Exam #2 Flashcards
(41 cards)
What is the original source of energy used to drive the light independent reactions of photosynthesis?
A. substrate level phosphorylation B. the breakdown of glucose C. photolysis of water to release electrons D. ATP produced by mitochondria E. photons absorbed by chlorophyll
E. photons absorbed by chlorophyll
This is actually a simple question. If you step back, the question is asking where the energy used in photosynthesis comes from. The energy used to drive photosynthesis comes from light, or photons, choice [E]. The light independent reactions (Dark reactions, also known as the Calvin-Benson Cycle) takes the energy produced in the light dependent reactions along with CO2 to produce glucose. Substrate level phosphorylation is related to glycolysis, or breaking down glucose, so [A] is out. The idea of photosynthesis is to produce glucose, not to breakdown glucose, so [B] is out. Choice [C] is a plausible distractor, but ultimately the energy used in the photolysis of water comes from light as well! Choice [D] is unrelated to photosynthesis.
Q: What is the original source of energy used to drive the light independent reactions of photosynthesis?
A. Substrate level phosphorylation
Substrate level phosphorylation produces ATP, and while ATP is consumed in the light independent reactions of photosynthesis, ATP is not the original source of the energy used to drive these reactions; therefore the answer choice is incorrect. Substrate level phosphorylation produces ATP via direct enzymatic transfer of a phosphate group to ADP without the use of any carriers.
Test your knowledge: during aerobic respiration, which processes produce ATP via substrate level phosphorylation, and which processes use oxidative phosphorylation?
B. The breakdown of glucose
Glucose is broken down by cells to produce ATP, and while ATP is consumed in the light independent reactions of photosynthesis, ATP is not the original source of the energy used to drive these reactions; therefore the answer choice is incorrect. The general breakdown of glucose via cellular respiration follows the following formula: C6H12O6 + 6O2 -> 6CO2 +6H2O + energy. The amount of energy (ATP) produced varies based on aerobic vs anaerobic pathways.
C. Photolysis of water to release electrons
Photolysis is the splitting of water molecules which yields electrons, protons, and O2. None of these products are used as an energy source to drive the light independent reactions of photosynthesis; therefore the answer choice is incorrect.
D. ATP produced by mitochondria
ATP produced via mitochondria are generally used as energy to power cellular activities, so this answer may seem appealing. ATP is consumed in the light independent reactions of photosynthesis, but the ATP used is not the original source of the energy used to drive these reactions; therefore the answer choice is incorrect. ATP is produced in the mitochondrial matrix of the mitochondria. While plants can produce ATP via noncyclic phosphorylation, they still have mitochondria which produce ATP used for general cellular function.
E. Photons absorbed by chlorophyll When light (photons) is present, the light-absorbing pigments absorb energy. This energy excites electrons, which become unstable and re-emit the absorbed energy, which is then absorbed and re-emitted by electrons of nearby pigment molecules until this energy is absorbed by chlorophyll molecules. This process allows for noncyclic photophosphorylation to occur, which in turn provides the ATP molecules used for energy in the light independent reactions of photosynthesis. Since the original source of this energy is the photons from light absorbed by chlorophyll, the answer choice is correct.
While it is tempting to select an answer that states ATP is the source of the energy since it is used for energy in the light independent reactions, remember that it is the photons from light that allow this ATP to be made in the first place, making “photons absorbed by chlorophyll” the best answer.
[Answer to Test your knowledge: glycolysis and the Krebs cycle produce ATP via substrate level phosphorylation. The electron transport chain produces ATP via oxidative phosphorylation].
If 2n=8, how many chromosomes are present during anaphase?
A. 2 B. 4 C. 8 D. 16 E. 32
D. 16
Before anaphase, the DNA in a cell has duplicated and condensed, given us 2 chromatids per chromosome. During anaphase, the chromatids split and begin to migrate towards opposite sides of the cell. Because of this, the number of chromosomes during anaphase doubles from the usual chromosome count. So 8 x 2 = 16 chromosomes. Asking about the number of chromosomes or chromatids during the different stages of replication is a hot topic on the DAT and likely to show up, so study this material well.
Q: If 2n=8, how many chromosomes are present during anaphase?
D. 16
In a cell with a diploid number of 8, we expect to see 8 chromosomes (as chromatid pairs) aligned at the equatorial plane at metaphase. During anaphase of mitosis, the chromatid pairs split apart. Each chromatid is now considered a separate chromosome, but since the cells have not yet separated, this means there are twice the number of chromosomes present as the diploid number – a total of 16; therefore the answer choice is correct.
An unknown biological sample is exposed to several enzymes and is found to react only with lipase. What is this sample composed of?
A. Nucleic acids B. Adipose tissue C. Glycogen stores D. Skeletal fragments E. Actin and myosin
B. Adipose tissue
Lipases are enzymes that digest fats. Adipose tissue is also known as body fat. Fats are made of triglycerides, which contain a glycerol backbone and fatty acid chains, which make up lipids. You could conclude that lipases likely digest lipids given their similar names. Nucleic acids are what DNA and RNA are made of, and are digestible by nucleases. Glycogen stores are long chains of glucose molecules. Skeletal fragments are bones and made of bone matrix, an organic and inorganic mixture. Actin and myosin make up muscles and are made of proteins.
Q: An unknown biological sample is exposed to several enzymes and is found to react only with lipase. What is this sample composed of?
A. Nucleic acids
Nucleic acids do not contain lipid molecules and would remain unaffected by lipase; therefore the answer choice is incorrect. Nucleic acids are polymers of nucleotides which consist of a pentose sugar, phosphate group(s), and nitrogenous base. These nucleotide monomers are held together on a phosphate backbone via phosphodiester bonds.
B. Adipose tissue
Adipose tissue consists primarily of lipids; therefore they would be sensitive to the action of a lipase enzyme, so the answer choice is correct. You should recall that enzymes are generally named according to the action they carry out: the suffix -ase is combined with the substrate the enzyme acts upon. In this case, the prefix “lip” should automatically direct you towards a lipid. Since only adipose tissue among the answer choices has lipids, it is the only biological sample a lipase would react with.
C. Glycogen stores
Glycogen is a polymer of glucose molecules, which are carbohydrates. A lipase enzyme would not react with a carbohydrate polymer; therefore the answer choice is incorrect. Glycogen primarily serves to store energy in animal cells.
D. Skeletal fragments
Skeletal fragments would be expected to have a composition similar to that of bone, which is primarily collagen fibers and inorganic bone minerals in the form of hydroxyapatite. While the yellow bone marrow of bone can serve as a storage site for fats, one would not expect to find fat to any appreciable degree in skeletal fragments. Furthermore, the question states that the biological sample reacts only with lipase, which rules out skeletal fragments as an option; therefore the answer choice is incorrect.
