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Who was the only member of genus Homo during nearly a million years?
According to scientists, Homo Habilis lived as the only member of genus Homo for nearly a million years.
This species with a slightly larger braincase and smaller face and teeth than older hominin species is widely considered to be the first member of the genus Homo that evolved from apes. But it still retained some ape-like features, including long arms and a moderately-prognathic face.
Its name, which means ‘handy man’, was given in 1964 because this species was thought to represent the first maker of stone tools. Currently, the oldest stone tools are dated slightly older than the oldest evidence of the genus Homo.
Researchers believe that Homo Habilis lived in Eastern and Southern Africa between 2,4 and 1,4 million years ago, its average height was 100-135 cm (3 ft 4 in – 4 ft 5 in) and its average weight was 32 kg (70 lbs).
Look at one of facial reconstructions of Homo Habilis ⬆️.
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What are some surprising facts about leap years?
ℹ️ 2024 is a leap year with an extra day on February 29.
✍️ Here are some interesting facts about leap years and February 29 ⬇️.
📍🗓 In his Julian calendar, Julius Caesar introduced the first leap year around 46 B.C., but this calendar had only one rule: Any year evenly divisible by four would be a leap year. That created too many leap years, but the math wasn't tweaked until Pope Gregory XIII introduced his Gregorian calendar more than 1,500 years later.
📍 All the other months in the Julian calendar have 30 or 31 days, but February lost out to the ego of Roman Emperor Caesar Augustus. Under his predecessor Julius Caesar, February had 30 days and the month named after him - July - had 31. August had only 29 days. When Caesar Augustus became Emperor he added two days to 'his' month to make August the same as July. So February lost out to August in the battle of the extra days.
📍 Without an extra day on February 29 nearly every four years, we would lose almost six hours every year. After only 100 years, our calendar would be off by approximately 24 days.
📍 People born on February 29 are called "leaplings" or "leapers".
📍 The odds of being born on a leap day are 1 in about 1500.
📍🔮 Astrologers believe people born on February 29 have unusual talents
📍🇮🇹🇬🇷🇷🇺🏴 Some countries, e.g. Italy, Greece, Russia and Scotland, consider Leap Year and Leap Day to be the unluckiest of times.
📍💍 In some countries, it's OK for a woman to propose to a man on February 29.
📍🐸 In some countries, the frog is a symbol associated with February 29.
📍🇺🇸 The twin cities of Anthony, Texas, and Anthony, New Mexico, are the self-proclaimed Leap Year Capital of the World. They hold a four-day leap year festival that includes a huge birthday party for all leap year babies. (ID required.)
📍🇫🇷 🗞 Since 1980, a special French newspaper has only been published on Leap Day. La Bougie du Sapeur is only available on February 29, and it usually outsells all other newspapers on that day.
📍🎂 Many companies don’t recognize Leap Day as a “valid day.” They make leapers choose Feb. 28 or March 1 as their birthday instead.
📍🫰💳 Most employees who are paid fixed monthly incomes will work for free on Feb. 29 because their wages are likely not calculated to include the extra day.
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Why is International Polar Bear Day celebrated on 27 February?
🐻❄️International Polar Bear Day was first initiated in 1994 by Polar Bear International.
📌This non-profit organization founded the day to coincide with the time period when polar bear moms and cubs are snug in their dens.
🐻❄️Each year, in early January, polar bear females give birth to tiny helpless cubs in a snow den where they spend several months until cubs are big and strong enough for a life in the Arctic.
ℹ️Polar bears, the largest carnivorous land animals, are considered a keystone species in the Arctic ecosystem, playing a crucial role in maintaining the balance of their habitat. However, they are facing numerous threats, primarily due to human activities and climate change.
International Polar Bear also serves
📌as a platform to promote conservation measures that can help to safeguard the future of the Arctic
📌as a reminder of the importance of collective efforts to protect this vulnerable species.
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Why is the Earth an ever-changing landscape?
🔺 The theory of plate tectonics, developed during the mid-20th century, revolutionized scientific understanding of the Earth’s dynamics. It proposes that the Earth’s lithosphere consists of several tectonic plates that float on the semi-fluid asthenosphere beneath.
