Unit 2 Adaptation to the Environment

By:
Remil Lanto
Rachel Lebanan
Hannah Ruth Caro
Gylza Jordan
Jenny De Pedro
Mary Nelodie Polido
Melmar Allaga
Mayfrel Jito
Rences G. Gardose
Course Facilitator
Unit 2

* One of the most fundamental characteristics of
plants is their ability to photosynthesize.
Photosynthesis, the conversion of light energy to
chemical energy of organic molecules, is the basis
for the life of plants-their growth, reproduction,
and so on- and the ultimate source of energy for
most heterotrophic organisms.

*Photosynthesis can be summarized by the
following equation
*This equation indicates that as light interacts with
chlorophyll, carbon dioxide and water combine to
produce sugar and oxygen.

*Extreme temperatures generally reduce the rate of
photosynthesis by plants. Pleurozium schreberi,
and desert shrub, Altriplex Lentiformis. The moss
and the desert shrub both photosynthesize at a
maximum rate over some narrow range of
temperatures. Both plants photosynthesize at
lower rates at temperatures above and below this
range.

*The results shown in figure 5.11 demonstrate that
moss and the shrub have substantially different
optimal temperatures for photosynthesis. At 15oC,
where the moss photosynthesizes at maximum
rate, the desert shrub photosynthesizes at about
25% of its maximum. At 44o C, where the desert
shrub is photosynthesizing at its maximum rate,
the most probably die.

*These physiological differences clearly reflect
differences in the environments where these
species live and to which there are adapted. While
moss lives in the cool burial forest of Finland, the
study population of the desert shrub, A.
Lentiformis, Lives near thermal, California, in one
of the hottest desert on earth.

*Plant reponses to temperature, as well as those of
animals, can also reflect the short-term
physiological adjustment called acclimation.
Acclimation involves physiological not genetics,
changes in reponse to temperature; Acclimation is
generally reversible with changes in environmental
conditions. Studies of A. Lentiformis by Robert
Pearcy (1997) clearly demonstrate the effect of
acclimation on photosynthesis.

*Pearcy located of population of this desert shrub in
death valley and grew plants for his experiments
from cuttings. By propagating plants from cuttings,
he was able to conduct his experiments on
genetically identical clones. The clones from the
death valley plants were grown under the
temperature regimes: One set in hot condition of
43oC during the day and 30oC at night; the other
set under cool conditions of 23oC during the day
and 18oC at night.

*Pearcy then measured the photosynthetic rates of
two sets of plants. The grown in a cool
environment photosynthesize at a maximum rate
at about 32oC. Those grown in a hot environment
photosynthesized at a maximum rate at 40oC, a
difference in the optimum temperature for
photosynthesis of 8oC. The physiological
adjustments made by A. Lentiformis correspond
these plants do during an annual cycle.

*The plants is ever green and photosynthesizes
throughout the year in the cool of winter and in
the heat of summer the physiological adjustments
suggest that acclimation by A. Lentiformis may
shift its optimal temperature for photosynthesis to
much seasonal changes in environmental
temperature.

*Microbes appear to have adapted to all
temperatures at which there is liquid water, from
the frigid waters around the Antarctica to boiling
hot springs. However, while each of these
environments harbors one or more species of
microbes, no known species thrives in all these
conditions.

All microbes that have been studied, like the
plants and animals discuss in this section, perform
best over fairly narrow range of temperatures.
Let’s look at two microbes that live in
environments at opposite extremes of the aquatic
temperature spectrum.

*Richard Morita (1975) studied the effect of
temperature on population growth among cold-
loving, or Psychrophilic, marine bacteria around
Antarctica. He isolated one of those bacteria,
Vibrio sp., in temperature-gradient incubator for
80 hours. During the experiment, the temperature
gradient within the incubator range from about -
2oC to just over 9oC.

*The result of the experiment show that this
vibrio sp. Grows fastest at about 4oC. At
temperatures above and below this, its
population growth rate decreases. As figure 5.13
shows, Morita recorded some growth in the
Vibrio populations did not grow at temperatures
above 9oC. Morita has recorded population
growth among some cold-loving bacteria at
temperatures as low as -5.5oC.

*Some microbes can live at very high
temperatures microbes have been found living in
all of the hot springs that have studied. Some of
these heat loving, or thermophilic, microbes grow
at temperature above 40oC in variety of
experiments. The most heat loving microbes are
hyperthermophilic, which have temperature
optima above 80oC.

*Some hyperthermophiles grow best at 110oC!
Some of the moss intensive studies of
thermophelic and hyperthermophilic microbes
have been carried out in Yellowstone National
Park by Thomas Brock (1978) and his students
colleagues. One the genera have studied in
Sulfolobus, A member of microbial domain
archaea, which obtains energy by oxidizing
elemental sulfur.

