Which of the following are the two major parts of the nervous system?

To determine the second lowest molecular weight, calculate the molar mass of each substance using the atomic masses provided.

Hydrogen peroxide (H₂O₂)

Hydrogen peroxide contains 2 hydrogen atoms and 2 oxygen atoms:

(2 × 1.008) + (2 × 15.999)

= 2.016 + 31.998
= 34.014 g/mol

Glycerol (C₃H₈O₃)

Glycerol contains 3 carbon atoms, 8 hydrogen atoms, and 3 oxygen atoms:

(3 × 12.011) + (8 × 1.008) + (3 × 15.999)

= 36.033 + 8.064 + 47.997
= 92.094 g/mol

Octane (C₈H₁₈)

(8 × 12.011) + (18 × 1.008)

= 96.088 + 18.144
= 114.232 g/mol

Mercury (Hg)

Mercury consists of a single type of atom, so its molar mass is simply:

200.59 g/mol

Putting them in order from lowest to highest:

Hydrogen peroxide: 34.014 g/mol
Glycerol: 92.094 g/mol ← second lowest
Octane: 114.232 g/mol
Mercury: 200.59 g/mol

Therefore, glycerol has the second lowest molecular weight.

Why the Other Choices Are Wrong

Hydrogen peroxide (H₂O₂) has the lowest, not the second lowest, molecular weight at approximately 34.014 g/mol.

Octane (C₈H₁₈) has a molecular weight of approximately 114.232 g/mol, making it the third lowest of the substances listed.

Mercury (Hg) has a molar mass of 200.59 g/mol, which is the highest value among the choices.

Key Takeaways

• Calculate molecular weight by multiplying each element's atomic mass by the number of its atoms and adding the results.
• Subscripts in a chemical formula tell you how many atoms of each element are present.
• Always calculate all choices when a question asks for the lowest, highest, second lowest, or second highest value.
• The order here is:

H₂O₂ < C₃H₈O₃ < C₈H₁₈ < Hg

• Therefore, the second lowest molecular weight is glycerol (C₃H₈O₃), approximately 92.094 g/mol.

A bolus is a mass of chewed food mixed with saliva that is formed in the mouth before swallowing. After swallowing, the bolus enters the esophagus.

The esophagus moves the bolus toward the stomach through peristalsis. Peristalsis consists of coordinated, wave-like contractions of smooth muscle in the wall of the digestive tract. Muscles contract behind the bolus and relax ahead of it, pushing the food toward the stomach.

Why the correct answer is correct

Esophagus, peristalsis: This pairing is correct because the esophagus uses peristaltic contractions to propel swallowed food from the pharynx toward the stomach.

Why the other choices are wrong

Large intestine, secretion of salivary amylase: Salivary amylase begins carbohydrate digestion and is secreted primarily by the salivary glands, not the large intestine.

Small intestine, mastication: Mastication means chewing, which occurs in the mouth through the action of the teeth and jaw, not in the small intestine.

Tongue, neutralization of acid: The tongue helps manipulate food, form a bolus, and initiate swallowing. Neutralization of acidic chyme occurs mainly in the small intestine, especially through bicarbonate released in pancreatic secretions.

Key Takeaways

• Bolus means chewed food mixed with saliva.
• Peristalsis is a wave-like muscular contraction that moves material through the digestive tract.
• The esophagus uses peristalsis to move a bolus toward the stomach.
• Mastication occurs in the mouth.
• Salivary amylase is produced by the salivary glands.

A decrease in bone density correlates with an increase in hip fracture probability for all ages.

Explanation

The question tells us that a lower T score indicates lower bone density. Therefore, moving from a T score of 0 toward -3 means that bone density is decreasing.

Now look across every age group:

• At age 50, fracture probability increases from 3% → 5% → 8% → 9% as the T score decreases.
• At age 60, it increases from 6% → 8% → 12% → 13%.
• At age 70, it increases from 9% → 12% → 18% → 20%.
• At age 80, it increases from 14% → 20% → 28% → 32%.

The same pattern occurs at every age: lower bone density is associated with a higher percentage of hip fractures. This is why the conclusion that a decrease in bone density correlates with an increase in hip fracture probability for all ages is best supported by the data.

The table also shows that age matters: for the same T score, fracture percentages generally rise as age increases.

Why the Other Choices Are Wrong

“A 70-year-old with a bone density of -1 has a lower risk of fracture than a 50-year-old with a bone density of -3.”

According to the table:

Age 70, T score -1 = 12%
Age 50, T score -3 = 9%

Since 12% is greater than 9%, the 70-year-old actually has the higher, not lower, fracture probability.

