2. Describe how this phrase shows that the lynx and snowshoe hare (in part C) example is an example of negative feedback.

Transcription

1 Biological Feedback Loops and Homeostasis Name: Per: # Background: Today, you will learn about two forms of feedback that biological systems use to both maintain homeostasis and to amplify, or increase, the sending of a biological signal. As you watch the video clips that follow, pay specific attention to the loops of cause and effect that represent this important concept. PART 1: Ted Ed - Feedback Loops I. What is Feedback? A. Example: Plant Death - Positive Feedback 1. Diagram the feedback loop: 2. Explain the loop in words: B. Example: Lynx and Snowshoe Hares - Negative Feedback 1. Diagram the feedback loop: 2. Explain the loop in words: C. Each feedback loop is the product of the links in the loop 1. Describe how this phrase shows that the plant death example (in part B) is an example of positive feedback. 2. Describe how this phrase shows that the lynx and snowshoe hare (in part C) example is an example of negative feedback. PART 2: Bozeman Science - Positive and Negative Feedback Loops (first 8 min 15 sec only) I. Feedback Loops Overview A. Negative Feedback Loops: try to stay at/around B. Positive Feedback Loops: move away (aka ) from the target set point II. Homeostasis: A. Definition: III. Positive and Negative Loops: A. Life strategies and negative feedback loops 1. Thermoregulation life strategies: a) Ectotherms - organisms that b) Endotherm - organisms that 2. Negative Feedback Loops: a) What happens when a human s internal temperature INCREASES?

2 b) What happens with a human s internal temperature DECREASES? c) **Make the connection: Using the phrase from the first video: each feedback loop is the product of the links in the loop, how can you tell that the body s response to both increasing temperatures and decreasing temperatures are BOTH examples of negative feedback? 3. Positive Feedback Loops a) Example: Fruit Ripening (1) gas given off by ripe fruit (2) picked up by b) What is meant by amplification? PART 3: Interpret the Loops DIRECTIONS: In the human endocrine system, chemical messengers called hormones send signals throughout the body from one organ to another. Cells that receive the message sent by the hormone respond to the signal in a specific way. In the examples below, identify what the signal is (what message is being sent) and what the response of the cells receiving the signal. Diagram the feedback loop. Then, identify whether it is an example of a positive or negative feedback loop and explain your reasoning. The first is done for you as an example. Scenario During childbirth, a baby s head presses against the mother s cervix. This pressure causes the release of a hormone called oxytocin. The release of the hormone oxytocin causes contractions to occur, which causes more pressure and release of oxytocin. The release of more oxytocin causes more contractions, and the cycle continues until the baby is delivered. Blood sugar levels drop over a fasting period. The drop in blood sugar levels triggers the release of a hormone called glucagon. This hormone signals the body to release sugar that is being stored in liver and muscle cells into the blood so that blood sugar levels rise back to normal. The body works to maintain the concentration of water in the blood. If a human is dehydrated, the concentration of water in their blood decreases. When the pituitary gland senses that water levels have decreased, it releases a hormone called ADH. ADH signals the kidneys to retain (hold on to / not release) water through urine. As a result, the kidney holds on to more water so that water can be returned to the blood and not excreted (given off as waste). Signal Pressure / Release of oxytocin Response Increased contractions Diagram

3 Type of Feedback Loop Reasoning POSITIVE or NEGATIVE POSITIVE or NEGATIVE POSITIVE or NEGATIVE The two connections in this feedback loop are positive - MORE oxytocin causes MORE contractions. The product of these two positives (a + times a +) is a positive, therefore, the feedback loop is positive. Also, this feedback loop works to amplify a signal, rather than to maintain a stable set point. PART 4: C-E-R Explanation Construction DIRECTIONS: Use the background information and data provided to create an explanation, supported by evidence and reasoning, of two different homeostatic loops. The first one has the evidence completed for you. 1. Blood Glucose Homeostasis Background: Insulin is a hormone released from the pancreas when blood sugar (glucose) levels are high that signal cells in the body to take glucose out of the blood and store it for later. Data: Time 7a 9a 11a 1p 3p 5p Blood Glucose Level (mg/dl) Insulin Level (uu/ml) Claim: Insulin regulation of blood glucose is an example of a feedback loop. Evidence: Reasoning:

4 2. Female Menstrual Cycle Background: There are many hormones involved in regulating the female menstrual cycle. There are also multiple feedback loops these hormones are involved in. One loop involves the hormone LH - luteinizing hormone. This hormone is responsible for encouraging the development of an immature egg cell in the ovaries into a mature egg cell. At the mid-point of the menstrual cycle, there is a strong surge in another hormone called estradiol which causes a surge in LH concentrations. This increase in LH causes the brain to signal another gland to release even more LH. The increase in LH ultimately causes a mature egg cell to be released from the ovaries in a process called ovulation. Data: Cycle Day LH Level Estradiol Level C-E-R Explanation Claim: The surge in estradiol resulting in a surge in LH is an example of a feedback loop. Evidence: (create the graph using the data above!) Reasoning:

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