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?

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

3. Two lakes of ducks during one year (model data)

   lake	ducks at the start	births
   A	400	60
   B	100	20

4. 2.

   Bo reads the table. Which lake has the higher per-capita birth rate?

   • Lake A: it had more births, 60 against 20 for lake B
   • Lake A: it started with more ducks, 400 against 100
   • Lake A: 0.15 births per duck, against 0.20 for lake B
   • Lake B: 0.20 births per duck, against 0.15 for lake A

5. 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

6. 3.

   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?

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

7. 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

8. 4.

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

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

9. 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

10. 5.

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

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

11. 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

12. 6.

    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 4: births and deaths are both 28, so it fell
    • Year 3: deaths, 22, are more than births, 15
    • Year 1: deaths, 20, and emigrants, 4, make 24 lost, so it fell

13. 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

14. 7.

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

    • 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
    • Density-independent: both plots kept 60%, sparse or crowded
    • Density-independent: the frost did not change the seedlings in either plot

15. 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

16. 8.

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

    • A density-dependent effect: a larger share survives as crowding rises
    • 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-independent effect: weather reached the three plots alike

17. 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

18. 9.

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

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

19. 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

20. 10.

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

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