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Cell division is the process of a single cell turning into two nearly identical copies of itself. To do this, the original cell needs to make copies of all its cellular components, including its DNA. Divvying up other cellular components (like organelles and cytoplasm) between the daughter cells happens at random, but a fair and equal splitting of the genetic material is critical. This is why eukaryotes evolved very complex machinery to ensure that the DNA is split equally between the daughter cells. Here, you will take a journey through the major stages of cell division to explore how a cell is able to accomplish this fundamental task.

Written by Noah Green, HHMI's Janelia Research Campus

Background Image by Dylan T. Burnette; Vanderbilt University; Tennessee, USA

Multicellular organisms are a mosaic of different cells, tissues, and systems, each with their own specific function and interactions with other cells within the organism and/or the larger environment. The cells of the immune system are the guardians of these organisms – able to distinguish friend from foe and self from nonself. To accomplish this task in an organism with perhaps trillions of cells, the cells of the immune system must be ever vigilant and ready to respond at a moment’s notice. Many immune cells patrol other systems (such as the respiratory, digestive, and circulatory systems) and tissues as part of a broad surveillance system that seeks out invading pathogens or damaged cells, while other immune cells respond en masse when an alarm is raised.

Written by Jim Lane; Mahtomedi High School; Minnesota, USA 

Background Image by Julien Resseguier; University of Oslo; Norway

Coronavirus disease 2019 (COVID-19) is a disease caused by SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2). These have become household terms since the start of the global COVID-19 pandemic, but the microscopic size of the virus means that most people are unfamiliar with what the infection process actually looks like, even though many have experienced it themselves. This set of images and animations uses the incredible power of electron microscopy to unmask SARS-CoV-2.

Written by Kasey Christopher; Duquesne University; Pennsylvania, USA

Background image by National Institute of Allergy and Infectious Diseases, U.S. National Institutes of Health (NIH)

Flowers – we see them everywhere, from the grocery store (roses, carnations) to our front yards (dandelions, clover). They come in a variety of shapes, colors, sizes, and scents. The flower pictured here belongs to a white thistle. It can be tempting to think that the beauty we see in flowers is for our own enjoyment, but flowers evolved to house a reproductive system. That’s right – flowers are where babies are made (baby flowering plants, that is)! The outer parts of a flower, including the petals, attract pollinators like insects that facilitate fertilization, and the structures inside a flower produce gametes (a plant’s versions of eggs and sperm), which allow for the development of seeds.

Let’s take a closer look at the inner workings of a flower to see how it does the important work of reproduction in flowering plants.

Written by Kristen Short; Fort Wayne Community Schools; Indiana, USA

Background image by Jan Martinek; Charles University; Prague, Czech Republic

What criteria or characteristics would you use to group living things versus nonliving things? Scientists have grappled with this question for years, and the debate is still ongoing in the scientific community. Some characteristics of living things that scientists have agreed on include the ability to grow and develop, reproduce, maintain homeostasis, process energy (that is, obtain and use energy for various activities), and respond to the environment.

What about viruses? Would you consider them living or nonliving? Let’s look closely at the life cycle of the human immunodeficiency virus (HIV) – the virus that causes AIDS – to find out.

Written by Nadeene Riddick, HHMI

Background image by National Institute of Allergy and Infectious Diseases, U.S. National Institutes of Health (NIH)

When we extend our hand to touch something and explore the world around us, the bones and muscles within our hands are what allow us to do this. Our bones give our hand and arm their structure, and our muscles and tendons move our bones. While the cells in our bodies don’t have bones and muscles, they do have components that give them structure and allow them to move. When cells “put out feelers” to explore the world around them, they deploy their cytoskeletons. A cell’s cytoskeleton is very complex, but there are three major parts that compose most of it and that all work together: actin filaments, intermediate filaments, and microtubules. But unlike your bony skeleton, which stays rigid, the cytoskeleton is dynamic, always changing, building up, and rearranging to allow cells to carry out their functions and explore their world.

Written by Christina Wilson Bowers; Amherst College; Massachusetts, USA 

Background image by Andy Moore, HHMI's Janelia Research Campus, and Erika Holzbaur, University of Pennsylvania; Pennsylvania, USA

For centuries, curious observers have been grappling with the question “What is life?” Early naturalists documented observations about the living world long before anyone knew about cells. Their descriptions captured considerable detail, highlighting structures that exposed patterns that in turn hinted at relationships within and among organisms. Microscopy expanded the field of exploration, revealing hidden layers of life and paving the way for newer vistas of scientific inquiry. Here, the use of the term “scale” refers to relative size but also establishes new boundaries for comparison and exploration. To provide perspective on this site’s exploration of life from a macro to a microscopic scale, consider that the palm of an average human hand is approximately 10 centimeters across (or about 4 inches) and keep that in mind on the journey that follows, further and further into the microscopic world.

Written by Christina Wilson Bowers; Amherst College; Massachusetts, USA 

Initial Idea by Katrina Velle; University of Massachusetts Dartmouth; Massachusetts, USA

Background images by (from the left) Igor Siwanowicz, HHMI’s Janelia Research Campus; National Institute of Allergy and Infectious Diseases, U.S. National Institutes of Health (NIH); and David Bushnell, Ken Westover, and Roger Kornberg, Stanford University, California, USA

Cells are the building blocks of life that can survive and function as single cellular organisms like bacteria or protists, or band together by the hundreds or trillions to make multicellular organisms like humans and other complex life. All of these cells must receive and respond to input from their environment, and each other, to maintain the fragile state of life. This vast cellular network of communication is mirrored within each cell as it efficiently creates and sends messages and materials around the interior of the cell. To start our journey in understanding how cells work, we will zoom into just one of the many cells illustrated in this image. These cells are HeLa cells, one of the most studied lines of cells in scientific research. HeLa cells represent just one of the thousands of different eukaryotic cell types found on Earth. Each of the videos featured in this narrative were created using actual cellular data which mapped the positions and structure of the featured organelles. 

Written by Jim Lane; Mahtomedi High School; Minnesota, USA

Image created by Tom Deerinck, National Center for Microscopy and Imaging Research