<span>Levels of OrganizationIn unicellular (single-celled) organisms,
the single cell performs all life functions. It functions independently.
However, multicellular (many celled) organisms have various levels of
organization within them. Individual cells may perform specific
functions and also work together for the good of the entire organism.
The cells become dependent on one another.Multicellular organisms have
the following 5 levels of organization ranging from simplest to most
complex:<span><span>LEVEL 1 - Cells<span><span>Are the basic unit of structure and function in living things. </span>May serve a specific function within the organismExamples- blood cells, nerve cells, bone cells, etc.</span></span><span>LEVEL 2 - Tissues<span>Made up of cells that are similar in structure and function and which work together to perform a specific activity Examples - blood, nervous, bone, etc. Humans have 4 basic tissues: connective, epithelial, muscle, and nerve.</span></span><span>LEVEL 3 - OrgansMade up of tissues that work together to perform a specific activityExamples - heart, brain, skin, etc.</span><span>LEVEL4 - Organ Systems <span>Groups of two or more tissues that work together to perform a specific function for the organism. Examples - circulatory system, nervous system, skeletal system, etc. The
Human body has 11 organ systems - circulatory, digestive, endocrine,
excretory (urinary), immune(lymphatic), integumentary, muscular,
nervous, reproductive, respiratory, and skeletal.</span></span><span> LEVEL 5 - Organisms <span> Entire
living things that can carry out all basic life processes. Meaning they
can take in materials, release energy from food, release wastes, grow,
respond to the environment, and reproduce. <span>Usually made up of organ systems, but an organism may be made up of only one cell such as bacteria or protist. </span>Examples - bacteria, amoeba, mushroom, sunflower, human</span></span></span></span>
The reasons are: - the blood is very low on nutrition - the leech is not feeding itself regularly
The leech slows it metabolism a lot, so it can survive on very low nutrition. The blood is very low on nutrition, and it is the leech's food source, so the evolution made it preserve energy.
The leach doesn't have the opportunity to feed itself on regular basis, so it takes maximum advantage of any opportunity and consumes as much blood as possible so that it can survive long term when it will not have food at disposal.
DNA is important because it is a molecule that encodes the genetic instructions used in the development and functioning of every living thing.
DNA replication is important because cells multiply through replication, and if DNA could not replicate then cell replication would not be possible. This is important for growth and healing.
Without DNA and DNA replication almost all living organisms would not exist.
