Coordination and Response

• Neurons connect the sense organ to the brain and the brain to muscles
• Neurons send impulses from the sense organ to the brain
• Brain processes information and sends instructions to muscles in majority of life situations
• Myelin sheath


  • Helps to keep impulses inside the neuron
• Peripheral nervous system


  A set of nerves that connect the brain to the rest of the body
• Sense organ

  A group of receptor cells that respond to specific stimuli
• Motor neurons

  Carry impulses from the brain to effectors
• Cell body location differs in sensory and motor neurons
• Central nervous system

  Made up of the brain and the spinal cord
• Effector


  A set of muscles or glands which respond when they receive impulses from motor neurons
• Sensory neurons

  Deliver information from sensory receptors to the brain
• Parts of the nervous system

  • Central nervous system
  • Peripheral nervous system
• Skin acts as a sense organ
• In sensory neurons, dendrites are at the end of the transmission, while in motor neurons, dendrites are at the start
• Neurons send impulses from the brain to effectors
• Brain processing information and sending signals to muscles

  Decides to scrunch up the paper and throw it into the bin
• Direction of impulses is crucial for efficient transmission, especially in reflex arcs
• Reflex arc

  Sensory neuron takes information from sensory organ to spinal cord, relay neuron connects to motor neuron, muscles automatically react without waiting for brain signal
• Neurons communicate through synapses, which are connection points between neurons
• Impulses can only be delivered from neurons with neurotransmitters to neurons with specific receptors
• In some situations, the brain's processing time is too slow, leading to the use of reflex arcs for quick responses
• Majority of life situations involve the brain processing information and making decisions
• Impulses travel unidirectionally from neuron to neuron through neurotransmitters released at synapses
• Reflex arc involves three components: sensory neuron, relay neuron, and motor neuron, all connected within the spinal cord
• Impulses cannot travel in the opposite direction due to the specific layout of synapses
• Reflex actions are a form of survival instinct for quick responses
• The testa of the seed prevents damage to the embryo and entry of bacteria and fungi. It has a micropyle for water absorption
• One pollen grain can only fertilise one ovule. Multiple pollen grains are needed if there are many ovules in the ovary
• Embryo development

  The zygote divides by mitosis to form an embryo plant
• The ovary grows and is called a fruit
• Wind-pollinated flowers have inconspicuous petals or no petals at all
• Embryo structure

  The embryo consists of a radicle (root) and a plumule (shoot)
• Key definitions:
• Once the ovules have been fertilised, many of the parts of the flower are not needed any more. The sepals, petals and stamens wither and fall off
• Fertilisation process

  After pollination, the pollen tube grows down through the style and ovary to reach the ovule. Fertilisation occurs when the pollen nucleus fuses with the ovule nucleus
• Contents of a bean seed

  • Stored food in cotyledons (starch and protein), enzymes, protective testa
• Seed formation

  The ovule grows into a seed, with the integuments becoming the testa. Water is withdrawn from the seed, making it dormant
• The hilum is a scar near the micropyle where the seed was joined to the pod (ovary)