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Praxis Biology Content 5235 Exam | Questions Solved 100% Correct Answers| Already Passed
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Praxis Biology Content 5235 Exam |Questions Solved 100% Correct Answers|
Already Passed
A sample of peritoneal fluid from a laboratory mouse is placed between a slide and a 20 mm ×
20 mm cover slip to count the number of viable white blood cells. The thickness of the
peritoneal fluid sample between the slide and the cover slip is 0.1 mm. What is the volume of
the sample? - ANSWER If the dimensions of the cover slip are 20 mm × 20 mm, the surface area
of the sample is 400 mm2. If the thickness of the sample under the cover slip is 0.1 mm, then
the total volume of the sample is 400 mm2 × 0.1 mm = 40 mm3.
Which of the following experimental methods is most appropriate for separating pigments
extracted from plant leaves? - ANSWER Pigments extracted from plant leaves are typically
separated from each other by chromatography. A drop of liquid from an extract of ground
leaves is placed on a strip of chromatography paper close to the bottom, and the very bottom
of the paper, below the extract drop, is placed in an organic solvent. As the solvent travels up
the strip, the pigments in the extract separate based on their solubility in the solvent and their
attraction to the hydrated cellulose in the chromatography paper.
Gregor Mendel - ANSWER Augustinian monk and botanist whose experiments in breeding
garden peas led to his eventual recognition as founder of the science of genetics (1822-1884)
By examining the phenotypes of the plants for many generations, he developed several basic
principles of genetics, including one that states that traits are passed in discrete units (that
we now know as alleles of genes) and produce predictable outcomes in offspring.
Which of the following properties of water is responsible for the solubility of many molecules
in aqueous fluids such as blood and urine? - ANSWER The polarity of water molecules. Water
molecules are polar because oxygen is more electronegative than hydrogen. The oxygen region
of a water molecule has a partial negative charge, and the hydrogen regions have partial
positive charges.
,Restriction endonuclease - ANSWER A degradative enzyme that recognizes specific
nucleotide sequences and cuts up DNA. Many recognize and cleave at palindromic sequences
and create nucleotide overhangs such as that shown in the figure of the cleaved plasmid.
cristae of mitochondria - ANSWER Where does the electron transport chain occur?
Which of the following is most likely to increase transcription of a particular gene? - ANSWER
Acetylation of histone proteins associated with the gene. DNA is negatively charged because
of its phosphate groups and so readily bonds with positively charged histone proteins that
contribute to the nucleosome structure of DNA in eukaryotic cells. When DNA is tightly bound
by histone proteins, the transcription machinery of a cell cannot gain access to the DNA, and
transcription is blocked. However, many transcription factors are associated with proteins that
add negatively charged acetyl groups to the histones, which loosens the interactions between
the DNA and histones and thus facilitates transcription of particular genes.
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy - ANSWER In the summary formula shown for
aerobic cellular respiration, C6H12O6 is oxidized and O2 is reduced. The electrons of H atoms
removed from C6H12O6 during glycolysis and the citric acid cycle reduce O2, the final
electron acceptor of each electron transport chain, to produce H2O.
Interphase is the part of the cell cycle that includes which of the following? - ANSWER
Interphase is the nonmitotic part of the cell cycle when a cell is growing and carrying out its
normal metabolic processes. Replication of DNA occurs during interphase, specifically during
S phase of the cell cycle.
Which of the following structures is typically found in eukaryotic cells but not in prokaryotic cells? - ANSWER The
mitochondrion is a membrane‑bound organelle that is required for aerobic cellular respiration in eukaryotes. Depending
on the type of cell, the number of mitochondria per cell can vary from only one to a couple of thousand.
By which of the following processes is newly synthesized albumin typically transferred from
the cytosol of a hepatocyte to the blood? - ANSWER Secreted proteins such as serum albumin
are released from cells by exocytosis. A protein that is destined for secretion enters the rough
,endoplasmic reticulum (ER) as it is translated, then is moved in a vesicle from the ER to the
Golgi apparatus, where it is transported in vesicles from one cisterna to the next, and finally a
secretory vesicle that contains the protein fuses with the plasma membrane, releasing the
protein from the cell.