🔺 There are seven major plates ⬆️⬇️
1️⃣The African Plate
2️⃣The Antarctic Plate
3️⃣The Eurasian Plate
4️⃣The Indo-Australian Plate (sometimes divided into Indian Plate and Australian Plate)
5️⃣The North American Plate
6️⃣The Pacific Plate
7️⃣The South American Plate
There are also smaller plates like the Nazca, Cocos, Scotia, Caribbean, Arabian, and Philippine Sea Plate.
🔺 The largest plates, like the Pacific and Eurasian plates, span thousands of kilometers across. Smaller plates are just a few hundred kilometers across.
🔺 Plates’ size and shape continually change over geological time due to the dynamic nature of plate tectonics.
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What is Earth made of?
🌐 Earth is made up of several layers.
🌏 Earth's layers can be assigned according to chemical composition (what they're made of) or mechanical properties (rock strength and elasticity) ⬆️.
🌍 According to chemical composition Earth's layers are
☑️ the core
☑️mantle, the largest and thickest layer, making up 84% of the planet's total volume
☑️ crust
🌎 According to mechanical properties, Earth's layers are
☑️ the lithosphere, divided into oceanic crust (primarily composed of dark basalt rocks rich in elements such as silicon and magnesium) and continental crust (made of light-colored granite rocks containing oxygen and silicon)
☑️ asthenosphere
☑️ lower mantle (also known as mesospheric mantle),
☑️ outer core
☑️ inner core
ℹ️ The term lithosphere is derived from the Greek words "lithos," meaning stone, and "sphaira," meaning globe or ball.
ℹ️ The term asthenosphere originates from the Greek "asthenes" meaning weak.
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What are some fascinating facts about pollen?
🟡 Not All Pollen Types Trigger Allergies
Pollen is an allergen and plants that release it into the air, such as ragweed, oaks, elms, maple trees, and grasses, are most often responsible for triggering allergy in humans, having a hypersensitivity to this type of pollen. However, because most plants that flower transfer pollen via insects and not via the wind, flowering plants are not typically the cause of allergic reactions.
🔴 Plants Use Trickery to Spread Pollen
Flowers that have white or other light colors are more easily seen in the dark by nocturnal insects like moths. Plants that are lower to the ground attract bugs that can't fly, such as ants or beetles. Some plants also cater to insects' sense of smell by producing a rotten smell to attract flies. Still, other plants have flowers that resemble the females of certain insects to lure males of the species.
🟠 Plant Pollinators Can Be Large or Small
When we think of pollinators, we usually think of bees. However, a number of insects such as butterflies, ants, beetles, and flies and animals such as hummingbirds and bats also transfer pollen. Two of the smallest natural plant pollinators are the fig wasp and the panurgine bee. The female fig wasp, Blastophaga psenes, is only about 1.55mm ( in length. One of the largest natural pollinators happens to be the black and white ruffed lemur from Madagascar.
🟤 Pollen is the Primary Source of Protein for Bees
The protein content of pollen varies between 2.5% and 61%, depending on the plant species. For context, beef is approximately 26% protein.
🟣 Pollen Contains the Male Sex Cells in Plants
Pollen is the male sperm producing gametophyte of a plant. A pollen grain contains both non-reproductive cells, known as vegetative cells and a reproductive or generative cell. In flowering plants, pollen is produced in the anther of the flower stamen. In conifers, pollen is produced in the pollen cone.
⚪️ Pollen Grains Must Create a Tunnel for Pollination to Occur
In order for pollination to occur, the pollen grain must germinate in the female portion (carpel) of the same plant or another plant of the same species. In flowering plants, the stigma portion of the carpel collects the pollen. The vegetative cells in the pollen grain create a pollen tube to tunnel down from the stigma, through the long style of the carpel, to the ovary. Division of the generative cell produces two sperm cells, which travel down the pollen tube into the ovule. This journey usually takes up to two days, but some sperm cells can take months to reach the ovary.
🟢 Pollen Is Required for Both Self-Pollination and Cross-Pollination
In flowers that have both stamens (male parts) and carpels (female parts), both self-pollination and cross-pollination can occur. In self-pollination, sperm cells fuse with the ovule from the female part of the same plant. In cross-pollination, pollen is transferred from the male portion of one plant to the female portion of another genetically similar plant. This helps in the development of new species of plants and increases the adaptability of plants.
🔵 Some Plants Use Toxins to Prevent Self-Pollination
Some flowering plants have molecular self-recognition systems that help prevent self-fertilization by rejecting pollen produced by the same plant. Once pollen has been identified as "self", it is blocked from germination. In some plants, a toxin called S-RNase poisons the pollen tube if the pollen and pistil (female reproductive part or carpel) are too closely related, thus preventing inbreeding.
