Indholdsfortegnelse for Understanding Biology i Understanding Biology

Biology is the branch of science that explores all living organisms and the processes that create and govern them. It studies the animal kingdom, humans, plant life (including fungi and moulds) and the tiny world of microbiology, including microorganisms like bacteria and viruses, and the cells that make up the building blocks of all living things. In this book, from the makers of How It Works, you’ll discover more about these branches of biology and some of their key processes, like evolution, hormones, germ theory and photosynthesis, along with many other fascinating aspects of the study of life.…

1 Rupture Ecdysis begins when a membrane connecting the crab’s thorax and abdomen ruptures. 2 Head separates The head of the crab divides from the thorax and the abdomen, revealing the start of a new head. 3 Abdomen splits The abdomen underneath the crab breaks away from the new body, creating enough space for the crab to escape the old shell. 4 Slipping out of the legs The legs of the crab, called the pereiopods, are pulled free from the old shell. 5 Final push In the last phase of ecdysis, the abdomen is fully withdrawn. 6 Free at last Once the claws, also known as the chela, are free from the shell, ecdysis is complete.…

Pinched nerve Excessive pressure from nearby tissue, including spinal discs, can ‘pinch’ nerves and interfere with their signalling. This results in pain, tingles, weakness or numbness as the nerve misfires Disc bulge Spinal discs rest between the vertebrae of the spine, where they act as shock absorbers. They are formed of a softer centre and tougher outer band. As we age, cartilage in the disc dries and stiffens and the outer layer bulges. lateral disc herniation When the outer layer of the spinal disc ruptures, it’s known as a herniation, which allows the softer centre of the disc to ooze out. In laterally herniated discs, this places pressure on the nerve root of the spinal cord. central disc herniation Central herniation can place excessive pressure on the spinal cord, causing…

1 Milking A single dairy cow can produce around 28 litres of milk per day, which is extracted via vacuum cups attached to the udders. 2 Temperature Milk is typically heated to around 74 degrees Celsius for 20 seconds. 3 Pasteurisation Milk-filled pipes are surrounded by water at two different temperatures – one to heat the milk and the other to cool it back down to four degrees Celsius. 4 Destruction The proteins and enzymes in spoilage icroorganisms are denatured and broken down, ultimately killing them. 5 Separation Milk is spun to separate and remove fat to make the variety of milks on store shelves, such as semi-skimmed. 6 Homogenisation Pressure is applied to the milk to prevent cream separation and to blend the mixture together. 7 Storage Pasteurised milk…

The smallest object visible to the naked eye is a human egg cell. It measures just 0.1 millimetres in length. Beyond that limit, the world is completely invisible. Nanotechnology is the field of science and engineering at a scale of one to a hundred nanometres. That’s a thousand to a hundred thousand times smaller than the smallest thing we can see. Particles at this tiny scale behave completely differently to the full-size structures we are used to. Gold changes colour from yellow to purple and becomes liquid at room temperature. Carbon transforms into an extraordinary electrical conductor. And copper gains the ability to kill bacteria. Discovering this invisible world and harnessing its power is the domain of nanotechnology. The first person to measure and name a nanoparticle was Richard Zsigmondy.…

Factory production Many microplastics are produced in factories, such as pellets and powders. Other products are broken down into microplastics after entering the ocean. Beach litter The plastic we see washed up on beaches is only a a small part of the problem. Tiny pollutants Combined, small particles in the oceans are equivalent to around 30 billion 500-millilitre plastic water bottles. River entry Microplastics travel into oceans through rivers, but sometimes these plastics are caught in riverbeds for several years. Floating debris Around one per cent of microplastics in the ocean, such as those containing polypropylene, float at the surface and are easily transported by currents. Negative buoyancy When microplastics sink, they are often mistaken for food by marine animals. Bed burial Microplastics can be buried under layers of sediment,…

