The correct answer to this question is option 1 - cellulose.

Green plants are capable of synthesizing cellulose, a complex carbohydrate, through the process of photosynthesis. Cellulose is a structural component of plant cell walls, providing rigidity and support to the plant. Animals, on the other hand, lack the necessary enzymes to synthesize cellulose and therefore cannot produce it themselves.

Option 2 - fats, and option 3 - proteins, are incorrect. Both fats and proteins can be synthesized by both plants and animals. Fats are important for energy storage and insulation, while proteins have various functions in organisms including enzyme activity, cell structure, and transportation of molecules.

Option 4 - cellulose and proteins, is also incorrect. As mentioned earlier, plants can synthesize cellulose, but proteins are synthesized by both plants and animals. Proteins play a vital role in the growth, development, and maintenance of cells and tissues in both organisms.

Therefore, the correct answer is option 1 - cellulose.