biology 2

responding to change;

• the nervous system has receptors to detect stimuli.
• the receptors are found in sense organs, the eye, ear, nose, tongue and the skin.
• light simulates the eye and electrical impulses then pass to the brain along neurones (nerve cells).
• other stimuli include sound chemicals, temp change, tough or pain.
• the brain coordinates responses to many stimuli.
• the brain and spinal hord form the centeral nervous system (CNS) 
• nerves contain nurones:
• sensory neurones carry impuleses from receptors to the CNS.
• Motor neurones carry impulses from the CNS to the effector organs which may be muscles or glands.

reflex actions:

the main steps are:

•  receptor detects a stimulus (e.g a sharp pain).
• a sensory nurone transmits the impulse to the CNS.
• a relay nurone passes the impulse on.
•  a motor nurone is stimulated.
• the impulse passes to an effector (muscle or gland)
• action is taken (the response) 
• the gaps between the nurones are called synapses.
• THIS IS CALLED THE REFLEX ARC

hormones and the menstral cycle

• FSH is made in the pituitary gland- this makes the egg mature.
• oestrogen is produced by the ovaries and stops any more FSH being made.
• this stimulates LH to be made and stimulates the womb linng. LH releases the egg.

the artificial control of fertility:

• the contraceptive pill (oral contraceptive) may conatin oestrogen and progesterone. some pills are progesterone only pills and have fewer side effects.
• these pills stop the production of FSH so no eggs are matured.
• if a woman cannot produce mature eggs FSH and LH can be given. ths is known as fertility treatment. the FSH causes the egg to mature and LH releases it.

controling conditions

• the body controls its internal enviroment. internal condition that include: water content, ion content, temprature and blood sugar level. 
• water leaves the body as we breath, sweat and pee.  we loose ions in our sweat and the urine.
• the level if sugar in our bodies is contolled by the pancreas.

hormones nad the conrol of plan growth;

• plants are sensitive to gravity, light and moisture.
• plants shoot towards light (phototropism)
• roots grow towards gravity (gravitropism)
• roots also grow towards water.
• auxin is a hormone that controls phototropism and gravitropism.
• un equal auxin can cause un equal growth and bending stems.

using hormones;

• plant hormones can be used by gardeners and farmers on their crop.
• weed killers are used to kill unwanted plants.
• when cuttings are taken from plants, hormones are used to encourage roots to grow before the cutting is planted.
• some hormones are used to encourage fruit to ripen.