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Survival
AQA A-level biology survival year 13
| Term | Definition |
|---|---|
| Taxis (taxes) | A directional response to a stimulus where an organism either moves towards or away from the stimulus |
| 4 main types of taxes | Phototaxis - response to light Chemotaxis - response to certain chemicals Gravi-geotaxis - response to gravity or position Thigmotaxis - response to physical touch |
| Positive and negative reactions | Positive taxis is when an organism moves towards a stimulus, negative taxis is when it moves away from a stimulus |
| Example of different life stages having different taxes (flies) | Fly larvae are negatively phototaxic because when they hatch inside the source of sustenance, they burrow down away from the light until they mature and become positively phototaxic so they burst up from the sustenance |
| Kinesis (kineses) | A non-directional response to a stimulus to move either towards or away from a stimulus |
| 2 main types of kineses | Orthokinesis - change in rate of movement in response to a stimulus Klinokinesis - change in rate of turning or changing direction in response to a stimulus |
| Difference between taxes and kinases | Taxes are innate behavioural responses to stimuli by changing proximity whereas kineses are changes in overall activity |
| Tropism | The growth or movement in a plant in response to a directional stimulus |
| Different types of tropism | Phototropism - response to light Geo/gravitropism - response to gravity Thigmotropism - response to physical contact Hydrotropism - response to water |
| Plant hormone growth factors | Substances that accelerate, inhibit, or otherwise alter how a plant grows e.g., indoleacetic acid (IAA), a type of auxin which regulates cell elongation |
| Role of IAA | Activates proton pumps which lowers the PH to the optimum for enzymes that loosen the cell wall, allowing in more water and making the cell become turgid causing shoot cells to elongate but root cell growth is inhibited |
| How IAA causes positive phototropism | Unilateral light causes IAA to be actively transported to the shady side of the plant and making a gradient of the hormone. The cells on the shady side elongate more than the bright side causing the shoot to bend towards the light |
| How IAA causes negative gravitropism | IAA is transported to all sides of the shoot but gravity causes it to flow to the bottom of the shoot, this causes those cells to elongate more than the cells on the top and the shoot bends away from gravity |
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