Biology — Semester B Practice

Question 1 of 10

TEKS 6A-6H Easy Word

In DNA, adenine (A) always pairs with:

A cytosine

B uracil

C thymine

D guanine

Explanation

📌 Base pairing rules: A-T (2 hydrogen bonds), G-C (3 hydrogen bonds).
In RNA: A-U instead of A-T.

Question 2 of 10

TEKS 6A-6H Medium Word Diagram

The diagram shows the process of DNA replication. What does the enzyme helicase do?

A Joins DNA fragments

B Unwinds and separates the DNA strands

C Adds new nucleotides

D Proofreads the new DNA

Explanation

📌 Helicase UNWINDS and SEPARATES the two DNA strands by breaking hydrogen bonds between base pairs.
This creates the replication fork where new nucleotides can be added.
DNA polymerase then adds complementary nucleotides to each strand.

Question 3 of 10

TEKS 10A-10C Easy Word

Homeostasis is:

A the study of ecosystems

B the classification of organisms

C the process of cell division

D maintaining stable internal conditions

Explanation

📌 Homeostasis = maintaining stable internal conditions (body temp, blood sugar, pH, water balance) despite external changes.

Question 4 of 10

TEKS 6A-6H Easy Word

DNA is made up of repeating units called:

A amino acids

B nucleotides

C monosaccharides

D fatty acids

Explanation

📌 DNA is a polymer of nucleotides. Each nucleotide = phosphate group + deoxyribose sugar + nitrogenous base (A, T, G, C).

Question 5 of 10

TEKS 9A-9D Easy Word

Which biomolecule is the primary source of quick energy?

A Carbohydrates

B Proteins

C Nucleic acids

D Lipids

Explanation

📌 Carbohydrates = quick energy (glucose, starch).
Lipids = long-term energy storage. Proteins = building/repair. Nucleic acids = genetic info.

Question 6 of 10

TEKS 6A-6H Medium Word Diagram

The diagram shows the central dogma of molecular biology. What process occurs at step 2?

A Translation

B Mutation

C Transcription

D Replication

Explanation

📌 Central Dogma: DNA → mRNA → Protein
Step 1 = Transcription (DNA → mRNA, in nucleus)
Step 2 = Translation (mRNA → Protein, at ribosomes)

mRNA carries the genetic code from DNA to the ribosome where proteins are assembled.

Question 7 of 10

TEKS 11A-12F Easy Word

Which of the following is a biotic factor?

A Bacteria

B Water

C Temperature

D Sunlight

Explanation

📌 Biotic = living things (plants, animals, bacteria).
Abiotic = non-living (temperature, water, sunlight, soil).

Question 8 of 10

TEKS 6A-6H Medium Word Diagram

Based on the Punnett square below, what is the probability of the offspring being heterozygous?

A 75%

B 25%

C 50%

D 100%

Explanation

📌 From Bb × Bb cross:
BB = 1/4 (homozygous dominant)
Bb = 2/4 = 1/2 (heterozygous) ← THIS
bb = 1/4 (homozygous recessive)
Probability of heterozygous = 50%

Question 9 of 10

TEKS 11A-12F Medium Word Diagram

The energy pyramid below shows energy transfer between trophic levels. Approximately how much energy is available to secondary consumers if producers have 10,000 kcal?

A 1,000 kcal

B 5,000 kcal

C 100 kcal

D 10 kcal

Explanation

📌 The 10% Rule: Only ~10% of energy transfers to the next trophic level.
Producers: 10,000 → Primary: 1,000 → Secondary: 100 → Tertiary: 10
Secondary consumers get approximately 100 kcal.

Question 10 of 10

TEKS 11A-12F Easy Word Diagram

In the food web below, what would happen if all the frogs were removed?

A Snake population increases

B Insect population increases and snake population decreases

C Nothing changes

D All organisms die

Explanation

📌 If frogs are removed:
• Insects (grasshoppers) they ate would INCREASE (no predator)
• Snakes that ate frogs would DECREASE (less food)
• This demonstrates how removing one species affects the entire food web.

Explanation

Explanation

Explanation

Explanation

Explanation

Explanation

Explanation

Explanation

Explanation

Explanation

Want unlimited practice?