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all of the ecosystems on Earth, the part of Earth where life exisits

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Welcome TrekEarth users! - FlyerTalk Forums

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Travel Photography - Welcome TrekEarth users! - Hello everyone, For those unaware, we recently, regrettably, shuttered another site. It was home to some of the best photos from around the world I've ever seen.

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a community of organisms and their non living environment consists of biotic and antibiotic factors

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all of the population of different species that live in the same area

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Watching as a massive collection of birds float across the sky like an unpredictable wave, it's difficult to comprehend how birds can fly in formation without the aid of the high- tech location equipment used by aerobatic teams like the Red Arrows.

Such patterns may look like the result of extrasensory communication, but they're in fact the product of emergent animal group behaviour known as flocking. Every change of direction comes not as a result of an individual member of the flock, but rather of the snap decisions made by those individuals in response to the movements of their neighbours.

To comprehend how it works, in 1986 American computer programmer Craig Reynolds applied simple rules to bird behaviour to simulate flocking in his computer program Boids. The three rules he outlines include the fact that each bird steers itself to avoid crowding or bumping its neighbours (separation), each bird tries to match the average heading of its neighbours (alignment), and that each bird steers towards the average position of its neighbours, maintaining flock structure (cohesion).
1) Leader
Flying in a V formation is a good way to reduce fatigue in the members of the flock and a large or strong bird will take the lead.
2) Followers
Each bird will benefit from the updraft created by the flapping of the bird in front's wings (which creates currents of circulating air), generating lift for the birds behind to take advantage of.
3) Replacement
When the flock changes direction, a new leader will take the helm.
4) Sick birds
A sick or wounded bird will drop out of formation and one other bird will follow it until it recovers or dies.
5) Fatigue
If the leader becomes tired it will rotate back into formation and another bird will then take the lead.
6) Resistance
If a bird falls out of formation it will notice the extra resistance and immediately get back in line.

The benefit of the flock

There are several benefits to flying as a flock. It improves a bird's chance of survival against predators because a large group of birds is stronger and better protected and with many eyes the flock is far more likely to spot a would-be marauder. Also, the predator will find it harder to concentrate on a single victim, increasing the individual member of the flock's chance of survival.

Flocking also enables birds to fly further using less energy because when the strong leader bird flaps its wings it creates uplift for the birds behind - each bird (except the leader) is flying in the up-wash from the wing of the bird in front. This enables the flock to use less energy and reduces fatigue.

Top 5 Flocking Facts
1) When to watch
The best time of year to witness flocking is winter as migratory birds prepare to head for warmer climes, and those that stick around for winter will be foraging and roosting together.
2) Honk honk
Sometimes geese at the back of their flock will make honking sounds to encourage the birds ahead to maintain their speed.
3) Sort Sol
Twice a year in Denmark massive flocks of starlings block out the sun during an event called Sort Sol or 'Black Sun'.
4) Movie sims
Craig Reynolds' Boids program inspired the film Batman Begins to simulate a swarm of bats. It was also the simulation behind the stampede of wildebeest in The Lion King animation.
5) Big flocks
There are more sub-Saharan red-billed Queleas in the world than any other species and their flocks can comprise tens of thousands - the flock can take hours to pass by.

Discover more amazing facts in the latest issue of How It Works magazine. It's available from all good retailers, or you can order it online from the ImagineShop. If you have a tablet or smartphone, you can also download the digital version onto your iOS or Android device. To make sure you never miss an issue of How It Works magazine, make sure you subscribe today!

Plus take a look at:
Which bird migrates the furthest in winter? Which is the smallest bird? How do birds know when to migrate?

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Why do birds flock together? - How It Works

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Watching as a massive collection of birds float across the sky like an unpredictable wave, it's difficult to comprehend how birds can fly in formation without the aid of the high- tech location equipment used by aerobatic teams like the Red Arrows.

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a group of individuals of the same species that live together in the same area

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Organism Images, Stock Photos & Vectors | Shutterstock

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Find organism stock images in HD and millions of other royalty-free stock photos, illustrations and vectors in the Shutterstock collection. Thousands of new, high-quality pictures added every day.

