Ask the Science Editor

By Henry Shi

Grace Raskopf: What is photosynthesis?

Photosynthesis is a process by which plants harness the energy of the sun to produce food. It takes place inside the chloroplasts of plant cells. First, sunlight is absorbed by green chlorophyll molecules, exciting an electron to be carried. The electron’s energy is used to pump hydrogen (H+) ions across the thylakoid membrane to create a high-concentration gradient inside the thylakoid of the chloroplast. The protons then diffuse back across the membrane to generate ATP, a rechargeable molecule of energy for plants. ATP is a then used to build sugars. Sunlight splits a water molecule into oxygen, electrons, and protons to resupply this process.

In the fluid-filled space (stroma) of the chloroplast, carbon dioxide gas is used to build sugar molecules. Through the Calvin cycle, the chloroplast joins carbon dioxide molecules together and uses the energy from ATP. For every three CO2 molecules, a single G3P is produced. The chloroplast connects the ATP-producing light reactions of photosynthesis with the sugar-building reactions of the Calvin Cycle. Over time, the chloroplast synthesizes simple sugars that it exports to the plant cells. These sugars are used by the plant to build proteins, lipids, and cellulose cell walls. The forests and fields you see around you are built by the elegant metabolic process of photosynthesis!

Jackson Blanchard, Jessica Spitzer: What is the difference between a comet, meteorite, and asteroid?

A comet is a space rock, composed of ice and dust, that orbits the sun in outer space. As comets travel close to the sun, their ice and dust layers vaporize. Due to their small size, comets have very weak gravity so they disintegrate rapidly. The comet’s spectacular tail, called a coma, is formed by the ice and dust being blown by the sun’s solar wind, akin to wind on earth. Most comets in the solar system originate from the Kuiper Belt, the region of icy bodies beyond Neptune. Hence, they can only be seen from Earth every few decades, centuries, or even millennia. So you should watch a comet when you have the chance–truly a once in a lifetime experience!

Our solar system is full of floating debris. Most space rocks that enter Earth’s atmosphere burn up due to air resistance. This is akin to your hands heating up when you rub them together. These space rocks are called meteoroids, producing meteor showers that you can see at night when skies are clear. Occasionally, a space rock penetrates the Earth’s atmosphere and hits the ground; in this case, it is called a meteorite. Meteorite impacts generate shockwaves through the ground and heat up the surrounding air, creating the equivalent of a 1-megaton TNT explosion in a radius of only a few miles. However, meteorite damage is not widespread. Plants may be killed by a meteorite, but the global climate will not be affected and most life on Earth will not be in imminent harm.

An asteroid is a large meteorite, at least 100 meters (330 feet) wide. Most asteroids remain in the Asteroid Belt between Mars and Jupiter, but occasionally, one may pass too close to Earth and enter the atmosphere. All asteroids that enter Earth will hit the ground, causing widespread catastrophic damage to the planet. Asteroids can alter the global climate. An asteroid impact can send a large amount of debris into the atmosphere, blocking out the sun and causing global cooling. With diminished sunlight, plants cannot perform photosynthesis, leaving less food for animals to eat. Many life-forms would starve to death in such an environment. Notably, an asteroid 6 miles wide struck the Yucatan Peninsula in southern Mexico 65 million years ago, wiping out the dinosaurs. Such impacts happen every 26 million years; the next one is expected to occur in 10 million years, so you shouldn’t worry.