BIOL 107 606 Fundamentals of Microbiology

Correct Answer A: Pyruvate

Detailed Explanation of the Correct Answer:

Pyruvate is not a product of the Krebs cycle; it is actually a reactant that enters the mitochondrial matrix before the cycle begins. Specifically, pyruvate is produced during glycolysis, which occurs in the cytoplasm. Once formed, pyruvate is transported into the mitochondrion, where it is converted into acetyl-CoA during a process called pyruvate oxidation. Acetyl-CoA then enters the Krebs cycle to be further broken down.

The actual products of the Krebs cycle (per one glucose molecule, which generates two turns of the cycle) include:

– 6 NADH (3 per cycle)

– 2 FADH₂ (1 per cycle)

– 4 CO₂ (2 per cycle)

– 2 ATP (or GTP) (1 per cycle)

Explanation of Why the Other Options Are Correct Products:

NADH is a key product of the Krebs cycle and serves as an electron carrier that delivers high-energy electrons to the electron transport chain.

Carbon dioxide (CO₂) is released as a waste product during the decarboxylation steps in the cycle, when carbon atoms are removed from intermediates.

ATP (or in some cells, GTP) is produced directly through substrate-level phosphorylation during one of the steps of the Krebs cycle.

Summary:

Pyruvate is not produced by the Krebs cycle—it is converted before the cycle begins

Correct answer D: As cells grow, their volume gets bigger faster than their surface area

Detailed explanation:

Cells remain small because of limitations related to the surface area-to-volume ratio. This ratio is critical for the exchange of materials (like nutrients and waste) between the cell and its environment.

As a cell increases in size:

The volume (the inside of the cell) increases faster than the surface area (the outer membrane).

The surface area is what allows the cell to take in nutrients and eliminate waste.

The volume represents the metabolic demands of the cell.

When the volume becomes too large relative to the surface area, the cell cannot efficiently move materials in and out fast enough to support its activities.

This means that larger cells are less efficient, and they may not be able to sustain themselves. That's why cells typically divide when they grow too large, maintaining an efficient surface area-to-volume ratio.

Why the other options are incorrect:

A As cells grow, their surface area gets bigger faster than their volume

Incorrect. The volume increases faster than surface area, not the other way around.

B As cells grow, their surface area decreases

Incorrect. Surface area increases, but not as quickly as volume.

C As cells grow, their surface area to volume ratio increases

Incorrect. The ratio decreases, meaning less surface area per unit of volume as the cell grows.

Summary:

Cells are small because as they grow, their volume increases faster than their surface area, reducing efficiency in exchanging materials. Thus, the correct answer is D.

Correct Answer B: Life needs to arise from pre-existing life

Explanation:

The theory of biogenesis states that all living organisms come from other living organisms, not from non-living material. This concept was solidified by Louis Pasteur’s experiments, which disproved the idea of spontaneous generation (the belief that life could emerge from non-living matter).

Why the other options are incorrect:

A) Bacteria can reproduce using the process of binary fission:

This describes a method of reproduction, not the core principle of biogenesis.

C) Life can arise from non-living matter:

This reflects spontaneous generation, which is the opposite of the theory of biogenesis.

D) A specific bacteria can be identified as the cause of a specific disease:

This refers to Koch’s postulates, which relate to germ theory, not biogenesis.

Correct Answer D: Net movement of particles from areas of high concentration to areas of low concentration

Simple diffusion is the process where molecules move passively down their concentration gradient, meaning they move from a region where they are more concentrated to where they are less concentrated. This process does not require cellular energy or assistance from transport proteins, and it occurs until equilibrium is reached.

Why Other Options are Incorrect

A)Net movement of particles between cells:  Movement between cells describes transport across cell junctions or extracellular spaces, not diffusion across a plasma membrane.

B) Net movement of particles from areas of low concentration to areas of high concentration:  Movement from low to high concentration requires energy input and is characteristic of active transport, not simple diffusion.

C) Net movement of particles into and out of the cell using vacuoles for bulk transport:  Movement involving vacuoles refers to bulk transport mechanisms such as endocytosis or exocytosis, which are energy-dependent and different from diffusion.

Summary:

Simple diffusion is the passive movement of particles directly through the plasma membrane from an area of higher concentration to lower concentration, without energy or specialized transport mechanisms.

Correct Answer B: Adenosine triphosphate (ATP)

Explanation:

ATP (adenosine triphosphate) is known as the "molecular currency" of the cell because it directly provides usable energy for a wide range of cellular processes, including:

Muscle contraction

Active transport across membranes

Protein synthesis

Cell signaling

Metabolic reactions

ATP stores energy in its high-energy phosphate bonds and releases it when a phosphate group is removed (hydrolysis to ADP), fueling essential cellular activities.

