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 guanine

D thymine

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 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

DNA is made up of repeating units called:

A fatty acids

B amino acids

C nucleotides

D monosaccharides

Explanation

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

Question 4 of 10

TEKS 11A-12F Easy Word Diagram

The diagram shows a carbon cycle. Which process RELEASES carbon dioxide into the atmosphere?

A Photosynthesis

B Cellular respiration

C Nitrogen fixation

D Condensation

Explanation

📌 Processes that RELEASE CO₂:
• Cellular respiration (animals AND plants)
• Combustion (burning fossil fuels)
• Decomposition

Process that ABSORBS CO₂:
• Photosynthesis

Question 5 of 10

TEKS 10A-10C Easy Word

Homeostasis is:

A maintaining stable internal conditions

B the classification of organisms

C the study of ecosystems

D the process of cell division

Explanation

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

Question 6 of 10

TEKS 11A-12F Easy Word

Which of the following is a biotic factor?

A Temperature

B Sunlight

C Bacteria

D Water

Explanation

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

Question 7 of 10

TEKS 11A-12F Easy Word Diagram

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

A Insect population increases and snake population decreases

B All organisms die

C Nothing changes

D Snake population increases

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 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 50%

C 100%

D 25%

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 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 Proofreads the new DNA

D Adds new nucleotides

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 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 100 kcal

C 5,000 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.

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