E. Actin and myosin
Actin and myosin are protein microfilaments, not lipids. Proteins would remain unaffected by a lipase enzyme; therefore the answer choice is incorrect. Actin and myosin are involved in the cleavage furrow of animal cells, and also make up the thin and thick filaments of the sarcomeres used in skeletal muscle contraction.
Topic: Cell and Molecular Biology
Which of the following statements accurately describes cytokinesis in mammals?
A. Molecular chaperones pull each cell to opposing ends.
B. Vesicles migrate and fuse to form a cell plate.
C. Microfilaments encircle the center of the cell and shorten.
D. Microtubules pull apart the homologous chromosomes.
E. RNA is spliced before it migrates into the cytoplasm.
C. Microfilaments encircle the center of the cell and shorten
Cytokinesis is the last stage of mitosis and actually begins occurring at the end of anaphase. It is the process of dividing the cytoplasm to form 2 cells. In mammals, a cleavage furrow develops from microfilaments encircling the cell and pulling the plasma membrane into the center. In plants, vesicles from the Golgi bodies migrate and fuse to form a cell plate to separate the two cells (Choice B). Choice [A] is incorrect, molecular chaperones are typically used in protein synthesis, not in cytokinesis. Choice [D] refers to anaphase directly where the microtubules shorten to pull apart chromosomes. Choice [E], while true, is not related to cytokinesis.
Q: Which of the following statements accurately describes cytokinesis in mammals?
A. Molecular chaperones pull each cell to opposing ends.
Molecular chaperones primarily assist in the folding of complex proteins. This process is unrelated to cytokinesis; therefore the answer choice is incorrect. Chaperones can also assist in the folding and unfolding of other types of macromolecules; they help prevent newly synthesized subunits from aggregating into non-functional structures.
B. Vesicles migrate and fuse to form a cell plate.
During cytokinesis of plant cells, vesicles migrate and fuse to form a cell plate. However, the question specifies cytokinesis in mammals, which means animal cells. In animal cells, there is no cell plate formation; therefore the answer choice is incorrect.
C. Microfilaments encircle the center of the cell and shorten.
During cytokinesis of animal cells, actin and myosin microfilaments encircle the center of the cell and shorten, pulling the plasma membrane towards the center of the cell, eventually resulting in two separate cells. This is the only option that describes a set of events specific to cytokinesis in mammals, so the answer choice is correct.
D. Microtubules pull apart the homologous chromosomes.
During anaphase of meiosis, homologous chromosomes are pulled apart as the microtubules shorten. However, this describes one of the mitotic phases, which is separate from the process of cytokinesis; therefore the answer choice is incorrect. Remember that cytokinesis can overlap with the later stages of mitosis, generally beginning towards the end of anaphase.
E. RNA is spliced before it migrates into the cytoplasm.
RNA splicing occurs in eukaryotic cells during the processing of pre-mRNA. This process is completely unrelated to cytokinesis; therefore the answer choice is incorrect. During RNA splicing, introns are removed from the transcript and the remaining exons are spliced back together. Prokaryotic DNA does not contain introns.
Topic: Cell and Molecular Biology
A researcher extracts a biomolecule from a cell and finds its molecular makeup is comprised of a large amount of nitrogen, no sulfur, and is found in both the cytoplasm and the nucleus. Which of the following is most likely the biomolecule the researcher extracted?
A. Glycogen B. Actin C. DNA D. RNA E. Cholesterol
D. RNA
A. Glycogen
The molecular makeup of glycogen does not contain any nitrogen; therefore the answer choice is incorrect. Furthermore, glycogen is not found in the nucleus. Glycogen is a carbohydrate polymer of alpha glucose molecules that stores energy in animal cells.
B. Actin
Actin is found in both the cytoplasm and the nucleus, so this may initially appear to be a tempting answer choice. As a protein (comprised of multiple amino acids), it also contains nitrogen. However, the question points out that no sulfur is found in the extracted biomolecule. Knowing that actin is a protein microfilament, one should be aware that cysteine and methionine – amino acids found in many proteins, including actin – contain sulfur; therefore the answer choice is incorrect. Actin is found in microfilaments, which play important roles in skeletal muscle contraction, the cleavage furrow formed during cytokinesis, and the structure of pseudopods.
C. DNA
DNA is abundant in nitrogen (due to the nitrogenous bases that are part of nucleotide structure). Additionally, DNA contains no sulfur and is found in the nucleus – but only the nucleus. It is not present in the cytoplasm; therefore the answer choice is incorrect. Note that the cellular processes involving DNA – replication and transcription – take place solely within the nucleus.
D. RNA
Do not let the application style of the question overwhelm you; answering this question is a straightforward matter of identifying which of the biomolecules presented in the answer choices match the criteria of the question. RNA is abundant in nitrogen (due to the nitrogenous bases that are part of nucleotide structure). Additionally RNA contains no sulfur and is found in both the nucleus (as a result of transcription) and the cytoplasm (where mRNA, tRNA, and rRNA are all found in the process of translation). As RNA is the only biomolecule that fits all the criteria specified in the question, it is the most likely biomolecule extracted by the researcher, there the answer choice is correct.
E. Cholesterol
The molecular makeup of cholesterol does not contain any nitrogen; therefore the answer choice is incorrect. Furthermore, cholesterol is not found in the nucleus. Cholesterol, a type of steroid, is an amphipathic lipid 4-ringed structure. It is a critical component of animal cell membranes and plays an important role in maintaining membrane fluidity and rigidity.
Which organelle modifies products from the endoplasmic reticulum and is responsible for protein packaging?
A. Golgi complex B. Ribosomes C. Nucleus D. Centriole E. Lysosome
A. Golgi complex
You should definitely know all of the organelles and their functions in animals, plants, and bacteria for the DAT. They are common topics. The Golgi complex (or Golgi apparatus) is composed of stacks of membrane bound discs known as cisternae. It works with the endoplasmic reticulum to package and sort proteins and is specifically important in secreting proteins such as hormones. Choice [C] is not involved in protein packaging. Ribosomes can be associated with the endoplasmic reticulum, especially when synthesizing glycoproteins, but they are not responsible for protein packaging. Centrioles and lysosomes are not associated with the endoplasmic reticulum or deal with protein packaging.
Further Details – useful if you had trouble with the question
Q: Which organelle modifies products from the endoplasmic reticulum and is responsible for protein packaging?
