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 40C may cause damage to proteins and those above 75C 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 mid- day 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 32C. 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**