Cellulose, a complex carbohydrate, or polysaccharide, consists of glucose units forming long chains and is chiefly found in the cell walls of plants, providing structural support. Unlike starch, cellulose is not digestible by humans due to the absence of the enzyme required to break down its beta linkage. All animals, including humans, lack this enzyme, meaning that while ruminants and some insects can digest cellulose thanks to symbiotic microorganisms in their guts, humans and other non-ruminants cannot. Therefore, the statement "All animals can digest cellulose due to the presence of specific enzymes" is not true. Cellulose is significant in the human diet as dietary fiber, aiding in digestion by promoting bowel movement but is not broken down into glucose for energy.

Amino acids, the building blocks of proteins, are not highly reactive under physiological conditions. Their reactivity is moderated because they exist primarily in their zwitterion form at physiological pH, balancing charges within the molecule. However, the reactivity of amino acids can greatly vary depending on their side chains. For instance, amino acids with side chains that contain functional groups such as amine (e.g., lysine) or thiol (e.g., cysteine) tend to be more reactive, particularly in facilitating enzymatic reactions or forming disulfide bonds that are crucial for protein structure. Their moderate reactivity is ideal for the precise and controlled reactions required for biological processes, enabling the formation of peptides and proteins through peptide bonds without unwanted side reactions.

The yarn emoji is a representation of a ball of yarn, often used to denote knitting, crochet, crafts, or warmth. It's a part of the Unicode Standard, which means it can be used across different platforms (iOS, Android, Windows) and social media. The appearance might vary slightly depending on the platform due to design customizations. It can usually be found in the "activities" or "objects" section of your emoji keyboard. Its addition to the emoji library came with the aim of representing hobbies and activities more comprehensively, catering to a wider range of users' interests and promoting expressions related to handcraft and creativity. If you're having trouble finding it, make sure your device's software is up-to-date, as newer emojis are often included in software updates.