*They studied the microbes from a series of hot
springs in Yellowstone National Park that range in
temperature from 63oC to 92oC. The temperature
optimum for sulfolobus population range 63OC to
80oC and was related to the temperature of the
particular spring from which the microbes came.

*For instance, one stain isolated from a 59oC spring
oxidized sulfur at a maximum rate at 63oC. This
sulfolobus population oxidizes sulfur at a high rate
within a temperature range of about 10oC. Outside
of this temperature range, its rate sulfur oxidation
is much lower.

*We have reviewed how temperature can affect
microbial activity, plant photosynthesis and
animal performance. These example
demonstrate that most organisms perform best
over a fairly narrow range of temperatures.
Considered the effects of temperature on the
performance of all organisms relative to our
discussions of how temperature can vary
greatly over small distances.

Many organisms have evolved ways
to compensate for variations in
environmental temperature by regulating
body temperature. So, how do organisms
respond to the juxtaposition of thermal
heterogeneity in the environment and
their own fairly narrow thermal
requirements? Do they sit passively and
let environmental temperatures affect
them as they will, or do they take a more
active approach? Many organisms have
evolved ways to regulate body
temperature.

Organisms regulate body
temperature by manipulating
heat gain and loss. An equation,
used by K. Schmidt-Nielsen
(1983), can help us understand
the components of heat that may
be manipulated.

* H s = H m ± Hcd ± Hcv ± H r - H e
H s = Total heat stored in an organism
Hm = Gained via metabolism
Hcd = Gained / lost via conduction
Hcv = Gained / lost via convection
H r = Gained / lost via electromagnetic
radiation
H e = Lost via evaporation.
These heat components represent ways
that heat is transferred between an
organism and its environment.

Metabolic Heat (Hm) – is the energy
released within an organism during the
process of cellular respiration.
Conduction – is the transfer of heat
between objects in direct physical contact,
as occurs when you sit on a stone bench
on a cold winter’s day.

Convection – is the process of heat flow
between a solid body and a moving fluid,
such as between you and wind on a cold
day.
Radiation – Heat may also be transferred
through electromagnetic radiation. All
objects above absolute 0, above -273°C,
give off electromagnetic radiation, but
the most obvious source in our
environment is the sun.

Curiously, we are blind to most of this
heat flux, because at sea level over half of the
energy content of sunlight falls outside our
visible range. Much of this radiation that we
cannot see is in the infrared part of the
spectrum. The electromagnetic radiation
emitted by most objects in our environment,
including our own bodies, is also infrared light.
Infrared light is responsible for most of the
warmth you feel when standing in front of a
fire or that you feel radiating from the sunny
side of a building on a winter’s day.

Evaporation – Heat may be lost by an
organism through evaporation. In
general, we need only consider the
heat lost as water evaporates from
the surface of an organism. The
ability of water to absorb a large
amount of heat as it evaporates
makes cooling system based on the
evaporation of water very effective.

* So how can organisms regulate body
temperature? First of all, many
organisms don’t. The body temperature
of these organisms, called
poikilotherms, varies directly with
environmental temperatures. Of the
organism that regulate body
temperature, most use external sources
of energy and a combination of anatomy
and behavior to manipulate Hc, Hr, and
He. Animals that rely mainly on external
sources of energy for regulating body
temperature are called ectotherms.

Organisms that rely heavily on
internally derived metabolic heat energy,
Hm, are called endotherms. Among
endotherms, birds and mammals use
metabolic energy to heat most of their
bodies. Other endothermic animals,
including certain fish and insects, use
metabolic energy to selectively heat
critical organs. Endotherms that use
metabolic energy to maintain a relatively
constant body temperature are called
homeotherms. The only homeothermic
organisms are birds and mammals.

Temperature regulation presents
both plants and ectothermic animals
with a similar problem. Both groups
and organisms rely primarily on
external sources of energy. Despite
the much greater mobility of most
ectothermic animals, the ways in
which plants and ectothermic
animals solve these problems are
similar.

TEMPERATURE REGULATING
BY
ECTOTHERMIC
& ENDOTHERMIC
ANIMALS

Endothermic
Animal
Ectothermic
Animal

Temperature regulation is the most noticeable form
of homeostasis. All enzymes have their happy place, and
in our case, it happens to be a particular reading on the
thermometer. If the body goes outside of the acceptable
range, the cells can't perform their chemical reactions.
Plus, if the cellular go inside our cells freeze, we're
pretty sure that's going to be bad.