A. Golgi complex
The golgi complex is responsible for the transport of various substances in vesicles, and modifies the products of the endoplasmic reticulum: proteins can be glycosylated, phosphorylated, or sulfonated in the golgi complex so the answer choice is correct. The golgi complex consists of flattened sacs called cisternae.
B. Ribosome
The ribosome is responsible for synthesis of proteins, but not their subsequent packaging or modification; therefore the answer choice is incorrect. Ribosomes can be found freely in the cytosol or on the rough endoplasmic reticulum, where they allow the synthesized protein to be transferred into the endoplasmic reticulum for further modification.
C. Nucleus
The nucleus of a cell is responsible for packaging and replication of DNA, as well as the transcription of RNA. It does not participate in the packaging of proteins, and does not import or modify products from the endoplasmic reticulum; therefore the answer choice is incorrect.
D. Centriole
A pair of centrioles make up a centrosome, found in the nucleus of animal cells which serve as microtubule organizing centers during cell division. These processes are unrelated to protein packaging and modification of the endoplasmic reticulum’s products; therefore the answer choice is incorrect.
E. Lysosome
Lysosomes are vesicles produced from the golgi that contain digestive enzymes for breaking down nutrients, cell debris, and bacteria. These activities are unrelated to protein packaging and product modification; therefore the answer choice is incorrect. The interior of lysosomes have a lowpH; they are also known to function in apoptosis (by releasing their contents to destroy cells) and autophagy (intracellular breakdown of unneeded cell components).
Note that while the endoplasmic reticulum and golgi complex can both be involved in protein modification, the question specifies the organelle that modifies the products from the endoplasmic reticulum, narrowing the correct answer down to the golgi complex.
Topic: Cell and Molecular Biology
Test Your Knowledge: During cellular respiration, does the pH of the intermembrane space become higher or lower?
pH becomes lower, due to the build-up of H+
In the mitochondria, what occurs in the intermembrane space opposed to the innermembrane space?
Intermembrane space:
Remember that the mitochondria has a double layered membrane – outer and inner – and the intermembrane space (not the matrix) is what lies in between. The intermembrane space is where protons are pumped into during the electron transport chain, making this area acidic, thus giving this area of the mitochondria a relatively low pH. The citric acid cycle does take place in the matrix, where the arrow is pointing.
Innermembrane space:
Oxidative phosphorylation takes place across the inner membrane of the mitochondria. Neither the part of the mitochondria nor the function that takes place there is correctly identified; therefore the answer choice is incorrect. This should be an easy answer choice to rule out: the arrow is clearly not pointing to a membrane which the process of oxidative phosphorylation must take place across in order to establish the gradient required by ATP synthase to produce ATP.
An animal cell was lysed, placed in a test tube, and centrifuged. Which organelle would pellet from the centrifuge first?
A. Ribosome B. Lysosome C. Mitochondria D. Golgi complex E. Nucleus
E. Nucleus
Centrifugation works by spinning a tube of components at high velocities to create a force. The heavier a component is, the faster it will pellet out of the solution. The nucleus is the largest and most dense organelle in the cell and will pellet first. All the other organelles are smaller and less dense than the nucleus and will pellet later or not at all depending on the speed of the centrifuge.
Q: An animal cell was lysed, placed in a test tube, and centrifuged. Which organelle would pellet from the centrifuge first?
A. Ribosome
If an animal cell was lysed and centrifuged, ribosomes would be expected to pellet out last due to their small density and size; therefore the answer choice is incorrect.
B. Lysosome
If an animal cell was lysed and centrifuged, lysosome would not be expected to centrifuge first since they are not the largest in density and size; therefore the answer choice is incorrect. Lysosome would be expected to pellet out after the nucleus, but before the smaller and less dense ribosomes.
C. Mitochondria
If an animal cell was lysed and centrifuged, mitochondria would not be expected to centrifuge first since they are not the largest in density and size; therefore the answer choice is incorrect. Mitochondria would be expected to pellet out after the nucleus, but before the smaller and less dense ribosomes.
D. Golgi complex
If an animal cell was lysed and centrigufed, the golgi complex would not be expected to centrifuge first since it is not the largest in density and size; therefore the answer choice is incorrect. The golgi complex would be expected to pellet out after the larger nucleus, but before the smaller and less dense ribosomes.
E. Nucleus
If an animal cell was lysed and centrigufed, the nucleus would be expected to centrifuge first since it is the largest and most dense organelle; therefore the answer choice is correct.
Centrifugation Summary
Differential centrifugation spins and separates on the basis of size and density. Larger and denser particles pellet out first at lower centrifugal speeds. Then, the pellet is removed and the remaining supernatant is centrifuged again at higher speeds, and the process is repeated.
In cell fractionation, cells are first lysed or homogenized in a blender to break them up. Then, differential centrifugation can be used for the separation of organelles. The order of separation for cell components is as follows:
- Whole cells and nuclei
- Mitochondria, choloroplasts (if present), lysosomes,
peroxisomes, golgi - Microsomes (vesicles of disrupted endoplasmic
reticulum and pieces of plasma membrane) - Ribosomes, viruses, larger macromolecules
Topic: Cell and Molecular Biology
A scientist wishes to create bacterial colonies on an agar plate for observation of growth. Unfortunately, directly adding bacteria from the original culture results in too many bacterial colonies to count. In order to create a solution of proper bacterial concentration for observation, the scientist performs a three-step 1:100 serial dilution of the original bacterial culture. What is the dilution factor of the final solution?
A. 10^-9 B. 10^-3 C. 3.0 D. 10^3 E. 10^6
E. 10^6
Since the scientist used a 1:100 dilution, this means with every dilution the concentration was multiplied by 10^-2. In this problem, the scientist performed a three-step 1:100 dilution, meaning they diluted the original concentration first to 10-2, then to 10-4, and finally to 10-6. The question asks for the dilution factor, which is the final volume divided by the original volume (or the inverse of the concentration), so we flip 10-6 to 106 to get answer choice [E] as our final answer.
To answer this question correctly, it is first necessary to understand what a serial dilution is: a series of repeated dilutions to create a more dilute solution from a concentrated one. The question gives us necessary information to determine the dilution factor.
First, we are told that the scientist performs a three step serial dilution, which means that three separate dilutions take place – the original solution is diluted, then that (now diluted) solution is further diluted, and then the resulting solution is diluted once more for a total of three dilution steps.
We are also told that these dilutions are 1:100. This means that each dilution step makes the previous solution 1/100th of its original concentration (in practical terms, think a 1:100 dilution as adding 1 mL of a pure solution to 99 mL of water). Since three of these dilutions successively took place, the final concentration is now 1/100 * 1/100 * 1/100 of the original – or 10^-6.