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Why is February 15 important for science?
📌 February 15 is important for modern science as it is Galileo Galilei’s birthday.
📌 Galileo (1564-1642) ⬆️ was an Italian natural philosopher who made several major contributions to scientific progress.
📌 Before Galileo, science was not considered a profession. Typically, people who did ‘science’ were considered natural philosophers and held positions as medical doctors, mathematicians or priests with extra time on their hands.
📌 Galileo was one of the first to express the belief that the basic laws of science could be broken down into mathematics.
📌 🔭 He studied speed and gravity to predict paths of projectile motion. He was among the first to take a closer look at the skies above with a telescope.
📌 His life is generally used as the beginning point of the history of modern science.
📌 His philosophy of observing first, explain second and then observe some more would become the foundation of the modern scientific method.
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How the longest-lived mammals resist cancer?
Massive creatures like whales have roughly 1,000 times the number of cells humans do, but their rates of cancer are much lower. This inconsistency, called Peto’s paradox, has long puzzled scientists.
Bowhead whales ⬆️ are the longest-lived mammals on Earth, with a life span that can exceed 200 years. In 2023, researchers may have discovered one of the keys to their longevity.
In the study, researchers severed both strands of the DNA molecule in cells from humans, cows, mice and bowhead whales. This kind of damage, called a “double-strand break,” is known to increase cancer risk.
The research showed the whales’ ability to repair DNA. Proteins called CIRBP and RPA2 were much more common in bowhead whales and may play a role in this gene repair.
Scientists say, this one of the most important biological discoveries of 2023 can help fight cancer.
ℹ️The bowhead is also the second-largest animal on Earth, reaching over 80,000 kg.
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How does the Vangunu giant rat look like?
🐀🏝🇸🇧 The Vangunu giant rat (Uromys vika or U. vika) from the South Pacific island of Vangunu in the Solomon Islands was first described ⬆️ in 2017, when one representative of the species was found dead after loggers took out a section of forest.
✍️ It was the first new species of rodent described in the Solomon Islands in more than 80 years.
⚠️ Due to logging of its lowland forest habitat this one of the world’s rarest giant rodent was considered critically endangered and researchers long feared that it had gone extinct.
❎ For several years, periodic efforts to scientifically identify and document this species were fruitless.
✅ Recently, researchers finally captured images of four of these creatures ⬆️.
🐀🥥🏝 The Vangunu giant rats are about twice the size of common rats, and can chew through coconuts.
🙏🌳🌴 According to scientists, the future of the species relies on the preservation of Zaira primary forests.
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What cells have the unique ability to develop into other cell types?
Our body is made up of many different types of cells, most of which are ‘specialized’ – with different functions. E.g., red blood cells are specialized to carry oxygen in the blood, while some gut cells are specialized to absorb nutrients from food.
However, there are also stem cells that have the unique ability to develop into other specialized cell types.
Stem cells are different from other cells in several ways:
✔️ They can divide and renew themselves over a long time
✔️ They are unspecialized, so they cannot do specific functions in the body
✔️ In a developing embryo, they can develop into any type of cell.
✔️ Once the body is grown, they can develop into specific cell types, to replace old or damaged cells.
ℹ️ The concept of a stem cell was first proposed by researchers working on embryonic development in the nineteenth century. They saw such cells as the starting point for biological processes.
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What are critical functions of meiosis?
Meiosis has several critical functions in organisms:
1️⃣ Production of Gametes is one of the primary functions. In animals, these gametes are the sperm and egg cells. In plants, meiosis leads to the formation of spores, which then develop into gametophytes that produce gametes.
2️⃣ Halving the Chromosome Number:
The chromosome number of a species remains constant from one generation to the next. By reducing the chromosome number by half, gametes form with a haploid (n) set of chromosomes. When two gametes fuse during fertilization, this restores the diploid (2n) number of chromosomes in the zygote, ensuring genetic stability across generations.
3️⃣ Promotion of Genetic Variation in multiple ways:
▪️Crossing-over: During prophase I, homologous chromosomes undergo crossing-over, where sections of chromatids exchange places. This results in new combinations of genes on each chromatid.
▪️ Independent Assortment: During metaphase I, how the pairs of homologous chromosomes line up at the metaphase plate is random. This means that different combinations of maternal and paternal chromosomes end up in each gamete.
