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## Can bone structure determine who is Native American?

Kate M.
Featured 4 months ago

No, bone structure alone cannot determine with 100% accuracy if someone is Native American.

#### Explanation:

Bone structure alone cannot determine if someone is Native American with 100% accuracy. This is due to:

1) Diversity within human populations
2) Mixed ancestry of people
3) Certain populations better studied than others/sample size

1) There is a tremendous amount of diversity in humans, and this includes within specific populations of humans. While we may be able to say that, generally speaking, people of European descent are taller than people of Asian descent or people of European descent are more likely to have overcrowding of teeth compared to those of African descent, these are generalizations. While the traits described may be true much of the time, they are not always true.

A great example of when skeletal features did not align with an individual's origin is the famous Kennewick man, remains found in Washington state that were thought not to be Native American based on skeletal features. However, DNA analysis has finally lead to the conclusion that Kennewick man is Native American. Read more here.

2) We know the most about groups of people we have studied the most. Thus, while we have studied the bones of many Europeans, we have not studied as many individuals from Laos or the Beothuk indigenous tribe. The more we study, the more we know. We may currently believe the tibia of one ethnicity are longer on average than a second ethnicity, but, with a larger sample size, we may find out this is not true.

3) Many people cannot call themselves 100% of any one ethnicity. Native Americans came into contact (and are still in contact) with people from other continents. They reproduce with people from various ethnicities, resulting in a mix of traits in the same way that can be expected if a Chinese person and a Danish person reproduce.

There are some general traits many Native American share. Native Americans typically have rounded eye orbits and prominent cheekbones compared to individuals from Sub-Saharan Africa, who typically have eye orbits that are of a rectangular shape and who lack prominent cheekbones. They tend to have a wider face than Europeans. It can be challenging to distinguish Native Americans from East Asians. It is important to remember that these traits are generalizations and not rules!

## How can blood clotting be bad?

BioBallplayer25
Featured 4 months ago

Blood clotting is bad when it occurs within blood vessels.

#### Explanation:

Blood clotting is a very crucial part of the survival of humans because without it, even minor cuts could result in massive blood loss.

But with the process of clotting, our blood is able to stop the body from losing blood.

However, sometimes these clots form within the blood vessels. When this happens, blood flow through that vessel is reduces, and, if the clot is big enough, could be completely stopped.

This could result in massive tissue death, and a blood clot in the wrong blood vessel could cause death.

Also, parts of blood clots could break off and flow through the bloodstream, but then get stuck in one of the smaller arteries in the body, like in the brain or lungs, causing tissue death there.

So blood clotting is vital to our survival, but when it occurs within the body in the blood vessels, it can lead to very serious problems.

## How does the human digestive system change food into nutrients?

Mohan M.
Featured 3 months ago

Complex food is converted to absorbable molecules in human digestive system

#### Explanation:

Food consists of complex carbohydrates, fat and proteins.
Digestive system is designed to convert complex food to absorbable, smaller molecules.

Food is first broken down mechanically when we chew it in our mouths. Some chemical digestion also occurs in our mouth as saliva breaks down food. Once food has reached the stomach, it is churned and broken down further with the aid of enzymes.

In the small intestine, some chemical digestion occurs, as enzymes break down food, but this is the main site where what remains of our food is absorbed into our body. In the small intestine, nutrients and minerals are absorbed through the villi. Nutrients absorbed through the cell wall of the villi enter the bloodstream and are then transported throughout the body. In the large intestine, more water is absorbed.

This short video covers the basics of the digestion system:

Only glucose can enter the cell membrane. Other monosaccharied absorbed are fructose and galactose.

Only individual amino acids are absorbed in digestive system. Complex proteins are degraded to amino acids.

Lipids are digested to free fatty acids are absorbed.
In short, digestive system degrades food in nutrients.

The reason is through cell membrane molecules of a certain size can be penetrated.

## Why is alveoli lined up with capillaries?

Sarkis McSavage
Featured 1 month ago

This is vital because the diffusion of carbon dioxide and oxygen between blood and lungs takes place at the surface of alveoli: so the capillaries are responsible for allowing this. Please read this as well.

#### Explanation:

Air breathing vertebrates possess a pair of lungs. They breathe in air which supplies much needed oxygen to the body and breathe out to expel carbondioxide generated in body tissues (a by product of cellular respiration).

