Carnivorous Plants, Thesis Paper Example
Words: 3838Thesis Paper
Carnivorous plants derive the bulk of their nutrients via small animals and insects which they entrap by various trap mechanisms. Of the nearly four hundred carnivorous plants none of them they eat meat yet animals are often caught in their traps. The best known carnivorous plant is the Venus Flytrap, which captures insects, and consumes them for the vital nitrogen and potassium nutrients they contain or release upon digestion. The leaves on this particular plant are coated with honey and sensitive trigger hairs that unsuspecting visitors touch when they land on them, triggering a snap trap. Carnivorous plants generally grow in nitrogen deficient soils and bogs. According to Charles Darwin, (1:1) carnivorous plants are âthe most wonderful plants in the worldâ. It is believed that carnivorous plants have at least ten separate lineages with about twelve genera in five families, comprising 625 species. There are also another 300 species of plants that exhibit carnivorous-like traits and characteristics. After an introduction of the types of carnivorous plants and their trap mechanisms, his paper will discuss the method that carnivorous plants use to acquire essential nutrients; what they depend on in acquiring nutrition; the various mechanisms deployed by the plants to absorb nutrients; and, the types of environments where carnivorous plants are found. (2:310)
Most plants extract and absorb essential nutrients from the soil through a root system. Carnivorous plants however get their food from capturing, ingesting, and then digesting insects and small animals and fish. They grow mainly in wetlands-swamps, bogs, and savannas where the soil lacks nutrients such as nitrogen. They have evolved finding other methods to feed. Their success at trapping small animals is so great that they survive in the most inhospitable of environments. Most carnivorous plants trap insects and are often called insectivorous. The larger ones are able to trap and digest reptiles, frogs, birds, and small mammals. They can range in size from a few millimeters to several meters in height. They snare prey by trickery, luring them into traps made from leaves of the plant itself. Once the victim has been snared, digestive fluids break the dead insect down into a form that can be absorbed by the plant. (2:310; 302)
The Pitcher Traps catch victims in a container which is shaped like a pitcher or trumpet. The pitcher sits atop the plant sometimes with a hood or lid, usually with a pool of digestive fluid in the base and more often than not using color and nectar as lures. Victims crawl into the opening at the top of the pitcher, slide down the slippery wall on the inside and prevented from leaving by downward pointing hairs. They fall into the pool of liquid, drown, and then the pitcher produces digestive fluid to digest the insect. (3:156)
The sticky traps or adhesive fly traps are very effective at snaring insect victims. The leaves of the sundew plant for example are coated with thin hairs triggered with a drop of mucilage that glistens in the sunlight attracting insects. When the prey touches the nectar it is stuck and the more it struggles the greater amount of fluid that is secreted and that it comes in contact with by disturbing other trigger hairs in its desperate attempts to free itself. (4:16; 220)
Bladderworts live in water and trap insects and invertebrates by sucking them into their tiny underwater bags which are called bladders. The bladder has door at one end with hairs that hang from the mouth of the bladder which is flat when empty. Insects like gnats and water fleas follow the longer guide hairs until contact is made with the trigger hair, snapping the trap door open and sucking the insect in with the rushing water. Enzymes in the bladder break the insect down into nutrients the plant is able to absorb. (4:615)
Hinged traps such as the Venus Flytrap capture prey with a hinged leaf trap not unlike jaws. They snap shut on the victim and the prey is slowly digested over a period of several days. The waterwheel plant is found in parts of Africa, Europe, Asia, and Australia has tiny underwater traps that snap shut in an instant when triggered.
There are five kinds of trapping mechanisms in carnivorous plants: Pitfalls found on pitcher plants where a rolled leaf that contains a pool of enzymes; Flypaper traps as the name suggests uses a sticky mucilage; Snap traps like the Venus Flytrap employ very fast leaf movement to trap prey; Bladder traps suck in their prey by means of a valve system and rushing water; and, Lobster-pots which forces the victim to move towards a plant part that has inward or downward pointing hairs making it impossible to exit.(3:180)
Traps are active or passive. For example, Triphophyllum is a passive flypaper trap which secretes mucilage but its leaves do not snap shut or otherwise move to capture prey. Sundews, on the other hand, are active flypaper traps because their leaves grow quickly and operating as food retainers for digestion purposes.
There are two groups of carnivorous plants, namely those with passive traps and those with active traps. Decomposition is accomplished via digestive enzymes produced by the plant as well as bacteria. Darlingtonia and Sarracenia (sarraceniaceae) and Nepenthes (Nepenthaceae) are examples of pitfall traps that capture prey when it falls into its vase-like leaf. The internal structure contains hairs that point downwards on the slippery walls. This acts to prevent the insectâs escape. The insect eventually drowns in pool of digestive enzymes.
