Which of the following is the neurotransmitter that causes skeletal muscle contraction?

The correct answer is B. Cell membrane because both prokaryotic and eukaryotic cells have a cell membrane.

The cell membrane, also called the plasma membrane, is the thin boundary that surrounds the cell and separates the inside of the cell from the external environment. It helps control what enters and leaves the cell, which is essential for survival in all cells.

Since both prokaryotic and eukaryotic cells need to:

• maintain internal conditions
• regulate movement of substances
• protect the cell contents

they both have a cell membrane.

Why the Other Choices Are Incorrect

A. Chloroplast

Chloroplasts are found in plant cells and some algae, where they carry out photosynthesis.
They are not found in prokaryotic cells, and they are also not found in all eukaryotic cells.

B. Cell membrane

This is correct because all cells have a cell membrane, including:

• prokaryotic cells
• eukaryotic cells

It is one of the basic features shared by both cell types.

C. Golgi apparatus

The Golgi apparatus is a membrane-bound organelle found only in eukaryotic cells.
Prokaryotic cells do not have membrane-bound organelles.

D. Endoplasmic reticulum

The endoplasmic reticulum is also a membrane-bound organelle found only in eukaryotic cells.
Prokaryotes do not have an ER.

Key Concept

This question tests the difference between prokaryotic and eukaryotic cells.

Prokaryotic cells

• do not have a nucleus
• do not have membrane-bound organelles
• do have:
  • cell membrane
  • cytoplasm
  • ribosomes
  • genetic material

Eukaryotic cells

• do have a nucleus
• do have membrane-bound organelles
• also have:
  • cell membrane
  • cytoplasm
  • ribosomes
  • genetic material

So the overlap between the two includes structures such as:

• cell membrane
• cytoplasm
• ribosomes
• DNA

Among the answer choices given, cell membrane is the only structure found in both.

Helpful Test Tip

When you see answer choices like Golgi apparatus, endoplasmic reticulum, or chloroplast, remember these are specialized structures associated with eukaryotic cells.

When the question asks what is found in both prokaryotes and eukaryotes, think of the most basic cell structures:

• membrane
• ribosomes
• cytoplasm
• DNA

Take Away Points

• Cell membrane is present in both prokaryotic and eukaryotic cells.
• Prokaryotes do not have membrane-bound organelles.
• Golgi apparatus and endoplasmic reticulum are only in eukaryotic cells.
• Chloroplasts are only in photosynthetic eukaryotes like plants and algae.
• Common structures in all cells include cell membrane, cytoplasm, ribosomes, and DNA.

comparison chart of prokaryotic vs eukaryotic cells

The correct answer is B. Venn diagram because the question asks for a graph that can show overlap between different organisms.

That phrase is the biggest clue in the question.

A Venn diagram is specifically designed to show:

• relationships among groups
• shared characteristics
• areas of overlap between categories

In this case, the information describes animal classification groups and how different organisms belong to broader biological categories. A Venn diagram is the best choice when the goal is to visually represent how groups relate and where they may share common traits or connections.

Why a Venn Diagram Fits Best

The passage discusses:

• Bilateria
• two major superphyla:
  • protostomes
  • deuterostomes
• examples of organisms within each group

When a reader needs to understand how categories connect or compare, a Venn diagram is useful because it can visually organize:

• what belongs to one group
• what belongs to another group
• what traits or characteristics may be shared

Even in a general newspaper article, a Venn diagram can simplify complex biological classification by showing relationships in a visually easy format.

Why the Other Choices Are Incorrect

A. Histogram

A histogram is used to show the distribution of numerical data, usually grouped into intervals.
It is not used to show relationships or overlap among biological groups.

B. Venn diagram

This is correct because Venn diagrams are ideal for showing overlap and shared features among categories.

C. Pie chart

A pie chart shows parts of a whole as percentages or proportions.
It does not effectively show overlap between groups.

D. Scatter plot

A scatter plot is used to show the relationship between two numerical variables.
It is not appropriate for showing category overlap in classification groups.

Key Concept

This question is testing your ability to choose the correct type of graph based on the information being presented.

A quick guide:

• Venn diagram = overlap/shared traits between groups
• Pie chart = parts of a whole
• Histogram = frequency distribution of numerical data
• Scatter plot = relationship between two numerical variables

Because the question specifically says show overlap, the best answer is immediately Venn diagram.

