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The TX PACT 738 exam has 125 questions and runs 3 hours.
These 10 free TX PACT 738 questions are organized by exam domain, so you can see how each part of the TX PACT: Life Science: Grades 7-12 (738) blueprint is tested. Reveal the answer and explanation under each question.
Before weighing dried leaf samples, a technician checks a balance with a 20.00-g reference mass. Five readings range from 20.39 to 20.41 g. No leaf samples have been weighed. The most appropriate next step is to:
Correct answer: D - Recalibrate the balance, then verify its readings against the reference mass.
During a biology investigation, a corrosive solution splashes into a student's eye. A functioning eyewash is beside the bench, and a partner is present. What should the student do first?
Correct answer: C - Start flushing at the eyewash while the partner calls for assistance.
Isolated mitochondria receive a continuous supply of fuel, oxygen, ADP, and inorganic phosphate. Adding a compound increases oxygen consumption but decreases both the proton gradient across the inner membrane and ATP production. The compound most likely:
Correct answer: B - Lets protons return to the matrix without passing through ATP synthase.
An enzyme reaches the same maximum reaction rate with or without compound P, but a much higher substrate concentration is needed to approach that rate when P is present. Enzyme concentration, temperature, and pH are unchanged; P concentration is held constant in assays containing P. These findings are most consistent with P acting as:
Correct answer: C - A competitive inhibitor that competes with substrate for the enzyme's active site.
Two tissues from the same person have identical DNA sequences for a gene and produce the same initial RNA transcript. One tissue produces mature mRNA containing exons 1, 2, and 4; the other produces mature mRNA containing exons 1, 3, and 4. Which process generates these different mature transcripts?
Correct answer: C - Different exons are joined during alternative RNA splicing.
A woman passes a mitochondrial DNA variant to both her son and her daughter. Neither of their partners carries the variant. Through which family branch could this variant normally pass to the next generation?
Correct answer: D - Her daughter's children, but not her son's children.
Two people have difficulty taking up enough oxygen. Person X has inflamed, narrowed bronchioles but intact alveolar walls. Person Y has extensive destruction of alveolar walls. What is the most direct functional consequence of each finding?
Correct answer: A - X: increased resistance to airflow; Y: reduced gas-exchange surface area
A fern sporophyte produces spores, which grow into gametophytes that produce sperm and eggs. A student labels both spore production and gamete production as meiosis. What correction does the life-cycle diagram need?
Correct answer: A - Change gamete production to mitosis; retain meiosis for spore production.
A field study follows low-, medium-, and high-density populations of the same species. A freeze kills 30% of the individuals at each density. A disease outbreak in otherwise comparable populations kills 8%, 24%, and 48%, respectively. How should the two mortality patterns be classified?
Correct answer: B - Only the outbreak is density dependent because mortality per individual increases with population density.
Ecologists measure a woodland's annual carbon budget. Plants fix 1,400 g C/m²/year, plant respiration releases 800 g C/m²/year, and respiration by animals and decomposers releases another 450 g C/m²/year. Which entry correctly reports net primary productivity and its meaning?
Correct answer: D - 600 g C/m²/year: net carbon production by plants after subtracting their own respiration.
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