All living organisms were classified into three major domains viz: Eukarya, Archaea and Bacteria. Eukarya are referred to as EUKARYOTES while the other two domains are collectively referred to as PROKARYOTES.
The major basis of this classification is the presence or absence of a membrane bound NUCLEUS. Eukaryotes are organisms characterized by the possession of a membrane-bound nucleus that houses their genetic material (DNA) while prokaryotes lack a nucleus and hence, their genetic material is found naked in the cytoplasm. Although, prokaryotic cells lack other membrane-bound organnelles like Chloroplast, mitochondria etc. but nucleus is the basis of this classification:
EU meaning TRUE, KARYA meaning NUCLEUS, hence Eukarya means organisms will true nucleus.
Answer: Leaves in a cactus are modified into spines to reduce loss of water from leaves by transpiration. Then the plant makes from the process of photosynthesis which is performed by the stem.
