1 / 18

Factors Affecting Plant Growth

Factors Affecting Plant Growth. External Factors - Light. Terrestrial plants use pigments to capture light Chlorophyll Absorbs light in the red and blue areas of the spectrum Carotinoids Absorb in the blue-green spectrum Quantity of light depends on Geographical area

tino
Télécharger la présentation

Factors Affecting Plant Growth

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Factors Affecting Plant Growth

  2. External Factors - Light • Terrestrial plants use pigments to capture light • Chlorophyll • Absorbs light in the red and blue areas of the spectrum • Carotinoids • Absorb in the blue-green spectrum • Quantity of light depends on • Geographical area • Competition from taller plants • Cloud cover, shading, time of day etc...

  3. External Factors – Light cont’d • Photoperiod • The number of daylight hours • Triggers flowering and dormancy in plants • Short-day plants • Flower and reproduce when the photoperiods are shortening ie, late summer • E.g. chrysanthemum • Long-day plants • Flower and reproduce when the photoperiods are lengthening i.e. spring. • E.g. spinach

  4. External Factors - Nutrients • Soil Nutrients • Requirements vary between species • Inorganic nutrients are released by the weathering of rocks or the breakdown of dead organic matter by bacteria and fungi • Absence can cause death or serious weakening

  5. External Factors – Nutrients cont’d • Macronutrients: • 9 nutrients required in relatively large quantities • Carbon, oxygen, hydrogen make up 95% of the dry mass of plants • Other 5%: nitrogen, potassium, phosphorus, calcium, magnesium, sulfur • Micronutrients: • 8 nutrients needed in much smaller amounts • Iron, chlorine, boron, manganese, zinc, copper, molybdenum, and nickel

  6. External Factors- Nitrogen • Most needed macronutrient • Important part of protein, high protein plants need a lot of nitrogen • Dead organic material • Bacteria and fungi breakdown organic nitrogen compounds into a form plants can use – nitrate ions (NO3-)

  7. External Factors- Nitrogen cont`d • Atmosphere – Nitrogen Gas • Nitrogen-fixing bacteria convert nitrogen gas into a usable form • Bacteria live freely in the soil or form a symbiotic relationship with plants • Symbiotic bacteria - Grow within plant root cells and cause bulges called nodules • Occurs most often in legumes (peas, beans, clover, and alfalfa) • Bacteria supply the legumes with nitrates in exchange for carbohydrates from the plants • Most nitrates produced are not used by the plant but are instead added to the soil

  8. Internal Factors - Overview • Growth controlled by • Tropisms • growth responses toward or away from unidirectional stimuli • Due to differential growth; positive response if toward stimulus, negative if away • Allow plants to alter their growth so they can grow into more favorable conditions • Hormones • Internal chemical regulators • 5 main hormones

  9. Tropisms • Phototropism • Plants detect blue-light in special receptors called phototropins

  10. Tropisms cont`d • Gravitropism • Plant will grow so that it stays oriented relative to the source of gravity (the earth). • Dependent on the presence of starch-filled plastids (amyloplasts) in specialized cells. • Starch is heavy, plastids sink to the lower end of the cell, allows plant to identify up and down! • Thigmotropisms • Response to touch • vines

  11. Negative geotropism • Fig 10.20

  12. Hormones- Auxins • Stimulate cell division and elongation in apical buds • Inhibit these same processes in lateral buds • Influence fruit ripening and dropping of fruit • Synthetic Auxin • Can be used as a herbicide • Triggers production of fruit from unpollinated flowers • E.g. tomatoes and cucumbers • Increases root production in cuttings

  13. Hormones - Gibberellins • Promote cell division and elongation in plant stems • Can cause bolting • Sudden growth of stem just before flowering • Raises flower above leafy structures • Synthetic Gibberellins • Cause fruit to enlarge (are often used with grape crops, etc.) • Herbicide

  14. Effects of gibberellins • Fig 10.16

  15. Hormones - Cytokinins • Stimulates cell division • High levels in endosperm and young fruit • Stimulates the growth of lateral buds by blocking apical dominance • Wider not taller! • Synthetic Cytokinins • Used to produce clones in tissue cultures • Can be sprayed on cut flowers to make them last longer

  16. Hormones - Ethylene Gas • Key in fruit development • Causes • Increased rate of ripening • Sweetness of fruit • Sugar content • Colour change • Tissue softener • Can be applied externally to fruit to ripen faster • Also why 1 bad apple spoils the bunch!

  17. Functions of ethylene • Fig 10.18

  18. Hormones - Abscisic Acid • Stress Hormone • Growth regulator, acts as an inhibitor • Slows down and stops growth • Promotes the closure of stomata • Induces seed and bud dormancy • Helps resist water stress

More Related