This question tests your ability to interpret scientific graphs, specifically graphs showing enzyme activity vs. pH.

The graph shows:

• Activity Rate (y-axis)
• pH (x-axis)

Two curves represent:

• Enzyme A
• Enzyme B

Each enzyme has a specific pH at which it functions best, called its optimal pH.

1. Enzyme A Activity

Looking at the curve for Enzyme A:

• The curve rises sharply from pH 0
• The peak activity occurs around pH 2–3
• After that, activity declines rapidly

This means the optimum pH for enzyme A is between 2 and 3.

Therefore, the correct statement is:

✅ The highest activity rate for enzyme A occurs at a pH between 2 and 3.

2. Enzyme B Activity

The curve for Enzyme B shows:

• Activity increases around pH 5
• Maximum activity occurs around pH 8
• Activity decreases after that

This means enzyme B works best in a slightly basic environment.

3. Why the Other Options Are Incorrect

The highest activity rate for enzyme B occurs at a pH of 11.

From the graph, enzyme B peaks around pH 8, not 11.

At pH 11 the activity is already declining toward zero.

At a pH of 0, enzyme A has no activity.

The graph shows enzyme A has some activity at pH 0.

Its activity is low but not zero.

At a pH of 4, enzyme A and enzyme B have the same activity rate.

The graph shows enzyme A has higher activity than enzyme B at pH 4.

Their curves intersect closer to pH 6, not 4.

Understanding Enzyme Optimum pH

Different enzymes work best at different pH levels.

Examples:

This is because enzyme shape and active site structure depend on pH.

Extreme pH values can denature enzymes, reducing activity.

Key Takeaway Points

Enzymes have an optimal pH

Each enzyme functions best at a specific pH level.

Enzyme activity graphs show peaks

The highest point of the curve indicates the optimal pH.

Extreme pH decreases enzyme activity

Very acidic or very basic environments can reduce enzyme efficiency.

The correct answer is A. Divide by 1,000.

The question asks how to convert from grams per cubic meter (g/m³) to kilograms per cubic meter (kg/m³).

The key conversion is:

1 kilogram = 1,000 grams

So when converting from grams to kilograms, you divide by 1,000.

Why this works

A kilogram is a larger unit than a gram. Whenever you convert from a smaller unit to a larger unit, the numerical value becomes smaller.

For example:

• 1,000 g = 1 kg
• 500 g = 0.5 kg
• 2,500 g = 2.5 kg

The per cubic meter (m³) part does not change, because the volume unit stays the same. Only the mass unit changes.

So:

g/m³ ÷ 1,000 = kg/m³

Example

Suppose the solubility is:

3,500 g/m³

To convert to kg/m³:

3,500 ÷ 1,000 = 3.5 kg/m³

So:

3,500 g/m³ = 3.5 kg/m³

Why the Other Choices Are Incorrect

B. Multiple by 10

This is incorrect. There is no grams-to-kilograms conversion factor of 10.

C. Multiply by 1,000

This would be used if converting from kilograms to grams, not from grams to kilograms.

D. Divide by 10

This is incorrect because grams and kilograms differ by a factor of 1,000, not 10.

Key Concept

Metric conversions depend on the relationship between units.

For mass:

• 1,000 milligrams = 1 gram
• 1,000 grams = 1 kilogram

A quick way to think about it:

• going from g → kg, divide by 1,000
• going from kg → g, multiply by 1,000

Since the denominator m³ stays the same, only the mass unit changes.

Take Away Points

• 1 kilogram = 1,000 grams
• To convert g/m³ to kg/m³, divide by 1,000
• The m³ unit stays the same during this conversion
• Converting from a smaller unit to a larger unit makes the number smaller
• Watch for metric conversion traps using 10 instead of 1,000

This question tests your understanding of protein structure and the types of chemical bonds that hold proteins together.

Proteins are made of amino acids, which are the building blocks of proteins.

The primary structure of a protein is the linear sequence of amino acids linked together in a chain.

The bonds that connect these amino acids are called peptide bonds.

1. What is a Peptide Bond?

A peptide bond is a type of covalent bond formed between two amino acids.

