bioilluminations

Every single living thing, from a plant to a human being, exists and grows because of dividing cells. In multicellular organisms such as humans, this process - known as mitosis - begins instantly after a sperm fertilizes an egg. Just before mitotic cell division, all the genetic material (DNA) of the cell is copied and then coiled into extremely compact chromosomes inside the nucleus. These chromosomes align near the center and then pull apart, creating two genetically identical cells. One cell has now become two. By staining the nucleic acid and using a light microscope, this process - most often studied by viewing illustrations in textbooks - comes magnificently into focus.

Land plants have regions of growth that contain areas of constantly dividing cells (stem cells) called apical meristems. These regions are found at the tips of roots, shoots, and leaves.

Oedogonium is a genus of filamentous green algae commonly found in freshwater ecosystems such as ponds, lakes, or even puddles. One way this algae reproduces is by producing asexual spores called zoospores. These asexual spores break out of the filaments they are contained in and instantly begin to swim with a crown of flagella. Zoospore flagella are short lived and germination occurs rapidly once the spore becomes immobile. It is common for these newly germinated spores to attach themselves to parental filaments and continue to grow, forming newly branched structures.

One of the most common characteristics of the plant kingdom is autotrophic metabolism. This is performed by using the green pigment chlorophyll to trap and convert light energy to sugar in organelles called chloroplasts. But not all plants have chlorophyll or stomata, the openings that allow for gas exchange when performing photosynthesis. These plants, which make up about 1% of all angiosperms (flowering plants), acquire their energy by other means such as parasitism. While hemiparasitic plants can still produce some of their own energy like American mistletoe, others rely entirely on the nutrition production of other organisms. Fully paristic plants almost certainly evolved from photosynthetic ancestral plants and have lost their chloroplasts and stomata altogether, which also means losing their green color entirely. By using modified roots called haustoria, parasitic plants can tap into the host plant’s conductive systems, stealing nutrients and water or parasitize entirely from root fungi (mycorrhizae), a relationship called myco-heterotrophy.

Spores and swimming gametes in land plants indicate an ancient evolutionary history that existed millions of years before seeds and flowering plants. The oldest lineage of land plants form the group known as the bryophytes. This ancient group consists of the hornworts, liverworts, and most widely known mosses. If fertilized (sperm meets egg), mosses give rise to a structure called a sporophyte, a capsule that sits upon a stalk (seta) containing millions of spores. Spores are typically dispersed by air currents and if one lands in a favorable location, germination will occur. From the spore, a seedling like filament will emerge. This chain of newly formed cells is called a protonema and will continue to elongate and spread horizontally by way of cell division. After this protonema is well established, the leaflike structures (gametophores) most commonly attributed to what moss looks like begin to grow vertically. Sex structures containing gametes (sperm and eggs) will eventually begin to form from these gametophores and the life cycle will begin again.

SEXUAL REPRODUCTION

Angiosperms, also known as flowering plants, evolved over time more efficient ways of living in terrestrial environments. One of these key adaptations was the creation of the pollen grain. It allowed male gametophytes to travel through harsher, drier conditions and in much greater numbers. Once the pollen grain attaches onto the stigma (the sticky top surface of the female structure) it sends out a protuberance called a pollen tube. When the tube elongates down the style and reaches the ovule, 2 sperm cells (created by simple cell division inside a pollen grain) will travel and fertilize the egg inside.

A reddish color in a bird bath is a common sight but the organism responsible is mostly overlooked. The reddish orange color is produced by a type of green microalgae in the genus Haematococcus. When exposed to stressful conditions, this motile green algae begins to degrade its green chlorophyll and lose its flagella. The newly formed cyst cell gets its reddish color from accumulating a type of pigment called a carotenoid, the same type of pigment that gives carrots their orange color. This particular carotenoid is called astaxanthin and it acts as a strong antioxidant that can act as a protectant against things like the Sun’s harmful UV rays.

