Chapter ncert biology

1. 3 MS AND POPULATICDNS
Our líving world is fascinatingly diverse and amazingly
complex. We can try to understand its complexity by
investigating processes at various levels of biological
organisation-macromolecules, cells, tissues, organs,
individual organismns, population, Communities and
ecosystems and biomes. At any level of biological
organisation we can ask two types of questions - for
example, when we hear the bulbul singing early morning
in the garden, we may ask -How does the bird sing?
Or, Why does the bird sing ? The how-type' questions
seek the mechanismbehind the process while the why
type questions seek the significance of the process. For
the firstquestion in our example, the answer might be in
terms of the operation of the voice box andthe vibbrating
bone in the bird, whereas for the second question the
answer maylie in the bird's need to communicate with its
mate during breeding season. When youobserve nature
around you with a scientific frame of mind you will
certainly come up with many interestig questions ofboth
types - Why are night-blooming flowers generally white?
How does the bee know which flower has nectar? Why
does cactus have so many thorns? How does the chick
recognise her own mothef, and so on.

2. Latúudes iu tie oean. l'ou an readily appreciate the siniflauce
tenprlure to ivnu
organisI15 wBheu you realise that it allce
tsihe kinetie
phvstologkalluncions of the organisn. A WOrganisn1s
,can lolerale ad
thrveiHa widerge of(Cnperatures (they arc calledeuvthela) but a
of enAmes d throigh it the basal metabolism. acivity and othet
organts]s re calledStenoterah.The terels DÍ thermal iolerance of
ast LajoritV of heiIe rstictedto anTOW range ofe
iemperatures (suh
ditterent speces
dlerinineto a large extent heir geographical1
distributon,
Caù you thunk of a few
uryhenal and stenothermal
aninnals anc
plants:
increasing average global tempratures (Ciapter 16) If this trend
Inrentyeurs. here has been a growing cOncerI about the gradually
Continues. wOuldyOu expect the distributional range of SOme spdes ta
BI013e
be aflected?
the ile of
organisns. In fact. life on earth originated in water and is
Water: Next to Lemperature. water is the mostimportantfactor influencing
unsustainable without water. Its availability is so limited in deserts that
and
distribution of plantsis also heavily dependent on water.
You might
ony special
adaptations makeit possible to live there. The
producivity
tinkthat organisms livingin oceans,lakes and rivers should not face
any
water-related
problens. but iti
is not true. For aquatic
organismsthe
concenration
(measured as salinity in parts per thousand). is lessthan
quality(chemical
composition. pH) of water becones important. The salt
lagoos. Some organismns are tolerant of a wide range of salinities
5in inland waters, 30-35in thesea and >100 per cent in some
hypersaine
(eurvhaline) but others arc restricted Lo a HarroW range
(stenphaline).
Manv reshwater animals cannot live for long in sea water and vice versa
because of the osmotic problems, they would face.
Light: Sinceplarnts producefoodthrough photosynthesis, a process which
is only possible when sunlight is available as a Source of energy. we can
quicklv understand the importance of light for living organisns,
particularly autotrophs. Manyspecies ofsmall plants(herbs and shrubs!
growing in forests are adapted to photosynthesise optimally under ve
low light conditions because they are constantly overshadowed by ,n
canopied trees. Many plants are also dependenton sunlight to meet their
photoperiodic requiremnentfor flowering. For many animals too, lightis
mportant inthat they use the diurnal and seasonal variations in light
intensity and duration (photoperiod) as cues for timing their foraging
reproductive and migratory activities. The availability oflight on land is
closeiv linked with that of temperature since the sun is the source for
both. But. deep (>500m) in the oceans, the environmernt is perpetualy
dark andits inhabitants are not aware of the existence of a celestial souee
ofeergVcalled Sun. What, then is their source of energy? The spectr
quality olsolar radiatíon isalso important for life. The UV component
the spectrum is harrnful to many organisms while not all the colour
cOmponents ofthe visible spectrum are available for marine plantsIrg

