Reference Terms
from Wikipedia, the free encyclopedia
Pupil
In the eye, the pupil is the opening in the middle of the iris. It appears black because most of the light entering it is absorbed by the tissues inside the eye. In humans and many animals (but few fish), the size of the pupil is controlled by involuntary contraction and dilation of the iris, in order to regulate the intensity of light entering the eye. This is known as the pupillary reflex. In bright light, the human pupil has a diameter of about 1.5 millimeters, in dim light the diameter is enlarged to about 8 millimeters. The shape of the pupil varies between species. Common shapes are circular or slit-shaped, although more convoluted shapes can be found in aquatic species. The reasons for the variation in shapes are complex; the shape is closely related to the optical characteristics of the lens, the shape and sensitivity of the retina, and the visual requirements of the species.
Related Stories
1
2
Plants & Animals News
October 6, 2026
Oct. 5, 2026 Predatory wasps are hijacking shelters built by tropical trees for their ant defenders, potentially disrupting an ancient partnership that protects the plants from hungry insects. The takeover is far more common in disturbed landscapes such as oil ...
Oct. 5, 2026 Scientists found that prolonged fasting triggers major changes throughout the body, but many of the most interesting effects only appeared after about three days without food. The results suggest fasting may influence health in ways that go beyond ...
Oct. 5, 2026 Scientists have discovered a human gene with a remarkable double life: it appears to play an important role in brain cells while still retaining the ability to jump around the genome. Called BC200, the gene evolved millions of years ago from a ...
Oct. 4, 2026 Scientists have discovered that E-cadherin, a protein best known as the “glue” holding cells and tissues together, has a surprising second job: helping epithelial cells swallow nearby dead cells. Using live zebrafish and mouse embryos, ...
Oct. 4, 2026 A 30-year forestry experiment in Australia found that heavily thinned mountain ash forests grew unusually large trees while recovering enough carbon to match or exceed untouched areas. The results suggest carefully managed thinning could support ...
Oct. 3, 2026 The essential amino acid leucine can boost cellular energy production by protecting key proteins on mitochondria from being destroyed. The discovery reveals a new connection between nutrition and metabolism that could eventually lead to new ...
Oct. 1, 2026 A new protective fabric boosted strawberry yields by as much as 3.56 times while blocking insects and still allowing sunlight, rain, and airflow to reach the plants. Originally inspired by research on military clothing, Plant Armor could also help ...
Sep. 30, 2026 Mulberry compounds may reshape the gut microbiome in ways that support intestinal health and metabolism, with some combinations showing especially strong effects in animal studies. However, the results vary depending on the plant part and processing ...
Sep. 28, 2026 Yellow-morph green sea turtles in the Galápagos surprised scientists by staying remarkably close to home instead of making the long journeys typically associated with sea turtles. Satellite tracking showed that none left the marine reserve during ...
Sep. 28, 2026 Scientists have discovered a new tick-borne virus in China that causes flu-like illness and may account for previously unexplained cases of fever, fatigue, digestive problems, and low platelet counts. Most patients with ALTNV alone recovered, but ...
Sep. 27, 2026 Scientists have streamlined a method for measuring DNA-bound phosphorus in soil, making it cheaper and easier while preserving its accuracy. The technique could reveal how soil microbes help recycle phosphorus and ultimately support more sustainable ...
Sep. 27, 2026 Scientists studying ancient Australian rocks uncovered more than 12,000 fossils from some of the oldest known eukaryotes on Earth. These early complex cells lived in settings ranging from coastal ...
Latest Headlines
updated 12:56 pm ET
Oct. 2, 2026 Mysterious 97-million-year-old magnetic fossils may be the oldest evidence of an animal using Earth’s magnetic field like a built-in GPS. Their sophisticated magnetic structure could have helped an ...
Oct. 1, 2026 Scientists may have found a clue to one of the biggest mysteries surrounding the origin of life: how fragile RNA molecules could gather and survive ...
Oct. 1, 2026 Scientists have identified two new species of large Australian stick insects, including one that lays extraordinary “lidded” eggs never before recorded in the group. The discovery also revealed ...
Sep. 30, 2026 A huge genomic and fossil study suggests bats first evolved in Europe around 65 to 60 million years ago before spreading across the globe. The findings also indicate that flight and echolocation ...
Sep. 29, 2026 Wild blacktip sharks can detect low-frequency sounds from nearly 250 feet away, according to experiments conducted off the Florida coast. The sharks not only heard the sounds but sharply changed ...
Sep. 29, 2026 A 245-million-year-old marine reptile fossil preserves an astonishing amount of detail, including its stomach, liver, and intestines. The discovery reveals that Austronaga minuta was highly adapted ...
Sep. 29, 2026 Enceladus may naturally separate and concentrate chemicals from its hidden ocean as droplets slowly freeze and shatter on their way into space. The ...
Sep. 28, 2026 A beautifully preserved fossil from Mongolia’s Gobi Desert has solved a mystery that puzzled paleontologists for nearly 40 years. Tamirkhan balcarceli shows that zhelestids were not early relatives ...
Sep. 26, 2026 Scientists have mapped the genetics of cat cancer on an unprecedented scale and found surprising similarities with tumors in humans. The findings ...
Sep. 25, 2026 Scientists think beneficial fungi could help transform nutrient-poor lunar and Martian regolith into a material capable of supporting crops. By helping plants access nutrients and withstand harsh ...