Natural Defense In Plants

Certain plants have specific characteristics that can protect themselves from enemies.  Can you name some of the characteristics?

Pineapple plants and fruits have many sharp thorns.  Thorns on plants serve as a form of protection.  Since plants are unable to move or escape from threats.  They develop thorns as a means to keep from attack.  The thorns are evolutionary developments that allow for group defense when plants grow in bunches.  Pineapple can be cumbersome when you try to cut them.  The top of the fruit has sharp, pointy leaves that makes harvesting the delicious fruit challenging and the outside is rough and bumpy, which makes it difficult to cut.  Pineapple leaves are waxy, strap-sharped leaves 2 to 6 feet in length.  They usually have a sharp point on the tip of the leaf and spines along the margins of the leaves.  The leaves may be green or variegated in color.  The pineapple "fruit" is not really a fruit at all but is a mass of individual berries fused to the central stalk.  This is why the "fruit" has leaves on top.  They are actually the continued growth of the stalk beyond where the berries are attached.

Precaution

Be careful of the sharp thorns when you handle a pineapple fruit.

Natural Defense In Plants

Plants have specific characteristics to protect themselves from enemies. Mimosa plants fold their leaflets when touched.  The leaves also close under various other stimuli, such as touching, warming, blowing or shaking.  This types of movement have been termed seismonastic movements.  The movement occurs when specific regions of cells lose turgor pressure, which is the force that is applied onto the cell wall by water within the cell vacuoles and other cell contents.  When the plant is disturbed, specific regions on the stem are stimulated to release chemicals including potassium ions which force water out the cell vacuoles and the water diffuses out the cells, producing a loss of cell pressure and cell collapse; this differential turgidity between different regions of cells results in the closing of the leaflets and the collapse of the leaf petiole.

           

      Mimosa prior to a touch.             

           

    

     
Mimosa with folded-in leaves immediately after a touch.

Survival

We have learnt that animals have specific characteristics and behaviours to protect them from enemies weather.  This enable them to survive.  How do animals protect themselves from their enemies and extreme weather conditions?

1.   Armadillos 

Armadillos find food at night.  When they are attack by their enemies, they curl their bodies into a ball.  The hard scales protect them against their enemies.

Armadillos live in temperate and warm habitats, including rain forest, grasslands and semi-deserts.  Because of their low metabolic rate and lack of fat stores, cold is their enemy and spates of intemperate weather can wipe put out whole populations.

                                  

2.   Arctic fox

Arctic foxes are able to survive changes in the weather.  Their fur is brown in summer but turns into white in winter.  This help them hide from their enemies.

It has furry soles, short ears and a short muzzle-all important adaptations to the chilly clime.  Arctic foxes live in burrows and in a blizzard they may tunnel into the snow to create shelter.

Arctic foxes have beautiful white (sometimes blue-gray) coats that act as very effective winter camouflage.  The natural hues allow the animal to blend into the tundra's ubiquitous snow and ice.  When the seasons change, the fox's coat turns as well, adopting a brown or gray appearance that provides cover among the summer tundra's rocks.

                                     

                                      

Living In Extreme Weather

Penguins have thick layers of fat under their skins to keep their bodies warm.

The top layer of a penguin's skin is made of thousand of small, stiff feathers.  The air between the feathers is good insulation.  To make their 'coat' even more water and windproof penguins spread some oil on it (this oil comes from a gland above their tail).  Below the feathers is a thick layer of blubber to keep the penguins warm.

Once a year, penguins shed their feathers and grow new ones.  This is called molting.  The old feathers come off in patches and at the same time new feathers grow.  This take about three weeks and during this period the penguins do not eat nor swim.  

All penguin backs are black and all bellies are white.  This has to do with swimming camouflage.  The black back looks like the bottom of the ocean and the white belly looks like the water surface.  Some species, like king and emperor penguins, have yellow, orange or red areas on their head or neck.

Living In Extreme Weather

Do you know the name of animals that live in very cold weather?

How do they survive?

Polar bears
Polar bears have thick furs to enable them to live in very cold weather.  Polar bears' fur consists of a dense, insulating undercoat topped by guard hairs of various lengths.  It is not actually white.  It just looks that way.

Each hair shaft pigment-free and transparent with a hollow core that scatters and reflects visible light, much like what happens with ice and snow.

Polar bears look whitest when they are clean and in sunlight, especially just after the molt period, which usually begins in spring and is complete by late summer.  Before molting, oils from the seals they eat can make them look yellow.

In zoos, polar bears have been known to turn green due to colonies of algae growing in their hallow hair shafts.  This happened at San Diego Zoo in 1979.  No harm came to the bears, and zoo veterinarian Phillip Robinson restored the bears to white by killing the algae with a salt solution.

Polar bears have black skin under which there is a layer of fat that can measure 4.5 inches (11.5 centimeters) thick.  But it is their fur, not their fat, that prevents bears from suffering nearly any heat loss.  In fact, adult males quickly overheat when they run.

Living In Extreme Weather

Desert foxes have long ears to lose heat easily.

The desert fox is a beautiful species, slender in form, and extraordinarily quick and graceful in its movements, but so generally nocturnal in habits as to be rarely seen by the desert traveler.  The desert fox digs  burrow, with several entrances, in a small mound. or at times on an open flat, and there rears four or five young each year.  It main food consists of kangaroo rats, pocket mice, small ground-squirrels, and a variety of other small desert mammals.  

In early morning fox tracks, about the size of those of a house-cat, may be seen along sandy arroyos and similar places where these small carnivores have wandered in search of prey.  Like the kit, the desert ox has little of the sophisticated mental ability of the red fox and falls an easy prey to the trapper.  It is no where numerous and occupies such a thinly inhabited region that there is little danger of it numbers greatly decreasing in the near future.

Living In Extreme Weather

Kangaroo rats keep fat in their tails.  When there is no water, the fat can be changed into water.