A scanning electron microscope found bacteria arranged as shown. According to the flow chart, which of the following types of bacteria was found?

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)

This question tests your understanding of DNA base pairing rules and strand orientation.

DNA consists of two complementary strands arranged in an antiparallel direction. This means:

• One strand runs 5' → 3'
• The complementary strand runs 3' → 5'

The bases in DNA pair according to specific pairing rules:

Step-by-Step Base Pairing

Given DNA strand:

5' AGCTAGCGT 3'

We determine the complementary bases:

Complementary sequence:

TCGATCGCA

Because DNA strands are antiparallel, the complementary strand must run:

3' TCGATCGCA 5'

This matches the correct answer.

Why the Other Options Are Incorrect

5' UCGAUCGCA 3'

This contains U (uracil), which is found in RNA, not DNA.

DNA uses thymine (T) instead of uracil.

5' TCGUTCGCU 3'

This sequence also contains U, indicating RNA, not DNA.

Additionally, the sequence does not correctly follow DNA base pairing.

3' AGCTAGCGT 5'

This is simply the same sequence reversed, not the complementary strand.

DNA requires complementary bases, not identical bases.

Understanding DNA Strand Direction

DNA strands are always written using prime notation (').

• 5' end → phosphate group
• 3' end → hydroxyl group

DNA strands run in opposite directions, which is called antiparallel orientation.

Example:

5' → 3'
3' ← 5'

This structure helps stabilize the double helix.

Key Takeaway Points

DNA follows strict base pairing rules

• A pairs with T
• C pairs with G

DNA strands are antiparallel

One strand runs 5' → 3', the other runs 3' → 5'.

DNA does not contain uracil

Uracil (U) is only found in RNA.

Complementary sequences must follow pairing rules

You must both:

• match the correct bases
• reverse the direction.

TEAS Exam Memory Trick

Remember:

A ↔ T
C ↔ G

Think:

Apples in Trees
Cars in Garages

The correct answer is B because bile salts emulsify fats, meaning they break large fat globules into smaller fat droplets. This does not chemically digest the fat by itself, but it makes fat digestion much easier.

What bile salts do

Bile is produced by the liver and stored in the gallbladder. When fatty food enters the small intestine, bile is released. The bile salts in bile help by breaking up large clumps of fat into many smaller droplets.

This process is called emulsification.

Why smaller fat droplets help digestion

Fats do not mix well with water, and digestive enzymes work best when they can reach more surface area of the food being digested.

When bile salts break fat into smaller droplets:

• the surface area of the fat increases
• lipase can act more effectively
• fat digestion becomes faster and more efficient

So bile salts help digestion indirectly by making fats easier for enzymes to digest.

Important Note

Bile salts do not digest fat chemically the way enzymes do. Instead, they physically break up fat into smaller droplets so that pancreatic lipase can digest it more efficiently.

That is why the wording “decrease the size of fat droplets” is the best answer.

Why the Other Choices Are Incorrect

A. Decrease the size of starches to aid in digestion

This is incorrect because bile salts do not act on starches. Starch digestion is mainly done by enzymes such as amylase.

B. Decrease the size of fat droplets to aid in digestion

This is correct because bile salts emulsify fats, breaking large fat globules into smaller droplets.

C. Increase the size of fat droplets to aid in digestion

This is the opposite of what bile salts do. Increasing droplet size would reduce surface area and make digestion harder.

D. Increase the size of starches to aid in digestion

This is incorrect because bile salts do not function in starch digestion, and increasing size would not help digestion.

Core Biology Concept

This question is testing your understanding of the difference between mechanical/physical assistance in digestion and chemical digestion.

• Bile salts help with fat emulsification
• Lipase chemically digests fats
• Amylase digests carbohydrates like starch
• Proteases digest proteins

A useful shortcut:

• Bile = breaks up fat physically
• Lipase = breaks down fat chemically

Take Away Points

• Bile salts emulsify fats by breaking large fat globules into smaller droplets.
• This increases surface area for digestive enzymes.
• Bile helps fat digestion, not starch digestion.
• Bile salts do not chemically digest fat; lipase does that.
• The best way to remember this is: bile breaks fat apart, lipase breaks fat down.

