Stage 2: Sodium channels open very quickly and sodium ions diffuse into the neuron down the concentration gradient. This reduces the membrane potential and causes more sodium channels to open. The entry of positively charged sodium ions causes the inside of the neuron to develop a net positive charge compared to the outside – the potential across the membrane is reversed, aka depolarization.
Stage 3: Potassium channels open after a short delay. Potassium ions diffuse out of the neuron down the concentration gradient through the opened channels. The exit of positively charged potassium ions cause the inside of the neuron to develop a net negative charge again compared with the outside – the potential across the membrane is restored, aka repolarization.
Stage 4: Concentration gradients of sodium and potassium across the membrane are restored by the active transport of sodium ions out of the neuron and potassium ions into the neuron. This restores the resting potential and the neuron is then ready to conduct another nerve impulse. As before, sodium ions diffuse along inside the neuron from an adjacent region that has already depolarized and initiate depolarization.
Describe the principles of synaptic transmission in the nervous system:
Synaptic Transmission can be divided into 7 different stages.
Stage 1: Nerve Impulse reaches the end of the pre synaptic neuron.
Stage 2: Calcium diffuses in through the calcium channels to the synaptic knob.
Stage 3: Vesicles of neurotransmitters move to the membrane and release their content.
Stage 4: Neurotransmitters diffuse across the synaptic cleft and binds to the receptors.
Stage 5: Sodium ions enter the post-synaptic neuron and cause depolarization.
Stage 6: Nerve impulse sets off across the post synaptic neuron.
Stage 7: Calcium is pumped out of the pre-synaptic knob. Neurotransmitter is broken down in the cleft and reabsorbed into the vesicle.
Tuberculosis is a disease of the ventilation system. Explain how the white blood cells attack the pathogens:
B-cells or lymphocytes produce antibodies. The antibodies, which are proteins in the cell wall of the pathogen then recognize and bind to the specific antigen. There is then a macrophage presentation of the specific antigen. A clone is formed as the cells divide through the assist of t-helper cells. There then exists a neutralization as there is a formation of an antigen-antibody complex. Next, the phagocytes engulf and engest by endocytosis. The pathogen is killed and digested by enzymes in the lysosomes. It ends with a formation of memory cells.
Explain why carbohydrates and lipids are used as energy storage:
Lipids and carbohydrates are excellent for storing energy in living organisms. Carbohydrates are usually used to store energy in the short-term while lipids are used for the long-run.
Advantages of Lipids:
- Contain more energy per gram. Therefore lighter to store.
- Lipids are insoluble in water; do not interfere with osmosis.
Advantages of Carbohydrates:
- More easily digested, so energy is released more easily from them.
- Carbohydrates are soluble in water, so easier to transport.
Outline the four phases of mitosis:
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During , the mitotic spindle (made from ) starts growing (going from pole to pole). coil up to form distinct . (Each chromosome contains two identical sister chromatids, attached to each other at the centromere region.) The nuclear envelope starts breaks down.
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During , each chromosome attaches to two spindle microtubules (one going to each pole) at the centromere region, so that they line up at the (virtual) equator of the cell. The mitotic spindle is fully developed: some microtubules are attached to chromosomes and reach to the equator, whilst others go from pole to pole.
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During , the spindle microtubules pull the sister chromatids to opposite poles (each sister chromatid becomes one new chromosome of the daughter cell).
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During , each sister chromatid reaches its pole (becoming a chromosome). The nuclear envelope starts to reform. Spindle microtubles deteriorate. (division of the cytoplasm) takes place.