The characteristics of life are that all life is made up of small units called cells, all life responds to the environment, all life has DNA inside its cells, all life needs to be able to make more cells, this results in both growing and developing and reproduction, all life evolves, all life maintains a stable internal environment, and all life must have a way to get energy and matter to stay alive. I learned this by using the CK-12 textbook and finding more stuff to study online.

3. Scientific Theories
The three scientific theories are the Theory of Evolution, the Cell Theory, and the Germ Theory.  A hypothesis can also become a theory because if it is thoroughly tested and passes all tests, ensuring that there are no lingering problems with it, it can become a theory. I learned this by using the CK-12 textbook and finding more stuff to study online.

2. Enzymes
Enzymes are the biological substances (proteins) that act as catalysts and help complex reactions occur everywhere in life. Enzymes are involved in most of the biochemical reactions that take place in organisms. About 4,000 such reactions are known to be catalyzed by enzymes, but the number may be even higher. Enzymes allow reactions to occur at the rate necessary for life.

3. Proteins
A protein is an organic compound made up of small molecules called amino acids, the monomers of proteins. There are 20 different amino acids commonly found in the proteins of living organisms. Small proteins may contain just a few hundred amino acids, whereas large proteins may contain thousands of amino acids. The largest known proteins are titans, found in muscle, which are composed of over 27,000 amino acids. 

4. Carbohydrates
Carbohydrates are the most common type of organic compound. A carbohydrate is an organic compound such as sugar or starch and is used to store energy. Like most organic compounds, carbohydrates are built of small, repeating units that form bonds with each other to make a larger molecule. In the case of carbohydrates, the small repeating units are called monosaccharides. Carbohydrates contain only carbon, hydrogen, and oxygen.

2. Gene Expression
There are at least 20,000 genes in each of your cells. All of your cells, in fact, share the same genes. Do your cells all produce the same proteins? Clearly not. If they did, all of your cells would look the same. Rather, you'll find cells with various architectures and purposes. This is due to the fact that various cells produce different proteins. They accomplish this by using or expressing various genes. Gene expression is the process of using a gene to produce a protein. Gene expression is regulated to ensure that the right proteins are produced at the right time and in the right place. From the initiation of transcription until the processing of a protein after translation, regulation can occur at any step in the expression of a gene. The stages where gene expression is controlled are listed below: 

3. DNA Structure
After DNA was found to be the genetic material, scientists wanted to learn more about it. James Watson and Francis Crick are given credit for discovering that DNA has a double helix shape, like a spiral staircase. The discovery was based on the prior work of Rosalind Franklin and other scientists, who had used X-rays to learn more about DNA’s structure.

4. DNA Replication
DNA replication is the process in which DNA is copied. It occurs during the synthesis (S) phase of the eukaryotic cell cycle. Enzymes, catalytic proteins, are needed in order for a cell to do this process quickly and efficiently. Some of the main enzymes involved include:

5. Leading and Lagging Strands
DNA polymerase reads the parent strand in the 3' to 5' direction. This happens smoothly on one strand, known as the leading strand. As helicase opens the double helix, DNA polymerase can build continuously. The other lagging strand is built in small chunks, called Okazaki fragments. Ultimately two new strands are built that are identical.

3. Cell Division
Cell division is the process in which one cell divides to form two new cells. How this happens depends on whether the cell is called a prokaryote or eukaryote. Prokaryotes have a single circular chromosome, no nucleus, and few other cell structures. Eukaryotic cells have multiple linear chromosomes contained within a nucleus.

4. Cell division in Prokaryotes: 

5. Cell Division in Eukaryotes
Cell division is more complex in eukaryotes than prokaryotes. Prior to dividing, all the DNA in a cell's multiple chromosomes is replicated. Its organelles are also duplicated. These preparatory phases make up the majority of the cell's reproductive cycle. Then, when the cell divides, it occurs in two major steps:

Each gene for a feature might have many variations, which are referred to as alleles. An individual's genotype is made up of the alleles he or she inherits, and the phenotype is determined by how these alleles are expressed. The dominant allele is expressed when only one of two alleles is expressed, while the recessive allele is expressed when only one of two alleles is expressed.

