Answer the following question given this paragraph: 3.4 | The Cell Membrane By the end of this section, you will be able to: Understand the fluid mosaic model of membranes Describe the functions of phospholipids, proteins, and carbohydrates in membranes A cell's plasma membrane defines the boundary of the cell and determines the nature of its contact with the environment. Cells exclude some substances, take in others, and excrete still others, all in controlled quantities. Plasma membranes enclose the borders of cells, but rather than being a static bag, they are dynamic and constantly in flux. The plasma membrane must be sufficiently flexible to allow certain cells, such as red blood cells and white blood cells, to change shape as they pass through narrow capillaries. These are the more obvious functions of a plasma membrane. In addition, the surface of the plasma membrane carries markers that allow cells to recognize one another, which is vital as tissues and organs form during early development, and which later plays a role in the "self" versus "non-self" distinction of the immune response. The plasma membrane also carries receptors, which are attachment sites for specific substances that interact with the cell. Each receptor is structured to bind with a specific substance. For example, surface receptors of the membrane create changes in the interior, such as changes in enzymes of metabolic pathways. These metabolic pathways might be vital for providing the cell with energy, making specific substances for the cell, or breaking down cellular waste or toxins for disposal. Receptors on the plasma membrane's exterior surface interact with hormones or neurotransmitters, and allow their messages to be transmitted into the cell. Some recognition sites are used by viruses as attachment points. Although they are highly specific, pathogens like viruses may evolve to exploit receptors to gain entry to a cell by mimicking the specific substance that the receptor is meant to bind. This specificity helps to explain why human immunodeficiency virus (HIV) or any of the... Q: What encloses the border of animal cells? Choices: - Jacket membrane - dust membrane - cells membrane - plasma membrane A:
plasma membrane
Answer the following question given this paragraph: Intrusive igneous rocks cool from magma slowly in the crust. They have large crystals. Q: Intrusive igneous rocks cool from magma slowly in the crust and have large what? Choices: - pores - atoms - coal deposits - crystals A:
crystals
Q: Answer the following question given this paragraph: Hydrogen is a very reactive gas, and the alkali metals are even more reactive. In fact, they are the most reactive metals and, along with the elements in group 17, are the most reactive of all elements. The reactivity of alkali metals increases from the top to the bottom of the group, so lithium (Li) is the least reactive alkali metal and francium (Fr) is the most reactive. Because alkali metals are so reactive, they are found in nature only in combination with other elements. They often combine with group 17 elements, which are very "eager" to gain an electron. At the URL below, you can watch a video that shows just how reactive the alkali metals are. Q: Because alkali metals are so reactive, they are found in nature only in ________ with other elements? Choices: - isolation - cooperation - competition - combination A:
A: combination
Question: Answer the following question given this paragraph: Inside of elements, you will find identical atoms. An atom is the simplest and smallest particle of matter that still has chemical properties of the element. Atoms are the building block of all of the elements that make up the matter in your body or any other living or non-living thing. Atoms are so small that only the most powerful microscopes can see them. Q: The simplest and smallest particle of matter that still has chemical properties of the element is called? Choices: - a molecule - a nucleus - an isotope - an atom A:
Answer: an atom
*Question*
Answer the following question given this paragraph: A solution is a mixture of two or more substances, but it's not just any mixture. A solution is a homogeneous mixture. In a homogeneous mixture, the dissolved particles are spread evenly through the mixture. The particles of the solution are also too small to be seen or to settle out of the mixture. To put solutions in context as a type of mixture, watch the video at this URL: http://www. youtube. com/watch?v=z2vM-G5I92U . Q: A solution is what type of mixture, where the dissolved particles are spread evenly through the mixture? Choices: - saline - gaseous - heterogeneous - homogeneous A:
**Answer**
homogeneous
(Q).
Answer the following question given this paragraph: Each lymph organ has a different job in the immune system. Q: Each lymph organ has a different job in what system? Choices: - circulatory - respiratory - nervous - immune A:
(A).
immune