Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.

Context: A cell is the smallest structural and functional unit of an organism. Some organisms, like bacteria, consist of only one cell. Big organisms, like humans, consist of trillions of cells. Compare a human to a banana. On the outside, they look very different, but if you look close enough youll see that their cells are actually very similar. Most cells are so small that you cannot see them without the help of a microscope. It was not until 1665 that English scientist Robert Hooke invented a basic light microscope and observed cells for the first time, by looking at a piece of cork. You may use light microscopes in the classroom. You can use a light microscope to see cells ( Figure 1.1). But many structures in the cell are too small to see with a light microscope. So, what do you do if you want to see the tiny structures inside of cells? In the 1950s, scientists developed more powerful microscopes. A light microscope sends a beam of light through a specimen, or the object you are studying. A more powerful microscope, called an electron microscope, passes a beam of electrons through the specimen. Sending electrons through a cell allows us to see its smallest parts, even the parts inside the cell ( Figure 1.2). Without electron microscopes, we would not know what the inside of a cell looked like. The outline of onion cells are visible under a light microscope. In 1858, after using microscopes much better than Hookes first microscope, Rudolf Virchow developed the hypoth- esis that cells only come from other cells. For example, bacteria, which are single-celled organisms, divide in half (after they grow some) to make new bacteria. In the same way, your body makes new cells by dividing the cells you already have. In all cases, cells only come from cells that have existed before. This idea led to the development of one of the most important theories in biology, the cell theory. Cell theory states that: 1. All organisms are composed of cells. 2. Cells are alive and the basic living units of organization in all organisms. 3. All cells come from other cells. As with other scientific theories, many hundreds, if not thousands, of experiments support the cell theory. Since Virchow created the theory, no evidence has ever been identified to contradict it. Although cells share many of the same features and structures, they also can be very different ( Figure 1.3). Each cell in your body is designed for a specific task. In other words, the cells function is partly based on the cells structure. For example: Red blood cells are shaped with a pocket that traps oxygen and brings it to other body cells. Nerve cells are long and stringy in order to form a line of communication with other nerve cells, like a wire. Because of this shape, they can quickly send signals, such as the feeling of touching a hot stove, to your brain. Skin cells are flat and fit tightly together to protect your body. As you can see, cells are shaped in ways that help them do their jobs. Multicellular (many-celled) organisms have many types of specialized cells in their bodies. Red blood cells (left) are specialized to carry oxygen in the blood. Neurons (cen- ter ) are shaped to conduct electrical im- pulses to many other nerve cells. These epidermal cells (right) make up the skin of plants. Note how the cells fit tightly together. While cells are the basic units of an organism, groups of cells can perform a job together. These cells are called specialized because they have a special job. Specialized cells can be organized into tissues. For example, your liver cells are organized into liver tissue. Your liver tissue is further organized into an organ, your liver. Organs are formed from two or more specialized tissues working together to perform a job. All organs, from your heart to your liver, are made up of an organized group of tissues. These organs are part of a larger system, the organ systems. For example, your brain works
Question: when were cells observed for the first time?
1665

Context: After Atahualpa's execution, Pizarro installed Atahualpa's brother, Tupac Huallpa, as a puppet Inca ruler, but he soon died unexpectedly, leaving Manco Inca Yupanqui in power. He began his rule as an ally of the Spanish and was respected in the southern regions of the empire, but there was still much unrest in the north near Quito where Atahualpa's generals were amassing troops. Atahualpa's death meant that there was no hostage left to deter these northern armies from attacking the invaders. Led by Atahualpa's generals Ruminahui, Zope-Zupahua and Quisquis, the native armies were finally defeated, effectively ending any organized rebellion in the north of the empire.:221-223,226 Archaeological evidence of the rebellion incident exists. The remains of about 70 men, women, and adolescents were found in the path of a planned expressway near Lima in 2007. Forensic evidence suggests that the natives were killed by European weapons, probably during the uprising in 1536. Manco Inca initially had good relations with Francisco Pizarro and several other Spanish conquistadors. However, in 1535 he was left in Cuzco under the control of Pizarro's brothers, Juan and Gonzalo, who so mistreated Manco Inca that he ultimately rebelled. Under the pretense of recovering a statue of pure gold in the nearby Yucay valley, Manco was able to escape Cuzco.:235-237
Question: Who did Tupac Huallpa succeed as Inca ruler?
atahualpa

Context: Using tablet computers like Apple's iPad and Samsung's Galaxy Note just before bed can lead to a poor night's sleep, according to research. More and more people are taking their tablets to bed with them to surf the web, check Facebook or email before switching off the light. But researchers are warning that the blueish light their screens emit can stop users getting a good night's sleep. That is because this type of light mimics daylight, convincing the brain that it is still daytime. Blue light suppresses production of a brain chemical called melatonin, which helps us fall sleep. This is because our brains have evolved to be wakeful during daylight hours. By contrast, light which is more orange or red in tone does not reduce melatonin production, perhaps because our brains recognize it as a cue that the day is ending. Neurologists have known for years that staring at screens late in the evening can disrupt sleep. Researchers at the Lighting Research Centre, at the Rensselaer Polytechnic Institute in New York, are warning that looking at tablet displays for more than two hours "leads to a suppression of our natural melatonin levels as the devices emit optical radiation at short wavelengths" - in other words, they emit bluer light. They say: "Although turning off devices at night is the ultimate solution, it is recommended that if these devices are used at night displays are dimmed as much as possible and that the time spent on them before bed should be limited." They drew their conclusions after measuring melatonin levels in 13 volunteers, after they had spent time viewing iPads at full brightness at a distance of 10 inches, for two hours. Melatonin levels were significantly lower after they had done this, than they were after the volunteers had viewed their iPads for the same time, but while wearing orange glass goggles, which cut out the blue light. They wrote in the journal Applied Ergonomics that tablet makers could "tune the spectral power distribution of self-luminous devices " so that they disrupted the sleep patterns of users less. It is not just a good night's sleep that could be jeopardized by too much late night screen time. Researchers know that persistent disruption to sleep patterns can lead to an increased risk of obesity, and even breast cancer. However, these studies tend to be comparisons of those with chronic sleep disruption, such as long term shift workers, with those who have normal sleep patterns.
Question: What is it that stops users getting a good night's sleep?
blueish light