5.5.1(Plant responses)

Describe what is meant by a trospism

• A tropism is a directional growth in response to a stimulus

Name the 5 types of tropisms:

• Phototropism

• Geotropism

• Hydrotropism

• Chemotropism

• Thigmotropism(touch)

State what chemical is involved in tropisms

• Auxin

• Specifically it is Indoleacetic acid(IAA)

Describe how IAA is moved around the plant in short distances and in long distances

• Short distances: Active transport and diffusion

• Long distances: Via the phloem by mass flow

Name the 2 ways in which plant growth occurs

• Cell division

• Cell elongation

Explain why plants respond to stimulus

• This is to increase their chance of survival by responding to changes in their environment

Describe and explain the 3 chemical defences to deter herbivores

• Alkaloids: Chemicals which are toxic to microorganisms and herbivores

• Tannins: Bitter tasting chemicals which deter herbivores

• Pheromones: Chemicals which are released by one plant which affect the behaviour or physiology of another

Describe and explain how positive phototropism occurs

• In shoots, auxin promotes cell elongation.

• Auxin collects in the shaded side of the tip and causes cell elongation on that side

• This causes the stem to bend and grow towards the sunlight to allow for more photosynthesis

Describe and explain how positive geotropism occurs

• In roots, Auxin inhibits cell elongation

• Auxin collects at the bottom of the roots and inhibits cell elongation on that side

• This causes the stem to bend and grow downwards into the ground which allows it to access more nutrients, water and to also anchor the plant

Describe and explain use of Ethene commercially

• Fruit ripening

• Ethene stimulates enzymes that:

  • Break down cell walls

  • Break down chlorophyll

  • Convert starch into sugars

Describe and explain the uses of auxins commercially

1. Rooting powder

   • Auxins are used as rooting hormones

   • Low levels of IAA makes a cutting grow roots

   • Many cuttings can be taken from one plant, so lots of the same plant can grow quickly and cheaply

2. Selective weed killer

   • High levels IAA stimulates shoot growth and inhibits root growth

   • IAA causes the plant shoots of broad-leaved plants to grow so rapidly that it exhausts the plant and it dies

   • IAA has little effect on narrow leaved plants