Do you know why trees shed leaves?

Prof. Know Why explains:

Like people, the leaves of trees also age, but do so much more rapidly. Each spring the young leaves develop from buds and then rapidly mature to full size to carry on photosynthesis (the process that provides food needed for the tree to grow and maintain itself). By autumn, the leaves of many hardwood trees reach old age and do not function well. At this time a tree must also prepare for the harsher weather conditions of winter. Signals to the tree indicating it is time to prepare for winter include shorter days, less intense sunlight and cooler temperatures. Prior to the leaves falling, nutrients like nitrogen and phosphorus move from the leaf into the adjacent stem to be reused during the next growing season. The following spring a new crop of leaves are produced and the cycle is repeated.

To sum up, in early autumn, in response to the shortening days and declining intensity of sunlight, leaves begin the processes leading up to their fall. The veins that carry fluids into and out of the leaf gradually close off, as a layer of cells forms at the base of each leaf. Once this separation layer is complete and the connecting tissues are sealed off, the leaf is ready to fall.

Thus while trees can live for decades and even centuries, some parts of the tree like the leaves, live for only a few months or years (in certain varieties of trees).

Do you know why lizards lose their tails?

Prof. Know Why explains:

Lizards can lose their tails, but not all lizards can grow them back, though. Lizards that lose their tails also lose an important source of energy because they store fats at the base of their tails.

In lizards, the tail bones have central regions that break away easily when the tail is pulled. The muscles of the tail pull apart and the blood vessels constrict to stop the wounded tail from bleeding. So, if a predator attacks a lizard, the tail is designed such that it separates from the body allowing the lizard to escape while the predator gets the tail. Lizards that lose their tails grow them back but the replacement tail is never as long or as colorful as the original one. Replacement tails grow back in as little as three months or as long as two years.

In short, in order to defend it in a threatening situation, the lizard chooses to detach its tail by contracting a special muscle near a weakness in its vertebrae.

In lizards, especially big ones like Iguanas and Komodo Dragons, the tail bones are not designed to break easily and the tail muscles are also not designed to pull apart smoothly. These lizards however can also lose their tails, but it takes a much stronger pull to make this happen. With these types of lizards, the wound heals like others though, but the tail does not grow back.

Do you know why we cry?

Prof. Know Why explains:

Women cry 64 times a year on average, while men just 17, says a recent study. Actors and politicians do it on demand though! But why does crying happen in the first place?

When we become upset, our brains and bodies overreact and work overtime, producing chemicals and hormones. Crying helps eliminate t,hese extra chemicals that we don't need, in the form of tears. These tears are formed in tiny glands present in the upper eyelids of our eyes, called lachrymal glands.

Scientifically, emotional tears contain high levels of manganese and a chemical called prolactin.

As our tears flow, they sooth our sadness or distress by disposing of these chemical agents. That is why generally, we feel calmer or more refreshed after crying, because the tears get rid of these hormones that are produced when we are sad, happy, or distressed.