans where the water becomeswarmer, dissolved carbon dioxide is released back into the

atmosphere.


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Volcanic eruptions and metamorphism release gases into theatmosphere. Volcanic gases are primarily water vapor, carbon

dioxide and sulfur dioxide. The carbon dioxide released is

roughly equal to the amount removed by silicate weathering

[citation needed]; so the two processes, which are the

chemical reverse of each other, sum to roughly zero, and do

not affect the level of atmospheric carbon dioxide on time

scales ofless than about 100,000 years.

In the ocean

The oceans contain around 36,000 gigatonnes of carbon, mostly in

the form of bicarbonate ion (over 90%, with most ofthe remainder

being carbonate). Extreme storms such as hurricanes and typhoons

bury a lot of carbon, because they wash away so much sediment.

Forinstance, a team reported in the July 2008 issue ofthe journal

Geology that a single typhoon in Taiwan buries as much carbon in


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the oceanin the form of sedimentas all the other rains in that

country all year long combined. Inorganic carbon, that is carbon

compounds with no carbon-carbon or carbon-hydrogen bonds, is

important in its reactions within water. This carbon exchange

becomes important in controlling pH in the ocean and can also vary

as a source or sink for carbon. Carbon is readily exchanged

between the atmosphere and ocean. In regions of oceanic

upwelling, carbon is released to the atmosphere. Conversely,

regions of downwelling transfer carbon (C 2) from the atmosphere

to the ocean. When C 2 enters the ocean, it participates in a series

of reactions which are locally in equilibrium:

Solution:

C 2(atmospheric) C 2(dissolved)

Conversion to carbonic acid:

C 2(dissolved) + H2 H2C 3

First ioni ation:

H2C 3 H+

+ HC 3

(bicarbonate ion)

Second ioni ation:

HC 3 H

++ C 3

(carbonate ion)

This set of reactions, each of which has its own equilibrium

coefficient, determines the form that inorganic carbon takes in the

oceans. The coefficients, which have been determined empirically

for ocean water, are themselves functions of temperature, pressure,


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and the presence of other ions (especially borate). In the ocean the

equilibria strongly favor bicarbonate. Since this ion is three steps

removed from atmospheric C 2, the level of inorganic carbon

storage in the ocean does not have a proportion of unity to the

atmospheric partial pressure of C 2. The factor for the ocean is

about ten: that is, for a 10% increase in atmospheric C 2, oceanic

storage (in equilibrium) increases by about 1%, with the exact

factor dependent on local conditions. This buffer factor is often

called the "Revelle Factor", after Roger Revelle.

In the oceans, dissolved carbonate can combine with

dissolved calcium to precipitate solid calcium carbonate, CaC 3,

mostly as the shells of microscopic organisms. When these

organisms die, their shells sink and accumulate on the ocean floor.

ver time these carbonate sediments form limestone which is the

largest reservoir of carbon in the carbon cycle. The dissolved

calcium in the oceans comes from the chemical weathering of

calcium-silicate rocks, during which carbonic and other acids in

groundwater react with calcium-bearing minerals liberating

calcium ions to solution and leaving behind a residue of newly

formed aluminium-rich clay minerals and insoluble minerals such

as quart .


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A life cycle is a period involving all different generations of a

species succeeding each other through means of reproduction,

whether through asexual reproduction or sexual reproduction (a

period from one generation of organisms to the same identical). For

example, a complex life cycle of Fasciola hepatica includes three

different multicellular generations: 1) "adult" hermaphroditic;

2) sporocyst; 3)redia.

In regard to changes of ploidy, there are 3 types of cycles:

Haplontic life cycle Diplontic life cycle Diplobiontic life cycle

These three types of cycles feature alternating haploid and all

germinates To return to a haploid stage, meiosis must occur

(see Cell division). The cycles differ in the product of meiosis, and

whether mitosis (growth) occurs. Zygotic and gametic meioses

have one mitotic stage and form: during the n phase in ygotic

meiosis and during the 2n phase in gametic meiosis. Therefore,

ygotic and gametic meiosis are collectively

term hapl i tic (single mitosis per phase). Sporic meiosis, on

the other hand, has two mitosis events (dipl i tic): one in each

phase.


