Midterm Practice Exam

True or false: in an illustrative bottle-cap test, the detergent-water trials averaged 18 fewer drops than the tap-water trials; the honest conclusion is that this evidence supports the hypothesis that detergent lowers the drop count, without proving it.

True or false.

• True
• False

In an illustrative iodine test (constructed results), a student adds a drop of iodine to cooked rice, an apple slice, dissolved table sugar, and a cup of distilled water. Which sample is the negative control?

Select one.

• Distilled water, known to contain no starch
• Cooked rice, because it turns blue-black
• The apple slice, because it changes only a little
• The sugar solution, because sugar is a carbohydrate

A chloroplast turns light into stored sugar in two linked stages. Which option lists the stages in the order they occur and pairs each with its site?

Select one.

• Calvin cycle in the stroma, then light-dependent reactions in the thylakoid membranes
• Light-dependent reactions in the thylakoid membranes, then the Calvin cycle in the stroma
• Light-dependent reactions in the stroma, then the Calvin cycle in the thylakoid membranes
• Calvin cycle in the thylakoid membranes, then light-dependent reactions in the stroma

Sickle cell disease traces back to a single amino-acid change in the beta chain of hemoglobin. Which change is it?

Select one.

• Glutamic acid replaces valine
• Thymine replaces uracil
• One amino acid is deleted outright
• Valine replaces glutamic acid

True or false: once a raw egg white turns solid and white in a hot pan, its proteins have lost their amino-acid sequence because the cooking snapped the peptide bonds.

True or false.

• True
• False

In an illustrative test (constructed data, not real), a piece of raw liver dropped into hydrogen peroxide raised foam to heights of 6, 7, and 11 cm in three trials. What is the average foam height?

Select one.

• 24 cm
• 11 cm
• 7 cm
• 8 cm

In an illustrative test, a student dips identical strips of pH paper into several household liquids and writes down the color each strip shows. Which is the dependent variable?

Select one.

• The liquid each strip is dipped into
• The color each strip shows after dipping
• The size and brand of strip used each time
• The distilled-water cup kept as a reference

Which statements about how enzymes work are correct, as this course teaches them? Select all that apply.

Select every option that applies.

• One enzyme molecule can speed up the same reaction again and again.
• Once every active site is busy, more substrate no longer raises the rate.
• An enzyme is consumed in each reaction that it speeds up.
• Raising the temperature always speeds an enzyme, with no upper limit.
• In the induced fit model, the active site shifts its shape slightly to grip the substrate.

During a mountain hike, which of these is an example of stored potential energy rather than energy of motion?

Select one.

• A boulder resting at the top of a cliff
• A pebble tumbling down a steep slope
• A hawk flapping its wings in the wind
• A stream rushing over smooth rocks

Which of these is a molecule, two or more atoms bonded together, rather than a lone atom?

Select one.

• C, a single carbon atom by itself
• CO₂, one carbon bonded to two oxygens
• He, a single helium atom by itself
• Na, a single sodium atom by itself

Heart muscle cells need a great deal of ATP, and their mitochondria are packed with deep cristae. How do these folds help?

Select one.

• They hold spare glucose molecules until the cell needs them
• They keep oxygen from reaching the matrix of the mitochondrion
• They give more membrane area for the electron transport chain
• They let each mitochondrion split into two separate cells

Three classes of macromolecules are polymers made by linking many similar monomers. Which class is the exception?

Select one.

• Nucleic acids
• Proteins
• Lipids
• Carbohydrates

A potato stores starch as fuel, and plants build their tough structural fiber from cellulose. What explains why these two polysaccharides do such different jobs?

Select one.

• Both are chains of glucose, but the units are linked differently
• Starch is made of glucose, but cellulose is made of amino acids
• Cellulose is a fat that only resembles a carbohydrate in form
• Starch is a two-sugar unit, while cellulose is a long polymer

The two-layer sheet that forms a cell's outer boundary is built mostly of phospholipids. Which class of macromolecules includes phospholipids?

Select one.

• Proteins
• Nucleic acids
• Carbohydrates
• Lipids

In an illustrative test, a plastic jar lid held an average of 38 drops of plain water and 21 drops of water mixed with dish detergent. Which conclusion fits the chemistry of water and an honest verb?

Select one.

• The results prove detergent breaks every hydrogen bond in the water
• The detergent water is the control group, so it should hold the most
• Detergent makes each water molecule heavier, so drops spill sooner
• The evidence supports that detergent weakens water's surface tension

Each cycle of the sodium-potassium pump uses 1 ATP, sends 3 Na⁺ out, and brings 2 K⁺ in. If a nerve cell's pump completes 5 cycles, which ions has it moved?

