Friday

Rocket is at the Windowsill before breakfast, staring at the jar that used to live in the cupboard.

"Green," he whispers. "The new leaves at the top are turning green. Two days in the light."

Raven checks the ruler. "What do you notice about the old pale parts of the stem?"

"Still pale. Still floppy. Only the new growth changed." Rocket frowns. "So the environment changed the trait, but not the past."

Nova hovers over the jar. "You have a claim and you have evidence," she says. "Can you put them together?"

"The same seeds grew differently because the light was different," Rocket says. "And when the light changed, the growth changed."

A scientific explanation has three parts. A claim says what you think is true. Evidence is the data you collected. Reasoning connects them.

Claim: light is an environmental factor that changes how bean sprouts grow.

Evidence: your table. The dark jar's sprouts were taller and pale. The light jar's sprouts were greener and sturdier. The dry jars did not sprout.

Reasoning: the seeds were the same kind, so the genetic factor was the same. Only the environment differed, so the environment caused the difference.

Scientists list more examples of evidence. Drought decreases plant growth. Fertilizer increases it. Fish grow larger in large ponds than in small ponds.

Those are environmental: water, food and space. Genetic examples include large breeds of cattle and different species of grass.

The same two factors shape people. A trait like height is set by both the instructions you inherit and the conditions you grow in.

Next week you turn to the other half of life: how plants and animals make more of themselves.

Strong explaining, scientist. Tomorrow is Nature Day: a family look at how the same kind of plant grows in different spots.