My Science School

All cells have a cell wall, hut in plant cells this is made of a stiff, tough layer of cellulose. Cellulose is made of tiny fibres, layered together to form a strong sheet. Most plant cells also contain organelles called chloroplasts. It is in these that photo-synthesis takes place.

Animal cells and plant cells are similar in that they are both eukaryotic cells. These cells have a true nucleus, which houses DNA and is separated from other cellular structures by a nuclear membrane. Both of these cell types have similar processes for reproduction, which include mitosis and meiosis. Animal and plant cells obtain the energy they need to grow and maintain normal cellular function through the process of cellular respiration. Both of these cell types also contain cell structures known as organelles, which are specialized to perform functions necessary for normal cellular operation. Animal and plant cells have some of the same cell components in common including a nucleus, Golgi complex, endoplasmicreticulum, ribosomes, mitochondria, peroxisomes, cytoskeleton, and cell (plasma) membrane. While animal and plant cells have many common characteristics, they are also different.

Size

Animal cells are generally smaller than plant cells. Animal cells range from 10 to 30 micrometers in length, while plant cells range from 10 and 100 micrometers in length.

Shape

Animal cells come in various sizes and tend to have round or irregular shapes. Plant cells are more similar in size and are typically rectangular or cube shaped.

Energy Storage

Animal cells store energy in the form of the complex carbohydrate glycogen. Plant cells store energy as starch.

Proteins

Of the 20 amino acids needed to produce proteins, only 10 can be produced naturally in animal cells. The other so-called essential amino acids must be acquired through diet. Plants are capable of synthesizing all 20 amino acids.

Differentiation

In animal cells, only stem cells are capable of converting to other cell types. Most plant cell types are capable of differentiation.

Growth

Animal cells increase in size by increasing in cell numbers. Plant cells mainly increase cell size by becoming larger. They grow by absorbing more water into the central vacuole.

Cell Wall

Animal cells do not have a cell wall but have a cell membrane. Plant cells have a cell wall composed of cellulose as well as a cell membrane.

Centrioles

Animal cells contain these cylindrical structures that organize the assembly of microtubules during cell division. Plant cells do not typically contain centrioles.

Cilia

Cilia are found in animal cells but not usually in plant cells. Cilia are microtubules that aid in cellular locomotion.

Cytokinesis

Cytokinesis, the division of the cytoplasm during cell division, occurs in animal cells when a cleavage furrow forms that pinches the cell membrane in half. In plant cell cytokinesis, a cell plate is constructed that divides the cell.

Glyoxysomes

These structures are not found in animal cells but are present in plant cells. Glyoxysomes help to degrade lipids, particularly in germinating seeds, for the production of sugar.

Lysosomes

Animal cells possess lysosomes which contain enzymes that digest cellular macromolecules. Plant cells rarely contain lysosomes as the plant vacuole handles molecule degradation.

Plastids

Animal cells do not have plastids. Plant cells contain plastids such as chloroplasts, which are needed for photosynthesis.

Plasmodesmata

Animal cells do not have plasmodesmata. Plant cells have plasmodesmata, which are pores between plant cell walls that allow molecules and communication signals to pass between individual plant cells.

Vacuole

Animal cells may have many small vacuoles. Plant cells have a large central vacuole that can occupy up to 90% of the cell's volume.

Prokaryotic Cells

Animal and plant eukaryotic cells are also different from prokaryotic cells like bacteria. Prokaryotes are usually single-celled organisms, while animal and plant cells are generally multicellular. Eukaryotic cells are more complex and larger than prokaryotic cells. Animal and plant cells contain many organelles not found in prokaryotic cells. Prokaryotes have no true nucleus as the DNA is not contained within a membrane, but is coiled up in a region of the cytoplasm called the nucleoid. While animal and plant cells reproduce by mitosis or meiosis, prokaryotes propagate most commonly by binary fission.

Other Eukaryotic Organisms

Plant and animal cells are not the only types of eukaryotic cells. Protists and fungi are two other types of eukaryotic organisms. Examples of protists include algae, euglena, and amoebas. Examples of fungi include mushrooms, yeasts, and molds.

Everything in the universe is mare of atoms, arranged in different ways. But living things, unlike rocks or metal, have larger building blocks called cells. Some living things have only one cell, while others contain millions. Each cell has a job to do, but they all work together to make a living organism.

