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 B
Explanation
The corpus luteum is a structure that develops in the ovary after an egg has been released.
It secretes the hormone progesterone, which prepares the uterus for a fertilized egg to implant and helps maintain the uterine lining during pregnancy1.
Choice A.
Umbilical cord is not correct because it is a structure that connects the developing fetus to the placenta and provides nutrients and oxygen to the fetus, but does not secrete hormones.
Choice C.
Oviduct is not correct because it is a tube that transports eggs from the ovary to the uterus, but does not secrete hormones.
Choice D.
Oocyte is not correct because it is an immature egg cell, but does not secrete hormones.
Correct Answer is B
Explanation
The hypothesis should be modified to include the new findings that worm infestation can relieve the effects of certain autoimmune disorders.
A possible modification could be: “Parasitic worm infestation can have both damaging and beneficial effects on the host.
While it can cause harm, it has also been found to reduce the severity of certain autoimmune disorders.”
Choice A.
Worm infestation prevents the body from immune malfunction is not correct because it overstates the findings and implies that worm infestation completely prevents immune malfunction, which is not supported by the evidence.
Choice C.
Worm infestations exacerbate the body’s immune reactions is not correct because it contradicts the new findings that worm infestation can relieve the effects of certain autoimmune disorders.
Choice D.
Lack of worm infestations is the cause of some autoimmune disorders is not correct because it overstates the findings and implies a causal relationship between lack of worm infestations and autoimmune disorders, which is not supported by the evidence.
Correct Answer is A
Explanation
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.
Correct Answer is A
Explanation
Melanin.
Melanin is a pigment produced by cells called melanocytes in the skin.
It protects the skin from ultraviolet (UV) radiation by absorbing and dissipating over 99.9% of absorbed UV radiation.
This helps to prevent DNA damage and other adverse effects of UV radiation on the skin.
Choice B.
Perspiration is not correct because it is a fluid produced by sweat glands in the skin that helps to regulate body temperature, but it does not protect the skin from UV radiation.
Choice C.
Sebum is not correct because it is an oily substance produced by sebaceous glands in the skin that helps to lubricate and protect the skin, but it does not protect the skin from UV radiation.
Choice D.
Keratin is not correct because it is a fibrous protein that provides strength and durability to the skin, hair and nails, but it does not protect the skin from UV radiation.
Correct Answer is B
Explanation
The atomic number of an element represents the number of protons in the nucleus of an atom of that element.
Since lithium has an atomic number of 3, it has 3 protons in its nucleus.
Choice A is not correct because 7 is the mass number of lithium, not the number of protons.
Choice C is not correct because 12 is not the atomic number or mass number of lithium.
Choice D is not correct because 4 is not the atomic number or mass number of lithium.
Correct Answer is C
Explanation
Bag mass change is the dependent variable in this experiment.
In an experiment, the dependent variable is the variable that is being measured and is expected to change in response to changes in the independent variable(s).
In this case, the bag mass change is being measured and is expected to change in response to changes in the independent variable (sucrose concentration).
Choice A is incorrect because duration is not a variable in this experiment.
Choice B is incorrect because temperature is not a variable in this experiment.
Choice D is incorrect because sucrose concentration is an independent variable, not a dependent variable.
An independent variable is a variable that is manipulated by the experimenter to see how it affects the dependent
Correct Answer is B
Explanation
Calcium ions play a crucial role in initiating muscle contraction.
When a muscle cell is stimulated to contract by an action potential, calcium channels open in the sarcoplasmic membrane and release calcium into the sarcoplasm.
Some of this calcium attaches to troponin, which causes it to change shape.
This shape change exposes binding sites for myosin on the actin filaments.
Myosin’s binding to actin causes crossbridge formation, and contraction of the muscle begins.
The other ions mentioned in the question do not have this specific role in muscle contraction.
Potassium ions are important for maintaining the resting membrane potential of cells, but they do not bind to the troponin complex.
Phosphorus ions are important for energy metabolism, but they do not bind to the troponin complex.
Sodium ions are important for generating action potentials, but they do not bind to the troponin complex.
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
Proteins.
Proteins are made up of amino acids which are organic molecules that contain both an amine functional group (–NH2) and a carboxylic acid functional group (– COOH).
Choice A, Lipids, is not the correct answer because lipids are a group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins, monoglycerides, diglycerides, triglycerides, phospholipids, and others.
They do not contain both an amine and carboxyl group.
Choice B, Chitin, is not the correct answer because chitin is a long-chain polymer of N-acetylglucosamine, a derivative of glucose.
It does not contain both an amine and carboxyl group.
Choice C, Cellulose, is not the correct answer because cellulose is an organic compound with the formula (C6H10O5)n, a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units.
It does not contain both an amine and carboxyl group.
Correct Answer is C
Explanation
Other scientists can validate or disprove the findings.
It is important for new scientific findings to be published so that other scientists can review the research and either validate or disprove the findings.
This process of peer-review helps to ensure the accuracy and reliability of scientific research.
Choice A.
Scientists will get paid if their findings are published is not correct because while some scientists may receive funding or grants for their research, the primary goal of publishing scientific findings is not for financial gain.
Choice B.
Publishing findings will help scientists become more biased is not correct because the goal of publishing scientific findings is to share information and promote transparency, not to promote bias.
Choice D.
This prevents other scientists from performing similar tests is not correct because publishing scientific findings allows other scientists to build upon the research and perform further tests to validate or disprove the findings.
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