1.The nucleus<span> is the most </span>important<span> organelle in the </span>cell<span>. It contains the genetic material, the DNA, which is responsible for controlling and directing all the activities of the </span>cell<span>. 2. </span>Themembrane<span> keeps the </span>digestive<span> materials from leaking out into the cytoplasm and destroying the </span>cell<span>. Discuss how </span>cells<span>, tissues, organs, and organ systems are related. 3. </span>Cells<span>, </span>Tissues<span> and </span>Organs<span>. As we mentioned before, </span>cells<span> are the building blocks of life. When we have a group of </span>similar cells<span> working together this is called a </span>tissue.<span> 4. </span>Single-celled organisms<span> are made of only </span>one cell<span>. Multi-cellular </span>organisms<span>, such as plants and animals, have a higher degree of specialization where the </span>cells<span> work together and function to create a living </span>organism<span>. 5.</span><span>Structurally, </span>plant<span> and </span>animal cells<span> are very similar because they are both eukaryotic </span>cells<span>. They both contain membrane-bound organelles such as the nucleus, mitochondria, endoplasmic reticulum, golgi apparatus, lysosomes, and peroxisomes.</span>