Lower Secondary Science

[Dr.033430Daniel]

Answers in italics.....

Verysuperkiasu:

Which of the following statements is true?

A)Bacteria cannot form spores
B) Fungi can only reproduce sexually.
C) All viruses have the same capsid symmetry.
D) Protocists like Amoeba and Paramecium are motile.

Answer : D. Why?

Saying they are motile is just a fancy way of saying they can move around. Both Amoeba and paramecium live in water and swim around.

2) Object X has a melting point of 150 deg C and a boiling point of 350 deg C. In which of the following conditions does object X have the lowest density?
A) Object X at 0 deg C C) Object X at 350 deg C
B) Object X at 349 deg C D) Object X at 351 deg C

Ans : D. Why?

D would be a gas and the gas state has lower density than liquid or solid. Just as steam is less dense than liquid water.

3)Why do telephone wires in some countries snap on very cold nights?
A) The telephone wires expand when temp is low.
B) The wires were not given enough slack when they were first installed?
C) The wires were given too much slack when they were first installed?
D) The wires reached their melting point on cold nights.

Ans: B. I can understand B if they mention wires snap on hot days, but on cold nights, shouldn't wires contract? If so, why should they snap on cold nights?

B seems OK - by slack they mean extra length. If the wire contracts and there is no extra length it snaps. There are gaps in the MRT tracks so that when it is hot and the tracks expand they have room to expand. So heat a metal and it needs room to expand, cool a metal and it needs some slack.

[Verysuperkiasu]

Dr.Daniel:

Answers in italics.....


2) Object X has a melting point of 150 deg C and a boiling point of 350 deg C. In which of the following conditions does object X have the lowest density?
A) Object X at 0 deg C C) Object X at 350 deg C
B) Object X at 349 deg C D) Object X at 351 deg C

Ans : D. Why?

D would be a gas and the gas state has lower density than liquid or solid. Just as steam is less dense than liquid water.

.[/i]

[/quote]

Thank you....Dr Daniels...

But with regards to qn 2, just wondering if C is possible. Obj X at 350 deg C is still gaseous state? Or partially liquid partially gaseous?

[Dr.033430Daniel]

Sounds like they mean to imply that 350 would be liquid boiling, like water at 100C. One could argue also that the hotter the gas the lower the density (the principle behind hot air balloons).

[Verysuperkiasu]

Dr.Daniel:

Sounds like they mean to imply that 350 would be liquid boiling, like water at 100C. One could argue also that the hotter the gas the lower the density (the principle behind hot air balloons).

thanks

[Verysuperkiasu]

Hi I'm using my mom's account to ask a question: Are algae considered plants or protoctista? I know that blue-green algae are considered monera but what about the other types of algae? Thanks in advance

[Dr.033430Daniel]

Verysuperkiasu:

Hi I'm using my mom's account to ask a question: Are algae considered plants or protoctista? I know that blue-green algae are considered monera but what about the other types of algae? Thanks in advance

Classification can be tough sometimes. The term algae refers to a wide range of organisms. I would never create a multiple choice question classifying algae as either a) plants or b) protoctists. If you got such a question though, go with protoctists. Depending on the species, I think you could argue either way for some. To give a simple answer, I think the most common ones, like green algae, red algae and euglenoids are most commonly classified as protoctists.

You can check out this link where they talk about the different kinds of protoctists. By the way \"protist\"means single cell and \"protoctist\"means single or multicellular although very simple multicellular forms (some algae are multicellular)

http://archives.microbeworld.org/microbes/protista/

[Verysuperkiasu]

Dr.Daniel:

Verysuperkiasu:

Hi I'm using my mom's account to ask a question: Are algae considered plants or protoctista? I know that blue-green algae are considered monera but what about the other types of algae? Thanks in advance

Classification can be tough sometimes. The term algae refers to a wide range of organisms. I would never create a multiple choice question classifying algae as either a) plants or b) protoctists. If you got such a question though, go with protoctists. Depending on the species, I think you could argue either way for some. To give a simple answer, I think the most common ones, like green algae, red algae and euglenoids are most commonly classified as protoctists.

You can check out this link where they talk about the different kinds of protoctists. By the way \"protist\"means single cell and \"protoctist\"means single or multicellular although very simple multicellular forms (some algae are multicellular)

http://archives.microbeworld.org/microbes/protista/

Thanks for clarifying my doubts!

[Septima]

Past year papers are better!

[Happylady]

Hi, my child requested for a experienced 1 to 1 maths & sci tutor. Please recommend. He’s in sec 1 this year. I m staying in the east.

[Verysuperkiasu]

I have a chemistry question


In another thread, someone said to get the valency of polyatomic ions, like CO3 just add up the individual valencies of its components, that is, Carbon C has a valency of +4 and each Oxyen atom has a valency of -2. Hence valency of CO3 is +4+(-6)= -2.

If I apply this principle to NO3, it can’t work. N has valency of -3. Hence NO3 will be -3+(-6)= -9! But we know valency of NO3 is -1. Can anyone explain if this is the correct way to derive valency of polyatomic ions?