Maintaining a Balance
Topic 5: Temperature Regulation in Plants
Biology in Focus, HSC Course
Glenda Childrawi, Margaret Robson and Stephanie Hollis
DOT POINT
 Identify some responses of plants to temperature change
Introduction
Changes in temperature in the natural environment of plants
affect both their functioning and their growth. Maintenance of a
relatively stable internal environment is just as important for
plant metabolism as it is for animals.
solvencyiinews.com
Introduction
Plants respond to changes in light, water availability and
temperature, all of which are linked, since heat is often associated
with light and hot areas are often dry, compromising evaporative
cooling. A plant needs to strike a fine balance between the risks of
excess water loss during cooling versus heat build-up during
water conservation.
helsieshappenings.blogspot.com
High Temperatures
Temperatures above 40C may
cause damage to proteins and
those above 75C to chlorophyll
pigment within the plant. Since
plants cannot move into the
shade the way animals can, plant
responses to excessive
temperatures are mostly
structural and physiological.
news.bbc.co.uk
High Temperatures
Evaporative Cooling
(transpiration):
 Exposure to heat causes the
stomata in plants to open,
leading to a loss of water by
transpiration. The advantage
of this is that it decreases the
internal temperature by
evaporative cooling. The
plants run a risk of
dehydration.
abhyasika.com
High Temperatures
Turgor Response (wilting):
 Some plants respond with changes in turgor pressure, which
allows them to reduce the exposure of their surface area to the
sun. If water is available to the plant, this wilting is temporary,
but if not, permanent wilting is followed by death.
adailyrenaissance.blogspot.com
High Temperatures
Leaf Orientation:
 To overcome the problems of
overheating and excessive
water loss, some plants like
eucalypts, are able to change
the orientation of their leaves
so that they hang vertically
downwards in hot weather.
This reduces the surface area
that is exposed to the sun
during the heat of the midday sun.
mooseyscountrygarden.com
High Temperatures
Leaf Fall:
 Many trees lose their leaves during the cold winter months.
Eucalypts are evergreen trees that drop some of their leaves
during the dry season in hot climates to reduce the surface area
exposed to absorb heat. This also reduces the risk of losing too
much water by transpiration.
flickr.com
High Temperatures
Reseeding and re-sprouting in
response to extreme high
temperatures (fire):
 In Australia one of the
extreme temperature
changes plants have to
respond to is caused by
bushfires. Plants have two
general responses that ensure
their survival after the fire:
Re-sprouting or releasing
seeds.
gondwananet.com
High Temperatures
Re-sprouters such as the bottle
brush, tea trees and eucalypts,
have epicormic buds
underneath the bark that are
protected from damage by fire.
After the extreme temperature
change, they re-sprout. Or they
have lignotubers, which are
underground and sprout new
growth after the fire.
mjmphoto.com.au
High Temperatures
Seeders release seeds into the
environment after the plant is
exposed to extreme heat. Some
plants, for example banksia,
have seed pods that need to be
exposed to fire to release their
seeds. Other plants like
eucalypts release their seeds
from the top canopy in response
to intense heat.
journeyjottings.com
High Temperatures
Thermogenic Plants:
 Some flowers of plants are able to heat up by altering their
metabolic rates when the ambient temperature drops. An
example is the bud of the sacred lotus, which maintains a
steady temperature of 32C.
en.wikipedia.org
Cold Temperatures
Plants also have several responses to cold temperatures.
Organic Anti-freeze:
 The greatest risk of damage to plants is the water between
their cells freezing. Some plants produce organic compounds
that act as anti-freeze. This reduces the temperature at which
the cytoplasm or cell sap in the vacuole freezes. An example is
Antarctic hairgrass.
en.wikipedia.org
Cold Temperatures
Dormancy:
 Deciduous trees lose their
leaves in response to cold
winter temperatures and
undergo a period of dormancy.
This allows them to survive
extremely low temperatures
and also water shortages and
low sunlight. The deciduous
beech, is the only indigenous
Australian deciduous tree found
in Tasmania.
sansscience.wordpress.com
Cold Temperatures
To survive long periods of very
low temperatures, some plants
may produce seeds or spores, or
the plant parts above the
ground may die off, while the
parts beneath the ground
remain dormant, ready to grow
again when the warmer weather
returns. Alpine ash uses seed
dormancy to allow it to
withstand colder temperatures.
flickr.com
Cold Temperatures
Vernalisation:
 Some plants flower in response to low temperatures. For
example, tulip bulbs must be exposed to between 6 weeks and
3 months of intense cold before they will flower. Australian
gardeners often mimic this effect by removing tulip buds from
the ground in winter and storing them in the refrigerator,
before planting them in the spring, to ensure they flower.
srgc.org.uk
Summary
Many responses of plants to temperature change are the result of
temperature and/or light changing the concentration of chemical
growth regulators in plants. Responding to temperature change
and the regulation of internal temperatures is important not only
for the individual plant, but also for the continuation of the
species.
extraordinarylight.blogspot.com
Activity/Homework
-Students are to complete Revision Questions (pg 33 HSC Bio
in Focus Text)
**Use the ALARM scaffold for each question**