Transpiration occurs through the stomata. The stomata are primarily meant for absorption of CO₂ but the water vapors also escape through stomata and cause transpiration. Thus transpiration is called as a necessary evil because it is an inevitable process. The loss of water can lead to wilting, serious desiccation, and shortage of water. Transpiration helps in the ascent of the sap and the pulling of the water from the roots to the tips. Thus is it considered to be a necessary evil.

Primary Data : Primary Data is that data which is collected by the investigator or researcher himself. It is an original form of data collection.
1.Primary data is always original as it is col-lected by the investigator.
2.Suitability of the primary data is positive because it is systematically collected.
3.Primary data is expensive and time consum-ing.
4.Extra precautions are not required.
5.Primary data is in the shape of raw material.
6.Possibility of personal prejudice exists.
7.Investigating agency collects the data.
8.Requires long time for collection.
9.More reliable and suitable to the enquiry because the investigator himself collects it.
10.Requires elaborate organisation.
Secondary Data : Secondary Data refers to that data which is collected through other sources.
1.Secondary data lacks originality. The investi-gator makes use of the data collected by other agencies.
2.Secondary data may or may not suit the objects of enquiry.
3.Secondary data are relatively cheaper.
4. It is used with great care and caution.
5.Secondary data is usually in the shape of readymade products.
6.Possibility of lesser degree of personal prejudice.
7.Some other investigating agency collects it for its own use.
8.Requires less time for collection.
9.Less reliable and suitable as someone else has done that job of collection which may not serve the purpose.
10.Needs comparatively less funds.

In business, the Production Possibility Curve (PPC) is applied to evaluate the performance of a manufacturing system when two commodities are manufactured together. The management utilizes this diagram to plan the perfect proportion of goods to produce to reduce the wastage and cost while maximizing profits.

The two main characteristics of PPC are:

1. Slopes downwards to the right: PPC slopes downwards from left to right. It is because in a situation of fuller utilisation of the given resources, production of both the goods cannot be increased simultaneously. More of commodity A can be produced only with less production of commodity B.
2. Concave to the point of origin: It is because to produce each additional unit of commodity A, more and more units of commodity B will have to be sacrificed. Opportunity cost of producing every additional unit of commodity A tends to increase in terms of the loss of production of commodity B. Production will act upon the law of increasing marginal opportunity cost.