The flypaper trap or adhesive trap of sundews such as Drosera, and butterwort such as Pinguicula are unrelated genera whose leaves are plastered with sticky hairs (Drosera) while the layer of layer of mucilage on the leaves of the Pinguicula entangles and immobilizes its prey.
The evolution of pitfall traps seems to have occurred on four occasions from the sun pitcher Heliamphora, whose rolled leaf edges are sealed together. The plants live in high rainfall areas in South America such as Brazil. One problem they experience is an ability to keep their pitchers from flooding. Nature has graciously provided them with a gap in their leaf margins allowing water to channel out of the pitcher. Heliamphora is a member of the Sarraceniaceae and limited to South America but it has two other genera. (3:50)
Pitcher plants of the genera Sarracenia, Nepenthes, or Darlingtonia, have leaves that attract and then trap unsuspecting insects. The plantâs leaves are shaped like a cup or in other types can be water collecting pitchers. The insect prey falls into the water, drowns, and is then digested by the enzymes that are secreted by the cells in the wall of the plant. These plants have wisps the ends of which can develop into pitchers while serving to capture insects as well. Darlingtonia can be found in California while Sarracenia is commonly found in Florida. (3:170; 50)
Pitcher plants leaves which shaped like a pitcher or trumpet provide an appropriate name for the plant. Several families include pitcher plants, Nepenthaceae, Asclepiadaceae, and Sarraceniaceae to name but three. Pitcher plants tend to live in bogs, swamps, and savannas because of the high acidity in the soil in these areas. The soils found in savannas and bogs are also low in nitrates or phosphates, and as their name imply, are saturated with water. The leaves of the pitcher have glandular striations and which secrete the insect attractant-the nectar-that insects find irresistible culminating in their entering into the plantâs interior. When the prey enters the plant, they drown in a pool of liquid. The drowned insect triggers an enzyme which is secreted within the leaf as part of plants digestion, releasing nitrates and other nutrients which the plant absorbs. (ibid)
A flared leaf that is shaped like a balloon in the genus Sarracenia covers the aperture of the leaf tube and works like a valve to prevent the overflow of the pitcher as well as preventing rain from entering the pitcher and thus protecting the pitcher. The Sarracenia species secretes its enzymes into the fluid pool at the base of the pitcher while Heliamphoraâs digestion is strictly bacterial. Enzymes digest the proteins and nucleic acids in the victim which then releases amino acids and phosphates ions ultimately absorbed by the plant and forming part of its vital and essential nutrients. The chamber is pitted which allows sunlight light to enter the chamber. Insects such as ants have little difficulty to enter through an opening under the balloon. However, once inside, when they try to exit they are foiled in the attempt because of all the false exits created by the pinpoints of light. They soon tire, falling into the tube. The fish tails on the operculum give the plant its name.
Monkey cups of the gens Nepenthes are another group of pitcher plants with about a hundred species of the genus. Most species catch insects. However, the larger ones such N. ragah can absorb small mammals and reptiles. The pitchers are a food source for small insectivores. Typically, there are two thorns on the flap over the entrance to the pitcher on such as is found on N. bicalcarata. These thorns act as repellents to mammals. Western Australiaâs Cephalotus follicularis, is a small pitcher plant whose pitcher rim secretes nectar. The overhang is thorny and prevents insects trapped within the plant from climbing out to escape. There is loose coating of wax that acts like a lining and which is extremely slippery. The insects fall prey to the nectar secretions and the slippery walls prevent their escape. The nectar of Sarracenia flava contains a toxic alkaloid, and adds to the trapâs efficiency. (1:3)
Brocchinia reducta is the last of the carnivorous plants employing a pitfall trap. The leaves are tightly packed together and are waxy. The majority of the bromeliads collect water in an urn at the base of the plant which is shaped by the leaves. Frogs and insects use the urn live in the plant making their homes in the plantâs urn. The urn in Brocchinia has a loose waxy lining with digestive bacteria.
A large family of the bromeliads, Bromeliaceae is found in the tropical and warm temperate climate of the New World. Examples of this family are Tillandsia usneoides, an epiphyte and Ananas comosus, the pineapple. The overlapping leaves on the bases are tightly wrapped and serve as a water storage tank. Puya raimondii which grows to about three or four meters in height and whose flowers can reach a height of nine or ten meters making it the largest of the bromeliads.(2:81)
The bromeliad is a family found mostly in Brazil though they range from Chile in the south to as far north as Virginia in the United States which makes it a New World plant though a single species is found in West Africa. They grow at altitudes ranging from sea level to as much as 14,000 feet, growing in arid deserts and rain forests such as Brazil or in mountainous areas.