▪️ Random Fertilization: The fusion of any sperm with any egg during fertilization adds another layer of genetic variability.
4️⃣ Evolutionary Significance:
The genetic variation introduced by meiosis provides raw material for natural selection. Organisms with advantageous genetic combinations are more likely to survive and reproduce, passing on those beneficial genes to their offspring. Over time, this leads to evolutionary changes in populations.
5️⃣ Repair of DNA Damage:
Before entering meiosis, cells undergo DNA repair mechanisms. If there’s damage to the DNA, the processes within meiosis, especially recombination, help correct certain types of damage. This ensures that genetic information passes to the next generation as accurately as possible.
6️⃣ Prevention of Chromosomal Abnormalities:
Gametes receive the correct number of chromosomes. Errors in this process lead to conditions like Down syndrome, where an individual has an extra chromosome 21.
✍️ Summary: meiosis maintains the chromosome number across generations, generates genetic diversity, aids in evolutionary processes, repairs DNA, and prevents chromosomal abnormalities.
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What happens if cells do not go through all checkpoints?
Not all cells go through all checkpoints of the cell cycle. Some fast-track through certain phases. Also, the time it takes for cells to complete the cycle varies. In humans, it ranges from two to five days for epithelial cells to an entire lifetime for certain neurons and cardiac cells.
Disruption in these regulatory checkpoints can lead to cells with damaged or missing genetic material.
Deregulation of the cell cycle can have grave consequences. When the checkpoints fail, it can result in:
🆘 Cells with incomplete or damaged DNA.
🆘 Uncontrolled cell division.
This uncontrolled division and growth of cells leads to the formation of tumors. Not all tumors are malignant, but those that are can invade nearby tissues and spread to other parts of the body (metastasis), leading to cancer ⬆️.
ℹ️ Cancer is a disease in which some of the body’s cells grow uncontrollably and spread to other parts of the body.
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How is the proper growth and replication of cells ensured?
The process which is vital for the growth, development, repair, and maintenance of living organisms is called the cell cycle. It is a series of events that cells go through to grow, replicate their DNA, and divide.
The two broad phases of the cell cycle are:
1️⃣ Interphase, during which cells grow, replicate their DNA and organelles, and prepare for division.
2️⃣ Mitosis, a process of cell division that results in two genetically identical daughter cells from a single parent cell.
ℹ️ The term “mitosis” was coined by Walther Flemming (1843-1905) in 1882 while documenting the process of chromosomal division in salamander larvae. The term comes from the Greek word ‘mitos’ meaning ‘thread,’ referring to the thread-like appearance of chromosomes during mitosis. Other names for the process are ‘karyokinesis’ (Schleicher, 1878) and ‘equatorial division’ (August Weismann, 1887).
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How scientists were discovering the cell?
While the invention of the telescope made the Cosmos accessible to human observation, the light microscope opened up smaller worlds, showing what living forms were composed of.
🔬 The cell was first discovered and named by an English “natural philosopher” Robert Hooke (1635-1703) in 1665. Using three lenses and a stage light, he improved the design of his compound microscope ⬆️, which allowed to see tiny pores in a piece of cork. Hooke came to call his discovery “cells”, “small rooms” in Latina, because they reminded him of the cells in a monastery. However, Hooke didn't realize at that time that “cells” could be alive.
🔬🦠 The first man to witness a live cell was a Dutch scientist, often called the “father of microscopy”, Anton van Leeuwenhoek (1632-1723), who, in 1674, described the algae Spirogyra and also protozoa and bacteria that he called “animalcules”. He was also the first to observe and describe spermatozoa in 1677.
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What are key eukaryote features?
Plant and animal cells ⬆️ are examples of eukaryotic cells.
They have a true nucleus and membrane-bound compartments with specific functions – organelles.
Here are key eukaryote features ⬇️
Nucleus: contains DNA and oversees all cell processes
Nucleolus: site of ribosome biogenesis
Plasma membrane: encloses the cell
Cytoplasm: region between the nuclear and the plasma membranes
Cell wall: supports and protects plant, algae, and fungi cells
Centrosomes and Centrioles: play a role in cell division
Mitochondria: provide chemical energy
Chloroplasts: traps energy for photosynthesis in plant cells
Lysosomes: digests excess or worn-out organelles, food particles, and engulfed viruses or bacteria
Ribosomes: perform protein synthesis
Endoplasmic reticulum (ER): synthesizes proteins (rough ER) and lipids (smooth ER)
Golgi apparatus: sorts, packages, and processes proteins
Vesicles and vacuoles: membrane-bound storage and transportation sacs
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How many early human species existed on Earth?