Sensors in the blood vessels are constantly sending the
brain updates on internal temperatures. This information gets
sent to a part of the brain called the hypothalamus. The
hypothalamus analyzes the data, ten sends the animal a
message to do something. Shiver, run around, get a fanta or
whatever it takes to cool down or heat up.

Animals can be divided into three
categories, depending on how they regulate
their temperature
1. Homeotherms
Animals who maintain a constant internal body
temperature across wide range of environmental conditions.
2. Poikilotherms
Animals whose temperature changes depending on the
environmental temperature. Fish, amphibians, and reptiles are
poikilotherms, as are most invertebrates. The only mammal
known to be poikilothermic is the naked mole rat. But those
things are just weird.

3. Heterotherms
Animals which usually keep a constant body
temperature, but have specific periods where their
temperature is different, such as during hibernation. We
said most mammals were homeotherms. The ones that
aren't (except for the naked mole rat) are heterotherms.
Ground squirrels and bears are heterotherms, as are some
birds and reptiles.

Animals can also be divided by
another classification system based on
whether their primarily comes from
external source or an internal source.

Animals including birds and mammals. When the
outside temperature is too hot, an endothermic
animal can cool off by sweating, panting,
changing position, or changing location.
Sweating and panting generate heat loss through
evaporating water. Changing position and
location allow the animal to find a cooler
environment in the shade or shelter.

*Endothermic: warm-blooded; describes animals that
maintain a nearly constant internal temperature and do
not change with the temperature of the environment.
*Ectothermic: cold-blooded; describes animals which
have an internal body temperature that changes with
the temperature of the environment.

Endothermic animals must eat much
more often than ectothermic animals since it
takes energy to maintain a constant body
temperature. For example, a lion must eat
its weight in food every seven to ten days.

Animals including fish, amphibians, and reptiles.If
the temperature gets too hot, ectothermic
animals will need to find a cooler temperature or
burrow in the ground to keep cool.

If the environment is cold, ectothermic animals become slow
moving and sluggish. Some animals must bask in the Sun (for
example snakes or lizards) or move to a warmer area (for
example some fish) before they can move about to hunt for
food.

If an animal is cold blooded, they take on
the temperature of their surroundings so they
don't have to use food energy to keep warm. This
means they don't have to eat as often.

Temperature Regulation
by Plants

*
Regulations by plants?
Plant ecologists have typically concentrated their studies in
extreme environments, such as the desert and tundra, where
the challenges of the physical environment are greater and
where ecologists believed they would find the most dramatic
adaptations.

*
The desert environment challenges
plants to avoid overheating; that is,
plants are challenged to reduce their
heat storage, H s. how do desert
plants meet this challenge? They,
like plants from other environments,
use morphology and behaviour to
alter heat exchange with the
environment.

Evaporative cooling of
leaves, which would increase
heat loss, H e, is not a
workable option because desert
plants usually have inadequate
supplies of water. Also, for
most plants, we can ignore Hm.

Most produce only a small
quantity of heat by metabolism.
So, for a plant in a hot desert
environment, our equation for
heat balance reduces to : Hs5,
Hcd6, Hcv6, Hr to avoid heating,
plants in hot desert have three
main options.

Decreasing heating by
conduction, Hcd; increasing
rates of convective cooling,
Hcv; and reducing rates of
radiative heating, Hr. Many
desert plants place their
foliage far enough above the
ground to reduce heat gain by
conduction.

Many desert plants have also
evolved very small leaves and an
open growth form, adaptations
that give high rates of convective
cooling because they increase the
ratio of leaf surface area to
volume and the movement of air
around the plant’s stems and
foliage.

Some desert plants have low
rates of radiative heat gain, Hr,
because they have evolved
reflective surfaces. As we
observed in Chapter 2, many
desert plants cover their leaves
with a dense coating of white
plants hairs.

These hairs reduce Hr gain by
reflecting visible light, which
constitutes nearly half the
energy content of sunlight.

We can see how natural
selection has adapted plants to
different temperature regimes by
comparing species in the genus
Encelia, which are distributed
along a temperature and moisture
gradient from the coastal of
California to Death Valley.

James Ehleringer (1980)
showed that the leaves of the
coastal species, Encelia
Californica, lack hairs entirely and
reflect only about 15% of visible
light.

The desert species, Encelia
farinosa, produces two sets of
leaves, on set in the summer and
another when it’s cooler. The
summer leaves are highly
pubescent (hairy) and reflect more
than 40% of solar radiation while
the cool season leaves are not.

Plants can also modify radiative
heat gain, Hr, by changing the
orientation of leaves and stems. Many
desert plants reduce heating by
orienting their leaves parallel to the
rays of the sun or by folding them at
midday, when sunlight is most intense.