Living organisms are made up of cells. Cells are the structural and functional units of a living organism. In 1665, Robert Hooke discovered the existence of cells using a microscope, which further paved way for the discovery of various other microscopic organisms. Some organisms consist of a single cell, for example, the amoeba. Other organisms are multicellular, having millions of cells.

A single cell is able to produce many cells through a process known as cell division. Different organisms have different kinds of cells. A human body alone shows various kinds of cells such as – blood cells, nerve cell, fat cell etc. Shapes and sizes of cells depend upon the functions they perform. Amoeba has an ever-changing shape as it changes form to locomote. Some cells have a fixed shape and perform a specific function, such as nerve cells, which are usually shaped like trees.

An organism is any being that consists of a single cell or a group of cells, and exhibit properties of life. They have to eat, grow and reproduce to ensure the continuation of their species. Organ systems collectively work together for the proper functioning of a living organism, failure of even one of these systems has an impact on our lives.

A fast-flowing river sweeps soil from the riverbed so that plants cannot grow there. On the other hand, there is more oxygen dissolved in the water, so that fish such as salmon thrive. Rivers in areas where the soil is peaty often have very little wildlife, because acid from the soil washes into the water.

Unlike temperature and dissolved oxygen, the presence of normal levels of nitrates usually does not have a direct effect on aquatic insects or fish.  However, excess levels of nitrates in water can create conditions that make it difficult for aquatic insects or fish to survive.

Algae and other plants use nitrates as a source of food. If algae have an unlimited source of nitrates, their growth is unchecked.  So, why is that a problem?

A bay or estuary that has the milky colour of pea soup is showing the result of high concentrations of algae.  Large amounts of algae can cause extreme fluctuations in dissolved oxygen.  Photosynthesis by algae and other plants can generate oxygen during the day. However, at night, dissolved oxygen may decrease to very low levels as a result of large numbers of oxygen consuming bacteria feeding on dead or decaying algae and other plants.

Eutrophication – “The process by which a body of water acquires a high concentration of nutrients, especially phosphates and nitrates. These typically promote excessive growth of algae. As the algae die and decompose, high levels of organic matter and the decomposing organisms deplete the water of available oxygen, causing the death of other organisms, such as fish.

Anoxia is a lack of oxygen caused by excessive nutrients in waterways which triggers algae growth. When the plants die and decay, oxygen is stripped from the water, which then turns green or milky white and gives off a strong rotten egg odour.  The lack of oxygen is often deadly for invertebrates, fish and shellfish.

Beavers are rodents with very long, sharp front teeth. They use their teeth to gnaw down small trees for use in dam building or for food. Beavers build dams of sticks and mud across a river. This makes a calm pool the other side of the dam in which the beaver can build its home, or lodge. The inside of the lodge is reached by means of underwater tunnels. This keeps the beaver safe from predators such as wolves, even when the surface of the water is frozen in winter.

Dam-building is synonymous with beavers, the ultimate aquatic engineers. Using branches from trees they have felled, these large rodents dam lakes to create moat-like ponds of still water where they construct islands known as ‘conical lodges’ out of timber, mud and rocks. The body of water surrounding the lodges provides protection from predators – resident beavers enter and exit their sophisticated homes incognito via water-filled tunnels leading from the lodges to the pond. The largest lodge, found in Alberta, Canada, measures over 500m in length – though contrary to a widely circulated myth, it is not visible from space! In deep or fast-moving water areas, beavers simply excavate into river banks and set up home there instead.

Beaver dam building is a pretty fascinating topic. Unfortunately, no-one really knows how beavers evolved, let alone how dam building behaviour evolved. Beavers appear to build dams for two main reasons: protection from predators and to provide a stable source of food and easy access to it for themselves.

This offers some clues about how they evolved – almost certainly as a response to selection pressures for these two reasons avoid predation, obtain food. These dams are made of branches stuck down into the stream bed and then built up with a thick mortar of mud, gravel and interwoven branches.

The dam is constantly maintained to keep the water at the same level for beaver comfort and security. Beaver dams are sometimes maintained and expanded over many generations. They can be up to 1,000 feet long and 15-20 feet high.