The term ‘biodegradable’ is often used to describe a material’s ability to be broken down naturally by the environment through a process known as biodegradation. During this process, organic matter, such as that found in plants and animals, is torn apart, broken down and digested by fungi and microbes. What remains is a nutrient-rich biomass that fuels the growth of new plants and animals in a repeating and self-sustaining process – it’s quite literally the circle of life. One of the most important aspects of biodegradation is the transfer of carbon. Often referred to simply as the carbon cycle, this natural undertaking helps regulate the planet’s temperature, as well as provide food and energy to its inhabitants. During the cycle, carbon is exchanged with oxygen in the atmosphere through plant…

Mount Read Huon pine colony 10,500 years old West Tasmania, Australia The ancestry of the Huon pine plant family, Podocarpaceae, can be traced back to 200 million years ago through fossilised plant pollen records. But despite being called a pine, the Huon pine is actually another type of coniferous tree with scale-like leaves called a Podocarpus tree. In Tasmania, there’s one clonal population of this tree that covers an area of 10,000 square metres. Even though it’s a large population each one stemmed from a single male Huon pine tree that grew over 10,500 years ago. This makes it the world’s oldest colony of genetically identical trees. Today, each of these individual trees is an exact replica of the original, which shed its branches and so multiplied in number. After…

Miracle berries (Synsepalum dulcificum) are native to the tropical regions of West Africa but have been cultivated around the world for their miraculous abilities. Despite being tasteless, miracle berries possess a protein that transforms the taste of other acidic or bitter foods. After chowing down on these berries, they will make taking a bite out of a lemon taste like you’re drinking the sweetest lemonade and make a swig of apple cider vinegar bearable. The mysterious powers of the fruit come from a natural sweetener called miraculin. When ingested, miraculin binds to the sweet taste receptors on the tongue for up to around 60 minutes. When a bitter-tasting food comes into contact with the miraculin, it changes shape, causing the sweet receptor to think it’s come across a molecule from…

Like many of the plants on Earth, grass is mostly green. This is because there are millions of cells called chloroplasts in every blade of grass. Within these cells is a pigment called chlorophyll. We see grass as green because it is one of the few visible wavelengths from the Sun that chlorophyll doesn’t absorb. Instead, after sunlight reaches grass, the green wavelengths are reflected off the plant. So when they reach our eyes, we see grass as green. But the main role of these cells isn’t to look pretty. Grass gets its green colour as a consequence of one of the plant’s most vital processes – photosynthesis. Within chloroplasts, the green-giving pigments absorb large amounts of light so that they can use its energy to produce glucose for food.…

There are plenty of species of plants around the world that contain substances that could either kill you or cause you harm. However, there are also some species where humankind has figured out ways to bypass or remove them, making the plants safe to eat. For thousands of years, Aboriginal groups in northern Australia have been eating plant seeds that are so toxic that, when ingested, just two are strong enough to kill a canine. These potent plants are called cycads and can be found in tropical and subtropical regions around the world. The seeds of these plants are filled with a toxin called cycasin, which can wreak havoc on the human body. Once inside the body’s digestive system, intestinal bacteria alter the cycasin, releasing a toxic metabolite called methylazoxymethanol.…

The world’s mould species belong to the fungi kingdom. However, the two are distinctly different. Most fungi can be either multicellular or unicellular organisms, feasting on organic matter such as the carbon and glucose content found in decaying leaves. Moulds, on the other hand, are only ever multicellular organisms, which tend to extract nutrition from many different sources. There are more than 100,000 different species of moulds on Earth, many of which can be found in your home. As part of their reproductive cycle, moulds release their version of seeds, called spores. Moulds release hundreds of thousands of these, which measure between 1.0 and 40 micrometres, into the air – for comparison, the diameter of a human hair is 70 micrometres. Some of the spores will find a new home…