As you would probably predict,
temperature regulation by plants
in cold region, in most cases,
contrasts sharply with
temperature regulation by plants.

However, we can model
temperature regulation by
plants from cold
environments using the same
equation we used for heat
regulation in desert plants:
Hs5, Hcd6, Hcv6, Hr.

Heat gain by radiation (Hr)
Heat loss or gain by convection
(Hcv), Wind Heat gain by
metabolism (Hm), Heat loss or
gain by conduction (Hcd), Heat
loss by evaporation of water (He),
Heat loss by radiation (Hr).

*
The tendency of water to move down
concentration gradients and the
magnitude of those gradients from an
organism to its environment determines
whether an organism tends to lose or
gain water from the environment.

• To understand the water
relation of organism, we first
review the basic physical
behaviour of water in
terrestrial and aquatic
environments.

• We saw that water
availability on land varies
tremendously, from the tropical
rain forest with abundant
moisture throughout the year to
hot deserts with year-round
drought.

• We reviewed the considerable
variation in salinity among aquatic
environments, ranging from the
dilute waters of tropical rivers
draining highly weathered
landscapes to hypersaline lakes.

• The majority of aquatic
environments, including the
oceans, fall somewhere
between these extremes.
Salinity, as we shall see, reflects
the relative “aridity” of aquatic
environments.

• These preliminary descriptions in
chapter 2 and 3 do not include the
situations faced by individual organisms
within their microclimates-microclimates
such as those experienced by a desert
animal that lives at an oasis, where it has
access to abundant moisture, or a rain
forest plant that lives in the forest
canopy, where it is exposed to full tropical
sun and drying winds.

• As with temperature, to
understand the water relation of
n organism we must consider its
microclimate, including the
amount of water in the
environment.

• As we saw as we reviewed the
hydrologic cycle in chapter 3, water
vapour is continuously added to air
as water evaporates from the
surface of the oceans, lakes, and
rivers. On land, evaporation also
accounts for much of the water lost
by organisms

• As the amount of water
vapor in the surrounding air
increases, the water
concentration gradient from
organisms lose water to the
atmosphere decreases.

• This is the season that
evaporative air coolers work poorly
in humid climates, where the water
content of air is high. These
mechanical systems work best in
arid climates, where there is a steep
gradient of water concentration
from the evaporative cooler to the
air. A steep water concentration
gradient is conductive to a high rate
of evaporation.

• We know how temperature
are measured, but how is the
water content of air
measured? The quantity of
water vapor in air can be
expressed in relative terms.

• Since air is rarely completely
saturated with water vapor, we
can use its degree of saturation as
a relative measure of water
content. The most familiar
measure of the water content of
air is relative humidity, defined
as:

Relative humidity= x 100
Water vapor
density______
Saturation water vapor density

• The actual amount of water in
air is measured directly as the mass
of water vapor per unit volume of
air. This quantity, the water vapor
density, is the numerator in the
relative humidity equation and is
given either as milligrams of water
per liter of air (mg H2O/L) or as
grams of water per cubic meter of
air (g H2O/m3).

• The maximum quantity of
water vapour that air at a
particular temperature can
contain is its saturation water
vapour density, the denominator
in the relative humidity equation.
Saturation water vapour density
increases with temperature, as
you can see from the red curve
in figure 6.2.

• One of the most useful ways
of expressing the quantity of
water in air is in terms of the
pressure it exerts. If we express
the water content of air in terms
of pressure, we can use similar
units to consider the water
relations in air, soil, and water.
Using pressure as a common
currency to represent

water relation in very different
environments help us unify our
understanding of this very important
area of ecology. We usually think in
terms of total atmospheric pressure,
the pressure exerted by all the gases in
air, but you can also calculate the
partial pressures due to individual
atmospheric gases such as oxygen,
nitrogen, or water vapor. We call this
last quantity water vapor pressure.

• At sea level, atmospheric
pressure averages approximately
760mm of mercury, the height of a
column of mercury supported by the
combined force (pressure) of all the
gas molecules in the atmosphere.
The international convention for
representing water vapor pressure,
however, is in terms of the pascal
(Pa), where 1 Pa is 1 newton of
force per square meter.

• Using this convention, 760
mm of mercury, or one
atmosphere of pressure, equals
approximately 101,300 Pa,
101.3 kilopascals (kPa), 0r 0.101
megapascals (MPa=106 Pa).

• The pressure exerted by the
water vapor in air that is saturated
with water is called saturation
water vapor pressure. As the
black curve in figure 6.2 shows,
these pressures increases with
temperature and closely parallel
the increase in saturation water
vapor density shown by the red
curve.

