Wonders of Life, Brian Cox, 2013


But as is so often the case in the natural world, the superficial beauty of these butterflies is immeasurably enhanced by a deeper scientific understanding of their life cycle and biochemistry, and the reasons for their form and function.

The point of all this is to demonstrate that it takes a large amount of energy to split water into hydrogen and oxygen. Water is a very stable molecule.

In July 2011 NASA announced the discovery of the largest, most distant reservoir of water ever detected. A gigantic cloud of H2O containing 140 trillion times more water than all the Earth’s oceans combined, was sighted 12 billion light years away.….This reservoir is therefore very ancient and proves that life giving water is not only abundant, but had been present in the Universe for a large fraction of its lifetime.

The pond skater’s back pair of legs spreads the animal weight over a wider areas. The strong bonds between the water molecules help to prevent the insects from breaking the surface. Every square millimeter of its body is covered with tiny hairs that increase the surface area still further. These hairs are also hydrophobic, making the whole animal water resistant. The tiny hair traps air, adding buoyancy.

Fruit fly, bat sees in ultraviolet, snakes see in infrared.

Melanin is a complex molecule able to form polymers with varying structure depending on their location in the body. It’s active heart, however, is a series of rings of carbon atoms bound together by a sea of mobile electron. When high energy photon from the sun hits one of the electrons, it does not break the molecule apart. Instead the energy is dissipated in around a pico second. In that period the photon has been absorbed and converted into heat. Melanin is so efficient that 99.9% of the harmful UV radiation is absorbed in the way, protecting cells from damage.

The composition of the young earth’s atmosphere is unlikely that it was able to absorb such high levels of UV radiation (because the Sun’s outer layer were much hotter than they are today – hotter surface radiate more of their energy in the high energy, short wavelength part of the spectrum, in the ultraviolet). This suggest that it would have been necessary for life to deal with an intense UV onslaught, which may in turn have driven the evolution of pigments at a very early stage in its history.

Bacteria are prokaryotes, which means they do not have cell nucleus (same with archea). Eukaryotes have more complex structures. Biologist believe that they have emerged from prokaryotes around 2 billion years ago and that the change happened only once.

All life on earth stores energy in the same way, as a molecules called adenosine triphosphate, or ATP. This suggests that ATP is a very ancient invention, and the details of its production and function could provide clues as to life’s origin 4 billion years ago. Photosynthesis is about storing energy and making sugars.

Endosymbiosis allows for great leaps in the capability of living things – a merger of fully formed skills to produce a result greater than the sum of the parts. We owe the beauty of life on earth to cyanobacterium whose ancestors found their way inside another cell. The descendant of that cell are still present inside every leaf, every blade of grass, and the have filled our atmosphere with oxygen.

It is known that oxygen levels first increased on Earth around 2.4 billion years ago, a time when many great banded iron formations were laid down. This rise may have been triggered by the complete oxidation of the iron and other element, which until that time acted as a sink, removing the photosynthetic oxygen from the atmosphere as quickly as the bacteria could release it.  This is one plausible scenario…

First mammals around 225 million years. There is an explosion of complexity in the fossil record associated with the Cambrian period, 530 million years ago, which may have been related to a rise in oxygen levels. The first evidence of complex multicellular life appears around 600 million years ago in the form of the Ediacaran biota (Ediacaran hills in Australia). It has been suggested that they were neither animals, nor plants, nor fungi but some failed evolutionary experiment. Before the earliest Ediacaran fossils – 655 million years ago – the next major milestone occurred around 2 billion years ago with the emergence of the eukaryote life. Around 3.5 billion years ago we find the first prokaryotes.

Eukaryote emerged only once. There is no evidence of different version of eukaryote cell emerging from bacteria or archaea during the 4 billion-year tenure on Earth. Everybody agrees that eukaryotes is a chimera, formed by endosymbiosis. Evidence lies in the mitochondria, found in the majority of eukaryote cells today, and responsible for the generation of ATP through respiration. Eukariotes share genes with both prokaryote branches – bacteria and archaea – which suggest that they are the result of a merger of two prokaryote cells.

