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Many plants have seasonal rhythms as well. As spring melts the winter frost, phytochromes sense the longer days and increasing light, and a currently unknown mechanism detects the temperature change. These systems pass the news throughout the plant and make it produce blooming flowers in preparation for the pollinators brought out by warmer weather. Circadian rhythms act as a link between a plant and its environment. These oscillations come from the plants themselves. Each one has a default rhythm. Even so, these clocks can adapt their oscillations to environmental changes and cues. On a planet that's in constant flux, it's the circadian rhythms that enable a plant to stay true to its schedule and to keep its own time.

As the phytochromes detect increasing sunlight, the plant readies its light-capturing molecules so it can photosynthesize and grow throughout the morning. After harvesting their morning light, plants use the rest of the day to build long chains of energy in the form of glucose polymers, like starch. The sun sets, and the day's work is done, though a plant is anything but inactive at night. In the absence of sunlight, they metabolize and grow, breaking down the starch from the previous day's energy harvest.

The cells in stems, leaves, and flowers contain phytochromes, tiny molecules that detect light. When that happens, phytochromes initiate a chain of chemical reactions, passing the message down into the cellular nuclei. There, transcription factors trigger the manufacture of proteins required to carry out light-dependent processes, like photosynthesis. These phytochromes not only sense the amount of light the plant receives, but can also detect tiny differences in the distribution of wavelengths the plant takes in.

That's important, because the planet's rotations and revolutions put us in a state of constant flux, although it plays out in a repetitive, predictable way. Circadian rhythms incorporate various cues to regulate when an organism should wake and sleep, and perform certain activities. For plants, light and temperature are the cues which trigger reactions that play out at a molecular scale.

A closing white water lily signals that it's late afternoon, and moon flowers, as the name suggests, only bloom under the night sky. But what gives plants this innate sense of time? It's not just plants, in fact. Many organisms on Earth have a seemingly inherent awareness of where they are in the day's cycle. That's because of circadian rhythms, the internal timekeepers that tick away inside many living things. These biological clocks allow organisms to keep track of time and pick up on environmental cues that help them adapt.

In the 18th century, Swedish botanist Carolus Linnaeus designed the flower clock, a timepiece made of flowering plants that bloom and close at specific times of day. Linnaeus's plan wasn't perfect, but the idea behind it was correct. Flowers can indeed sense time, after a fashion. Mornings glories unfurl their petals like clockwork in the early morning.

But from what we do know,we can tell that they have a pretty diverse toolbox.Gordian worms seem to affect crickets' brains directly.The malaria parasite, on the other hand,blocks an enzyme that helps the mosquitoes feed,forcing them to bite over and over and over again.The rabies virus may cause that snarling, slobbering behavior by putting the immune system into overdrive.But whatever the method,when you think about how effectively these parasites control the behavior of their hosts,you may wonder how much of human behavior is actually parasites doing the talking. Since more than half of the species on Earth are parasites, it could be more than we think.

When a rat gets infected by eating cat feces, the parasite changes chemical levels in the rat's brain, making it less cautious around the hungry felines, maybe even attracted to them. This makes them easy prey, so these infected rodents get eaten and pass the parasite on. Mind control successful. There's even evidence that the parasite affects human behavior. In most cases, we don't completely understand how these parasites manage their feats of behavior modification.

There's also evidence that humans infected with malaria are more attractive to mosquitoes, which will bite them and transfer the parasite further. This multi-species system is so effective, that there are hundreds of millions of malaria cases every year. And finally, there are cats. Don't worry, there probably aren't any cats living in your body and controlling your thoughts. I mean, probably. But there is a microorganism called Toxoplasma that needs both cats and rodents to complete its life cycle.

Within several weeks, the stalk shoots off spores, which turn more ants into six-legged leaf-seeking zombies. One of humanity's most deadly assailants is a behavior-altering parasite, though if it's any consolation, it's not our brains that are being hijacked. I'm talking about Plasmodium, which causes malaria. This parasite needs mosquitoes to shuttle it between hosts, so it makes them bite more frequently and for longer.

