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Week 1 • Outline the need for communication systems within multicellular organisms, with reference to the need to respond to changes in the internal and external environment and to coordinate the activities of different organs. • State that cells need to communicate with each other by a process called cell signalling. • State that neuronal and hormonal systems are examples of cell signalling. © Pearson Education Ltd 2009 This document may have been altered from the original What environment do cells need? Right temperature Right amount of salts and glucose Right pH Right amount of water Right levels of gases enzymes No toxins or inhibitors Responses to changes in the environment • External environment – is the air, water or soil around an organism. • Any changes in the environment must be monitored and the organism must respond in order to reduce stress. • This response may be behavioural or physiological. Behavioural: Physiological: • The internal environment – refers to conditions inside the body. The environment influencing cells is the tissue fluid which surrounds them. • The internal environment may change due to the products of metabolism diffusing into the tissue fluid. E.g. CO2 is a waste product of respiration. If allowed to build up it changes the pH of the environment and therefore enzyme action. • Blood helps to maintain the internal environment by removing wastes or toxins, preventing them accumulating in the tissue fluid and allowing them to be excreted. Communication Systems • Multicellular organisms need to pass information between their different parts so they can coordinate the response to changes in the internal and external environment. • For example, if food is seen or smelt, saliva is produced. Covers the entire body Allows inter cellular communication A good communication system Can be short or long term Specific Rapid Cell signalling • This is the process by which information is passed from one cell to another. • One cell releases a chemical that is detected by another cell. The 2nd cell responds. • There are 2 main cell signalling systems: • Neuronal system, - a network of neurones which signal across synapses, bringing about rapid, short-term changes. • Hormonal system, where blood transports signals (hormones) which are recognized by specific target cells. Hormones usually act more slowly but have longer term effects. What is the standard pathway which enables cells to communicate with one another? Stimulus and response pathway Stimulus Receptor Communication system Effector Response Receptors and effectors • Receptors - monitor conditions inside the body. If a change is detected, the receptor is stimulated to communicate with the effector. • Communication systems – may be nervous or hormonal. They use cell signalling to transmit messages to the effector. • Effectors – are cells which respond to reverse the change.