One of the most important chemical processes in living things: the use of proton gradients, or waterfalls. A high concentration of protons on one side of a membrane can be used to power things. A battery consists of 2 half cells, one with an abundance of negative ions and the other with an abundance of negative ions. If the two half are connected this allows the ions to flow.

The vents would also have been rich in organic materials and minerals such as iron and nickel, which are held in high concentrations in porous chambers suspended in the middle of a powerful, naturally occurring proton waterfall. (The Lost City is seawater is highly alkaline and the Earth’s ocean water at the time were mildly acidic – this means a proton deficient water surrounded by proton rich oceans). Our common ancestor was not a cell but a set of chemical reactions occurring inside a small chamber of rock, rich in organics and lined with naturally occurring catalysts, suspended in naturally occurring proton waterfall. Life put a bag around the already established chemistry and floated away.

Endosymbiosis has certainly happened more than once in the history of life. Chloroplast inside all green plants and algae were once free living cyanobacteria. But the fusion of an ancient cell with a bacterium skilled in control of proton gradients and the efficient production of ATP via aerobic respiration may have been the origin of eukaryotic cell itself.

Thermodynamics: the first law deals with conservation of energy; energy can’t neither be created nor destroyed. The second law introduces entropy: at absolute zero (-273°C) all substances have zero entropy. Entropy always increases, never decreased. A heap of atoms have more entropy than a tea cup, because there are more ways of arranging atoms to form a heap rather than to form a tea cup. A teacup can easily be turned into a heap (increased entropy) but a pile of atoms will never assemble into a tea cup (which would be decrease in entropy). Life is a notable exception.  The ability to build complexity spontaneously – to lower the entropy of a group of atoms – might be taken as the defining property of life.  This is the Schrodinger paradox: life seems in contradiction with the second law of thermodynamic.

In gradient rich and ingredient rich environment of vents, complex molecules – more complex than sugars – form. The emergence of complexity is not a mystery. It is a feature of systems that are “far from equilibrium”, places where there are waterfalls to power the building process. The emergence of complex systems speeds up the equalization of all gradients (temperatures, PH etc.) helping to maximize the entropy of the universe. Gradients don’t last long in nature as they soon balance out.

At face value, the emergence of life is an inevitable consequence of the laws of classical thermodynamics.

Isolated from predators, Golden jellyfish – in Palau – have greatly reduced sting. They are less reliant on zooplankton than other jellyfish. They rely directly on photosynthesis for nourishment. They host photosynthetic algae as symbionts inside their domes. They “dance” around the lake in order to keep the algae illuminated. Those algae are also found living in corals and anemones. Jellyfish engulf algae as juvenile and algae make up to 10% of the jellyfish biomass.

Insects don’t have lungs and don’t transport the oxygen around in the blood as we do. Instead they rely on system of tubes, called trachea, connected to holes in their bodies.. Oxygen enters through those holes, and carbon dioxide is expelled. An animal volume, and therefore the amount of living tissue requiring oxygen, increase as the cube of its size.

In the universe, all atoms are the same size because of fundamental constants of nature are same everywhere. This imposes a non-negotiable limit on the size of living things in our universe, and that limit will be close to 0.2 microns, the size of the smallest free-living bacterium cells on earth.

For larger animals, the problem is not heat loss so much as heat build-up: large endotherms are in danger of cooking themselves from within because they cannot dissipate heat fast enough. This is one of the limiting factor that constrains the size of the largest animals.

Large animals have slower metabolic rates: why? One reason is that there is constraint at work which limits the metabolic rate of each cell in large animal. This could also be due to the way that supply networks such as blood vessels branch out from the animal’s core to its extremities. As more and more branching occurs, the supply of fuel to the cells at the edge of the network becomes compromised. The cell within large animal may have been forced to operate at a lower metabolic rate. Another maybe that because large animals retain more of their internal heat, their cells evolved to run at a lower rate. Ultimately the bigger you are, the longer you live.

