Question

a) Distinguish between primary productivity and secondary productivity in an ecosystem.
b) Define a food web.

Answer 1

a) In an ecosystem, productivity is used to describe the rate of production of biomass for the living organisms. Commonly there are two types of productivity studied which is primary productivity and the other is secondary productivity.
b) A food web is an interconnecting diagram that represents in detail the overall food relationships between organisms in a particular environment. It can be described as a ‘who-eats-whom’ diagram. A food web defines the complex feeding relationships for a particular ecosystem.

Complete answer:
a) The rate of biomass generation is called productivity, i.e productivity of an ecosystem refers to the amount of organic matter accumulated in any unit time. The portion of fixed energy, a trophic level passes on to the next trophic level is called production.
In an ecosystem, productivity is of two kinds; primary productivity and secondary productivity. When green plants function as producers, fix solar energy, and accumulate it in organic forms as chemical energy. As this is the first and basic form of energy storage, the rate at which the energy accumulates in the green plants or producers is known as primary productivity. So the rate of production of organic energy in an autotrophic organism in an ecosystem is called primary productivity. This productivity can be classified further into two types; gross and net productivity.
Secondary productivity is the rate of energy storage at consumers' levels-herbivores, carnivores, and decomposers i.e The rates at which the heterotrophic organisms resynthesize the energy-yielding substances are called secondary productivity.
So, the primary productivity is the production of organic matter by the producers while secondary productivity is the production of the organic matter by the consumers. In primary production the energy collected from the direct sunlight and food is generated, on the other side, energy is obtained by the transfer of energy through the food chain. It is also observed that the rate of production in primary productivity is fast while the rate in secondary productivity is quite slow.

b) All life needs energy. Whether living organisms make energy themselves or get it from the food they hunt. Reproduction, growth, cell division, and metabolism are all processes that require energy.
The sun is the ultimate source of energy for life on Earth. Without it, nothing can be able to survive. Living organisms have evolved special ways to harness the energy of the sun and use it for their own well-being. They have also developed special relationships and interactions that allow energy to be transferred. Once the energy has been captured, it gets passed around through the various organisms in a particular area. This transfer of energy is called a food web.
In a food web or food pyramid, there are no levels. At the first or at the base level there are producers, The producers are the organisms who produce their own food and serve as the foundation for all food webs. Organisms such as green plants, grass, algae, and even some bacteria act as producers. They make their own energy by converting carbon dioxide with the help of sunlight.
Then at the next level of food chains, there are primary consumers, who hunt producers as their food and obtain energy from them. They are also called herbivores. examples of primary consumers are some insects, birds, horse deer, etc.
Secondary consumers belong to the next level. These animals are fed on primary consumers and get energy. They are also known as predators. Snakes, coyotes, wolves, lions, and spiders are a few known examples of secondary consumers.
After that, the tertiary consumers come to the chain. They are the top predators. Generally humans belong to this category.
The last level of the food web is decomposers. Generally, they are microbes, defuse the dead body of consumers, and help to compose in soil.

Note:
a) Productivity is the rate at which energy is added to the bodies of organisms in the form of biomass. Biomass is simply the amount of matter that's stored in the bodies of a group of organisms. In primary productivity, biomass is produced by the producers with the help of direct sunlight, and in secondary productivity, biomass is produced by the transfer of energy through the food chain.

b) The food web is a network of food chains in an ecosystem where all are interconnected to each other. Each organism is eaten by the other organism and then those organisms are eaten by several other organisms, these series of organisms where one is dependent for food on another is called the food web. The flow of energy is unidirectional as the energy can never be transferred back.