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Body Lab 3-5 / Week 08 / Thursday
4/6
Week 08 · Eyes and Seeing

Thursday

Rods and cones
// How light becomes a picture
⏱ about 15 min

Thursday: Rods and Cones

At dusk, Rocket tries to sort his colored markers. "Is this one blue or green?" he asks. "They all look gray!"

Raven flips on the lamp. Now the colors pop. "What do you notice?" she asks.

Nova hovers between the markers. "Your eyes have two kinds of light catchers," she says. "One kind needs more light."

The retina's light catchers

The retina is a light-sensitive layer at the very back of the eye.

It has special cells called rods and cones.

They turn light into signals that travel to the brain.

Each eye has about 120 million rods and 7 million cones!

Light catcherHow many in each eyeWhat it does
RodsAbout 120 millionSee black, white and gray. Work in dim light.
ConesAbout 7 millionSense color. Need more light.

Rods cannot tell colors apart. But they are super sensitive, so they help in dim light.

Cones sense color. They work best in normal or bright light.

There are three kinds of cones. One senses red, one green and one blue.

Together, the cones let you see millions of colors.

ROD OR CONE?
  • Read the question.
  • Tap your answer.
You spot a bright red apple in sunlight. Which cells sense the red?
You see the shape of a chair in a dim room. Which cells help most?
Why did Rocket's markers look gray at dusk?
StatementTrue or false?
Each eye has more rods than cones.?
Rods sense color.?
There are three kinds of cones.?
Rods and cones are in the retina.?
WHY THIS EXERCISEThe retina holds many rods for dim light and fewer cones for color.
About how many million cones are in each eye?
WHY THIS EXERCISEEach eye has about 7 million cones and about 120 million rods.
Which does each eye have more of, rods or cones?
WHY THIS EXERCISEEach eye has about 120 million rods and only about 7 million cones.
Cells that sense color are called ____.
Cells that help most in dim light are called ____.
One kind of cone senses red, one senses green and one senses ____.
Try it
Pick five crayons of different colors. Do not look at them yet.
Ask a grown-up to make the room dim, but not totally dark.
Try to sort the crayons by color. Then turn the lights on and check.
Safety first
Sit still while the room is dim, so you do not trip.
A grown-up controls the lights.

Colorful work! Tomorrow we follow the signals from the retina all the way to the brain.

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