Defence against pathogens Flashcards
What are the animal defences?
Skin - acts as a physical barrier, blocking pathogens from entering the body. It also acts as a chemical barrier by producing chemicals that are antimicobial and can lowe pH, inhibiting the growth of pathogens
Mucous membranes - protect body openings that are exposed. Some secrete mucus - traps pathogens and contains antimicrobial enzymes
Blood clotting - mesh of fibrin. Blood clots plug wounds to prevent pathogen entry and blood loss. They’re formed by a series of chemical reactions that take place when platelets are exposed to damaged blood vessels
Inflammation - the signs are swellings, pain, heat and redness. Triggered by tissue damage - the damaged tissue releases molecules, which increase the permeability of the blood vessels, so they start to leak fluid into the ares. Causes swelling and helps to isolate any pathogens that may have entered the damaged tissue. Molecules also cause vasodilation which increases blood flow to the area. This makes the area hot and brings white blood cells to the area to fight off any pathogens.
Wound repair - the skin is able to repair itself and re-form a barrier against pathogen entry. The surface is repaired by the outer layer of skin cells dividing and migrating to the edges of the wound. The tissue below the wound then contracts to bring the edges of the wound closer together. It is repaired using collagen fibre - too many collagen fibres and you’ll end up with a scar
Expulsive reflexes - A sneeze happens when the mucus membranes in the nostrils are irritated by things such as dust/dirt. A cough stems from irritation in the respiratory tract. Both coughing and sneezing are an attempt to expel foreign objects, including pathogens, from the body. They happen automatically.
What are the plants physical defences?
Most plants have a waxy cuticle, which provides a physical barrier against pathogen entry. It may also stop water collecting on the leaf, which could reduce the risk of infection by pathogens hat are transferred between plants in water
Plant cells themselves are surrounded by cell walls. These form a physical barrier against pathogens that make it past the waxy cuticle.
Plants produce a polysaccharide (callose). Callose gets deposited between plant cell walls and membranes during times of stress. Callose deposition may make it harder for pathogens to enter cells. Callose deposition at the plasmodesmata may limit the spread of viruses between cells
What are the chemical ones?
They produce antimicrobial chemicals which kill pathogens or inhibit their growth
Other chemicals secreted by plants are toxic to insects- this reduces the amount of insect-feeding on plants and therefore reduces the risk of infection by plant viruses carried by insect vectors.
