All life (as we know it) are composed of cells and cells are the smallest things that can be, without dispute, called alive (viruses are still up for debate). The Friday, May 29 blog is all about cells. All life also must maintain a balanced internal environment. That's called "homeostasis" and it's addressed in the Tuesday, July 28 blog.
A third common property of life, intimately related to homeostasis is complex, organized structure. This is true from bottom up and all the way across.
Bottom up: complex structure is a characteristic of everything from single cells up to whole organisms and on to the whole planet biosphere.
All the way across: any living thing has multiple parts that carry on different functions but they communicate to coordinate their functions.
The simplest living thing would be the prokaryotic, single celled bacteria. You can see bacteria as tiny specks using 400x magnification but to really see them requires 1000x and an oil emersion objective. I'm avoiding the expense for this blog but you can find images of bacteria using a web search or just go to Wikipedia and search for bacteria.
Prokaryotes have the bare minimum for life, DNA (but no nuclear membrane), a cell membrane, cytoplasm, and ribosomes (those are necessary for producing proteins.) In respect to cell walls and membranes, there are three kinds of bacteria. Gram positive bacteria ( they stain purple or blue with Gram stain) have a cell membrane and a cell wall composed of a material called peptidoglycan. The Gram negative bacteria stain pink with Gram stain and have a thinner peptidoglycan wall sandwiched between two cell membranes. The cell wall gives extra protection for the bacteria. There are less common bacteria that do not have the cell walls and almost always have to live in host cells to survive.
Although there aren't a lot of recognizable structures (organelles) in bacteria, various proteins manage chemical reactions in the cell and provide functional organization.
Archea are similar to bacteria in that they lack a nuclear membrane but the way they handle DNA and protein production is much more similar to eukaryotes. They generally have cell walls and are often found in very unfriendly (hot, acid or alkaline, or deep sea) environments.
There are also single cell eukaryotes. Protozoa are common examples.
This is a slide from the pond at the Cahoon Park Sunken Garden in Roswell, New Mexico.
Some of the items have nuclei indicating that they're protista (protozoa). The one near the center of the photograph looks like one I found in soil in my yard. I'm not able to identify it but it might be giardia.
Eukaryotes contain organelles that are encapsulated in membranes....nucleus, endoplasmic reticulum, mitochondria, chloroplasts (in plant cells), Golgi bodies, etc
For a brief tour of the eukaryotic cell, see the May 29 blog.
The next level is the biofilm. A biofilm is a colony of otherwise unrelated microorganisms such as bacteria, algae, and fungi that stick together and attach to a surface in a slimy matrix composed of proteins, sugars, and DNA. The film can disperse by flaking off. Some examples are dental plaque, sludge in sink drains, and slime on rocks in streams.
Most of the eukaryotic cells (the ones with the darker nuclear regions in the centers) are epithelial cells from my mouth. Many of the specks are bacteria that are too small to be seen at 400x but have interference fringes where the illumination is passing around them Entamoebas are a kind of amoeba often found in the mouth. There is one in the photograph next to the bottom. It looks like it's eating something. I have no idea what the object in the circle is. My first guess is a protozoa of some kind but I've seen spore and egg cases that look like that. Who knows....
Here are some microphotographs of some of my dental plaque, scraped off with a tooth pick.
Which, of course, makes you want to go and brush your teeth several times
Mats of algae make up colonies of similar organisms that stick together as a group. Corals are another form of colonial organism. Often the algae will provide an anchor and shelter for other organisms
If you want to explore the microscopic world in pond scum, place a drop of pond water on a slide and add a strand of algae or twig of a plant from the water.
Here's another colonial organism called "volvox". These will reproduce to create daughter colonies that remain in the larger colony or they might just strike off on their own
Volvox prepared slide from Home Science Tools
Some colonial organisms can be complex like jellyfish that include several kinds of specialized cells such as tendrils with stinging cells and the jelly cells of the floating body.
