What are the three types of age pyramids for the human population?

Age pyramids are also known as population pyramids that are used to visualise the age and gender of the organism. These pyramids give information about the different age groups in a particular population. The base of the pyramid represents the pre-reproductive age group, above that reproductive age group and to part represents the old age group. Three types of age pyramids are there: Expanding, stable, and declining. Expanding pyramid: In this, the pre-reproductive age group is larger than the reproductive and old age groups. This type of pyramid indicates that the population is growing. Stable pyramid: Here, both pre-reproductive and reproductive age groups are the same while the post-reproductive age group is fewer. Hence, this pyramid shows a more or less stable population. Declining pyramid: Here, the pre-reproductive age group is fewer than the reproductive and old age groups. Here, the birth rate is less. So, it shows declining due to the death of old age people.

State the definition of gross primary productivity.

Gross primary productivity refers to the amount of carbon fixed during the process called photosynthesis by all producers in an ecosystem. However, a large part of the harnessed energy is used up by the metabolic processes (respiration) by the producers. The amount of fixed carbon not used by plants is called net primary productivity, which is available to various consumers in the ecosystem.