2. Sex-linked Traits
Male X-linked traits have a different pattern of inheritance than single-gene autosomal traits. Do you know why? It's because males have just one X chromosome. They always inherit their X chromosome from their mother, and they pass it on to all their daughters but none of their sons. X-linked recessive traits are less common in females than males, because females have two X chromosomes and males have just one X chromosome. An example of a recessive X-linked trait is red-green color blindness. People with this trait cannot distinguish between the colors red and green.

3. Chromosomal Disorders
Mistakes may occur during meiosis that results in nondisjunction. This is the failure of replicated chromosomes to separate during meiotic. Some of the resulting gametes will be missing a chromosome, while others will have an extra copy of the chromosome. If such gametes are fertilized and form zygotes, they usually do not survive. Most chromosomal disorders involve the X chromosome.

4. Genetic Disorders
A mutant dominant allele is expressed in every individual who inherits even one copy of it. If it causes a serious disorder, affected people may die young and fail to reproduce. Few genetic disorders are controlled by dominant alleles. A mutant recessive allele, such as the allele that causes sickle cell anemia (, is likely to pass on to the next generation rather than die out.

5.  Diagnosing and Treating Genetic Disorders
People with a genetic disorder in their family may be concerned about having children with the disorder. If they decide to have children, they may be advised to have prenatal testing to see if the fetus has any genetic abnormalities. One method of prenatal testing is amniocentesis, where a few fetal cells are extracted from the fluid surrounding the fetus and the fetal chromosomes are examined. Gene therapy is one potential cure for genetic disorders, but it is still in the early stages of development. If you could learn your risk of getting cancer or another genetic disease, would you? A number of companies now make it easy to order medical genetic tests through the Web.

2. Artificial Selection
Humans choose the winners & losers of a population Man chooses which organisms to breed together Examples:

3. Engineered Selection
HUMANS genetically alter the DNA of organisms; change the sequences. One organism can be altered or genes can be transferred into other organisms (transgenic organisms) 

A phospholipid is a Lipid molecule with a hydrophilic (water-loving) head and two hydrophobic (water-hating) tails; that make up the cell membrane. the phospholipid bilayer is a double layer of phospholipid molecules that makes up a plasma membrane cell membrane and forms a barrier between the cytoplasm and the environment outside the cell. The cell membrane has selective permeability. The cell membrane is primarily composed of phospholipids arranged in a bilayer, with the hydrophobic tails on the interior of the membrane, and the hydrophilic heads pointing outwards.

2. Cellular Transport
Cell transport refers to the movement of substances across the cell membrane. Probably the most important feature of a cell's phospholipid membranes is that they are selectively permeable. there are different types of transport:

3. Diffusion
Diffusion is the movement of molecules from an area of high concentration the molecules to an area with a lower concentration. The difference in the concentrations of the molecules in the two areas is called the concentration gradient. Diffusion will continue until this gradient has been eliminated. Since diffusion moves materials from an area of higher concentration to the lower, it is described as moving solutes "down the concentration gradient." The end result of diffusion is an equal concentration, or equilibrium, of molecules on both sides of the membrane.

4. Osmosis
Osmosis is the diffusion of water molecules across a selectively permeable membrane from an area of higher concentration to an area of lower concentration. It is a type of passive transport. Osmosis solely refers to the movement of water. Diffusion is the movement of other substances. Osmosis is the diffusion of water. In comparing two solutions of unequal solute concentration, the solution with the higher solute concentration is hypertonic, and the solution with the lower concentration is hypotonic. Solutions of equal solute concentration are isotonic. A contractile vacuole is a type of vacuole that removes excess water from a cell.