Consequently, virologists are not biologists, strictly speaking. Similarly, some biologists study the early molecular evolution that gave rise to life; since the events that preceded life are not biological events, these scientists are also excluded from biology in the strict sense of the term.
And once we know something is alive, how do we find meaningful levels of organization in its structure? And, finally, when faced with the remarkable diversity of life, how do we organize the different kinds of organisms so that we can better understand them? As new organisms are discovered every day, biologists continue to seek answers to these and other questions.
All living organisms whether they are bacteria, archaea or eukaryote share several key characteristics, properties or functions: order, sensitivity or response to the environment, reproduction, growth and development, regulation including homeostasis , energy processing, and evolution with adaptation.
When viewed together, these seven characteristics serve to define life. Organisms are highly organized, coordinated structures that consist of one or more cells. Even very simple, single-celled organisms are remarkably complex: inside each cell, atoms make up molecules; these in turn make up cell organelles and other cellular parts.
Tissues, in turn, collaborate to create organs body structures with a distinct function. Organs work together to form organ systems. Organisms respond to diverse stimuli. Even tiny bacteria can move toward or away from chemicals a process called chemotaxis or light phototaxis.
Movement toward a stimulus is considered a positive response, while movement away from a stimulus is considered a negative response. Video: Watch this video to see how plants respond to a stimulus—from opening to light, to wrapping a tendril around a branch, to capturing prey. Single-celled organisms reproduce by first duplicating their DNA, and then dividing it equally as the cell prepares to divide to form two new cells.
Multicellular organisms often produce specialized reproductive germline cells that will form new individuals. These genes ensure that the offspring will belong to the same species and will have similar characteristics, such as size and shape.
Organisms grow and develop following specific instructions coded for by their genes. Even the smallest organisms are complex and require multiple regulatory mechanisms to coordinate internal functions, respond to stimuli, and cope with environmental stresses. Two examples of internal functions regulated in an organism are nutrient transport and blood flow.
Organs groups of tissues working together perform specific functions, such as carrying oxygen throughout the body, removing wastes, delivering nutrients to every cell, and cooling the body. A special type of internal regulation is homeostasis.
In order to function properly, cells need to have appropriate conditions such as proper temperature, pH, and appropriate concentration of diverse chemicals. These conditions may, however, change from one moment to the next. For example, an organism needs to regulate body temperature through a process known as thermoregulation. Structures that aid in this type of insulation include fur, feathers, blubber, and fat. In hot climates, organisms have methods such as perspiration in humans or panting in dogs that help them to shed excess body heat.
All organisms use a source of energy for their metabolic activities. Evolution and adaptation rely on the cell's ability to copy its DNA replication and give that copy to the next generation reproduction. However, this copying is sometimes carried out with mistakes mutations. Chemicals and other mutagens anything that can cause a mutation can also cause mistakes that will potentially be passed down. These mutations are often though of as bad, but it depends on which piece of information was affected and how.
Sometimes these mistakes give advantages to the organism- like antibiotic resistance- that can allow the organism to adapt and overcome obstacles. We will discuss the mutations and how their changes play out further in later chapters.
Cell theory states that the cell is the fundamental unit of life. However, cells vary significantly in size, shape, structure, and function. At the simplest level of construction, all cells possess a few fundamental components. These include cytoplasm a gel-like substance composed of water and dissolved chemicals needed for growth , which is contained within a plasma membrane also called a cell membrane or cytoplasmic membrane ; within the cytoplasm are one or more chromosomes, which contain the genetic blueprints of the cell; and ribosomes, parts used for the production of proteins.
The cytoplasm is the entire region of a cell surrounded by the plasma membrane. It is made up of nutrients, enzymes and other chemicals suspended in the gel-like cytosol , and the cytoskeleton. Even though the cytoplasm consists of 70 to 80 percent water, it has a semi-solid consistency, which comes from the proteins within it.
However, proteins are not the only organic molecules found in the cytoplasm. Glucose and other simple sugars, polysaccharides, amino acids, nucleic acids, fatty acids, and derivatives of glycerol are found there, too.
Membrane bound proton pumps present on the lysosome maintain this condition. Similarly, a large membrane surface area is required by mitochondria to efficiently generate ATP from electron gradients across its lipid bilayer. This is achieved through the structural composition of this particular organelle. Importantly, individual organelles may be transported throughout the cell, and this essentially localizes entire subcellular processes to regions where they are required.
This has been observed in neurons, which have extremely long axonal processes and require mitochondria to generate ATP at various locations along the axon. It would be inefficient to rely on the passive diffusion of ATP down the length of the axon.
Compartmentalization can also have important physiological implications. For example, polarized epithelial cells, which possess distinct apical and basolateral membranes, can, for instance produce a secretory surface for various glands. Similarly, neuronal cells develop effective networks due to the production of dendrites and axonal processes from opposite ends of the cell body.
Moreover, in the case of embryonic stem cells, cell polarization can result in distinct fates of the daughter cells. With each organelle facilitating its own function, they may be considered as subcellular compartments in their own right. However, without a regulated supply of components to the compartment, the processes and mechanisms that produce their overall function will be impeded. With many proteins and molecular components participating in multiple subcellular processes, and therefore required throughout multiple subcellular compartments, effective transport of the protein and molecular components, either by passive diffusion or directed recruitment, is essential for the overall function of the cell.
Home About Us Resources. The fluid inside the mitochondria is called the matrix, which is filled with proteins and mitochondrial DNA. Chloroplasts are another organelle that contain a double membrane and retain their own DNA.
Unlike mitochondria, however, the inner membrane of chloroplasts is not folded. They do, however have a third, internal membrane called the thylakoid membrane, which is folded. In addition, unlike mitochondria, chloroplasts are only present in plant cells. They are responsible for converting sunlight into energy through a process called photosynthesis. Other organelles like lysosomes are responsible for digesting and recycling toxic substances and waste. They are embedded with proteins called enzymes, which break down macromolecules, including amino acids, carbohydrates, and phospholipids.
Lysosomes are produced by a larger organelle called the Golgi complex, which manufactures other cellular machinery as well. Whenever a cell dies, it self-destructs using its own lysosomes. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.
Tyson Brown, National Geographic Society. National Geographic Society. For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher.
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