Caffeine cause dose dependent prominent increase in force of contraction and period of contraction of muscle
<u>Explanation:</u>
Caffeine is widely used in foods and drinks. Its long time use can effect central nervous system include lethargy memory, sleep disorder and anxiety.
Increase in concentration of calcium ion will result increase number of power stroke and force for contraction. However latent period and relaxation period are unaffected by caffeine. Increase in concentration of calcium ion will result increase number of power stroke and force for contraction.
Because of calcium ion release in skeletal muscle, caffeine causes peripheral manifestation such as hyper-reflexia, muscle twitching etc.
High amount of caffeine leads to increase in release of Ca2+ from sarcoplasmic reticulum. It increases tension development in single tetanic contraction and re-initiate maximum tension in fatigue single myofibre by restoring Ca2+ release from sarcoplasmic reticulum to non-fatigued levels.
Answer:
Blood clothing is an example of positive feedback.
This type of feedback mechanism is useful to the body because it multiplies the factor that intervenes in clotting accelerating the process.
If a toxin affects the molecules that signal for platelets the feedback will not be effective enough to produce clotting and the body will keep bleeding.
Explanation:
Blood clotting is an example of positive feedback due to the fact that when the vascular endothelium is damaged platelets will go to this area and activate themselves once they are in contact with the collagen fibers of the damaged structure. When the platelets are activated they will release the contents that is stored in their granules. One of the contents is a Gq-linked protein receptor cascade, that will increase the concentration of calcium in the platelets. Calcium activates protein kinase C, which, in turn, activates phospholipase A2 (PLA2). PLA2 will modifies an integrin membrane increasing its affinity to bind fibrinogen. The activated platelets change their shape , and the fibrinogen cross-links with the integrin membrane aiding in the aggregation of adjacent platelets. After this the coagulation cascade takes place. there are two pathways the extrinsic and the extrinsic one.
The extrinsic pathway will be activated due to tissular factor released by the platelets and the intrinsic pathway will be activated due to endothelial collagen. The final product of both pathways is factor x.
Factor x will transform prothrombin into thrombin will activate the conversion of fibrinogen into fibrin. Thrombin will form a net of fibrin that will the clot.
A cascade reaction is useful because every component of the cascade are related making a quick reaction once that one of then is activated and can activate other or more factors.
If a toxin affects the molecules that signals for platelets, platelets will not go to the damaged area and in consequence there will not be thrombin and fibrin to form the clot together with platelets.
Answer:
D. Psychrophile
Explanation:
Psychrophiles or cryophiles are a type of extremophiles i.e. they live in extreme environment. They grow well in low temperatures ranging from -20 to +10 degree Celsius.
Here, the bacteria was incubated at different temperatures. It did not show growth at standard incubation temperature of 37°C which indicates that it might be an extremophile preferring either very hot or very cold environment. But it also did not show growth at 50°C which means that it does not survive well at high temperature.
Lab bench top has generally colder surface compared to the surrounding environment and a little growth was observed there which indicates that this bacteria might require cold temperature for growth. The result was finally confirmed with abundant growth observed inside refrigerator which is only possible if it is a psychrophile.
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Within a gymnosperm megasporangium, the following developmental sequences that are correct, assuming fertilization occurs is: megaspore, female gametophyte, egg cell, sporophyte embryo. The last Option (Option D) is correct.
In gymnosperm megasporangium, the meiotic division produces four haploid megaspores from a single cell, three of which generally degenerate. The female gametophyte is formed by mitosis from the surviving megaspore.
Prior to fertilization, the male mature gametophyte needs to be transferred to the female gametophyte for fertilization to take place.
When the nuclei of the sperm encounter the nucleus of the egg cell in gymnosperms, it fuses with the egg nucleus to produce a diploid zygote.
Mitosis occurs in the fertilized egg to initiate the growth of a new sporophyte generation (the multicellular embryo of the seed.)
Therefore, we can conclude that we've understood the mechanism of developmental sequence in the gymnosperm megasporangium.
Learn more about the gymnosperm here:
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