Many algae, fungi, plants and animals have vastly differentiated cells that make up organ systems. The different cells can't live independently and the whole organism would die without that kind of cell. Here's one of those....
Heh, I told you, it's my favorite selfie.
Individuals have levels, too.
For instance, trees and we are made up of a diversity of cells. The study of cells is cytology.
A lot of different kinds of cells come together to form a few kinds of tissue that do particular jobs. In humans, there are fours kinds of tissue.
Epithelial cells line things. They protect the materials they line and they also secrete and excrete stuff and sense the outside environment. The most visible epithelial tissue is our skin.
But part of the eyeball 's epithelial tissue includes another kind of tissue....nervous tissue. And the sensory cells in skin are also nervous tissue. They sense and interpret signals from the outside world and tell the rest of the body what to do
One kind of tissue that nervous tissue controls is muscle tissue. Zap a muscle cells and it contracts. Muscle tissue moves us and, in a human, there are three kinds:
Cardiac muscle
Smooth muscle
Striated muscle
The other kind of tissue make up the physical framework of bodies. In our case, that means bone, tendons, ligaments, cartilage. Together they're called "connective tissue'. Here's a microphotograph of bone tissue.
From the bottom up :
The basic unit of life is the cell. All life as we know it is composed of cells.
Cells of various kinds are collected together for the same purpose in tissues. The study of tissues is called "histology".
Various tissues are collected together for common purposes to form organs like the stomach which processes food and the heart which pumps oxygen and food carrying blood around the body.
The stomach brings together epithelial tissue that holds everything together, smooth muscles that kneed the swallowed food, glandular tissue that secrets acid and digestive enzymes into the food, and blood vessels that feed the organ itself
Organ systems connect diverse organs to perform related functions. The digestive system encompasses the gut from the mouth through the stomach and intestines to the anus where the used-up food is ejected from the body.
All the above is brought together in the whole organism. One difference between animals and other forms of life is that animals are encapsulated. For instance, you can look at a plant and, without dissection, you can see it's vascular system (roots, trunk, stems), epidermis (bark, skin), organs of transpiration and photosynthesis (leaves), and reproductive system (flowers). When you look at an animal, you mostly see it's integument (skin, hair, nails, etc.) Everything else is enclosed in the skin.
A collection of living things of the same kind (species) is called a population and there is usually some form of social organization. For instance, male and female members of the population often perform different functions in the group. For social animals, there will also be individual groups with specific hierarchies.
Beings don't live as single species. Groups of different living things live together in various different relationships. A group that lives together in a locality is called a community.
All the living things that live in a more or less independent environment....along with the environment, is an ecosystem. Bitter Lakes Wildlife Refuge, just outside Roswell, is an ecosystem. It has specific living things that have adapted to a land somewhat bounded by the Pecos River Valley. It certainly communicates with the ecosystems around it but it can be studied as an ensemble of land and life that operates on its own.
Bitter Lakes National Wildlife Refuge
Ecosystems are parts of larger ecological systems that contain multiple biomes that work together. Northern Alabama has a matrix of canyons that have similar climates, geology, living things, and even human cultures. That is a biome. If you go a little further south you see rolling hills with a different ensemble of living things including broadleaf forests. A little further south you hit another biome....rolling plains with primarily pine forests. Then you hit the coast, which is, again, a sharp change.
All the biomes on Earth form the planetary biome.....the biosphere.
The characteristic of "an organism" is that, if a part is missing, things don't work well. For instance, if a human's pancreas doesn't produce insulin, as is the case in the disease diabetes, medical intervention is required for the individual to survive.
That even applies to organisms at the ecosystem and biome levels. Animal populations are finely balanced. If there are too few predators, prey overpopulate and have too little food to go around If there are too few prey, predators go hungry and die or go in search of better hunting. If there aren't enough decomposers, dead material takes too long to return nutrients to the ground If primary producers....plants, plankton, and the animals that process chemicals in the ocean into food, then beings higher in the food chain doesn't have anything to eat plus carbon dioxide in the atmosphere doesn't get changed into oxygen.