Terrestrial or land species grow in the ground like most plants and are found in bright sunny areas on sandy beaches as well as living under the forestâs canopy where they soak up some nutrients from the leaves that fall from the higher branches around them and gather at the base of the plant. Another species, Saxicolous, grows on rocks, their roots penetrating the cracks seeking out moisture and nutrients. Saxicolous is an epiphytic species (plants that grow on top of or are supported by another plant but do not necessarily depend on it for nutrition. Mosses, tropical orchids, and many ferns are epiphytes) that grows on other plants, notably trees and cacti. They are often found attached to telephone lines and poles and are aptly named, âAir Plantsâ because they are able to take nutrition and moisture from the atmosphere. (2:209)
The spiral arrangement of the leaves varies amongst species but it allows the plant to grow with its leaves lined up in a single plane forming a rosette of overlapping leaves that create the reservoir or tank. This urn serves to collect leave litter and hapless insects. The terrestrial bromeliads rely on their root system for nutrients.
The water storing bromeliads are often called Tank bromeliad but do not necessarily rely solely on their roots for nourishment. They are more often found as epiphytes or growing on other plants. The roots harden and attach firmly to its host. Spanish speaking countries refer to them as parasites but in truth they are not since they do not derive any nutritional value or nourishment from their host whose lone function is structural, not nutritional. The small chambers formed by the leaf overlap often house insect waste acting as a fertilizer.
The flowers of some members of the bromeliad family open at night and close during the daylight hours to protect the plant from weevils (beetles with an elongated downward-curving snout rostrum many of which are pests and destroy plants). The bromeliads have tiny scales on their leaves called trichomes. The scales on the desert bromeliads where the air is very hot, act as sun shades to shield the plant from solar radiation. The scales give the plant a bleached or silver look. The scales are smaller on many species that live in humid areas and have a fuzzy feel.
The scape or stalk of the plant emanates from the rosetteâs center and can be flowered and long or it can be short with flowers within the rosette itself. It may have as few as one flower or many with appendages called scape bracts that attract pollinators. Bromeliads flower once after the plant ceases to produce leaves. Once the plant has gone to flower, it will not initiate the leaf making process again. It will however produce pups. The mother plant feeds the pups but once the pups root, they are able to survive on their own. The lifespan of the mother lasts a generation or two before she dies. Pups are produced inside the sheath of the leaf at the base of the plant. However, they can be produced on top of the plant as well making the leafy top of the pineapple a pup which if removed and planted, will grow as a new plant. (2:219)
Bromeliads are happiest in rainforests and as epiphytes they cling and climb on trees and stumps gaining most of their nutrients from the water tank and detritus collected in their leaf well. The tank can store water for long periods allowing bromeliads to withstand droughts.
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Mucilage, a sticky substance having glue like properties, is the basis of the flypaper trap. Mucilage secretion glands are on the leaf which can be plain as found on the butterwort or long like the ones on the sundews. Genus Pinguicula has mucilage secreting glands that are short and a shiny leaf but does not appear to be carnivorous. Still, the leaf is very effective in catching flying insects like gnats. Botanically speaking, the leaf surfaceâs response to invading prey is thigmotropic which implies very rapid growth. The leaf which is often dished beneath the victim forms a digestive pit. Thigmotropism is the response of a plant organ to contact with another solid object. Sweet pea tendrils are illustrative of this phenomenon where they react to the solid object by coiling. (3:94)
Drosera or sundew genus has more than a hundred species of flypapers traps. The ends of the long tentacles have mucilage glands and grow swiftly in response to prey. Tentacles can bend 180 degrees in a minute. The sole continent where sundews are not found is the Antarctic. The greatest diversification in the plants is in Australia, home to the tuberous and pygmy sundews. These species depend on insects for nitrogen and lack reductase which is enzyme that catalyzes the chemical reduction of an organic compound. This is the enzyme nitrate used by most plants to digest nitrates from the soil and turn them into organic compounds. Drosophyllum (Portuguese dewy pine) is different from other sundews because it is a passive plant whose leaves lack rapid movements and growth.
The last flypaper is the Triphyophyllum peltatum, a close relative of Drosophyllum. We usually find this plant as a climbing plant, but in its youth, the plant is carnivorous which could be related to nutrients for flowering.
