Sampling Ecosystems with Quadrats and Transects · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Counting nature without counting everything

Science · Scientific Inquiry · ages 15-16
Name ______________________   Date ____________

  1. Why are quadrat positions chosen at random?

    • Random spots are easier to reach
    • Only random spots represent the whole site fairly
    • Animals prefer random frames

  2. What do you do with a quadrat?

    • Place it at random spots and count what is inside
    • Walk it along a straight line
    • Use it to catch running animals

  3. You must track how plants change from a sunny edge into deep shade. Which tool fits?

    • A single quadrat by the gate
    • Scattered random quadrats
    • A transect sampled along the gradient

  4. Mean cover is 6 plants per 1 square metre quadrat in a 100 square metre field. Estimate the total plants.

    Answer: ______________

  5. Five quadrat counts are 4, 6, 5, 3 and 7. What is the mean count per quadrat?

    Answer: ______________

  6. A student counts only beside the pond where flowers crowd. What follows for the estimate?

    • It overshoots, since rich spots bias the mean up
    • It undershoots, since ponds repel plants
    • It stays exact, since flowers are flowers

  7. A report claims 600 plants but never states per what area, and its spots were hand picked. Name the two faults.

    • Wrong species and wrong season
    • Missing units and biased non random spots
    • Too many quadrats and too much maths

  8. Two estimates of one field use 4 quadrats and 40 quadrats. Why trust the second more?

    • Bigger frames attract more plants
    • The field grows extra daisies meanwhile
    • More frames shrink the wobble in the mean
LightMySky · lightmysky.comW1-mt_jI8rAOYdmb-s1

Answer key

For grown-ups. Fold this page away before handing over the rest.

Counting nature without counting everything W1-mt_jI8rAOYdmb-s1

  1. Only random spots represent the whole site fairly · Chosen spots drift toward rich or easy ground and bias the mean.
  2. Place it at random spots and count what is inside · Random frames plus counts give the mean to scale up.
  3. A transect sampled along the gradient · A line into the shade shows change with distance.
  4. 600 · Multiply 6 by 100 divided by 1 to get 600 plants.
  5. 5 · The total is 25 across 5 quadrats, so the mean is 5.
  6. It overshoots, since rich spots bias the mean up · Non random spots speak for the rich patch, not the site.
  7. Missing units and biased non random spots · An estimate needs units to mean anything and random spots to be fair.
  8. More frames shrink the wobble in the mean · Larger samples average out lucky and unlucky drops.
Worksheet · LightMySky