At the base of it all is the cell and we explored cell organization back in the June 5 blog. But there are a few things I want to emphasize here.
Cells are held together by a fluid phospholipid bilayer that is stuffed with proteins that act as nano machines and steroids that give it structural integrity. In prokaryotes like bacteria, the cell membrane is the only membrane in the cell. In eukaryotes, which includes many one celled creatures (such as protista and many algae) there are organelles in the cell that are bounded by phospholipid bilayers. In fact, there is some suggestion that cell organelles were once independent single celled organisms that set up home in larger cells in symbiotic relationships.
Although Linnaeus, the Swedish physician who originated the modern classification scheme of life (and minerals, for that matter), only recognized two forms of life - plants and animals - since he died in 1778, we have recognized that several kinds of organisms don't fit into the two kingdom classification and several such schemes (called "taxonomies") have been devised.
Most bacteria have cell walls like plants but where plants are eukaryotes and have cell walls composed of cellulose, the cell walls of bacteria, when they exist since some bacteria do not have cell walls, are made of a completely different substance, peptidoglycan..Bacteria are generally included in their own Kingdom today.
There are also a collection of primitive single celled organisms that don't quite fit anywhere else. Some of them create their own food like plants but unlike plants that use light energy to do so, these beings use various chemical reactions. Instead of being photosynthetic, they are chemo synthetic. Making up the kingdom Archaea, they resemble eukaryotes but it has been found that they are paraphyletic, meaning that eukaryotes evolved from them.
Algae
Another form that was once considered plants are the algae. Most of them are photosynthetic having light sensitive pigments that allow them to make their own food, and they also tend to have polysaccharides (not cellulose) and glycoprotein cell walls, most of them are single celled (although some of the seaweeds and kelps are multicellular with specialized regions like holdfasts that anchor them to rock and float bladders) and they're all eukaryotes. They are often placed in their own Kingdom Algae.
Fungi and slime molds also don't fit into other kingdoms and they're sometimes placed in the kingdom Fungi, but the slime molds are even weird for fungi and are sometimes placed in the kingdom Protista because part of their life cycles look like fungi and other parts look like protozoa.
Fungi include many single celled forms like yeasts and parasitic organisms like plant smuts and rusts. There are also multicellular firms such as the common mushrooms and toadstools. These organisms have cell walls composed of chitin, the same substance, or very similar substance that makes up insects exoskeletons.
Plant and animal cells have several similarities and differences.
All life as we know it (viruses, proto viruses, and prions being debatable exceptions) is composed of cells that are bound by phospholipid bilayers which contain embedded proteins at about equal amounts by weight. Eukaryotes include steroids in the cell membranes to give the fluid phospholipid bilayers some stiffness. Prokaryotes lack the steroids but usually have cell walls to give the boundaries some structure.
All cells also contain DNA which carries the instructions to run the cell. In prokaryotes, the genetic material isn't separated from the rest of the cell by a membrane. In Eukaryotes, it's contained in a nuclear region bounded by a phospholipid bilayers membrane.
Eukaryotes contain a variety of smaller membrane bound organelles that perform specific tasks. Prokaryotes do not. It's not that the same tasks aren't going on. It's just that the molecules that do those tasks float free in the cytoplasm.
Cytoplasm is the other thing that all cells have. It's mostly water but it's thick with large thick molecules such as steroids, lipids, and huge proteins. Generally, these molecules control the chemical business that goes on in the cell. Of course there's plenty of dissolved substances such as sugars, salts, minerals, vitamins, and metabolites. The cell membrane controls what goes into and leaves the cell and the cytoplasm determines what stays there
In eukaryotes, plants and animals have some obvious differences.