• We can also use water vapor
pressure to represent the relative
saturation of air with water. You
calculate this measure, called the
vapor pressure deficit, as the
difference between the actual water
vapor pressure and the saturation
water vapor pressure at a particular
temperature in terrestrial
environments, water flows from
organisms to the atmosphere at a rate
influenced by the vapor pressure deficit
of the air surrounding the organism.

• Figure 6.3 shows the
relative rates of water loss by
an organism exposed to air with
a low versus high vapor
pressure deficit. Again, one of
the most useful features of
water vapor pressure deficit is it
that it is expressed in units of
pressure, generally kilopascals.

• Water moves down concentration gradient
by diffusion. Water is more concentrated in
freshwater environments than in the
oceans.
• Aquatic organisms can be viewed as an
aqueous solution bounded by a selectively
permeable membrane floating in an another
aqueous solution
 Diffusion
 Osmosis
-Special case of diffusion -water
movement across a membrane.

• Salinity: concentration of dissolved salts
-salt water solution contains
relatively less water than fresh water
That means?
Water moves from area of less
dissolved salts to more dissolved salts
Water Concentration in Solutions

• Isosmotic – “balance”
• Hypoosmotic – “Low
Concentration”
• Hyperosmotic – “High
Concentration”

Organisms with
body fluids containing
the same concentration
of water as the external
environment are
isosmotic.
• Isosmotic

Salts Water
Isosmotic
In an isosmotic aquatic organism, internal
concentration of water and salt equal their
concentration in environment.
Salts and water diffuse at appropriately
equal rates into and out an isosmotic
organism.

• Hypoosmotic
Organisms with body
fluids with a higher
concentration of water
(lower solute
concentration) than the
external medium are
hypoosmotic and tend to
lose water to the
environment.

Salts Water
Hypoosmotic
Compared to the environment, a Hypoosmotic aquatic
organism has a higher internal concentration of water
and lower internal concentration of salts.
Marine bony fish are strongly Hypoosmotic,
thus need to drink seawater for salt influx.

Those with body fluids
with a lower concentration of
water (higher solute
concentration) than the
external medium are
hyperosmotic and are
subject to water flooding
inward from the
environment.

Hyperosmotic
Compared to the environment, a hyperosmotic aquatic organism has a
lower internal concentration of water and a higher internal concentration
of salts.
Salts Water
Hyperosmotic organisms that excrete excess
internal water via large amounts of dilute urine.
Replace salts by absorbing sodium and chloride at
base of gill filaments and by ingesting food.

On land, water flows from the organism to the
atmosphere at a rate influenced by the vapor pressure
deficit of the air surrounding the organism. In the aquatic
environment, water may flow either to or from the
organism, depending on the relative concentrations of
water and solutes in body fluids and the surrounding
medium. But here too, water flows down its concentration
gradient.

As shown in the Picture,
water moving from the soil
through a plant and into the
atmosphere flows down a
gradient of water potential.
Water in soils and plants
moves through the small pore
spaces within soils and within
the small water-conducting cells
of plants.
Therefore, water
potential in soils and plants is
determined by the concentration
gradient of water plus other
factors related to the movement
of water through these small
spaces.

Understanding water potential takes
some patience, but that patience will be
paid off by a significant improvement in
understanding the water relations of
terrestrial plants.
We can define water potential as
the capacity of water to do work.
Flowing water has the capacity to do
work such as turning the water wheel of
an old-fashioned water mill or the
turbines of a hydroelectric plant.

The capacity of water to do work
depends upon its free energy content.
Water flows from positions of higher to
lower free energy. Under the influence
of gravity, water flows downhill from a
position of higher free energy, at the top
of the hill, to a position of lower free
energy, at the bottom of the hill.

In the section "Water Movement in
Aquatic Environments,'' we saw that water
flows down its concentration gradient, from
locations of higher water concentration
(hypoosmotic) to locations of lower water
concentration (hyperosmotic). The
measurable "osmotic pressure" generated by
water flowing down these concentration
gradients shows that water flowing in
response to osmotic gradients has the
capacity to do work.

We measure water potential, like vapor
pressure deficit and osmotic pressure, in pascals,
usually megapascals (MPa = Pa x 106). By
convention, water potential is represented by the
symbol ψ and the water potential of pure water is
set at 0. If the water potential of pure water is 0,
then the water potential of a solution, such as
seawater, must be negative (i.e., < 0).

In nature, water
potentials are generally
negative. must be so since all
water in nature, even rainwater,
contains some solute or
occupies spaces where matric
forces are significant. So,
gradients of water potential in
nature are generally from less
negative to more negative water
potential. We can express the
water potential of a solution as:
ψ = ψ solutes
ψ solutes is the reduction in water
potential due to dissolved
substances, which is a negative
number.