It forms between:

• the carboxyl group (-COOH) of one amino acid
• the amino group (-NH₂) of another amino acid

During this reaction:

• a molecule of water is released
• this is called a dehydration synthesis reaction (or condensation reaction).

The result is a polypeptide chain, which later folds into a functional protein.

2. Protein Structural Levels

Proteins have four levels of structure:

Primary Structure

• The sequence of amino acids
• Held together by peptide bonds

Secondary Structure

• Folding patterns such as:
  • alpha helices
  • beta sheets
• Stabilized by hydrogen bonds

Tertiary Structure

• The 3D shape of the protein
• Stabilized by interactions such as:
  • hydrogen bonds
  • ionic bonds
  • disulfide bonds

Quaternary Structure

• Interaction of multiple polypeptide chains.

3. Why the Other Answers Are Incorrect

Phosphodiester bonds

Phosphodiester bonds connect nucleotides in DNA and RNA, not amino acids in proteins.

They form the sugar-phosphate backbone of nucleic acids.

Hydrogen bonds

Hydrogen bonds stabilize secondary structure of proteins, such as alpha helices and beta sheets.

They do not form the primary structure.

Disulfide bonds

Disulfide bonds form between sulfur atoms of cysteine amino acids.

They help stabilize tertiary protein structure, not the primary chain.

Key Takeaway Points

Proteins are made of amino acids

Amino acids are connected into chains called polypeptides.

Peptide bonds link amino acids

Peptide bonds form during dehydration synthesis and create the primary structure of proteins.

Primary structure determines protein function

The order of amino acids influences how the protein folds and what function it performs.

Different bonds stabilize different protein structures

TEAS Exam Memory Trick

Think:

Protein chain → Peptide bonds

Peptide bonds = protein backbone

The correct statement is Photosynthesis releases oxygen.

To understand why, it helps to compare photosynthesis and cellular respiration.

Photosynthesis

Photosynthesis occurs mainly in plants, algae, and some bacteria. In this process, organisms use:

• carbon dioxide
• water
• light energy

to make:

• glucose
• oxygen

The overall process can be summarized as:

Carbon dioxide + water + light energy → glucose + oxygen

This means that oxygen is released during photosynthesis, which makes D the correct answer.

Cellular Respiration

Cellular respiration is the process cells use to break down glucose to release usable energy in the form of ATP. In respiration, cells use:

• glucose
• oxygen

and produce:

• carbon dioxide
• water
• energy (ATP)

The overall process can be summarized as:

Glucose + oxygen → carbon dioxide + water + energy

This shows that respiration uses oxygen, not releases it.

Why the Other Choices Are Incorrect

A. Respiration produces glucose.

This is incorrect because respiration breaks down glucose to release energy. It does not make glucose.
It is photosynthesis that produces glucose.

B. Photosynthesis produces water.

This is incorrect in the basic biology comparison used for this type of exam question. Photosynthesis generally uses water as a reactant.
The main products emphasized are glucose and oxygen.

C. Respiration releases oxygen.

This is incorrect because respiration consumes oxygen and releases carbon dioxide and water.

D. Photosynthesis releases oxygen.

This is correct. During photosynthesis, oxygen is formed and released into the environment.

Deeper Concept

Photosynthesis and respiration are often considered complementary processes.

• Photosynthesis stores energy by making glucose.
• Respiration releases energy by breaking down glucose.

Also:

• Photosynthesis removes carbon dioxide from the atmosphere and releases oxygen.
• Respiration uses oxygen and releases carbon dioxide.

So in a simple way:

• Photosynthesis builds
• Respiration breaks down

That contrast helps answer many TEAS science questions.

Take Away Points

• Photosynthesis releases oxygen and produces glucose.
• Respiration uses oxygen and breaks down glucose.
• Photosynthesis uses carbon dioxide and water.
• Respiration produces carbon dioxide and water.
• The two processes are closely connected in living systems.

The best answer is Scanning electron microscope because the question is asking about observing the surface structures of a virus particle.

There are two key clues in the question:

• surface structures
• virus particle

These clues point directly to the scanning electron microscope (SEM).

Why SEM is correct

A scanning electron microscope is designed to produce highly detailed images of the surface of very small specimens. It scans the specimen with electrons and creates a detailed, often three-dimensional-looking image of the outside structure.

