BIOLOGY 252 EXAM 1 LATEST 2025 ACCURATE SUMMER TERM EXAM GRADED A+, Exams of Biology

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Biology 252 Exam 2 2025 Complete Question And

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Describe the cells of the bone tissue

• Osteogenic cells
• Osteoblasts
• Osteocytes
• Osteoclasts What membrane lines the internal canals and the small cavities of the compact and spongy bones? Endosteum What is the periosteum composed of?
• Dense irregular connective tissue
• Collagen fibers
• Outer fibrous layer has fibroblasts
• Inner layer has progenitor cells that become osteoblasts Describe the matrix of the bone tissue
• Stony matter surrounding osteocytes and lacunae
• 1/3 organic (collagen and protein-carb complex) and 2/3 inorganic (CaK, CaCO3...)
• gives bone flexibility and strength

• Minerals resist compression
• Collagen resists tension Compare the function of the organic and the inorganic material in the bone matrix
• Inorganic (minerals) resist compression
• Organic (protein-carb complex/collagen) resists tension Why does calcification result in death of chondrocytes, while ossification does not result in death of osteocytes? Chondroblasts are surrounded by cartilage matrix and receive oxygen and nutrients by diffusion through the matrix. When the matrix becomes calcified, diffusion is reduced the the point that the cells die. When osteoblasts form bone matrix, they connect to one another by their cell processes. Thus, when the matrix is laid down, canaliculi are formed. Even though the ossified bone matrix is dense and prevents significant diffusion, the osteocytes can receive gases and nutrients through the canaliculi or by movement form one osteocyte to another. Describe the process of endochondral ossification.

1. Hyaline cartilage is covered with fibrous perichondrium
2. In middle of cartilage (primary oss. center), chondrocytes die, and the thin wall calcify. Perichondrium cells become osteoblasts and form bony collar-periosteum.
3. Blood vessels grow into primary oss. center. Osteoclasts come and hollow out calcified center (primary marrow cavity). Osteoblasts come and deposit bone, thickening shaft. Second oss. center develops at ends of bone.
4. Second oss. center hollows out secondary marrow cavity. Dividing line is formed-metaphysis.
5. Epiphyseal plate surrounding by metaphysis exists; enables bones to grow in length and width.
6. No more cartilage=no more room to grow; only cartilage is articular cartilage, which needs to stay mushy

In Rickets the long bones become abnormally long. Why? Epiphyseal plates cannot be calcified, therefore they continue to widen and causes the ends of long bones to become abnormally long and enlarged Which of the following is correct? a. Calcified cartilage is the major component of the bone tissue b. The chondrocyets are responsible for calcification of the cartilage matrix c. The epiphyseal plate marks the primary ossification center d. During bone growth the diaphysis does not grow in length The cell responsible for secreting the matrix of bone is the. Osteoblast True or False: An osteon contains osteocytes, lamellae, and a central canal, and is found in compact bone only True In bone formation, a deficiency of growth hormone will cause a. inadequate calcification of bone b. decreased osteoclast activity c. decreased proliferation of the epiphyseal plate cartilage d. increased osteoclast activity

The structural unit of compact bone is osteon In the epiphyseal plate, cartilage grows by pushing the epiphysis away from the diaphysis Chondrocytes

• Cartilage cells
• Secrete matrix and are surrounded by it until they are trapped in lacunae
• Avascular; nutrition and waste removal depend on diffusion
• Low rates of metabolism and division (injured heals slowly)
• Differences in fibers-different classifications (hyaline, elastic, fibrocartilage) Tension Collagen fibers provide resistance to longitudinal tensile (pulliing) forces Compression Minerals provide resistance against this; without minerals, bones would be rubbery Torsion Collagen fibers in adjacent lamalae run in opposite directions