Beavers are famous for their logging skills, chiseling down trees up to 3 feet in diameter. However, they are not clever enough to aim a tree’s fall and on rare occasions a beaver has been crushed by a tree trunk. The beaver is a very powerful animal, capable of dragging a heavy log through the woods and down into the water.

Although they often lay hundreds or even thousands of eggs, some fish do build nests to protect their young. The stickleback, found in European ponds and rivers, builds a nest of plant fibres in which the male guards the eggs until they have hatched, chasing away even the female that laid them.

The most interesting habits of fishes are their parental behavior in guarding the eggs and caring the young ones. In Chondrichthyes, young ones hatch out in a fully developed condition. But, in Osteichthyes larvae hatch out from eggs and then metamorphose to young adults. In most cases these larvae are quite numerous and so chance will favor at least few of them to tide over adverse condition.

Nest and nursery building Nest building is the commonest method adopted by fishes to protect their eggs and young ones. It is exhibited mostly by fresh water fishes and also by marine fishes having demersal eggs. Nest building involves active participation of either males or females or both. The simplest form of nest building is exhibited by salmons, darters, sunfishes, cichlids, etc. Salmons select gravelly shallows of running streams as their spawning ground. Here they assemble in shoals. Female will make a nursery in the form of pit to lay eggs. After fertilization, she will cover them with layer of gravel. Similar method is adopted by Australian fresh water, Arius. In case of darters , sun fishes and cichlids males make shallow basin like dipressions on the bottom.

The male of N. American bowfin (Amia calva) constructs a crude circular nest of soft weeds and rootless amidst aquatic vegetation. Spawning takes place in the “weedy castle”. Sometimes later the young ones leave the nest in a swarm escorted by their watchful father. The male of N. American bowfin (Amia calva) constructs a crude circular nest of soft weeds and rootless amidst aquatic vegetation. Spawning takes place in the “weedy castle”. Sometimes later the young ones leave the nest in a swarm escorted by their watchful father.

The male of two-spinned stickle back builds an elaborate nest in fresh water, using twigs and weeds, fastened together by the threads of a sticky secretion from the kidney.

Nest building by female is rarely known. Female Heterotis has been shown to make nests in swamps. There are instances in which both the parents take part in nest building. Eg: Labrus Labrus.

Carrying the eggs on the body some fishes ensure protection to their eggs by carrying them safely either in the mouth or anywhere in the body. In Aspredo and Platystacus, the skin of the lower part of the female becomes smooth and spongy during breeding seasons. Fertilized eggs get attached to it.

 In some fishes like Arius and Tilapia mouth-brooding or buccal incubation is a characteristic property both the male and female carries eggs and young ones in their mouth. In oral incubation, the parent will not feed until young ones hatch out. male nursery fish krutus has a cephalic horn upon which female deposits grape like egg clusters.

Keeping the eggs in brood chambers in most species of Syngnathus, Hippocampus, siphonostoma, male has a brood pouch for the deposition of eggs. In Hippocampus, some sort of” placenta” may be formed for gas exchange between the father and the developing young ones. In syngnathus, brood pouch has a highly vascular spongy lining from which the developing young ones may draw nourishment. in unique pipe fish of Indian and pacific oceans, Salenostomus the inner side of the ventral fin of female coalesces with the integument forming a large pouch for keeping the eggs.

Coiling round the eggs The British gunnel or the butter fish has a peculiar way of parental care. The female roll the eggs to a ball and then curls around them. Often male may assist her in this process. Butter Fish.

Keeping the eggs in egg capsules Some chondrichthyes, gives maximum protection to eggs by enclosing them in an egg capsule. In Scyllium, Raja etc, fertilized eggs are kept in a specially designed horny egg capsule, popularly called “Mermaid’s purse”. Egg filled capsules get attached to aquatic weeds with the help of tendril like filaments. Development is completed inside the capsule, utilizing the yolk reserve. Young ones hatch out by breaking the capsule.

Oviposition means, act of laying or depositing eggs. It is mostly exhibited by central European bitterling. In this the genital papilla of the female serves as an ovipositor. With its help eggs may be introduced to the gill chamber of a pond mussel.  During this female takes to a vertical posture and spawning. Male swims around her and discharges sperms in to the mussel. Fertilization and development take place in the gill chamber and young ones leave the host later.

