Radius
Definition: A line segment from the center of a circle to any point on the circle.
Example: A circular garden with a radius of 5 meters measures 5 meters from its center to its edge.
Learn five precise words for measuring circles and tracing how energy moves through ecosystems.
I can use circle and ecosystem vocabulary to calculate measurements and explain feeding relationships, so I can communicate mathematical and scientific ideas clearly.
✓ I know I am successful when I can define all five terms.
✓ I know I am successful when I can use radius or diameter to calculate a circle’s circumference and identify consumers in a food web.
✓ I know I am successful when I score at least 3 of 4 on the exit check.
Say: “In math, a few precise measurements describe an entire circle. In science, a food web helps us describe many connected feeding relationships. Today’s words help us explain both kinds of connections accurately.”
Definition: A line segment from the center of a circle to any point on the circle.
Example: A circular garden with a radius of 5 meters measures 5 meters from its center to its edge.
Definition: A line segment that passes through a circle’s center and connects two points on the circle; it is twice the radius.
Example: A circle with a radius of 6 centimeters has a diameter of 12 centimeters.
Definition: The distance around a circle.
Example: A wheel with a diameter of 10 centimeters has a circumference of about 31.4 centimeters because C = πd.
Definition: An organism that gets energy by eating other organisms.
Example: A rabbit is a consumer because it gets energy by eating plants.
Definition: A model of connected food chains that shows many feeding relationships in an ecosystem.
Example: A pond food web may connect algae, insects, fish, frogs, and herons.
A circular pond-viewing platform has a radius of 4 meters. Nearby, students observe a pond ecosystem.
Worked example: The diameter is 2 × 4 = 8 meters. The circumference is C = 2πr ≈ 2 × 3.14 × 4 = 25.12 meters. In the food web, the snail, tadpole, bluegill, and heron are consumers because they eat other organisms.
Choose each answer, check your work, and retry anything you miss.
A circular habitat enclosure has a diameter of 18 meters. Inside it, grass is eaten by grasshoppers and rabbits; grasshoppers are eaten by frogs; frogs and rabbits are eaten by hawks.
Your task: Find the enclosure’s radius and approximate circumference using π ≈ 3.14. Then name two consumers and explain why the relationships form a food web instead of a single food chain.
Sentence frame: “The radius is ___ meters, and the circumference is about ___ meters. ___ and ___ are consumers. This is a food web because ___.”
Your answers stay only on this page.
Practice: 1 center to circle; 2 14 cm; 3 3.14 × 12; 4 caterpillar; 5 several connected feeding relationships.
Application: Radius = 9 m. Circumference = 3.14 × 18 = 56.52 m. Possible consumers include grasshoppers, rabbits, frogs, and hawks. It is a food web because multiple feeding paths are connected.
Exit: 1 12 cm; 2 31.4 m; 3 cricket, frog, and snake; 4 several connected feeding paths.