Within small spaces, such as the
interior of a plant cell or the pore spaces
within soil, other forces, called matric
forces, are also at work. Matric forces are a
consequence of water's tendency to
adhere to the walls of containers such as
cell walls or the soil particles lining a soil
pore. Matric forces lower water potential.
The water potential for fluids within plant
cells is approximately:
Ψ plant = ψ solutes + ψ matric

In this expression, ψ matric is the reduction
in water potential due to matric forces within
plant cells. At the level of the whole plant,
another force is generated as water evaporates
from the surfaces of leaves into the atmosphere.
Evaporation of water from the surfaces of leaves
generates a negative pressure, or tension, on the
column of water that extends from the leaf
surface through the plant all the way down to its
roots.

So, the water potential of plant fluids is affected by
solutes, matric forces, and the negative pressures exerted by
evaporation. Consequently, we can represent the water
potential of plant fluids as:
Ψ plant = ψ solutes + ψ matric + ψ pressure
ψ pressure is the reduction in water potential due
to negative pressure created by water evaporating from
leaves.

Matric forces vary considerably from one soil to
another, depending primarily upon soil texture and pore size.
Coarser soils, such as sands and loams, with larger pore sizes
exert lower matric forces, while fine clay soils, with smaller
pore sizes, exert higher matric forces. So, while clay soils can
hold a higher quantity of water compared to sandy soils, the
higher matric forces within clay soils bind that water more
tightly. As long as the water potential of plant tissues is less
than the water potential of the soil, ψ plant< ψ soil, water flows
from the soil to the plant.

The higher water potential of soil water
compared to the water potential of roots induces
water to flow from the into plant roots. As water
enters roots from the surrounding soil, it joins a
column of water that extends from the roots
through the water-conducting cells, or xylem, of
the stem to the leaves. Hydrogen bonds between
adjacent water molecules bind the water
molecules in this water column together.

Consequently, as water molecules at
the upper end of this column evaporate
into the air at the surfaces of leaves, they
exert a tension, or negative pressure, on
the entire water column. This negative
pressure further reduces the water
potential of plant fluids and helps power
uptake of water by terrestrial plants.

In picture, water
from the soil, they soon
deplete the water held in
the larger soil pore spaces,
leaving only water held in
he smaller pores. Within
these smaller soil pores
matric forces are greater
than in the larger pores.
Consequently, as
soil dries, soil water
potential becomes more
and more negative and the
remaining water becomes
harder and harder extract.

WATER REGULATION ON LAND
• Water Acquisition by
Animals
• Water Acquisition by
Plants

Terrestrial plants and
animals regulate their
internal water by balancing
water acquisition against
water loss. When organisms
moved into the terrestrial
environment, they faced
the two major challenges:

potentially passive losses of
water to the environment
through evaporation and
reduced access to replacement
water.
Terrestrial organisms
evolved by natural selection
to meet these challenges,

eventually acquired the
capacity to regulate their
internal water content on
land. We can summarize
water regulation by
terrestrial animals as:
Wia= Wd + Wf + Wa – We – Ws

This says simply that the
internal water of an animal
(Wia) results from a balance
between water acquisition and
water loss. The major source of
water are:
Wd = water taken by drinking
Wa = water absorbed in the air

The avenues of water loss
are:
We = water lost by evaporation
WS = water lost by various
secretion and excretions including
urine, mucus, and feces
We can summarize water by
terrestrial plants in a similar way:
Wip = Wr + Wa – Wt - WS

The internal water concentration
of plant (Wip) results from a
balance between gains and losses,
where the major sources of water
for plants are:
Wr = water taken from soil by
roots
Wa = water absorbed from the air

The major ways that plant
lose water are:
Wt = water lost by
transpiration
Ws = water lost with various
secretion and reproductive
structures, including nectar,
fruit and seeds

The figure presents a
generalized picture of the
water relations of terrestrial
organisms. However, organisms
in different environments face
different environmental
challenges to which they have
evolved a wide variety of
responses.

Water Acquisition by Animals
Many small terrestrial animals
can absorb water from the air,
most terrestrial animals, however
satisfy their need for water either
by drinking or by taking in water
with food. In moist climates, there
is generally plenty of water,

and, if water becomes scarce,
the mobility of most animals
allows them to go to sources of
water to drink. In deserts,
animals that need abundant
water must live near oases,
have evolved adaptations for
living in the arid environments.

Some desert animals
acquire water in unusual ways.
Coastal desert such as the
Namib Desert of southwest
Africa receive very little rain
but are bathed in fog. This
aerial moisture is the water
source for some animals in the
Namib.

