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Biological CellsCells are the basic units of all living things. In both unicellular (single-celled) and multicellular organisms, cells contain specialized sub-units called organelles that perform a variety of essential functions, including producing energy from nutrients, storing genetic material, and eliminating waste. Cells also provide structure, such as assembling into tissues that make up organs in complex organisms.
Robert Hooke discovered cells in 1665, naming the microscopic compartments in a slice of cork after cells in a monastery. Research in the centuries that followed revealed that all new cells arise from the division of preexisting cells, with evidence suggesting the first cell emerged about 4 billion years ago.
Scientists classify cells as prokaryotic or eukaryotic based on whether they lack or have a nucleus, which carries DNA. Eukaryotic cells are further divided into animal, plant, fungal, and protist cells based on differences in the organelles they contain (e.g., plant cells have chloroplasts for photosynthesis).
While all cells contain ribosomes—organelles that make proteins—and a membrane that protects organelles suspended in a jelly-like cytoplasm from the environment, they can become specialized through cellular differentiation. In humans, this process can turn stem cells into over 200 distinct cell types (e.g., neurons, white blood cells), each performing specific, critical tasks.Explore Biological Cells
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How women grow tiny humans inside of themPregnancy is a complex biological journey, lasting about 40 weeks. When a sperm fertilizes an egg, that event triggers intricate cellular and hormonal processes, driven by hardwired cellular instructions, which lead to cell division, differentiation, and development—ultimately culminating in the birth of a baby. CrashCourseThrough 2025, two-thirds of known exoplanets have been detected via transitsThis technique involves observing periodic, consistent dips in a star's brightness caused by an exoplanet passing in front of it. Observing wobbles in a star as it is pulled by an orbiting exoplanet's gravity has become the second most common detection method, followed by microlensing and direct exoplanet observation. IEEE SpectrumDe-extinction techniques create new species from existing organismsRather than recovering a genetic sample of a lost species and editing it with that of living creature—as has been depicted in science fiction—scientists begin with living cells from close genetic relatives and use tools like CRISPR to swap in extinct versions of specific traits to create new hybrid species. NOVA PBS OfficialSome organelles are believed to have once been independent cellsMitochondria and chloroplasts, which are both responsible for energy production in cells, have DNA distinct from that of their host cells and are surrounded by cellular membranes resembling those of bacteria. Through symbiogenesis, these and other specialized structures were absorbed into larger cells, forming the modern-day biological units. University of California BerkeleyA gallery of medical illustrations from NIHThe National Institutes of Health provides educational materials for broad use. The institute hosts a Flickr account with many different image galleries, including this one (with over 70 images to date) that illustrate and annotate curious phenomena, from the life cycles of a malaria parasite to the comparison of male and female bladders. Explore the gallery here. National Institutes of HealthComputer viruses' hijacking abilities led them to be named after biological virusesJust as their counterparts infect cells and take control of cellular processes to replicate endlessly, computer viruses cannot replicate on their own and must copy their code into host software before duplicating when the program or file is opened. The term "virus" comes from the Latin word for "venom." CertBrosThe structure of DNA helices comes in three major varietiesThe hereditary molecule can take the form of A-DNA, B-DNA, or Z-DNA based on environmental conditions such as ion concentration and humidity—a characteristic identified by Rosalind Franklin. A-DNA is the shortest and widest of the three, while Z-DNA is the longest and narrowest. B-DNA—the most common variety in living cells—is the intermediate. ChemTalkHalf of human DNA is inherited from each parentWithin most cells reside 23 pairs of chromosomes made of tightly wound DNA, and half of each pair is inherited from each parent. The 23rd pair consists of two X-shaped chromosomes, or one such chromosome paired with a Y chromosome, and determines biological sex. Sano GeneticsDeep sea fish rely on a molecular strengthener to prevent being crushedTrimethylamine N-oxide (TMAO) stabilizes hydrogen bonds and prevents water and proteins within organisms from being misshapen under immense pressure. Compounds called piezolytes protect cellular membranes from being crushed in regions like the Mariana Trench, where pressures are 1,100 times greater than surface atmospheric pressure. IFLScienceSome organisms are composed of a single cell visible to the naked eyeBy incorporating tough, cellulose-rich cell walls, rapid movement of molecules via cytoplasmic streaming, and other biological techniques, some unicellular organisms can bypass the physical limitations that restrict the size of cells. Organisms such as the Stentor coeruleus and Acetabularia can be seen without microscopes. SciShowComputational and biological systems share fundamental principles, like randomnessProposed by Alan Turing and John von Neumann, the concept originates from how DNA and computers run by executing encoded instructions in parallel. The advent of AI and the temperature parameter has seen neural networks mimic the randomness of protein encoding. The MIT Press ReaderThe world's first commercial biological computer combines neurons with siliconAustralian start-up Cortical Labs unveiled CL1, a hybrid chip designed to help scientists study brain function in real-time. The 800,000 lab-grown neurons on the chip are kept viable for six months via a built-in life support system. IEEE SpectrumAging is a complex biological process affecting our cells, tissues, and organsWith each passing decade, researchers uncover additional causes and effects of this seemingly unstoppable process. This visually stimulating video dives into our current understanding of aging, complete with the biological hallmarks researchers use to study aging at the cellular level (biological age). Science in MotionEpigenetic clock: DNA alterations on cells that predict biological ageEpigenetics refers to a biological process that controls whether certain genes are expressed or not. With a rising interest in the concept of biological age, researchers have discovered a cellular change known as DNA methylation that leaves a fingerprint on our genome as we age. FoundMyFitnessChronological versus biological ageScience has come to understand different types of aging. What we call age is simply the number of years since birth, or chronological age. At the cellular level, biological aging happens at different rates for different people, and explains why some seem to age more quickly (or slowly). The ConversationWhy are women more likely to suffer autoimmune diseases than men?A majority of Americans with autoimmune diseases have more than one X chromosome, a typical marker of the female biological sex, according to a study published in February of 2024. During fetal development, cells side with one X chromosome over the other, preventing the overproduction of X-chromosome-specific proteins and shutting down the twin chromosome. This article explores how this X-chromosome inactivation can lead to autoimmune disorders by generating antibodies to the body's own tissues. Stanford UniversitySeven things you might not know about bloodThe red stuff currently pumping throughout your body is a type of connective tissue that is both a solid and a liquid. The liquid portion—plasma—acts as a carrier for the solid portion, which includes blood cells and their biological brethren. Your body is constantly refreshing its supply of blood, creating new cells to replace those that have expired or died. This article overviews some lesser-known facts about blood (and why it's not always red). The ConversationThese cells 'taste' danger, trigger immune responsesTaste receptor-coated tuft cells are found throughout the body, where they communicate with and take part in a growing list of biological processes. In the intestines, these taste receptor-studded cells can sense byproducts of parasite metabolisms. This causes the taste receptors to release chemicals that alert the immune system, order nearby goblet cells to produce mucus, and trigger muscle contractions in attempts to launch the parasites from the intestines. Quanta MagazineHow does your body turn food into energy?Cells get energy via a process known as cellular respiration, which involves turning glucose into ATP or adenosine triphosphate. Breaking the phosphate bonds of ATP results in usable energy being released into cells, which can then use that energy to power biological processes. This 10-minute video explains how glucose turns into ATP, giving the body the energy it needs to survive. YouTubeThe secret lives of cellsCutting-edge microscopy has revealed previously unseen interactions of biological molecules within their cellular environment, enabling scientists to observe and analyze the molecules in a holistic view. This podcast explains the minute advancements made over the last few decades in observing cells, revealing how scientists have come and what the future holds for the field. Nature
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