Cell membranes are fragile, more or less soap bubble films. And they're permeable to water. Osmosis causes water molecules to pass through permeable and semi-permeable barriers to equalize concentrations of solutions on either side. If you put a cell in a more concentrated solution, water will pass out of the cell and it will shrivel up like a raisin and die. If the outside concentration is less that that of the cytoplasm, water will rush in until the cell bursts
Animals and plants deal with this problem differently. If you look at animal cells, they're usually rather formless and "glumpy".
Cheek epithelial cells
Plant cells, on the other hand, usually show some shape.
Carrot cells
The spikiness of these carrot cells are due to channels between cells that were pulled out when the carrot was sliced.
Animal cells generally reinforce themselves by clumping together and controlling any external solutions with special membranes around whole organs and organisms (like our skin). That's why wounds in animals can be so dangerous. They let the outside world in
Plants (like most bacteria, algae, and fungi) have extra barriers, cell walls, that maintain the shape of the cells. In plants, cell walls are composed of the polysaccharide, cellulose. Cellulose is what gives plants their rigidity and makes wounds somewhat less dangerous to the organism.
In addition, most plant cells have large bubbles inside called "contractile vacuoles" that store water and equalizes pressures inside the cells. In animals the largest cell organelle is the nucleus. In plants, it's often these vacuoles.
And the most obvious difference is that plants are usually autotropes. They make their own food (in contrast, animals are usually heterotropes. They have to eat to stay alive). Plants' ability to take carbon dioxide from the air and water from wherever and make food (sugar) are due to their inclusion of special organelles called "chloroplasts" that use energy from light to run a cascade of enzyme modulated chemical reactions to combine the water and carbon dioxide. Our bonus is that the reaction creates oxygen that we animals need to breathe.
Cells are tiny things. There are 30 to 40 trillion human cells (with human DNA) of them in a human body. But they have to be small. Cells run off chemicals that come through their surroundings membranes. A cell is dependent on the amount of stuff it can get into it's inside. Check out the formulas for the volume and surface area of a sphere (animal cells are sorta, kinda spherical) and a cube (plant cells tend to be blocky).
In these formulas, r is the radius of the sphere and a is the length of an edge of the cube. So, as the surface area grows by the second power of the distance across the shape, the volume grows by the third power of the distance. So, to be able to keep up with the amount of food coming in, cells have to stay small.
Here's another shocker. To go with the 30 to 40 trillion human cells that make up their body, each human has around 100 trillion bacteria cells that they need to survive. Largely, bacterial cells in the gut help to process food. Some bacteria even produce vitamins that we need, like B vitamins and vitamin K. They also fend off invading bacteria and produce signal chemicals that tell the brain what the gut is doing. Bacteria on your skin and and in your mouth also provide some defense against invading pathogens.
Adult living things grow from embryos that are basically tubes of undifferentiated cells. As the cells divide over and over, chemical signals begin telling specific cells that they should turn into specific types of cells.
Early with our understanding of the structure of DNA, we realized that there were sections of genetic materials that do not code for protein. We assumed that they were meaningless "junk DNA". More recently we have realized that these sections are far from "junk"
These non-coding "introns" tell cells how to interpret the "extrons" (coding segments). Cells, it turns out, can interpret DNA in different ways. The same region of DNA, for instance, can code for different proteins. These introns respond to signals from inside the cell, from other cells, and from the environment, even outside the organism.
Cells in the dividing embryo are undifferentiated to a point and then they start getting signals telling them to start making different proteins. Soon they differentiate into different kinds of cells that grow together into organs and organ systems until the fetus can be identified as a specific species.
You probably have a sense of how complicated organisms are from the cellular level to the complete organism. Even a single cell organism is fantastically complex. Biologists in all fields from research to applied fields like medicine have to have a way to talk about where things are. A surgeon has to know where to cut.
