Biology - MCAT Biological and Biochemical Foundations of Living Systems

A phase contrast microscope is best for the visualization of living things because the other types of microscopy require methods of mounting onto a slide that can kill the organisms.

Calcitonin lowers plasma calcium, while parathyroid hormone (PTH) increases it. Insulin and glucagon are responsible for blood glucose, not calcium.

Microvilli surround villa which line the small intestine. These structures greatly increase the surface area (and therefore nutrient absorption capability) of the small intestine.

The cross between two heterozygous plants (Tt and Tt) will result in 25% TT, 50% Tt and 25% tt.

Homeostasis, or "steady-state" physiology, is the system of feedback loops that enables an organism to create a stable, adaptive environment. For example, the pancreas and the brain together work to regulate the blood sugar levels via the hormones insulin and glucagon.

Gram-positive bacteria are able to retain the crystal violet stain found in gram stain because of their thick peptidoglycan cell walls. Consequently, these bacteria stain dark blue or purple by gram staining. Alternatively, gram-negative bacteria appear red or pink because they are unable to retain the dye due to thinner cell walls and less peptidoglycan.

E. Coli is a type of bacteria. Because bacteria are prokaryotes, they do not contain membrane-bound organelles. A nucleus is a membrane-bound organelle and therefore would not be found in bacteria.

Compact and spongy bone have similar chemical and structural compositions and are both hard and resistant to compression; however, due to the fact that compact bone is denser, nutrients are delievered through canals called Haversian systems in compact bone; spongy bone is less dense and lacks these specialized canals.

Bacilli is a genus of bacteria that are characterized by their rod-shaped cells. Bacilli can be either gram positive, such as Bacillus anthracis, or gram negative, such as Salmonella enterica. Bacilli bacteria can be either aerobic (require oxygen) or facultative anaerobes (can thrive in both oxygen rich and oxygen poor environment). Bacilli are not exclusively aerobic, nor are they exclusively gram positive.

Blood pressure tends to be the greatest near the heart, and decreases as blood flows to the capillaries. The pressure is greatest at the aorta and gradually decreases as blood moves from the aorta to large arteries, smaller arteries, and capillaries. The pressure is lowest in the venous system, which is why blood can pool in the veins and act as a "blood reservoir". Veins contain valves that allow them to pump blood back to the heart.

Both plants and fungi consist of eukaryotic cells. Their cells contain membrane-enclosed nuclei and organelles which is a defining characteristic of eukaryotic cells.

Fungi do not photosynthesize. While seedless plants and fungi use spores, this trait is not common to all plants. Plant cell walls are composed of collagen, while fungi use chitin.

Carbon dioxide is usually circulated in human blood in the form of , or bicarbonate. This is an important part of the blood buffering system, as the bicarbonate ion is the conjugate base of carbonic acid.

The lower esophageal sphincter separates the esophagus from the stomach. When stomach acid and contents leak through the lower esophageal sphincter, the acid irritates the esophagus and can lead to pain around the area of the heart. The heart is not actually affected.

During inhalation, the external intercostal muscles and diaphragm both contract to help expand the thoracic cavity and draw in air. The internal intercostal muscles are involved in exhalation, and compress the thoracic cavity during contraction.

The two muscles that help with breathing are the diaphragm and the external intercostal muscles. The diaphragm pulls the thoracic cavity downward and the external intercostal muscles expand the cavity outward. This expansion of the thoracic cavity leads to a decrease in pressure and allows air to be drawn into the lungs.

After the third cleavage, the embryo would be composed of 8 cells. If every cleavage step up up to this point was indeterminate, then each cell still has the necessary components to develop into a complete organism. The result would be 8 genetical identical organisms.

When blood returns to the heart via the superior and inferior vena cavae, it is deoxygenated. It remains this way as it passes through the right atrium, the right ventricle, and the pulmonary arteries, through which it travels to the lungs to conduct gas exchange with the alveoli. Both the right ventricle and the pulmonary artery contain deoxygenated blood.

All of the other answer choices contain at least one component that carries oxygenated blood.

Embryonic cleavage is the division of cells without cell growth. Once an ovum is fertilized by a sperm cell, it is called a zygote. The zygote undergoes multiple rapid cell cycles (rounds of mitosis) without significant growth, producing a dense cluster of cells that is the same size as the original zygote. This process is called cleavage.

The antifungal compound is likely specific to chitin, as it is a common material of many fungi cell wall structures. Chitin is resistant to breakdown, and is actually found in insect exoskeletons. The incorrect answers are found in skin cells as well as fungal cells, and would harm the skin if the chemical attacked these structures.