This question tests your knowledge of bone classification based on shape and structure.

Bones in the human body are classified into five main categories:

1. Long bones
2. Short bones
3. Flat bones
4. Irregular bones
5. Sesamoid bones

A long bone is characterized by:

• being longer than it is wide
• having a shaft (diaphysis)
• having two expanded ends (epiphyses)
• containing a medullary cavity (bone marrow cavity)

Long bones function primarily to:

• support body weight
• facilitate movement
• act as levers for muscles

The tibia, located in the lower leg, fits all these characteristics and is therefore classified as a long bone.

Structure of a Long Bone

Long bones have several important anatomical parts:

1. Diaphysis

The shaft of the bone.

• made mostly of compact bone
• provides strength and support

2. Epiphysis

The expanded ends of the bone.

• contain spongy bone
• help form joints

3. Medullary Cavity

The hollow center of the diaphysis that contains bone marrow.

4. Articular Cartilage

A smooth tissue covering the ends of bones at joints that reduces friction.

Why the Other Options Are Incorrect

Vertebrae

Vertebrae are classified as irregular bones.

They have complex shapes designed to:

• protect the spinal cord
• support the body
• allow spinal movement

Rib

Ribs are flat bones.

Flat bones:

• protect internal organs
• provide surfaces for muscle attachment

Examples include:

• ribs
• sternum
• skull bones

Carpal

Carpals are short bones found in the wrist.

Short bones:

• are roughly cube-shaped
• provide stability and limited movement

Examples:

• carpals (wrist)
• tarsals (ankle)

Key Takeaway Points

Long bones are longer than they are wide

They have a shaft and two ends.

Long bones help with movement

Muscles attach to them and use them as levers.

Examples of long bones

Common long bones include:

• Femur
• Tibia
• Fibula
• Humerus
• Radius
• Ulna

Bone classification depends on shape

Understanding bone types helps identify their functions in the body.

TEAS Exam Memory Trick

Remember:

Long bones are found in the limbs.

Think:

Arms and legs = long bones

Examples:

• femur
• tibia
• humerus

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

This question involves phase changes and gas pressure.

The key concept here is sublimation, which is when a substance changes directly from a solid to a gas without passing through the liquid phase.

Dry ice is the solid form of carbon dioxide (CO₂). When dry ice sublimates, it turns directly into CO₂ gas.

1. What Happens When Dry Ice Sublimates?

When dry ice changes from solid CO₂ to gaseous CO₂:

• Solid CO₂ molecules become free-moving gas molecules
• The gas molecules spread out and occupy more space
• The number of gas particles in the container increases

Because the container is sealed, the gas cannot escape.

2. Why Pressure Increases

Pressure in a gas occurs when gas molecules collide with the walls of a container.

As dry ice sublimates:

1. More CO₂ gas molecules are produced.
2. These gas molecules move freely throughout the container.
3. They collide with the container walls more frequently.

More collisions with the container walls result in greater pressure.

So the best explanation is that gas CO₂ particles occupy more space, leading to increased pressure.

3. Gas Behavior vs Solid Behavior

When CO₂ changes from solid → gas, the particles become much farther apart and mobile, which increases pressure inside a sealed container.

Why the Other Options Are Incorrect

Gas CO₂ molecules move faster when CO₂ is a solid.

Molecules in a solid move much less than gas molecules. Gas molecules move faster because they have greater freedom of movement.

CO₂ molecules combine to form larger molecules in the gas phase.

CO₂ molecules do not combine during sublimation. They remain individual CO₂ molecules.

CO₂ particles exert less force on the container walls as a gas.

Gas particles actually exert more force because they collide with the container walls frequently.

Key Takeaway Points

Sublimation

Sublimation is the change of state from:

Solid → Gas

Example: Dry ice (solid CO₂) → CO₂ gas

Gas pressure

Gas pressure is caused by collisions of gas particles with container walls.