Several fishes provide maximum pre-natal protection to their embryos by adopting ovoviviparity. Here the development is internal and the special portion of the oviduct serves as an unspecialized uterus.  A true mammalian type of placenta is absent. Nutrition is given either by yolk reserve or the uterine milk which is secreted by uterine wall. Eg: for ovoviviparous chondrichthyes are scoliodon, sphyrna, pristis, stegastoma, squalus, mustelus, myliobatis, trygon pteroplatea,etc. Eg: for ovoviviparous osteichthyes are Gambusia,poicilia,blennis,allis,zoarces,cymogaster etc.

Freshwater habitats include both still and moving water. Living things within rivers and streams can travel through the water to different areas. Many underwater inhabitants of ponds and Lakes, however, cannot escape from what may be quite a small area of water. However, even a tiny pool may have a complete, self-contained ecosystem. As well as plants and fish, freshwater ecosystems support living things that visit the water but spend part of their lives on land, such as amphibians, birds and insects. Many mammals also spend time in and around the water. Finally, the kinds of wildlife found in freshwater ecosystems will be affected by the climate and landscape around it. For example, the crocodile may be the fiercest predator in an African river, but its place may be taken by an otter in a European stream.

Cast out your fishing line or scoop your net through the water. You are bound to catch something when you are along the river's edge or at the lake. Catching fish is always exciting, but while you wait for that fish to come along.

Freshwater ecosystems include lakes, ponds, rivers, streams, springs, and wetlands. You will find them in many different sizes, from very small to very large. The water within the ecosystem can be still (not moving), like in a pond, or it can be running (moving), like a river or stream.

Freshwater ecosystems are broken into three zones: littoral, open water and deep water - we'll talk more about these below. The plants and animals within the ecosystem interact with light, food, oxygen, weather, and climate in different ways.

Plants and animals grow in different zones in freshwater ecosystems. The littoral (or marsh) zone refers to the plants and animals that grow closest to the edge of the water. The plants in this area can make great hiding spots for animals to hide from predators. You might find snails, clams, or even eggs and larvae from reptiles and insects in this area. Common predators (animals who prey, or feed, on other animals) in this zone include snakes, ducks and swans.

The open water zone refers to plants and animals that live near the top of the water. Some float on top of the water and have tiny roots that go down into the water, like duckweed. Others have their roots down in the mud at the bottom of the pond and leaves that float at the top of the pond, like water lilies. These plants get lots of sunlight, which makes them the top energy producers for the animals in the water. Many fish also swim in this open water zone.

Freshwater ecosystems play a fundamental ecological role and provide economically important products and services. They provide critical habitats for a large number of aquatic plants, fishes, reptiles, birds and mammals. They host many migratory and threatened species of birds, reptiles and fish. The freshwater ecosystems are areas of tourist attraction by providing recreation sites for game and bird watching.

Freshwater ecosystems, especially vegetated wetlands, play an important role in mitigation against climate variability. They do so through a number of ecosystem functions including flood control, water purification, shoreline stabilization and sequestration of carbon dioxide. At landscape level, wetlands control soil erosion and retain sediments and in so doing concentrate nutrients in the wetland soil. They also provide economic benefits such as fresh water, fisheries, fuel-wood, building material, medicinal products, honey and foliage for livestock and wildlife. Wetlands provide fertile land for agricultural, mineral salts, sand and soil for making pottery and building bricks. Wetlands are central to rural subsistence economies and livelihood activities of many rural communities in Kenya. Freshwater ecosystems in general are critical to poverty alleviation and creation of employment and wealth.

Oceans offer various habitats at different depths below the surface. These are called zones. The euphotic zone is at the top, ending at a depth of about 200m (660ft). Below this, very little light from the Sun can reach. The bathypelagic zone below is totally dark, so no plants can live there, but a number of fish, squid and crustaceans do make this zone their home, feeding on waste material that sinks down from above and on each other. Deep-sea creatures cannot see in total darkness, but their other senses help them to find food. Some, such as angler fish, carry their own lights. They are not bright enough to search for food by, but they may lure other fish towards them and help fish of the same species to recognize each other.

