<< Chapter < Page Chapter >> Page >

Control of transpiration

The atmosphere to which the leaf is exposed drives transpiration, but also causes massive water loss from the plant. Up to 90 percent of the water taken up by roots may be lost through transpiration.

Leaves are covered by a waxy cuticle    on the outer surface that prevents the loss of water. Regulation of transpiration, therefore, is achieved primarily through the opening and closing of stomata on the leaf surface. Stomata are surrounded by two specialized cells called guard cells, which open and close in response to environmental cues such as light intensity and quality, leaf water status, and carbon dioxide concentrations. Stomata must open to allow air containing carbon dioxide and oxygen to diffuse into the leaf for photosynthesis and respiration. When stomata are open, however, water vapor is lost to the external environment, increasing the rate of transpiration. Therefore, plants must maintain a balance between efficient photosynthesis and water loss.

Plants have evolved over time to adapt to their local environment and reduce transpiration( [link] ). Desert plant (xerophytes) and plants that grow on other plants (epiphytes) have limited access to water. Such plants usually have a much thicker waxy cuticle than those growing in more moderate, well-watered environments (mesophytes). Aquatic plants (hydrophytes) also have their own set of anatomical and morphological leaf adaptations.

Photo (a) shows a cactus with flat, oval, prickly leaves and a red cylindrical fruit on top; (b) is an orchid with a purple and white flower and glossy leaves; (c) shows a field of plants with long stems, many leaves and a bushy head of small golden flowers; (d) is a water lily in a pond. The water lily has round, flat leaves and a pink and white flower.
Plants are suited to their local environment. (a) Xerophytes, like this prickly pear cactus ( Opuntia sp. ) and (b) epiphytes such as this tropical Aeschynanthus perrottetii have adapted to very limited water resources. The leaves of a prickly pear are modified into spines, which lowers the surface-to-volume ratio and reduces water loss. Photosynthesis takes place in the stem, which also stores water. (b) A. perottetii leaves have a waxy cuticle that prevents water loss. (c) Goldenrod ( Solidago sp. ) is a mesophyte, well suited for moderate environments. (d) Hydrophytes, like this fragrant water lily ( Nymphaea odorata ), are adapted to thrive in aquatic environments. (credit a: modification of work by Jon Sullivan; credit b: modification of work by L. Shyamal/Wikimedia Commons; credit c: modification of work by Huw Williams; credit d: modification of work by Jason Hollinger)

Xerophytes and epiphytes often have a thick covering of trichomes or of stomata that are sunken below the leaf’s surface. Trichomes are specialized hair-like epidermal cells that secrete oils and substances. These adaptations impede air flow across the stomatal pore and reduce transpiration. Multiple epidermal layers are also commonly found in these types of plants.

Transportation of photosynthates in the phloem

Plants need an energy source to grow. In seeds and bulbs, food is stored in polymers (such as starch) that are converted by metabolic processes into sucrose for newly developing plants. Once green shoots and leaves are growing, plants are able to produce their own food by photosynthesizing. The products of photosynthesis are called photosynthates, which are usually in the form of simple sugars such as sucrose.

Questions & Answers

who proposed Cell doctrine
ANJOUS-YINKA Reply
biology introduction
Khab Reply
describe how the gurd cells regulate the movement of gases in and out of a leaf.
Tony
state the main functions of the leaf
kalisto Reply
what is the similarity between meiosis and mitosis
kalisto
Regulation of blood sugar level
Kyara Reply
Describes larmack theory
Mayiik Reply
Mention five modes of nutrition in ecology
Mayiik
Saprophytic
Evans
what is biology
Imisi Reply
Biology is the study of life
Aisha
Yea
Mayiik
Biology is the study of biography
Musoke
what is insulin and where is it found in the body
Cecilia Reply
An illustration of the negative feedback mechanism in homeostasis
Cecilia
How we know
Nhial
That is not the meaning
Mayiik
what are chromosomes
Ibrahim
factor that affect the diffusion of substance
Nwafor Reply
nature of substances size increase in temperature
Quadri
Explain the specialized functions of the organs involved in processing food in the body
Brah Reply
none
Emmanuel
Processing food involves ingestion eating, digestion mechanical and enzymatic breakdown of large molecules, absorption cellular uptake of nutrients, and elimination removal of undigested waste as feces. Many organs work together to digest food and absorb nutrients.
Timileyin
biology is the study of life
Evelyn Reply
introduction of biology
Alison Reply
what is biology
Alison
biology is the scientific study of life
Gloria
Biology is the study of science. living and non living things in our environment. that's biotics and abiotic components of life.
Oluwadare
what are limit factors of photosynthesis
Mpolokeng Reply
what are limit factors of photosynthesis
Friday
Light intensity Carbon dioxide Temperature
Timileyin
what is virus
Chidimmma
virus are said to be microscopic organisms that can't be seen with naked eyes. but With the aid of electron microscope.
Oluwadare
are they unicellular or multicellular
Samkelo
sunlight.. water Carbon dioxide glucose
Oluwadare
what is a cell
Veronica Reply
are building blocks of the body
Mercy
cell is a smalles unit of life
Joeflexy
Cell is the basic ,structural and functional unit of life
ANGELINA
cell is the microscopic unit makes up an organ
Lance
Cell is the basic, structural and functional unit of life.
Esther
A cell is a basic fundamental unit which all organisms obtain
Musoke
A cell is a basic fundamental unit of an organism
Musoke
why do phosphate group attaches to the protein?
Abel Reply
what are enzymes?
Reiah Reply
enzymes are chemical substances that speed up the rate of chemical reactions
Favour
yes it is still available
hashim
This are chemical compound that speed up the digestion of food
Mayiik
these are chemical substances that speed up the rate of reactions and remain the same at the end of the reaction
kalisto

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?

Ask