More particles = more collisions = higher pressure

Gas particles spread out

Gas molecules move freely and occupy more space than solid particles.

Sealed containers trap gases

If gas forms inside a sealed container, the pressure will increase because the gas cannot escape.

TEAS Exam Memory Trick

Remember:

More gas particles → More collisions → Higher pressure

The correct answer is A. Carbon dioxide.

Hyperventilation means a person is breathing faster or deeper than normal, which causes the body to blow off too much carbon dioxide (CO₂). As a result, the level of dissolved carbon dioxide in the blood becomes abnormally low.

This is the gas most directly associated with hyperventilation.

Why carbon dioxide is the correct answer

Carbon dioxide plays a major role in regulating breathing and blood pH.

When you breathe:

• oxygen enters the blood
• carbon dioxide leaves the blood

If a person hyperventilates, they exhale carbon dioxide too quickly. This causes:

• decreased blood CO₂
• a rise in blood pH
• respiratory alkalosis

So when the question asks which dissolved gas is abnormally low in hyperventilation, the answer is carbon dioxide.

What happens physiologically

Carbon dioxide in the blood is linked to carbonic acid levels. When CO₂ drops:

• less carbonic acid is formed
• the blood becomes less acidic
• pH rises

This change can lead to symptoms such as:

• dizziness
• lightheadedness
• tingling in the fingers or lips
• chest tightness
• faintness

That is why people who hyperventilate may feel unusual symptoms even though they are breathing rapidly.

Why the Other Choices Are Incorrect

B. Nitrogen

Nitrogen is present in the air we breathe, but it is not the main dissolved gas used by the body to regulate breathing in this context. Hyperventilation is not identified by abnormally low blood nitrogen.

C. Hydrogen

Hydrogen is not the correct answer here because the question asks about a dissolved gas. Hydrogen ions affect pH, but they are not the dissolved respiratory gas being tested in this question.

D. Carbon monoxide

Carbon monoxide is a poisonous gas that binds strongly to hemoglobin, but it is not the gas that becomes abnormally low during hyperventilation. It is associated with poisoning, not normal respiratory regulation.

Key Concept

The body’s breathing rate is strongly influenced by carbon dioxide levels.

A useful way to remember it:

• High CO₂ tends to stimulate breathing
• Low CO₂ is commonly seen with hyperventilation

Hyperventilation does not usually mean low oxygen is the main issue. In many test questions, the major abnormal change is too little carbon dioxide.

Take Away Points

• Hyperventilation lowers blood carbon dioxide levels.
• Low CO₂ can cause respiratory alkalosis.
• Carbon dioxide is a major regulator of breathing and blood pH.
• Symptoms of low CO₂ include dizziness, tingling, and lightheadedness.
• On TEAS questions, hyperventilation is most closely linked to decreased carbon dioxide.

The original hypothesis says that parasitic worm infestation is damaging to the host. Then the new finding adds an important detail: worm infestation can relieve the effects of certain autoimmune disorders.

That means the hypothesis should not be thrown out completely, but it should be revised to include this newly discovered benefit in some situations.

Choice B is best because it directly matches the new evidence:

• the worms can relieve effects
• relieving effects means they can reduce severity
• this applies to certain autoimmune disorders, not all disorders

Why the other choices are not correct:

A. Lack of worm infestations is the cause of some autoimmune disorders.
This goes too far. The question only says worm infestation can relieve the effects of some autoimmune disorders. It does not say that not having worms causes those disorders.

C. Worm infestations exacerbate the body's immune reactions.
“Exacerbate” means make worse. But the new finding says worm infestation can relieve effects, so this is the opposite of what the evidence supports.

D. Worm infestation prevents the body from immune malfunction.
This is too absolute. The question says worm infestation can relieve the effects of certain autoimmune disorders. It does not say worm infestation completely prevents immune malfunction.