The paramecium has no nervous system or brain, and yet it has a rudimentary sense of touch; when it bumps into something, it changes its behavior.  This biomechanical mechanical underlying this reaction is known as an action potential. It is near universal, very ancient and it is also electrical.

Thunderstorms demonstrate a simple physical process that is central to the operation of action potentials: charge separation.

Cell use their membrane potential for two main purposes: one is as a battery, processing different processes in the membrane itself. The other is for the transmission of signals via action potentials, which lie at the heart of animal senses. Flows of sodium ions are pumped out of the membrane through the membranes (and potassium ions are pumped into the cell) allow a net negative charge to build up along the interior side of the membrane, and a positive charge to accumulate on the outer side. When a paramecium bumps into an obstacle, its membrane is deformed. This opens ions channels in the membrane, allowing ions to flood back into the cell. The membrane potential become less negative.  Calcium channel closes and potassium channel closes re-establishing the membrane potential. At lower calcium concentration, the cilia beats forward but as calcium rises, they reverse, and the paramecium change direction.

Hairs attached to the basilar membrane (inner ear) pick up the vibrations (due to sound) and through the familiar process of opening ions channels and depolarization of membrane, action potentials travel along the nerves to the brain.

Action potentials are fast and reliable means of transmitting information, traveling along nerve cells at over 100m/s, and shape and intensity of the pulse does not change over long transmission distances.

A few species – bats, dolphins – have developed hearing as a means of seeing. This echolocation is one of the reasons that they have adapted to hear and produce sounds in very high frequencies which allows them to identify very small object.

The water surface is a near perfect reflector of sound waves: over 99.9% of the power bounces back. Thanks to the three ear bones, vibrations of the eardrum is transmitted into the inner ear (resulting in 60% of the sound being transmitted).

The underlying biochemistry of light detection turns out to be near-universal, and this strongly suggest a common evolutionary origin.

We possess rods and cones: rods for black and white, cones for color at different wavelength. All of these use the same biochemistry – the use of a family of molecules called rhodopsin. Photons enter the eye and are absorbed by rhodopsin molecules. This causes a changes to the molecules which results in an action potential being generated and whisked off down the optic nerve into the visual cortex. Rhodopsin is universal. Every eye in every animal on the planet uses rhodopsin (or closely related molecules). Our common ancestor with the mantis shrimp is 540 million years old and yet we share the same basic visula machinery, based on rhodopsin. But rhodopsin may be an invention that predates all animals by a long, long time. Volvox is a single celled green algae that can be found in freshwater ponds all over the world. Each single volvox has a flagella and a tiny red spot – an eye spot, photo sensitive that control the beating of the flagella. When the eye spots are stimulated by bright light, the flagella stops. When the light dims, the flagella move and the algae search for more light.  This microscopic visual system is based on a form of rhodopsin.

Model shows that to go from a single eye spot (rhodopsin molecules formed into a flat retina) to a complex camera eye is about half a million year. Eyes are not the mind-bogglingly complex things we might imagine. It has happened many times since the Cambrian explosion. And All are based on rhodopsin.

IN the case of compound eyes, the multiple lenses can be wired up so that the eye itself carries out a great deal of visual processing without having to trouble the brain. Thanks to this insects can react extremely fast to visual stimuli. Toads pre process visual data within the eye: photoreceptor cells are connected so that they only send a signal to the brain when a very specific pattern of movement is detected. And it detect things moving horizontally (worms) and dancing black blods (flies). It can react quickly because the brain is not used. But toads will starve if left in a tank full of dead worms.

We have measured the universe and found that the part we can see is 93 billion light year across.

Lignin is even tougher than cellulose. Rather than being composed of long chain, it is cross-linked into complex lattice structures comprising many tens of thousands of atoms. Wood with high lignin content is extremely resistant. There are no animal enzymes that can digest lignin. Termites grow a fungus in there mound that breaks down lignin (after termites have ingested it once) into a form that can be digested. Temperature and humidity within the mound are controlled to allow the fungus to grow – with conditions that were in place in tropical forest in the distant past. This is how lignin is returned to the food chain.