Why offspring produced by the same parents are different in appearance. The importance of hydrogen bonds in living organisms The movement of substances within living organisms How the structure of proteins is related to their functions The process of osmosis and its importance to living organisms Energy transfers which take place inside living organisms Inorganic ions include those of sodium, phosphorus and hydrogen.
Describe how these and other inorganic ions are used in living organisms. Follow 3 And you could try and order this book because I reckon it would help you in terms of structuirng essays and it gives 20 examples written out: Follow 4 Follow 5 Original post by artyfroggy And you could try and order this book because I reckon it would help you in terms of structuirng essays and it gives 20 examples written out: Follow 6 Follow 7 Churchgirl Follow 1 follower 0 badges Send a private message to Churchgirl.
Follow 8 I wanted that book but it was out of stock. This has me worried! Follow 9 Follow 10 Does anyone have any ideas for the hydrogen bonding one?
Are there any more? Follow 11 Follow 12 Original post by goosegooseholly Hi!! I just came across a website that may help!! There is a lot to read on there, but I found it useful!! There are lots 20!! Hopefully you get a chance to read some and look at the structure of these essays as exemplars!!
Even if it is only a quick 5 minute plan, do one!! Control in Cells and In Organisms This forum is supported by: GF never initiates sex. News and current affairs Replies: Advice on everyday issues Replies: The responses due to secretion of hormones often act over a longer period of time, yet are slower to act. Chemical mediators Nervous and hormonal forms of communication are only useful at coordinating the activities of the whole organism. At the cellular level they are complimented by chemical mediators.
Chemical mediators are secreted by individual cells and affect other cells in the immediate vicinity. A common example of this type of coordination is the inflammation of certain tissues when they are damaged or exposed to foreign agents. Two examples of chemical mediators are: Histamine — Stored in white blood cells and is secreted due to the presence of antigens.
Histamine causes dilation of blood vessels, increased permeability of capillaries and therefore swelling the infected area. Prostaglandins — Found in cell membranes and cause dilation of small arteries and arterioles. They release due to injuries and increase the permeability of capillaries.
They also affect blood pressure and neurotransmitters. In doing so they relieve pain. Hormonal system Nervous system Communication by chemicals Communication by nervous impulses. IAA is used to ensure that plant shoots grow towards a light source. Cells in the tip of the shoot produce IAA, which is then transported down the shoot. The IAA is initial transported to all sides as it begins to move down the shoot 3.
Light causes the movement of IAA from the light side to the shaded side of the shoot. A greater concentration of IAA builds up on the shaded side of the shoot 5. The cells on the shaded side elongate more due to the higher concentration of IAA 6. The shaded side of the root therefore grows faster, causing the shoot to bend towards the source of light IAA can also effect the bending of roots towards gravity. However in this case it slows down growth rather than speeds it up.
IAA decreases root growth and increases shoot growth Section Can remove cell debris and are associated with nerve regeneration. A nerve impulse is not an electrical current! It is a self-propagating wave of electrical disturbance that travels along the surface of an axon membrane.
Nerve impulse — temporary reversal of the electrical p. This is called the sodium potassium pump. Sodium being positively charged causes the axon to become more positive in charge. The myelin sheath — Prevents the action potential forming in myelinated areas of the axon.
The action potential jumps from one node of Ranvier to another salutatory conduction — this increases the speed of the impulse as less action potentials need to occur 2.
The greater the diameter of the axon the greater the speed of conductance — due to less leakage of ions from the axon 3. Temperature — Higher temperature, faster nerve impulse. Energy for active transport comes from respiration. Respiration like the sodium potassium pump is controlled by enzymes.
Refractory period After an action potential, sodium voltage-gated channels are closed and sodium cannot move into the axon. It is therefore impossible during this time for a further action potential to be generated.
This time period, called the refractory period serves two purposes: It ensures that an action potential can only be propagated in one direction — An action potential can only move from an active region to a resting region.
It produces discrete impulses — A new action potential cannot be generated directly after the first. It ensures action potentials are separated from one another.
It limits the number of action potentials — action potentials are separated from one another, therefore there is a limited amount that can pass along a neuron in a given time. All or nothing principle Nervous impulses are all or nothing responses.
