14.1 - Survival And Response Flashcards
What is a Stimulus?
- A stimulus is a detectable change in the internal or external environment of an organism
- Leads to a response in the organism
- Increases the chances of survival through their response
What is the Importance of Response to Stimuli
- Survival Advantage: Organisms that can detect and respond to harmful stimuli (e.g., predators, extreme temperatures) have a higher chance of survival.
- Reproductive Success: Surviving organisms are more likely to raise offspring and pass on their alleles to the next generation.
- Selection Pressure: Favors organisms with more appropriate responses to stimuli, ensuring the survival of the fittest.
What are the components of a Response
- Receptor: Detects the stimulus. Each receptor is specific to a particular type of stimulus.
- Coordinator: Processes information from receptors and formulates an appropriate response. Can involve molecular or large organ functions like the brain.
- Effector: Produces the response, either at a molecular level (e.g., enzyme activity) or through whole organism behavior.
- Communication: Happens via two systems:
1) Hormonal system (slow communication)
2) Nervous system (rapid communication
Describe how Communication works in Multicellular Organisms
- In Hormonal System: Involves chemical communication. Found in both plants and animals, but it is a relatively slow process.
- In Nervous System: Faster means of communication. It involves receptors, effectors, and a central coordinator (e.g., the brain).
- Each receptor is linked to an appropriate effector by the coordinator
What is the Sequence of Events in a Response
1) Stimulus: A change in the environment (e.g., light, temperature).
2) Receptor: Detects the stimulus.
3) Coordinator: Processes information and connects the receptor to the correct effector.
4) Effector: Produces the response.
5) Response: The organism reacts to the stimulus.
Define taxis
A simple response where the direction of movement is determined by the direction of the stimulus.
What are the Types of Taxis
Positive taxis: Movement towards the stimulus.
Negative taxis: Movement away from the stimulus.
Give some examples of taxis
- Positive phototaxis: Single-celled algae move towards light to perform photosynthesis.
- Negative phototaxis: Earthworms move away from light to conserve water and avoid predators.
- Positive chemotaxis: Bacteria move towards higher glucose concentrations to access food.
Define kinesis
- A form of response where an organism changes its movement speed and turning rate without moving directly towards or away from the stimulus.
- Organisms increase turning rates in unfavorable environments to return to favorable ones. If far into an unfavorable area, they move in long, straight lines to find a more favorable region.
Give an example of kinesis
Woodlice: Move rapidly and change direction more often in dry conditions to return to damp areas. In damp areas, they slow down and turn less to remain there, which helps conserve water.
What are tropisms
A plant’s growth response to a directional stimulus.
What are the different types of tropisms
- Positive tropism: Growth towards the stimulus.
- Negative tropism: Growth away from the stimulus.
Give some examples of tropisms
- Positive phototropism: Plant shoots grow towards light to maximize light absorption for photosynthesis.
- Negative gravitropism: Shoots grow away from gravity to position leaves for better light capture.
- Positive gravitropism: Plant roots grow towards gravity, helping roots anchor in the soil and absorb water and nutrients.
What is the Survival Value in phototaxis and chemotaxis
- Phototaxis: Algae moving towards light increases photosynthesis, essential for survival. Or Earthworms moving away from light reduces water loss and predator exposure.
- Chemotaxis: Bacteria moving towards glucose allows them to obtain energy for survival.
What is the Survival Value of Kinesis in humidity
- Woodlice in dry conditions move more frequently to return to moist environments.
- In moist conditions, woodlice slow down to stay longer in favorable areas, preventing dehydration and increasing survival chances.
What is the Survival Value of Tropisms (such as positive/negative phototropism and positive gravitropism
- Positive Phototropism: Maximizes light absorption for photosynthesis, increasing the plant’s energy production and survival.
- Negative Phototropism: Root growth away from light ensures roots grow into the soil, where they can access water and nutrients.
- Positive Gravitropism: Ensures roots grow downwards, anchoring the plant and enhancing nutrient uptake.
Describe Coordination at Different Levels
- Molecular Level: Can involve enzymes or hormones responding to internal stimuli.
- Organ Level: Large organs like the brain may process multiple stimuli and coordinate a complex response.
name the type of response described and the survival value of the response: Some species of bacteria move away from the waste products that they produce.
- (Negative chemotaxis )— wastes are often removed from an organism because they are harmful.
- Moving away prevents the waste harming the organism and so increases its chance of survival.
name the type of response described and the survival value of the response: The sperm cells of amoss plant are attracted towards a chemical produced by the female reproductive organ of another moss plant.
- (Positive chemotaxis — increases the chances of sperm cells fertilising the egg cells of other mosses and so helps to produce more moss plants / future generations.
- Cross-fertilisation increases genetic variability, making species better able to adapt to future environmental changes.
name the type of response described and the survival value of the response, The young stems of seedlings grow away from gravity.
- (Negative gravitropism — takes the seedlings above the ground and into the light, where they can photosynthesise.
- More photosynthesis means more carbohydrate and so a better chance of survival.
