practice exam questions thread

[Smiley_]

 what would you say is the answer for

The opening of stomata is caused by the movement of water. Which statement concerning
stomata is correct?
A. Guard cells have inelastic bands running from end to end.
B. Osmosis causes water to move out of the guard cells, making them turgid.
C. The cell walls of the guard cells are thicker on the side away from the stomatal pore.
D. Osmosis occurs as a result of the movement of potassium ions into the guard cells.


thanks

[psyxwar]

the answer says c would'nt it be a?

also what would you say is the answer for

The opening of stomata is caused by the movement of water. Which statement concerning
stomata is correct?
A. Guard cells have inelastic bands running from end to end.
B. Osmosis causes water to move out of the guard cells, making them turgid.
C. The cell walls of the guard cells are thicker on the side away from the stomatal pore.
D. Osmosis occurs as a result of the movement of potassium ions into the guard cells.


thanks

D. Movement of potassium ions in = higher solute concentration inside the guard cells. Osmosis goes from low solute -> high solute, thus water flows into the guard cells, making them turgid, and causing the stomata to open.

Also nah, it's C. Only animal cells have centrioles. It isn't A because onions are underground plants; they don't have chloroplasts (they're also not green so I guess even if you didn't know that C is the better choice)

[Yacoubb]

 what would you say is the answer for

The opening of stomata is caused by the movement of water. Which statement concerning
stomata is correct?
A. Guard cells have inelastic bands running from end to end.
B. Osmosis causes water to move out of the guard cells, making them turgid.
C. The cell walls of the guard cells are thicker on the side away from the stomatal pore.
D. Osmosis occurs as a result of the movement of potassium ions into the guard cells.

Answer is D. The movement of K+ ions into the guard cells results in an imbalance in concentrations on either side of the membranes of the guard cells; thus, free water molecules will move across the semi-permeable membrane from the area of low solute concentration, to the area of high solute concentration.

And the answer for that is C. Centrioles are only present in animal cells (i.e. they wouldn't be found in onion (plant) cells). Therefore, she made the error for the centrioles being present in onion cells, and C is the answer.

[Smiley_]

in which period would carbon 14/12 dating be useful

[Yacoubb]

in which period would carbon 1/12 dating be useful

For dating fossils that are up to 60 000 years old.

[Smiley_]

how would you make a hypothesis for the correct statement ?

which one is correct
Marsupials have a single common ancestor, and monotremes have a separate
common ancestor, so that marsupials and monotremes form two distinct groups
OR//
Marsupials and monotremes all share a single common ancestor and therefore form
a single combined group

[Snorlax]

For dating fossils that are up to 60 000 years old.

Isn't it more accurate at ~12,000 years old?

[psyxwar]

Isn't it more accurate at ~12,000 years old?

Source? That's only two half lives

[Smiley_]

what if it was 25 milliion years ago ?
How do you know ?

[Snorlax]

Source? That's only two half lives

My set of notes I'v received say ~50,000 years as it has a half life of 5730 years, and then my textbook asserts that carbon dating is only accurate for samples of ~12,000 years.

[Snorlax]

what if it was 25 milliion years ago ?
How do you know ?

Long range dating? (use of Uranium-238 or Potassium-40)

[Smiley_]

how would you make a hypothesis for the correct statement ?

which one is correct
Marsupials have a single common ancestor, and monotremes have a separate
common ancestor, so that marsupials and monotremes form two distinct groups
OR//
Marsupials and monotremes all share a single common ancestor and therefore form
a single combined group

[psyxwar]

My set of notes I'v received say ~50,000 years as it has a half life of 5730 years, and then my textbook asserts that carbon dating is only accurate for samples of ~12,000 years.

Your textbook is wrong then.
Edit:

"As I understand, previously carbon decay rates had only been calibrated to around 12,000 years ago, so the new ~50,000 year old calibration provides a enormous extension to C-14 dating precision for dates older than around 10,000 years ago."

Apparently it used to be 12k or something? But yeah, defs 50k now.

[Snorlax]

Your textbook is wrong then.
Edit:

"As I understand, previously carbon decay rates had only been calibrated to around 12,000 years ago, so the new ~50,000 year old calibration provides a enormous extension to C-14 dating precision for dates older than around 10,000 years ago."

Apparently it used to be 12k or something? But yeah, defs 50k now.

Ahh, stupid Nelson.
Could you perhaps teach me about the half life? How would you conclude ~12,000 years was only 2 half lives?

[psyxwar]

Ahh, stupid Nelson.
Could you perhaps teach me about the half life? How would you conclude ~12,000 years was only 2 half lives?

Half life is the time it takes for half a population of a particular radioisotope to decay. Decay is purely a probability; the chance of one particular radioisotope decaying over a period of time equal to its half life is 50%. Therefore, some isotopes will undergo decay in this time and others won't; it's this that leads to the number of isotopes halving over a half life.

Carbon-14's half life is something like 5,700 years, meaning that over 1 half life the amount of C-14 will half, and over 2 half lives (5700*2),  it will halve again (and thus you're left with a quarter of the original population).