Plant responses

• What are abiotic conditions?

  Componenets of an ecosystem that are non-living. Eg, Light intensity, water and oxygen availability.
• What are biotic conditions?

  Componenets of an ecosystem that are living. Eg, competition and diseases.
• What are key limitations of plant?

  -They are rooted so are not mobile

  They do not have a rapidly responding nervous system

  -Plant resonses are slower than animal responses.
• How does a plant repsond to high temperature? (Layers)

  Leaves deposit thicker layers of wax. This will reduce the rate of transpiration (evapouration of H2O) from upper surface of the leaf.
• How does a plant respond to very windy conditins? (Stems)

  More heavily lignified vascular tissue= stems less likely to snap in wind.
• How do plants respond to low water availability? (Stomata)


  They close their stomata to reudce rate of transpiration (loss of H2O) by abscisic acid.
• List 4 chemicals a plant can secrete (PAT):

  Phermones, Alkaloids and Tannins
• What are phermones?

  Chemicals released by one plant and detected by nearby plants of the same species.

  This can act as an alert for nearby plants to produce more chemicals which are harmful to insects.
• What are alkaloids?


  Derived from amino acids

  Found in growing tips, flowers and periphal cell layers of stems and roots

  They make the shoots and flowers taste bitter to deter animals from grazing
• What are tannins?


  Toxic to microorganisms and herbivores- taste bitter

  Found in upper epidermis

  In roots- they prevent infiltration by pathogenic microorganisms.
• What is thigmonasty and its effects?


  -A non-directional response to tough

  -Mimosa pudica quickly folds its leaves inwards if touched

  -To scare off herbivores due to the sudden movement; knock off small insects and the appearance of smaller leaves may appear less appetising to herbivores.
• EXTRA:: _________produce antifreeze proteins at _____ temperatures. The proteins bind to ____ ________ and ______ the temperature that water ____ at, stopping more ice crystals from growing.

  Carrots produce antifreeze proteins at low temperatures. The proteins bind to ice crystals and lower the temperature that water freezez at, stopping more ice crystals from growing.
• Tropisms:


  Directional growth response to enviroemntal stimuli such as light and gravity.
• Nastic Response

  Non-directional response to external stimuli. Eg, thigmonasty
• Complete the following phrases: Plants respond to stimuli ____ ____ ____. Positive tropism is growth ____ the stimulus. A negative tropisism is ____ from the stimulus.

  Regulating their growth

  Towards

  Away
• What is phototropism and what grows positively and negatively?

  The growth of a plant in response to light

  Shoots are positvely phototropic and grows towards the light for photosynthesis and the roots are negatively phototropic and grow away from light.
• What is geotropism and what grows positively and negatively?

  The growth of a plant in response to gravity.

  Shoots are negatively geotropic and grow gravity and roots are positively geotropic and grow downwards for support, mineral and water.
• What is chemotropism and what grows positively and negatively?

  Growth response to certain chemicals.

  The roots grow away from harmful acids in the soil- negative chemotropism.

  In a flower the formation of a pollen tube from the stigma to the ovary-positive chemotropism.
• What is positve thigmotropism?


  When stems and leaves such as ivy coil around physical structures is an example of positve thigmotropism.
• Recite Charles Darwin's 3 experiments:

  Look at google docs
• What conclusion did Darwin come to?

  The light stimulus must be detected by shoot tip for a phototropic response.
• Recite Boysen-Jensen's 3 experiments:

  Look at google docs
• What did Boysen-Jensen conclude?

  Auxin passes through the shaded part of the plant causing cell elongation which results in the bending of the plant towards the light. Movement of chemical messengers causes a phototropic response.
• Explain the method used to investigate geotropism:

  1. Get 3 Petri dishes with moist cotton wool. They should all have the same volume of water and amount of cotton wool.

  2. Plant 10 cress seeds in each dish.

  3. Tape a lid onto each dish and wrap each one in foil to prevent light affecting results. 4. Place dishes in a cupboard.