There are but two snap traps which are active-the Dionaea muscipula or Venus flytrap and the Alsrovana vesiculosa-the famous waterwheel plant. Both are believed to have had a common ancestor at some point in their evolution. The trapping mechanism is commonly referred to as a mouse trap and is very rapid. The aquatic Aldrovanda catches small invertebrates while Dionaea is land based and catches insects, centipedes and spiders.
Aldrovanda plants (Waterwheel) traps and digests water borne insects. The leaves snap shut if small animals contact the trigger hairs on each leaf. It floats below the surface of the water and its leaves are reddish colored. The flowers emerge from the water (either as white or pink) but the fruit capsules are submerged. Aldrovanda employs snap traps on its victims. This same plant group of carnivorous plants is related to cactus and rhubarb and all are part of the plant order Caryophyllales (3:109)
The terminal section of the leaves have two lobes which are hinged. Dionaea has three trigger hairs on each of the lobes but Aldrovanda has many more. The lobes themselves are touch sensitive. Essentially, when the hairs are bent by a visitor, it causes a channel in the cell membrane at the base of the hair to open. The cells immediately begin pumping ions in response to the intrusion which causes either water to flow or induces a very rapid secretion of acid. When the cells change shape, the lobes, which have been under tension, snap shut. This compels them to go from a convex configuration to a concave shape, capturing its prey within a second. With the Venus flytrap, the snap action does not occur should rain or debris contact the triggers because the lobes will not react unless there are two stimuli that occur a half second to thirty seconds apart. This leaf snapping illustrates an undirected movement responding to touch or what is commonly known as thigmonasty. The insectâs struggles stimulate the inner surface of the lobe, causing them to grow towards its captured prey making a hermetic or air tight seal and like a stomach it then digests the victim over a period of about two weeks. (3:111)
These carnivorous plants have underwater leaves and yellow flowers and a small bladder-like trap that captures invertebrates and tiny fish that trigger the trap door. A digestive enzyme is secreted that provides the plant with essential nutrients. Bladderworts are carnivorous and prey on minute insects. The Common Bladderwort (U. vulgaris) has large a bladder allowing it to feed on larger prey such as fleas and mosquito larvae. When prey animals brush the trigger hairs connected to the trapdoor, the victim and the water are sucked in by the bladder in a vacuum filling the bladder and shutting the trap door. The process from start to finish requires 15/1000 of a second to complete. This is a highly specialized plant in that it has no roots. The bladder trap is arguably one of the most sophisticated structures in the plant world and is exclusive to genus Utricularia or bladderwort. The small opening in the bladder is sealed with a hinge door. In the marine species there are two trigger hairs and when touched, they deform the door releasing the vacuum and suck in the prey where it is digested. (4:221: 615)
Lobster-Pot traps are chambers whose entrance is easy but whose exit is obstructed by bristles. This trapping mechanism is found in Genlisea, the so called corkscrew plants. A leaf shaped like a Y permits victims to enter the chamber. Inward pointing hairs facing the prey inhibit or obstruct its exit and force it to move in a specific direction towards the stomach at the lower end of the Y where they are digested.
Genlisea genus comprises twenty-one species of carnivorous plants and is part of the Lentibulariiaceae family. They are found in the African tropics, the coastal island of Madagascar and in Brazil. Its uniqueness is that it specializes in protozoa or single-celled organisms that live on organic compounds of nitrogen and carbon and which are the essential nutrients the plant needs. (1:533)
They have unusual traps which are underground. A pair of thin tubes forms a V with spiral grooves which allow invertebrates that live in the soil to enter the trap. The inward pointing hairs lining the grooves prevent escape and force the victim to move to the tubeâs center and then to the base of the V where it is digested. Its prey gives the plant the nutrients it lacks from the soil.
Fig. 1. Positions of carnivorous plant families in the current overall angiosperm phylogeny (Stevens, 2007; relationships within the Lamiales from MuÂ¨ ller et al., 2006). Families that are exclusively carnivorous are set in bold and highlighted in green; families with only one (Dioncophyllaceae) or two (Bromeliaceae) carnivorous genera are set in italic and highlighted in yellow; and the family (Martyniaceae) with the possibly carnivorous Ibicella lutea v.Eselt. is set in italic and highlighted in blue. Representative traps of each genus are illustrated (drawings by Elizabeth Farnsworth), and the number of species in each genus is given in parentheses. The phylogenetic tree was drawn
using the MrEnt software package (Zuccon and Zuccon, 2006); branch lengths are drawn only to emphasize the location of carnivorous families and otherwise are not meaningful (i.e., do not signify time since divergence or any other metric of relatedness). (1:7)
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