Weber State University -- Department of Botany |
BOTANY LS1203 - PLANT BIOLOGY
Carnivorous Plants (pdf version is in
soil.pdf)
c. 400 species are known. All angiosperms (250,000 species).
Have leaves modified to trap small animals (insects), digest their
prey (the soft tissues), and absorb small organic molecules.
Active trappers move to catch prey; passive trappers use sticky secretions and pitfalls to catch prey.
Venus flytrap
Active trapper. Insect touches trigger on leaf surface. The underside
of the leaf rapidly enlarges. This causes the leaf to rapidly fold shut
on the insect. Once the insect has been digested, the upper side of the
leaf grows. This opens the leaf again and resets the trap.
Bladderwort
Active trapper. Aquatic. A bladder is under tension. Aquatic critter
(usually insect larva) brushes against trigger at mouth of the bladder.
The bladder opens, a vacuum pulls in the larva, along with a lot of water.
Once the larva is digested, the water is removed from the bladder, and
the trap is reset.
Pitcher plant
Passive trapper. The leave forms a cone. A solution of digestive enzymes
is at the base of the cone. Insects fall into the cone, drown, and are
digested.
Sundew
Passive trapper. Sticky, stalked glands cover the leaves. Insects get
stuck and can't get away. Slowly, the stalks fold over the insects. Eventually,
the entire leaf can curl around the insect. By having the leaf in close
contact with the insect, you have more efficient digestion and uptake of
nutrients.
Butterwort
Passive trapper. Flat sticky glands on leaf surface. Insects get stuck.
Slowly, the leaf will curl around the insect for improved digestion and
nutrient uptake.
The carnivorous plants use a variety of features to attract insects: color, scent, nectar reward. These are the same features found in flowers to attract pollinators.
Glands for secretion and absorption ==> not unique to carnivorous plants.
Leaf modifications: common among plants. Even the parts of flowers (petals, sepals, pistils, stamens) are modified leaves.
Rapid movements. Some plants, like the sensitive plant, have rapid leaf movements that startle insects.
So the plant features found in carnivorous plants aren't unique to them.
However, the carnivorous plants have put the features together in such
a way that they can catch, digest, and absorb prey.
Why? Does this make carnivorous plants heterotrophic? No. They have perfectly good photosynthetic rates. Where do you find carnivorous plants? mineral poor soils. Most plants can't live in these habitats. Carnivorous plants can because they can use insects as source of essential elements.
Review
Be able to distinguish between active traps and passive traps. Be familiar
with examples of each: Venus flytrap, bladderwort, sundew, butterwort,
pitcher plants.
What features of carnivorous plants enable them to lure and capture
prey? Are the individual features unique to the carnivorous plants? What
abilities do the features provide that are the criteria for being carnivorous?
In what sort of habitat do you find carnivorous plants? How does carnivory
enable them to live in this habitat?
Links
http://www.sarracenia.com/faq.html A list of frequently asked questions about carnivorous plants. Under the heading "General Questions," start with the fourth question down: What is a "carnivorous plant?" You can go to the next question and its answer by clicking on a link at the end of each answer. You can stop when you get to the animations. (Want to know more and see lots of pictures? Keep going.)
http://www.ipm.iastate.edu/ipm/hortnews/1998/12-11-1998/carnplants.html A short summary about carnivorous plants.
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Last modified 18 October 02 by Sue Harley (sharley@weber.edu). All rights reserved.
Links checked 9 Jan 03.