Coordination and Response in Plants and Animals

1. Coordination and Response in Plants and Animals Introduction

2. Response of Plants and Animals • Syllabus Objectives • Define ‘stimulus’ and ‘response’ • Describe the response of: • Green plants to unilateral stimuli of light and gravity • Invertebrates to variations in light intensities, temperature and moisture • Explain why the response to stimuli is important for the survival of organisms

3. Stimuli and response • Plants and Animals receive information about changes in conditions both inside and outside their bodies • Any information to which an organism reacts is known as a stimulus because it stimulates the organism to make a response

4. Stimuli and Response • A stimulus could be an external event • Change in direction of light • Change in light intensity or • Change in temperature • Internal events include • Arrival of food in the stomach • Changes in blood glucose level • Entry of foreign organisms in the body or change in water content of cells

5. Stimuli and Response • Some changes can be • positive or advantageous, • unfavourable or harmful, • unimportant • Question • Can you list 2 favourable stimuli, 2 unfavourable stimuli and 2 that are unimportant

6. Stimuli and Response • Response can be through • the movement of the whole animal • E.g. earthworm moving away from light • the movement of part of the animal • E.g. closing of the pupil of the eye to bright light • Response in plants • Movement through part of the organism • E.g. tip of a plant grows in the direction of light

7. Response and Stimuli • Can you list 3 examples of what a response to an internal stimulus could be? • Secretion of enzymes in response to food • Production of antibodies in response to foreign organisms • Secretion of hormones in response to changes in blood glucose levels • An increase in heart rate in response to an increase in CO2 content of the blood

8. The Importance of response • Response to stimuli is important for the survival of organisms • Shoots of green plants grow toward the light so that they could make food • Roots grow in the direction of gravity. They grow towards moisture and provides stability for the plant • Animals avoid unsuitable conditions by moving to suitable ones

9. The Importance of response • Hunted animals avoid predators when they see, hear or smell their approach • A male moth is attracted to a female moth by being able to detect and respond to chemical signals released by the female • This response ensures that reproduction takes place and the species survives • The Sensitive plant (Mimosa pudica) folds its leaves quickly when touched. This makes it more difficult for animals who eat them to see them.

10. Practice Investigative Questions • How do the shoots of seedlings respond to receiving light from one direction only? • Will roots grow downwards regardless of how the rest of the seed or seedling is positioned? • How do millipedes, earthworms and/or woodlice respond to variations in light intensities? • How do small invertebrates respond to temperature changes? • How do small invertebrates respond to different levels of moisture?