3. tattitlae.e, whnich
POPtJLAiONS
-sliCUlly i
s e a l
:nd DrOperies of oii in clifferent places varV: it is
he weathcring proresN, whether sol is
HEdiMCnta adhow soil development oCCUITed. Various
of thc soil
Criy he percolation nd waler hnolding capacity orUie
haracieristiCs WirpararIetrs Such as pi. mineral
(Opogruphy deteImine Lo a large cxtent the vegetatiön in
tC
quatic vironment,the sedinent-haracteristics often
RespOnses to Abiotic Factors
kd have
such as sgi CONp)sitio), grain siZe and
realised
thhat tlhe abiotic conditions of many habitats may vary
tes ie Iypcol anirnals lhat can be Supported.
of benthic animals that canthrive there.
CDVironCnt
naage with stresstul conditiong But before attenpting
SWerthis
question, we should perhaps ask first wiy a highly variable
tiniC, we noW ask -how do the organisms living in such
s tle
Ourse of millions of years of their existence. many species
ODrent that
permits all biochemical reactions and physiological
ehouldbother organisms after all. One would expect
¬Volved a relativel COnstant internal (within the body)
to
proceed wit1 maxinal
ency
and thus.
enhance the overall
ofthe
speCies. This constanCy, for
oaiple.
could be in terms of optimal
npetature
and OSmotic COncentration of
Quids.
Idealy then, the organism
hild ryto
maintain the COnstancy of its
sternal
environment (a process called
meostasis) despite varying external
sitonnentaI Conditions that tend 10
Let us take an
Aet its hoIeOstasis.
auiogy io clarily this importantConcept.
ppose a personis able to performhis/
Internal
level’
Conformers
Reglators
Partial regulators
External level
Figure 13.3 Diagrammatic Tepresentatic
Organismic reSposc
best whenthe tenperatureis 2PC and
Hshes to maintain it so. even when it is
rThingty hot or freezingly cold outside.
routdbe achieved at home, în the car while travelling, and at workplace
USng anair COnditioner in summner and heater in winter. Then his/
r petÍormanre wold be always mnaximal regardless of the weather
Ough phvsiological, but artilicial means. How do ot her iving
Stns cope with the situatioé Lei us ook at varous possibiiitics
gre 13.3}.
t tn/heT. Ilere the perSon's hoeostasis is accompliShed. not

4. M.HIals
Ionn
Coller
clatesge
to
mininise
heat
lass.
(Ihis1s
Called
uquaic
mminals
IIke
seals hayc o
klayeLuL al
(olyiiiltgT
Skin
that
acts asan
lnsuWator
- and
reduceslogs
me
ofganisns
pOSseS9
Adaptations that re phyait,lr,
quicklyto a
stressful sitution.
Howthenn
( ° e
place
(>3.500n
RohtangPuD9
been
to
ny
high
Mansarovat.fn
Chna
occpredTIbet) you must have
is
called
altitude
sBckriess Its
synptoInsincude natiea.
high
atutudçs, the
body
does not get enoUgh oXygen. But, J
3duyyns
aet
acclimaised and stop
experiencings altttude sicknes,
fow1d yoon
body
solvethis
problenp The body
compensates tow oxVREnaVailabtRty
heart
palpitations.
Thisis
because i the lowasOsppti
pure
of
hemoglobi
and by
increasing breathing rate. Many tribes live in i
high
atrrudeof
Himalayas. Find 6ut if they normnally have a
higher nd
by
increasing
red
blood cell
productlon.
decreasing the
binding affiity
bloodcell
count (or total
hemodobin)than people living in the plains
Ca nnost
animals,the
metabolic reactions and
hence all the
phystologtcal
fiunctions
proceced optimallytn a narrow
ternperature rang
flourish in hot
spríngs and deep sea
hydrothermal vents where
(in
humans. it is
37°C). But there are
microbes
(archaebacteria)that
temperaturesfar
exceed 100°) Howis this possíble?
Manv ishthrivein
Antarctic
waters
where the temperature /s always
belowzero. How dothey
manage to keep their body fluids fromfreezing
A
large variety of
marine
invertebrates and fish live at great depthsin
the ocean wherethe
pressure could be.>100timesthe normal atmospherse
pressurethat we
experience.
How do they live under such cTusting
pressures anddothey have any special enzymes? Organisms livtng in
such
extreme
environments show a fascinating array of biochemicai
adaptations
Some
organismnsshow
behavioural responses to cope with variations
intheir
environment, Desert lizards lack the physiological ability that
mammals haveto deal with the high temperatures of their habitat. but
manage tokeep their body temperature tairly constant by beha
bask in the sun and absorb heat when their bod
They
means,
temperature drops below the comfort zone, but move into shade
the amblent temperature startsincreasing.Some species are capableof
burrowing into the soil to hide and escape from theabove-ground heat
13,2 PapUiATIøNS
13.2. 1Population Attributes
in nature. we rarely find isoBated, single individualsofany specdes: majonty
ofthen Itve ingroups in a well defined geographical area, share or ompe
Jor similar resources, potentially interbreed and thus consturute &