Homeostasis & Response

• Homeostasis is the maintenance of a constant internal environment.
• Mechanisms are in place to keep optimum conditions despite internal and external changes.
• Homeostasis is needed for enzyme action and all cell functions.
• Homeostasis controls blood glucose concentration, body temperature, and water levels in the human body.
• Nervous and hormonal communication is involved in the automatic control systems, which detect changes and respond to them.
• All control systems have receptors, coordination centres, and effectors.
• The nervous system allows us to react to our surroundings, and coordinate actions in response to stimuli.
• Receptor cells convert a stimulus into an electrical impulse.
• The electrical impulse travels along cells called sensory neurons to the central nervous system (CNS).
• In the CNS, the information is processed and the appropriate response is coordinated, resulting in an electrical impulse being sent along motor neurons to effectors.
• The effectors carry out the response, which may be muscles contracting or glands secreting hormones.
• Automatic responses which take place before you have time to think are called reflexes.
• Reflexes are important as they prevent the individual from getting hurt.
• Reflexes take place quickly because the information travels down a pathway called a reflex arc, allowing vital responses to take place quickly.
• The impulse does not pass through the conscious areas of your brain when it reaches the end of the first neuron.
• Synapses are the gaps between two neurons.
• When the impulse reaches the end of the first neuron, a chemical is released into the synapse.
• This chemical diffuses across the synapse when the chemical reaches the second neuron, it triggers the impulse to begin again in the next neuron.
• Your reaction time is how long it takes you to respond to a stimulus.
• The brain is made up of many connected neurons and controls complex behaviour.
• The brain is part of the central nervous system, along with the spinal cord.
• The plant is exposed to light on one side, which can lead to multiple births and may be a risk to the babies and the mother.
• Gibberellins are used for ending seed dormancy, promoting flowering, and increasing fruit size.
• When the auxin distribution becomes equal on both sides, the plant grows straight in that directions.
• This is beneficial as there are more likely to be increased levels of water and nutrients lower down, and it provides stability for the plant.
• Auxin is used as weed killers, affecting broad-leaved plants, causing the cells to grow too rapidly, resulting in the weed dying.
• If a root is horizontal, auxin moves to the lower side, stimulating cells to grow more on the side with less auxin, causing the root to bend and grow downwards.
• If a shoot is horizontal, auxin moves to the lower side, stimulating cells to grow more on the side with most auxin, causing the shoot to bend and grow away from the ground.
• Auxin, a hormone, moves to the shaded side of the shoot, stimulating cells to grow more here, causing the shoot to bend towards the light.
• Humans can use plant hormones to alter plant growth, they are used in areas such as agriculture and horticulture for many reasons: to increase yield, obtain desirable features and to lower costs.
• Different regions of the brain control different functions.
• Most roots show positive gravitropism as they grow towards gravity.
• Auxin is used as rooting powders, stimulating the growth of roots and shoots in cloned plants.
• Ethene is involved in controlling cell division and stimulates enzymes that result in fruit ripening, reducing wastage as more fruit is suitable to be sold and it does not ripen too early.
• This is beneficial as light levels are likely to be higher further away from the ground.
• The plant receives more light, meaning photosynthesis can occur at a faster rate.
• Most shoots show negative gravitropism as they grow away from gravity.
• The cerebral cortex controls consciousness, intelligence, memory and language; it is the outer part of the brain.
• The cerebellum controls fine movement of muscles; it is a rounded structure towards the bottom/back of the brain.
• The medulla controls unconscious actions such as breathing and heart rate; it is found in the brain stem in front of the cerebellum.