CLEP Practice Test Biology
Farm runoff washes fertilizer into a pond, causing increased algal growth, decreased oxygen, and eventually the death of the fish. Which of the following processes best describes this sequence of events?
Correct answer: Eutrophication
Eutrophication can occur naturally, but it is frequently accelerated and exacerbated by human activity. Eutrophic lakes can sometimes completely disappear, being filled in by sediments from dead organisms and bacteria.
Dogs, bats, whales, and humans all have a long bone in their front limbs that is attached to two parallel bones at a joint. Anatomical structures such as these are referred to as
Correct answer: Homologous
Because the same basic body plan appears to have been adapted over time to perform different functions, homologous structures are thought to be evidence of evolution. Vestigial structures are homologous structures that have lost their function, such as the human tailbone's tiny vestigial tailbone. Although analogous structures perform the same functions, they are not related. Analogous structures include the wing of a butterfly and the wing of a bird.
Why is it likely that a single nucleotide substitution of uracil for thymine in a DNA strand's coding region will have little effect on the organism?
I. Uracil and thymine nucleotides will both bind to adenosine
II. The genetic code is duplicative
III. Single nucleotide substitutions rarely have a significant impact
IV. Because uracil is not normally found in DNA, the substitution is likely to be detected and repaired.
Correct answer: I and IV
Adenine, thymine, guanine, and cytosine, or A, T, G, C, are the four nucleotide bases found in DNA. Adenine is paired with thymine, while guanine is paired with cytosine. Uracil is a nucleotide found exclusively in RNA, where it replaces thymine and, like thymine, pairs with adenosine. So, yes, “I” is correct: both the original and mutated DNA will function to produce the same messenger RNA—but which is the best? The genetic code IS redundant (II), which means that there are multiple ways to code for many of the amino acids in the proteins that will be built using the DNA code, but this has nothing to do with this particular mutation. Because single nucleotide substitutions CAN have a significant impact, the answer "III" is incorrect. (For example, try having sickle cell anemia!) But what about "IV," will the substitution be repaired? It will most likely be fixed because, as previously stated, DNA does not contain uracil, and mechanisms are in place to remove and replace uracil when it is detected. So “c,” “I,” and “IV” are the best. The substitution will most likely be repaired, but if it isn't, it won't affect the messenger RNA produced by the DNA.
In humans, what is the end result of anaerobic respiration?
Correct answer: Lactic acid
When humans engage in vigorous exercise, such as sprinting, the muscles may require more oxygen than the lungs and circulatory system can provide immediately. Normally, glucose is broken down into carbon dioxide and water, but aerobic respiration necessitates the presence of oxygen. If there is a lack of oxygen, the glucose will be temporarily converted into lactic acid. Later on, oxygen will be required to break down the lactic acid. As a result, a sprinter may be gasping for air for a few moments after crossing the finish line. They're repaying their "oxygen debt." If only student loans were that simple to repay.
Chyme is a semi-fluid mass of partially digested food. Chyme formation takes place in
Correct answer: Stomach
Chyme is the semifluid mass of partially digested food in the stomach before it enters the duodenum. The churning movements of the stomach's muscular wall thoroughly mix the food with the acidic gastric juice, resulting in the formation of chyme.
During the metabolization of glucose molecules in an aerobic cell, the energy is used to produce ATP through a series of biochemical steps. Put these events in the correct order.
I. Acetyl Coenzyme A is synthesized from pyruvate.
II. Electron carriers in the mitochondrion donate electrons to the electron transport chain, resulting in a proton gradient.
III. A molecule enters the citric acid cycle, also known as the Krebs cycle, producing 3 NADH, 1 FADH2, and 1 ATP.
IV. During glycolysis, a molecule is cleaved into two parts, giving NADH molecules and two ATP molecules.
V. ATP synthase allows protons into the mitochondrion's interior matrix, producing up to 34 ATP.
Correct answer: IV, I, III, II, V
A glucose molecule is split in two (IV) during glycolysis, yielding two molecules of pyruvate. Acetyl Coenzyme A (I) is formed from pyruvate and enters the citric acid cycle in the mitochondrion, where electron carriers NADH and FADH2 are produced (III). These electron carriers donate their electrons to the electron transport chain, resulting in a proton, or H+, gradient across the mitochondrion's inner membrane (II). ATP synthase transports these protons back into the mitochondrion's inner chamber, where they are converted into ATP (V). In a nutshell, this is glycolysis and cellular respiration. If you've forgotten them, you'll have to buckle down and study, but try to keep this "nutshell" view as a framework in mind so you don't get lost.
Which of the following bacteria is an example of denitrifying bacteria?
Correct answer: Pseodomonas sp
Denitrification is the process by which nitrate is reduced to molecular nitrogen by microbial action. Denitrifying bacteria include Pseodomonas sp. Nitrifying bacteria include Nitrosomonas sp. and Nitrobacter sp. Nitrogen-fixing bacteria include Rhizobium sp.
What is Engrailed proteins?
Correct answer: Transcription factors
Engrailed proteins are transcription factors that play an important role in the development of the brain in many species. They help to guide neuronal axons and determine the midbrain/hindbrain border.
Which of the following cellular organelles are more likely to be present in a cell that produces steroid hormones?