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anything that can carry out life process

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Fish-1 « CREAM – A Marie Curie Initial Training Network

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Predicting toxicity to fish based on in vitro data via a two step model

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anything that can carry out life processes

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So Many Systems - Human Body Systems Rap

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a group of organs that work together to perform functions

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There are more than 22 organs in the human body. This is a list of the ten most vital organs which are usually taught about in elementary school. You will learn about the organ's job or function, as well as some interesting facts!

Skin

The skin is the largest organ in the human body. Its main job is to maintain the body's temperature, which means that sweat is created to cool the body, and goosebumps or raised hair occur to trap heat in the body. Along with sweat glands, the skin contains oil glands. The oil your skin releases helps to keep your skin from drying out and your hair from becoming brittle. The skin also regularly sheds cells to maintain its effectiveness. If you can imagine, there are about 19 million skin cells in every square inch of the human body! Skin is the largest organ!

Brain

The human brain is the command center

The brain is the controller of your body, and stores information, allows you to think and learn, as well as controls vital daily functions like digestion, heart rate and breathing. The brain receives impulses from your nerves, which are located throughout your body and respond to pain and other stimulation. Even though the brain is so important, it is also very delicate. The brain is made of soft tissue and is protected only by the skull, which is why head injuries can be so serious. The average adult brain weighs 3 pounds.

Heart

The heart is another vital organ. The heart's job is to pump oxygenated blood throughout your body and receive deoxygenated blood back in return. Without your heart, your other organs would not receive oxygen or have carbon dioxide removed. In an average lifetime, the heart beats more than 2.5 million times!

Kidneys

The kidneys are located under the rib cage in your lower back. The job of the kidneys is to filter things like water and salts out of your blood and to produce urine. The kidneys also produce an enzyme called renin. This enzyme plays a big role in regulating your blood pressure. Did you know that a healthy person is able to live with only kidney?

Liver

The liver is located in the upper abdomen, slightly more to the left side. The main job of the liver is to produce bile, which it sends to the stomach for digestion. The liver also filters out toxins and regulates blood sugar. Blood sugar is regulated because the liver converts sugars and stores them, releasing them when more sugar is needed in the blood. The liver is also in charge of releasing cholesterol, breaking down fats, and producing blood proteins. It is the largest internal organ!

Pancreas

The pancreas is located in the abdomen, behind the stomach. The job of the pancreas is to produce enzymes necessary for digestion and send them to the stomach. The pancreas also regulates blood sugar and does this through its process of creating insulin. The pancreas also creates glucagon which has the opposite effect of insulin and also helps to maintain blood sugar levels.

Stomach

The stomach receives food from the esophagus and sends it into the small intestine. The stomach's role in digestion is to break down food and mix it with digestive juices or enzymes.

Small Intestine

The job of the small intestine is to digest food. It does this using chemicals, such as enzymes. The small intestine also absorbs nutrients from the food through villi and gives these nutrients to your blood. The small intestine is 5 meters long! The food moves from your small intestine to your large intestine with a series of muscle contractions.

Large Intestine

The large intestine is located in your abdomen and is 1.5 meters in length! The large intestine is involved in digestion, and receives undigested food from the small intestine. The large intestine then absorbs as much water as possible and then expels the waste and any excess fiber.

Lungs

The lungs are located in your chest and are protected by your rib cage. The lungs take in oxygen which goes into the blood through the heart, and expels carbon dioxide as the heart receives unoxygenated blood.

Websites for Practice

There are lots of great websites on the Internet to help increase your understanding of the body's organs, as well as help you to practice learning and remembering them. These are my favorites: BBC Science Interactive Body: This game is like a giant jigsaw puzzle of the organs in the human body. It has a list of organs in the human body which you click on and drag it to the right place in the body, rotating if necessary. There are also a number of interesting facts for each organ. All Systems Go!: This game is a puzzle as well. A picture of a character named Arnold is shown, along with his missing organs. You have to place the organs back in his body in the correct place. If you put an organ in the wrong place, all of the organs fall out of his body and you have to start again! This list of organs in the human body and these practice sites will help you learn how your body works and help you ace your test at the same time.

References

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List of 10 Vital Organs of the Body Essential to Human Life

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There are more than 22 organs in the human body. This is a list of the ten most vital organs which are usually taught about in elementary school. You will learn about the organ's job or function, as well as some interesting facts! The skin is the largest organ in the human body.