Oxygen from lungs must be taken up by the blood, and distributed to various tissues. Similarly blood is involved in carrying carbondioxide from all body parts to lungs.

Alveolar surface of lungs is where gaseous exchange between air and blood takes place. Presence of pulmonary capillaries around alveoli help in easy loading and unloading of gases. Both alveoli and capillaries are lined by very thin simple squamous epithelia which allow gases to diffuse faster.

## What is homeostasis? How is it maintained in a cell?

TheSiameseCat
Featured 1 month ago

Homeostasis refers to the ability of the body to maintain constant internal conditions (such as osmotic pressure and temperature) while dealing with external conditions.

#### Explanation:

In other words, homeostasis is a state of balanced equilibrium.
The image shows homeostasis at a cellular level.

At a cellular level, homeostasis is maintained chiefly by the plasma membrane, a phospholipid bilayer that surrounds a cell.

It keeps the contents of a cell in and foreign bodies out, and maintains pathways for the controlled transport of materials (such as proteins, sugars, ions, and other biomolecules) in and out of the cell.

Without its plasma membrane, a cell would look like a popped balloon.

You should keep in mind that if a cell is completely isolated, it would soon run out of essential materials, like fluid and other solutes, and end up swamped in metabolic waste.

The plasma membrane allows the diffusion of water (fluid), oxygen, and carbon dioxide across the membrane by passive diffusion - without the use of ATP, the energy currency of the cell.

This makes sure that fluid levels are maintained at the right level, and waste products like $C {O}_{2}$ are exchanged for useful materials like ${O}_{2}$.

However, only some materials are allowed to pass the membrane by passive diffusion (osmosis). If all sorts of molecules were allowed to float through, it wouldn't be a barrier.

To transport other biomolecules like ions ($N {a}^{+} , {K}^{+}$), the membrane has a variety of transport systems involving carrier proteins that are embedded in the membrane that act as gates.

There are three main types of gates - pumps, channels, and transporters.Pumps and transporters use ATP to function, so they are a part of the active transport network.

Lysosomes also consume waste products and prevent build-up.

For information on concentration gradients and cellular homeostasis, visit http://education.seattlepi.com/cell-membrane-play-role-homeostasis-4707.html

## What are the the body's defenses? How do they differ from each other?

Martin M.
Featured 1 week ago

There are different stages of defence, the so-called 'Lines of Defence'. They are explained below.

#### Explanation:

First line of defence:
The first line of defence is the first barrier to encounter diseases. This defence can also be seen as the outside defence system.
The first line of defence contains for example:

• Skin
• Mucus
• The epithelium of our intestines

All off the above prevent a disease from easily entering our body. A disease enters when it has crossed a membrane. So a particle inside our intestines is not yet inside our body since it has not crossed any membrane.
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Second line of defence:
The second line of defence is necessary once a disease has bypassed the first line of defence. The second line of defence is non-specific. Some examples are for example:

• Phagocytosis. Phagocytes can find cells that are not our own, and kill it via apoptosis. There are a few types of phagocytes which work non-specifically. Some phagocytes can engulf infected cells and 'lock them away'. This is showed schematically in the picture below. The phagocyte can then kill it and become an antigen presenting cell (APC).
• Fever. By increasing the body temperature, some diseases cannot function properly, for example, proteins can get denatured.
• Complement system. This system helps the phagocytes to find the infected body cells or other stuff that is not working properly. Cytokines are used as transmitter particles, that can signal other cells to do something.

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Third line of defence:
In this line of defence, antibodies and lymphocytes encounter the diseases. The third line of defence is specific and can be adapted to many forms of diseases. This type of defence is activated by a phagocyte. The phagocytes take a part of the virus with it and present it (as an APC, antigen presenting cell) to a T helper cell.
In a series of reactions and the making of different types of cells, the following cells are made:

T cells:
- Cytotoxic T cell (will search cells with a specific antigen)
- Memory T cell (will cause cellular immunity)

B cells:
- Plasma cell (will make antibodies)
- Memory B cell (will cause humoral immunity)

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So the lines of defence differ in their specificity. Fever can counter a few diseases, but one cytotoxic T cell can counter only one disease. The time to counter a disease also differs from disease to disease.
The three lines of defence work together to be able to counter diseases efficiently. If you remove one, the others will probably lose efficiency, since they have to work harder.

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