This makes SEM especially useful for seeing:

• texture
• shape
• outer features
• surface projections

Since a virus is extremely small, it cannot be seen clearly with ordinary light microscopes. And because the question specifically asks about the surface, SEM is the best choice.

Why the other choices are incorrect

A. Compound light microscope

A compound light microscope uses visible light and lenses. It is useful for viewing cells, tissues, and some microorganisms, but viruses are too small to be seen clearly with this microscope. Its resolution is not high enough for detailed virus surface structure.

B. Fluorescence microscope

A fluorescence microscope is useful when specimens are stained with fluorescent dyes or tagged molecules. It helps identify specific parts of cells or molecules, but it is not the best choice for detailed surface structure of a virus particle. It is better for locating or labeling substances than for showing fine surface detail.

C. Scanning electron microscope

This is correct because SEM gives a highly detailed image of the outside surface of tiny objects. Since the question asks about surface structures, SEM matches perfectly.

D. Stereoscopic microscope

A stereoscopic microscope is used for larger, solid objects and provides a three-dimensional view at low magnification. It is useful for things like insects, leaves, rocks, or small tools, but not for virus particles, which are far too small.

Important Concept Behind the Question

This question is really testing two ideas:

1. Size of viruses

Viruses are much smaller than most cells and are generally too small to be resolved with standard light microscopes.

2. Function of different microscopes

Different microscopes are used for different purposes:

• Compound light microscope: cells and basic microscopic specimens
• Fluorescence microscope: labeled structures, specific molecules, stained samples
• Scanning electron microscope: detailed surface view
• Transmission electron microscope: detailed internal structures
• Stereoscopic microscope: larger objects, low magnification, 3D external view

A helpful shortcut is:

• SEM = Surface
• TEM = Inside/internal detail

That memory trick is very useful for TEAS science questions.

Take Away Points

• Scanning electron microscope (SEM) is best for viewing surface structures.
• Viruses are too small to be observed in detail with a standard light microscope.
• SEM shows outer detail, while TEM shows internal detail.
• A question asking about the outside of a tiny object usually points to SEM.
• A stereoscopic microscope is for larger visible objects, not viruses.

This question tests your understanding of pH, hydrogen ion concentration (H⁺), and hydroxide ion concentration (OH⁻).

The pH scale measures how acidic or basic a solution is.

Where:

• H+= hydrogen ion concentration.

1. Determine the Hydrogen Ion Concentration

If the pH = 10, we can determine the hydrogen ion concentration:

So the hydrogen ion concentration is:

2. Relationship Between H⁺ and OH⁻

Water maintains a constant relationship:

So if:

Then:

Thus, the hydroxide ion concentration is 10⁻⁴.

This matches the correct answer.

3. Why the Other Answers Are Incorrect

The solution is a weak acid.

A solution with pH = 10 is basic, not acidic.

Acids have pH less than 7.

The solution is neutral.

Neutral solutions have:

A pH of 10 is basic.

The solution has a hydrogen ion concentration of 10⁻⁴.

If hydrogen ion concentration were 10⁻⁴, then:

That would be acidic, not basic.

Understanding the pH Scale

Examples:

Since pH 10 is above 7, it is a basic solution.

Key Takeaway Points

1️⃣ pH measures hydrogen ion concentration

Higher pH = lower hydrogen ion concentration.

2️⃣ H⁺ and OH⁻ are inversely related

If hydrogen decreases, hydroxide increases.

3️⃣ Basic solutions have higher OH⁻

At pH 10:

• low H⁺
• high OH⁻

4️⃣ Each pH unit is a 10× change

For example:

• pH 9 → 10× more basic than pH 8
• pH 10 → 100× more basic than pH 8

TEAS Exam Memory Trick

Think:

pH + pOH = 14

For pH 10:

Urea is a waste product produced during protein metabolism. It forms when the body breaks down amino acids, which are the building blocks of proteins.

When proteins are digested and used by the body, excess amino acids cannot be stored. Instead, they are broken down in the liver through a process called deamination.

During deamination:

• the amino group (-NH₂) is removed from the amino acid
• this process produces ammonia (NH₃)

Ammonia is highly toxic to cells, especially brain cells. To prevent toxicity, the liver converts ammonia into urea through a metabolic pathway called the urea cycle.

