Does a chemical reaction change the number of atoms?

In a chemical reaction, the number of atoms of each individual element remains conserved and are unchanged. The atoms may be rearranged, but their number stays constant. In comparison, in a nuclear change, the atoms of one species may change into that of another. Thus conservation of mass is applicable in case of chemical reactions. This is the basis for writing balanced chemical equation, in which the number of atoms of each species are same on both sides of chemical reaction. 

For example:  `2H_2 + O_2 -> 2H_2O`

In this chemical reaction, oxygen and hydrogen combine to form water. This reaction represents rearrangement of atoms (combination of hydrogen and oxygen atoms in 2:1 ratio). The number of hydrogen atoms are 4 on both sides of the reaction and that of oxygen is 2.

Hope this helps. 

What is a summary of chapter 1?

Chapter 1: Shotgun Cheatham's Last Night Above Ground.

In the book, the narrator, Joey Dowdel, tells stories about his childhood, summer adventures at his grandmother's.

In the summer of 1929, Joey is nine, while his sister, Mary Alice, is seven. They lament that they have never seen a dead body before, which is unusual since they live in Chicago during the era of Al Capone and Bugs Moran. Instead, Joey remembers that they had to travel to St. Louis, where their grandmother lived, in order to see a 'stiff.' He relates that he felt happy to be traveling by train to their grandmother's house.

Mary Alice, on the other hand, isn't too enthusiastic about staying at their grandmother's. She frets that there is never anything interesting to do there. However, things change when a supposed Civil War hero by the name of Shotgun Cheatham dies in St. Louis. Joey and Mary Alice soon spread the rumor that a reporter has been asking around about Cheatham. When they tell their grandma about the reporter, their grandmother scoffs that the reporter just wants to write a sensational story about the supposedly backward people living in St. Louis. She says that Cheatham was just an 'old reprobate who lived poor and died broke.'

Not to be deterred, the children apprise Grandma Dowdel of all the stories people are telling about Cheatham at the Coffee Pot Cafe. Their grandmother counters that these stories are probably the work of Effie Wilcox and that they should never trust the words of an ugly, old woman. She argues that Cheatham came to be known as Shotgun when he indiscriminately shot off a round of bullets and killed off a cow when he was ten.

Soon, the reporter comes calling to ask about Shotgun. In response, Grandma Dowdel tells the reporter that Shotgun was a decorated Civil War veteran. The kids are astounded at the fantastic tales their grandmother seems to be spouting off. When she is done, Shotgun has evolved from being a disreputable gunslinger to a courageous war veteran with philanthropic tendencies. Grandma Dowdel even adds that Shotgun jilted Effie Wilcox and that she never got over it. Before the reporter leaves, Grandma Dowdel tells the reporter to let everyone in town know that Shotgun will be buried with full honors from her house.

Despite their curiosity about Grandma Dowdel's gesture, many people make their way to her house for the vigil. The reporter is also there, and he finds himself distressed when Effie Wilcox takes a seat next to him. The story is that Effie has just been dismissed from an insane asylum; her comment about the 'natural' look of the dead man doesn't help either.

As the night wears on, the gauze hanging from the coffin appears to move. Some unspecific and ambiguous movement appears to mimic the hand of the dead man reaching up out of the coffin. Meanwhile, Grandma Dowdel grabs her twelve-gauge Winchester and fires off both barrels. The reporter and Effie Wilcox exit the house in great alarm, not sure whether they are more troubled by an awakening dead man or Grandma's shotgun skills. Mary Alice says that the whole event gave her nightmares for years to come.

The reality is that Grandma's 'snaggletoothed tomcat' was actually the culprit batting at the gauze; Joey is pretty sure that his grandmother saw her cat jump out of the coffin. He thinks that's when she got the idea to have fun at the reporter and Effie Wilcox's expense. Joey relates that his grandmother probably wanted to chase off the nosy reporter, believing that he had no right to pry into the affairs of the town. Nevertheless, Joey asserts that Grandma Dowdel's actions gave the town much to talk about for the rest of the summer and that she also earned a reprieve from the machinations of nosy neighbors for long years to come.

Pencils, paper, tables and chairs are all made of tiny moving particles. What stops these objects from flying apart?

The items you listed are all made of mixtures of substances in the solid phase. The molecules of a solid aren't flying around, they're vibrating in place. The reason they're not flying around is that they're attracted to each other. A solid has a definite volume and shape because the molecules are close together, locked into position and can't move past each other. Of the three states of matter, gas molecules have the most kinetic energy and solids have the least. Gas molecules are in rapid motion, moving around and colliding with other molecules. There are no significant attractions between gas molecules at normal temperatures and pressures. 

The molecules of a liquid also move around, but they have less kinetic energy than gas molecules. They are much closer together and move more slowly than gas molecules as they move past each other. Attractions between molecules have a bigger effect in the liquid phase than in the gas phase because the molecules are closer together.

As liquid cools attractions between molecules take over and a solid forms, in which molecules are no longer able to move past each other.

I want to know how I can be specific and write a great book report about Paul Zindel's The Pigman.

When writing a book report, consult the teacher's requirements first. If the report is simply to summarize the reading, then focus on the main points of the story that move the plot forward. If, on the other hand, the assignment is to compare and contrast characters, show cause and effect, or argue a point, then your report will be structurally different.