Plants in the legume (pea) family such as clovers have acquired a special way of fixing the elusive and vital element nitrogen into their cells. Through coevolution, these plants have formed a mutual symbiotic relationship with the bacteria (rhizobia) associated with their root filaments. Even though nitrogen makes up 78% of the atmosphere, processing it is difficult due to the incredibly strong triple bonds which bind together the atoms of the nitrogen molecule.

Amazingly, some organisms such as rhizobia have protein complexes able to break down this bond, allowing atmospheric nitrogen (N2) to be available for consumption. When the soil is nitrogen deficient, legume roots form nodules full of these bacteria. The rhizobium cells break down the atmospheric nitrogen into a “fertilizer” in the form of ammonia (NH3) which is absorbed by amino acids in the plant. In a mutualistic manner, the bacteria are benefited by being provided sugar that the plant obtained through photosynthesis.

Another interesting observation is the red color of the nodules which is due to the hemoprotein called leghemoglobin.  This protein is both chemically and structurally similar to the hemoprotein that carries oxygen in our blood, hemoglobin.  Like our blood, the red color comes from the interaction between iron and oxygen which is bound to the heme compound.

A lichen is a symbiotic organism - a relationship between a fungus and photosynthetic partner. Most lichen fungi belong to the ascomycetes and reproduce sexually by forming circular structures called apothecia. These cup shaped apothecium have sacs (ascus) that typically contain 8 spores. Once mature, the ascus will rupture and the ascospores will be dispersed.

All life on earth is currently categorized into 6 kingdoms: Animalia, Plantae, Fungi, Protista, Bacteria, and Archaea

As plants colonized land, they grew in size and developed new structures that helped adapt to the new environment. One such adaptation was the evolution of a complex organ that increased surface area to capture sunlight, the photosynthetic organs we know as leaves. With greater size and complexity, vascular tissue was needed, with branching veins to support these larger structures. All leaves are categorized into two categories: microphylls and megaphylls. Microphylls are currently only found in the group of land plants known as the lycophytes and form only a single strand of vascular tissue. All other vascular plants have leaves classified as megaphylls. These leaves form a much more complex vascular system. Microphylls have been found all the way back to 410 million years ago while megaphylls date to around 370 million years ago.

Nitrogen is a vital element to all living things and makes up 78% of our atmosphere on Earth. Unfortunately, atmospheric nitrogen (N2) forms incredibly strong triple covalent bonds with itself making it very hard for organisms to take it up as a nutrient. Cyanobacteria such as Nostoc have evolved the ability to fix nitrogen in the atmosphere (N2) by creating anaerobic conditions inside cells called heterocysts. These specialized cells use the enzyme nitrogenase to convert nitrogen (N2) into ammonia (NH3). By performing this conversion, nitrogen is not only available for uptake to adjoining bacterial cells but also made available to other forms of photosynthetic life such as algae and plants.

Wood lice, also known as roly polies or pill bugs, are usually thought to be closely related to other “bugs” such as insects. But by looking at their evolution and biology, certain characteristics show how different they really are. Insects breathe through holes on the sides of their body called spiracles. By using certain muscles, air is taken up through these holes and diffused down a system of connected tubes called trachea. This efficient respiratory system adequately supplies the insects cells with the oxygen they need. Pill bugs on the other hand are actually crustaceans that breathe through modified gills called pleopods, located on their lower abdomen underneath. Just like other arthropods in the crustacean taxon, pill bugs have to have water pass over their gills in order to diffuse oxygen to the rest of their body. But by evolving folds in their pleopods, lung like structures enabled their gills to function out of water which led to the colonization of the terrestrial world.

An easily overlooked organism, terrestrial algae in the genus Pleurococcus covers many different surfaces with a beautiful green coating. At a cellular level, arrangement of cells shows why this form of life is so prevalent and successful. The spherical algal cells reproduce asexually by mitosis (cell division). When a cell lands on a surface, rapid cell division creates a slimy, carbohydrate abundant substrate. This helps additional algal cells adhere and spread. It also provides other organisms a platform on which to establish themselves. Green algae gave rise to all land plants and Pleurococcus evolved similar strategies to coping with life outside the water. By having a thick cell wall, cells are protected from desiccation.