“A 50-year-old with a bone density of -2 has a higher risk of hip fracture than an 80-year-old with a bone density of 0.”

The table shows:

Age 50, T score -2 = 8%
Age 80, T score 0 = 14%

Because 8% is less than 14%, this statement is incorrect.

“A higher bone density is correlated with an increased risk of hip fracture for all ages.”

This is the opposite of the pattern in the table. Higher bone density corresponds to a higher T score, such as 0, and these patients consistently have lower fracture percentages than patients with T scores of -1, -2, or -3.

For example, at age 80:

T score 0 = 14% fracture rate
T score -3 = 32% fracture rate

Thus, lower, not higher, bone density is associated with increased hip fracture probability.

Key Takeaways

• A more negative T score means lower bone density.
• As the T score decreases from 0 to -3, hip fracture probability increases at every age shown.
• Increasing age is also associated with increasing hip fracture probability in the table.
• When interpreting a data table, compare the actual numerical values rather than relying only on general assumptions.
• The best-supported conclusion is: A decrease in bone density correlates with an increase in hip fracture probability for all ages.

The human nervous system is divided into two major structural parts: the central nervous system (CNS) and the peripheral nervous system (PNS).

The central nervous system consists primarily of the:

Brain + Spinal cord

It acts as the body's main processing and control center. It receives information, processes it, and coordinates appropriate responses.

The peripheral nervous system includes the nerves and associated structures located outside the brain and spinal cord. It connects the CNS with muscles, organs, glands, and sensory receptors throughout the body.

The basic organization is:

Nervous System → Central Nervous System + Peripheral Nervous System

The peripheral nervous system can then be further divided into somatic and autonomic components.

Why the other choices are wrong

“Autonomic nervous system and central nervous system”

The autonomic nervous system is not one of the two major structural divisions of the entire nervous system. It is primarily considered a functional subdivision of the peripheral nervous system, regulating involuntary functions such as heart rate, digestion, and glandular activity.

“Autonomic nervous system and somatic nervous system”

These are important subdivisions of the peripheral nervous system, rather than the two major divisions of the entire nervous system. The somatic system is associated mainly with voluntary skeletal muscle control and conscious sensory information, while the autonomic system regulates involuntary functions.

“Peripheral nervous system and somatic nervous system”

The somatic nervous system is a subdivision within the peripheral nervous system. Therefore, these two are not equivalent major divisions.

Key Takeaways

• The nervous system has two major divisions: CNS and PNS.
• Central nervous system (CNS) = brain + spinal cord.
• Peripheral nervous system (PNS) = nerves and related structures outside the brain and spinal cord.
• The PNS includes somatic and autonomic divisions.
• The somatic nervous system mainly handles voluntary skeletal muscle activity and sensory information.

The autonomic nervous system regulates involuntary functions involving structures such as the heart, smooth muscle, and glands.

The endometrium is the inner lining of the uterus. During each menstrual cycle, hormones—particularly estrogen and progesterone—cause its functional layer to thicken and become highly vascularized in preparation for possible implantation of an embryo.

If implantation does not occur, there is no sustained hormonal signal to maintain the uterine lining. The corpus luteum degenerates, causing progesterone and estrogen levels to fall. The decline in these hormones leads to breakdown of the functional layer (stratum functionalis) of the endometrium.

This tissue, along with blood and other material, is then discharged during menstruation.

The sequence can be summarized as:

No implantation → corpus luteum degenerates → estrogen and progesterone decrease → functional endometrium degenerates → menstruation

The deeper basal layer of the endometrium remains and helps regenerate the functional layer during the next menstrual cycle.

Why the other choices are wrong

“The myometrium is reabsorbed.”

The myometrium is the thick muscular layer of the uterus. It produces uterine contractions and is not normally shed or reabsorbed during menstruation. The tissue that undergoes cyclic breakdown is the functional layer of the endometrium.

“The myometrium undergoes meiosis.”

Meiosis is the specialized type of cell division used to produce gametes, such as eggs and sperm. The muscle cells of the myometrium do not undergo meiosis as part of the menstrual cycle.

“The endometrium persists until the next ovulation.”

Without implantation, the functional layer does not simply remain intact until the next ovulation. Falling progesterone and estrogen levels cause it to degenerate and be shed during menstruation. The basal portion remains and generates a new functional layer during the next cycle.

Key Takeaways

• Endometrium: inner lining of the uterus.
• Myometrium: muscular middle layer of the uterus.
• The functional endometrium thickens in preparation for implantation.
• Without implantation, estrogen and progesterone levels decline.
• The functional layer of the endometrium degenerates and is shed during menstruation.
• The basal layer remains and helps rebuild the endometrium for the next cycle.

