📚 Edexcel Biology 5.5 Plant and Animal Responses | 爱德思生物 5.5 植物与动物反应
In Edexcel Biology Topic 5.5, you will learn how plants and animals detect changes in their environment and coordinate appropriate responses. Plants are sessile and rely mainly on chemical signals and growth movements, while animals use fast nerve impulses and slower hormonal signals. This topic covers plant tropisms, the role of auxin, action potentials, synapses and the comparison between nervous and hormonal control.
在爱德思生物 5.5 中，你将学习植物和动物如何检测环境变化并协调适当的反应。植物固着生长，主要依靠化学信号和生长运动；动物则使用快速的神经冲动和较慢的激素信号。本主题涵盖植物向性、生长素的作用、动作电位、突触以及神经与激素控制的比较。
1. The Need for Coordinated Responses | 协调反应的必要性
All organisms need to detect changes, called stimuli, in their internal and external environment and produce appropriate responses to survive. Plants are stationary, so their responses often involve changes in growth or turgor. Most animals can move and have evolved rapid electrical signalling through the nervous system, supported by slower chemical signalling through hormones.
所有生物都需要检测体内和体外环境中的变化（刺激）并作出适当的反应才能生存。植物固着不动，因此其反应通常涉及生长或膨压的变化。大多数动物可以运动，并进化出通过神经系统进行快速电信号传导，同时辅以通过激素进行的较慢化学信号传导。
2. Plant Tropisms: Directional Growth | 植物向性：定向生长
A tropism is a directional growth response determined by the direction of an external stimulus. Phototropism is growth towards or away from light; gravitropism is growth in response to gravity. In shoots, phototropism is usually positive because the shoot bends towards light, while in roots it is usually negative. In gravitropism, roots grow downwards, showing positive gravitropism, and shoots grow upwards, showing negative gravitropism.
向性是由外部刺激方向决定的定向生长反应。向光性是指朝向或远离光的生长；向地性是指对重力的生长反应。
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