Which of the following occurs during the processing of a eukaryotic pre-mRNA molecule? -
ANSWER The pre-mRNA is cleaved at its 3' end, and approximately 200 AMPs are added to
the cleaved end.
Hormone H binds to both liver and lung cells. It causes liver cells to release glucose but does not cause any
response by lung cells. Of the following, which is the most likely explanation? - ANSWER Hormone H binding
activates a glucose transporter gene‑specific transcription factor in liver cells but not in lung cells. The binding of a
hormone to its receptor on the plasma membrane of a cell typically signals the cell to make a specific response.
Which TWO of the following pose the greatest obstacle to the random passive diffusion of ions
across the plasma membrane of a cell? - ANSWER The hydrophobic interior of the plasma
membrane's lipid bilayer and The large size of ions that are hydrated by water molecules. Ions
typically require a transmembrane protein channel with a hydrophilic interior to facilitate their
diffusion across the membrane.
A particular anticancer drug binds to microtubules‚ preventing disassembly of microtubules into
individual tubulin dimers. - ANSWER Mitotic spindles are composed of microtubules. Aligning
the chromosomes at the equator of a mitotic cell requires both microtubule assembly and
disassembly. Additionally, separating the chromatids to daughter cells involves microtubule
disassembly. If the drug blocks microtubule disassembly, then it interferes with spindle
formation and chromosome alignment and separation, blocking cell division. Such a drug
typically manifests its greatest toxicity on rapidly dividing cells, including cancer cells.
Which of the following occurs as a part of the noncyclic photophosphorylation pathway of photosynthesis? - ANSWER Water is split to two
electrons, two protons, and an oxygen atom. The splitting of water and the associated oxygen‑generating reaction can be written as: 2 H2O
→ 4 H+ + 4 e− + O2.
, Induction of the lac operon in E. coli is most likely to occur under which of the following
environmental conditions? - ANSWER The lac operon of E. coli encodes enzymes that enable
the bacteria to take up the disaccharide lactose from the environment and hydrolyze the
lactose to glucose and galactose. The operon is maximally active when the concentration of
glucose is low in the environment and the concentration of lactose is high.
If a messenger RNA contains the codon 5'-UCA- 3', the corresponding nucleotide sequence in
the DNA template strand is most likely which of the following? - ANSWER The template strand
for transcription of a DNA sequence to mRNA runs antiparallel to the mRNA and utilizes
thymine (T) in the place of the uracil (U) found in RNA. If the sequence 5'−UCA− 3' is found in an
mRNA, then the template DNA sequence must be 5'−TGA− 3'.
Which of the following best explains why silent mutations in the coding region of a gene do
not change the amino acid sequence of the protein encoded by the gene? - ANSWER Most,
although not all, amino acids are encoded by more than one mRNA codon, with the difference
between the codons frequently in the third base, the wobble position. A nucleotide change in
this position is referred to as a silent mutation because it does not change the coded amino
acid.
The growth hormone (GH) receptor is a cell surface transmembrane protein with a cytosolic domain that
becomes phosphorylated in response to growth hormone binding to the extracellular domain. Which of the
following is correct about the location of the GH receptor protein during its synthesis? - ANSWER Translation
of proteins such as the GH receptor that will be embedded in the plasma membrane is carried out by
ribosomes on the cytosolic surface of the rough endoplasmic reticulum (ER). During translation of the
protein, it starts (from its amino‑terminus end) to enter the ER through pores in the ER membrane. The
amino terminus of the protein is typically the domain to which a ligand such as GH will bind. Insertion of the
protein into the ER is halted when amino acids of the transmembrane portion of the protein form bonds
with components of the ER membrane; the cytosolic domain of the protein that contains the
phosphorylation sites remains in the cytosol of the cell. Vesicles that contain the receptor protein pinch off
the ER and fuse with the membrane of the Golgi apparatus such that the extracellular ligand‑binding domain
of the receptor is located in the cisternae of the Golgi apparatus, while the cytosolic domain remains in the
cytosol. When vesicles containing the receptor pinch off the Golgi apparatus and fuse with the plasma
membrane, the receptor becomes incorporated into the membrane with the ligand‑binding domain on the
extracellular surface of the cell and the cytosolic phosphorylation sites in the cytosol.
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