Urea is much less toxic and can safely circulate in the bloodstream until it is removed by the kidneys and excreted in urine.

The Urea Cycle Process

The formation and removal of urea follow this pathway:

1. Protein digestion produces amino acids.
2. Excess amino acids are broken down in the liver.
3. Ammonia is produced from the amino group.
4. The liver converts ammonia into urea through the urea cycle.
5. Urea enters the bloodstream.
6. The kidneys filter urea from the blood.
7. Urea leaves the body through urine.

Why the Other Options Are Incorrect

Production of ammonia in the heart

Ammonia is produced primarily during amino acid metabolism in the liver, not the heart.

Breakdown of carbohydrates in the intestine

Carbohydrate digestion produces glucose, not nitrogen-containing waste like urea.

Removal of bases from nucleic acids in cell cytoplasm

Breakdown of nucleic acids produces uric acid, not urea.

Key Takeaway Points

Urea is a nitrogen waste product

It results from protein metabolism.

The liver produces urea

The liver converts toxic ammonia into urea.

Kidneys remove urea

Urea is filtered from the blood by the kidneys and excreted in urine.

Protein metabolism produces nitrogen waste

The body cannot store excess amino acids, so they must be broken down and converted into waste products.

TEAS Exam Memory Trick

Think:

Protein → Amino acids → Ammonia → Urea → Urine

It is likely to lose one electron to form a positive ion.

Explanation

To understand this question, we must first understand valence electrons and atomic stability.

1. What are Valence Electrons?

Valence electrons are the electrons in the outermost energy level (outer shell) of an atom. These electrons determine how atoms react and bond with other atoms.

Atoms tend to react in ways that allow them to achieve a stable electron configuration, usually following the octet rule, which means having 8 electrons in the outer shell.

2. What Happens When an Atom Has One Valence Electron?

Atoms with one valence electron are very unstable, because their outer shell is far from full. The easiest way for such an atom to become stable is to lose that single electron.

When it loses one electron, the atom will then have:

• More protons than electrons
• A net positive charge

This forms a positive ion, also called a cation.

Example reaction:

Na → Na⁺ + e⁻

Sodium loses its one valence electron and becomes a Na⁺ ion.

3. Why Losing One Electron Is Favorable

It is much easier for the atom to lose one electron than to gain seven electrons to fill the shell.

After losing the electron, the atom's electron configuration resembles that of a noble gas, which is very stable.

4. Real-World Example: Alkali Metals

Elements in Group 1 of the periodic table (alkali metals) all have one valence electron.

Examples include:

• Lithium (Li)
• Sodium (Na)
• Potassium (K)
• Rubidium (Rb)

These elements are extremely reactive because they easily lose their single valence electron.

For example:

2Na + Cl₂ → 2NaCl

Sodium loses one electron and chlorine gains one electron to form ionic bonds.

Why the Other Options Are Incorrect

It has a high ionization energy and will not lose its electron easily.

Atoms with one valence electron actually have LOW ionization energy, meaning their electron is easy to remove.

It is unreactive.

Atoms with one valence electron are actually highly reactive, particularly the alkali metals.

It will resist forming any bonds due to a full outer shell.

Atoms resist bonding only when they already have a full valence shell, like noble gases (Ne, Ar, Kr).
An atom with one valence electron does not have a full shell, so it reacts easily.

Key Takeaway Points

1️⃣ Valence electrons control chemical behavior

The number of valence electrons determines how an atom reacts and what type of bonds it forms.

2️⃣ Atoms seek stability

Most atoms try to achieve 8 electrons in their outer shell (octet rule).

They do this by:

• Losing electrons
• Gaining electrons
• Sharing electrons

3️⃣ Atoms with one valence electron form +1 ions

Elements with one valence electron tend to:

• Lose 1 electron
• Form a +1 ion (cation)
• Become chemically stable

Examples:

4️⃣ Ionization Energy Concept

Ionization energy is the energy required to remove an electron.

For atoms with 1 valence electron:

• Ionization energy is low
• The electron is easily removed

TEAS Exam Memory Trick

1 valence electron = wants to get rid of it

So remember:

Lose 1 electron → Positive ion (cation)