However, the question does not ask us for the concentration of the final solution, but the dilution factor. The dilution factor is the final volume divided by the original volume, or the inverse of the concentration. In a 1:100 dilution, the dilution factor is 100 (or 102). Correspondingly, the dilution factor for three successive 1:100 dilutions is 1,000,000 (or 106). Therefore, answer choice [E] is the correct answer.
*Note: Imagine in the above diagram you took 1 mL of the final solution of the 10-6 concentration and inoculated an agar plate. What is the concentration of the solution on the agar plate? The concentration is still just 10-6.
However, what if we took 0.01 mL of the final 10-6 solution and inoculated an agar plate? Well, now you’re essentially diluting the solution by taking a smaller volume than what you were using for the serial dilution. Since 0.01 mL is 1/100 of 1 mL (the original amount of volume you took from the original solution), you’re diluting by another factor of 100. Thus, the bottom agar plate in the diagram is inoculated with a 10^-8 concentration, and its dilution factor is 108.
Topic: Cell and Molecular Biology
What is the purpose of SDS (sodium dodecyl sulfate) in protein analysis?
A. Denature non-covalent bonds in a protein
B. Decrease the surface area of the protein
C. Impart a positive charge on the protein
D. To cut the protein at specific sequences
E. Dye the proteins to track their run
A. Denature non-covalent bonds in a protein
Sodium dodecyl sulfate is a very strong anionic detergent that is used in gel electrophoresis to separate proteins based on their electrophoretic mobility (a function of the length of a protein and its charge). SDS is used to denature and linearize proteins and to impart a negative charge to the proteins. You could deduce it would impart a negative charge and not a positive one because sulfate is very negative and anionic. With this method, only the protein’s size and charge will be compared. Generally, all gel electrophoresis will denature a protein to compare its size.
Fun fact: SDS is also known as sodium lauryl sulfate, which is used in your shampoo and some toothpastes.
Q: What is the purpose of SDS (sodium dodecyl sulfate) in protein analysis?
A. Denature non-covalent bonds in a protein
SDS denatures the non-covalent bonds in a protein, which removes the tertiary structure of the protein and linearizes it, so the answer choice is correct.
B. Decrease the surface area of the protein
Since SDS denatures the non-covalent protein bonds and removes the tertiary structure, the protein is subsequently linearized (no longer folded). This increases the surface area of the protein, the opposite of the answer choice; therefore the answer choice is incorrect.
C. Impart a positive charge on the protein
The use of SDS on a protein imparts a negative charge on the protein. This is the opposite of the answer choice; therefore the answer choice is incorrect. The negative charged imparted by the use of SDS allowed for electrostatic repulsion to be used to separate proteins by size in gel electrophoresis, where smaller proteins travel further than larger proteins.
D. To cut the protein at specific sequences
SDS does not cut protein sequences or shorten proteins in any way; therefore the answer choice is incorrect.
Test your knowledge: What is the name of an enzyme that cuts DNA at specific sequences?
E. Dye the proteins to track their run
SDS does not dye proteins in any way; therefore the answer choice is incorrect. A blue dye can be used with SDS to dye proteins to locate them after their separation via electrophoresis; the dye forms a complex with the SDS molecules.
SDS Summary
SDS (sodium dodecyl sulfate) has three primary effects on protein:
Denatures the protein
Linearizes the protein
Adds negative charge to the protein
The SDS-PAGE (polyacrylamide gel electrophoresis) is used to separate proteins on the basis of size (molecular weight). Smaller proteins will travel further than large proteins from the negative cathode to the positive anode.
[Answer to Test your knowledge: Restriction endonuclease]
Topic: Cell and Molecular Biology
Catabolism can be described as a(n):
A. Isotonic process B. Endergonic process C. Exergonic process D. Endothermic process E. Hypertonic process
C. Exergonic process
Catabolism is the breaking down of materials to smaller units, such as when glucose is broken down to release energy. If we’re breaking down glucose, we’re releasing energy, so this is an exergonic reaction.
It is the opposite of anabolism, a set of metabolic pathways to create molecules from smaller units. Think of anabolic steroids, they develop bigger muscles because they build up molecules. It takes energy to build up those muscles, so anabolism is an endergonic process.
Q: Catabolism can be described as a(n):
A. Isotonic process
An isotonic process does not exist – it is a meaningless answer choice here. Isotonic can refer to the tonicity of solutions (a cell in an isotonic solution has a solute concentration equal to the surrounding solution), or muscle contractions (an isotonic contraction is one where the muscle length changes as it contracts, in contrast to an isometric contraction where the muscle length does not change as it contracts). Neither of these uses of isotonic is relevant to metabolism; therefore the answer choice is incorrect.
B. Endergonic process
An endergonic process is one that requires energy, whereas catabolism (the breakdown of molecules) is a metabolic process that releases energy; therefore the answer choice is incorrect. It is anabolism (the metabolic process of building up molecules from smaller units) that is endergonic.
C. Exergonic process
An exergonic process is one that releases energy. Catabolism is the metabolic breakdown of larger molecules accompanied by a release of energy used to power cell functions like growth and maintenance, so the answer choice is correct.
D. Endothermic process
An endothermic process is one which absorbs heat. Catabolism results in a release of energy, which is not necessarily determined by the absorption or release of heat (recall that the formula to determine Gibbs free energy change is ∆G = ∆H – T∆S. Change in heat is represented by ∆H, but metabolic processes are concerned with the overall change in energy, which is ∆G).
E. Hypertonic process
A hypertonic process does not exist – it is a meaningless answer choice here. Hypertonic refers to the tonicity of solutions (if a cell is in a hypertonic solution, the surrounding solution has a higher solute concentration than the inside of the cell).
Test your knowledge: What would you expect to happen to a cell in a hypertonic solution?
Metabolism Summary
Metabolism is the sum of catabolism, anabolism, and energy transfer in cells. In catabolism, larger molecules are broken down, releasing energy. In anabolism, larger molecules are built up, which requires energy. An easy way to distinguish the two is to remember that athletes take anabolic steroids to build muscle.
[Answer to Test your knowledge: The cell would shrivel as water leaves it]
Topic: Cell and Molecular Biology
All of the following directly use an electrochemical gradient EXCEPT one. Which one is the EXCEPTION?