For The Pigman, though, show how the interaction between John, Lorraine, and Mr. Pignati developed into a loving and respectful friendship. Then, consider what obstacles their friendship faces as the story progresses and identify the climax and resolution. Create a thesis statement that will drive your essay forward towards the main point of the essay. For example, a thesis statement could be: "John and Lorraine learn that not all adults are difficult to be with as Mr. Pignati laughs with them, gives them gifts, and creates a safe environment for them."

The next step after creating a thesis is to structure your paragraphs to explain and support it. In the above example, there are three items to address in your essay that could also be topics for three different paragraphs. Remember to provide quotes with citations for each topic addressed because this solidifies your main idea and thesis statement.

Don't forget to provide a strong conclusion that elaborates on why your topics and thesis are important to understanding the book. Discuss how the book can help to address social issues for teenagers based on the topics you mention.  The following are quotes that could go with the topics given in the above thesis statement example:

He laughs with them:

"We must have looked just like three monkeys. The Pigman, John, and me--three funny little monkeys" (97).

He gives them gifts:

"'I don't want you spending all that money, Mr. Pignati,' I said.

'Nonsense,' he insisted.

But I really didn't. And still it felt good. No one had ever bought me stuff like this before--something I just liked and didn't need and didn't even ask for" (90).

He provides safety:

"Lots of times I'd cry myself to sleep, but more and more I felt myself thinking of the Pigman whenever I felt sad. Sometimes just after I put the light out, I'd see his face smiling or his eyes gleaming as he offered me the snails--some little happy detail I thought I had forgotten--and I'd wish my mother were more like him. I'd wish she knew how to have a little fun for a change" (86).

During DNA replication,a DNA strand that has the bases CTAGGT will produce a strand with what bases?

During DNA replication, the original DNA strand "unzips" or splits where the two bases join together to form the rungs of the DNA ladder.  There are four nitrogenous bases, cytosine, thymine, adenine and guanine.  The sides of the unzipped DNA serve as a template for which other nitrogenous bases may be paired to make new strands of DNA.  The pairing goes like this:  adenine pairs to thymine, while guanine pairs to cytosine.  I teach my students to remember the word "AT", since adenine pairs to thymine.  That leaves guanine to pair to cytosine.  The correct pairing for this DNA sequence , then, would be GATCCA.  Guanine would pair to cytosine, adenine to thymine, thymine to adenine.  Cytosine would pair to guanine, cytosine to guanine, and adenine to thymine.

How do plant cell undergo mitosis in the absence of centrioles ?

Mitotic cell division is for the purpose of producing more of the same cells for growth and for repair or to replace old worn out cells. A parent cell's genetic material must first be replicated before it can be distributed to two daughter cells at the conclusion of mitosis.

Before mitotic division occurs, during interphase --specifically the S phase of interphase, the DNA of the organism is replicated. Now, chromosomes are in pairs called sister chromatids.

Centrioles are tiny organelles with the purpose in animal cells to separate and take up a position on opposite sides of the cell. These centrioles are found in the centrosome, an area of the cell where the spindle is organized. The spindle contains fibers that the replicated chromosomes attach to at their centromeres. The spindle fibers help to later pull apart sister chromatids to opposite poles so that later, two new daughter cells will each have a set of chromosomes. 

Plant cells lack centrioles, however, they are still able to form a mitotic spindle from the centrosome region of the cell just outside of the nuclear envelope. They go through the stages of mitotic division as do animal cells-prophase, metaphase, anaphase and telophase, followed by cytokinesis.

The end of mitosis is when cytokinesis occurs-- the division of the cytoplasm, which is accomplished in plants by the production of a cell plate, made from vesicles inside the cell. This step occurs during telophase and the materials inside vesicles collect together to form the growing cell plate, which eventually fuses with the cell membrane. Ultimately, it divides the cytoplasm into two daughter cells and later becomes part of the cell wall.

Animals form a cleavage furrow and eventually pinch apart to form two daughter cells. 

I hope this clarifies mitosis in plant vs. animal cells! I have attached a diagram of mitosis in plant cells.

`sec(v - u)` Find the exact value of the trigonometric expression given that sin(u) = 5/13 and cos(v) = -3/5 (both u and v are in quadrant II.)

There are a lot of ways to solve this problem. For instance, one can use the secant sum/difference identity. This identity, however, has a lot of terms. A more elegant solution would be to use the cosine sum/difference identity, and relating cosine to secant.

Note that `sec(x) = 1/(cos(x))` .Such that we only need to get the reciprocal of the value of cosine at our given angle to get the corresponding secant. Both u and v are in the second quadrant implying that the x-components are both negative and the y-components positive. 

The cosine sum/difference identity is: `cos(v-u) = cos(v)cos(u) + sin(v)sin(u)` .

We already know some of the terms here, namely: `sin(u) = 5/13` and `cos(v) = -3/5` .To get the remaining terms, we simply use the Pythegorean identity: `sin^2(x) + cos^2(x) = 1` .

Hence:

`cos^2(u) = 1 - 25/169 = 144/169` , and `cos(u) = -12/13` . Note that we could have chosen the positive root, but since u is in the second quadrant, we get the negative one.

Similarly:

`sin^2(v) = 1 - 9/25 = 16/25` , and `sin(v) = 4/5` . We are getting the positive root since v is in the second quadrant.

Now, we can solve for the cosine:

 `cos(v-u) = (-3/5)(-12/13) + (4/5)(5/13) = 36/65 + 20/65 = 56/65.`

Which means:

`sec(v-u) = 65/56.`