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Hapl tic life cycle

A zygotic meiosis is a meiosis of a ygote immediately after

karyogamy, which is the fusion of two cell nuclei. This way, the

organism ends its diploid phase and produces several haploid cells.

These cells divide mitotically to form either larger, multicellular

individuals, or more haploid cells. Two opposite types of gametes

(e.g., male and female) from these individuals or cells fuse to become a ygote.

In the whole cycle, ygotes are the only diploid cell; mitosis occurs

only in the haploid phase.

The individuals or cells as a result of mitosis are haplonts, hence

this life cycle is also called haplontic life cycle. Haplonts are:

Most fungi Some green algae Many proto oa


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Diplontic life cycle

In gametic meiosis, instead of immediately

dividing meiotically to produce haploid cells, the ygotedivides mitotically to produce a multicellular diploid individual or

a group of more unicellular diploid cells. Cells from the diploid

individuals then undergo meiosis to produce haploid cells

or gametes. Haploid cells may divide to form more haploid cells, as

in many yeasts, but the haploid phase is not the predominant life

cycle phase. In most diplonts, mitosis occurs only in the diploid

phase, i.e. gametes usually form quickly and fuse to produce

diploid ygotes.

In the whole cycle, gametes are usually the only haploid cells,

and mitosis usually occurs only in the diploid phase. The diploid

multicellular individual is a diplont, hence a gametic meiosis is

also called a diplontic life cycle. Diplonts are:

Animals Some brown algae Some fungi, e.g. brewer's yeast


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Haplodiplontic life cycle

In sporic meiosis (also commonly known as intermediary

meiosis), the ygote divides mitotically to produce a multicellular

diploid "sporophyte". The sporophyte creates spores via meiosis

which also then divide mitotically producing haploid individuals

called "gametophytes". Gametophytes now produce gametes via

mitosis. In many plants the gametophyte is not only small-si ed but

also short-lived.

In the whole cycle, gametes are usually the only haploid cells,

and mitosis usually occurs only in the diploid phase.

Haplodiplonts are:

Most plants Some fungi


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Water cycle

The water cycle, also known as the hydrologic cycle or H2

cycle, describes the continuous movement of water on, above and

below the surface of the Earth. Water can change states

among liquid, vapour, and ice at various places in the water cycle.Although the balance of water on Earth remains fairly constant

over time, individual water molecules can come and go.


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Description

The sun, which drives the water cycle, heats water in oceans

and seas. Water evaporates as water vapor into the air. Ice and

snow can sublimate directly into water vapor. Evapotranspiration is

water transpired from plants and evaporated from the soil. Rising

air currents take the vapor up into the atmosphere where cooler

temperatures cause it to condense into clouds. Air currents move

water vapor around the globe, cloud particles collide, grow, and

fall out of the sky as precipitation. Some precipitation falls as snow

or hail, and can accumulate as ice caps and glaciers, which can

store fro en water for thousands of years. Snowpack can thaw and

melt, and the melted water flows over land as snowmelt. Most

water falls back into the oceans or onto land as rain, where the

water flows over the ground as surface runoff. A portion of runoff

enters rivers in valleys in the landscape, with stream flow moving

water towards the oceans. Runoff and groundwater are stored as

freshwater in lakes. Not all runoff flows into rivers, much of it

soaks into the ground as infiltration. Some water infiltrates deep

into the ground and replenishes aquifers, which store freshwater for

long periods of time. Some infiltration stays close to the land

surface and can seep back into surface-water bodies (and the

ocean) as groundwater discharge. Some groundwater finds

openings in the land surface and comes out as freshwater springs.

ver time, the water returns to the ocean, where our water cycle

started.

Biological Cylcle

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