1. Taxes, Kineses and Tropisms Pages 142 – 143 Syllabus 3.5.1
Response to stimuli
Taxes, Kineses and Tropisms
Pages 142 – 143
Syllabus 3.5.1

2. Survival and response
Organisms increase their chance of survival by responding to changes in the environment. e.g. moving towards food / light or away from predators
Those that survive have a greater chance of raising offspring and passing their alleles to the next generation.

4. Taxes and Kineses
Taxes and kineses are simple forms of behaviour that rely almost entirely on simple reflex actions
Taxes and kineses involve the locomotion of whole organisms or cells in response to a specific external stimulus
The adaptive value of taxes and kineses is their role in helping to maintain organisms in the most favourable environment for their survival

5. Taxis
A taxis or tactic response is the movement of a whole organism or cell in response to the direction of a stimulus
Certain organisms may move directly towards or away from a specific stimulus; they may show positive (towards) taxis or negative (away from) taxis
Movement of an organism directly towards a light source is described as positive phototaxis; other taxes include chemotaxis, hydrotaxis and aerotaxis

6. Chlamydomonas is a motile, photosynthetic protoctistan that
swims directly towards regions of optimum light intensity;
this species displays positive phototaxis

7. Positive Chemotaxis
Scent-tracking in humans and maggots. (A) Tracking of a trail of chocolate essential oil (faint white line) by a human subject in an open 10 m × 10 m arena (corners marked by blue squares). The track (red line) represents 5 min 34 s. Image courtesy of J. Porter. (B) Chemotaxis of a Drosophila larva across an agarose surface towards 50 μl isoamyl acetate (banana odour) in the cap of a centrifuge tube. The track (red line) represents 20.7 cm covered over 3 min 50 s. Image courtesy of M. Louis.

8. Dictyostelium chemotaxis to pipette with cAMP in it
Male, silkworm moths display positive chemotaxis when they fly directly towards the chemical bombykol, secreted from the abdominal regions of the female moth; the feathery antennae of the males contain millions of bombykol chemoreceptors

9. This water flea swims directly towards low-intensity light and towards oxygen-rich environments; it displays positive phototaxis and positive aerotaxis

10. It occurs where the stimulus is diffuse and from no defined direction
Kinesis
A kinetic response is a non-directional response in which the rate of movement is related to the intensity of the stimulus, but not its direction
It occurs where the stimulus is diffuse and from no defined direction
There are two aspects to kinesis:
1: the rate of movement changes in response to a stimulus
2: the rate of turning changes in response to a stimulus

11. Click in image for a video clip and explanation of ‘Kinesis’

12. Woodlice display kinetic behaviour when they encounter atmospheres of different humidity; in drier environments they increase their rate of movement and decrease their rate of turning

13. Example of a tracing from a low humidity chamber

14. Example of a tracing from a high humidity chamber

15. Tropisms in plants
Plants respond to a range of different stimuli that are all around them in their immediate environment. Their responses occur by means of growth.
A tropism is a response to a directional stimulus.
Phototropism is a response to light.
Hydrotropism is a response to water.
Geotropism is a response to gravity.
Thigmotropism is a response to touch.
( Mimosa)
( tendrils)

16. Positive or Negative Tropism?
If the response is towards the stimulus the response is described as a positive tropic response and if the growth is away from the stimulus the response is described as a negative tropism.
For example, shoots are positively phototropic and roots are negatively phototropic.
However, shoots are negatively geotropic and roots are positively geotropic.

17. Demonstrating Phototropism
Phototropism can be easily demonstrated in broad beans by setting up three different conditions...
Light
Dark A B C
A Plant grown out-of-doors grows straight up.
B Plant grown in the dark develops a long, thin, spindly stem and yellow leaves. This condition is known as ‘etiolation’.
C Plant illuminated from one side curves towards the light.

18. Using a Clinostat to Demonstrate Phototropism
The significance of the direction of the light can also be easily demonstrated in any plant by setting up two different conditions...
A A plant illuminated from only one side curves towards the light.
B A plant illuminated from one side while on a rotating clinostat is evenly illuminated, and so grows straight up.
Light
Light
Clinostat

19. These seedlings have been grown on a clinostat that is rotating once every 15 seconds. Although auxin still "tries" to concentrate on the bottom of the stem because the stem is rotating it is distributed all around the stem so the stems grow horizontally. So this experiment nullifies the effect of gravity.

20. To do Answer summary questions page 143 Exam style Question 1 page 153
Complete 2 worksheets on taxis and kinesis

21. Woodlice are invertebrates belonging to the phylum Arthropoda, the class Crustacea and the order Isopoda
Woodlice are terrestrial species that lack many of the water-conserving adaptations found among other members of their phylum
Woodlice display a relatively high surface area to volume ratio and lack a waxy, waterproof cuticle covering their exoskeleton – their primitive respiratory surfaces (a pair of ‘pleopod lungs’) open to the atmosphere through a permanently open pore
Woodlice display patterns of behaviour aimed at limiting water loss and promoting their survival in a range of terrestrial habitats

22. Students investigated the behaviour of woodlice when given a choice between dry
and humid conditions
Twenty woodlice were introduced into a choice chamber that provided them with a choice between dry and humid atmospheres
The distribution of woodlice was recorded after a period of three minutes and the investigation was repeated to include six trials

23. The choice chamber consisted of two halves, with distilled water introduced into one side and calcium chloride (a drying agent) into the other
distilled water
calcium chloride
In this investigation, tactic responses are being observed as the woodlice demonstrate their preference for a particular environment by movement towards or away from a stimulus (level of humidity)

24. The results of this investigation (six trials) are shown in the following slide
Use these results to determine the total number of woodlice, found in each environment, after the three minute period
distilled water
calcium chloride
State a Null and Alternative Hypothesis for this investigation and analyse the results statistically using the Chi-square test

26. Table of critical values of chi square at different levels of P
Degrees of Freedom
Probability, p
0.99
0.95
0.05
0.01
0.001 1
0.004
3.84
6.64
10.83 2
0.02
0.103
5.99
9.21
13.82 3
0.115
0.352
7.82
11.35
16.27 4
0.297
0.711
9.49
13.28
18.47 5
0.554
1.145
11.07
15.09
20.52 6
0.872
1.635
12.59
16.81
22.46 7
1.239
2.167
14.07
18.48
24.32 8
1.646
2.733
15.51
20.09
26.13 9
2.088
3.325
16.92
21.67
27.88 10
2.558
3.94
18.31
23.21
29.59