The most important abnormal finding is the very high glucose level in the urine.

The patient's urine glucose is:

200 mmol/L

The expected result is:

<0.8 mmol/L

This is a major elevation and indicates glycosuria, which means glucose is present in the urine in an abnormally high amount.

Normally, glucose that is filtered by the kidneys is almost completely reabsorbed back into the blood. However, when blood glucose becomes excessively high, the kidneys may not be able to reabsorb all of it. The excess glucose then remains in the urine. This commonly occurs in diabetes mellitus, where blood glucose levels may become abnormally elevated.

The other test results are generally within the expected ranges:

• Protein: 0 g/L — within the expected range of 0–0.08 g/L.
• Leukocytes: 0 per hpf — within the expected range of 0–4 per hpf.
• pH: 5.5 — within the expected range of 4.6–8.
• Glomerular filtration rate: 125 mL/min — above the expected minimum of 90 mL/min.

Because glucose is the only strikingly abnormal result, diabetes is the most logical conclusion.

Why the Other Choices Are Wrong

The patient may be experiencing kidney failure.

This is not well supported because the glomerular filtration rate is 125 mL/min, which is within the expected range given in the table. Kidney failure is generally associated with a significantly reduced GFR. The absence of abnormal protein in the urine also makes this choice less consistent with the results.

The patient may be on an extreme, low-calorie diet.

An extreme low-calorie diet may cause metabolic changes such as increased fat breakdown and ketone production, but it does not best explain the extremely elevated urine glucose level shown here.

The patient may have a urinary tract infection.

A urinary tract infection often causes an increase in leukocytes in the urine because white blood cells respond to infection. This patient's leukocyte count is 0 per hpf, which is within the expected range. Therefore, the results do not strongly support a urinary tract infection.

Key Takeaways

• Glycosuria means glucose is present in the urine.
• A very high urine glucose level can be associated with diabetes mellitus.
• High urine leukocytes would be more suggestive of a urinary tract infection.
• A substantially low GFR would be more concerning for impaired kidney function.
• In this table, the main abnormal finding is the glucose level: 200 mmol/L compared with an expected value of less than 0.8 mmol/L.

After a person eats a sugary candy bar, carbohydrates are digested and glucose is absorbed into the bloodstream. This causes blood glucose levels to rise.

The increase in blood glucose stimulates the beta cells of the pancreas to release insulin into the bloodstream. Insulin helps return blood glucose toward its normal range by promoting glucose uptake by cells, particularly muscle and adipose cells. It also encourages the liver and muscles to store excess glucose as glycogen.

The basic sequence is:

Sugary food → Blood glucose rises → Pancreas releases insulin → Cells take up glucose → Blood glucose decreases toward normal

Why the correct answer is correct

Insulin is the primary hormone released when blood glucose becomes elevated after a carbohydrate-rich meal. It lowers blood glucose by promoting glucose uptake and storage.

Why the other choices are wrong

Progesterone: This is primarily a reproductive hormone involved in regulating the menstrual cycle and maintaining the uterine lining. It is not the main hormone released in response to elevated blood glucose.

Cortisol: Cortisol is a glucocorticoid released by the adrenal cortex, particularly during stress. Among its metabolic effects, it can increase blood glucose, rather than serving as the primary response to a sugary meal.

Glucagon: Glucagon generally has the opposite effect of insulin. It is released mainly when blood glucose is low and stimulates the liver to release glucose into the bloodstream.

Key Takeaways

• High blood glucose → insulin release.
• Low blood glucose → glucagon release.
• Insulin is produced by pancreatic beta cells.
• Insulin promotes glucose uptake and glycogen formation.
• After eating a sugary food, insulin levels normally increase.

The kidneys filter the blood and help maintain the body's balance of water, electrolytes, and other dissolved substances called solutes. Their functional units, called nephrons, filter blood and determine which substances should be returned to the bloodstream and which should be eliminated in urine.

Blood filtration begins at the glomerulus. Useful substances can be reabsorbed, while excess ions, metabolic wastes such as urea, and excess water can ultimately be removed in urine.

Why the correct answer is correct

Kidney: The kidneys regulate the composition of the blood by filtering it and removing excess solutes, water, and metabolic wastes. They are also important for maintaining electrolyte and acid-base balance.

Why the other choices are wrong

Spleen: The spleen filters blood cells, removing old or damaged red blood cells, and contributes to immune function. It is not the primary organ for removing excess dissolved solutes.

Gallbladder: The gallbladder stores and concentrates bile produced by the liver. It does not filter blood.

