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Biology Paper 2 (Ecology (Communities and Habitats (Definitions (Habitat =…

- - - - Habitat = the place where an organism lives.
      - Community = the population of different species living in a habitat.
      - Ecosystem = the interaction of a community of living organisms (biotic) with the non living (abiotic) parts of their environment.
- - - - Homeostasis: is the maintenance of a stable internal environment.
      - Provides: Optimum conditions for enzymes. - avoids damage to cells due to changes of water potential, some element of independence of the external environment.
  - - - This information is sent as electrical impulses to neurons nerves.The impulses travel along the neuron until it reaches the central nervous system.
        
        Once sensory neurons transport the impulses from your sense organs organs to the central Nervous System. The brain coordinates a response and sends impulses out along motor neurons.
        
        To the effector which responds:
        
        salivary glands -- produce chemical substances (saliva)
        
        muscles --contract
        
        pancreas -- produces insulin.
  - - - receptor is stimulated
        
        electrical impulse travel along a sensory neuron
        
        impulses are passed along a relay neuron via a synapse
        
        Impulses travel along a motor neuron via a synapse.
        
        Impulses reach effector
        
        response
    - - The diffusion of the chemical across these synapses is slower than the electrical impulse in the neurons this allows impulses to cross the gap.
      - The connection between two neurons is called a synapse.
        
        The nerve signal is transferred by chemicals which diffuse cross the gap.
        
        These chemicals then set off a new electrical signal in the next neuron.
  - - - The pancreas produces little or no insulin.
        
        This means a person's blood glucose level can rise to a level that can kill them.
      - People with type 1 Diabetes need insulin therapy.
        
        This involves
  - - - If the egg is fertilised by the sperm, then the pregnancy may take place. The lining of the uterus provides protection and food for the developing embryo.
      - If the egg is not fertilised about 14 days after ovulation the lining of the uterus and the egg are shed from the body in the period.
    - - In men: the main reproductive hormone is testosterone, produced by the testes and stimulates sperm production.
      - In women: the main reproductive hormone is oestrogen, produced by the ovaries.
        
        Once a month a surge of hormones from the pituitary gland in the brain starts egg maturation in the ovaries and stimulate the ovaries to produce hormones including oestrogen.
      - FSH (Follicle-Stimulating Hormone):
        
        produced in the pituitary gland.
        
        causes egg to mature in one of the ovaries.
        
        stimulates the ovaries to produce oestrogen.
      - Oestrogen:- produced in the ovaries.- causes the lining of the uterus to grow. - stimulates the release of LH (which causes the release of an egg) and inhibits release of FSH.
      - LH (Lusteinising Hormone):-produced by the pituitary gland. - Stimulates the release of an egg at day 14 ovulation.
      - Progesterone:
        
        Produced in the ovaries by the remains of the follicle after ovulation.
        
        Maintains the lining of the uterus.
        
        Inhibits the release of LH and FSH
  - - - Oral contraceptives (contraceptive pills) use female hormones to prevent pregnancy: is a mixed pill containing low doses of oestrogen along with some progesterone. The hormones inhibit the production and release of FSH by the pituitary gland; affecting the ovaries so no eggs mature preventing pregnancy. The pill also stops the uterus lining from developing, preventing implantation. They also produce mucus in the cervix thick to prevent sperm reaching the egg. Side effects include: raised blood pressure, head aches and nausea. Non mixed pills have fewer side effects
      - Progesterone-only pill- has fewer side effects
      - Contraceptive Patches also contain oestrogen and progesterone.
    - - Condoms are the only forms of contraception will protect against sexually transmitted diseases.
      - Spermicide can be used alone as a form of contraception or with a diaphragm, which is a shallow plastic cup that fits over the cervix to form a barrier.
  - - - Some women have low levels of FSH which means the eggs an not mature. This means no eggs are released and the women cn not get pregnant.
        The hormones of FSH and LH can be given to women as a fertility drug to stimulate ovulation.
      - Pros
        
        Allows some women to have children when they could not.
      - Cons
        
        Doesn't always work. Can be expensive.
        
        Too many eggs could be stimulated, resulting in unexpected multiple pregnancies.