The answer to this question depends on the definition of a human, the definition of a species and the degree to which you accept variation within a species.
Most experts agree that our species, Homo sapiens (Latin for “wise men”), may be the ninth and youngest human species.
H. habilis: the handyman (2.4 million – 1.4 million years ago)
H. erectus: the enduring hiker (1.89 million to 110.000 years ago)
H. rudolfensis: the stranger (1.9 million to 1.8 million years ago)
H. heidelbergensis: the hunter (700,000 to 200,000 years ago)
H. floresiensis: the Hobbit (100,000 to 50,000 years ago)
H. neanderthalensis: The Neanderthal (400,000 – 40,000 years ago)
H. naledi (335,000 to 236,000 years ago)
H. luzonensis (at least 67,000 years ago)
Some scientists say that there were up to twenty early human species.
There is also a growing debate about whether H. sapiens, Neanderthals and Denisovans are in fact all one species.
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What is the importance of February 28 for India?
🇮🇳🗓 Since 1986, every year in India, National Science Day is observed on February 28.
This date is related to the time period in 1928 when Indian Physicist Chandrasekhara Venkata Raman (1888-1970) ⬆️ announced discovery of the Raman Effect, or the Raman scattering.
The Raman Effect is the phenomenon where light gets scattered when passed through a transparent material, leading to changes in wavelength and energy.
CV Raman also received the Nobel Prize in Physics in 1930 due to his significant contribution in this field of science.
The day aims to raise awareness about the importance of scientific applications in our daily lives.
The day also aims to celebrate and acknowledge the efforts and achievements of scientists in human welfare.
The theme for National Science Day 2024 is - Indigenous Technologies for Viksit Bharat.
💬✍️"Success can come to you by courageous devotion to the task lying in front of you." - CV Raman
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What happens when tectonic plates meet?
The edges where tectonic plates meet are known as plate boundaries ⬆️
There are three main types:
1️⃣Convergent Boundaries (Destructive Boundaries/Active Margins): Plates move towards each other, forming either a continental collision or else a subduction zone where one plate moves under the other⬆️. The oceanic plate always subducts beneath the continental plate.
2️⃣Divergent Boundaries (Constructive/Extensional Boundaries): Plates move apart.
3️⃣Transform Boundaries (Conservative/Strike-Slip Boundaries): Plates slide past each other along transform boundaries. The motion of the plates relative to each other is either sinistral (left side toward the observer) or dextral (right side toward the observer).
Sometimes over time it isn’t easy to define just one boundary type.
🗻Mountains form primarily at convergent boundaries.
🌋Volcanoes can occur at both convergent and divergent boundaries.
Plate boundaries also cause earthquakes.
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What are Earth’s layers interesting facts?
🔘 Inner core is at the very center of Earth.
✔️ Radius: 1,221 km (759 miles)
✔️ Temperature: About 5,200 degrees °C (9,392 degrees Fahrenheit)
✔️ Pressure: Nearly 3.6 million atmospheric pressure (atm)
✔️ State: Solid
✔️ Composition: Mostly iron and some nickel
🔁 Inner core rotates in the same direction as the surface of the planet but rotates ever so slightly faster, completing one extra rotation every 1,000 years or so.
⚫️ Outer core is sandwiched between the inner core and the mantle. The boundary between the inner and outer core is known as the Lehman Seismic Discontinuity.
✔️ Thickness: 2,300 km (1,400 miles)
✔️ Temperature: Between 4,500 degrees °C and 5,500 degrees °C (8,132 degrees F and 9,932 degrees F).
✔️ State: Fluid
✔️ Composition: Iron and nickel
🧲 The swirling motion of the outer core generates Earth's magnetic field in a process called geodynamo. Magnetism inside Earth's core is approximately 50 times stronger than it is on the surface. Eventually, the entire core will solidify and Earth's magnetic field will cease to exist. That will be bad news for our planet as the magnetic field protects us from harmful cosmic radiation. We still have a few billions of years of protection left though.
🔴 The mantle can be divided into the upper and lower mantle (also known as the mesospheric mantle), with the upper mantle containing two distinct regions: the asthenosphere and the lower portion of the lithosphere.
