Biology is Too Hard
And the Mark Schemes are never clear
Response to Stimuli
Stimulus: A detectable change in the internal and/or external environment of an organism that produces a response in the organism.
Responses to different stimuli by any organism help it to do one thing, which is to survive. There the organisms with the most favourable stimuli at that time will be favoured and pass on their alleles. So there is always a selection pressure on these responses.
Stimuli are detected by receptors - these are usually a certain type of cell. The response is carried out by effectors - either a muscle or a gland usually. The pathway can be summarised:
effectors > receptor > coordinator > effector > response
You need to know two different types of whole organism response - Taxes and Kinesis.
Different taxes (plural of taxis) result in response to different types of stimuli. Each of these forms of taxis can be described by simply adding a prefix to the word taxis. The table below shows the most common forms of taxis.
From these terms you can describe almost any directed movement. For instance, phototaxis would be movement in response to light. Chemotaxis means movement in response to a chemical. Any combination of these words can be used. Movements toward a stimulus are positive taxes, while movements away from the stimulus are negative taxes. You can also combine the two terms e.g. positive chemotaxis would be movement towards a chemical stimulus and negative phototaxis would be movement away from the light.
Some examples would be:
Menotaxis: This refers to an animal maintaining a constant angle to a stimulus. The Silkworm moth, for instance, flies at an angle perpendicular to the direction of the wind in order to pick up a scent trail. Once the moth detects the trail, it turns upwind to find the chemical gradient of the trail.
Magnetotaxis is orientation in response to magnetic cues. Wide varieties of animals use magnetic cues to navigate. Aquaspirillum bacteria burrow in the mud, and use the magnetic field of the earth to determine position.
A kinesis is a response to a stimulus but it does not involve a specific direction, i.e. it does not move move directly towards or away from a stimulus. The more unpleasant the stimulus, the more rapidly it moves and the more rapidly it changes direction. This type of response is designed to bring the organism back into favourable conditions. The best and most looked at example of this are woodlice. When woodlice find themselves in a dry area they move about more and change direction more often - this increases their chances of moving into a different area, which is more favourable - thus increasing its chances of survival.
Tropisms
This is a growth movement of part of a plant in response to a directional stimulus. The part of the plant either moves toards a positive stimulus or away from a negative one. Again - the clue is in the name - positive phototropism means growing towards the light. Positive geotropism means growing towards gravity - etc.
Quite a tough question! - The key is to use the command prompt in the question - 'using information in the diagram'. By looking at the microbe you see it has a chloroplast so therefore it will need light to photosynthesize. Too much light intensity usually means unpleasntness for most species. However because it has an eyespot and a chloroplast this will usually mean some form of positive phototaxis.
This is a data/experimental design question based on taxis of maggots. The first question is testing you on drawing sound conclusions from a set of data. I went for maggots tend to respond more to colour than light intensity point.