After Ophiocordyceps spores pierce the ant's exoskeleton, they set off convulsions that make the ant fall from the tree. The fungus changes the ant's behavior, compelling it to wander mindlessly until it stumbles onto a plant leaf with the perfect fungal breeding conditions, which it latches onto. The ant then dies, and the fungus parasitizes its body to build a tall, thin stalk from its neck.

But before it does, it often increases its host's aggressiveness and ramps up the production of rabies-transmitting saliva, while making it hard to swallow. These factors make the host more likely to bite another animal and more likely to pass the virus on when it does. And now, meet Ophiocordyceps, also known as the zombie fungus. Its host of choice is tropical ants that normally live in treetops.

The worm then wriggles out to mate and its eggs get eaten by little water insects that mature, colonize land, and are, in turn, eaten by new crickets. And thus, the Gordian worm lives on. And here's the rabies virus, another mind-altering parasite. This virus infects mammals, often dogs, and travels up the animal's nerves to its brain where it causes inflammation that eventually kills the host.

Our parasites elegantly achieve this by manipulating their host's behavior, sometimes through direct brain hijacking. For example, this is the Gordian worm.One of its hosts, this cricket. The Gordian worm needs water to mate, but the cricket prefers dry land. So once it's big enough to reproduce, the worm produces proteins that garble the cricket's navigational system. The confused cricket jumps around erratically, moves closer to water, and eventually leaps in, often drowning in the process.

Which of these entities has evolved the ability to manipulate an animal many times its size? The answer is all of them.These are all parasites,organisms that live on or inside another host organism,which they harm and sometimes even kill.Parasite survival depends on transmitting from one host to the next,sometimes through an intermediate species.

But even peas have a lot of characteristics. For example, besides being yellow or green, peas may be round or wrinkled. So we could have all these possible combinations: round yellow peas, round green peas, wrinkled yellow peas, wrinkled green peas. To calculate the proportions for each genotype and phenotype, we can use a Punnett square too. Of course, this will make it a little more complex. And lots of things are more complicated than peas, like, say, people. These days, scientists know a lot more about genetics and heredity. And there are many other ways in which some characteristics are inherited. But, it all started with Mendel and his peas.

Let's look at Mendel's peas, for example.Let's write the dominant yellow allele as an uppercase "Y"and the recessive green allele as a lowercase "y."The uppercase Y always overpowers his lowercase friend,so the only time you get green babies is if you have lowercase Y's.In Mendel's first generation,the yellow homozygous pea mom will give each pea kid a yellow-dominant allele, and the green homozygous pea dad will give a green-recessive allele.So all the pea kids will be yellow heterozygous.Then, in the second generation, where the two heterozygous kids marry,their babies could have any of the three possible genotypes,showing the two possible phenotypes in a three-to-one proportion.

Now we know that these factors are called alleles and represent the different variations of a gene.Depending on which type of allele Mendel found in each seed,we can have what we call a homozygous pea,where both alleles are identical,and what we call a heterozygous pea, when the two alleles are different.This combination of alleles is known as genotype and its result, being yellow or green, is called phenotype. To clearly visualize how alleles are distributed amongst descendants, we can a diagram called the Punnett square. You place the different alleles on both axes and then figure out the possible combinations.

In one of most classic examples,Mendel combined a purebred yellow-seeded plant with a purebred green-seeded plant,and he got only yellow seeds.He called the yellow-colored trait the dominant one,because it was expressed in all the new seeds. Then he let the new yellow-seeded hybrid plants self-fertilize.And in this second generation,he got both yellow and green seeds,which meant the green trait had been hidden by the dominant yellow.He called this hidden trait the recessive trait.From those results, Mendel inferred that each trait depends on a pair of factors,one of them coming from the mother and the other from the father.

These days scientists know how you inherit characteristics from your parents.They're able to calculate probabilities of having a specific trait or getting a genetic disease according to the information from the parents and the family history.But how is this possible?To understand how traits pass from one living being to its descendants,we need to go back in time to the 19th century and a man named Gregor Mendel. Mendel was an Austrian monk and biologist who loved to work with plants.By breeding the pea plants he was growing in the monastery's garden,he discovered the principles that rule heredity.