Hint: Life span and life expectancy are related to the number of years an organism lives. While lifespan is the maximum number of years an organism or an individual can live, life expectancy is an average of the number of years an individual is expected to live.
Complete answer: Life Span: An individual has a definite beginning and an end. Life span is defined as the period between life and death of an individual. Some organisms live for several thousand years like bristlecone pines whereas for some the life span is a day as in case of mayfly. The lifespan is mainly determined by the hereditary. The genetic code determines the lifespan of an organism beyond which the species does not exist even under favourable conditions. The environmental factors also determine the lifespan of an individual. For some individuals, the growth is unlimited and is irreversible unless they meet with any sort of accident.
The lifespan of an individual is dependent on disease, food, metabolism, habitat etc.
Life Expectancy- It is a statistical measure which describes the average time an individual is expected to live. It is based on factors like the year of its birth, present age, gender etc. The life expectancy increases with age as the mortality rate is greater in childhood.
The life expectancy varies with the region. In some areas people show greater life expectancy than in others. The life expectancy also differs based on the economic status of an individual. Rich has greater life expectancy than poor. The life expectancy varies with gender. Females have greater life expectancy than males.
Note: The unicellular organisms do not have a lifespan as they do not die. The average lifespan of a human is 100 years. The age of the plant can be calculated by counting the annual rings. The life span of an elephant is 60-90 years.