plant responses to the environment

• what are the types of stimuli that plants respond to?

  Tannins

  Alkaloids

  Pheromones
• Responding to the environment may help plants to survive long enough to reproduce. For example, in higher temperatures, plants may deposit thicker layers of wax on their leaves; in very windy conditions, they may have vascular tissue which is more heavily lignified.
• Tannins are toxic to microorganisms and larger herbivores. In leaves, they are found in the upper epidermis, and make the leaf taste bad. In roots, they prevent infiltration by pathogenic microorganisms.
• Alkaloids are derived from amino acids. In plants, scientists think that alkaloids are feeding deterrents to animals so that the plants taste bitter. They are located in growing tips, flowers, and peripheral cell layers of stems and roots.
• Pheromones are chemicals which are released by one individual and which can affect the behaviour or physiology of another
• what are tropisms?

  Tropisms are directional growth responses of plants
• What are the types of tropsisms?

  Phototropisms

  Geotropisms

  Chemotropism

  Thigmotropisms
• What is a phototropism?

  Shoots grow towards light, they are positively phototrophic, which enables them to photosynthesize.
• what is a geotropism?

  When roots grow towards the pull of gravity. This anchors them in the soil and helps them to take up water, which is needed for support- this keeps cells turgid. there will alsp be minerals such as nitrate in the water which is needed for the synthesis of amino acids.
• what are chemotropisms?

  On a flower, pollen tubes grow down the style, attracted by chemicals towards the ovary where fertilization can take place
• What is a thigmotropism?

  Shoots of climbing plants, like ivy, wind around other plants or solid structures for support.
• if a plant responds towards a stimulus it is a positive tropic response. If a plant responds away from a stimulus, it is a negative tropic response.
• hormones coordinate plant responses to environmental; stimuli. like animal hormones, plant hormones are chemical messengers that can be transported away from the site of manufacture to act in other target tissues and cells. Plant hormones are not produced by glands but by tissues instead.
• when plant hjormones rerach their target cells, they bind to receptors on the plasma membrane. specific hormones have specific shapes which can only bind to specific receptors with complementary shapes on the membranes of particular cells. This specific binding makes sure that the the hormopnes only act upon the correct tissues.
• Plant hormones can influence cell division, cell elongation, or differentiation.
• What are the effects of cytokinins?

  Cell division, shoot growth, delay in leaf senescence.
• What are the effects of abscisic acid on plants?

  Inhibits seed germination and growth, causes stomatal closure when the plant is stressed by low water availability
• what are the effects of auxins?

  promotes cell elongation, inhibits growth of side shoots, inhibits leaf abscission (falling of leaves)
• In plants, what is the effect of ethene?

  Promotes the ripening of fruits