Correct answer: Smooth endoplasmic reticulum
Smooth ER generates cellular products like lipids and steroids. Rough ER generates proteins. Mitochondria generate ATP for energy, while lysosomes degrade and recycle waste.
What is the process by which the endosperm of a flowering plant's seeds is produced?
Correct answer: Two sperm enter the pollen tube and travel to the embryo sa. The one fertilizes the egg, while the other fertilizes the two polar nuclei, resulting in triploid endosperm.
Two sperm pass through the pollen tube on their way to the embryo sac. The one fertilizes the egg, while the other fertilizes the two polar nuclei, resulting in triploid endosperm. This type of "double fertilization" is a defining aspect of flowering plants.
Human babies with low birth weights and high birth weights have a lower chance of survival than those with average birth weights. Which of the following is an example of a process?
Correct answer: Stabilizing selection
Stabilizing selection favors intermediate traits and causes traits to cluster more tightly around an optimum value. Directional selection causes traits to become more extreme in a preferred direction. For example, if the fastest cheetah captures more prey and thus has a higher chance of survival, then there is selective pressure for cheetahs to become faster and faster. Disruptive, or diversifying, selection favors a lot of variation. The human immune system is being disrupted by selection, because the more variation we have in our receptors to recognize invading pathogens, the better.
Foreign proteins that bind to an antibody are referred to as
Correct answer: Antigens
Antigens are foreign proteins that are bound by antibodies in order for them to be neutralized in the body.
The molecule used by animals as a quick energy source is
Correct answer: Glycogen
Glycogen stores are used by animals as a source of quick energy. Glycogen is converted into glucose.
When a neuron reaches the action potential threshold:
Correct answer: The sodium channels are open.
The sodium channels open when a neuron reaches a threshold for an action potential.
Catabolic reactions necessarily require:
Correct answer: None of the above
Catabolic reactions breakdown molecules and generate energy as a result.
Approximately 99% of blood cells are involved in what process?
Correct answer: Transporting oxygen
Red blood cells' primary function is to transport oxygen from the lungs to the tissues. Hemoglobin is abundant in red blood cells.
What is an example of a cofactor?
Correct answer: Zinc
An inorganic substance that is required for an enzymatic reaction to occur is known as a cofactor. Cofactors bind to the enzyme's active site, allowing the substrate to fit properly. Metal ions, such as zinc, iron, and copper, are common cofactors.
Enzymes catalyze biochemical reactions by what process?
Correct answer: Reducing the reaction's activation energy
Catalysts for biochemical reactions are enzymes. A catalyst does not consume itself in a reaction; rather, it reduces the activation energy of that reaction. The potential energy of the substrate and product remain constant, but the activation energy, or the energy required to move the reaction forward, "can be reduced with the help of an enzyme."
Which of the following is most likely to perform CAM photosynthesis?
Correct answer: Cacti
Cacti, for example, exhibit CAM photosynthesis because water loss must be kept to a minimum. At night, these plants open their stomata and fix CO2. Stomata close during the day, reducing water loss. As a result, photosynthesis can continue without losing any water.
The combination of DNA and histones is known as
Correct answer: Chromatin
Chromatin is DNA wrapped around histone proteins. DNA is always associated with protein in eukaryotic cells; it is not "naked" as in prokaryotic cells.
When an animal consumes more energy than it uses over a long period of time, the excess chemical energy is stored as:
Correct answer: Fat
Animal fat is used for long-term energy storage. Animals and plants both store energy in the form of glycogen and starch, but these substances are only for short-term use. Fats are a good form of chemical energy storage because fatty acids bond to glycerol in a condensation reaction to form fats (triglycerides). This reaction, which produces water, enables the compacting of high-energy fatty acids in a concentrated form.
Which of the following molecules is thought to have treated as the first enzyme in the evolution of life on Earth?
Correct answer: RNA
Some RNA molecules in living organisms have enzymatic activity; for example, an RNA molecule catalyzes the formation of peptide bonds on ribosomes. This and other evidence has led scientists to believe that RNA molecules were the most likely to exhibit enzymatic activity first.
When the plasma membrane surrounds a particle outside of the cell, which of the following organelles is/are formed?
Correct answer: Endocytic vesicles
Endocytosis is the process by which cells absorb larger molecules or even tiny organisms like bacteria that would otherwise be unable to pass through the plasma membrane. Once inside the cell, endocytic vesicles containing molecules from the extracellular environment are frequently processed further.
Which of the following plant organelles contains the pigment responsible for the color of the leaves?
Correct answer: Chloroplasts
Chloroplasts contain chlorophyll, a light-absorbing compound that is required for photosynthesis. This is what gives the leaves their green color. Chloroplasts also contain yellow and red carotenoid pigments, which cause leaves to turn red and yellow in the fall when the chloroplasts lose their chlorophyll.
Which of the following cell types has a cell wall made up of peptidoglycans?
Correct answer: Bacteria
Cell walls in bacteria and cyanobacteria are made of peptidoglycans, which are a polysaccharide and protein molecule. Other types of organisms with cell walls, such as plants and fungi, have cell walls made up of different polysaccharides. Plant cell walls are made of cellulose, whereas fungal cell walls are made of chitin.