Q: 12. The actual weight of a molecule of water is -

The correct answer is: $2.99\times10^{-26}\text{ kg}$ Explanation We find the mass of one water molecule by dividing the molar mass of water by Avogadro's number. Steps: Molar mass of water: $$M_{\mathrm{H_2O}}=18.01528\text{ g/mol}=0.01801528\text{ kg/mol}$$ Avogadro's number: $$N_A=6.02214076\times10^{23}\text{ mol}^{-1}$$ Mass of one molecule: $$m=\frac{M_{\mathrm{H_2O}}}{N_A}=\frac{0.01801528\text{ kg/mol}}{6.02214076\times10^{23}\text{ mol}^{-1}}=2.99\times10^{-26}\text{ kg}$$ Therefore, a single water molecule has a mass of about $2.99\times10^{-26}\text{ kg}$ (equivalently $2.99\times10^{-23}\text{ g}$). Note: If by "weight" you meant the force due to gravity on Earth, multiply by $g\approx9.81\text{ m/s}^2$ to get $W\approx2.93\times10^{-25}\text{ N}$.

Q: How many sphincter are in human body

The short answer: About a dozen major named sphincters (roughly 12), but many more if you count small/physiological and microscopic sphincters. Explanation “Sphincter” means a circular muscle that closes or opens a passage. Which structures you count depends on your definition: If you count the common, anatomically named sphincters used in clinical anatomy, you get about 12 major ones. If you also count physiological sphincters (areas of tonic muscle without a distinct ring), ureteric/vesical valves, and the countless micro‑sphincters in blood vessel beds (precapillary sphincters), the total is much larger and not a single fixed number. Commonly listed major sphincters (≈12) Orbicularis oculi (eyelid sphincter) Orbicularis oris (lip/mouth sphincter) Sphincter pupillae (iris, constricts pupil) Upper esophageal sphincter (cricopharyngeus) Lower esophageal (cardiac) sphincter (physiologic LES) Pyloric sphincter (stomach → duodenum) Sphincter of Oddi (bile/pancreatic outflow) Ileocecal valve (ileum → cecum) Internal anal sphincter (smooth muscle) External anal sphincter (skeletal muscle) Internal urethral sphincter (bladder neck, mainly smooth) External urethral sphincter (skeletal sphincter urethrae) Note: anatomists/clinicians sometimes list additional sphincteric regions (ureterovesical junction, pelvic floor muscles like puborectalis acting as a sphincteric sling, precapillary sphincters in microcirculation), so counts vary. If you want, I can: Give a diagram or map showing these sphincters, or List a longer set including physiological/microscopic sphincters and explain how each works. Which would you prefer?

Q: Q8. A SimCell with a water-permeable membrane that contains 50 dextrose molecules, 25 glucose molecules, 25 hemoglobin molecules and 900 water molecules is placed in an extracellular fluid that is one part solute to 15 parts water (its solute-to-solvent ratio is 1:15). Which of the following should happen? Q9. A SimCell has a special membrane that is permeable to alcohol but not to water. This SimCell contains 20% alcohol and 80% water and is placed in a solution containing 40% alcohol and 60% water. What will happen to the cell?

Q8: Water will flow into the SimCell (the cell is hypertonic to the outside), so the cell will swell and may burst. Q9: Alcohol will diffuse into the SimCell until alcohol concentrations equalize (reach ~40% inside); because water cannot cross, the cell will take up alcohol and increase in volume (swell), possibly rupturing if the membrane cannot stretch. Q8 — Explanation The cell contains 50 dextrose + 25 glucose + 25 hemoglobin = 100 solute molecules and 900 water molecules, so the intracellular solute-to-water ratio is $100:900 = 1:9$ (solute:water), i.e. solute fraction $= \dfrac{1}{1+9}=0.10$ (10%). The extracellular fluid has solute-to-water ratio $1:15$, solute fraction $=\dfrac{1}{1+15}=0.0625$ (6.25%). Because the inside has a higher solute concentration than the outside, the inside is hypertonic relative to the outside. With a membrane permeable to water, osmosis will move water from the extracellular solution (lower solute concentration) into the cell (higher solute concentration). That influx of water causes the cell to swell and can lead to lysis if the membrane cannot accommodate the increased volume. Q9 — Explanation Initial concentrations: inside 20% alcohol / 80% water; outside 40% alcohol / 60% water. The membrane is permeable to alcohol but impermeable to water, so: Alcohol will diffuse down its concentration gradient from outside (40%) into the cell (20%) until alcohol concentrations equalize (about 40% inside at equilibrium). Water cannot cross the membrane, so there is no compensating osmotic movement of water. As alcohol molecules enter, the total volume (and solute content) inside increases, so the cell will swell (increase in volume). If the membrane cannot expand enough, it can rupture. Note: If the membrane were freely permeable to both alcohol and water, both would redistribute and osmotic/equilibrium effects would differ; because water is blocked here, solute diffusion alone changes internal volume.

Q: What is transported in the phloem and what is the direction of transport?

Phloem transports organic solutes (mainly sugars such as sucrose, plus amino acids, hormones, RNAs and other organic molecules) and moves them from source to sink — i.e., from tissues that produce or release assimilates (usually mature leaves) to tissues that consume or store them (growing tips, roots, fruits, storage organs). Transport can be upward, downward or lateral depending on where sources and sinks are. Explanation What is transported: Primarily sugars (sucrose) produced by photosynthesis. Also amino acids, organic acids, hormones, small RNAs, proteins, some ions and sometimes pathogens (e.g., plant viruses). Direction of transport: Phloem flow is source → sink. Typical examples: leaves → roots (downward), leaves → developing fruits/flowers (upward), leaves → young growing leaves or shoot tips (upward/lateral). Because sources and sinks can change with development and season, phloem transport is effectively bidirectional at the whole-plant level (different sieve tubes can carry sap in different directions). How it works (brief—pressure-flow hypothesis): Sugars are actively loaded into sieve-element/companion-cell complexes at the source, increasing solute concentration. Water enters the phloem by osmosis from the xylem, creating high turgor pressure at the source. Sap flows down a pressure gradient toward the sink, where sugars are unloaded and used or stored, lowering solute concentration and pressure. Water returns to the xylem and circulates back to sources. This source-to-sink mechanism explains why flow direction depends on which tissues are acting as sources or sinks at a given time.

Question

12. The actual weight of a molecule of water is -

Accepted Answer

The correct answer is: $2.99	imes10^{-26}	ext{ kg}$

Explanation

We find the mass of one water molecule by dividing the molar mass of water by Avogadro's number.

Steps:

Molar mass of water: $$M_{\mathrm{H_2O}}=18.01528	ext{ g/mol}=0.01801528	ext{ kg/mol}$$
Avogadro's number: $$N_A=6.02214076	imes10^{23}	ext{ mol}^{-1}$$
Mass of one molecule: $$m=\frac{M_{\mathrm{H_2O}}}{N_A}=\frac{0.01801528	ext{ kg/mol}}{6.02214076	imes10^{23}	ext{ mol}^{-1}}=2.99	imes10^{-26}	ext{ kg}$$

Therefore, a single water molecule has a mass of about $2.99	imes10^{-26}	ext{ kg}$ (equivalently $2.99	imes10^{-23}	ext{ g}$).

Note: If by "weight" you meant the force due to gravity on Earth, multiply by $g\approx9.81	ext{ m/s}^2$ to get $W\approx2.93	imes10^{-25}	ext{ N}$.

12. The actual weight of a molecule of water is –