plant diseases and defences

• What are 'aphids'?

  sap-sucking insects.

  
• What do aphids do?

  penetrate into the phloem vessels to feed on the sugar-rich phloem sap. This damages and weakens the plant.
• How can you destroy aphids?

  chemical pesticides

  aphid-eating insects (ladybirds)
• What are nitrate ions needed for?

  Plant growth (protein synthesis)
• What happens if there is a nitrate deficiency in a plant?

  -protein synthesis will be limited

  -stunted growth

  -reduced crop yield (agricultural production)
• What are magnesium ions used for in a plant?

  to make chlorophyll.
• What happens if the level of magnesium ions is low in a plant?

  -not enough chlorophyll made

  -yellow leaves

  -growth slows down due to lack of glucose
• What is chlorosis?


  Yellowing of plant leaves due to a lack of chlorophyll.
• What are the symptoms of plant diseases?

  Wilting, yellowing, spots, stunted growth.
• What physical barriers are there in plants?

  cellulose cell wall = strengthens plant cells & help resist invasion

  tough waxy cuticles

  bark on tree = layer of dead cells

  leaf fall
• What chemical barriers are there in plants?

  -antibacterial chemicals

  -poisons to deter herbivores, eg: foxgloves
• What are mechanical barriers in plants?

  -thorns which makes plants unpleasant to eat

  -hairy stems (some combine hairs with poison)

  -drooping/curling when touched (dislodges insects + frightens animals)

  -mimicry (some plants mimic unhealthy plants)
• What are placebos?


  An inactive substance made to resemble a drug for researchers to use as a control.
• How can plant diseases be identified?

  test the DNA of the pathogens

  using test kits that contain monoclonal antibodies

  taking the infected plant to a lab to identify the pathogen