I think the answer is skin. Skin contains sweat glands which secrete a fluid waste called sweat or perspiration; nonetheless, its primary functions are temperature control and release of pheromone. Its role as a part of the excretory is therefore minimal. Additionally, sweating also maintains the levels of salt in the body.
D. The Krebs cycle
Here’s the Explanation for it:
The Cellular respiration refers to the biochemical pathway in which the cells release energy from chemical bonds of food molecules. The energy that is provided is very important to the creation of life itself.
The aerobic phases of the cellular respiration in eukaryote is seen within mitochondria (organelles). This is know as the Krebs Cycle and the electron transport chain which are aerobic phases.
Hope this helps!
<span>It began with selective breeding in the ancient times where a population with desirable traits were bred with other population to achieve a desired set of traits. It then continued with the advance in the discovery of bacteria (Escherichia coli) and antibiotics. Then Watson and Crick discovered the structure of DNA. The latest advance being that of gene sequencing and gene editing tools. </span>