plant hormones + uses of plant hormones

• what is a tropism?

  Plants detect stimuli in their environment and can respond by growth in a particular direction
• what is a positive tropism?


  If a part of a plant grows towards a stimulus
• what is a negative tropism?

  If a part of a plant grows away from the stimulus
• what is phototropism and what are its benefits?

  Growing towards the light, when a stem grows towards a light then the plant can photosynthesise more which means more food is produced for the plant and it can grow faster. this increases the plant's chances of survival
• what is gravitropism and what are its benefits?

  Growing in the same direction as gravity, it is important for roots to grow downwards as growing deeper into soil helps to provide anchorage and normally takes the roots nearer to water
• what is important about gravitropism and phototropism?


  When seeds are scattered they often land the wrong way up, but these responses ensure that the plant grows correctly and keep adult plants growing successfully
• what is auxin?


  A plant hormone that enables a plant to grow towards or away from a stimulus
• where is auxin made and what is its job?


  It is made in cells near the tips of plant shoots or roots, the response to a stimulus occurs due to an uneven distribution of auxin, which in turn causes an unequal growth rate and results in the shoot or the root bending
• what does auxin stimulate and inhibit?

  Stimulates shoot cells to grow more but inhibits the growth of root cells
• how do plants respond to light?

  When light hits one side of the shoot tip, the auxin moves to the other side of the shoot which causes the concentration of auxin to build up in the unlit side. cells then respond by elongating which increases the length of this side of the shoot so the shoot bends towards the light
• what happens when light falls evenly on the shoot?

  The level of auxin is evenly distributed throughout the tip, all the cells in the tip grow at the same rate so the shoot grows straight
• What happens in roots with auxin?

  The shaded side also contains more auxin but these cells elongate less so the root bends away from light
• describe the different effect that auxin has on root and shoot cells?

  shoot cells bend towards light and root cells bend away from light
• where is gravitropism seen?

  In both roots and shoots, the uneven distribution of auxin causes unequal growth resulting in the shoots growing up and roots growing down
• what does a plant use hormones for?

  They are produced by cells in one area of the plant and then transported to a different area to produce a response
• what are the 3 main plant hormones?

  auxins, ethene, gibberellins
• what is the function of auxins?

  Stimulate growth by causing cell elongation and also help to regulate fruit development, without auxins fruits are often too small
• what is the main function of ethene?

  Causes plant fruits to ripen by stimulating the conversion of starch into sugar which is why a ripe fruit tastes sweeter than an unripe one, it is the only plant hormone that exists as a gas.
• what is the main function of gibberellins?

  Promote growth, and particularly stem elongation. they can also end the dormancy period of seeds and buds which leads to shoots and flowers opening
• what are some commercial uses of plant hormones?

  Killing weeds, promoting root growth, delaying ripening, ripening fruit, producing seedless fruits and controlling dormancy
• why are plant hormones used by farmers?

  They are commercially used to speed up or slow down plant growth, which helps to create more plants and enable farmers and growers to make more money
• how are plant hormones used to kill weeds?

  Many weed killers contain auxins, and are selective herbicides. they kill weeds that are broad-leaved plants (dicotyledons) but do not affect narrow-leaved plants (monocotyledons) eg grass. the auxin weedkiller makes the weeds grow too fast and the rapid uncontrolled growth kills the plant.
• how are plant hormones used to promote root growth?

  Rooting powder contains auxin and gardeners (horticulturists) use auxin to produce identical plants or clones from cuttings. they cut off a plant shoot, dip it into rooting powder and plant it. after a few days, roots develop from the cut stem and the new roots anchor into the soil and take up water and minerals.
• how are plant hormones used to delay ripening?

  Auxin is sprayed on fruit trees to delay ripening, this allows a harvest to be collected all at the same time and can prevent fruit from dropping off trees early
• which hormone would you spray onto fruit to prevent it ripening when being transported to shops?

  auxin
• how are plant hormones used to ripen fruit?

  Ethene is sprayed on fruit trees and plants so that their fruits ripen quicker, this allows fruit to be ready earlier in the growing season
• which hormones are used to ripen and which to delay fruit?

  ripen= ethene

  delay= auxin
• how are plant hormones used to produce seedless fruits?

  using auxin, seeds are produced after a plant is pollinated by insects or the wind so if auxins are applied to unpollinated flowers then the plant produces seedless fruit.
• how are plant hormones used to control dormancy?

  Seeds remain dormant until ideal conditions for growth, which normally means they germinate at the end of summer and survive the winter. but commercial growers trigger seeds to germinate in the winter by spraying them with gibberellins or auxins in the greenhouse
• Explain why fruits keep fresh for longer if bananas are stored separately?

  The banana gives off ethene gas which makes other fruit ripen too quickly , so fruits stay fresh stored away from bananas