Cahaba lilies (Hymenocallis coronaria) at the Cahaba River National Wildlife Refuge in Bibb County, AL. Cahaba lilies are aquatic, perennial plants in the amaryllis family that grow from bulbs and seeds in the riverbed. It is native to the Southeastern United States.

Honey bees and other insects are able to see light outside the limited spectrum visible to humans. Since receptors in their eyes can sense short, ultraviolet waves of light, patterns on certain flowers become visible to them. In addition, parts such as pollen can generate ultraviolet fluorescence, guiding insects to both nectar and pollen, increasing fertilization of the plant’s flowers.

Trilobites were ancient marine animals that lived as far back as 540 millions years ago and lasted into the Permian period (250 million years ago) before going extinct. During this time there was an evolutionary arms race known as the Cambrian explosion, where only the fittest animals survived. Organisms adapted by evolving strategies to either become more elusive prey or to dominate as predators. These strategies were based on the ability to sense other animals and having a better sense of sight became vital. Trilobites, like other Arthropods (a phylum that also includes insects), had compound eyes, but it was the material that composed their eyes which is so unusual. The lenses of trilobite eyes were made of calcite (CaCo3), a calcium carbonate mineral. These eyes made of stone gave trilobites an advantage which helped them thrive and teem the oceans for almost 300 million years.

One way plants adapted to arid, hot environments is through a process called CAM photosynthesis (crassulacean acid metabolism). Most plants take in carbon (CO2) during the day through openings on their leaves called stomata but by doing so lose water through evaporation. CAM plants have the amazing ability to open their stomata at night and store their carbon in malate (a four-carbon acid). Once light is converted to chemical energy the following day, carbon is available for sugar production (Calvin-Benson cycle). This evolved adaptation severely reduces the water loss most plants experience during gas exchange.

Cytoplasmic streaming is a type of motion that helps speed up the distribution of materials inside certain cells. By using the proteins actin and myosin, a circular flow is created. This type of streaming typically occurs in larger cells.

Cytoplasmic streaming can be spectacularly observed in a spiderwort (Tradescantia) stamen hair cell.

Plants, like all other living organisms are susceptible to viruses. Many cause diseases that can lead to illness or even death, but some cause only mild symptoms with interesting physical effects. By most definitions, a virus is a non-living agent because it cannot reproduce on its own. It is made up of genetic material (RNA or DNA) encapsulated by a protein coat. A virus reproduces by entering a cell and hijacking machinery used for replication. Once this is completed, viral spread begins as the cell lyses (ruptures), spilling new viruses which infect adjacent cells.

Plant growers have adapted a technique for purposefully injecting a virus into a plant for desired effects such as floral color. This technique is known as “viral variegation”. An example of this is purposely using a virus that is injected into a camellia plant. Once the virus penetrates a cell’s nucleus and hijacks its pieces used for replication, the camellia is infected. Beautiful water-mark like colors in the petals are then expressed. Yellowing variegation in leaves is another type of side effect of viral infection.

Interestingly, the first discovery of a virus was found in tobacco: tobacco mosaic virus. It was discovered by running sap from an infected plant through tiny filters, that wouldn’t even allow the passage of bacteria. This evidence suggested agents smaller than bacteria were causing the disease and the term “virus” was ultimately coined.

Leukocytes, more commonly known as white blood cells are one of the body’s first defenses. While red blood cells (erythrocytes) outnumber them about 700 to 1, their function is vital. In mammals, the most common type of white blood cells (about 60 to 70%) are neutrophils which have the amazing ability to patrol and hunt harmful foreign organisms such as bacteria and yeast that may have penetrated the skin. They do this by a process known as phagocytosis using foot like protrusions called pseudopodia to crawl around and capture the pathogen. Once contained by this amoeboid movement, enzymes will break it down. Using a simple light microscope and time lapse camera, the commonly assumed static cells come spectacularly to life.

