Responses in Living Organisms 🌱

• Tropic Response 🌱: Occurs in plants, involves growth towards or away from a stimulus. Generally slower and only part of the plant responds.
• Taxic Response 🐜: Occurs in invertebrates, involves movement towards or away from a stimulus. Generally faster, and the entire organism responds.

1. Tropic Responses (Tropisms) 🌞

Tropic responses are plant responses involving growth either towards or away from a specific stimulus. Growth towards a stimulus is called a positive tropic response, while growth away from a stimulus is a negative tropic response. 🌱➡️🌞

Phototropism 🌞

The response of a plant to light. Shoots are positively phototropic (grow towards light ☀️), while roots are negatively phototropic (grow away from light 🌑).

Experiment 🔬: Investigating Light's Effect on Maize Coleoptiles 🌽

• Materials 🧪: Maize seedlings 🌱, cardboard box 📦 with a hole, two tins 🥫
• Method 📝: Place coleoptile seedlings in tins; one in a box with a light hole and one in direct sunlight ☀️.
• Observation 👀: Coleoptiles in the box grow towards the light; control coleoptiles grow straight.
• Conclusion ✅: Plant shoots are positively phototropic.
• Significance 🌟: Positive phototropism helps ensure leaves are exposed to sunlight for photosynthesis.

Geotropism 🌍

The response to gravity. Roots are positively geotropic (grow towards gravity ⬇️), while shoots are negatively geotropic (grow away from gravity ⬆️).

Experiment 🔬: Investigating Gravity's Effect on Bean Seedlings 🌱

• Materials 🧪: Germinating bean seeds 🌱, petri dish 🍽️, moist cotton wool, clinostat
• Method 📝: Place germinating seeds horizontally; one set on a still dish and the other on a rotating clinostat.
• Observation 👀: On the still dish, radicles grow towards gravity; on the clinostat, growth remains straight.
• Conclusion ✅: Roots are positively geotropic, while shoots are negatively geotropic.
• Significance 🌟: Positive geotropism helps roots grow towards water 💧 and nutrients in the ground.

Hydrotropism 💧

A plant's growth response to water. Roots are positively hydrotropic, growing towards water, which is essential for the plant's water absorption.

Chemotropism 🧪

Plant's response to chemicals, such as the pollen tube growing towards the ovary for fertilization. 🌸

Auxins are growth substances produced in shoot and root tips, promoting growth in shoots and inhibiting it in roots. They play a crucial role in tropisms:

• Phototropism 🌞: Auxins concentrate on the shaded side of the shoot, causing it to bend towards the light.
• Geotropism 🌍: Auxins accumulate on the lower side due to gravity, promoting downward growth in roots and upward growth in shoots.

2. Taxic Responses (Taxism) 🐜

A taxic response is a reaction in invertebrate animals involving movement towards or away from a stimulus.

• Woodlice 🦠: Positively hydrotaxic, negatively phototaxic
• Earthworms 🐍: Positively hydrotaxic, positively geotaxic
• Cockroaches 🪳: Negatively phototaxic

Animals coordinate responses through two main systems:

• The Endocrine System 🧬
• The Nervous System 🧠

Both systems work together to allow animals to respond quickly and adaptively to stimuli. ⚡