2.C.2

2.C.1 – Organisms use feedback mechanisms to maintain their internal environments and respond to external environmental changes.

·      Discuss how negative feedback works. Discuss the following two examples – Thermoregulation in animals and plant responses to water limitations.

Negative feedback loops work by receiving a signal from some part in the animal and responding in a way that returns the signal’s origins to a normal level.

Thermoregulation works by when the stimulus of the animal’s body being cold, it sends a signal to the brain and the brain then sends out signals to the muscles to make more heat (shiver) and for the blood vessels to dilate and conserve heat/

Plants respond to say a drought by when the turgidity of the plant lessens, they close their stomata during the hottest hours of the day to prevent water loss. When water becomes normal again, plants no longer need to do this.

·      Discuss how positive feedback works. Discuss the following three examples – lactation in mammals, onset of labor in childbirth, and ripening of fruit.

Positive feedback loops work by sending a signal to have a huge reaction that keeps going until the stimulus is gone. In lactation of mammals, the stimulus is the offspring suckling and when that ceases the reaction, lactation, also ceases.

The baby’s head hitting the cervix stimulates childbirth. This sends signals to the brain, which then signals the muscles in the abdomen to contract. It ceases when the child is born.

When one fruit ripens it gives off a hormone that stimulates other fruit around it to ripen. When the fruit fall off/rot the stimulation is gone and the loop ceases.

·      Discuss how an alteration in the mechanism of feedback can result in dire consequences by using the following three examples: diabetes mellitus in response to decreased insulin, dehydration in response to decreased antidiuretic hormone and Grave’s disease.

Alterations in feedback loops can cause biological processes (like blood glucose level regulation, for example) to spiral out of control. This can cause serious damage to the organism or death.

2.C.2 – Organisms respond to changes in their external environments.

·      Discuss how organism respond to changes in their environment by using the following examples:

o   Photoperiodism and phototropism

o   Hibernation and migration in animals

o   Taxis and kinesis in animals

o   Chemotaxis in bacteria, sexual reproduction in fungi

o   Nocturnal and diurnal activity: circadian rhythms

o   Shivering and sweating in humans