For around 3.7 billion years, life has followed a roadmap of evolution. The journey to modern-day life and the more than 2.16 million known species that reside on Earth has been guided by several different evolutionary pathways. The naturalist known as ‘the father of evolution’, Charles Darwin, first proposed the theory of evolution by natural selection after he jumped aboard the HMS Beagle in 1831 and sailed around the world for five years. On his travels, he discovered diverse wildlife, observing that they had anatomy specially adapted to their environments. He concluded that a species’ survival depends on traits that suit its environment. This survival-of-the-fittest approach means that only animals with beneficial characteristics can continue to reproduce and pass them onto their offspring. Darwin proposed that through forces of evolution,…

Many creatures throughout the animal kingdom undergo a process of physical transformation called moulting. Whether they create ghostly serpent sleeves as a result or just ditch clumps of old skin and fur, shedding is an important stage in an animal’s growth and survival. The terms moulting and shedding are often used interchangeably, but there’s a slight difference between each process. Moulting is the removal of an animal’s entire skin, feathers, shell or exoskeleton as it grows, which often occurs on a seasonal basis. For example, elephant seals (Mirounga leonina) undergo what is known as a ‘catastrophic moult’ during late summer. As dramatic as it sounds, the ‘catastrophic’ nature of these moults merely relates to the large patches of skin that shed at one time. During this time, blood flow within the…

Neurons are the agents of signalling in our bodies, but they don’t work alone. Axons, which carry signals away from the neuron’s cell body, are coated in a sheaf of myelin. Myelin sheaves are produced in the central nervous system by cells called oligodendrocytes, enabling myelin’s function of protecting and facilitating nerve conductivity. In multiple sclerosis, a severe abnormal immune response within the central nervous system strips away the protective myelin and subsequently causes lots of nerve scarring, or sclerosis, which gives the disease its name. Research efforts are underway to treat the disease by encouraging myelin regeneration. Peripheral neuropathy While several degenerative disorders primarily or exclusively impact the central nervous system, there are a collection of diseases that instead impact the peripheral nervous system, called peripheral neuropathies. As the impacted…

Diabetes Diabetes occurs when the body is unable to produce the hormone insulin or use it effectively. This can lead to dangerously high blood sugar levels. Diabetes can occur in two forms: type 1 is an autoimmune condition that tends to develop in childhood or teen years. The body’s immune system attacks cells in the pancreas, stopping the production of insulin. With type 2 diabetes, the body becomes resistant to insulin, causing a spike in blood sugar levels. Unlike type 1 diabetes, type 2 tends to occur in adults and can sometimes be brought about by eating too many sugary foods. Both type 1 and type 2 can be caused by a combination of genetic and environmental factors. Symptoms can include feeling exceptionally thirsty, having blurry vision, needing to urinate…

1 B cell These are covered with antibodies. When they come into contact with an antigen in the blood or the spleen, they immediately bind to it. 2 B cell army Once a B cell has bound to the antigen, it rapidly multiplies with the same antibodies. 3 Send in the antibodies The B cells begin producing thousands of antibodies and release them into the blood. 4 Memory cells Some B cells stay away from the fighting to preserve their antibodies in case of a future attack. 5 Marking the intruder The antibodies seek out the matching pathogen and bind to it. 6 Neutralisation By completely covering the pathogen with antibodies, the pathogen is unable to bind to healthy cells and infect them. 7 Call in the big guns Antibodies…

Household bleach is a bactericide; it kills bacteria on contact. It’s one of the cheapest and most powerful microbe busters on the planet. But how does it work? The bleach under your sink is a solution of sodium hypochlorite, which has the chemical formula NaClO. That means that each molecule contains one sodium atom, one chlorine atom and one oxygen atom. In water it produces hypochlorous acid (HOCl), which can steal electrons from other molecules. It uses this ability to attack bacteria and viruses, breaking their proteins apart and splitting them open. Hypochlorous acid also damages pigment molecules, turning them white, which is where bleach gets its name from. In its pure form, bleach is extremely corrosive. It has a pH of 13, making it just about as alkaline as…

