A-level Biology OCR [New Spec] - Homeostasis: The Negative Feedback Response | A-level Biology | OCR, AQA, Edexcel

Homeostasis: The Negative Feedback Response in a Snap! Unlock the full A-level Biology course at http://bit.ly/2KuD0Z1 created by Adam Tildesley, Biology expert at SnapRevise and graduate of Cambridge University. The key points covered of this video include: 1. What is Negative Feedback 2. Mechanism of Negative Feedback 3. Co-ordinated Response 4. Positive Feedback Introduction to Negative Feedback Organisms need to maintain their internal environments - this is called homeostasis. This is achieved through having an optimum point for things like pH, water potential, and temperature. If there is a change away from this set optimum point, the internal environment needs to return back to the optimum point. An increase in temperature would result in control mechanisms lowering the tempreature. The mechanism that reverses the change in internal conditions is called negative feedback. Negative feedback is the body’s mechanism for reversing a change so that it returns back to the optimum. Mechanism of Negative Feedback The optimum point for the body is monitored by receptors. When the receptors detect any change away from the optimum they send signals to a co-ordinator. The co-ordinator then decides which response is appropriate and carries it out by sending signals to effectors. Effectors bring about the change that returns the internal conditions to their optimum. Co-ordinated Response Co-ordinators receive signals from many different sources - to act effectively these need to be analysed before making a response. For instance, there are temperature receptors in both the skin and in the hypothalamus. When we exercise we sweat, which reduces the temperature of the skin. If the co-ordinator only used information from the skin it would act to increase the temperature of the body when we exercise. Instead the co-ordinator uses information from the hypothalamus as well to make an appropriate response. Positive Feedback Positive feedback is the opposite of negative feedback - any change away from a set point is increased. This is a mechanism that brings about a large, unstable change in the body. It is usually harmful, but there are some examples of where it can be of use - for instance action potentials in neurones. The influx of sodium ions causes depolarisation that results in more voltage-gated sodium channels opening. This results in even more depolarisation. Summary Negative feedback is the body’s mechanism for reversing a change so that it returns back to the optimum Changes away from the optimum are detected by receptors, which send signals to a co-ordinator The co-ordinator sends signals to the appropriate effector which brings about an effect This reverses the change and returns the internal conditions back to the optimum The co-ordinator takes information from many receptors to bring about an informed response Positive feedback is where a change away from a set point is amplified to bring about a large response