What is the approximate threshold value for mammalian neurons?
-55 mV
-80 mV
+35 mV
0 mV
Correct Answer : A
The approximate threshold value for mammalian neurons is -55 mV.
The threshold potential is the critical level to which a membrane potential must be depolarized to initiate an action potential.
Most often, the threshold potential is a membrane potential value between –50 and –55 mV
The membrane potential of a neuron is determined by the distribution of ions across the cell membrane.
At rest, the inside of a neuron is more negative than the outside due to the presence of negatively charged proteins and other molecules.
The movement of ions across the cell membrane can change the membrane potential.
For example, when sodium ions enter the cell, they make the inside of the cell more positive (less negative), causing depolarization.
Choice B is incorrect because -80 mV is below the typical threshold value for mammalian neurons.
Choice C is incorrect because +35 mV is above the typical threshold value for mammalian neurons.
Choice D is incorrect because 0 mV is above the typical threshold value for mammalian neurons.
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Correct Answer is A
Explanation
As a solid turns to a liquid, the particles become less ordered and more free to move around.
Choice B is not correct because particles have an increase in mobility as a solid turns to a liquid.
Choice C is not correct because particles move further apart as a solid turns to a liquid.
Choice D is not correct because intermolecular forces between particles become weaker as a solid turns to a liquid.
Correct Answer is C
Explanation
A tsunami is a catastrophic ocean wave that is usually caused by a submarine earthquake.
It can also be caused by an underwater or coastal landslide, the eruption of a volcano, or the impact of a meteor or comet in a body of water.

Choice A is not correct because sunspot activity does not cause tsunamis.
Choice B is not correct because lightning strikes do not cause tsunamis.
Choice D is not correct because flooding does not cause tsunamis.
Correct Answer is B
Explanation
The atomic number of an atom is equal to the number of protons in its nucleus.
In this case, the atom has 12 protons, so its atomic number is 12.

Choice A, 24, is not the correct answer because it represents the sum of the number of protons and neutrons in the atom’s nucleus, which is known as the mass number.
Choice C, 1, is not the correct answer because it does not represent the number of protons in the atom’s nucleus.
Choice D, 144, is not the correct answer because it represents the square of the mass number and does not represent any property of the atom.
Correct Answer is D
Explanation
Genes are used in the process of DNA sequencing to determine the order of nucleotides in a DNA molecule.

Choice B.
Blood types is not the correct answer because blood types are determined by the presence or absence of specific antigens on the surface of red blood cells and are not directly related to DNA sequencing.
Choice C.
Hormones is not the correct answer because hormones are chemical messengers produced by glands in the body and are not directly involved in DNA sequencing.
Choice D.
Genes is the correct answer because genes are used in the process of DNA sequencing to determine the order of nucleotides in a DNA molecule.
Correct Answer is A
Explanation
Urea is a substance that is excreted by sweat glands in response to the breakdown of proteins and the formation of ammonia.
When proteins are broken down, they produce ammonia, which is a highly toxic compound for the body.
Ammonia is then converted into urea and released out of the body through sweat glands.
Choice B.
Sebum is not correct because it is an oily substance secreted by sebaceous glands to lubricate and protect the skin, but it is not related to the breakdown of proteins or the formation of ammonia.
Choice C.
Water is not correct because while it is a component of sweat, it is not specifically related to the breakdown of proteins or the formation of ammonia.
Choice D.
Lysozymes are not correct because they are enzymes found in tears, saliva and other body fluids that have antibacterial properties, but they are not related to the breakdown of proteins or the formation of ammonia.
Correct Answer is D
Explanation
Triple covalent bonds.
Nitrogen gas (N2) is an extremely stable molecule because it consists of two nitrogen atoms bonded together by a triple covalent bond.
A covalent bond is a type of chemical bond where atoms share electrons to form a molecule.
In a triple covalent bond, three pairs of electrons are shared between the two atoms, resulting in a very strong bond that makes the molecule extremely stable.

Choice A.
Ionic bonds is not correct because ionic bonds involve the transfer of electrons from one atom to another to form ions, which are then attracted to each other due to their opposite charges.
Nitrogen gas does not contain ions and is not held together by ionic bonds.
Choice B.
Hydrogen bonds is not correct because hydrogen bonds are weak electrostatic attractions between molecules that contain hydrogen atoms bonded to highly electronegative atoms such as oxygen or nitrogen.
Nitrogen gas does not contain hydrogen atoms and is not held together by hydrogen bonds.
Choice C.
Resonance bonds is not correct because resonance refers to the delocalization of electrons in a molecule where multiple Lewis structures can be drawn to represent the molecule.
Nitrogen gas has a single Lewis structure and does not exhibit resonance.
Correct Answer is D
Explanation
The polarity of water molecules explains its solvent abilities for certain substances.
Water is a polar molecule because it has a partial positive charge on one end and a partial negative charge on the other end due to the unequal sharing of electrons between the oxygen and hydrogen atoms.
This polarity allows water to dissolve other polar substances and ionic compounds.

Choice A.
Kinetic energy of liquid water molecules is not the correct answer because kinetic energy refers to the energy of motion and does not directly explain water’s solvent abilities.
Choice B.
High specific heat is not the correct answer because specific heat refers to the amount of heat required to raise the temperature of a substance and does not directly explain water’s solvent abilities.
Choice C.
High surface tension is not the correct answer because surface tension refers to the cohesive forces between liquid molecules and does not directly explain water’s solvent abilities.
Correct Answer is C
Explanation
Ovulation is the process in which an ovarian follicle matures and releases a reproductive egg.
During ovulation, a mature egg is released from the female ovary, enabling it to be fertilized by male sperm cells 1.

Choice A is incorrect because menstruation is the process of shedding the uterine lining, which occurs when an egg is not fertilized.
Choice B is incorrect because fertilization is the process of a sperm cell joining with an egg cell to form a zygote.
Choice D is incorrect because oogenesis is the process of forming female gametes (eggs) in the ovaries.
Correct Answer is D
Explanation
Microtubule organization.
Centrosomes are organelles that serve as the main microtubule-organizing centers for animal cells.
They regulate the movement of microtubules and other cytoskeletal structures, thereby facilitating changes in the shapes of the membranes of animal cells.

Choice A, Organelle trafficking, is not the correct answer because while centrosomes do play a role in intracellular trafficking during interphase by organizing an astral ray of microtubules, their main function is microtubule organization.
Choice B, Pathogen digestion, is not the correct answer because centrosomes do not play a direct role in pathogen digestion.
Choice C, Cytoplasm formation, is not the correct answer because centrosomes do not play a direct role in cytoplasm formation.
Correct Answer is C
Explanation
Heavier objects fall faster than lighter objects.
The data in the table shows that as the number of filters (and therefore the mass) increases, the terminal velocity also increases.
This means that the heavier objects (with more filters) are falling faster than the lighter objects (with fewer filters).
Choice A is not supported by the data in the table as much as it is true.
Terminal velocity is indeed when the force of gravity is equal to air resistance, but this definition does not provide any information about the relationship between mass and terminal velocity.
Choice B is also not supported by the data in the table.
The data does not provide any information about the time it takes for an object to reach terminal velocity.
Choice D is not supported by the data in the table.
The data shows that as the number of filters increases, the terminal velocity also increases.
This means that the greater the number of filters, the greater (not smaller) the terminal velocity.
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