A stimulus must exceed a certain threshold value to trigger an action potential A stimulus that exceeds the threshold value by a significant amount, will produce the same strength of action potential as if it has only just overcome the threshold value A stimulus can therefore only produce one action potential An organism can perceive different types of stimulus in two ways: The number of impulses in a given time larger stimulus, more impulses per second Having neurons with different threshold values — depending on which neurons are sending impulses, and how frequently impulses are sent, the brain can interpret the strength of the stimulus Section This means that several responses can be combined to give on single response Neurotransmitters are made in the presynaptic cleft only When an action potential reaches the presynaptic knob, it causes vesicles containing the neurotransmitter to fuse with the presynaptic membrane The neurotransmitter will the diffuse across the synaptic cleft The neurotransmitter then bind with receptors on the postsynaptic membrane, in doing so generating a new action potential in the postsynaptic neuron Features of synapses Unidirectionality.
Eventually the neurotransmitter will accumulate so as to overcome the threshold value of the postsynaptic membrane. Therefore generating a new action potential Inhibition Some postsynaptic membranes have protein channels that can allow chloride ions to diffuse into the axon making it more negative than usual at resting potential. This type of hyperpolarisation inhibits the postsynaptic neuron from generating a new action potential.
The importance of these inhibitory synapses is that it allows for nervous impulses to be controlled and stopped if necessary Transmission across a synapse When the neurotransmitter across a synapse is the chemical acetylcholine it is called a cholinergic synapse Acetylcholine is made up of acetyl ethanoic acid and choline Cholinergic synapses are more common in vertebrates Cholinergic synapses occur in the central nervous system and at neuromuscular junctions 1.
When an action potential reaches the presynaptic knob, calcium channels open allow calcium to diffuse into the presynaptic knob 2. The influx of calcium ions causes presynaptic vesciles containing acetylcholine to fuse with the presynaptic membrane, releasing the neurotransmitter into the synaptic cleft 3. Acetylcholine diffuses across the cleft and fuses with receptor sites on sodium channels found on the presynaptic membrane.
When they do so, the sodium channels open, allowing sodium ions to diffuse along their concentration gradient into the postsynaptic knob.
The influx of sodium ions, generates a new action potential in the postsynaptic neuron 5. Acetylcholinesterase hydrolyses acetylcholine back into the acetyl and choline which will the diffuse back across the synaptic cleft into the presynaptic neuron. In this way acetylcholine can be recycles and reused and also is prevented from continuously generating new action potentials on the postsynaptic neuron.
ATP is released by mitochondria, providing energy to recombine acetyl and choline. Sodium channels on the postsynaptic membrane are now closed due to the absence of acetylcholine attached to receptor sites. Cardiac muscle which is found only in the heart Smooth muscle which is found in the walls of blood vessels Skeletal muscle which is attached to bone and is the only type of muscle under conscious control Muscles are made up of many muscle fibres called myofibrils.
If the cells of muscles were joined together from the end of one cell to another, the point between cells would be a point of weakness Because of this, the muscle cells are fused together into muscle fibres Cells of the same myofibrils share the same nuclei as well as cytoplasm sarcosplasm. Within the sacroplasm are many mitochondria as well as endoplasmic reticulum Microscopic structure of skeletal muscle Myofibrils are made up of two types of protein filament Actin — thinner, consists of two strands twisted around each other Myosin — thicker and is made up of long rod shaped fibres with bulbous heads projecting outwards Myofibrils have coloured bands.
The isotropic I bands appears lighter since it consists only of actin no overlap The anisotropic A bands are darker since this is where acting and myosin overlap The H zone is the region in the centre of the sarcomere that is lighter in colour since there is only myosin The z line lies at the centre of the I bands Types of muscle fibre Slow-twitch fibres — Contract more slowly, less powerful.
Large store of myoglobin, Supply of glycogen, Rich supply of blood vessels, Numerous mitochondria Fast-twitch — Contracts more rapidly with more power but only for a short period of time. Adapted for intense exercise by:. Having hicker and more numerous myosin filaments, having a high concentration of enzymes used for anaerobic respiration, a large store of phosphocreatine to provide phosphate to make ATP Neuromuscular junctions Many neuromuscular junctions are spread through the muscle for simultaneous contraction Each muscle fibre has one motor neuron associated with it.
The muscle fibre and the neuron make up one motor unit When only a small force is needed only a few motor units are stimulated When a nerve impulse reaches the neuromuscular junction, the synaptic vesicles join with the presynaptic membrane and release acetylcholine which diffuses across to the postsynaptic membrane and stimulates it to allow sodium ions to enter.
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