When the ancestors of cave fish and certain crickets moved into pitch-black caverns, their eyes virtually disappeared over generations. But fish that ply the sea at depths greater than sunlight can penetrate have developed super-vision, highly attuned to the faint glow and twinkle given off by other creatures. They owe this power, evolutionary biologists have learned, to an extraordinary increase in the number of genes for rod opsins, retinal proteins that detect dim light. Those extra genes have diversified to produce proteins capable of capturing every possible photon at multiple wavelengths—which could mean that despite the darkness, the fish roaming the deep ocean actually see in color.

The finding "really shakes up the dogma of deep-sea vision," says Megan Porter, an evolutionary biologist studying vision at the University of Hawaii in Honolulu who was not involved in the work. Researchers had observed that the deeper a fish lives, the simpler its visual system is, a trend they assumed would continue to the bottom. "That [the deepest dwellers] have all these opsins means there's a lot more complexity in the interplay between light and evolution in the deep sea than we realized," Porter says.

At a depth of 1000 meters, the last glimmer of sunlight is gone. But over the past 15 years, researchers have realized that the depths are pervaded by faint bioluminescence from flashing shrimp, octopus, bacteria, and even fish. Most vertebrate eyes could barely detect this subtle shimmer. To learn how fish can see it, a team led by evolutionary biologist Walter Salzburger from the University of Basel in Switzerland studied deep-sea fishes' opsin proteins. Variation in the opsins' amino acid sequences changes the wavelength of light detected, so multiple opsins make color vision possible. One opsin, RH1, works well in low light. Found in the eye's rod cells, it enables humans to see in the dark—but only in black and white.

Salzburger and his colleagues searched for opsin genes in 101 fish species, including seven Atlantic Ocean deep-sea fish whose genomes they fully sequenced. Most fish have one or two RH1 opsins, like many other vertebrates, but four of the deep-se species stood apart, the researchers report this week in Science. Those fish—the lantern-fish, a tube-eye fish, and two spinyfins—all had at least five RH1 genes, and one, the silver spinyfin (Diretmus argenteus), had 38. "This is unheard of in vertebrate vision," says K. Kristian Donner, a sensory biologist at the University of Helsinki.

To make sure the extra genes weren't just nonfunctional duplicates, the team measured gene activity in 36 species, including specimens of 11 deep-sea fish. Multiple RH1 genes were active in the deep-sea species, and the total was 14 in an adult silver spinyfin, which thrives down to 2000 meters. "At first it seems paradoxical—this is where there's the least amount of light," Salzburger says.

While many fish swim in shoals, eating plankton as they flash through the water, others spend most of their time on the ocean bed. As the fish evolved, their eyes developed on the same side, so that both can see into the water above.

These quick-change artists have eyes on top of their heads, yet marvelously mimic the surfaces they sit on. This prompted Clayton Louis Ferrara to ask Weird Animal. Flatfish have eyes on the top of their heads, how do they see what's going on the ocean floor?”

Flatfish, found all over the world, range from the angler fin whiff which is about three inches (eight centimeters) to the Pacific halibut, which can get up to around nine feet (three meters) long. This fish group includes species familiar to seafood lovers—not only halibut, but flounder, sole, and turbot.

All flatfish have eyes on the end of stalks, so they pop out of the head “kind of like the eyes we saw in cartoons—ba-boing!” 

Flatfish eyes can also move independently, widening their field of vision. Once flatfish eyes get the lay of the land, they message the brain, which in turn sends signals back to the skin. This organ contains color-changing cells such as melanophores, which either expand or contract according to the background the fish is trying to match.

For instance, expanding their cells would make their color darker. All this neurological relaying is “a pretty sophisticated thing to do,” Burgess says—not to mention it takes flatfish between two and eight minutes to blend in.

Even more impressive than how the eyes work is how they get on top of the head in the first place. Flatfishes don’t start out flat. They start out looking like regular fish, kind of diamond shaped, and “as larvae, the eyes are in regular position on each side,” As they develop “the eye begins to migrate, moving over the top of the head, eventually settling on one side or the other”. This also requires the bones in their heads to move.

The flatfish’s bones are pretty pliable at this point, like the soft spot on an infant’s skull, so “as the eye moves, the bones in the head warp in that direction,” An additional bone, found only in flatfish, develops right under the migrating eye, giving them that goofy asymmetrical look.