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a combination of two or more tissues that work to get them to perform a certin task

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A simple question deserves a simple answer. How many cells are in your body?

Unfortunately, your cells can't fill out census forms, so they can't tell you themselves. And while it's easy enough to look through a microscope and count off certain types of cells, this method isn't practical either. Some types of cells are easy to spot, while others-such as tangled neurons-weave themselves up into obscurity. Even if you could count ten cells each second, it would take you tens of thousands of years to finish counting. Plus, there would be certain logistical problems you'd encounter along the way to counting all the cells in your body-for example, chopping your own body up into tiny patches for microscopic viewing.

For now, the best we can hope for is a study published recenty in Annals of Human Biology, entitled, with admirable clarity, "An Estimation of the Number of Cells in the Human Body."

The authors-a team of scientists from Italy, Greece, and Spain-admit that they're hardly the first people to tackle this question. They looked back over scientific journals and books from the past couple centuries and found many estimates. But those estimates sprawled over a huge range, from 5 billion to 200 million trillion cells. And practically none of scientists who offered those numbers provided an explanation for how they came up with them. Clearly, this is a subject ripe for research.

If scientists can't count all the cells in a human body, how can they estimate it? The mean weight of a cell is 1 nanogram. For an adult man weighing 70 kilograms, simple arithmetic would lead us to conclude that that man has 70 trillion cells.

On the other hand, it's also possible to do this calculation based on the volume of cells. The mean volume of a mammal cell is estimated to be 4 billionths of a cubic centimeter. (To get a sense of that size, check out The Scale of the Universe.) Based on an adult man's typical volume, you might conclude that the human body contains 15 trillion cells.

So if you pick volume or weight, you get drastically different numbers. Making matters worse, our bodies are not packed with cells in a uniform way, like a jar full of jellybeans. Cells come in different sizes, and they grow in different densities. Look at a beaker of blood, for example, and you'll find that the red blood cells are packed tight. If you used their density to estimate the cells in a human body, you'd come to a staggering 724 trillion cells. Skin cells, on the other hand, are so sparse that they'd give you a paltry estimate of 35 billion cells.

So the author of the new paper set out to estimate the number of cells in the body the hard way, breaking it down by organs and cell types. (They didn't try counting up all the microbes that also call our body home, sticking only to human cells.) They've scoured the scientific literature for details on the volume and density of cells in gallbladders, knee joints, intestines, bone marrow, and many other tissues. They then came up with estimates for the total number of each kind of cell. They estimate, for example, that we have 50 billion fat cells and 2 billion heart muscle cells.

Adding up all their numbers, the scientists came up with...drumroll...37.2 trillion cells.

This is not a final number, but it's a very good start. While it's true that people may vary in size-and thus vary in their number of cells-adult humans don't vary by orders of magnitude except in the movies. The scientists declare with great confidence that the common estimate of a trillion cells in the human body is wrong. But they see their estimate as an opportunity for a collaboration-perhaps through an online database assembled by many experts on many different body parts-to zero in on a better estimate.

Curiosity is justification enough to ponder how many cells the human body contains, but there can also be scientific benefits to pinning down the number too. Scientists are learning about the human body by building sophisticated computer models of lungs and hearts and other organs. If these models have ten times too many cells as real organs do, their results may veer wildly off the mark.

The number of cells in an organ also has bearing on some medical conditions. The authors of the new study find that a healthy liver has 240 billion cells in it, for example, but some studies on cirrhosis have found the disease organ have as few as 172 billion.

Perhaps most importantly, the very fact that some 34 trillion cells can cooperate for decades, giving rise to a single human body instead of a chaotic war of selfish microbes, is amazing. The evolution of even a basic level of multicellularity is remarkable enough. But our ancestors went way beyond a simple sponge-like anatomy, evolving a vast collective made of many different types. To understand that collective on a deep level, we need to know how big it really is.

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A simple question deserves a simple answer. How many cells are in your body? Unfortunately, your cells can't fill out census forms, so they can't tell you themselves. And while it's easy enough to look through a microscope and count off certain types of cells, this method isn't practical either.

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a group of similat

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smallest unit of building blocks of life.