David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.
How Are Living Organisms Organized?
You are a living organism, but so is every other animal and plant on Earth. An organism is a living system that can respond to stimuli, grow, reproduce, and maintain a consistent state (homeostasis). Or at least that's our current definition of a living organism; there is definitely room for debate. But we're pretty sure we know a living organism when we see it in most cases. Living organisms include animals, plants, fungi, and microorganisms.
But how are living organisms structured? What makes them up? Living organisms have lots of parts and those parts combine together to form a whole that works seemingly as one. It's an amazing system, especially in the case of plants and animals. Plants and animals are structured into cells, tissues, organs, and organ systems. Those organ systems together form the whole organism.
Cells are the basic unit of life - they are the smallest functional units of an organism and are microscopic objects which contain cytoplasm and a nucleus surrounded by a cell membrane. Microscopic organisms are often just a single cell: in that case that's the whole organism. But humans have trillions of cells.
Tissues are groups of cells of the same type or from the same place that accomplish a particular task. For example, humans have muscle tissue, connective tissue, nervous tissue and others.
Organs are part of an organism that's usually self-contained and has a specific purpose or function. For example, the human heart is an organ with the function of pumping blood around the body.
An organ system is a group of organs that collectively do a particular job or function. For example, the digestive system contains the stomach, esophagus, small intestine, large intestine, pancreas, liver, gallbladder, rectum, and anus. An organ can be part of multiple organ systems.
So that's how organisms are organized. But how those individual parts structured? And how are the functions of organisms achieved?
Structure and Function
Within each part of a living organism is its own structure. Each cell is structured into parts called organelles and include membranes, walls, nuclei, chloroplasts, mitochondria, and vacuoles. Each part of a cell has its own function or job. For example, the cell membrane controls what comes in and out of the cell. The nucleus is in charge of a cell and contains the DNA that will help it reproduce. The mitochondria break down food and turn it into energy. The vacuoles are storage areas, and the chloroplasts are found in plant cells where they store food for the plant. Everything has its function.
These cells work together in a tissue to perform a greater function. Then, tissues can work together to form an organ that performs an overall function, which then in turn works with other organs in the body to do things like digest food or respire. Living organisms contain parts that work together, from the smallest to the largest, in ways that achieve a variety of functions, which allows an organism to live and continue to reproduce.
An organism is a living system that can respond to stimuli, grow, reproduce, and maintain a consistent state, known as homeostasis. They include animals, plants, fungi, and microorganisms. Although some organisms only have one cell or a small number of cells, the large organisms are structured at several levels: cells, tissues, organs, and organ systems.
Cells are considered to be the basic units of life, but they also contain their own organization: parts that work together to achieve a goal. Those parts are called organelles and include membranes, walls, nuclei, chloroplasts, mitochondria, and vacuoles, depending on the exact type of cell. Those cells form tissues like muscle tissue and connective tissue. And those tissues together form organs, like hearts, livers, and kidneys. Organs work together to form an organ system, like the digestive system. And the organ systems work together to form a whole organism, like us.
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