Pearl oysters are molluscs. Their soft bodies are protected by a tough outer shell, hinged at one side. When a piece of grit becomes embedded in the soft body of the oyster, it protects itself by building up layers of a shiny, shell-like material around the foreign body. This happens naturally, but today many pearls are cultivated in oyster farms, where “seeds” are injected into the oysters so that they will form pearls.

Most jewelry is fashioned out of precious metals and jewels that are found buried in the Earth, but pearls are found inside a living creature, an oyster. Pearls are the result of a biological process -- the oyster's way of protecting itself from foreign substances.

Oysters are not the only type of mollusk that can produce pearls. Clams and mussels can also produce pearls, but that is a much rarer occurrence. Most pearls are produced by oysters in both freshwater and saltwater environments. To understand how pearls are formed in oysters, you must first understand an oyster’s basic anatomy.

Oysters are bivalves, which mean that its shell is made of two parts, or valves. The shell's valves are held together by an elastic ligament. This ligament is positioned where the valves come together, and usually keeps the valves open so the oyster can eat.

As the oyster grows in size, its shell must also grow. The mantle is an organ that produces the oyster's shell, using minerals from the oyster's food. The material created by the mantle is called nacre. Nacre lines the inside of the shell.

­The formation of a natural pearl begins when a foreign substance slips into the oyster between the mantle and the shell, which irritate­s the mantle. It's kind of like the oyster getting a splinter. The oyster's natural reaction is to cover up that irritant to protect itself. The man­tle covers the irritant with layers of the same nacre substance that is used to create the shell. This eventually forms a pearl.

So a pearl is a foreign substance covered with layers of nacre. Most pearls that we see in jewelry stores are nicely rounded objects, which are the most valuable ones. Not all pearls turn out so well. Some pearls form in an uneven shape -- these are called baroque pearls. Pearls, as you've probably noticed, come in a variety of various colors, including white, black, gray, red, blue and green. Most pearls can be found all over the world, but black pearls are indigenous to the South Pacific.

Cultured pearls are created by the same process as natural pearls, but are given a slight nudge by pearl harvesters. To create a cultured pearl, the harvester opens the oyster shell and cuts a small slit in the mantle tissue. Small irritants are then inserted under the mantle. In freshwater cultured pearls, cutting the mantle is enough to induce the nacre secretion that produces a pearl -- an irritant doesn't have to be inserted. While cultured and natural pearls are considered to be of equal quality, cultured pearls are generally less expensive because they aren't as rare.

It is like that life on our planet began in the oceans. As much more of the Earth is covered with water than with land, and the sea can be thousands of metres deep, there is simply more space for living things in the oceans. However, the conditions that they experience there are not so varied, so there are fewer different species than there are on land. Well over 90% of the living things that thrive in the oceans are found in the fairly shallow waters around the continents. However, scientists have found that there is life even in the deepest oceans, although it is not easy to study wildlife in such remote areas.

The deep sea is an extremely harsh environment. It is dark, below 200m the light levels are too low for photosynthesis (the twilight zone), and not a glimmer of sunlight remains beyond 1,000m (the midnight zone). The water is very cold (37-50oF/3-10oC) and consequently has low levels of oxygen. The pressure at a depth of 2.5 miles is about 400 atmospheres, 400 times the pressure on the surface and equivalent to half a tonne per square centimeter. The density of organisms is therefore low. 25% of the estimated 8,700,000 species on earth live in the ocean depths, and 91% of those have yet to be discovered, described and catalogued (CoML). Many of these could potentially hold cures and new treatments for cancer, arthritis and other diseases.

The organisms of the deep sea are truly amazing and extraordinary, with every journey down uncovering more of the mysteries. This month a study published in Proceedings B of the Royal Society described a new species of deep-water acorn worms found 2,700m deep near the Mid-Atlantic Ridge with extremely long "lips" to help them capture prey in a habitat deficient of food.

Living in an environment where food is scarce, organisms need to be able to eat anything and everything that comes their way, the fangtooth (Anoplogaster cornuta) accomplishes this with its large cavernous mouth, and large dagger-like teeth (in fact, the teeth are so large is it difficult to close its mouth).

The deep sea anglerfish (Melanocytes Johnson) is aptly named for its elongated dorsal spine that extends forwards and lures prey towards its wide mouth and sharp teeth, with a glowing lure (containing bioluminescent symbiotic bacteria). The density of organisms in the deep sea is so low, that finding a mate in the right place at the right time can be quite a challenge. To avoid this potential problem, when they do meet, the male anglerfish will bite onto the female, their blood vessels fuse, and he will spend the rest of his life as a sperm producing appendage.

