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Cell Basics Vocabulary: axon, ATP, cell, cell membrane, cell theory, cell wall, chloroplast, circulation, contractile vacuole, coordination, cyton, digestion, dendrite, DNA, dynamic equilibrium, endoplasmic reticulum, enzymes, eukaryotic, excretion, food vacuole, homeostasis, hormones, immunity, life processes, locomotion, mitochondrion, movement, nucleus, neurotransmitter, organ system, organs, organelles, progesterone, prokaryotic, receptor molecules, reproduction, respiration, ribosome, synthesis, system, target cell, target organs, terminal branches, tissue Living VS. Non-Living Complex organisms, such as humans, require many systems for their life processes. Less complex living things may lack the complex systems of more complex organisms, but they still carry on the basic life activities. While non-living things may carry on some of these life processes, they do not carry on all of them, or these activities do not interact in a manner allowing the non-living thing to reproduce itself. Living things carry out almost all the life processes or activities. These life processes include digestion, respiration, circulation, excretion, locomotion, immunity, coordination, and synthesis. Non-living things are incapable of carrying out at least one or more of the life processes. The sum of the energy used in all the life processes represents the metabolism of the organism. Homeostasis The ability to carry on the life processes allow a living thing to maintain dynamic equilibrium or homeostasiswith their surroundings. Homeostasis is a state of balance or steady state between a living thing and its environment. Homeostasis in an organism is constantly threatened. Failure to respond effectively to a failure of homeostasis can result in disease or death. The components of living things in humans and other organisms, from organ systems to cell organelles, interact to maintain a balanced internal environment. This balanced internal environment is called dynamic equilibrium or homeostasis. To successfully accomplish this, organisms possess many control mechanisms that detect internal changes and correct them to restore the internal balance of the organism. If an organism fails to maintain homeostasis, this may result in disease or death. Non-living things possess few control mechanisms to maintain homeostasis. Organizational Levels Important levels of organization for structure and function of living things include cells, tissues, organs, organ systems, and whole organisms. The organs and systems of the body help to provide all the cells with their basic needs to carry on the life functions. The cells of the body are of different kinds and are grouped in ways that help their function. All living things are composed of one or more cells, each capable of carrying out the life functions. The organelles present in single-celled organisms often act in the same manner as the tissues and systems found in many celled organisms. Singlecelled organisms perform all of the life processes needed to maintain homeostasis, by using specialized cell organelles. Living things have different levels of organization. The simplest level of organization is that of the cell. A group of cells with a similar function is called a tissue. Groups of tissues working together to perform a common function are called organs. An example of this would include the nervous, muscle, and other tissues which make up the heart. Groups of organs working together to perform a common function are referred to as a system or organ system. The blood vessels, blood, and the heart are organs which work together to form the circulatory system. Many different systems function together to allow a complex organism to function. Cell Structure Cells have particular structures or organelles that perform specific jobs. These structures perform the life activities within the cell. Just as body systems are coordinated and work together in complex organisms, the cells making up those systems must also be coordinated and organized in a cooperative manner so they can function efficiently together. Inside the cell a variety of cell organelles, formed from many different molecules, carry out the transport of materials, energy capture and release, protein building, waste disposal, and information storage. Each cell is covered by a membrane that performs a number of important functions for the cell as well. Cell Theory All organisms contain one or more cells which are capable of carrying on the life activities needed by the organism. This idea is often referred to as the cell theory. Parts of the Cell Theory The cell is the unit of structure in all living things. The cell is the unit of function in all living things. All cells come from preexisting cells. A few exceptions to this theory exist. Viruses lack typical cellular structure. There also is some question as to how the the first cell arose. In general, the cell theory holds true for most living things, however. Cell Types There are two distinct types of cells. Prokaryotic cells lack a nucleus and other organelles. Two domains of organisms have this type of cell - Archaebacteria and Eubacteria, the simplist of all organisms. They still perform life functions but all activities must be accomplished in the cytoplasm. Eukarotic cells are found in organisms from the domain Eukarya, which includes all protists (Ameoba and Paramecium are examples), Fungi (yeast and mushrooms are examples), Plants (mosses, ferns, gymnosperm pines and angiosperm flowering plants are examples), and Animals (humans are examples). Cell Organelles Cells have particular structures that perform specific jobs. These cell structures are called organelles and perform the actual work of the cell. These organelles are formed from many different molecules. Some functions carried out by organelles include the transport of materials, energy capture and release, protein building, waste disposal, and information storage. Single celled organisms also have organelles similar to those in more advanced organisms to complete their life processes. Many enzymes are needed for the chemical reactions involved in cellular life processes to occur. A Typical Animal