Plant Defence

Some plants have to defend themselves against attack from pests and pathogens by the following physical and chemical barriers:

Physical defences:

  1. Thick bark - external layer of dead cells to act against infection
  2. Cellulose cell wall - barrier against infection. Pectin is added into the cell wall to keep it strong, and prevention from fungi
  3. Waxy cuticle on the leaf - stops cells from getting infected by bacteria and fungi
  4. Hardened cells which forms horns or spines - prevents the plant from being eaten.

Chemical defences:

  1. Production of enzymes or toxic chemicals - attacks pathogens and insects
  2. Production of terpenes when being attacked - it also has a strong odour
  3. __Development of stinging cells and trichomes __- irritates the skin of whichever animal that has tried to consume the plant.

Detect and Identify Plant Diseases

It is vital to detect and identify plant diseases so that the correct support can be put in place for the plant so that it can survive.

Infected plants can show signs of abnormal growth, production of slime__ and __insect larvae.

Individuals may take a cutting off an infected plant to seek help from professionals. If the professionals cannot help, the cutting can be brought to scientists where they can place the pathogens on agar plates. The virus would then be cultured in controlled conditions and biochemical tests will be carried out in order to identify the bacteria and virus.

Other visible symptoms of an infected plant are:

  1. Stunted growth (nitrate deficiency)
  2. Spots on leaves (black spot fungus on roses)
  3. Areas of decay (black spots on roses or blights on potatoes)
  4. Growths (crown galls caused by bacterial infections)
  5. Malformed stems or leaves (aphid or nematode infestation)
  6. Discolouration (yellowing, chlorosis in magnesium deficiency or mosaic patterns resulting from tobacco mosaic virus)

Infections, figure 1

Human Body Defences

Humans have physical barriers__ and chemical defences__ in order to protect them from pathogens.

Physical barriers:

  1. Mucus - produced by cells in the nose. The mucus will trap pathogens before it can go down the trachea, and into our lungs. If there is any remaining mucus with the trapped pathogen, it will be broken down by the acid in the stomach.
  2. Cilia - hair cells that are lined in the trachea. They will move the mucus and pathogen upwards so that it can be coughed out
  3. Skin - the biggest organ in the body that protects us from infections. If we get a cut, it tends to heal itself through time as the blood will clot to prevent further blood loss

Infections, figure 1

Chemical defences:

  1. Lysozymes - an enzyme that is found in tears. It is used to protect the eye from any bacteria
  2. Hydrochloric acid - found in the stomach. It makes it an acidic environment, which would allow a lot of pathogens to get killed.

Specific Immune System

The immune system is the body’s__ second line of defence__, where it tackles the pathogens that has gone past the first line of defence (the physical and chemical defences listed above).

  1. When exposed to pathogens, the antigens trigger an immune response
  2. This causes the production of antibodies
  3. The antigens also trigger production of memory lymphocytes. Memory lymphocytes will have remembered how to fight this pathogen, therefore it will work quickly to destroy the pathogen if infection occurs again at a later date
What kind of acid is found in the stomach? Why is it there?
Your answer should include: Hydrochloric / Acidic / Kills / Pathogens
Explanation: Hydrochloric acid can be found in the stomach. It is acidic so that it kills a lot of pathogens.
What is the biggest organ in the body that protects us from infections?
How can we prevent the spread of HIV?
Your answer should include: Use / Education / Educating / Protected Sex / HIV
Explanation: Encourage the use of protected sex, educating the community about the importance of protected sex, and the implications of having HIV

Detect & Identify Plant Diseases