Biology - 5 Communicable Diseases - 5.9 Human Defence Responses & 5.10 More About Plant Diseases & 5.11 Plant Defence Responses

Skin defences [4]

- barrier to microorganisms
- if cut, platelets cause clotting and create a scab; a barrier
- produces antimicrobial secretions to destroy pathogens
- covered in 'healthy' microorganisms that form another barrier

Respiratory and digestive defences [3]

- nose is full of hairs and mucus that trap pathogens and particulates
- trachea and bronchi secrete mucus to trap pathogens, then cilia waft it up to the throat where it is swallowed
- stomach produces acid that destroys pathogens in this mucus as well as in food and drink

Phagocyte

white blood cell that destroys pathogens by engulfing and digesting them

Lymphocyte

white blood cell that produces antibodies or antitoxins

Antibody

a protein that acts against a specific antigen and destroys it

Antigen

substance that triggers an immune response

Antitoxin

agent that works to destroy (cancel out) toxins

Aphid

any of various small plant-sucking insects

What do aphids do to plants? [3]

- use their mouth to pierce and drink from the sugar-rich phloem sap
- take away products of photosynthesis
- act as vectors of disease

How can aphids be destroyed?

- chemical pesticides
- biological pest control (ladybirds) in enclosed spaces

Nematode worms and insect larvae...

feed on or in the plant roots and damage them, limiting the plant's water supply

Nitrate deficiency in plants [2]

- needed for production and synthesis of proteins
- growth will be stunted

Magnesium deficiency in plants [3]

- needed to produce chlorophyll
- yellowing leaves (chlorosis)
- stunted growth

Chlorosis

yellowing of leaves

Physical barriers (plants) [4]

- cellulose walls
- waxy cuticle is waterproof and acts as barrier
- bark on trees/layer of dead cells on stems
- leaf fall in Autumn

Chemical barriers [3]

- for example, mint and witch hazel
- plants produce antibacterial chemicals
- can be extracted for use

Defences against herbivores

- poisons
- thorns
- hairy stems and/or leaves
- drooping or curling when touched
- mimicry

Poison examples [3]

- foxglove
- deadly nightshade
- yew

Thorn examples [3]

- brambles
- cacti
- gorse

Hairy stems/leaves examples [3]

- lamb's ears
- pelargoniums
- nettles

Drooping or curling when touched example

mimosa pudica

How can mimicry be used?

imitating butterfly eggs to deter butterflies/caterpillars