module 5 part end of unit test

• Sodium ions are actively transported out of the axon and potassium ions are transported into the axon by an instrinsic protein known as the sodium potassium pump. Their movement is not equal. Every 3 sodium ions that are pumped out, two potassium ions are pumped in.
• As a result there are more sodium ions outside the membrane than inside the axon cytoplasm, whereas there are more potassium ios inside the cytoplasm than outside the axon. Therfore sodium ions diffuse back into the axon down an elctrochemical gradient, where as potassium ions diffuse out of the axon.
• Most of the gated sodium ion channels are closed , preventing the movement of sodium ions, whereas many potassium ions are open allowing potassium ions to diffuse out of the axon. Therefore there are more positively charged ions outside the axon than inside the cell. Creating a resting potential across the membrane of -70mV.

• Energy to the stimulus triggers some sodium voltage gated channels to open, making the membrane more permeable. Sodium ions diffuse into the axon, down an electrochemical gradient, inside of the neurone is then less negative.
• change in charge causes more sodium ion channels to open, allowing more sodium ions in - postitive feedback
• When potential reaches +40mV voltage gated sodium channels close and voltage gated potassium ion channels open.
• Potassium ions diffuse out of the axon down an electrochemical gradient, reducing the charge, resulting in the inside becoming more negative than the outside.
• The voltage gated potassium channels now close. Sodium potassium pump causes sodium ions to move out of the cell and potassium ions to move into the cell.
• Goes back to resting potential 

• axon membrane is polarised, more positive on the outside and negative in the inside.
• Stimulus causes the sudden influx of sodium ions and hence a reversal of charge on the axon membrane. Action potential and the membrane is depolarised.
• Localised electrical circuits established by the influx of sodium ions cause the opening of sodium voltage gated channels a little further along the axon. Behind the new region of depolarisation the sodium voltage gated channels close and the potassium ones open, potassium leaves the axon along electrochemical gradient
• Action potential is propogated in the same way further along the axon. Outward movement of potassium has continued to the extent that the axon membrane behind the action potential has returned to its original charged state, repolarised

Cerebrum - controls voluntary actions, such as learning, memory, personality and concious thought. Highly convoluted, increasing surface area so more complex. Split into left and right and controls opposite sides of the body. Each sensory area in cerebral hemispheres recieve information from receptor cells, info is then passed on to association areas to be analysed and acted upon.

Cerebellum - concerned with muscular movement, body posture and balance, coordinates movement. Recieves info from organs of balance in the ears and information about the tone of muscles and tendons, then relays info to cerebal cortex.

Medulla oblongata - Regulatory centres of the autonomic nervous system. Controlling reflex activities, such as ventillation and heart rate.

Hypothamulus - Main controlling region for the autonomic nervous system, centre for symapthetic and one centre for parasympathetic system. Controls comple patterns of behaviour like feeding sleeping and agression. Monitoring composition of blood plasma and producing hormones.

Pituitary gland - controls glands in the body. Anterior - produces six hormones. Posterior - stores and releases hormones 

• auxins - control cell elongation, prevent leaf fall, maintain apical dominance, involved in tropisms, stimulate the release of ethene, involved in fruit ripening
• gibberellin - cause stem elongation, trigger the mobilisation of food stores in a seed at germination, stimulate pollen tube growth in fertilisation
• ethene - causes fruit ripening, promotes abscission in deciduous trees
• ABA - maintains dormancy of seeds and buds, stimulates cold protective responses, for example antifreeze production, stimulates stomatal closing

Scientists are still unsure about the details of many plant responses. Plant hormones work at very low concentrations so isolating them and measuring changes in concentrations is hard. The multiple interactions between the different chemical control systems also make it difficult for researchers to isolate the role of a single chemical in a specific response.

Seed Germination:

Seed absorbs water and embryo is activated, and begins to produce giberellins. They stimulste the production of enzymes that break down food stores found in the seed. Embryo used food stores to produce ATP for building materials so it can grow and break out through seed coat. Gibberellins switch on genes that code for amylases and proteases - digestive enzymes required for germination

Experimental evidence supporting role of gibberellins in germination:

• Mutant varieties of seeds have been bred that lack the gene enablling them to make gibberellins, so they do not germinate
• gibberellin biosynthesis inhibitors are applied to seeds they do not germinate as cannot make gibberellins needed for them to break dormacy.

Auxins:

• growth simulant, made at tip of roots and shoots.
• Presence of auxin means the cell wall stretches more easily.
• high concentrations of auxin suppress the growth of lateral shoots, resulting in apical dominance
• low conc of auxin promote root growth 

Gibberellins:

• important in elongation of plant stems during growth
• affect the length of the internodes - regions between leaves on a stem

Falling levels of light levels result in falling concentrations of auxin. Leaves respond to falling auxin concentrations by producing the gaseous plant hormone ethene. Base of the leaf stalk is a region called absicisson zone , made up of 2 layers of cells sensitive to ethene. Ethene seems to initiate gene switching in these cells resulting in the production of new enzymes. These digest and weaken the cell walls in the outer layer of the abscission zone, known as the separation layer. This layer forms a protective scar when the leaves fall, preventing the entry of pathogens. Cells deep in the separation zone respond to hormonal cues by retaining water and swelling, putting more strain on the already weakened outer layer. 

Cytoplasm of plant cells and sap contain solutes which lower the freezing point. Some plants produce sugar, polysaccharides, amino acids and even proteins which act as antifreeze to prevent the cytoplasm from freezing.

Stomata opens to cool plants as water evaporates from cells, or to close stomata to prevent water loss. This is largely under the control of the hormone ABA, causing stomatal closure.

Physical:

Thorns, spikes, spiny leaves, fibrous and inedible tissue, hairy leaves and stings.

Chemical:

• Tannins - can make up to 50% of dry weight in leaves. They have a bitter taste, and toxic to insects - they bind to digestive enzymes produced in saliva and inactivate them. rich in Wine
• Alkaloids - Bitter tasting, nitrogenous compounds found in many plants. Act like drugs affecting metabolism of animals and poison them. Include caffeine, which is toxic to fungi and insects.
• Terpenoids - often form essential oils but also act as toxins to insects and fungi that attack the plant. Pyrethrin acts as insect neurotoxin, interferring with nervous system. Some act as insect repellents.