Water molecules enter cells by which of the following transport mechanisms?

A. Skeletal muscles are not autorhythmic; this term refers to the ability to generate a rhythmical electrical impulse without the need for nervous stimulation, which is a characteristic of cardiac muscles.

B. Cardiac muscles contain intercalated discs, which are unique structural formations that allow for the rapid transmission of electrical impulses between cardiac cells. This feature is not found in skeletal muscles, which are composed of individual muscle fibers that are controlled voluntarily.

C. Cardiac muscles are involuntary, meaning they function without conscious control, which is necessary for the continuous pumping action of the heart. In contrast, skeletal muscles are under voluntary control, allowing for movement of the body in response to conscious decisions.

D. Skeletal muscles are not found in the viscera; they are attached to bones and are responsible for body movements. Cardiac muscles, on the other hand, are located in the heart, which is not in the cranium but in the thoracic cavity. The term 'viscera' refers to the internal organs in the main cavities of the body, especially those in the abdomen, not the cranium.

A. The cell membrane, also known as the plasma membrane, is a common structure found in both prokaryotic and eukaryotic cells. It is a phospholipid bilayer that encloses the cell, providing a barrier to control the movement of substances in and out of the cell, thus maintaining homeostasis. It also plays a role in cell communication and signaling due to the presence of various proteins and carbohydrates on its surface.

B. The Golgi apparatus is an organelle found only in eukaryotic cells. It is involved in modifying, sorting, and packaging proteins and lipids for secretion or for use within the cell. It is part of the endomembrane system and works closely with the rough endoplasmic reticulum.

C. The endoplasmic reticulum (ER) is another organelle that is exclusive to eukaryotic cells.

It comes in two forms: rough ER, which is studded with ribosomes and is involved in protein synthesis, and smooth ER, which is involved in lipid synthesis and detoxification processes.

D. Chloroplasts are specialized organelles found in the cells of plants and some algae, which are eukaryotes. They are the site of photosynthesis, where light energy is converted into chemical energy in the form of glucose. Chloroplasts contain their own DNA and are part of the group of organelles known as plastids.

A. The rectum is the final section of the large intestine, terminating at the anus. It functions as a temporary storage site for feces before they are expelled from the body.

B. The jejunum is the second part of the small intestine, located between the duodenum and the ileum. It is specialized for the absorption of nutrients during digestion.

C. The cecum is a pouch connected to the junction of the small and large intestines. The vermiform appendix extends from the cecum, and although its function in humans is not entirely clear, it is believed to play a role in the immune system.

D. The ischium is not part of the digestive system; it is one of the three bones that make up the pelvis. It is important for sitting and is connected to the lower limbs.

A. Centrosomes are the microtubule-organizing centers in cells, playing a critical role in the spatial arrangement of cell structures and in cell division.

B. Ribosomes are the molecular machines within the cell that facilitate the production of proteins by translating messenger RNA into polypeptide chains.

C. Mitochondria are known as the powerhouses of the cell, generating most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy.

D. Lysosomes are membrane-bound organelles that contain enzymes capable of breaking down all types of biological polymers—proteins, nucleic acids, carbohydrates, and lipids. They are essential for intracellular digestion, the recycling of a cell's organic materials, and programmed cell death (apoptosis).

A. The nucleus is the command center of a eukaryotic cell, containing most of the cell's genetic material and regulating gene expression to control cell growth, division, and differentiation.

B. Lysosomes are membrane-bound organelles that contain enzymes for digesting macromolecules, old cell parts, and foreign invaders, acting as the waste disposal system of the cell.

C. Mitochondria are known as the powerhouses of the cell. They are responsible for producing adenosine triphosphate (ATP), the cell's main energy-carrying molecule, through a process called cellular respiration.

D. Centrioles are cylindrical structures that are involved in the organization of microtubules during cell division, playing a crucial role in the formation of the spindle fibers that separate chromosomes during mitosis and meiosis.

A. This plate represents good antibiotic activity against Escherichia.

B. This is the plate that represents the highest number of bacteria. The bacteria that grow on this plate are the most resistant to the antibiotic because they can survive in a high concentration of the substance. In the other plates, the antibiotic inhibits the growth of the bacteria to a greater or lesser extent, depending on their sensitivity.

C. This plate represents partial antibiotic activity against Escherichia.

D. This represents no activity that may be due to inappropriate media.

A. The rate of fall is affected by mass of the object, since object D and C fall at a faster rate than A. However it is important to consider other factors such as shape and size of the object.

B. Although objects A and B have the same mass, they do not fall at the same rate, as evidenced by their different times of fall.

C. The data does not support the conclusion that greater mass leads to a faster fall. Object C, with a mass of 30.0g, falls in 0.5sec, while object D, with a greater mass of 35.0g, falls in a longer time of 1.5sec.

D. A and B have the same mass but have different rates of fall. This indicates that air resistance is greater for A, hence the slower rate of fall.

A. This option changes the population, which could introduce new variables related to gender differences in metabolism or physical performance.

B. This option introduces another variable by using two different energy drinks, which could have different ingredients and effects.

C. This option changes the distance run, which could affect the endurance aspect rather than the speed.

D. To best support the conclusion that energy drinks increase the speed of running in women, it would be most effective to conduct a controlled experiment where a variable is changed while others are kept constant. By giving half of the women water and the other half the energy drink, researchers can directly compare the effects of the energy drink against a baseline (water), which has no enhancing properties on running speed. This comparison would help to isolate the effect of the energy drink on running performance

A. Parathyroid hormone (PTH) is secreted by the parathyroid glands and plays a critical role in regulating calcium levels in the blood. It acts on bones, kidneys, and the intestine to increase blood calcium levels when they are low. In the bones, PTH stimulates osteoclasts, which break down bone tissue, releasing calcium into the bloodstream. In the kidneys, it increases the reabsorption of calcium, preventing its loss through urine. Additionally, PTH influences the intestines to absorb more calcium from the food we eat.

B. Norepinephrine is a hormone and neurotransmitter involved in the body's fight or flight response. It does not regulate blood calcium levels but rather affects heart rate, blood pressure, and blood glucose levels.

C. Growth hormone, produced by the pituitary gland, stimulates growth in children and adolescents and helps to maintain muscle mass and bone density in adults. It does not directly regulate calcium levels in the blood.

D. Melatonin is a hormone secreted by the pineal gland, primarily influencing sleep-wake cycles and circadian rhythms. It does not have a role in regulating blood calcium levels.

A. Histones are proteins that provide structural support to chromosomes. They act as spools around which DNA winds, and play a role in gene regulation.

B. Chromatin is a complex of DNA and protein found in eukaryotic cells. Its primary function is packaging long DNA molecules into more compact, dense structures. This packaging allows for DNA to fit within the cell nucleus and protects DNA structure and sequence. Chromatin also plays an essential role in regulating gene expression and DNA replication. The hereditary information of humans is encoded in the DNA.

C. ATP, or adenosine triphosphate, is the energy currency of the cell. It is used to power various biochemical reactions within the cell and is not involved in storing genetic information.

D. Plasmids are small DNA molecules within a cell that are physically separated from chromosomal DNA and can replicate independently. They are most commonly found in bacteria and are not typically involved in the storage of hereditary information in humans. Plasmids are used in biotechnology to manipulate genes and are important tools in genetic engineering.