Signals and responses to stimuli

Weekender
SCIENCE IN ACTION
Insectivorous plants. – Picture from indiamart.com

By MICHAEL JOHN UGLO
THIS is the sixth lecture in the Science in Action series.
You know the saying in life; what goes around comes around. For people who have lived long enough these events unfold in life. It is sort of becomes a norm so when you say what goes around doesn’t come around people may be very interested to know what your explanation is because you are saying something that is not normal.
Ii is always better to try to do something new outside the common understanding and reasoning because this is where breakthroughs and innovations happen.
Mind you, generally, innovations happen in the private sector and the public copies those ideas.
Due to public demand and request I have put together the Technology and Science in Action series into a breakthrough and innovative textbook. Parts of this textbook are published in this space every Friday.
Any organisation or institution, particularly secondary, national high schools and primary schools who want to use this textbook, please keep reading this section on the National Weekender till I make the announcement that the book is ready for purchase so you could place your order. It is an all-in-one shop as all the sciences are built into this text book.
A primary school student can buy this text book and use it all the way to Grade 12.
This text book will also sell around the world as it is an innovation. It is relevant for Science, Technology, Engineering and Mathematics learning in PNG, Australia, China, Malaysia, Fiji, Singapore and elsewhere.

Responses to stimuli
When an action such as a force is applied it is a stimulus. The result of that action is the response. It can also be a series of responses from the one stimulus. When you apply a stimulus or a force to a non-living thing, it will move according to mathematical dimensions that can be measured.
However, if you apply the same stimulus to any living thing, they will respond in many different ways.
Such as a cat running away from you, a dog or a snake turning around to bite you, a bird flying away from you or a bee which flies back and stings you.
Responses in plants sensitive to touch such as a leaf closing itself up and opens up again like the Mimosa pudica also known as the humble plant. There are some insectivorous plants closing their flowers up to catch insects such as the Venus flytrap, Drosera capensis, California pitcher plant.
Plants respond to sunlight by growing towards it, a response known as phototropism. A plant hormone called auxin in plants stays away from the sunlight at the root tips, shoots and promote cell division to promote growth towards the sunlight or light.

Artificial stimulus-response. – Picture from science.org

The plant roots respond to gravity, a process known as geotropism. Plants also respond to stimuli from chemicals and that is called chemotropism. The ants respond to chemicals such as pheromones to alert the other ants in the colony from danger and also alert other ants to food sources.
Response to stimuli is a process of an activity or a change in the state of an organism or a cell whereby there is an enzyme production, a gene expression, a secretion or simply a movement as a result of a stimulus. The animals can respond to external stimulus such as the sensory receptors as touch, sight, smell, taste and hearing.
The sensory receptors that send these impulses that do not reach the absolute threshold level are sent to the central nervous system which integrates it and produces a response. Stimuli that are strong enough reach an absolute threshold level which is the minimum stimulus needed to effect an appropriate response such as moving your hand away from a hot object or scratching an itchy part of your body.
Others are internal receptors known as chemoreceptors and mechanoreceptors.
The responses to stimuli internally follow a series of responses such as when someone is angry, or when someone is preparing to play rugby or even fight.
The adrenal medulla generates the adrenaline hormone to burn up the glycogen in respiration to provide the necessary energy to flex up the muscles for the action also known as the fight or flight response.
The heart rate increase because of dilation of cardiovascular tube, dilation of bronchi for increased breathing rate, dilation of blood vessels serving the muscles for increased blood flow.

Sensory receptors. – Picture from sensory.lumenlearning.com

A result of that will produce perspiration in the form of sweat to keep the balance and homeostasis with the negative effect for the cooling of the body.
The stimulus and responses produce negative impacts to the maintain balance. This is particularly the internal condition to attain homeostasis. Negative feedback is attained the organism’s ideal state for its normal physiological processes and functions. For instance, when we are cold, we shiver. This burns up the sugar to supply the energy to keep us warm.
The pancreas supplies the insulin hormone after we eat to provide the blood sugar when we do not have much sugar level in the blood.
In the cells, including unicellular organisms, the responses to stimuli are seen on the cell organelles’ level within the cytoplasm and the permeable plasma membrane.
The three cellular responses that occur is that firstly the signaling molecule is received by the target cell.
That pathway of the target cell and the signaling molecule involve in the second process called the transduction whereby all necessary steps as hydrophobic (water fearing) intracellular ligand molecule is taken to the permeable membrane where cell-surface binding receptors extracellular ligand molecule convert an extracellular signal into an intracellular signal for the target cell to respond.
Thirdly the target cell responds to the stimulus or the signal.
My Prayer for PNG today is: “If when this life of labour is ended and the reward of the race you have run. Oh the sweet rest prepared for faithful. Will be his blest and final, “well done”
Next week: Organisms’ transport systems

Michael Uglo is a science textbook author and lecturer in Avionics, Auto-Piloting and Aircraft Engineering. Please send comments to [email protected]