biology lessons 1 to 5
- Created by: Mike1234
- Created on: 09-11-15 11:21
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- communication & homeostasis lessons 1-5
- the need for communication
- a stimulus is any change in the environment that cuases a response
- a response is a change in behaviour or physiology as a aresult of the change in the environment
- cells need to communicate with each ther by a process called cell signalling
- this is whereone cell will release a chemical that is detected by another cell. the second cell will respond to the signal released by the first cell
- one of the communication system that work by cell signalling is the neuronal system, an interconnected network of neurones that signal to eachother across synapse junctions. the nerones can conduct signals and enable responses to stimuli very quickly.
- the other is the hormonal system whihch uses blood to transport its signals to be carried all over the body but hormones are only recognised by specific target cells. longer term responses
- the external environement changes. this places stress on an organism. the environmental change is the stimulus and the way in which the oraism changes its nehaviour or physiology in order to adapt to the change is the response. stimulus must be monitored.
- most multicellular organism also have an internal environment made uo of tissues etc. which re protected by epithelial tissues e.g. skin/bark. in animals the environment of the cells is tissue fluiud. cells undergo various metabolic activitieswhch can lead to an accumulation of excess toxins or waste. this acts as a stimulus for these wastes to be removed so cells can live.
- to moniter these stimuli, multicellular organism must have a good communication system including: whole body coverage, allows cell communcaition, rapid communication aswell as anabling long and short term responses
- homeostasis and negative feedback
- homeostasis is the maintenance of the internal environment in a constant state despute external changes e.g. body temp, blood pressure
- negative feedback is apricess that brings about ta reversal of any change in conditions. it ensures that an optimum stready state can be maintained as the internal environment is returned to its original set of conditons after change
- positive feedback is a process that increases any change detected by receptors. tends to be harmful. doesn't lead to homeostasis
- in homeostasis a change is detected by receptors, the communication system/ cell signalling transmits message from the receptor to the effector and, through negative feedback, the effector revereses the change
- maintaining body temp
- physiological response- the horned lizard expands it rubcage to expand its surface area to absrb more heat from the sun. locuts increase breathing wto increase rate of water losss if too hot.
- behavioural response e.g. snakes expose their body to the sun so more heat absorbed
- physiological response- the horned lizard expands it rubcage to expand its surface area to absrb more heat from the sun. locuts increase breathing wto increase rate of water losss if too hot.
- ectotherms-external sources
- endotherms= internal sources
- physiological responses e.g. sweat glands secrete sweat on to the skin when hot using heat from the blood to provide latent heat for evaporation the water evaporates, cooling the skin
- behavioural responses e.g when hot remain inactive and spread out limbs to allow more SA for heat loss
- blood temp monitored in hypothalamus
- peripheral temperature receptors monitor the extremities
- sensory receptors
- specialised cells that can detect changes in our surroundings. they are energy transducers. stimulus causes the sensory receptors to convert the energy into a form of electrical energy-a nerve impulse
- light sensitive cells in the retina detect light intensity and range of wavelength
- motor neurone has a cell body at the end with a large nucleus and lots of rough ER and Golgi bodies. they have many short dendrites that carry impulses to the cell body as well as a long axon which carries an impulse from the cell body to the effector
- the sensory neurone has: long processes on either side of cell body, a Dendron carrying nerve impulses from a receptor to the cell body and an axon carrying an impulse from the cell body to the central nervous system.
- motor neurone has a cell body at the end with a large nucleus and lots of rough ER and Golgi bodies. they have many short dendrites that carry impulses to the cell body as well as a long axon which carries an impulse from the cell body to the effector
- neuroes have specialesd channel proteins specific to sodium or potassium ions. they have a gate that can open or close the channel.
- nerve cell membranes contain carrier proteins that actively transport sodium ions out of the cell and potassium ions into the cell (Na/K pumps) inside is negatively charged. the membrane is polarised.
- a nerve impulse is created by altering the permeability of the nerve cell membrane to sodium ions. depolarisation occurs.
- a small change in potential caused by one or tow sodium ion channels opening is called a generator potential. if enough sodium ions enter the cell the potential difference changes significantly anf will iniate an action potential
- the need for communication
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