A. Flagella rotation B. Mitochondria C. Chloroplasts D. Aquaporins E. Neurons
D. Aquaporins
An electrochemical gradient is one where an electrochemical imbalance exists between a membrane. A great example is a proton gradient in ATP synthesis. Protons are pumped out of the mitochondrial matrix to create a proton force made of electrical charge (protons are positively charged) and a chemical gradient (made up of H+), or an electrochemical gradient. Flagella use proton force to spin and give locomotion to bacteria. Mitochondria use a proton force in ATP synthesis as well as chloroplasts, where they also produce NADPH. Neurons use Na+/K+ ATPase to create an electrochemical gradient by pumping 3 sodium ions out of the cell and 2 potassium ions into the cell. Aquaporins are protein structures in the membrane that help water passively flow into or out of the cell, a process known as facilitated diffusion.
Q: All of the following directly use an electrochemical gradient EXCEPT one. Which one is the EXCEPTION?
A. Flagella rotation
In prokaryotes, the flagella uses a proton motive force to spin and give locomotion. This proton motive force makes of the flow of protons (hydrogen ions) across the bacterial membrane – this is an electrochemical gradient; therefore the answer choice is incorrect.
B. Mitochondria
Mitochondria must establish an electrochemical gradient in order to produce ATP; therefore the answer choice is incorrect. When NADH and FADH2 are oxidized in the electron transport chain, protons are transported from the mitochondrial matrix to the intermembrane space. This creates an electrochemical gradient within the mitochondria; ATP synthase utilizes the kinetic energy established by this electrochemical gradient to produce ATP as protons flow from the intermembrane space into the mitochondrial matrix.
C. Chloroplasts
Chloroplasts use an electrochemical gradient to produce ATP; therefore the answer choice is incorrect. During photolysis and the transfer of electrons from photosystem II to photosystem I, protons accumulate in the thylakoid lumen of the chloroplast. This establishes an electrochemical gradient within the chloroplast; ATP synthase utilizes the energy established by this electrochemical gradient to produce ATP as protons flow from the thylakoid lumen out into the stroma.
D. Aquaporins
Aquaporins are integral membrane proteins that allow for the facilitated diffusion of water across the cell membrane. The only gradient involved in facilitated diffusion is movement down a concentration gradient, not electrochemical, so the answer choice is correct.
E. Neurons
Neurons are the functional unit of the nervous system. The membrane of neurons are maintained at resting potentials with an electrochemical gradient consisting of a higher concentration of K+ inside the cell and a higher concentration of Na+ outside the cell, and an overall excess of negative charge inside the cell relative to the outside; therefore the answer choice is incorrect. This gradient acts as a means of transmitting nerve impulses – voltage-gated channels opening allows for the movement of Na and K across the membrane, resulting in an action potential.
Topic: Cell and Molecular Biology
In the alternation of generations, what do spores directly give rise to?
A. Gametes B. Zygotes C. Gametophyte D. Sporophyte E. Seeds
C. Gametophyte
The alternation of generations is a common topic on the DAT regarding plants. It’s worthwhile to memorize this picture. As we can see, haploid spores divide by mitosis to form the gametophyte stage. These gametes fuse together to form the diploid stage and develop into a sporophyte, which then divides by meiosis to get back to the haploid stage.
Q: In the alternation of generations, what do spores directly give rise to?
A. Gametes
Gametes are produced from mitosis via the gametophyte structure in alternation of generations; therefore the answer choice is incorrect.
B. Zygotes
Zygotes – the fusion of sperm and egg – are not produced from spores, but rather the fusion of gametes (which are produced by the gametophyte); therefore the answer choice is incorrect.
C. Gametophyte
In the alternation of generations, spores produced by the sporophyte go through mitosis and form the multicellular gametophyte structure, so the answer choice is correct.
D. Sporophyte
The sporophyte is the multicellular structure that produces spores via meiosis, but the question asks what spores give rise to – not where they come from – therefore the answer choice is incorrect.
E. Seeds
A seed consists of a protective coat, some kind of storage material (usually food), and the developing plant embryo (developed from the zygote). The seed allows for the eventual formation of the sporophyte, and does not develop from spores; therefore the answer choice is incorrect.
Topic: Cell and Molecular Biology
Which of the following lack a true coelom?
A. Flatworms B. Annelids C. Echinoderms D. Chordates E. Mollusks
A. Flatworms
A coelom is a cavity lined by an epithelium derived from mesoderm. Mollusks have a reduced, but still true, coelom. A flatworm(also known as planarian) is an acoelomate because it does not have a coelom within its mesoderm layer.
Q: Which of the following lack a true coelom?
A. Flatworms
Flatworms – from the phylum Platyhelminthes – are acoelomate, which means they lack a true coelom, so the answer choice is correct. The coelom is a cavity derived from the mesoderm in certain animals. Platyhelminthes is the only phylum of triploblasts that lacks a coelom. Other examples of Platyhelminthes include trematodes, flukes, tapeworms, and planarians.
B. Annelids
Annelids are coelomate, which means they possess a coelom; therefore the answer choice is incorrect. The coelom is a cavity derived from the mesoderm in certain animals. The Annelid phylum includes earthworms and leeches.
C. Echinoderms
Echinoderms are coelomate, which means they possess a coelom; therefore the answer choice is incorrect. The coelom is a cavity derived from the mesoderm in certain animals. Examples of the Phylum Echinodermata include starfish, sea cucumbers, and sea urchins. Echinoderms (along with Chordates) are the only phyla with endoskeletons.
D. Chordates
Chordates are coelomate, which means they possess a coelom; therefore the answer choice is incorrect. The coelom is a cavity derived from the mesoderm in certain animals. Examples of the Phylum Chordata include tunicates, lancelets, and all vertebrates.
E. Mollusks
Mollusks – from the phylum Mollusca – are coelomate, which means they possess a coelom; therefore the answer choice is incorrect. The coelom is a cavity derived from the mesoderm in certain animals. The Mollusca phylum includes the bivalves (clams, oysters), gastropods (snails, slugs) and cephalopods (octopus and squid).
Coelomate Summary – The parazoa animals of the animal kingdom lack true tissues (those of the phylum Porifera), and the phylum Cnidaria are diploblast, having only two tissue types. Of the triploblast animals, there are three types: acoelomate (lack a true coelom), pseudocoelomate (have an internal cavity, but one that is not completely lined by mesoderm derived tissue), and coelomate (have a cavity lined by mesoderm derived tissue).
Acoelomates: Platyhelminthes
Pseudocoelomates: Nematodes, Rotifers
Coelomates: Annelids, Mollusks, Arthropods, Echinoderms, Chordates
Topic: Taxonomy
Which of the following pairs of classification levels are most closely related?
A. Kingdom and Order B. Family and Genus C. Phylum and Order D. Family and Species E. Class and Genus
B. Family and Genus
To solve this question you need to know the classification system in biology. In descending order, it is: Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species. You can memorize this by learning the mnemonic “Dumb Kings Play Chess On Fine Green Sand”, where the first letter corresponds to the classification level. The two classifications that are the most related would be the ones closest to each other, and only Family and Genus are right next to each other in the hierarchy. All the other choices list classifications that are multiple degrees apart.