“A rotating magnetic field can make a helical robot spin” 5 Facts Nanotech that already exists 1 Computer processors The processor that powers your computer or your phone contains hundreds of tiny switches called transistors. Each one measures less than ten nanometres across. 2 Quantum displays  Ultra-high-definition QLED screens contain tiny nanocrystals called quantum dots – the Q in QLED stands for quantum. They contain nanoscale semiconductors that emit different coloured light depending on their size. 3 Molecular printers It’s now possible to 3D print at nanoscale using an AI-powered scanning tunnelling microscope. The powerful piece of kit can pick up and lay down molecular building blocks. 4 Flexible screens Advances in nanotechnology have made it possible to bend, roll and even fold electronic screens. They use flexible plastic polymers and ultrafine conductive…

1 Methuselah 4,854 years old In the White Mountains of California, a chunky bristlecone tree reaches to the sky like a twisted claw. The bends of each branch are the final remnants of the tree, which germinated before the Egyptian pyramids were built. Only a small portion remains living, and continues to bear pinecones and needles. It measures 70 metres tall and has a diameter over eight metres at ground level. 2 Sarv-e Abarkuh 4,500 years old This bushy evergreen can be found at the heart of Yazd, Iran, in the ancient city of Abarkuh. The Persian cypress tree symbolises long life and beauty in Iranian culture and is likely to be the oldest living organism on the Asian continent. 3 Llangernyw Yew 4,000 years old Since the Bronze Age,…

Rotting onions, old socks, bin juice and raw sewage are all ways in which the smell of the durian fruit (Durio zibethinus) has been described. The smell of durian is so potent that consumption of the fruit has been banned on public transport in Singapore, and in some hotels in Thailand. A durian’s scent stems from its ripened pulp and is the result of the release of a combination of more than 50 compounds, including an odorous sulphur-smelling chemical called ethanethiol. On their own the individual compounds aren’t particularly powerful in their odours, nor does any smell like a durian. However, when they all come together they create the symphony of durian smell. The reason behind the odorous nature of this fruit is like any other: to entice animals that…

1 Rhizoid The root-like anchor of the mould, this releases digestive enzymes into the substance below. 2 Stolon The horizontal network of hyphae from which spore-carrying bodies emerge. 3 Sporangiophores The stalks that hold the spore nurseries, called sporangia. 4 Sporangia At the apex of the sporangiophores are the spherical ‘fruits’ that house the mould spores. 5 Spores The spores are the mould’s reproductive cells. They float through the air, land on more bread to multiply and form new mould. The miracle fungus If you’ve ever had a serious bacterial infection, you’re likely to have been treated with a little white pill made from mould. Discovered by chance in 1928, Penicillium chrysogenum can fight invading bacterial forces and prevent them from regrowing. While studying Staphylococcus bacteria, Dr Alexander Fleming discovered…

Slowly crawling along the forest floor are a diverse group of organisms we’ve come to know as slime mould. These unusual life forms were once thought to be a type of fungus. However, scientists have discovered that they belong to another group called Protozoa. This group of organisms includes free-moving single-celled organisms such as amoebae. Once slime mould has matured, it will cease to move and bear sporangia ‘fruits’, similar to moulds. These fruits will then release spores that will go on to grow into new slime moulds. However, unlike mould and other fungi, slime moulds don’t have penetrating hyphae to dig into wood and extract nutrients. Instead their amoeba-like movements allow them to freely crawl their way along the surfaces of plants and trees, engulfing bacteria along the way.…

Slow loris and cobra These furry tree climbers are surprisingly similar to snakes and have evolved to mimic some of their notable traits. The slow loris is one of the only known mammal species to produce venom for defence, which it secretes from a gland in its elbow and then licks to create a venomous saliva in its mouth that coats its teeth. When threatened, the slow loris hisses and will cross its arms over its head, making its face, complete with large eyes, resemble the shape and markings of a cobra. Wasps inside figs Figs produced by the fig tree (Ficus carica) are known as an inflorescence, not a fruit, where the inside of its bulbous body is full of clusters of small flowers and seeds. With its flowers…