Osteon Repetitive unit that forms compact bone Osteoblast

• Synthesize the organic matter of bone and deposit matrix
• Lots of mitochondria and ER Osteoclast
• Bone-dissolving cells
• Really big, lots of nuclei, bone surface location
• Secretes HCl and enzymes to dissolve tissue Osteocyte
• Former osteoblasts that have become trapped in matrix
• Reside in lacunae
• Connected by canaliculi
• Pass nutrients, wastes, and chemical signals to each other through gap junctions Articular cartilage
• Thin layer of hyaline cartilage that cover the ends where two bones meet
• Eases joint movements

Calcification Also called mineralization: the process of deposition of mineral salts such as calcium and magnesium phosphates into a tissue. (Book 2, Chapter 4) PTH

• Secreted by parathyroid glands
• Respond to a drop in blood calcium by secreting this
• Stimulates osteoclast activity, calcium reabsorption by kidney, and promotes calcitriol synthesis Calcitonin
• Secreted by thyroid gland
• Response to high calcium level
• Promotes deposition of excess calcium into skeleton
• Important role for children and pregnant women` Calcium
• Deficiency (Hypocalcemia)- muscle tremors to tetanus
• Excess (hypercalcemia) depresses nervous, muscular, and cardiac function Osteoporosis
• Loss of bone tissue (porous and brittle bones)
• Aging, menopausal women, astronauts
• Fractures are common

• ACh diffuses across the cleft and binds to ACh receptors in the sarcolemma. Each receptor is a gated channel that opens in response to ACh, letting sodium quickly diffuse into the muscle fiber and K diffuses out
• Na and K diffusion excites sarcolemma and starts action potentials that spread out in all directions away from neuromuscular junction and pass down into the T tubules Describe in detail the events taking place from the moment action potential is generated in the sarcolemma until thin filaments start to slide past the thick ones.
• Excitation of T tubule opens up Ca channels in terminal cisternae of SR. Calcium escapes SR and flood cytosol of muscle fiber
• Ca binds to troponin of thin filaments of sarcomeres
• Tropomyosin moves out of the way of the active sites on actin of thin filaments. Muscle contraction can begin Muscle contraction
• Each myosin head binds an ATP molecule and splits it into ADP and a phosphate group. The head moves from a bent elbow shape to an extended, high energy position
• Cocked myosin binds to active site on thin filament (link is a cross bridge)
• Myosin releases ADP and P and goes back to low energy position, tugging the thin filament with it (power stroke). THe head remains bound to actin until it binds to a new ATP
• Upon binding more ATP, the myosin head releases the actin. Rigor mortis defines the state of the skeletal muscles after death. A few hours after death skeletal muscles become rigid and stiff. How do you explain that at the molecular level (at the level of thin and thick filaments)?
• SR deteriorates after death, releasing calcium into the cytosol. Ca also leaks into cell from ECF. Ca ions activate myosiin-actin cross bridging. Once bound to actin, myosin cannot release it

without ATP. Thus, the thick and thin filaments remain rigidly cross linked until the myofilaments begin to decay. During squats we are performing both types of isotonic contractions (shortening and lengthening), as well as isometric contractions. By doing a few squats, check when each contraction is taking place in your quadriceps.

• Downward phase (quadriceps work eccentrically at the knee-lengthens=isotonic)
• Upward phase (concentric=shortens; muscles of trunk do isometric)
• Holding squat is isometric What is the major function of myoglobin?
• Supplements hemoglobin in providing oxygen for aerobic muscle metabolism (first source of oxygen
• makes muscles red What ultimately stops muscle stimulation when the motor neuron ceases firing? The ultimate switch is the enzyme acetylcholinesterase. When the neuron stops releasing ACh, the muscle would not stop contracting if the acetylcholinesterase did not split the ACh into its two components, acetyl and choline, making them release their binding sites How does a muscle respond to increasingly stronger stimuli?
• recruitment of multiple motor units
• recruitment of larger motor units with more muscle fibers per motor neuron

