Q&A - PSLE Science

[atutor2001]

Sun_2010:

.... Part of the energy is turned into heat energy when the muscles are used in exercise.....

The source of heat energy does not come from movement of the muscles alone. In fact, during the conversion from food to energy, heat is inevitably produced during the chemical reaction, regardless of whether we need it or not, that is :

food + oxygen = water + CO2 + heat + useful energy.

In cold weather, our body will convert the food into mostly heat energy to keep us warm :

food + oxygen = water + CO2 + heat + heat (useful energy)

[atutor2001]

starlight1968sg:

Another Q:
porcelain vs styrofoam.
Both are poor conductors of heat. Which one is worse?
Thanks.

Styrofoam is worse conductor of heat than porcelain. Furthermore, there are air space in styrofoam. Air is also a very poor conductor of heat.

[starlight1968sg]

atutor2001:

Styrofoam is worse conductor of heat than porcelain. Furthermore, there are air space in styrofoam. Air is also a very poor conductor of heat.

Thanks a lot, atutor2001.

[atutor2001]

Hi starlight1968sg, you are most welcome.

[starlight1968sg]

May I ask:

What are the main points to note in Plant Transport System, Human Respiratory System?
Many thanks.

[atutor2001]

starlight1968sg:

May I ask:

What are the main points to note in Plant Transport System, Human Respiratory System?
Many thanks.

I remembered this question is usually comparing the human circulatory system with the plant transport system. In this case, the following points may be useful.

Similarities :

1. Both uses tubes to transport materials.
2. Both transport water and nutrients/food.

Differences :

1. Plants' systems have 2 types of tubes (xylem & phloem) while humans only have 1 type of tube (blood vessels).
2. Humans' systems need a pump while plants do not.
3. Humans' systems transport oxygen & carbon dioxide but plants do not



If we are talking of human respiratory system alone, then the following point may be of help :

1. Function : It enable gaseous exchange to take place, replacing carbon dioxide in the blood with oxygen.
2. Parts : nostril, windpipe, lungs
3. The nostril helps to moisturize and warm the air and has hairs to trap dust.
4. Exhaled air still contain oxygen (many kids thought that there is no oxygen in the exhaled air) though its % is lower than inhaled air
5. Lung has no muscles, it depends on the movement of the diaphragm to expand and contract.
6. During inhalation, the diaphragm contracts. During exhalation, the diaphragm relaxes.
7. Lungs are made of many tiny air sacs.
8. The surfaces of the air sacs are covered with tiny blood vessels called capillaries where gaseous exchange takes place.
9. The lungs are made of many tiny air sacs so as to increase the total surface area. With greater surface area, it can accommodate more capillaries to carry out gaseous exchange.

Sorry, that's all that I can remember. Hope it is useful

[starlight1968sg]

Hi atutor2001,

Thanks so much for sharing.
Air enters through our nose and goes into our lungs through the windpipe.
When air reaches the alveoli which are covered by the thin walled capillaries, oxygen passes through the thin walled capillaries and enters the bloodstream. This oxygenated blood then leaves the lungs and goes to the heart before it is pumped to the rest of the body.
At the same time, carbon dioxide from the blood, passes through the thin walled capillaries and reaches the alveoli. The air then is rich in carbon dioxide is exhaled out from the lungs.

Am I correct? I am unsure about the exchange of gases at the alveoli part.

Thanks.

[atutor2001]

starlight1968sg:

Hi atutor2001,

Thanks so much for sharing.
Air enters through our nose and goes into our lungs through the windpipe.
When air reaches the alveoli which are covered by the thin walled capillaries, oxygen passes through the thin walled capillaries and enters the bloodstream. This oxygenated blood then leaves the lungs and goes to the heart before it is pumped to the rest of the body.
At the same time, carbon dioxide from the blood, passes through the thin walled capillaries and reaches the alveoli. The air then is rich in carbon dioxide is exhaled out from the lungs.

Am I correct? I am unsure about the exchange of gases at the alveoli part.

Thanks.

Hi starlight1968sg

I share the same idea as you.

[starlight1968sg]

Hi,

I need some help on \"human skeleton\" in Q11 of
http://www.orlesson.org/orp/09Sc/2009-Sc-SA2-MGS.pdf.

Is the option 3 (model ans) correct?
Why?
Many thanks.

[Sonshine]

starlight1968sg:

Hi,

I need some help on \"human skeleton\" in Q11 of
http://www.orlesson.org/orp/09Sc/2009-Sc-SA2-MGS.pdf.

Is the option 3 (model ans) correct?

Many thanks.[/img]

Yes, it is no. 3.