Stomach: The stomach is primarily involved in the mechanical and chemical digestion of food. It does not regulate blood solute concentrations through filtration.

Key Takeaways

• The kidneys filter the blood and produce urine.
• The nephron is the functional unit of the kidney.
• Filtration begins in the glomerulus.
• Kidneys regulate water, electrolytes, pH, and metabolic waste levels.
• The spleen filters blood cells, whereas the kidneys filter blood plasma and regulate its dissolved substances.

The experiment investigates the relationship between light intensity and plant growth. Four groups of plants were exposed to different light intensities—30%, 50%, 70%, and 100%—while all other growth conditions were kept controlled.

The most important observation is that plants exposed to 50% light intensity showed the best growth.

This finding indicates that increasing light intensity can benefit plant growth, but only up to an optimal level. In this experiment, the optimum among the tested intensities was 50%. Increasing the light intensity beyond this level to 70% or 100% did not produce better growth.

Why “Growth improves with light intensity up to a point and then decreases” is correct

Plants require light for photosynthesis, the process through which they convert light energy into chemical energy that can be used for growth.

At relatively low light intensities, increasing the amount of available light can increase photosynthesis because more light energy is available. Consequently, plant growth may increase.

However, this relationship does not necessarily continue indefinitely. Eventually, a plant reaches an optimal light intensity. Beyond the optimum, additional light may provide no further benefit and, under sufficiently intense conditions, may contribute to stress or reduced photosynthetic performance.

The experimental result fits this general pattern because 50% light intensity produced greater growth than the other tested intensities. Therefore, the evidence supports the idea that there is an intermediate optimum rather than assuming that either the lowest or highest light level is always best.

One qualification is important: from the wording provided, we know that 50% produced the greatest growth, but we are not given the exact growth measurements for 30%, 70%, and 100%. Thus, the first hypothesis is the best-supported choice among those provided, rather than a complete mathematical description of the relationship.

Why the Other Choices Are Wrong

“Plants with low light intensity grow best.”

This is not supported by the experiment.

The lowest light intensity tested was 30%, but the plants at 50% intensity showed the best growth. Therefore, the results do not support the general claim that plants receiving the lowest amount of light grow best.

Plants need adequate light for photosynthesis, so insufficient light can also limit growth.

“Light intensity has no effect on plant growth.”

This contradicts the experimental findings.

If light intensity had no effect, changing the light intensity from 30% to 50%, 70%, or 100% should not systematically influence growth. Yet the experiment specifically found that the plants receiving 50% light intensity had the best growth.

Because light intensity was the variable deliberately changed while the other growth conditions were controlled, the differences in growth support a relationship between light intensity and plant growth.

“Plants at the highest light intensity grow best.”

This is directly contradicted by the observation.

The highest light intensity tested was 100%, but the plants at 50% intensity showed the best growth. Therefore, the experiment does not support the idea that continually increasing light intensity results in continually increasing plant growth.

More light is not necessarily always better. Biological processes frequently have an optimal range, with performance decreasing or leveling off when environmental conditions move beyond that range.

Key Takeaways

• Independent variable: Light intensity (30%, 50%, 70%, and 100%).
• Dependent variable: Plant growth.
• Controlled variables: All other growth conditions were kept consistent across the groups.
• Main observation: Plants exposed to 50% light intensity showed the best growth.
• The results suggest that plant growth has an optimal light intensity rather than simply increasing as light intensity increases.
• An intermediate treatment producing the best result can indicate an optimum relationship, where increasing a factor helps only up to a certain point.
• The experiment does not support the claim that the lowest or highest light intensity necessarily produces the greatest growth.
• Controlling other growth conditions is important because it allows differences in plant growth to be associated more confidently with the variable being tested—light intensity.

Density describes how much mass is contained in a given volume. It is calculated using:

Density = Mass ÷ Volume

The object's mass is 10 g. Because the submerged object displaces 5 mL of water, its volume is 5 mL.

Therefore:

Density = 10 g ÷ 5 mL

Density = 2 g/mL

So, the correct answer is 2 g per mL.

Why the other choices are wrong

0.5 g per mL: This results from dividing the volume by the mass, 5 ÷ 10. The density formula requires mass divided by volume, not volume divided by mass.

5 g per mL: The value 5 mL represents the object's volume, not its density.

10 g per mL: The value 10 g represents the object's mass. It must be divided by the volume to determine density.

Key Takeaways

• Density = mass ÷ volume.
• Water displacement can be used to determine the volume of an irregular object.
• A 5 mL water displacement means the object's volume is 5 mL.

For this object: 10 g ÷ 5 mL = 2 g/mL.