1 Hormones Days before shedding begins, hormones are released throughout the snake’s body that trigger ecdysis. 2 Cell proliferation During moulting, all the cells in the snake’s outermost layer, called the epidermis, rapidly increase in numbers. 3 Differentiation Cells called keratinocytes change to form new layers that make up the snake’s epidermis. 4 Terminal differentiation The old epidermis breaks away from the hardest surface layer of the snake’s skin, called the oberhautchen. 5 Eyes During the moulting stage, the eyes first turn a milky blue colour as the spectacle cap separates. 6 Head stretching With its vision impaired, the snake carefully rubs its head on an abrasive surface to form a tear in the epidermis. 7 Snake skin undress Crawling through tight spaces and weaving through rocks and plants causes…

If you’ve ever wondered why you never seem to get any taller while your friends are regularly growing out of their clothes, why your skin always breaks out in spots when you want to look your best and why you’re always hungry no matter how much you eat, you need look no further than your hormones. But what exactly are hormones, and why do they seem intent on interfering in almost every aspect of your life? In simple terms, hormones are chemical molecules that act like an internal postal service. These specialised proteins carry vital messages around the body via the bloodstream – thanks to the circulatory system and a strong, beating heart – to their target cells, where they give out clear instructions. Different types of hormones will give…

Every day your immune system is working tirelessly to fend off harmful invading pathogens such as bacteria and viruses. Our understanding of the immune system began in the late-19th century when Russian zoologist Élie Metchnikoff identified a group of white blood cells called phagocytes, whose purpose is to seek out, engulf and eliminate pathogens. During the same period, the discovery of antibodies and their role in neutralising pathogens also came to light thanks to German physiologists Emil Behring and Paul Ehrlich. Since then, scientists from around the world have come to understand the complexity of our immune system and the many ways it has evolved to fight off bacterial baddies and villainous viruses. Part of our immune system is passed on to us as newborns from our mothers through the…

The process of pasteurisation is a centuries-old method of preparing food, giving it a longer life in larders and today on supermarket shelves. Since the 11th century, people have been using heat to battle against microorganisms to preserve their food. Ancient Chinese wine makers used hot clay jars to heat wine before burying them in cool soil to preserve them. However, it wasn’t until the late-19th century that a name was attributed to this process. Pasteurisation is used to combat the harmful pathogens that reside within raw foods, often referred to as spoilage microorganisms. These can be transferred to our bodies when we consume these foods in their raw state. Pathogens such as E. coli and Salmonella can be found in raw milk, and when ingested can cause serious health…

Could lab-grown meat be the compromise that settles the conflict between meat-eaters and vegetarians? For more than 2.5 million years humans have eaten the flesh of other animals. During this time, the world’s agriculture industry has boomed, with 26 per cent of Earth’s ice-free land dedicated to livestock, which comes at a cost to the environment. On average, the livestock industry is responsible for around 18 per cent of global greenhouse gas emissions. To help minimise environmental impact and reduce the space needed to house livestock, scientists have started growing food far from the fields, inside their laboratories. Scientists care for a collection of tiny cells that have been extracted from the genuine article without the need to slaughter a living animal. A small sample of stem cells, typically taken…

Plastics are made from materials such as oil and plant minerals found naturally on Earth, but the end product itself is entirely unnatural. This synthetic product can now be found in every corner of the world, in remote places like the deep ocean and Antarctica, and even inside our bodies. This is because plastic doesn’t fully decompose. Every piece of plastic produced still exists in some form, even if it’s out of sight. In most instances, plastic products have been broken down into microplastics, tiny fragments that have been reduced to a length of five millimetres or less, too small to see with the naked eye. The first evidence of microplastic pollution was discovered in the oceans, where scientists have estimated that there are 24.4 trillion microplastic particles in the…