Cell Some Cell Organelles Cell Organelle Function control center of the cell nucleus mitochondrion contains DNA which directs the synthesis of proteins by the cell carries on the process of cell respiration converting glucose to ATP energy the cell can use endoplasmic reticulum transport channels within the cell ribosome found on the endoplasmic reticulum and free within the cell responsible for the synthesis of proteins for the cell cell membrane selectively regulates the materials moving to and from the cell food vacuole stores and digests food contractile vacuole found in many single celled aquatic organisms pumps out wastes and excess water from the cell chloroplast cell wall found in plant cells and algae carries on the process of photosynthesis surrounds and supports plant cells Life Functions Humans and many other organisms require multiple systems for digestion, respiration, reproduction, circulation, excretion, movement, coordination, and immunity. The systems collectively perform the life processes. Once nutrients enter a cell, the cell will use those raw materials for energy or as building blocks in the synthesis of compounds necessary for life. The energy we initially obtain must must be changed into a form cells can use. A type of protein called an enzyme allows for these changes to occur within the cell. Humans and other complex organisms require many different organ systems to carry on the activities required for life. These life activities or processes include digestion, respiration, reproduction, circulation, excretion, movement, coordination, and immunity. Life Processes Digestion breakdown of food to simpler molecules which can enter the cells Circulation the movement of materials within an organism or its cells Movement (locomotion) change in position by a living thing Excretion removal of cellular waste products by an organism (wastes may include carbon dioxide, water, salt, and urea and are released during exhalation, perspiration, and urine formation.) Respiration process which converts the energy in food to ATP(the form of energy which can be used by the cells) Reproduction the making of more organisms of one's own kind -not needed by an individual living thing but is needed by its species Immunity the ability of an organism to resist disease causing organisms (pathogens) and foreign invaders Coordination the control of the various activities of an organism (mostly involves the nervous system and endocrine glands in complex animals) Synthesis the production of more complex substances by combining two or more simpler substances It is important to realize that cell organelles are involved in many of these life processes, as well as the organ systems of complex organisms. Cellular Communication Neurotransmitters and hormones allow communication between nerve cells and other body cells as well. If nerve or hormone signals are changed, this disrupts communication between cells and will adversely effect organism homeostasis. Additionally, the DNA molecule contains the instructions that direct the cell’s behavior through the synthesis of proteins. Cell Membrane Receptors Cell Membrane Receptors Many cell membranes havereceptor moleculeson their surface. These receptor sites play an important role in allowing cells and organs to communicate with one another. Hormonal Regulation Hormones provide a primary way for cells to communicate with each other. A hormone is a chemical messenger with a specific shape that travels through the bloodstream influencing another target cell or target organ. Upon reaching the cell the hormone is targeted for, the hormone often activates a gene within a cell to make another necessary compound. One example of this is provided by the pituitary gland. This gland at the base of the brain makes a hormone called LH (luteinizing hormone). This hormone travels through the bloodstream and stimulates the ovary to produce yellow tissue that produces the hormone progesterone, which maintains the thickness of the uterus lining. The graphic below illustrates how this kind of hormonal regulation can work in a plant cell. Animal cell hormonal regulation involves a similar mechanism. A Hormonal Feedback Mechanism The diagram at the right illustrates how a hormone can bind to receptors on a cell membrane and trigger that cell to produce a needed compound. Nervous Regulation Nerve cells or neurons also allow cells to communicate with each other. Neuron communications are one way organism can detect and respond to stimuli at both the cellular and organism level. This detection and response to stimuli helps to maintain homeostasis in the cell or organism. Neurons may stimulate other nerve cells or muscle cells, thus causing the later to contract and produce movement. Structure and Function of a (Neuron) Nerve Cell Structures and their Functions 1. dendrite -- neuron branch which detects stimuli (changes in the environment) 2. cyton -- cell body of the neuron where normal metabolic activities occur 3. axon -- longest dendrite covered by a myelin sheath which provides electrical insulation -- carries nerve message or impulse to the terminal branches 4. terminal branches -- release nerve chemicals calledneurotransmitters which stimulate adjacent dendrites on the next neuron or a muscle cell Any change in nerve or hormone signals will change the communication between cells and organs in an organism and thus may cause problems for organism’s stability and ability to maintain homeostasis. Cell Membrane The cell membrane or plasma membrane performs a number of important functions for the cell. These functions include the separation of the cell from its outside environment, controlling which molecules enter and leave the cell, and recognition of chemical signals. The cell membrane consists of two layers of phospholipids with proteins embedded within these layers. The surface of the cell contains molecules which recognize other molecules which may attach to or enter the cell. Cell Membrane Structure Membrane Processes The processes of diffusion and active transport are important in the movement of materials in and out of cells. Diffusion Diffusion or passive transport is the movement of materials from a region of higher to