Select one.

• 10 Na⁺ out and 15 K⁺ in
• 3 Na⁺ out and 2 K⁺ in
• 5 Na⁺ out and 5 K⁺ in
• 15 Na⁺ out and 10 K⁺ in

A glucose molecule is broken down completely inside a liver cell. Which sequence gives the stages in order, each paired with where it runs?

Select one.

• Pyruvate oxidation (cytoplasm) → glycolysis (mitochondrion) → citric acid cycle (matrix) → electron transport chain (inner membrane)
• Glycolysis (cytoplasm) → citric acid cycle (matrix) → pyruvate oxidation (mitochondrion) → electron transport chain (outer membrane)
• Glycolysis (matrix) → pyruvate oxidation (cytoplasm) → electron transport chain (inner membrane) → citric acid cycle (matrix)
• Glycolysis (cytoplasm) → pyruvate oxidation (mitochondrion) → citric acid cycle (matrix) → electron transport chain (inner membrane)

A cell links two glucose molecules to form a disaccharide. Which reaction makes the link, and what happens to water?

Select one.

• Hydrolysis, which releases a water molecule as the new bond forms
• Hydrolysis, which uses up a water molecule to build the new bond
• Dehydration synthesis, which adds a water molecule into the new bond
• Dehydration synthesis, which removes a water molecule at the new bond

These approximate pH values come from the body and the kitchen: stomach acid at about pH 1 to 2, white vinegar at about pH 3, blood at about pH 7.4, and baking-soda solution at about pH 9. Which one is the most acidic?

Select one.

• Stomach acid, because its pH number is the lowest
• Baking-soda solution, because its pH number is the highest
• Blood, because a buffer keeps it close to neutral
• White vinegar, because it tastes the sourest of the four

In an illustrative test (constructed data, not real), a student times how long an ice cube takes to melt in plain water and then in salt water, three trials each. What is the dependent variable?

Select one.

• Plain water versus salt water in the cup
• The same cup size and water volume in every trial
• The time each ice cube takes to melt completely
• The plain-water cups that act as the baseline

In an illustrative leaf disk test (constructed data, not real), a cup of basil disks under a dim lamp had 0, 2, 4, 7, and 9 disks floating out of 10 at 0, 4, 8, 12, and 16 minutes. What is the average number floating across the five readings?

Select one.

• 5.5 disks, from 22 ÷ 4
• 9 disks, the final reading
• 4.4 disks, from 22 ÷ 5
• 22 disks, the sum of the readings

In a population of beetles living on dark tree bark, birds catch the dark beetles less often than the pale ones. Which statements fit evolution by natural selection as this course teaches it? Select all that apply.

Select every option that applies.

• Dark beetles tend to leave more offspring, so the share of dark beetles can rise over generations.
• A pale beetle turns dark during its own lifetime because it needs to hide.
• Evolution here means a change in the heritable traits of the beetle population over generations.
• Calling evolution a theory means it is only an untested hunch.
• Beetles and birds use nearly the same genetic code, evidence that they share common ancestors.

In an illustrative yeast test (constructed data, not real), bottles of warm water and yeast with 0, 5, 10, and 20 grams of sugar inflated balloons to circumferences of 0, 10, 16, and 19 cm. Which statements do these results support? Select all that apply.

Select every option that applies.

• Doubling the sugar from 10 to 20 grams doubles the balloon circumference.
• The bottle with no sugar serves as the control group.
• The balloons fill with carbon dioxide released by alcoholic fermentation.
• The balloons fill with oxygen gas that the yeast give off.
• The gains of 10, 6, and 3 cm shrink as sugar is added, a pattern of diminishing returns.

A cell builds a short peptide by joining 6 amino acids end to end through dehydration synthesis. How many water molecules does it remove?

Select one.

• 6 water molecules, one for each amino acid
• 5 water molecules, one for each new peptide bond
• 1 water molecule for the whole peptide
• 7 water molecules, one per amino acid plus one extra

In an illustrative bottle-cap test, plain tap water averaged 40 drops and water mixed with dish detergent averaged 22 drops, a gap of 18 drops. Measured against the tap-water control, about what percent fewer drops did the detergent water hold?

Select one.

• About 82%, because 18 ÷ 22 ≈ 0.82
• About 55%, because 22 ÷ 40 = 0.55
• About 18%, because 40 − 22 = 18
• About 45%, because 18 ÷ 40 = 0.45