1.1.2 Homeostasis and negative feedback

Question 1

What is homeostasis?

Answer 1

Homeostasis is the maintenance of the internal environment in a constant state despite external changes.

Question 2

Give four examples of things that need to be kept constant in most organisms?

Answer 2

1. Body temperature
2. Body glucose concentration
3. Water potential of the blood
4. Blood pressure

Question 3

What is negative feedback?

Answer 3

Negative feedback is a process by which any change in a parameter brings about the reversal of that change so the parameter is kept fairly constant.

Question 4

Outline how negative feedback takes place?

Answer 4

The change in the internal environment( stimulus) is detected by a sensory receptor The sensory receptor then uses a communication pathway (cell signalling). The effector cells reciveve this message and will bring about a response that reverse the changes detected by the receptor cells.

Question 5

What is positive feedback?

Answer 5

Positive feedback is a process in which any change in a parameter brings about an icrease in that change.

Question 6

Give an example of where positive feedback can be harmful?

Answer 6

When the body gets too cold. Below a certain body temperature enzymes become less active. This means that the exergonic reactions are slower and release less heat. The means that the body will cool further and slows down the enzyme controlled reactions even more, so the body temeprature spirals downwards.

Question 7

Give an example where positive feedback is helpful?

Answer 7

At the end of pregnancy. As the cervic begins to stretch the change is signalled to the anterior pituitary gland, stimulating it to secrete the hormone oxytocin. Oxytocin increases the uternine contractions, which stretches the cervix even more, which causes more oxytocin to be released. Once the cervix is fully dilated the baby can be born.

Question 8

S&C

As core body temperature rises the increase will affect the activity of enzymes. This can lead to exhaustion and even death.

1. Describe the effect of increasing temperature on enzyme action.
2. Suggest what actually causes death as the body temeprature rises.

Answer 8

1. As temperature increases the rate of enzyme action increases. However after around 50° C, the enzymes will begin to denature and the reaction rate will fall quickly.
2. If the enzymes denature then enzyme-controlled reactions will not be able to take place. Also certain channels, pumps and electron carriers will denature, meaning important processes cannot be carried out.

Question 9

S&C

Answer 9

The response to adrenaline may have evolved as it causes the “fight or flight” response. This reponse in either way will help the organism to survuve by either evading danger or fighting more agressively. If the organism does survive it will be able to pass on its alleles that enabled it to survive. The response to oxytocin may have evolved as it causes the “tend or befriend response”. The female will attempt to pacify predators and therefore be able to pass on her alleles to her offspring.