Responses to Stimuli

Japanese Blood Grass: 

There are several ways plants such as Japanese blood grass respond to stimuli. These responses are called tropisms. There are two main tropisms which apply to how Japanese blood grass responds to stimuli.

The first is phototropism. This is when plants grow towards light. Stems display positive phototropism and roots display negative photo tropism. Photo receptors detect a light source and the plant hormone auxin gathers furthest from the light, so the stem goes towards the light. 

The second tropism is geotropism. This is a response to gravity, so stems grow upwardsdisplaying positive geotropism and roots grow down, displaying negative geotropism. 


Figure 1: how auxin works in response to light for phytotropism 


Brewers Yeast: 

Brewers yeast respires by taking in sugar/glucose and oxygen to gain energy by breaking down the sugars, then water and carbon dioxide are released as by-products. 

When oxygen is not present, yeast ferments instead to survive. In this instance, the stimulus is oxygen depletion and the switch from one metabolic process to another is the response.

This process is used every day to make things such as bread and beer. When making beer, the lower glucose levels are, the more ethanol, or alcohol, is produced.  


Figure 2: diagram of fermentation input and output in yeast 


How do they compare? 

Both organisms are similar in that they both respond to naturally occurring stimuli in the environment around them. However, they differ is the sense that one responds with metabolic processes and the other is growth to survive. 


Sophie Evans