Natality (Birth Rate) and Mortality (Death Rate) Explained
Biology · Organisms and Populations · NEET
Natality is the birth rate of a population (new individuals added by reproduction), and mortality is the death rate (individuals lost by death) over a given time period. Both are measured per capita, meaning "per individual", not as a total count. Memory hook: Natality = New lives added, Mortality = Members removed.
Natality (birth) and immigration add individuals, raising density; mortality (death) and emigration remove individuals, lowering it. Natality and mortality are per-capita rates and are usually the most important factors.
Your doubts, answered
Is natality just another word for birth rate?
Yes. In NCERT, natality means the birth rate of a population, that is, the number of new individuals added to the initial density by reproduction during a given time. NEET has directly asked 'Natality refers to' with the answer 'Birth rate' (NEET 2018). So treat natality = birth rate and mortality = death rate.
Why do we say 'per capita' birth rate and death rate?
A single organism only has a birth or a death; a population has rates. 'Per capita' means 'per individual'. So we divide the number of births or deaths by the number of individuals in the population. NCERT: if 4 fruitflies out of 40 die in a week, death rate = 4/40 = 0.1 individuals per fruitfly per week, not just '4'.
Are natality and mortality attributes of an individual or a population?
They are attributes of a population, not of an individual. An individual can have a birth and a death, but only a population has birth rates and death rates. This is a favourite NEET point (NEET 2020 asked which is NOT a population attribute; species interaction was the odd one out because it is a community-level event).
How do I calculate birth rate from the NCERT lotus example?
Per-capita birth rate = number of new individuals added / initial population. NCERT: 20 lotus plants last year, 8 new plants added, so birth rate = 8/20 = 0.4 offspring per lotus per year. Use the initial number in the denominator, not the final number. (Full worked sums are on the birth-rate and death-rate numericals page.)
Do natality and mortality increase or decrease population density?
Natality increases population density (adds individuals), and mortality decreases it. Along with immigration (increase) and emigration (decrease), these four factors change density. Under normal conditions natality and mortality are the most important factors deciding whether a population grows or shrinks.
⚠️ The NEET trap ✗ Natality = the total number of births (a plain count like 8 births) ✓ Natality = the per-capita birth RATE (births divided by initial population, e.g. 8/20 = 0.4 per lotus per year) 🧠 NEET writes 'per snail per year' or 'per fruitfly per week' on purpose. If you forget to divide by the initial population, you pick the count and lose the mark. Always divide by the STARTING number.
Real NEET questions
2018
Natality refers to
A · Number of individuals leaving the habitat
B · Birth rate ✓
C · Death rate
D · Number of individuals entering a habitat
Solution: Natality is the number of births added to the initial density during a period, that is, the birth rate. Individuals leaving = emigration, individuals entering = immigration, and death rate = mortality. So natality = birth rate (B).
2020
Which of the following is not an attribute of a population?
A · Mortality
B · Species interaction ✓
C · Sex ratio
D · Natality
Solution: Population attributes include natality (birth rate), mortality (death rate), sex ratio, age distribution and density. Species interaction happens between two different species and is a community-level phenomenon, not a population attribute. Hence (B) is the odd one out.
Solved Organisms and Populations NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
What is the difference between natality and mortality in one line?
Natality is the birth rate (individuals added by reproduction) and mortality is the death rate (individuals lost by death) of a population over a given time.
Is natality a population attribute or an individual attribute?
It is a population attribute. Individuals have single births and deaths, but only populations have birth rates and death rates.
What does per capita mean in birth rate and death rate?
Per capita means 'per individual'. You divide the number of births or deaths by the population size, for example 8 births / 20 lotus = 0.4 per lotus per year.
Which four factors change population density?
Natality and immigration increase density; mortality and emigration decrease it. Natality and mortality are usually the most important.
Has NEET asked natality directly?
Yes. NEET 2018 asked 'Natality refers to' (answer: birth rate), and NEET 2020 asked which term is NOT a population attribute (answer: species interaction).
