Biology — Semester B Practice

Question 1 of 10

TEKS 6A-6H Medium Word Diagram

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

A 25%

B 50%

C 100%

D 75%

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 2 of 10

TEKS 6A-6H Medium Word Diagram

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

A Replication

B Mutation

C Translation

D Transcription

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 3 of 10

TEKS 6A-6H Easy Word

In DNA, adenine (A) always pairs with:

A guanine

B thymine

C cytosine

D uracil

Explanation

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

Question 4 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 5,000 kcal

B 100 kcal

C 1,000 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 5 of 10

TEKS 11A-12F Easy Word

Which of the following is a biotic factor?

A Water

B Temperature

C Sunlight

D Bacteria

Explanation

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

Question 6 of 10

TEKS 11A-12F Easy Word Diagram

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

A All organisms die

B Insect population increases and snake population decreases

C Snake population increases

D Nothing changes

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.

Question 7 of 10

TEKS 6A-6H Easy Word

DNA is made up of repeating units called:

A monosaccharides

B nucleotides

C amino acids

D fatty acids

Explanation

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

Question 8 of 10

TEKS 9A-9D Easy Word

Which biomolecule is the primary source of quick energy?

A Carbohydrates

B Nucleic acids

C Lipids

D Proteins

Explanation

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

Question 9 of 10

TEKS 6A-6H Medium Word Diagram

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

A Adds new nucleotides

B Unwinds and separates the DNA strands

C Proofreads the new DNA

D Joins DNA fragments

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 10 of 10

TEKS 11A-12F Easy Word

In a food chain, which organism is the primary consumer?

A Eagle

B Fox

C Rabbit

D Grass

Explanation

📌 Primary consumer = herbivore = eats producers (plants).
Producers → Primary consumers → Secondary consumers → Tertiary consumers

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