Why the other options are incorrect:

A) Proteins:

Proteins perform structural and functional roles (e.g., enzymes, transport), but they are not the main energy source for cellular work.

C) Glucose:

Glucose is a primary fuel molecule, but it must first be broken down via cellular respiration to produce ATP—it is not used directly for most cellular work.

D) Fatty acids:

Fatty acids are a long-term energy storage molecule and are metabolized to generate ATP, but they are not the direct energy currency of the cell.

Correct Answer A: only plants contain this organelle

Explanation of the Correct Answer:

The image shows a chloroplast, which is a double membrane-bound organelle found exclusively in plant cells and some protists like algae. Chloroplasts contain the green pigment chlorophyll and are the site of photosynthesis, the process by which light energy is converted into chemical energy (glucose).

Chloroplasts are not found in animal cells or bacterial cells. Their presence is a defining feature of plant cells, and they are essential for the autotrophic lifestyle of plants.

Why the other options are wrong:

B. plants, animals, and bacteria can all contain this organelle

Incorrect. Chloroplasts are not found in animal or bacterial cells. Animals are heterotrophs and do not photosynthesize, and bacteria do not have membrane-bound organelles like chloroplasts.

C. only animals contain this organelle

Incorrect. Animals do not contain chloroplasts, as they do not carry out photosynthesis.

D. only bacteria contain this organelle

Incorrect. Bacteria do not contain chloroplasts or any membrane-bound organelles. While some bacteria (like cyanobacteria) perform photosynthesis, they do so without chloroplasts, using simpler internal membrane systems.

E. both plants and animals contain the organelle, but not bacteria

Incorrect. While this eliminates bacteria correctly, it mistakenly includes animals. Animals do not contain chloroplasts.

Summary:

The organelle in the image is a chloroplast, which is found only in plant cells and certain protists. Therefore, the correct answer is A. only plants contain this organelle.

Correct Answer B: DNA, blood cell, muscle tissue, heart, circulatory system, wolf

Detailed Explanation of the Correct Answer:

B is correct because it follows the proper biological organizational hierarchy from the smallest unit to the most complex in a multicellular organism like a wolf:

DNA – The genetic material found in cells; it provides instructions for building proteins.

Blood cell – A type of cell, which is the basic structural and functional unit of life.

Muscle tissue – A group of similar cells working together to perform a specific function.

Heart – An organ made up of multiple tissues (including muscle tissue, blood tissue, and connective tissue) that work together to pump blood.

Circulatory system – An organ system composed of the heart and blood vessels that transports blood throughout the body.

Wolf – The organism, which is the complete living being made of multiple organ systems.

Explanation of Why the Other Options Are Incorrect:

A. Muscle tissue, blood cell, DNA, organ, circulatory system, wolf

This sequence is out of order—DNA should come before cells and tissues, not after them.

C. Blood cell, organ, circulatory system, muscle tissue, DNA, wolf

This sequence jumps around and is disorganized; for example, muscle tissue and DNA should come before organs and systems, not after.

D. Circulatory system, DNA, muscle tissue, blood cell, heart, wolf

This sequence is incorrect because it begins with a system and mixes different levels of organization out of order.

Summary:

The correct sequence of biological organization from smallest to largest in a wolf is: DNA → cell → tissue → organ → organ system → organism, which is correctly represented in B. DNA, blood cell, muscle tissue, heart, circulatory system, wolf.

Correct Answer B: Locus

Detailed Explanation of the Correct Answer:

B. Locus is the correct answer because it refers to the specific, fixed position on a chromosome where a particular gene or genetic marker is located. Each gene has a designated locus on a chromosome, which can be mapped and used to identify its location in genetic studies.

Explanation of Why the Other Options Are Incorrect:

A. Genotype – This refers to the genetic makeup of an individual, including the combination of alleles they inherit, not the physical location of a gene.

C. Allele – This is a version or variant of a gene found at a particular locus, but it is not the location itself.

D. Base – This refers to the individual units of DNA (adenine, thymine, cytosine, and guanine), not the location of an entire gene.

Summary:

The term that describes the precise physical location of a gene on a chromosome is locus. Therefore, the correct answer is B. Locus.

Correct Answer B: It is covered with ribosomes

Explanation:

The rough endoplasmic reticulum (RER) appears "rough" under a microscope because its outer surface is studded with ribosomes. These ribosomes are the sites of protein synthesis, giving the RER its characteristic bumpy texture.

Why the other options are incorrect:

A) It has a high density of receptor proteins on its membrane:

While membranes can have receptors, this is not what gives the RER its rough appearance.

C) Its surface is highly folded to increase surface area:

This describes many cellular membranes, but folding alone does not make the RER rough.

D) It is covered with cilia:

Cilia are hair-like structures found on the surface of some cells, not on internal organelles like the RER.