Mussel power In 2021, studies carried out at the UK’s Plymouth Marine Laboratory found that mussels – and in particular their poop – could help scientists remove microplastics from rivers and estuaries. The experiment, which focused on blue mussels, uncovered that because these creatures can filter microplastic pieces out from their bodies and into their faeces, they become buoyant when excreted. By using this method, a quarter of all waterborne microplastics that these mussels encounter can be released to the water’s surface for collection. The scientists discovered that 300 blue mussels can filter out 250,000 microplastics per hour using this method. Since the experiment, trials have begun to find an effective system for mussel microplastic removal. These involve submerging masses of mussels in containers, with nets attached to collect the…

Hheat and maize are used to make bread, pizza and other delicious foods, but in a few years they could also power your car. Renewable biofuels could soon replace the harmful fossil fuels that we’re used to using. It’s now well-established that fossil fuels are incredibly harmful to our health and the environment, and they’re not renewable, either. When so many people rely on petrol and diesel to power vehicles, it makes sense to develop a renewable alternative that’s easy to use. That’s where biofuel comes in. The most common biofuel produced globally is ethanol, and it’s used frequently in Brazil and the US, while biodiesel is more popular in Europe. Ethanol is a clear, flavourless alcohol that’s created by fermenting and distilling sugary crops like wheat, corn and sugar…

The world is full of interesting and delicious fruits. From sour grapes to giant pumpkins, there are around 2,000 different types of fruits growing around the globe. In botanical terms, a fruit is a ripened ovary, a reproductive structure that bears the plant’s ovule, also known as the seeds. Once a plant is pollinated, fruits begin to emerge from the fertilised flower and develop, mature and ripen, by which time the encapsulated seeds are ready for dispersal. When it comes to identifying fruits, there are a whole host of subcategories they fall into. However, they largely sit within one of three categories: simple, aggregate and multiple. Simple fruits include the majority of fruits, such as stone fruits, pome and berries. Their anatomy is typically divided into three parts; the exocarp,…

In many parts of the world, the end of the summer season is marked by drastic changes in the trees’ appearance. Leaves of red, orange, yellow and brown dance through the breeze before landing to create a crunchy layer on the ground. Autumn can produce distinctive colours, but for some plants it’s a time to take drastic action for survival. Evergreens aside, trees have very thin leaves. To keep them attached throughout winter would be dangerous as they would freeze – their cells would rupture and lose vital nutrients. The usual food-making process of converting sunlight and carbon dioxide into sugars is put on hold. The production of green cells called chloroplasts that enable this process is halted and nutrients are absorbed into the core of the tree to be…

Spices have been part of human diets for thousands of years, and chilli peppers are now staple ingredients in many parts of the world. Chilli peppers are fruits and are part of the nightshade family, which contains members such as tomatoes, avocados and potatoes. Within this family lies the genus Capsicum that hosts peppers, a group of related species that are carefully cultivated to produce fruits with a spectrum of flavour and heat. From the mild bell pepper and the lively jalapeño to the unrelenting brutality of the Trinidad Moruga scorpion and Carolina reaper, peppers come in all ranges of spiciness. The heat, or pungency, of a chilli pepper is a product of its DNA, the environment it’s grown in and its ripeness. DNA can be changed by cross-breeding two…

1 Mycelium These are root-like fungal structures from which mushrooms grow. They break down nutrients in the soil for food. 2 Button stage The first mushroom structure to appear above ground. It’s odourless, unlike its sweet-smelling adult form. 3 Volva The universal veil – a layer of tissue that once surrounded the baby mushroom – forms a bag at the base of the adult mushroom called the volva. 4 Mature mushroom A mature death cap mushroom will measure around 15 centimetres tall and have a domed white cap with a white stem. 5 Gills In the gills of the mushroom are structures called basidia that bear reproductive spores. 6 Spores Billions of spores are released from the gills, carrying the genetic information of the mushroom away. 7 Germination Just like…