  5. Label one dish 90 degrees and place it uprgiht at 90 degrees. Place another dish at 45 degrees (slope) and make sure it is labelled. Lastly place the third dish flat on a surface (horizontal) and label it 180 degrees.

  6. Leave the seeds for 4 days. Then observe the shoots and root growth. Measure the angle of the root and shoot growth.
• What are the results of the geotropism experiment?

  The angles of growth should be around the same degree the dish what placed at. Should find that whatever angle the dish was placed at, the shoots have all grown away from gravity (negative geotropism) and the roots have grown towards gravity (positive geotropism).
• Why do plants grow more rapidly in the dark than when thney are illuminated?

  When in the dark the plants grow upwards rapidly (gibberellins) to reach the light to be able to photosynthesise.
• What are plant hormones?

  Chemical messengers that corrdinate plant responses to stimuli (tropisms) by influencing cell, division, cell elongation and cell differentitation.
• How are plant hormones transported around the plant?

  Active Transport

  Diffusion or mass flow in the phloem and xylem
• What are the roles of auxin (IAA)? (5)

  -Controls cell elongation

  -Inhibition of side shoots (maintains apical dominance)

  -Inhibits leaf abscission (leaves falling off)

  Low auxin-high abscission

  -High auxin= inhibits root growth

  -Involved in phototropism

  -Stimulates the release of ethene
• What are the roles of gibberellins?

  -Causes stem elongation

  -Involved with seed germination

  -Stimulate the production of enzymes that breakdwon food stores found in seeds

  -Switches on genes that code for amylase and protease digestive enymes required for germination= increasing timing of growth
• What are roles of ethene?

  Causes fruit ripening

  Promotes absicission in decidous trees
• What is the role of abscisic acid (ABA) & WHYY?

  Causes the stomata to close- WHY: Low water availability

  Inhibits seed germnation and growth
• What is apical dominance?


  Suppression of growth of lateral buds caused by hormones produced by the apical bud.
• Explain the experimental evidence for the role of auxin in the control of apical dominance:

  -The auxin production in the apex maintains high levels of abscisic acid= inhibiting the growth of side shoots.

  -When the apex is removed, the auxin levels drop thus causing the abscisic acid levels to drop as a result, therefore allowing the growth of side shoots.

  -The bud growth is promoted by cytokinins, which is concentrated near the auxin reserve in the bud, therefore when the bud is removed, the cytokinins spread out more evenly thus allowing the growth of lateral buds.
• Explain the experiemental evicence that gibberellins control stem elongation and germination:

  Stem elongation: Tall plants have higher gibberellin concentration than dwarf plants.

  Germination: Mutant seeds with non-functional gibberellin gene do not germinate unless gibberellin is applied externally. Inhibitors of gibberellin production prevent germination.
• How is auxin used commercially? (4)

  -To prevent leaf and fruit drop

  -To reat unpollinated flowers to allow seedless fruits to be produced

  -Used as herbicides to kill weeds- promotes shoot gowth so much that the stem cannot support itself so it dies.

  -Put in rooting powder- to encourage the dwonwards root growth of plant cuttings.
• How do the roles of cytokinins relate to its commerical uses?

  Preventing leaf senescence:

  -Prevent decay and yellowing of leaves. Eg, for lettuce after being picked

  Promoting bud and shoot growth:

  -Used in tissue culture to help mass produce plants
• What commerical uses does gibberellin have?

  -Used in fruit production. Eg, elongate stems= more space= more/bigger fruits

  -Used to speed up beer production because they stimulate the production of the enzyme amylase

  -To increase sugar production in sugar canes by causing stem elongation

  -Used to speed up plant breeding because they induce seed formation in young plants
• Commerical uses of ethene:

  -Controls ripening and rotting

  -Speeds up the ripening of fruits

  -Promotes fruit drop from trees

  -Reduces chances of self-pollination in cucumber

  -Can slow doen ripening by inhibiting ethen synthesis to store fruits for longer- lower temp and oxygen levels and increase CO2 levels= increasing shelf-life.