A2 Biology

A2 Biology

1. Ecosystems

   • Producers
     • Synthesises their own glucose
     • e.g. plants
   • Consumers
     • Obtain energy by feeding
   • Decomposers
     • Feed on dead waste
     • e.g. bacteria, fungi, maggots
   • Trophic Levels
   • Energy Losses
     • 1-3% lost from sun to producer
       • May not hit a leaf
       • 90% of sun reflected or absorbed by atmosphere, clouds & dust
       • Only 680 & 700 nm wavelengths used in photosynthesis
     • 5-10% lost from producer to consumer
       • Energy used in respirtation
       • Movement
       • Heat Loss
       • Some organisms left uneaten
       • Some material is egested as faecal matter

2. Pests and Productivity

   • 'Pests are any organisms that have a negative impact on food or space for humans, or cause disease
   • Control pests = increased productivity
   • Effective pesticide
     • Cost Effective
     • Specific
     • Easy to apply
     • Kills pests quickly
     • Not accumulate
     • Biodegrades
   • Chemical
     • +
       • Fast Acting
       • Easy to apply / acquire
     • -
       • Non-specific
       • Can pollute water
       • Reduce Biodiversity
       • Resistance
       • Expensive
   • Biological
     • Uses natural enemies to control pests
     • +
       • Specific
       • 1-time application
       • No resistance possible
     • -
       • Can affect non-pests
       • Expensive
       • Time lag
       • Control may become a pest

3. Senses

   • Used to respond to stimuli and enable survival
     • Better senses = better ability to respond = survival
     • A stimulus is a detectable change in the internal or external environment
     • Stimuli are detected by receptors in sense organs
       • A receptor is a cell which transforms energy from the stimulus to another form
   • Stimulus
     • Receptor
       • Sensory Neurone
         • Intermediate Neurone
           • Motor Neurone
             • Affector Organ
               • Response
   • Messenger Systems
     • Chemicals / Hormones
     • Neurones / Nervous System
   • Responses
     • Taxis
       • Simple response with a direction
     • Kinesis
       • Rapid , random movement in unpleasent stimulus
       • Until -ve stimuli is gone
     • Tropisms
       • Growth movement of a plant
         • Cels on outside of the turn must grow most
         • Growth hormone is Auxin aka IAA
           • Accumulates on lower side of plant
       • Light - phototropism
       • Into ground - geotropism
       • Water - hydrotropism
     • Nervous Systems
       • Central (CNS)
         • Brain
         • Spine
       • Peripheral (PNS)
         • Nerves (Neurones)
           • Sensory
           • Motor
             • Voluntary
               • Muscles
             • Autonomic
               • Cardiac
               • Muscles
               • Glands
       • Autonomic
   • Reflex Arcs
     • Involuntary, so keeps brain free
     • Protects the body from harmful stimuli, effective at birth.
     • Fast, few synapses