Coordination and Response in Plants and Animals: Form 1 Biology notes

25SCHOOLS FREE LEARNING NOTES FOR ZAMBIA FORM 1 Coordination and Response in Plants and Animals Biology Lesson notes for learners · Competence-Based Curriculum Stimulus, response and coordination Tropisms: responses in plants Why tropisms help the plant, and how to show one Taxic responses: responses in animals Check yourself INSIDE 1. 2. 3. 4. 5. 25schools.com · Notes, quizzes and lesson plans for Zambian learners Living things notice changes around them and react to them. A maize plant bends towards the sun, and a chicken runs away from a dog. This topic explains how plants respond through tropisms and how animals respond through taxic responses. AFTER THESE NOTES YOU SHOULD BE ABLE TO Define stimulus, response, coordination, tropism and taxis in correct terms Name and describe phototropism, geotropism, hydrotropism and thigmotropism in plants Explain the difference between positive and negative responses Describe taxic responses in animals such as phototaxis, chemotaxis and hydrotaxis, with examples Explain how plants and animals benefit from their responses KEY WORDS Stimulus A change in the surroundings that a living thing can detect, such as light, water, touch or gravity Response The way a living thing reacts to a stimulus Coordination The way parts of an organism work together so that it can detect a stimulus and respond to it Tropism A growth movement of part of a plant in response to a stimulus from one direction Positive response A response towards the source of the stimulus Negative response A response away from the source of the stimulus Taxis Movement of a whole animal towards or away from a stimulus Hormone A chemical made in one part of an organism that controls growth or activity in another part 1 Stimulus, response and coordination All living things are sensitive. This means they can detect changes around them. A change in the surroundings that an organism can detect is called a stimulus. Examples are light, temperature, water, touch, gravity and chemicals such as the smell of food. The reaction of the organism to a stimulus is called a response. When you touch a hot pot and pull your hand away, the heat is the stimulus and the movement of your hand is the response. • • • • • Form 1 Biology Lesson notes 25schools.com Page 2 of 6 For this to work, the parts of the organism must act together. This working together is called coordination. First the stimulus is detected. Then a message passes to the part that will act. Finally that part makes the response. Plants and animals do this in different ways. A plant responds mainly by growing. An animal can move its whole body from place to place. Figure 1. From stimulus to response 2 Tropisms: responses in plants A plant is fixed in the soil and cannot walk away. It responds by growing a part of itself towards or away from a stimulus. A growth response in which the direction of growth is decided by the direction of the stimulus is called a tropism. A tropism is positive if the part grows towards the stimulus. It is negative if the part grows away from the stimulus. Plant tropisms are controlled by chemicals called hormones. In phototropism, for example, a hormone collects on the shaded side of the shoot and makes the cells there grow longer than the cells on the lit side. The shoot then bends towards the light. Tropism Stimulus Response of the shoot Response of the root Phototropism Light Positive: grows towards light Negative: grows away from light Geotropism Gravity Negative: grows upwards Positive: grows downwards Hydrotropism Water Not usually important Positive: grows towards water Thigmotropism Touch Climbing stems and tendrils coil round a support Not usually important Figure 2. Tropisms in plants 3 Why tropisms help the plant, and how to show one Each tropism helps the plant to survive. Shoots that grow towards light get more light for photosynthesis, which is how the plant makes its food. Roots that grow downwards hold the plant firmly in the soil, and roots that grow towards water can take in the water and mineral salts the plant needs. Climbing plants such as beans and pumpkin use thigmotropism: their thin stems coil round …