One of these , a beetle in the
genus Lepidochora of the
family Tenebrionidae, takes an
engineering approach to water
acquisition.
These beetles dig trenches on
the face of the sand dunes to
condense and concentrate fog.

The moisture collected by
these trenches run down to the
lower end, where the beetle
waits for a drink. Another
tenebrionid beetle, Onymacris
unguicularis, collects moisture
by orienting its abdomen
upward (Hamilton and Seely
1976).

Fog condensing on this beetle’s
body flows to its mouth.
Onymacris also taken in water with
its food. Some of this water is
absorbed within the tissue of the
food. The remaining water is
produced when the beetle
metabolizes the carbohydrates,
proteins, and fats contained in its
food.

We can see the
source of this water if
we look at an equation
for oxidation of
glucose:
C6H12O6 + 6 O2  6 CO2 + 6 CO2 + 6
H2O

As you can see, cellular
respiration liberates the
water that combined with
carbon dioxide during the
process of photosynthesis.
The water released during
the cellular respiration is
called metabolic water.

Paul Cooper (1982) estimated
the water budget for free
ranging Onymacris from the
Namib desert near Gobabeb.
He estimated the rate of water
intake by this beetle at 49.9 mg
of water per gram of body
weight per day.

Of this total, 39.8 mg came
from fog, 1.7 mg came from
moisture contained within
food, and 4.8 mg came from
metabolic water. The rate of
water loss by these beetles,
41.3 mg of water per gram per
day, was slightly less than
water intake.

Of this total, 2.3 mg were
lost with feces and urine,
and 39 mg by evaporation.
While onymacris gets most of
its water from fog, other
small desert animals get the
most of their water from
their food.

Kangaroo rats of the genus
Dipodomys in the family
Heteromyidae don’t have to drink
at all and can survive entirely on
metabolic water. Knut Schmidt-
Nielsen (1964) showed that the
approximately 60 ml of water
gained from 100 g

of barley makes up for the
water a Merriam’s kangaroo
rat, D. merriami, loses in
feces, urine and evaporation
while metabolizing the 100 g
of grains. The 100 g of barley
contains only 6 ml of
absorbed water--

that is, water that can be
driven off by drying. The
remaining 54 ml of water
is released as the animal
metabolizes the
carbohydrates, fats, and
proteins in the grain.

While animals are generally
obtain most of their water by
drinking or with their food, these
option are not available to plants.
Though many plants can absorb
some water from air, most get the
bulk of their water from the soil
through their roots.

Water Acquisition by Plants
The extent of root
development by plants often
reflects differences in water
availability. Studies of root
System in different climates
show that plants in dry climates
grow more roots than do plants
in moist climates.

In dry climates plants roots
tend grow deeper in the soil
and to constitute a greater
proportion of plants biomass.
The taproots of some desert
shrubs can extend 9 or even 30
m down into the soil, giving
them access to deep
groundwater.

Roots may for up to 90% of
total plant biomass in
deserts and semiarid
grasslands. In coniferous
forests, roots constitute only
about 25%of total plant
biomass.

You don’t have compare forests
and deserts, however, to
observe differences in root
development. R. Coupland and
plants growing in the
temperate grassland of western
Canada.

During their study they
carefully excavated the roots of
over 850 individual plants,
digging over 3 m deep to trace
some roots. They found that
microclimate affects root
development in many grassland
species.

For instance, the roots of
fringed sage. Artemesia
frigida, penetrate over 120
cm into the soil on dry sites;
on moist sites, its roots grow
only to a depth of about
60cm.

Deeper roots often help plants
from dry environments extract
water from deep within the soil
profile. This generalization is
supported by studies of
common grasses that grow in
Japan, Digitaria adscendens
and Eleusine indica.

The grasses overlap
broadly in their distribution
in Japan; however, only
Digitaria grows on coastal
sand dunes, which are
among the drought-prone
habitats in Japan.

Y.-M. Park (1990) was
interested in understanding
the mechanism allowing
Digitaria to grow on coastal
dunes where Eleusine could
not. Because of the
potential for drought in
coastal dunes.

Park studied the responses of
the two grasses to water
stress. He grew both species
from seeds collected at the
Botanical Garden at the
University of Tokyo.

Seeds were germinated in
moist sand and seedlings
were later transplanted into
10 cm by 90 cm polyvinyl
chloride(PVC) tubes filled
with sand from coastal dune.

Park planted two
seedlings of Digitaria in each
of 36 tubes and two eleucine
in 36 other tubes. He
watered all 72 tubes with
the nutrient solution every
ten days for 40 days. At the
end of 40 days,

Park divided the 36 tubes of
each species into two groups
of 18. One group each
species was kept well
watered for the next 19
days, while the other group
remained unwatered.