Anatomical language is very extensive with lots and lots of precise words. For instance, they might talk about an imaginary "sagittal plane" which divides a body into a left and right half. Or a surgeon might say that they're making a ventral incision, meaning a cut in the belly wall. Knowing about word etymologies helps to remember a lot of this stuff. The art of ventriloquism, casting voice, comes from Latin terms meaning "belly speaking". If you can remember this weird little factoid, you can remember that "ventr-" means "belly". Or, if you remember that a shark's dorsal fin is the one that sticks out of the water, you might remember that "dorsal" means "back".
If you want to look further into anatomical language, Wikipedia has a useful article called "Anatomical Terminology". Otherwise, if I use one of these esoteric words, I will explain myself.
To complicate things, botanists have an equally voluminous vocabulary to describe plants. For instance, leaves on a stem might be alternate, opposite, or whorled. Wikipedia also has a "Glossary of Botanical Terms", and, again, I will try to be clear when I write about plants
From one cell organisms to entire ecosystems, all the cells in an organism communicate and cooperate. In single cell organisms, it's all chemical signals inside cells and between organisms. In plants and simple organisms (up to worms), hormones appear. There's the same kind of chemical signals between adjacent cells seen in unicellular beings but there are also chemicals that are secreted into intercellular fluids (in higher animals, the bloodstream carries them around to all the cells in the body.....those are endocrine hormones.) That's an effective way of getting the whole body on the same page but it's slow.
In higher animals, there's a faster way. We have nerves. The central, peripheral. autonomic, and enteric nervous systems are still in communication with hormonal signals but once a nerve fires, the signal can go from one part of the body to the other in a second. Nerve impulses can travel from 0.5 meter per second to 120 meters per second
Different organisms can communicate by sound, behavior, and, again, by chemical signals. Fairly recently in biology we have realized that organisms release chemicals, for instance, pheromones, that can alter the behavior of other organisms.
We're in the process of moving and our dog is anxious about it all. He hears us talking and he seems to understand far more than the average human words that dogs understand. He also recognizes what we're doing. He's been through two moves before. But beyond that, we smell different. We can even smell the chemical signals on ourselves. Most of his anxiety probably comes from having lost members of our family at times and he doesn't know who will still be around after the move. That, we can't communicate effectively.
Species adapt into a niche in their ecosystem. In other words, they evolve to take a specific place in their environment. As consumers, they can take one of three positions.
Producers produce food for other organisms.
Consumers take in other organisms.
Decomposers break down organic materials and return them to the nutrient cycle to be used again by the producers
It's not actually that simple. Any organism may play multiple parts. A deer, for instance, might be a consumer of vegetation but be a producer of food for a cougar
Producers tend to be autotropes. In other words, They turn inorganic material into food. A maple tree takes carbon dioxide from the air and water from the air and the ground and uses energy from sunlight to turn them into the primary biological food....sugar. In the process, it produces another necessity for our global ecosystem....oxygen.
By the way, we worry a lot about deforestation because trees create oxygen for us to breathe, and we should, but consider this. 50 to 80 % of atmospheric oxygen is created by phytoplankton, tiny plants and algae in the sea. Phytoplankton are the primary producers in the sea and, by extension, on Earth.
There is a cycle of nutrients on Earth that keeps food available for organisms. Everything is recycled. For instance, carbon is taken in by autotropes in the form of carbon dioxide from the atmosphere to produce sugars. They are eaten by consumers which are eaten by other consumers. Consumers eventually die so where does all that carbon go?
It's consumed by the decomposers. Those can be microorganisms, fungi, or carrion eaters like vultures that also die and are food for the smaller decomposers. They, in turn die and the carbon goes into the soil. It ends up oxidizing to form carbon dioxide, which is also breathed out by living organisms and may wait their turn to be taken in by autotropes again or organisms that store it in their makeup as calcium carbonate may die and be buried where they become limestone and marble for long term storage. Eventually, even rock erodes, breaks down, and the carbon returns to the atmosphere.
Each trophic level loses energy. Any level tends to store 10% less energy than the level below it.
Life and our world is far more complex than I could ever hope to capture in a blog.
If all this interests you, there is plenty to explore.
What does your local ecosystem look like?
