Biology and Life Sciences - GED Science

Alleles are different forms of the same gene. For example, the gene for flower color in a plant may come in two allele varieties: white or purple. Both alleles code for flower color (the same gene), but represent different types of the genetic expression.

Humans are diploid organisms, meaning that they carry two alleles for each gene, one from each parent. Organisms with two copies of the same allele are considered homozygous, while those with copies of two different alleles are considered heterozygous.

When an organism has only one type of allele for a given gene, it is described as homozygous ("homo-" meaning one). Organisms can be either homozygous dominant, meaning they have two dominant alleles, or homozygous recessive, meaning they have two recessive alleles.

A heterozygote, or hybrid, has two different types of alleles for a given gene. When the dominant allele causes the recessive trait not to be represented in the phenotype, the organism is considered a carrier for the recessive trait.

When a gene is sex-linked, it means that the gene is located on one of the sex chromosomes. These chromosomes are the X and Y chromosomes, with the Y chromosome only being found in males. Sex-linked genes provide the opportunity for the frequency of a phenotype to be seen more often in one gender than the other.

Sex-linked genes can be represented in either sex; if the trait is on the X chromosome, it can be displayed in both males and females but may appear more frequently in males.

Nonsense mutations alter the position of the stop codon in the mRNA strand, which creates a different product. The result is a shorter polypeptide chain that may not be able to function.

Silent mutations do not alter the final protein product. A missense mutation causes an amino acid to be replaced by another, different amino acid. A frameshift mutation changes how the mRNA strand is read by the ribosome, resulting in a dramatically different product.

In the case of the giraffe, chameleon, and rose, the species naturally adapted in order to survive. However, in the case of the dogs, there was intervention by man. Certain species and individuals were crossed to select for the desired genes that result in hypoallergenic fur, allowing the dogs to be kept by owners who would otherwise be allergic. Therefore, the dogs are an example of ARTIFICIAL selection, while the other choices demonstrate NATURAL selection. Natural selection is also referred to as survival of the fittest.

Natural selection is when nature makes certain traits more common due to their inherent advantage in a given environment. When a prairie dog is better hidden based on its fur color, that color will become more common over time as the darker fur colors are eaten away by predators. Humans can also make certain traits more common over time, such as in dogs, but this is an example of artificial selection, not natural.

The esophagus assists moving food into the stomach using a wave-like contracting motion called peristalsis. Swallowing initiates the process of peristalsis, but unlike swallowing, peristaltic contractions are not voluntary and are generated by smooth muscle.

Mastication is another term for "chewing." Emulsification refers to the grouping together of fat molecules when in an aqueous environment, particularly during digestion in the small intestine.

Food is digested to some degree in many different parts of the digestive system. The mouth, stomach, and small intestine all contribute to food digestion. The mouth contains salivary amylase, which breaks down carbohydrates. The stomach contains pepsin, which breaks down proteins. The small intestine contains several enzymes, such as lipase and trypsin, and breaks down carbohydrates, lipids, and proteins.

The esophagus, however, does not contribute to chemical digestion in any way.

Bile is created by the liver and released into the small intestine from the gall bladder during digestion. Because fat tends to clump in the aqueous environment of the duodenum, bile helps to increase the surface area of fat, a process called emulsification. This helps lipase break down the fats adequately.

There are three primary types of hormones: peptide hormones, steroid hormones, and tyrosine derivative hormones. Of the three, peptide hormones are the only polar hormones, so they cannot pass the cell membrane. As a result, they must attach to a membrane-bound receptor in order to elicit a response in the cell.

Tyrosine derivatives and steroid hormones are smaller, nonpolar molecules. This allows them to pass directly through the membrane, rather than binding to a receptor on the surface. Steroid hormones are derived from cholesterol, but there is no such thing as "cholesterol hormones."

Steroid hormones are created in the gonads and the adrenal cortex. They include testosterone, estrogen, cortisol, aldosterone, and progesterone.

Human growth hormone, oxytocin, and insulin are all peptide hormones, meaning that they are proteins made of amino acids. In contrast, steroid hormones are derived from cholesterol and have distinct ring structures.

Managing blood sugar levels is primarily the responsibility of the pancreatic hormones glucagon and insulin. Glucagon is responsible for raising blood sugar levels while insulin helps reduce the sugar levels.

Oxytocin is a hormone secreted from the posterior pituitary gland; it induces labor and contractions during childbirth. Thyroxine (also known as thyroid hormone or T4) is secreted from the thyroid and helps regulate metabolism.

The pituitary gland is responsible for a number of peptide hormones, including follicle-stimulating hormone, thyroid-stimulating hormone, and prolactin. Aldosterone, however, is produced in the adrenal cortex and functions to raise blood pressure by preventing fluid loss via urination.

B-cell lymphocytes are responsible for the production of antibodies. These white blood cells secrete antibodies, which bind to and promote the destruction of pathogens

Macrophages attack pathogens directly. T-cell lymphocytes can help attack pathogens as well, and can also trigger B-cells to release antibodies. Red blood cells (erythrocytes) are not involved in the immune response.

When it comes to blood type, the type of blood you have is determined by the type of antigens present on your red blood cells. For example, people with type A blood have the A antigen on their red blood cells, but not the B antigen. People with O blood have no antigens on their red blood cells. The immune system of a person with A blood will respond negatively to B blood if it is introduced into the body.

A person with type A blood could receive type A blood (A antigens) or type O blood (no antigens), but could not receive type B blood (B antigens) or type AB blood (A and B antigens).

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.

Muscles do not attach directly to bones. Instead, a tendon is used to attach the two structures. Ligaments connect a bone to another bone, while joints are the locations where bones move around one another.

There are three types of muscle in the body: skeletal, cardiac, and smooth muscle. Of the three, skeletal muscle is the only one that can be consciously controlled. Cardiac and smooth muscle are controlled involuntarily.

An example of skeletal muscle is your biceps brachii muscle; you can voluntarily control this muscle to flex your arm. An example of smooth muscle is the muscle surrounding your arteries; you cannot voluntarily contract this muscle to constrict your arteries. Cardiac muscle is found in the heart; you cannot voluntarily choose to slow your heart rate.

Red bone marrow is found in the ends (epiphyses) of long bones such as the femur and is responsible for red blood cell development. Yellow bone marrow is found in the center (diaphysis) of long bones and can store fat for energy.

Blood filtration primarily occurs in the spleen or kidney. Glycogen is primarily stored in the liver. Calcium is released from the mineral matrix of the bone, but is not actually found in the bone marrow.