a region of lower substance concentration. The diagram at the right shows the movement of molecules from higher concentration on side A to a lower concentration on side B. Active Transport In active transport, molecules move from a region of lower concentration to a region of higher concentration. As this process does not naturally occur, the cell has to use energy in the form of ATP to make active transport occur. Cell Chemistry Many organic and inorganic substances dissolved in cells allow necessary chemical reactions to take place in order to maintain life. Large organic food molecules such as proteins and starches must initially be broken down through the life process of digestion in order to enter cells. Organic Molecules and Digestive End Products Organic Molecule Digestive End Product(s) carbohydrates simple sugars (glucose) proteins amino acids lipids (fats) fatty acids and glycerol Asexual Reproduction Species are maintained in existence through the life spans process of reproduction. Asexual reproduction produces genetically identical offspring from a single parent cell. The process of mitosis is associated with asexual reproduction and the growth and repair of cells in sexually reproducing organisms. Reproduction and development are necessary for the continuation of any species. Asexual reproduction is a method of reproduction with all the genetic information coming from one parent. Some Methods of Asexual Reproduction 1. binary fission -- involves an equal division of both the organism cytoplasm and nucleus to form two identical organisms -- the diagram of the protist at the right is example of this 2. budding -- involves one parent dividing its nucleus (genetic material) equally, but cytoplasm unequally -- the diagram of a yeast at the right is an example of this 3. sporulation (spore formation) -- is reproduction involving specialized single cells coming from one parent -- the diagram of mold spores being formed at the right is an example of this Asexual reproduction is sometimes called cloning. Cloning is the production of identical genetic copies. All forms of asexual reproduction are variations of the cell division process of mitosis. Mitosis is associated with asexual reproduction, as well as growth and repair in sexually reproducing organisms. Mitosis Mitosis is the method used for cell division and reproduction in cells not involved in sexual reproduction. This process starts with one replication (copying of the chromosome material) and one division of the chromosome material. This results in the chromosome numbers in the two cells produced being the same as in the parent cell. This process is represented in the graphic which follows. An Overview of the Process of Mitosis The Cell Cycle The cell cycle is the lifespan of a cell. It is divided into three parts: Interphase, Mitosis, and Cytokinesis. Interphase is divided into three parts. G1 - or the first growth phase, is the stage in a cells life when normal cell functioning is occurring. A cell will remain in this stage unless it receives a signal to reproduce. Cells can receive signals from neighboring cells during development of a multi-cellular organism, or it may receive a signal for repair of neighboring cells or a cell may receive a signal to divide if the cell becomes too large for intracellular transport to occur effectively. When a cell receives the signal to divide, it moves into the second stage of interphase called synthesis. Synthesis is the longest part of the cell cycle because this is the stage when a cells DNA replicates. DNA replication involves separating the double helix, complimentary nucleotides finding their match (Adenine joins with Thymine, Cytosine joins with Guanine) and two identical strands of DNA forming. Once this is accomplished, and proteins have confirmed its success, a cell moves into the third phase of interphase called G2, or the second growth phase. Here, organelles replicate and the cell grows in anticipation of dividing into two smaller cells. If everything goes according to plan, a cell is ready to move into the mitotic stage of the cell cycle. Mitosis is the division of the nucleus stage. It is a choreographed mechanism to efficiently and accurately divide the two identical copies of DNA into the newly forming cells and it is done the same way in every living cell. The four parts of this cycle are prophase, metaphase, anaphase and telophase (PMAT). In prophase, the DNA which is in long, stringy chromatin form condenses and coils up into chromosomes. The identical pieces of DNA are joined together with a centromere. During this phase, the nuclear membrane in eukaryotes begins to disintegrate. In metaphase, the pairedchromatids line up (chromosomes) single file down the equator of the cell. In anaphase, the sister chromatids separate and identical chromatids each move to opposite poles.Telophase is when the chromosomes begin to uncoil again back into chromatin and new nuclear membranes begin to form in eukaryotes. The final stage of the cell cycle begins in telophase when the cells cytoplasm begins to divide. In animal cells, the cell membrane pinches in during this stage called cytokinesis. In plant cells, a cell plate forms between the newly forming nuclei as the cell wall can't pinch in. This continues until two new cells are formed with identical DNA. 2 Key Results of Mitosis 1. The same chromosome number is retained from generation to generation. 2. Each daughter cell receives an exact copy of the chromosomes of the parent cell. (clones) Asexual Heredity Every organism requires a set of coded instructions for specifying its traits. For offspring to resemble their parents, there must be a reliable way to transfer information from one generation to the next. Heredity is the passage of these instructions from one generation to another. The DNA molecule provides the mechanism for transferring these instructions. In asexually reproducing organisms, all the genes come from a single parent. As asexually produced offspring are produced by the cell division process of mitosis, all offspring are normally genetically identical to the parent. CREDIT: http://www.regentsprep.org/regents/biology/2011%20Web%20Pages/Cells%20Cell%20Division.htm