✔️ Thickness: Approximately 1,800 miles (2,900 km)
✔️ Temperature: 3,700 degrees °C to 1,000 degrees °C (6,692 degrees F to 1,832 degrees F)
✔️ State: Solid
✔️ Composition: Magnesium, silicon and oxygen
🌡 The immense pressure keeps this layer solid despite the high temperatures capable of softening the rocks. Though geologists are yet to agree on a definitive structure of the lower mantle.
💎 Diamonds are forged within the mantle approximately 150 to 200 km (93 to 124 miles) below the surface.
🟥 The asthenosphere is a 110 miles (180 km) thick layer of the upper mantle that sits between the lower mantle and the lithosphere.
✔️ Temperature: 1,500 degrees °C (2,732 degrees F)
✔️ Thickness: 180 km (110 miles)
🪨 Rocks in the asthenosphere are "on the verge" of melting.
🟫 The lithosphere is the outermost layer of Earth, composed of the crust and the brittle part of the upper mantle.
✔️ Depth: 8 to 32 km (5 to 20 miles)
✔️ Temperature: Range from 0 to 500 degrees °C (32 to 932 degrees F).
↔️ The boundary between the brittle part of the upper mantle and the crust (both oceanic and continental) is known as the Mohorovičić Discontinuity (Moho), which depth varies from about 8 km (5 miles) below oceanic crust to 32 km (20 miles) below continental crust.
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How bananas may be used to fight the plastic waste crisis?
🛍 Plastic bags take up to 20 years to decompose. With very little plastic being recycled, most end up in landfills or littered in the greater environment, creating serious environmental consequences. Finding a plastic-like alternative that will decompose relatively quickly would go a long way in fighting the ongoing plastic waste crisis.
🍌ℹ️ Bananas are the fourth most grown crop in the world, trailing only rice, wheat and corn, and almost 36 million tons of banana peels are produced yearly.
🍌➡️🛍 According to a new study, banana peels may be utilized to create biodegradable films and one day replace plastic as the dominant food packaging material.
✅ A produced film was strong, transparent, and more importantly, biodegradable within 30 days at 21% soil moisture content ⬆️.
✔️ Further research will look to improve the film's flexibility and investigate the scalability and commercialization of this preparation process.
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Is Pollen always yellow?
🟨 Pollen is the fertilization agent of plants and the essential element for the survival of many plant species. It is responsible for the formation of seeds, fruit.
🟨 Pollen is a botanical term that referred to "the fertilizing element of flowers" and was first used as long ago as 1760 by Carl Linnaeus. it has come to be known as "fine, powdery, yellowish grains or spores."
🟨 🟥🟪🟫 Though pollen is associated with the color yellow, pollen can come in many vibrant colors, including red, purple, white, and brown ⬆️.
🟨 Since insect pollinators such as bees, can't see red, plants produce yellow (or sometimes blue) pollen to attract them. This is why most plants have yellow pollen, but there are some exceptions. For instance, birds and butterflies are attracted to red colors, so some plants produce red pollen to attract these organisms.
ℹ️ The scientific study of living and fossilized pollen grains is known as palynology.
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When were the first books made?
This papyrus fragment ⬆️, unearthed at the Egyptian site of El Hibeh in 1902, began as a bound document dating to 260 B.C. that recorded taxation rates for beer and oil scrawled in Greek letters using black ink.
Having used modern microscopic and multispectral imaging, researchers now believe that it is part of the world’s first book. And, like many of the ancient volumes, it has had many lives.
According to scientists, this sheet of papyrus was first bound within an ancient manuscript. It was then removed from its binding and sent as a letter to a creditor or a debtor before being transformed once again and reused as wrapping for a mummy during the Ptolemaic period (304–30 B.C.).
The oldest book previously known being from the first or second century A.D., the discovery pushes the origins of bookbinding back by about 400 years and shows that the structure of the book, as opposed to a scroll, existed well before researchers thought.
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What is Peto’s Paradox?
In a multicellular organism, cells must go through a cell cycle that includes growth and division.
Every time a cell divide, it must copy its millions/billion base pairs of DNA, and it inevitably makes some mistakes. These mistakes are called somatic mutations.
If every cell division carries a certain chance that a cancer-causing somatic mutation could occur, then the risk of developing cancer should theoretically increase with both the number of cells and the lifespan of an organism.