Chloroplasts are the small structures inside certain photosynthetic cells that capture light, making sugar. These organelles capture light using a green pigment called chlorophyll. Organisms such as plants appear green because the chlorophyll reflects green light rather than absorbing it.

One way algae was originally classified was by putting organisms into large groups based on the most visible color of pigment. After more genetic and evolutionary information was discovered, some organisms shifted around. The three main groups are green algae (chlorophyll), brown algae (fucoxanthin), and red algae (phycoerythrin). Red algae forms a group called Rhodophyta literally meaning “red plant.” It is an ancient group that evolved by engulfing a cell that had already gone through a primary endosymbiosis. This primary event was when a photosynthetic cyanobacterium was absorbed by a heterotrophic cell, resulting in a eukaryotic organism. Because of the secondary endosymbiosis, red algae has two membranes around its chloroplasts. Interestingly, some red algae such as algae in the genus Batrachospermum, is in fact, not red. This is due to the abundance of the phycobiliprotein pigment called phycocyanin. This bluish green pigment masks any phycoerythrin, making the algae appear a blue green color instead of red.

Night blooming epiphytic cactus (Epiphyllum phyllanthus)

Starch granules inside seed cells. Most plants store the sugar they produce in the form of starch. Seeds are very high in starch, giving the developing embryo the energy it needs before being able to photosynthesize. (Stained with Lugol’s iodine solution)

Rotifers are ecologically important organisms that help clean mostly fresh water habitats. Even though microscopic, rotifers are multicellular animals with specialized organ systems. They feed by creating a water vortex using spinning cilia crowns that circulates food in front of their mouths. By using jaws called trophi and an alimentary canal containing a digestive tube, large populations of rotifers aid ecosystems by breaking down organic matter and freeing up nutrients for other life.

All land plants seen today evolved from a type of green algae. Through molecular sequencing, the taxonomic class thought to be most closely related is called the zygnematophyceae. Spirogyra is a genus in this class consisting of some 400 different species. These are filamentous green algae that live in freshwater. They contain chloroplast arranged in beautiful spiral structures giving them their name. The nucleus and nucleolus can be observed suspended in the middle of the cell. While asexual reproduction is more common, sexual reproduction can happen when the organism becomes stressed such as being in water with depleted nitrogen levels. This type of reproduction occurs with the formation of conjugation tubes which then transfers one cell's material into the other adjacent cell. After this fusion and transfer is complete, a diploid zygote is formed called a zygospore. This zygospore has a thick wall and is able to survive tough conditions until a favorable environment presents itself.

In temperate regions, fall colors are one indication of the upcoming winter, where most plants go into dormancy. And while the photosynthetic organs we know as leaves are slowly dropping, the reasoning behind the bright yellow, orange, and red colors might be a bit different than one would assume. Chlorophyll, the green pigment mostly responsible for photosynthesis is not just thrown away by trees but rather absorbed for its supply of the vital and limited element nitrogen. While the chlorophyll is absorbed, the green color of leaves begins to fade and accessory pigments that have been in the leaves all summer begin to come into focus. Some of these accessory pigments, which aid in the plants ability to efficiently photosynthesize by absorbing different spectrums of light, are called carotenoids. Carotenoids are pigments that give things like carrots and fall leaves their orange and yellow colors. But perhaps the most fascinating aspect of deciduous leaf color is the production of anthocyanin, the pigment which turns the leaves bright red. Anthocyanin is also the pigment responsible for some flower petal colors such as blues, purples and reds. Unlike the carotenoids, anthocyanin begins synthesis during the fall and it’s levels inside the leaves are drastically higher before the leaves fall off. While the tree is absorbing the chlorophyll from the chloroplasts, anthocyanins are produced to protect these photosynthetic organelles by absorbing potentially harmful rays of light. Studies have shown that the more anthocyanin in leaves, the more nitrogen the trees were able to store for winter.

A transit occurs when a celestial body passes in front of another one in line with the viewer. Mercury and Venus transits in front of the Sun have been observed for centuries, proving the prophetic brilliance of mathematics. While not as rare as Venus transits, transits of Mercury typically happen 13 to 14 times a century.