In the mesopelagic (twilight zone) where light levels are low, large eyes and reflective retinas are advantageous to make use of any vestiges of sunlight that penetrate down. Many deep sea fish possess photospheres (light producing organs), these aid in species identification, attracting food, or deterring predators. The lanternfish (small mesopelagic fish of the family Myctophidae) have photophores paired and concentrated in rows on their body and head in species-specific patterns. In some the pattern varies between males and females, with males having concentrations of photophores above the tail, and females below.

The Swimming Green Bomb (Swima bombiviridis) discovered in 2009, armed with "bombs" (shown by the arrow below) that glow a brilliant green when dropped, which they use as a distraction tactic to escape predators.

The Barrel Eye (Macropinna microstoma) is certainly a bizarre looking creature, with two green rotating eyes embedded in their transparent head. The dark "eye" like patches are in fact olfactory organs. Due to the lack of light even further below becomes a less important sense, and in many fish their eyes are considerably reduced, or even degenerate. Watch the video below to see this unique organism in action.

Winning the most awards for “ugliest fish” the Blowfish (Psychrolutes marcidus). This "grumpy", "frowning" "blob" is able to withstand crushing pressure at 1,000m as its body is mostly a gelatinous mass with a density just less than water. It hovers with minimal energy expenditure just above the sea floor waiting for passing food particles.

During the breeding season, walruses gather on the Arctic ice. The males fight each other for the females, often causing serious wounds with their long tusks. But the main reason for these impressive extended teeth is for digging up shellfish from the ocean floor.

The mustached and long-tusked walrus is most often found near the Arctic Circle, lying on the ice with hundreds of companions. These marine mammals are extremely sociable, prone to loudly bellowing and snorting at one another, but are aggressive during mating season. With wrinkled brown and pink hides, walruses are distinguished by their long white tusks, grizzly whiskers, flat flipper, and bodies full of blubber.

Walruses use their iconic long tusks for a variety of reasons, each of which makes their lives in the Arctic a bit easier. They use them to haul their enormous bodies out of frigid waters, thus their “tooth-walking” label, and to break breathing holes into ice from below. Their tusks, which are found on both males and females, can extend to about three feet, and are, in fact, large canine teeth, which grow throughout their lives. Male walruses, or bulls, also employ their tusks aggressively to maintain territory and, during mating season, to protect their harems of females, or cows.

The walrus' other characteristic features are equally useful. As their favorite meals, particularly shellfish, are found near the dark ocean floor, walruses use their extremely sensitive whiskers, called mustacial vibrissae, as detection devices. Their blubbery bodies allow them to live comfortably in the Arctic region—walruses are capable of slowing their heartbeats in order to withstand the polar temperatures of the surrounding waters.

The two subspecies of walrus are divided geographically. Atlantic walruses inhabit coastal areas from northeastern Canada to Greenland, while Pacific walruses inhabit the northern seas off Russia and Alaska, migrating seasonally from their southern range in the Bering Sea—where they are found on the pack ice in winter—to the Chukchi Sea. Female Pacific walruses give birth to calves during the spring migration north.

Penguins are only found in the southern hemisphere, not in the Arctic. Many penguins lay only one egg during the dark days of winter. The female and male penguin’s first bond and then mate to lay an egg the size of a softball on the ice in midwinter. The male thrusts the egg up onto his feet, where it is protected and cushioned by the male’s “brood patch,” a warm fold of feathers and his bulging stomach which rests atop the feet. The egg remains in that place for 9 weeks until it hatches during the coldest months of the Antarctic winter.

Both female and male penguins protect their eggs and newly hatched chicks by enveloping them under a fold of body skin. During the reproductive cycle of the first part the mother penguin has to fast, but after eggs are laid, they go away to fatten them.

The adult males then take over, incubating the eggs and the newly hatched chicks for the 9 weeks in midwinter. The part of the bird’s belly touches the egg and the bare of feathers to facilitate the waft of heat from the father penguin to his offspring. At the end of their babysitting stint, the fathers turn the chicks over to their returning mother penguin and cross the sea again.

