Nerves and Hormones
The nervous system- allows the body to respond to changes in the environment coordinated by the Central nervous system (Brain and spine)
Reflex actions are faster responses to stimuli and involves the spine.
Receptors are groups of specialized cells that detect changes in the environment called stimuli.
They are located in sense organs:
Eye has light receptors
Ears have sound receptors and also sense position of the head
Tongue has chemical receptors which detects chemicals in food
Nose has chemical receptors which detect chemicals in the air
Skin has touch receptors and detect pressure, pain and temperature
Cells
Neurones are nerve cells, which allows electrical impulses to travel.
Sensory neurones carry signals from receptors to the spinal cord and brain
Relay neurones carry messages from one part of the CNS to the other.
Motor neurones carry signals from CNS to effectors.
Synapses are where two neurones meet.
Signals cross this gap using chemicals, one neurons releases the chemical in the gap and it diffuses and the next neurone transmit and electrical signal.
Reflex actions
When a receptor is stimulated it sends a signal to the central nervous system where the brain coordinates the response. But in a reflex action, it does not involve the brain.
Stimulus > receptor > sensory neurone > relay neurone > motor neurone > effector.
An effector produces the response e.g muscles, glands.
Reflex actions are rapid and does not require us to think.
Control in the human body
Hormones are chemical substances that regulate processes in the body.
They are secreted by glands and travel through the bloodstream to their targeted organ.
Control of internal conditions-
Homeostasis is the maintenance of a constant internal environment.
Water in the body has to be controlled to protect cells from either too much water entering or leaving.
Water is lost through breathing, sweating and urine.
Hypothalamus in our brain detects water in blood, they make the pituitary gland to release more or less ADH depending on the water level in our blood. We produce More ADH if we have too little water in our blood. ADH reduces kidney blood water levels so we excrete less water in our urine ( more concentrated urine).
Salt content is also controlled to protect cells from having too much water entering or leaving them, we lose ions through sweat and urine.
Blood sugar levels is controlled, to provide cells with a constant supply of energy. It is controlled by insulin and the release and storage of glucose is controlled.
Thyroid gland produces thyroxine - controls rate of metabolism
Adrenal gland produces adrenaline - prepares for rapid activity increases heart rate and level of sugar in the blood
Pancreas produces insulin which controls blood sugar level.
Testes produces testosterone which causes the changes at puberty and stimulates sperm production
Ovary produces oestrogen which causes changes at puberty and controls the menstrual cycle.
Menstrual cycle
Monthly recurring process which the lining of the uterus is prepared for pregnancy. if pregnancy does not happen, the lining is shed at menstruation.
FSH produced in the pituitary gland and causes an egg to mature + stimulates the ovaries to release oestrogen.
Oestrogen is secreted by the ovaries. Stops FSH being produced and stimulates the pituitary gland to release LH which triggers ovulation ( release of egg)
Day 1-4 Menstruation
4- 14 Lining of uterus builds up
Day 14 egg released
14-28 lining maintained
Contraceptives
The pill (oral contraceptive) reduces the chance of mature eggs being produced, it contains oestrogen or progesterone and inhibits the production of FSH.
+
Allows couples to choose time to start a family
-
Side effects include changes in wright, mood and blood pressure, Progesterone has less side effects
Fertility treatments
Helps women becoming pregnant, fertility drugs contain FSH and LH
It does not always work and multiple conceptions sometimes occur ( twins/ triplets)
Increases risk in pregnancy and may lead to premature babies.
In vitro fertilisation
Egg is fertilised outside the womb and planted in her uterus,
ethical concerns (designer babies)
Control in Plants
Tropism is growth in response to a stimulus
Auxin is a plant hormone produced in stem tips and roots and controls direction of growth.
Plant grow towards water in soil and light from the sun.
Sensitivity in plants
Positive tropism where plants grow towards stimulus
Negative tropism where plants grow away from stimulus
Phototropism- light
geotropism- gravity
Shoot- Positive phototropism/ Negative geotropism
Root- Negative phototropism/ Positive geotropism
This allows shoots to grow upwards towards the sun and roots to grow downwards towards the soil + water.
Auxins
Made at tip of roots and shoots and can diffuse to other parts of the root or shoot.
They change the rate of elongation controlling how long they become.
Cells in shoots grow more
Cells in roots grow less.
In shoots, auxin mores towards the shaded side increasing the grow on the shaded side so the plant bends towards the lighter side.
In roots, Auxin moves to the shaded side but it slows down grown so it grows towards the shaded side.
Geotropism
In shoots, bottom side has more auxin and grows faster so the shoot bends upwards.
In roots the bottom side has more auxin and the side grows slower so it bends downwards.
Plant hormones can be used as weed killers or rooting powders
Weed killers contain growth hormones that cause weeds to grow too quickly and die, it is absorbed in larger quantities in weeds than other plants. so wanted plants stay healthy
Rooting powders contain growth hormones to make stem cuttings develop roots more quickly
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