Write a difference between net primary productivity and gross productivity

Companion cells are the thin-walled elongated cells which are the characteristic feature of phloem tissue in angiosperms. In gymnosperms and pteridophytes, phloem lacks companion cells.In gymnosperms, the endosperm is haploid (n) which is formed before fertilisation while in angiosperms, the endosperm is triploid (3n) which is formed after fertilisation. In angiosperms, one of the two male gametes which is haploid(n) fuses with the central cell in the ovule which is diploid(2n), to form primary endosperm nucleus which is triploid (3n) and forms triploid endosperm.In gymnosperms, ovule or megasporangium is present on the megasporophylls which aggregate together to form strobilus or cones. The ovule is naked and after fertilisation, the naked ovule develops into the seed and the seed coat is formed by the ovular integuments. While, in angiosperms, ovule is present inside the ovary present at the base of the pistil or carpel. Angiosperms do not have cones like gymnosperms, instead, they have flowers and the ovule is protected by the carpel which after fertilisation forms the seed. The similarity between angiosperms and gymnosperms is that both have leaves, stem and roots.So, the correct answer is D.