Unwatered Digitaria and
Eleusine responded differently.
The root mass of Digitaria
increased almost sevenfold
over the 19 days of no
watering, while the root mass
of Eleusine increased about
threefold.

In addition, the roots of
Digitaria were still growing
at the end of the
experiment, while those of
Eleusine stopped growing
about 4 days before the end
of the experiment.

Park found out that the
differences in root growth were
greatest in the deepest soil
layers. Below 60 cm in the
growing tubes, the unwatered
group of Eleusine showed
suppressed root growth, while
Digitaria did not.

With its greater mass of
more deeply penetrating
roots, Digitaria maintained
high leaf water potential
throughout the 19 days of no
watering. During the same
period, Eleusine showed a
substancial decline in leaf
water potential.

Park’s results suggested that
Digitaria can be successful in
the drier dune habitat
because it grows longer
roots, which exploit deeper
soil moisture. With these
deeper roots,

Digitaria can keep the
water potential of its
tissues high even in
relatively dry soils., while
Eleusine suffers lowered
water potential. In other
words,

Digitaria maintains higher
leaf water potentials
because its greater root
development maintains a
higher rate of of water
intake– higher Wr.

The examples we’ve just
reviewed concern rooting by
individual plant species either
in the field or under
experimental conditions. An
important question that we
might ask is whether there
have been enough root studies

to make tentative
generalization about the
rooting biology of plants.
Jochen Schenk and Robert
Jackson (2002) conducted an
analysis of 475 root profile (see
fig. 6.11) studies from 209
geographic localities from
around the world.

In over 90% of the 475
root profiles, at least 50%
of roots were in the top
of 0.3 m of the soil and at
least 95% of roots were in
the upper 2 m.

However, there were
pronounced geographic
differences in rooting depth.
Scheck and Jackson found
that rooting depth increases
from 800 to 300 latitude—that
is,

from Acrtic tundra to
Mediterranean woodlands
and shrublands and
desert. However, there
were no trends in rooting
depth in the tropics.

Consistent with our
present discussion,
deeper rooting depths
occur mainly in water-
limited ecosystem.

179
Water
Conservation
by Plants and
Animals

*Water Conservation by Plants
and Animals
*Many terrestrial organisms equipped with waterproof outer
covering.
*Concentrated urine / feces.
*Condensing water vapor in breath.
*Behavioral modifications to avoid stress times.
*Drop leaves in response to drought.
*Thick leaves
*Few stomata
*Periodic dormancy

(a) plants of
the Sonoran Desert devel
op leaves and flower;
(b) during dry periods
they lose their leaves
and blossoms
Changing leaf area:

183
Wilting to reduce water loss rates (data
from Chiariello, Field, and Mooney 1987)

184
Dissimilar Organisms with Similar
Approaches to Desert Life
*Camels
*Can withstand water loss up to 20%.
*Face into sun to reduce exposure.
*Thick hair: Increased body temperature lowers heat
gradient.
*Saguaro Cactus
*Trunk / arms act as water storage organs.
*Dense network of shallow roots.
*Reduces evaporative loss.

(a) saguaro cactus;
and
Two desert
dwellers:
(b) camel

186
Water and Salt Balance
in Aquatic Environments

Two Arthropods with Opposite
Approaches to Desert Life
*Scorpions
*Slow down, conserve, and stay out of sun.
*Long-lived
*Low metabolic rates
*Cicadas (Diceroprocta apache)
*Active on hottest days.
*Perch on branch tips (cooler microclimates).
*Reduce abdomen temp by feeding on xylem fluid of pinyon pine trees.

190
Illustrates how Diceroprocta uses
mesquite trees to get access to deep
soil moisture.

191
Water and Salt Balance in Aquatic
Environments
*Marine Fish and Invertebrates
*Isosmotic organisms do not have to expend
energy overcoming osmotic gradient.
*Sharks, skates, rays - Elevate blood solute
concentrations hyperosmotic to seawater.
*Slowly gain water osmotically.
*Marine bony fish are strongly hypo-osmotic, thus
need to drink seawater for salt influx.

192
Osmoregulation by Marine Organisms

193
Water and Salt Balance in Aquatic
Environments
*Freshwater Fish and Invertebrates
*Hyper-osmotic organisms that
excrete excess internal water via
large amounts of dilute urine.
*Replace salts by absorbing sodium and
chloride at base of gill filaments and by
ingesting food.

194
Osmoregulation by Freshwater Organisms

Unit 2 Adaptation to the Environment

More Related Content

What's hot (20)

Similar to Unit 2 Adaptation to the Environment (20)

Recently uploaded (20)

Unit 2 Adaptation to the Environment