Bacteria have cell walls composed of peptidoglycans and plants have cell walls which contain cellulose and other complex carbohydrates. Yeast like plants have cells with large central vacuoles . All cells both eukaryotes and prokaryotes have plasma membranes that surround the cytoplasm . Mitochondria are double membrane bound structures found in eukaryotes which are the site of aerobic ATP synthesis. Note in Figure 3 the many mitochondria just inside the plasma membrane.
Protists are single cell eukaryotes found in aquatic environments.
Note that in this image a clear nucleoli in the center of the nucleus is seen. The nucleolus is the site of ribonucleic acid synthesis. RBC transport gases to and from tissues. Cells come in different shapes. Shapes reflex the function of the cells.