Births, deaths, immigration and emigration

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   One frog pond during one year (model data)

   measure	frogs
   frogs at the start of the year	200
   births in the year	30
   deaths in the year	10

2. 1.

   Ari reads the model data for one frog pond. What is the per-capita birth rate for the year?

   • 30 births per frog: the total number of births
   • 6.67 births per frog: 200 ÷ 30
   • 0.15 births per frog: 30 ÷ 200
   • 0.05 births per frog: 10 ÷ 200, the deaths row

3. Turtles in one year with no moves in or out (model data)

   measure	value
   turtles at the start of the year	500
   births per turtle	0.20
   deaths per turtle	0.08

4. 2.

   Esme reads the model data for 500 turtles. No turtles move in or out. What is the change in the number of turtles in one year?

   • +60: (0.20 − 0.08) × 500
   • +140: (0.20 + 0.08) × 500, the two rates added
   • +0.12: 0.20 − 0.08, a rate and not a count
   • +100: 0.20 × 500, the births alone and no losses

5. Birds in one wood, starting with 120 birds (model data)

   year	births	deaths	immigrants	emigrants
   1	15	6	4	3
   2	12	9	2	8
   3	18	7	5	4

6. 3.

   Jun reads the table. Immigrants moved in; emigrants moved out. How many birds are in the wood at the end of year 3?

   • 143 birds: 120 plus births minus deaths, no moves
   • 165 birds: 120 plus the births of the 3 years
   • 132 birds: 120 plus the year 3 change alone
   • 139 birds: 120 + 10 − 3 + 12

7. Snails in one marsh for one year (model data)

   count	snails
   at the start of the year	200
   births	30
   deaths	12
   immigrants (moved in)	5
   emigrants (moved out)	?
   at the end of the year	205

8. 4.

   Kira reads the table of snails in one marsh for a year. How many emigrants moved out?

   • 18 snails: 200 + 30 + 5 − 12 − 205
   • 5 snails: 205 − 200, the net change
   • 23 snails: 30 + 5 − 12, the gain of the year
   • 13 snails: 200 + 30 − 12 − 205, no arrivals

9. Turtles on one island (model data)

   year	births	deaths	immigrants	emigrants
   1	30	20	6	4
   2	40	25	5	30
   3	15	22	20	3
   4	28	28	2	2

10. 5.

    Luz reads the table of turtles on one island. Immigrants moved in; emigrants moved out. In which year did the number of turtles fall?

    • Year 2: a fall of 10, as 30 moved out
    • Year 3: deaths, 22, are more than births, 15
    • Year 1: deaths, 20, and emigrants, 4, make 24 lost, so it fell
    • Year 4: births and deaths are both 28, so it fell

11. Two plots of seedlings after one night of frost (model data)

    plot	seedlings before	seedlings after	percent that survive
    sparse plot	50	30	60
    crowded plot	400	240	60

12. 6.

    Milo reads the model data after one night of frost. Which type of factor is the frost?

    • Density-independent: both plots kept 60%, sparse or crowded
    • Density-independent: the frost did not change the seedlings in either plot
    • Neither type: a frost is not a factor that changes a population
    • Density-dependent: the crowded plot had 160 fewer seedlings, the sparse plot 20 fewer

13. Plants per square meter and the percent that survive the year (model data)

    plants per square meter	percent that survive
    10	90
    40	70
    80	45

14. 7.

    Noah reads the model data. Which statement fits the table?

    • A density-dependent effect: a smaller share survives as crowding rises
    • A density-independent effect: the share that survives is the same in each plot
    • A density-dependent effect: a larger share survives as crowding rises
    • A density-independent effect: weather reached the three plots alike

15. Four factors that change a plant population (model data)

    factor	what happens
    flood	water covers a whole meadow
    competition for space	crowded plants share limited ground
    frost	one cold night reaches a whole meadow
    drought	a dry season reaches a whole meadow

16. 8.

    Pia reads the factor cards. Which choice sorts two of the factors correctly?

    • Competition for space: density-independent. Frost: density-dependent, as crowds hold heat
    • Flood: density-independent. Competition for space: density-dependent
    • Frost: density-dependent. Drought: density-independent, as the ground is crowded
    • Drought: density-dependent. Competition for space: density-dependent, as both are crowded

17. Mark and recapture on one pond (model data)

    step	frogs
    marked and released in the first catch	45
    caught in the second catch	60
    marked frogs in the second catch	18

18. 9.

    Tala reads the model data for one pond. Estimate the number of frogs in the pond.

    • 150 frogs: (45 × 60) ÷ 18
    • 60 frogs: the number caught the second time
    • 87 frogs: 45 + 60 − 18, the counts added
    • 13.5 frogs: (45 × 18) ÷ 60, flipped

19. Two ways a second catch of 90 turtles can go, with 60 turtles marked (model data)

    marked turtles	marked turtles in the second catch	estimate
    mix freely	15	360
    avoid the traps	10	540

20. 10.

    Zee reads the table. Marked turtles learn to avoid the traps. How does that change the estimate?

    • It is too low: fewer marked turtles caught means a smaller population
    • It is too high: fewer marked turtles are recaptured, so 540 not 360
    • It cannot be found: the estimate needs each marked turtle recaptured
    • It stays the same: 60 turtles were marked and 90 were caught either way