Population density and growth rate: Class 12 practice
Density = number of individuals ÷ area. Read the method, follow the three worked examples, then try the six questions.
What you should know first
- Percentages
The idea behind population density and growth rate
Density = number of individuals ÷ area. Over a period, growth = births + immigration − deaths − emigration. Per-capita birth rate = births ÷ starting population.
Step-by-step method
- Count changes during the period.
- New size = N + B + I − D − E.
- Rates are per individual (or per 1000).
Worked example 1 (Basic)
190 deer live in 3 km². Find the population density.
- 190 ÷ 3
- Answer: 63.33 per km²
Worked example 2 (Standard)
A pond has 710 frogs. In a year 46 are born, 23 die, 16 arrive and 4 leave. Find the new population.
- 710 + 46 + 16 − 23 − 4
- Answer: 745
Worked example 3 (Challenge)
A population of 230 has 38 births and 30 deaths in a year. Find the birth rate and death rate per individual.
- b = 38/230
- d = 30/230
- Answer: 0.165 and 0.13 per individual
Common mistakes and misconceptions
- Ignoring migration
- Dividing by the final population
Practice questions
- (Basic) 700 deer live in 6 km². Find the population density.
- (Basic) 690 deer live in 8 km². Find the population density.
- (Standard) A pond has 710 frogs. In a year 37 are born, 37 die, 0 arrive and 5 leave. Find the new population.
- (Standard) A pond has 900 frogs. In a year 24 are born, 38 die, 13 arrive and 2 leave. Find the new population.
- (Challenge) A population of 280 has 31 births and 27 deaths in a year. Find the birth rate and death rate per individual.
- (Challenge) A population of 840 has 34 births and 24 deaths in a year. Find the birth rate and death rate per individual.
Answer key with full working
- Q1: 700 ÷ 6 → Answer: 116.67 per km²
- Q2: 690 ÷ 8 → Answer: 86.25 per km²
- Q3: 710 + 37 + 0 − 37 − 5 → Answer: 705
- Q4: 900 + 24 + 13 − 38 − 2 → Answer: 897
- Q5: b = 31/280 → d = 27/280 → Answer: 0.111 and 0.096 per individual
- Q6: b = 34/840 → d = 24/840 → Answer: 0.04 and 0.029 per individual
Syllabus note
This skill is listed under "Organisms and Populations" for Class 12 in the NCERT/CBSE books. ICSE, IGCSE, IB and state boards may teach it in a different chapter or year.
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.
Related practice and notes
Frequently asked questions
Which chapter is population density and growth rate in?
"Organisms and Populations", Class 12 Biology (NCERT/CBSE). Other boards may place it differently.
How were the answers checked?
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.