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Cells and Systems 6-8 / Week 10 / Thursday
4/6
Week 10 · Growing Up: Environment and Inheritance

Thursday

Reading a table of plant responses
// Two kinds of factors shape every living thing
⏱ about 20 min

Thursday: Reading a Table of Plant Responses

Raven has a new printed table. This one lists things a plant can sense, and what it does about each one.

"Direction of light, length of the day, moisture," Rocket reads. "Plants notice all that?"

"What do you notice about the last two rows?" Raven asks. "They are about seeds."

Rocket reads them twice. "Small seeds wait for light. Big seeds can sprout deep down. Because of stored food?"

Nova brightens. "You just used two kinds of factors in one sentence," she says. "Which was which?"

"Seed size is inherited," Rocket says. "Light and depth are the environment." Raven nods. "Now read the whole table."

A table from a college biology textbook

The free textbook Biology 2e has chapters on how plants sense their world and how seeds germinate.

This table gathers what those chapters say. Each row names a signal from the environment and the plant's response.

Read the signal column first. Then ask which factor is at work: the environment, inheritance, or both.

What the plant sensesResponseFactor at work
Direction of blue lightPhototropism: the stem bends toward the lightEnvironment
Day length through the yearPhotoperiodism: controls flowering and setting winter budsEnvironment
Moisture after heavy rainDormant seeds germinate and many seedlings emergeEnvironment
Light reaching a small seedSmall seeds use light as a cue to germinate near the surfaceBoth: small seed size is inherited
Stored food in a large seedLarge seeds can germinate deep underground and still reach the surfaceBoth: large seed size is inherited
USE THE TABLE
  • Read the question.
  • Tap your answer.
A plant uses day length to decide when to flower. What is that response called?
Why do small seeds usually need light before they germinate?
Seed size is set by the kind of plant. Which factor is that?

Why day length and not temperature

The textbook explains why plants track day length. Temperature and light intensity influence plant growth, but they vary from one year to the next.

Day length is a better indicator of the time of year. So plants use it to time flowering and winter buds.

That is an environmental factor plants have inherited the ability to read. Both kinds of factors work together.

Scientists give another example of both at once: different varieties of plant seeds growing at different rates in different conditions.

The response that lets a plant track the time of year is called ____.
After heavy rains, many new ____ emerge.
StatementTrue or false?
Day length is a more reliable sign of the season than temperature.?
Large seeds can germinate deeper underground than small seeds.?
Phototropism is a response to day length.?
Seed size is an environmental factor.?
WHY THIS EXERCISEEvery row shows a plant reading its environment with abilities it inherited.
A SMALL SEED NEAR THE SURFACE, IN ORDER
  • ?The seed germinates
  • ?Light reaches the small seed near the surface
  • ?Leaves begin photosynthesis
  • ?The seedling bends toward the light
  • ?Rain brings moisture to the soil
WHY THIS EXERCISESeveral environmental signals, in order, turn one seed into a growing plant.
Try it
Look at the seeds in your pantry with a grown-up: dried beans, lentils, rice. Line up one of each by size.
Which would you expect to sprout from deepest in the soil? Write your reasoning in your Windowsill Log.
Draw two seeds underground, one small near the surface and one large deeper down. Show which sprout reaches the light.

Excellent table reading. Tomorrow you check the dark jar in its new sunny spot and review the week.

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