Key Reasoning

When a hypothesis is modified based on new findings, the best answer usually:

• keeps as much of the original idea as possible
• adds only what the new evidence supports
• avoids extreme words like cause, prevents, or always, unless the evidence clearly proves them

Here, the evidence supports a limited revision:
worm infestation may be harmful in general, but it may also reduce the severity of some autoimmune conditions.

Takeaway Points

• A hypothesis should be revised, not automatically discarded, when new evidence appears.
• The best revision is the one that matches the evidence exactly.
• Be careful with extreme answer choices that go beyond the information given.
• In science questions, wording matters:
  • relieve effects = reduce severity
  • not necessarily cause, prevent, or cure

Meiosis is the cellular process that produces gametes (sex cells) such as sperm in males and eggs (ova) in females.

Key features of meiosis:

• It occurs in reproductive organs (gonads) — the testes and ovaries.
• It involves two rounds of cell division: Meiosis I and Meiosis II.
• It produces four haploid daughter cells, each with half the number of chromosomes of the original cell.

Humans normally have 46 chromosomes (diploid, 2n) in body cells.
Meiosis produces gametes with 23 chromosomes (haploid, n) so that when fertilization occurs, the embryo returns to 46 chromosomes.

Why the Other Options Are Incorrect

Apoptosis

• Programmed cell death used to remove damaged or unnecessary cells.
• Does not produce new cells or gametes.

Glycogenesis

• A metabolic process where glucose is converted into glycogen for storage in the liver and muscles.
• Related to energy storage, not cell reproduction.

Mitosis

• Produces two identical diploid cells.
• Used for growth, tissue repair, and cell replacement.
• Does not produce gametes.

Key Takeaway Points

• Meiosis produces gametes (sex cells).
• Gametes are haploid (23 chromosomes in humans).
• Meiosis involves two divisions → Meiosis I and Meiosis II.
• It creates genetic variation through:
  • Crossing over
  • Independent assortment

Quick TEAS Memory Tip

• Meiosis = Making eggs & sperm
• Mitosis = Making body cells

This question tests your understanding of factors that affect the rate of chemical reactions.

The rate of a reaction refers to how fast reactants are converted into products.

Several factors can increase reaction rates:

• concentration of reactants
• temperature
• surface area
• catalysts

The key concept here is collision theory.

1. Collision Theory

Collision theory states that chemical reactions occur when:

1. Reactant particles collide
2. Collisions have enough energy
3. Particles collide in the correct orientation

The more frequent the collisions, the faster the reaction occurs.

2. Increasing the Concentration of Reactants

When the concentration of reactants increases:

• there are more reactant particles in the same volume
• particles collide more frequently
• more effective collisions occur

As a result, the reaction rate increases.

This applies to both endothermic and exothermic reactions.

3. Why the Other Options Are Incorrect

Decreasing the temperature

Lower temperature causes particles to:

• move more slowly
• collide less frequently
• have less kinetic energy

This slows the reaction rate, not increases it.

Decreasing contact area of reactants

Contact area (surface area) matters especially for solid reactants.

If contact area decreases:

• fewer particles are exposed
• fewer collisions occur

This slows the reaction.

Increasing the concentration of products

Increasing product concentration does not speed up the forward reaction.

According to Le Chatelier's Principle, it may actually:

• push the reaction backward
• reduce the forward reaction rate.

Important Note About Endothermic Reactions

An endothermic reaction is a reaction that:

• absorbs heat
• takes energy from its surroundings.

However, the question asks about reaction rate, not energy absorption.

Factors affecting reaction rate apply regardless of whether the reaction is endothermic or exothermic.

Key Takeaway Points

Reaction rate depends on collisions

More particle collisions = faster reactions.

Increasing reactant concentration increases reaction rate

More particles in the same space → more collisions.

Lower temperature slows reactions

Particles move slower → fewer successful collisions.

Surface area affects reactions

More surface area = faster reaction
Less surface area = slower reaction.

TEAS Exam Memory Trick

Remember the four main factors affecting reaction rate:

CATS

C – Concentration
A – Area (surface area)
T – Temperature
S – Speed up with catalysts

Increasing any of these (except reducing area) usually increases reaction rate.