Q: Which of the following pairs of classification levels are most closely related?
A. Kingdom and Order
Kingdom and Order are not the most closely related classification levels of the answer choices presented; therefore the answer choice is incorrect.
B. Family and Genus
A genus is the level of organization directly below family in taxonomic rank, so the answer choice is correct. To answer this question correctly, it is necessary to understand the relative progression of each of the taxonomic ranks. The higher a taxonomic rank (e.g. the highest is domain), the more general of a category it is. The lower the taxonomic rank (e.g. the lowest is species), the more specific and descriptive it is of the organisms within the group. The classification levels most closely related would be those closest in taxonomic rank.
C. Phylum and Order
Phylum and Order are not the most closely related classification levels of the answer choices presented; therefore the answer choice is incorrect.
D. Family and Species
Family and Species are not the most closely related classification levels of the answer choices presented; therefore the answer choice is incorrect.
E. Class and Genus
Class and Genus are not the most closely related classification levels of the answer choices presented; therefore the answer choice is incorrect.
Taxonomic Ranking System
The taxonomic ranking system, from highest to lowest, is as follows:
Domain > Kingdom > Phylum > Class > Order > Family > Genus >Species
A helpful mnemonic to remember the taxonomic ranking system is:
Dumb Kings Play Chess On Fine Green Sand
Topic: Taxonomy
The bacteria depicted in the image belong to which genus? Assume all bacteria depicted in the image belong to the same genus.
Image: Spherical bacteria in long chains
A. Streptococcus B. Staphylococcus C. Streptobacillus D. Spirilla E. Diplococcus
A. Streptococcus
A. Streptococcus
There are two important pieces of information about appearance given to us in the name of the bacteria: Strep indicates that these bacteria grow in a chain along a single axis, while coccus indicates a spherical shape (to each individual bacteria in the chain). These characteristics match the circled image above, so the answer choice is correct.
B. Staphylococcus
Staph indicates these bacteria grow in clusters (similar to grapes), but the circled image shows bacteria growing in a single axis chain (indicating this is in fact Streptococcus). The second part of the name, coccus, indicates a spherical shape to each individual bacteria and is consistent with the image.
C. Streptobacillus
The second part of the name, bacillus, indicates a rod-like shape to the bacteria (you may have thought that the bacteria in the image are not perfectly sphere-like and mistakenly selected this answer instead, but the bacillus shaped bacteria are far more rod-like than spherical: see the image below for an example of streptobacillus). The first part of the name, Strep, indicates that these bacteria grow in a chain along a single axis which is consistent with the image.
D. Spirilla
Bacteria from the genus Spirilla are spiral shaped, while the circled image demonstrates a spherical shape (coccus); therefore the answer choice is incorrect. In addition, the image indicates bacteria growing in chains, whereas spirilla do not form chains.
E. Diplococcus
Deduce the appearance of this bacterium from the name: the first part of the name, diplo, indicates that these bacteria appear in pairs (rather than the longer Strep chains seen in the image above). The second part of the name, coccus, indicates a spherical shape to each individual bacteria and is consistent with the image.
Note: Important pieces of knowledge on appearance of bacteria from naming: Diplo-: pairs Strep-: chain Staph-: grape-like clusters -coccus: spherical -bacillus: rod-like Spirilla/spirochetes: spirals
Fun fact: This is streptococcus mutans, a prevalent bacterium found in dental caries.
Topic: Taxonomy
What is the function of the epiglottis?
A. Support the opening of the trachea.
B. Produce digestive enzymes in the mouth.
C. Close the trachea when swallowing.
D. Prevent reflux in the stomach to the esophagus.
E. Control the intake of food in the stomach.
C. Close the trachea when swallowing.
Q: What is the function of the epiglottis?
A. Support the opening of the trachea.
The epiglottis does not function in the opening of the trachea, in fact it functions to do the opposite; therefore the answer choice is INCORRECT. The airway of the trachea is supported by C-shaped rings of cartilage. The trachea itself connects the lungs to the pharynx and larynx.
B. Produce digestive enzymes in the mouth.
The epiglottis does not have any digestive functions whatsoever; therefore the answer choice is INCORRECT. The digestive enzymes in the mouth (primarily amylase, which begins the breakdown of carbohydrates) are secreted in saliva by salivary glands.
C. Close the trachea when swallowing.
The epiglottis is a flap of cartilage that closes access to the trachea during swallowing to prevent food from entering your lungs, instead diverting it to the esophagus for digestion; therefore the answer choice is correct. If you ever choked on some food, it’s because your epiglottis didn’t do its job!
D. Prevent reflux in the stomach to the esophagus.
The epiglottis is not present, functionally or anatomically, in the connection of the stomach to the esophagus; therefore the answer choice is INCORRECT. It is the lower esophageal sphincter, also known as the cardiac sphincter, that allows food to move from the esophagus into the stomach and prevents reflux from the stomach back into the esophagus.
E. Control the intake of food in the stomach.
The epiglottis does not function in control of food movement directly into the stomach; therefore the answer choice is INCORRECT. It is the lower esophageal sphincter, also known as the cardiac sphincter, that allows food to move from the esophagus into the stomach and prevents reflux from the stomach back into the esophagus.
Be familiar with the anatomy air and food pathways in humans:
All of the following are digestive enzymes EXCEPT one. Which one is the EXCEPTION?
C. Acetylcholinesterase
Acetylcholinesterase is a protease that hydrolyzes the neurotransmitter acetylcholine. It is mainly found at neuromuscular junctions and brain synapses. Amylase is a digestive enzyme in the mouth that digests carbohydrates. Pepsin breaks down proteins in the stomach and is produced by chief cells. Chymotrypsin and trypsin are digestive enzymes secreted by the pancreas and break down proteins.
Q: All of the following are digestive enzymes EXCEPT one. Which one is the EXCEPTION?
A. Amylase
Amylase is a digestive enzyme that functions in the breakdown of polysaccharides; therefore the answer choice is incorrect. Amylase is secreted in saliva by the salivary glands (breaking polysaccharides such as starch and glycogen into smaller polysaccharides), and the pancreas (breaking down smaller disaccharides into monosaccharides).
B. Pepsin
Pepsin is a digestive enzyme that functions in the breakdown of proteins; therefore the answer choice is incorrect. Pepsin, the only digestive enzyme secreted in significant quantities by the stomach, breaks proteins down into smaller polypeptides, which then undergo further digestion in the small intestines.
