Plant Tropisms: Bio Ten PDF

2.9 Response in plants  At the end of this section, the student will be able to:  recognize that plants are capable of giving response  explain some common responses in plant  tell theBrainstorming importance questions response in plants. 1.W...

2.9 Response in plants  At the end of this section, the student will be able to:  recognize that plants are capable of giving response  explain some common responses in plant  tell theBrainstorming importance questions response in plants. 1.What is tropism? 2.If you have potted plant placed near the window of your room, to which direction does the plant turn its shoot? Why is this so?  2.9.1 Tropism as growth  Tropism: Growthresponse responses to environmental stimuli.  The cause of the response is a unilateral stimulus, which causes unequal production of growth hormone resulting in unequal growth.  This means one side grows more or less than the other side and these results in bending towards or away from the stimulus.  Bending towards the stimulus is called positive response.  A growth responses(bending) away from stimulus is called negative response  Tropism is exhibited by the shoot and root of a plant due to unequal concentration of growth hormone, commonly auxin, resulting in unequal growth.  Cont’d…  Auxin, particularly Indole Acetic Acid (IAA):  is plant growth hormone.  It is produced at the tips of shoot and root.  It is transported to the region of active growth and affects cell elongation, Shoot and roots respond differently to different auxin concentration.  There are five most commonly known plant hormone:  Cytokinin-Promotes cell division.  Gibberellins-Helps in breaking seed dormancy.  Abscisic acid- promotes dormancy in seeds and buds.  Ethylene –Promotes fruit ripening  Auxin(IAA)-Promote cell growth(Apical dominance)  Effects of auxin concentrations on the growth of shoots and roots  This figure shows that auxin concentration that promotes shoot growth( ppm) inhibits root growth.  It also shows that root requires minimum auxin concentration, which is about ppm and such concentration has no effect on the shoot growth.  How shoot and root respond to unilateral light  As a result of unilateral light, auxin move from illuminated side to shaded side of shoot and root.  In shoot higher auxin concentration on the shaded side causes more growth by cell elongation than the illuminated side.  As a result, the shoot bends towards light.  In the mean time, more auxin on the shaded part of the root inhibits cell elongation as compared to Three common and useful types of tropisms  The most commonly known types of tropisms are: i)Phototropism(plants respond to light) ii)Hydrotropism(Plants respond to water) iii)Geotropism(Plants respond to gravity). Thus, we will deal with these three common and useful tropisms.  i)Phototropism  Phototropism is a plant response to light, mainly exhibited by the shoot.  The tips of the plant shoot bend towards the side where there is sunlight.  Thus shoot is positively phototropic.  The earliest experiment on phototropism was conducted by Charles Darwin, “father of evolution. Darwin’s experiment on phototropism  He noticed that if the light is shone on a coleoptile (shoot tip of young seedling) from one side, the shoot bends or curves toward the light (Seedling ‘1’ and partially seedling ‘4’).  When the tip is removed (Seedling ‘2’) or covered Therefore, he conclude that “some influence is with opaque foil (Seedling transmitted from the tip to ‘3’), the shoot could no the more basal regions of the longer bend toward the shoot thereby regulating growth and inducing light. curvature or bending”  ii) Hydrotropism  Hydrotropism is growth response to water stimulus.  Roots search for and grow toward water because it is needed for photosynthesis and to support cell structure (make them turgid and strong).  Thus, Plant roots grow towards water(They are positively hydrotropic.  Hydrotropism exhibited by root is biologically important and vital for the survival of plants.  iii).Geotropism Geotropism:- is the direction growth movement of plant in response to gravity. Root is positively geotropic (grow downward or towards gravity) and Shoot is negatively geotropic (grow upward or against gravity). seedling (young plant) stands erect as the result of a response to gravity, known as geotropism. The root progressively bends downward while the shoot bends upward until root–shoot system  Effect of clinostat on geotropism  The effect of gravity in a horizontally placed seedling can be overcome by a clinostat, which is a rotating instrument.  A seedling fixed horizontally in a rotating clinostat grows straight , because the rotation overcome the effect of gravity(gravity acts equally for all sides).  Summary of tropic response in plants Types of tropism Plant Direction of Advantage parts growth Positive Tips of Growth Allow maximum light phototropism shoot toward light for photosynthesis Negative Tips of Growth away Avoid drying out phototropism root from light Positive Tips of Growth Give chance for hydrotropism root toward water getting water needed for photosynthesis Negative Tips of Growth away Increases chance of hydrotropism shoot from water finding light and upright (standing position) Positive geotropism Tips of Growth Give more chance to root toward get moisture and gravity Negative Tips of Growth away Increases chance of geotropism shoot from gravity finding light and upright (standing  2.10 Medicinal plants  Globally, more than 60 % of the total world population depends on traditional or locally available plant medicines for their health care.  According to WHO, nearly 3.5 billion people in developing countries including Ethiopia believe in the efficiency of plant medicines and widely use them to overcome their health problems.  List of medicinal plants and disease treated N Scientific local name Habi Plant R. of Disease o. name t part administrati treated on used 1 Ruta Teenadem Herb Leaf Oral Leaf Oral Abdominal chalepensis pain 2 Zingiber Jinjibil Herb Rhizome Oral Tonsilitis , officinalis (undergr abdominal ound pain, cough stem) 3 Hagenia heexoo Tree flower Oral Tapeworm abysinica 4 Alium Qullubbii adii Herb bulb Oral Abdominal pain, sativum toothache, tonsillitis, common cold 5 Ocimum Damakesse Leaf Nasal Headache, lamifolium Shru General b body illness ( Mich) 6 Ipomoea Baalbakkoo shrub Protrude Oral Malfunction kituiensis root of penis  Some photographs of MPs Kalanchoe Datura stramonium marmorata(Wiixxuu 15  Some photographs of MPs… Ipomoea kituiensis(baalbakkoo Moringa stenopetala 16