Praxis Elem CKT Science common mistakes
Praxis Elem CKT Science · Understand the traps and how to avoid them.
On a day/night gas-exchange item, the candidate selects that a plant takes in oxygen and releases carbon dioxide only at night, and that it performs cellular respiration only in darkness.
They memorize photosynthesis and respiration as opposite day/night processes and overlook that plants respire continuously while photosynthesis occurs only in light.
What to do instead
Compare net gas exchange: in light photosynthesis usually exceeds respiration; in darkness only respiration occurs. Locate chloroplasts and mitochondria and state that both processes run in plants, with respiration continuous.
When shown a food web, the candidate says energy is recycled and that the top predator has the largest energy store.
They conflate matter cycling with energy flow and memorize the pyramid shape without the 10 percent transfer and heat loss.
What to do instead
Trace arrows as energy flow, not only who eats whom; identify producers, consumers, and decomposers; state that energy decreases at each level and is lost as heat, while matter is recycled.
For a simple dominance cross, the candidate calls the dominant phenotype the most common and assumes an affected child must have an affected parent.
The everyday meaning of dominant as stronger or more frequent overrides the genetic definition; autosomal recessive inheritance is overlooked.
What to do instead
Separate genotype from phenotype; dominant means masking, not prevalence. Use Punnett squares and pedigree reasoning: two carrier parents can have an affected child; dominant traits can be rare.
The candidate says a rock has less mass on the Moon or reports weight in kilograms, and treats a balance and a scale as measuring the same quantity.
Mass and weight are used interchangeably in daily language; gravity's role and unit distinctions are not applied.
What to do instead
Define mass as amount of matter in kilograms, unchanged by location; weight as gravitational force in newtons, changing with gravity. Match a balance to mass comparison and a scale to weight.
The candidate says a battery creates energy, a bulb uses up energy, or a stopped pendulum has no energy left.
Conservation is stated as a slogan but energy forms, transfers, and dissipation are not tracked.
What to do instead
Use an energy chain: source, transfer, transformation, output, dissipated heat. State that energy is conserved, not created or destroyed; a stopped object still has internal energy, and a battery stores chemical energy.
The candidate says a large tub of warm water has less heat than a small cup of boiling water because its temperature is lower, or expects temperature to rise throughout boiling.
Heat and temperature are treated as synonyms; latent heat and dependence on mass are ignored.
What to do instead
Distinguish temperature as average particle kinetic energy from heat as energy transferred due to temperature difference. Compare mass and temperature; during a phase change at constant pressure, added energy changes arrangement, not temperature.
The candidate explains summer as Earth being closer to the Sun and predicts the same season in both hemispheres.
The distance misconception and the tilt model compete; the hemisphere effect is not applied.
What to do instead
Use a lamp and tilted globe: season depends on angle and daylight, not distance. Earth's tilt points one hemisphere toward the Sun; the other has winter simultaneously.
The candidate says moon phases are caused by Earth's shadow and that a lunar eclipse occurs every month.
Phase geometry and eclipse alignment are merged; the Moon's orbital tilt is ignored.
What to do instead
Model the Moon as half lit, with phase set by viewing angle from Earth. An eclipse requires Sun-Earth-Moon alignment and a near-plane orbit; most months the shadow misses.
When asked to improve a student investigation, the candidate changes several variables at once and treats any result as proof of cause.
They focus on hands-on activity and a desired outcome rather than a fair test with one independent variable.
What to do instead
Identify independent, dependent, and controlled variables; design a comparison with one change, repeated trials, and appropriate measurement. Explain that correlation or a single trial does not establish cause.
For a student who says heavy objects always fall faster, the candidate responds by restating the correct definition instead of selecting an instructional move that elicits and tests the misconception.
Content knowledge is used to correct wording, but pedagogical knowledge of eliciting prior ideas and using evidence is not applied.
What to do instead
Choose probes and discrepant events: predict, observe equal-size objects of different mass, discuss air resistance, and revise the explanation. Target the misconception with evidence rather than repeating the law.