C. Acetylcholinesterase
Acetylcholinesterase is an enzyme that breaks down the neurotransmitter acetylcholine. It is found in neural and neuromuscular synapses but not as a digestive enzyme, therefore the answer choice is correct. The breakdown of acetylcholine causes termination of the neural signal at the synapse.
D. Chymotrypsin
Chymotrypsin is a digestive enzyme that functions in the breakdown of polypeptides (also known as proteins); therefore the answer choice is incorrect. The pancreas secretes chymotrypsin and trypsin, which break small polypeptides down into even smaller polypeptides.
E. Trypsin
Trypsin is a digestive enzyme that functions in the breakdown of polypeptides; therefore the answer choice is incorrect. Trypsin is secreted by the pancreas and along with chymotrypsin, breaks small polypeptides down into even smaller polypeptides.
Digestive Enzymes Summary
Be familiar with the digestive enzymes, what they breakdown, and where they are secreted.
Mouth: salivary amylase (carbohydrates)
Stomach: Pepsin (proteins)
Pancreas: pancreatic amylase (carbohydrates), pancreatic trypsin and chymotrypsin (proteins), carboxypeptidase (proteins), nucleases (DNA, RNA), lipase (fats) [Note: these digestive enzymes are secreted by the pancreas but carry out their function in the small intestine]
Small Intestine: Disaccharidases (carbohydrates), dipeptidases and aminopeptidases (proteins), nucleotidases (nucleotides), nucleosidases (nucleosides)
Topic: Anatomy and Physiology
What is the role of calcium in muscle cells?
A. To expose the binding sites on actin filaments B. To initiate a membrane potential C. Increase Na+/K+ ATPase activity D. Increase osteoblast activity E. Regulate transcription of myosin
A. To expose the binding sites on actin filaments
During a muscle contraction, a neuron releases acetylcholine which triggers an action potential on the muscle cell. This signal is propagated by T tubules and releases Ca2+ from the sarcoplasmic reticulum and initiates contraction of the muscle cell. The calcium binds to actin filaments called troponin, which allows it to change its shape and expose binding sites for myosin. The myosin binds to the actin by using ATP and shortens, creating a contraction. When the action potential passes, the calcium gets removed from the troponin and the binding sites are no longer available, relaxing the cell.
Q: What is the role of calcium in muscle cells?
A. To expose the binding sites on actin filaments
In muscle cells, calcium ions bind to the troponin located on the actin filaments, which in turn causes tropomyosin covering the myosin binding sites on the actin filament to pull back, exposing the binding sites. This answer choice is correct.
B. To initiate a membrane potential
Calcium in muscle cells do not initiate membrane potentials; therefore the answer choice is incorrect. Membrane potentials in muscle cells are initiated by the release of acetylcholine at the neuromuscular junction, which triggers an action potential that travels down the T tubules and triggers the release of calcium ions stored in the sarcoplasmic reticulum.
C. Increase Na+/K+ ATPase activity
One would not expect the activity of Na+/K+ ATPase (aka the sodium potassium pump) to increase in response to calcium ions in muscle cells, nor is regulation of this pump its primary role; therefore the answer choice is incorrect This function of this pump is to maintain the resting potential of cells, and removes Na+ from the inside of the cell in exchange to bring K+ into the cell, both actively against their concentration gradient.
D. Increase osteoblast activity
Osteoblasts are not found in muscle cells, therefore one should eliminate this answer choice as incorrect knowing it functions in the skeletal system, not the muscular system. Osteoblasts primarily function to build bone. While calcium is an important element of the skeletal system, the question asks for its role specifically in muscle cells, which are entirely unrelated to osteoblasts.
E. Regulate transcription of myosin
Calcium in muscle cells does not function in the control of myosin transcription; therefore the answer choice is incorrect. Transcriptional regulation is much more complex than simple regulation from ions and is subject to a number of control mechanisms such as transcription factors, which we will get to in genetics questions.
Muscle Contraction
Note that calcium binding to troponin is necessary for exposure of the binding sites on actin filaments, which in turn allows binding of the myosin heads.
Topic: Anatomy and Physiology
Where is ADH stored in the body?
A. Thyroid B. Pancreas C. Pineal gland D. Posterior pituitary E. Anterior pituitary
D. Posterior pituitary
ADH is produced in the hypothalamus. The posterior pituitary stores oxytocin and ADH (also known as vasopressin). The pineal gland produces melatonin to help regulate our sleep patterns.
The anterior pituitary produces the following, you can remember most of them with the acronym FLAT, for: FSH, LH, ACTH, and TSH.
Q: Where is ADH stored in the body?
A. Thyroid
The thyroid does not store ADH; therefore the answer choice is incorrect. The thyroid is located just in front of the trachea and is responsible for the production of thyroxine (T4) and triiodothyronine (T3), which increase metabolic rate, and calcitonin, which lowers blood calcium ion levels.
B. Pancreas
The pancreas does not store ADH; therefore the answer choice is incorrect. The pancreas is both an exocrine and endocrine gland and has bundles of cells called islets of Langerhans. Alpha cells of the pancreas secrete glucagon, a catabolic hormone that converts glycogen to glucose and raises blood glucose levels. Beta cells of the pancreas secrete insulin, an anabolic hormone that converts glucose to glycogen and lowers blood glucose levels. Delta cells of the pancreas secrete somatostatin, which inhibits the release of insulin, glucagon, and other gastrointestinal hormones.
C. Pineal gland
The pineal gland does not store ADH; therefore the answer choice is incorrect. The pineal gland (located in the brain) secretes melatonin, which plays a role in maintaining the circadian rhythm, including the timing of sleep.
D. Posterior pituitary
The posterior pituitary stores ADH and oxytocin produced by the hypothalamus, so the answer choice is correct. It is important to note that the posterior pituitary itself does not synthesize these hormones – the neural cell bodies of the hypothalamus synthesize them, then they are transferred down axons to the posterior pituitary for storage and release into the blood.
For reference, ADH stands for anti-diuretic hormone (anti-diuretic meaning you don’t urinate as often), and can also be referred to as vasopressin. When you drink coffee or beer you may urinate more often, these are known as diuretics.
E. Anterior pituitary
The anterior pituitary does not store ADH; therefore the answer choice is incorrect. The anterior pituitary is responsible for releasing the tropic hormones (hormones that stimulate other endocrine glands) ACTH, TSH, LH, and FSH and the non-tropic hormones (hormones that stimulate their target organ directly) HGH, prolactin,MSH (melanocyte stimulating hormone), and endorphins. The anterior pituitary is often regulated by the hypothalamus. You can remember the hormones released by the anterior pituitary with the mnemonic “FLAT PiG” (FSH, LH, ACTH, TSH; Prolactin and Growth hormone).
