Q: Answer the following question given this paragraph: As the membrane depolarizes, another set of ion channels called voltage-gated sodium channels are triggered to open. Sodium ions enter the muscle fiber, and an action potential rapidly spreads (or "fires") along the entire membrane to initiate excitation-contraction coupling. Things happen very quickly in the world of excitable membranes (just think about how quickly you can snap your fingers as soon as you decide to do it). Immediately following depolarization of the membrane, it repolarizes, re-establishing the negative membrane potential. Meanwhile, the ACh in the synaptic cleft is degraded by the enzyme acetylcholinesterase (AChE) so that the ACh cannot rebind to a receptor and reopen its channel, which would cause unwanted extended muscle excitation and contraction. Propagation of an action potential along the sarcolemma is the excitation portion of excitation-contraction coupling. Recall that this excitation actually triggers the release of calcium ions (Ca++) from its storage in the cell's SR. For the action potential to reach the membrane of the SR, there are periodic invaginations in the sarcolemma, called T-tubules ("T" stands for "transverse"). You will recall that the diameter of a muscle fiber can be up to 100 m, so these T-tubules ensure that the membrane can get close to the SR in the sarcoplasm. The arrangement of a T-tubule with the membranes of SR on either side is called a triad (Figure 10.7). The triad surrounds the cylindrical structure called a myofibril, which contains actin and myosin. Q: What is the arrangement of a t-tubule with the membranes of sr on either side called? A:

OPTIONS:
- aracnid
- orchid
- acid
- triad

A: triad

input: OPTIONS:
- veins
- arteries
- valves
- capillaries Now, answer this question: Answer the following question given this paragraph: Q: What are microscopic vessels with very thin, porous walls? A:
A:
output: capillaries

Answer the following question given this paragraph: 22.10 Protozoa As heterotrophs, protozoa scavenge materials from their surroundings. Others are predators which actively hunt or ambush small organisms such as bacteria and other protozoa for a source of nutrition. Protozoa can be parasitic as well; they may live inside larger organisms, like humans. Most protozoa live as single cells, although a few form colonies. Protozoa are generally difficult to identify due to their varied shape. They may appear as jelly-like blobs, spherical sunbursts, or a flattened leaf. Tiny blood parasites may be only 2 m long. On the other hand, shell-covered marine may be 5 cm or more in diameter. Furthermore, different protozoans have their own complex life cycles. The complexity has led certain organisms to be mistakenly classified for other species. Nevertheless, protozoa can move, and so, they are classified based on their methods of locomotion. Characteristics of Protozoa : About 30,000 species known About 10,000 species are pathogenic, including some of the worst human diseases heterotrophic highly variable in form and life cycle. Q: Protozoa are generally difficult to identify due to what? A:

OPTIONS:
- their hidden shape
- their resting shape
- their formation shape
- their varied shape

Answer: their varied shape

Problem: OPTIONS:
- contaminants
- crystals
- plasma
- chemicals
Q: Answer the following question given this paragraph: The liver, gallbladder, and pancreas contribute chemicals that aid in digestion. Q: What do the liver, gallbladder, and pancreas contribute that aid in digestion? A:
Answer: chemicals

Problem:OPTIONS:
- uterus
- embryo
- appendix
- placenta

Answer the following question given this paragraph: The placenta is a temporary organ that begins to form from the trophoblast layer of cells shortly after implantation. (For an animation showing how the placenta forms, go to link below. ) The placenta continues to develop and grow to meet the needs of the growing fetus. A fully developed placenta, like the one in Figure above , is made up of a large mass of blood vessels from both the mother and fetus. The maternal and fetal vessels are close together but separated by tiny spaces. This allows the mother's and fetus's blood to exchange substances across their capillary walls without the blood actually mixing. Q: What is the name of the temporary organ that begins to form from the trophoblast layer of cells shortly after implantation? A:
****
A: placenta

Problem:OPTIONS:
- digestion muscle fibers
- coronary muscle fibers
- capillaries
- skeletal muscle fibers

Answer the following question given this paragraph: Q: Slow-twitch or fast-twitch and oxidative or glycolytic describe what type of fibers? A:
****
A:
skeletal muscle fibers