However, multiple studies showed that gigantic animals do not only get more cancer than humans, but actually even get less, suggesting that super-human cancer suppression has evolved numerous times across the tree of life. This is the essence and promise of Peto’s Paradox ⬆️.
Peto’s Paradox is named after a British epidemiologist Richard Peto (1943-), who noted the relationship between time and cancer when he was studying how tumors form in mice.
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How many types of stem cells are there?
Today, researchers classify three types of stem cells (SC).
The two types of SC ⬆️ are ‘natural’:
1️⃣Embryonic SC supply new cells for an embryo as it grows and develops into a baby. Being ‘pluripotent’, they can change into any cell in the body.
2️⃣ Adult SC replace old or damaged cells as an organism grows. Being ‘multipotent’, they can only change into some cells in the body – not all cell types, because they have already started to specialize, so can only develop further into a specific type of cell.
The third type ⬆️ is ‘artificial’.
3️⃣ Induced pluripotent SC (or ‘iPS cells’) are made in the laboratory. Normal adult cells (often skin cells) can be reprogrammed to become stem cells. This is called ‘inducing’ the stem cells. iPS cells are pluripotent so can, theoretically, like Embryonic SC, develop into any cell type.
ℹ️ In medicine, stem cells are used to replace cells and tissues that have been damaged or lost due to diseases.
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Mitosis vs Meiosis: what are main differences and similarities?
Both being vital for cell division in eukaryotes, mitosis and meiosis are however fundamentally different in their functions and outcomes ⬆️.
✅ Similarities
Both mitosis and meiosis:
📍 begin with a single parent cell;
📍 have an interphase stage where DNA replication occurs;
📍 have similar fundamental stages such as prophase, metaphase, anaphase, and telophase.
🆚 Differences
📍 Meiosis ensures genetic diversity and the continuity of species through sexual reproduction, while mitosis facilitates growth, repair, and maintenance of an organism.
📍 Both mitosis and meiosis start out with DNA replication, but with different ultimate goals.
Mitosis has one round of cell division, while meiosis has two rounds.
📍 While mitosis yields two daughter cells that are genetically identical (2n) to the parent cell, meiosis produces four haploid (n) cells that are genetically different from the parent cell.
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Which type of cell division is crucial for sexual reproduction and genetic diversity?
🟢↔️🟢 A type of cell divison that ensures genetic diversity and the continuity of species through sexual reproduction is called meiosis.
It is the process that is not part of the cell cycle and where a cell replicates DNA once but divides twice, producing four cells that have half the genetic information of the original cell. It is how organisms produce gametes or sex cells, which are eggs in females and sperm in males.
Meiosis involves 2️⃣ divisions, so it’s typically broken down into meiosis I and meiosis II ⬆️.
✔️ Cells enter meiosis I from interphase, which is much like interphase in the cell cycle. When cells commit to meiosis, DNA replicates. It consists of:
Prophase I
Metaphase I
Anaphase I
Telophase I
✔️ Meiosis II is similar to mitosis but involves the division of haploid cells. It consists of:
Prophase II
Metaphase II
Anaphase II
Telophase II
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What are cell cycle phases in detail?
1️⃣ Interphase, the period preceding mitosis, is the longest phase of the cell cycle and has three distinct sub-stages.
🔻G1 Phase (Gap 1): right after cell division cells increase in size, produce RNA and synthesize proteins. Importantly, this phase ensures that everything is in place for DNA synthesis to occur in the next phase.
🔻S Phase (Synthesis): the cell’s DNA replicates, and at the end of this phase, each chromosome consists of two chromatids attached at the centromere.
🔻G2 Phase (Gap 2): the cell continues growing and prepares for mitosis, ensuring that all the DNA has been replicated without any errors.
2️⃣ Mitosis or the M phase, has multiple steps:
🔻Prophase: Chromosomes condense and become visible, the nuclear envelope starts to disintegrate, and the mitotic spindle begins to form.
🔻Metaphase: Chromosomes line up along the cell’s equatorial plate, and spindle fibers attach to the centromeres.
🔻Anaphase: Sister chromatids are pulled apart towards opposite poles of the cell.
🔻Telophase: The chromatids or chromosomes move to opposite ends of the cell and two nuclei form.
🔻Following mitosis (or as its final step), the cell undergoes cytokinesis where the cytoplasm divides, creating two daughter cells.
