• The number of protons in an atom is equal to its atomic number.
• The periodic table shows that phosphorus (P) has an atomic number of 15.
• This means every phosphorus atom has 15 protons in its nucleus.

Analysis of Other Options:

• A. 30 → This is close to the atomic mass (30.97), but the atomic mass is not the same as the number of protons. ❌
• B. 16 → This is incorrect; sulfur (S) has an atomic number of 16, not phosphorus. ❌
• D. 31 → This is rounded from the atomic mass (30.97), but atomic mass ≠ number of protons. ❌

Down syndrome is a genetic disorder caused by the presence of an extra copy of chromosome 21. It is also known as trisomy 21, because affected individuals have three copies of chromosome 21 instead of the normal two.

The extra chromosome 21 in Down syndrome occurs due to a random error in cell division, which leads to the production of an abnormal gamete (egg or sperm) with an extra copy of the chromosome. When this gamete fuses with a normal gamete during fertilization, the resulting zygote has 47 chromosomes instead of the usual 46, and develops into a fetus with Down syndrome.

Down syndrome is characterized by a range of physical and intellectual symptoms, including developmental delays, intellectual disability, distinctive facial features, heart defects, and increased risk of certain medical conditions such as leukemia and Alzheimer's disease. However, the severity and expression of these symptoms can vary widely among affected individuals.

Insulin is a hormone produced by the pancreas that plays a crucial role in regulating the levels of glucose (sugar) in the blood. After a person eats a meal, the levels of glucose in the blood rise, which stimulates the pancreas to release insulin into the bloodstream. Insulin acts on various cells in the body, particularly those in the liver, muscles, and adipose tissue, to promote the uptake, use, and storage of glucose.

Insulin helps to lower the levels of glucose in the blood by increasing the uptake of glucose by cells, stimulating the liver and muscle cells to store glucose in the form of glycogen, and inhibiting the production and release of glucose by the liver. This process is known as glucose homeostasis, and it helps to keep the levels of glucose in the blood within a normal range.

Deficiencies or abnormalities in insulin production or function can lead to a range of metabolic disorders, including type 1 and type 2 diabetes. In type 1 diabetes, the body does not produce enough insulin, while in type 2 diabetes, the body becomes resistant to the effects of insulin, leading to elevated levels of glucose in the blood.

In the diagram, the circular molecules represent sugar. The square molecules represent hormones that regulate blood sugar levels. Among the answer choices:

• Insulin (A): Lowers blood sugar by promoting glucose uptake in cells.
• Norepinephrine (B): Involved in the fight-or-flight response, not directly related to blood sugar regulation.
• Calcitonin (C): Regulates calcium levels, not glucose.
• Glucagon (D): Raises blood sugar by promoting glucose release from the liver.

Since the diagram involves sugar regulation and the square molecules are coming from the liver, the square molecules represent glucagon hormones.

Ligaments are tough bands of fibrous ssue that connect two bones together in a joint. They provide stability and support to the joint, prevenng excessive movement and helping to maintain proper alignment of the bones.

The chemical formula for water is H2O. It consists of two hydrogen atoms and one oxygen atom.

Transfer RNA (tRNA) is a type of RNA molecule that carries amino acids to the ribosome during protein synthesis. Each tRNA molecule has a specific sequence of three nucleotides called an anticodon, which pairs with a complementary codon in the messenger RNA (mRNA) sequence. Each tRNA also carries a specific amino acid that corresponds to the codon it recognizes, allowing the ribosome to link the amino acids together in the correct order to form a protein.

In contrast, messenger RNA (mRNA) carries the genetic information from the DNA to the ribosome, where it serves as a template for protein synthesis. Ribosomal RNA (rRNA) is a component of the ribosome itself, where it helps to catalyze the formation of peptide bonds between amino acids. Small nuclear RNA (snRNA) is involved in splicing of pre-mRNA molecules during post-transcriptional processing.

The kidneys secrete a number of hormones, which are important for normal functioning of the body.

If blood pressure falls, renin is secreted by the kidneys to constrict the small blood vessels, thereby increasing blood pressure. If the kidneys aren’t functioning correctly, too much renin can be produced, increasing blood pressure and sometimes resulting in hypertension (high blood pressure). This is why a number of people with kidney diseases also have high blood pressure.

The unit used to indicate length is the meter (m). It is the base unit of length in the Internaonal System of Units (SI).