All of the following are connective tissues EXCEPT for one. Which one is the EXCEPTION?
A. Adipose B. Neurons C. Cartilage D. Bones E. Blood
B. Neurons
There are four general classes of biological tissues: connective, epithelial, muscular, and nervous. Neurons, although connected, are not a connective tissue in the musculoskeletal system. Adipose, or body fat, is a connective tissue. Cartilage connects bones to other bones. Bones are a connective tissue as well. Blood, interestingly enough, is considered a connective tissue. Blood is derived from the mesoderm and connects the body systems together by providing nutrients and removing waste.
Q: All of the following are connective tissues EXCEPT for one. Which one is the EXCEPTION?
A. Adipose
Adipose tissue, or fat tissue, is classified as a type of loose connective tissue. Adipose tissue forms a major storage site for energy, stored in the form of fatty lipids. However, since it is classified as connective tissue, this answer is incorrect.
B. Neurons
There are four main types of human tissues: connective, muscular, neural, and epithelial. All of the other answer choices fall under the category of connective tissue, while neurons are one of the primary cell types of neural tissue. Thus, this answer is correct.
C. Cartilage
Cartilage is a type of avascular connective tissue that is located throughout the body. It often develops with the purpose of holding cavities open (such as in the nostrils or the ears) or with the purpose of helping provide cushioning at joints. However, since it is classified as connective tissue, this answer is incorrect.
D. Bones
Bone is a type of dense connective tissue, making this answer incorrect. Bones make up the skeletal system of vertebrates and are largely made of hydroxyapatite. Bone is made of both mineralized tissue (i.e. cortical bone / cancellous bone) as well as soft tissue (bone marrow).
E. Blood
Blood is classified as special connective tissue, making this answer incorrect.
Connective tissue is important for determining body structure, supporting organs, and keeping some tissues separated, while connecting others. It is one of the four main types of human tissues (the others being neural, muscular, and epithelial).
Topic: Anatomy and Physiology
An increase in calcitonin would lead to which of the following?
A. Increase calcium concentration in blood
B. Decrease calcium reabsorption in bones
C. Stimulate osteoblast activity
D. Stimulate osteoclast activity
E. An increase in muscle contractions
C. Stimulate osteoblast activity
Two hormones regulate calcium levels in blood: calcitonin (produced by the thyroid), and parathyroid hormone (produced by the parathyroid). Calcitonin serves to lower calcium levels in blood. It does this by stimulating osteoblast activity, which builds up bone, which requires using calcium in the blood. Parathyroid hormone is the opposite, if calcium levels are too low in the blood, it will stimulate osteoclast activity to release calcium from the bones to the blood.
Q: An increase in calcitonin would lead to which of the following?
A. Increase calcium concentration in blood
The hormone calcitonin produces the exact opposite effect of the parathyroid hormone (PTH); calcitonin decreases blood calcium concentration, making this answer incorrect. In fact, calcitonin is secreted by the thyroid, often in response to a state of hypercalcemia.
B. Decrease calcium reabsorption in bones
The main effect of calcitonin is to decrease blood calcium concentration; one of its main mechanisms is to sequester calcium in bone tissue. Since decreasing calcium reabsorption in bones would actually lead to an increase in serum calcium levels, this answer is incorrect.
C. Stimulate osteoblast activity
Osteoblasts are cells that aid in bone production. They use calcium and other nutrients in the blood as raw materials for building new bone tissue. This leads to a decrease in serum calcium, which is the same effect as increased calcitonin. Thus, it makes sense that calcitonin increases osteoblast activity, making this answer correct.
D. Stimulate osteoclast activity
Osteoclasts are monocyte-derived cells that primarily serve the function of breaking down bone and releasing calcium and other nutrients back into the bloodstream. Since calcitonin leads to a decrease of blood calcium, this answer is incorrect. Calcitonin increase would lead to a sequestration of calcium in bones, and would thus inhibit the actions of osteoclasts rather than stimulate them.
E. An increase in muscle contractions
Muscle contractions are calcium-driven phenomena. Since calcitonin release decreases blood calcium levels, this would actually more likely lead to a decrease in muscle contractions, not an increase. Thus, this answer is incorrect.
Topic: Anatomy and Physiology
Which layer of the skin helps the body conserve heat and protects the body from injury by acting as a “shock absorber”?
A. Epidermis B. Dermis C. Endodermis D. Subcutaneous layer E. Mesoderm
D. Subcutaneous layer
The subcutaneous layer contains a network of fat cells and collagen. It is the deepest layer of skin and the fat cells help insulate the body and act as a shock absorber to protect it from minor damage. The top layer of skin is the epidermis, which usually contains dead skin cells and contains melanocytes (produce melanin). The dermis is the middle layer and is highly vascularized. The dermis contains blood vessels, hair follicles, sweat glands, and nerves.
Fun fact: The dermis is where tattoo machines inject their ink.
Q: Which layer of the skin helps the body conserve heat and protects the body from injury by acting as a “shock absorber”?
A. Epidermis
The epidermis is the outermost layer of the skin. The primary function of the epidermis is to serve as a barrier against pathogens and environmental dangers. Since the epidermis is not composed of fatty adipose tissue, and is mostly used for fighting off infections, this answer is incorrect.
B. Dermis
The dermis is primarily composed of flexible connective tissue. The dermis has many functions and is where sensory cells are anchored. The dermis is also responsible for supplying nutrients to the epidermis. The highly vascularized and flexible dermis is adapted for sensation and nutrient recycling, not insulation or shock absorption, making this answer incorrect.
C. Endodermis
The endodermis is not a layer of human skin; instead it is found in vascular land plants, making this answer incorrect. The endodermis regulates the flow of water and nutrients through the symblast pathway. This is possible due to the hydrophobic properties of the Casparian Strip located in the endodermis.
D. Subcutaneous layer
The subcutaneous layer, part of the hypodermis, has a number of functions, including insulation and shock absorption, making this answer correct. The fatty, adipose tissue that makes up the subcutaneous layer of the skin is what helps it have functions such as shock absorption, insulation, and (in some species) energy storage.
E. Mesoderm
The mesoderm is not actually a layer of the skin; instead, it is one of the three germ cell layers formed by gastrulation in developmental biology. The mesoderm gives rise to a number of different tissue and cell types, including muscle tissue, mesenchyme, mesothelial tissue, and some blood cells. Since the mesoderm is not a part of the skin, the answer is incorrect.
Topic: Anatomy and Physiology
