Science Sunday: Self Defence!
Much in the way that humans might carry pepper spray or learn martial arts, plants and animals also have their own unique and interesting defence mechanisms. You might not catch a fig trying to karate chop you- but the flora and fauna of the natural world have found varied and surprisingly interesting ways of keeping predators at bay.
Some plants have obvious defence mechanisms which protect them from grazing- trees have tough bark, gorse and cacti have spines, roses and brambles have thorns. Nettles are even cooler- their stings aren’t just prickly; they’re filled with a mixture of irritating chemicals which deter many grazing animals (and nosy children). Plants which use chemicals to defend themselves are just as interesting as the flashy, dangerous-looking types. Elderberry, clover and certain types of apple are cyanogenic– they produce cyanide! Other chemicals which are distasteful or toxic to animals include tannins and nicotine. Some plants will produce resin or latex to seal an area of damage- this traps pathogens such as bacteria, fungi and viruses in an eternal sticky grave.
Many plants have also adapted to tolerate grazing- grasses have their meristems very close to the ground so that they are missed by hungry herbivores and the plant can continue to grow from the bottom up. Some grasses have completely underground stems, so that they can regenerate even if the surface plant is completely destroyed. Other plants just have incredible powers of regeneration, where a tiny piece of root left in the soil might be enough for a whole plant to grow.
Animals also have their own defence mechanisms to ward off predators- these can be split into ‘individual’ and ‘group’ mechanisms. Some are obvious- and some you might not even have thought of!
– Speed (i.e. gazelles)
– Camouflage (i.e. stick insects)
– Displays to confuse predators, such as eye-spot markings on some species of moth
– Warning colouration (i.e. the poison dart frog)
– Foul-smelling secretions (i.e. skunks)
– And my personal favourite- the ability to detach a body part in order to escape, such as some species of lizard!
Forming a group for defensive reasons can work for animals in many different ways. If an animal travels in a large flock or herd, there is less chance for the individual of being picked from the group and attacked. Defensive formations may be formed- for example, male musk oxen will form a defensive barrier around females and calves in order to ward off predators with their horns. A group of animals also has a greater chance of scaring off predators- crows and gulls group together to harrass potential predators such as foxes and birds of prey.
Cellular Defence Mechanisms
Much like plants, animals have cellular defence mechanisms which ward off smaller predators such as bacteria and viruses. The first lines of defence for a human are the barriers provided by the skin, stomach acid and the mucus lining of the air passages. However, if these mechanisms fail, there are two types of white blood cell which will act against the attacker.
Phagocytes: Phagocytes move around the body until they encounter any foreign particles. They then flow around these particles and engulf them in a vacuole within the cellular cytoplasm. Lysosomes which contain powerful enzymes are released to digest the harmful particle.
Lymphocytes: Lymphocytes work differently from phagocytes in that they produce antibodies which are specific to the antigen (foreign protein) of the virus or bacteria. If the antibody successfully binds with the antigen, then the antigen is rendered harmless.
So if you get sick, don’t blame your body- it’s doing a whole lot to help you!
Do you know of any plants or animals with cool defence mechanisms? If so, let us know in the comments section below!
Image Credit: Wikimedia Commons