⚪️ The G0 phase is a “resting” phase where the cell exits the cell cycle and stops dividing. Some cells, like neurons and muscle cells, enter this phase semi-permanently and may never undergo division again. It is crucial for:
✔️Conserving energy and resources in non-dividing cells.
✔️Specializing cells for specific functions.
✔️Regulation of the Cell Cycle:
🟩 Checkpoints tightly regulate the cell cycle to prevent errors:
✅ G1 Checkpoint ensures that the cell has adequate energy resources and that the surrounding environment is favorable for DNA replication. If conditions aren’t right, the cell can exit to G0 phase.
✅ G2 Checkpoint confirms that DNA has replicated properly.
✅ M Checkpoint (Spindle Assembly Checkpoint) occurs during metaphase in mitosis and ensures that all chromosomes properly align and attach to the spindle fibers.
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How the scientific study of cells was founded and developed?
ℹ️ Cytology or Cell biology is the scientific study of cells.
📍 German scientists Theodore Schwann (1810–1882) and Mattias Schleiden (1804–1881) studied cells of animals and plants respectively. They identified key differences and similarities between the two cell types and in 1838-39 put forth the idea that cells were the fundamental units of both plants and animals. Thus, Schwann and Schleiden are generally regarded as the first scientists to establish cell theory.
☑️ However, both Schwann and Schleiden misunderstood how cells grow.
▪️ Schleiden believed that cells were “seeded” by the nucleus and grew from there.
▪️ Similarly, Schwann claimed that animal cells “crystalized” from the material between other cells. He summarized his observations into three conclusions about cells:
✅ The cell is the fundamental unit of structure, physiology, and organization in living things.
✅ The cell retains a dual existence as a distinct entity and a building block in the construction of organisms.
❌Cells form by free-cell formation, similar to the formation of crystals (spontaneous generation).
Today it is known that the first two tenets are correct, but the third is clearly wrong.
📍 Another piece of the cell theory puzzle was identified by another German researcher Rudolf Virchow (1821-1902) in 1855, who stated that all cells are generated by existing cells – Omnis cellula e cellula: “All cells only arise from pre-existing cells”.
📍 The key tenets of the modern cell theory are:
✅ All known living things are made up of cells.
✅ The cell is the structural & functional unit of all living things.
✅ All cells come from pre-existing cells by division. (Spontaneous Generation does not occur).
✅ Cells contain hereditary information, which is passed from cell to cell during cell division.
✅ All cells are basically the same in chemical composition.
✅ All energy flow (metabolism & biochemistry) of life occurs within cells.
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What are differences and similarities between prokaryotes and eukaryotes?
Prokaryotes are primitive organisms lacking a nucleus and membrane-bound organelles. The term ‘prokaryote’ is derived from the Greek words ‘pro’, meaning ‘before’ and ‘karyon’, meaning ‘kernel’ – ‘before nuclei’.
Eukaryotes are advanced organisms with a well-defined nucleus and membrane-bound organelles. The term ‘eukaryotes’ is derived from the Greek words ‘eu’, meaning ‘good’ and ‘karyon’, meaning ‘kernel’ – ‘true nuclei’.
The main differences and similarities between prokaryotic and eukaryotic cells are given above ⬆️.
ℹ️ According to scientists, cells, which were very simple prokaryotes, started forming on Earth at least 3.5 billion years ago. Eukaryotes are supposed to arose from symbiosis between prokaryotic cells. Eventually, an ancestral prokaryote endosymbiosed other cells, which became mitochondria and chloroplasts. The origin of other organelles is less clear.
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What is found inside a prokaryotic cell?
A prokaryotic cell ⬆️ is usually small and relatively simple in structure.
Its components are ⬇️:
Capsule: layer of carbohydrates that surrounds the cell wall of some bacteria and helps them attach to surfaces
Cell wall: consists of peptidoglycans that give the cell structure and protection
Cell/plasma membrane, which encloses the cytoplasm and separates the cell from the environment
Cytoplasm: region enclosed by the cell membrane, where genetic material and processes occur
Nucleoid: region that contains DNA
Plasmids: independently reproducing DNA
Ribosome: performs protein synthesis
Flagella: thin, tail-like structures that aid movement
Pili/sex pilus: short, rod-shaped structures involves in attachment to surfaces and DNA transfer
Fimbriae: thin, hair-like structures used for attachment
Vesicles: sacs released by the membrane that perform a variety of functions
Vacuoles: storage sacs found in some bacterial cells
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