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By the end of this section, you will be able to:
  • Discuss the relationships between matter, mass, elements, compounds, atoms, and subatomic particles
  • Distinguish between atomic number and mass number
  • Identify the key distinction between isotopes of the same element
  • Explain how electrons occupy electron shells and their contribution to an atom’s relative stability

The substance of the universe—from a grain of sand to a star—is called matter    . Scientists define matter as anything that occupies space and has mass. An object’s mass and its weight are related concepts, but not quite the same. An object’s mass is the amount of matter contained in the object, and the object’s mass is the same whether that object is on Earth or in the zero-gravity environment of outer space. An object’s weight, on the other hand, is its mass as affected by the pull of gravity. Where gravity strongly pulls on an object’s mass its weight is greater than it is where gravity is less strong. An object of a certain mass weighs less on the moon, for example, than it does on Earth because the gravity of the moon is less than that of Earth. In other words, weight is variable, and is influenced by gravity. A piece of cheese that weighs a pound on Earth weighs only a few ounces on the moon.

Elements and compounds

All matter in the natural world is composed of one or more of the 92 fundamental substances called elements. An element    is a pure substance that is distinguished from all other matter by the fact that it cannot be created or broken down by ordinary chemical means. While your body can assemble many of the chemical compounds needed for life from their constituent elements, it cannot make elements. They must come from the environment. A familiar example of an element that you must take in is calcium (Ca ++ ). Calcium is essential to the human body; it is absorbed and used for a number of processes, including strengthening bones. When you consume dairy products your digestive system breaks down the food into components small enough to cross into the bloodstream. Among these is calcium, which, because it is an element, cannot be broken down further. The elemental calcium in cheese, therefore, is the same as the calcium that forms your bones. Some other elements you might be familiar with are oxygen, sodium, and iron. The elements in the human body are shown in [link] , beginning with the most abundant: oxygen (O), carbon (C), hydrogen (H), and nitrogen (N). Each element’s name can be replaced by a one- or two-letter symbol; you will become familiar with some of these during this course. All the elements in your body are derived from the foods you eat and the air you breathe.

Elements of the human body

This figure shows a human body with the percentage of the main elements in the body, in the left panel. In the right panel, a table lists the elements and the percentages in the body.
The main elements that compose the human body are shown from most abundant to least abundant.

In nature, elements rarely occur alone. Instead, they combine to form compounds. A compound    is a substance composed of two or more elements joined by chemical bonds. For example, the compound glucose is an important body fuel. It is always composed of the same three elements: carbon, hydrogen, and oxygen. Moreover, the elements that make up any given compound always occur in the same relative amounts. In glucose, there are always six carbon and six oxygen units for every twelve hydrogen units. But what, exactly, are these “units” of elements?

Questions & Answers

sorry what are the common meaning of haemostatis
Juma Reply
what are the negatives feedback regulation of ADH
Nansi Reply
what is the the differences between DNA and RNA?
The major differences between the DNA and RNA are contain of double stranded and single stranded which the DNA contain duoble stranded and RNA contain single stranded.
what are the negatives feedback regulation of ADH before this we confused just verify long term of ADH firstly
How many genes consist of DNA?
omaryare muhyadiin when you talk about genes, is the material formed in a DNA genes have form like plasma have many genes round there
aldosterone, renin
to know the different structures of the body To know how the body works To know more about our body parts
Deitdre Reply
hi Deitdre you tock about knowledge or you ask the question
do you need any explanation when reading this book?
janet Reply
Its Good
if have many ability just do it!!
compare and contrast the operation of homeostasis
Dinelle Reply
what is the difference between an ionic, polar covalent and nonpolar covalent bond?
In summary, the bond has different in electronegativity.
sorry help me to get the definition of hemostasis or the meaning
the definition of distal
Dinelle Reply
farthest away from the attachment point.
Distal, is the farthest possition from the origin or midle point
exercise physiologist how ?
Noor Reply
hi noorr. when you talk about physiologist its a person who study physiology but exercise physiologist is what an exercise doing by physiologist in physiologican
can I get the questions of human physiology that is present in HSC 2nd semester
Rafiullah Reply
in my lerning the question com like for example ni eassy qustion must understand the the part of the body and how it work or mechanisms of each part learned
how can I memorize
mukhtaar Reply
which part of the body produces blood
give me answer
Red blood cells are formed in the red bone marrow ofbones. Stem cells in the red bone marrow called hemocytoblasts give rise to all of the formed element
what is hemocytoblasts
hemocytoblasts are stem cells in red bone marrow which give rise the all of formed elements
Discuss clonal theory in physiology and its application in measles infection in a 6yr child? Can anyone help me
Isaac Reply
Capillary permeability
what do you want to know about it?
Hello, I want to search about the topic, information and pictures
syncitium is the property of which of the following muscle
Shahab Reply
can I get the questions of human physiology that is present in HSC 2nd semester
Sai Reply
i now madam
ha can u please send me the PDF of questions
it's important to me to have that information please send as fast as u can
me too if possible?
of course
I want too
now you want to look the format of question or because i need to explain on you?
If a molecule can only pass through a membrane with the assistance of a membrane protein, but the direction of its travel is controlled only by its concentration, the process is called?
A 52 year old woman turned her head quickly, during a tennis game and suddenly felt a sharp pain in her neck along her upper limb. Physical examination and medical imaging revealed a herniated degenerated IV disc in the cervical region of her vertebral column.
a. What probably caused the IV disc herniation? b. What cause IV disc degeneration? c. What are the result of disc degeneration?
Describe the neural control of erection and ejaculation.
Nana Reply
A 52 year old woman turned her head quickly, during a tennis game and suddenly felt a sharp pain in her neck along her upper limb. Physical examination and medical imaging revealed a herniated degenerated IV disc in the cervical region of her vertebral column. a)What probably caused the IV di
a) What probably caused the IV disc herniation? b) What cause IV disc degeneration? c) What are the result of disc degeneration?
iv disc herniation compress the nerve cause numbness tingling sensation even paralysis in severe cases...

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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