Biology and Life Sciences - GED Science

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.

Bacteria are prokaryotic organisms and are considered alive. Bacteria can survive and reproduce independent of a host (consider a colony of bacteria cells growing in a Petri dish). Though they do not have membrane-bound organelles, like a nucleus or mitochondria, bacterial cells do have DNA and are still able to produce cellular energy.

This question confuses many properties of viruses with those of bacteria. Viruses are not generally considered alive and require a host cell in order to replicate.

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.

Cellular respiration is composed of many steps used to break down glucose and convert the chemical energy into ATP. Of the four steps described in the answer choices, oxidative phosphorylation via the electron transport chain is the most effective step for producing ATP. The electron transport chain can produce between 32 and 38 ATP from a single glucose molecule.

Glycolysis is the first step of glucose breakdown in cells. This process takes place in the cytosol.

The second step of cellular respiration, the citric acid cycle, takes place in the mitochondrial matrix. The third step, the electron transport chain, takes place on the inner mitochondrial membrane and requires protons to be concentrated within the intermembrane space.

Glycolysis is the first step in cell metabolism. It is responsible for converting glucose (a 6-carbon sugar) into two molecules of pyruvate (a 3-carbon sugar). Glycolysis occurs in the cytoplasm, where the sugar molecules interact directly with enzymes. After pyruvate is created, it is transported to the mitochondria for the remainder of cellular respiration (the citric acid cycle and electron transport chain).

Though plants undergo photosynthesis, they also use cellular respiration. Glycolysis takes place in both animal and plant cells.

Photosynthesis is the process by which plants use the sun's energy to convert water and carbon dioxide into glucose and oxygen .

The equation is the equation for cellular respiration. Cellular respiration happens inside the mitochondria and chloroplast for those cells containing chloroplasts.

The circulatory system is responsible for transporting blood, oxygen, nutrients, and wastes throughout the body. The vessels of the circulatory system include arteries, arterioles, capillaries, venules, and veins. The heart is responsible for pumping the fluids of the circulatory system through these vessels, and is a major component of the circulatory system.

The respiratory system is responsible for transporting air to and from the lungs, and facilitates gas exchange with the capillaries of the circulatory system. The lymphatic system helps regulate fluid balance and immune system function; it consists of lymphatic vessels, the spleen, and the thymus. The digestive system breaks down and absorbs nutrients; it consists of the digestive tract from the mouth, through the stomach and small intestine, and to the rectum.

The heart has four chambers: two atria and two ventricles. The atria are responsible for receiving blood returning from the body, while the ventricles pump blood out of the heart. The right ventricle pumps blood to the lungs, while the left ventricle pumps blood to the rest of the body.

The flow of blood through the heart is: right atrium, right ventricle, lungs, left atrium, left ventricle, body.

Arteries are the high pressure blood vessels responsible for carrying blood away from the heart. All arteries in the body travel away from the heart toward other tissues.

Most arteries carry oxygenated blood, but the pulmonary arteries carry deoxygenated blood; these vessels are responsible for transporting deoxygenated blood from the right side of the heart to the lungs. Veins are responsible for returning blood back to the heart. Arteries do not allow for diffusion of nutrients; this process primarily occurs in capillaries.

The heart is able to pump independently of the brain thanks to a collection of cells that fire impulses automatically. These cells are located in the sinoatrial node, which leads to the node's nickname as the "pacemaker" of the heart. Even without stimulation by a nerve, the heart can continue beating.

The heart is made of cardiac muscle tissue; smooth muscle tissue lines internal organs and blood vessels. Both sides of the heart pump at the same rate, but the left side pumps with more force. Each side of the heart must pump the same volume, but the left side must pump it a greater distance since it pushes blood to the entire body. A normal resting heart rate is around 60-80 beats per minute. A heart rate of 120 would be more typical during exercise.

The respiratory system allows air to travel to the lungs. Air enters the mouth or nasal passages, travels through the trachea, and then into the bronchi. The bronchi split into smaller and smaller bronchioles before terminating in small sacs called alveoli.

The aorta is a major artery that carries blood away from the heart. The urethra carries urine from the bladder. The small intestine is a portion of the digestive tract that carries nutrients from the stomach to the large intestine.

Blood is composed of multiple cell types that have specific functions in the body. The red blood cells (erythrocytes) help carry oxygen to the tissues in the body. The white blood cells (leukocytes) help defend the body from bacteria and other illnesses. Platelets are cell fragments responsible for helping blood clot, and are created by megakaryocytes.

The chief cells are responsible for releasing pepsinogen. Pepsinogen is an inactive enzyme that will only become activated in acidic conditions, such as those found in the stomach. Acid converts pepsinogen into pepsin, which helps chemically digest protein nutrients in the stomach.

Parietal cells release hydrochloric acid into the stomach, which activates pepsinogen. Goblet cells, or mucous cells, secrete mucous to help prevent degradation of the stomach lining.

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.