If the weather conditions come to be so severe that a parent’s resources can no longer deal with the cold, it abandons the egg to save itself, as it could do under other cases. All penguins are littered with abandoned eggs and dead chicks.

Females lay a single egg in midwinter and then promptly leave it behind. Depending on the volume of the ice, the females might also need to travel some 50 miles to attain the open ocean, in which they will feed on squid, fish, and krill.

In very cold climates, animals need excellent insulation to stop their body heat from escaping. This may be on the outside, in the form of dense hair, fur or feathers, or on the inside, in the form of a thick layer of fat or blubber.

The North Pole and South Pole are covered with snow and ice, the North Pole and South Pole are really cold all the time, we identified polar animals and where they live, learned penguins live at the South Pole and polar bears live at the North Pole.

Polar bears lose so little heat to their environment that they are almost invisible to thermal imaging cameras. But a recent study at the University of Buffalo found that polar bears have also evolved genes that produce more nitric oxide than other bear species. Nitric oxide is a signalling molecule and one of the mechanisms it controls is whether cells use their available nutrients to produce metabolic energy, or simply convert it into body heat. Polar bears seem to be able to divert more of their body’s resources into generating heat. This relies on them getting enough fuel for this process and adult polar bears have a high calorie diet; they mostly eat seal blubber.

Polar bears are found in very cold parts of the world where temperatures can drop as low as -20° Fahrenheit (-29° Celsius). Without proper protection, this weather can be deadly, so polar bears stay warm by utilizing their thick fur and fat, or blubber. Polar bears have evolved along with other Arctic animals to take advantage of minimal warmth, and can sometimes actually become too warm because their bodies are so efficient at trapping heat.

A polar bear's fur is the first step in keeping warm. Polar bears actually have two types of fur: long oily guard hairs and short insulating hairs. Polar bears stay warm by combining the properties of these two hairs. The guard hairs are actually hollow, and look like very small tubes of glass. The hollow guard hairs trap warmth and bring it close to the skin while also providing an oily outer layer that prevents the polar bear from getting wet. The insulating hairs trap heat close to the skin, much like insulating underwear on humans.

As in other extreme climates, only specially adapted plants and animals can live in the coldest parts of the world. In fact, at the North and South Poles, almost nothing can survive, but around the edges of the Arctic and Antarctic there are seas rich in plant and animal life. This means that larger animals, living on the edge of the ice, can find food in the teeming waters.

Air temperatures averaging below freezing over the year (usually well below freezing) with a range in many places around -40°C to +10°C (-40°F to +50°F) and highs (very briefly and rarely) up to +22°C (+72°F) amongst rocks and moss banks. Much of Antarctica is a cold largely featureless icy desert where above freezing temperatures are hardly reached if ever at all. The temperature of the Antarctic Ocean that surrounds the continent varies from -2°C to +2°C (+28.4°F to +35.6°F) over the year. Seawater freezes at -2°C (+28.4°F) so it can't get any colder and still be water.

Arctic and Antarctic birds and mammals such as penguins, whales, bears, foxes  and seals - are warm blooded animals and they maintain similar internal body temperatures to warm blooded animals in any other climate zone - that is 35-42°C (95-107°F) depending on the species. They have to keep high body temperatures to remain active. These animals are known as endotherms (endo-inside + therm-heat) as they generate their heat internally. The Polar Regions' cold and wind mean that this heat can very quickly be lost leading to hypothermia (hypo-under).

Many (non-polar) animals are ectotherms (ecto-outside) , which means that they generate so little heat internally they are dependent on the external environment to warm them up to a level where their body and enzymes function sufficiently well enough for an active and functional life. Typically they raise their temperature by basking in the sun until they are warm enough to become active. Reptiles and amphibians do this while invertebrates are usually small enough to be able to warm up quickly to the ambient temperature from the air alone without basking in direct sunlight.

A large ectothermic Arctic or Antarctic land animal would never get enough energy regularly enough from the surroundings to become sufficiently active once it had cooled. All polar land animals of any size therefore need to be warm-blooded to be active. The environment is so extreme that the size limit in Antarctica for an ectotherm is about 13mm, the size of the largest fully terrestrial (land) animal in Antarctica. In other words any animal larger than this would be unlikely to be able to warm up enough to become active before it started to get cold again.