Your innate immunity is the generalized system responsible for first attacking incoming infectious agents and toxins. Innate means that it is not necessary to have previously seen the pathogen, and the body always has these general defense mechanisms. Macrophages, neutrophils, and basophils are some of the primary cell types of innate immunity.

In contrast, the adaptive immune system is only effective against pathogens that have previously entered the body. A previous infection will result in the body producing antibodies during any later infections. T-cells and B-cells (lymphocytes) are the primary cell types of adaptive immunity.

The germ cells (eggs/oocytes and sperm) contain only one copy of each chromosome. This reduction in the amount of DNA occurs through meiosis. Most cells in the body contain two copies of each chromosome and are considered diploid. Since they only contain ne copy of each chromosome, germ cells are considered haploid.

Neurons and lymphocytes (white blood cells) contain two copies of each chromosome; they are diploid. Erythrocytes (red blood cells) do not have nuclei, and do not contain any genetic material.

Ovulation, or the release of the egg from its follicle, is initiated by a temporary spike in estradiol (estrogen) levels. This positive feedback event is referred to as the luteal surge.

Menstruation follows ovulation. Gastrulation is a phase of development during which the primary germ layers are generated in an embryo, and is not related to the female cycle.

Following gastrulation, the three primary germ layers are formed. They are the ectoderm, the mesoderm, and the endoderm. The ectoderm develops into the skin and the nervous system. The mesoderm develops into the bones and muscle. The endoderm develops into the lining of the digestive tract and most internal organs.

Spermatozoa formation is accomplished in the seminiferous tubules in the testes. Once created, the spermatozoa are taken to the epididymis for storage and maturation. During ejaculation, the sperm is expelled through the vas deferens then through the urethra and out of the penis.

There are several stages of embryonic development. The first stage is the zygote, which is simply a single cell formed after the sperm fuses with the egg. The cell then begins to divide, creating more cells without actually expanding in size. This process is called cleavage and the embryo is now call a morula. Eventually, the cells orient such that they form a ball with a hollow center and begin to expand in total size. This stage is known as the blastula or blastocyst stage. During this stage, the embryo will enter the uterus and implant into the uterine wall. As the cells continue to divide and orient, the blastocyst develops an inner cell mass, which will be become the new organism. The cells in this area begin to differentiate into the different germ layers through a process known as gastrulation; the resulting embryo is known as a gastrula.

Tundra is primarily located near the Arctic Circle and is characterized by a cold, dry climate that does not facilitate the growth of many trees. The tundra is generally thought of as a large flat, and largely barren land.

Desert is essentially the equivalent of tundra, but in a warm/hot climate. Tropical rainforest is classified as a biome where it is warm and humid, and where rain is known to fall throughout the year. Woodland biomes are largely populated with trees and experience seasonal precipitation, with rainy winters and drier summers.

Biomes are typically divided based on yearly temperatures and precipitation amounts. Deserts have high temperatures with very low precipitation. Rainforests have high amounts of precipitation with high temperatures. Tundras have very low temperatures with little to no precipitation.

Because RNA is usually single-stranded (vs. double-stranded DNA), it is more susceptible to degradation by nucleases; therefore, RNA is NOT more stable than DNA.

RNA does contain the carbohydrate sugar ribose in its backbone, while DNA contains the sugar deoxyribose. RNA contains the nitrogenous base uracil; in contrast, DNA contains thymine.

Transcription is initiated when RNA polymerase attaches to DNA at the promoter site. This allows the RNA polymerase to be appropriately positioned so that the whole gene is transcribed.

The origin of replication is the site that allows the initiation of DNA replication. Operators are segments of DNA that can bind transcription factors and regulate certain genes.