Sarcolemma The plasma membrane of a muscle fiber T-tubules Tunnel like infoldings of the sarcolemma that penetrate through the fiber and emerge on the other side; carries electrical current from the surface of the cell to the interior when the cell is stimulated Myofibril Thick bundles of contractile proteins that make up one muscle fiber Z-line A plaque of protein that provides anchorage for thin filaments; bisects I band sarcomere the distance between 2 z discs. functional unit of muscle fiber. sarcomeres shorten and cause contraction Actin Compose thin filaments;

Myosin compose thick filaments; I band Only thin filaments H band Only thick filaments A band Thick and thin filaments Tropomyosin Lines of protein that covers actin; is removed when troponin comes off Troponin Calcium receptors on thin filaments Neuromuscular junction/Motor end plate The point where the end of a nerve fiber meets a skeletal muscle fiber

A somatic motor neuron and all the skeletal muscle fibers it innervates Isometric contraction muscles contract, but no length change or movement

• Sarcomeres shorten, but muscle fibers don't
• Increased elasticity of tendon
• works resistance harder Isotonic contraction
• Muscle changes length
• Shorten (concentric)
• Lengthen (eccentric) Twitch
• The response of a motor unit to a single action potential
• Twitch lengths correspond to organ (eye fast; heart and calf slow) How are the amino acid-based and the steroid hormones different from each other (e.g. chemical properties; transport in the blood; interactions with target cells)? Amino (water soluble, short duration, act via second messengers, membrane bound receptors) Steroid (lipid soluble, attached to proteins so longer effect, intracellular receptors)

I gave one example of a second messenger. Try to find another example. How is the latter regulated by hormones? cGMP; Hormones bind to surface receptors and activate intracellular processes, working through secondary messengers What are the interactions between the hypothalamus and the posterior pituitary gland? How is the "message" transmitted?

• Posterior pituitary is extension of hypothalamus
• Terminals of axons
• Neurohormones made in hypothalamus and stored in posterior pituitary
• Action potentials trigger release of hormones What are the interactions between the hypothalamus and the anterior pituitary gland? How is the "message" transmitted?
• Hypothalamus controls synthesis and secretion of hormones in the anterior pituitary
• Hypophyseal portal system
• Hormones secreted by hypothalamus influence secretion of anterior pituitary hormones Surgical removal of the posterior pituitary gland in experimental animals results in marked symptoms, but the symptoms associated with hormone shortage are temporary. Explain these results. Because the hypothalamus is the actually synthesizer of the hormones, the hormones will still be produced, but probably not as effectively secreted and regulated as normal Mr. Hoops has a son who wants to be a basketball player almost as much as Mr. Hoops wants him to be one. He knows a little bit about growth hormone and asks his son's doctor if she

The secretion of a hormone counteracts a change in a regulated variable. The body senses a change in a variable, an endocrine gland responds by altering the rate of hormone secretion, and target cells respond in a way that will ultimately bring the variable back to its original state. How do glucagon and insulin antagonize each other? (study picture) When one is high, the other is low. Insulin promotes storage of glucose, so glucose levels are low; Glucagon promotes release of glucose, so insulin is low A person with a hypoglycemia will secrete which hormones? Insulin Insulin secretion is increased in response to Parasympathetic stimulation because of rest and digest As blood calcium levels increase, calcitonin levels increase Epinephrine causes the liver to change glycogen into glucose True The endocrine gland that is probably malfunctioning if a person has a high metabolic rate is the parathyroid.

False Growth hormone always exerts its influence by targeting other endocrine glands to produce hormones False Gluconeogenesis occurs in the liver due to the action of Cortisol While taking cortisol as a dietary supplement by healthy people might have negative consequences, cortisol can help people who suffer from Multiple sclerosis Several hormones are synthesized in the hypothalamus and transported to the anterior pituitary gland. The mechanism of transportation from hypothalamus to anterior pituitary gland is through the hypophyseal portal system Hormones often cause a cell to elicit multiple responses; this is because during cellular enzymes activation, enzymes phosphorylate many other enzymes The most important regulator of electrolyte concentrations in extracellular fluids is