food_soup.jpg

GTranslate

English Chinese (Simplified) Chinese (Traditional) French German Japanese Korean Malay

Announcements

  


"Strengthening Teachers’ Professional Development
is the First Step Towards Becoming a Good School"


"加强教师专业培训是学校成为好学校的第一步"


Dr. James Li new article published at Singapore Education magazine "EduNation" issue6.




"小学科学的一些错误概念 — 光合作用 Misconceptions in Primary Level Science — Rate of Photosynthesis"

 

Dr. James Li recently published at Singapore education magazine "EduNation", you can find the details here.

 

 

小校小班是新加坡教育未来方向

 

最近GreatMinds (博思书院)校长李宏珉博士接受媒体采访针对新加坡小学教育发表了一些个人看法,引起很大反响。

请参考以下报道:

李宏珉校长采访

2012 December Holiday Program (26th – 30th Nov, 3rd – 7th Dec)

Latest Headlines

competitions

News image

Singapore Mathematical Olympiad for Primary School SMOPS    WINNERS:  Chen Le Meng (2011) National 2nd place!!!   &...

Achievement

Read more...

Achievement

  2012 Congratulations to all our students for achieving excellent PSLE results!!!   22% students scored 260 and above! 40% s...

Achievement

Read more...

Welcome to Join GreatMinds





Once your account is created,it must be activated before you can use it. To activate the account,please click on the link in your received email

Login
Register

Operating Hours

 

Wednesday – Friday (10am to 6pm)


Saturday and Sunday (9am to 6pm)

Close on Monday, Tuesday and


Chinese New Year, National Day


and Teacher's Day

________________________________

1  

 

 

2011 Time Table

                        Read More      

1

 

 

 

 

 

2010 Dec Study Camp Schedule

 

 

                        Read More      

1

 

Who's Online

We have 57 guests online
How do you like the articles?
 
Misconceptions in Primary Level Science — Rate of Photosynthesis PDF Print E-mail
Written by Administrator   
Friday, 09 August 2013 13:08

Misconceptions in Primary Level Science
— Rate of Photosynthesis
小学科学的一些错误概念 — 光合作用

 

Singapore’s Maths and Science teaching is widely
regarded to be amongst the best in the world.
Indeed, Singapore regularly ranks either at or
towards the top in international comparisons such as
the Trends in International Mathematics and Science
Study (TIMSS) which looks at student performance from
Primary 4 to Secondary 2 in these subjects. However,
misconceptions about certain aspects of Science still exist,
as is evident from their appearance in many schools’ test
papers. In this column In the Classroom we would like
both to address some of these and to provide a platform
for further discussion.

 

新加坡学的数理教学是全球最好的系统之一。
一直以来,它都获得了非常好的成绩,包括
最近对小四和中二学生进行评估的TIMSS。
尽管如此,学校试卷的科学考题仍然出现一些错误概
念。在新加坡,有相当多的教师、学生和家长在使用这
些题目。为了厘清这些概念以方便大家的使用,也为了
提供一个平台供进一步的讨论,“新学教室”栏目以这
篇文章做个开始,欢迎大家讨论和指正,以起到抛砖引
玉的作用。

 

1. Question 问题
The following question (Figure 1) is from a
Primary 6 Science preliminary examination paper.
以下题目出自一所小学的小六会考模拟试卷。
The graph below shows the percentage of
carbon dioxide within a greenhouse in one day.
下图记录了某一天温室中二氧化碳百分浓度的
变化。
At what time was the rate of photosynthesis the
highest on that day?
这天中,最高的光合作用速率发生在何时?
The answer provided by the paper is 3 pm.
试卷提供的答案是下午3点。

 

2. Discussion 讨论
The question setter here might think that the plants in the
greenhouse would absorb the most carbon dioxide when
the rate of photosynthesis was at its height, and therefore
as 3 pm was the time at which the level of carbon dioxide
in the air in the greenhouse was at its lowest then this was

also the time at which the rate of photosynthesis was at
its highest. Unfortunately, this is not necessarily the case.
出题者也许认为,当光合作用速率最大时,植物吸入最大
量的二氧化碳,从而导致最低浓度的二氧化碳含量。下午
3点的二氧化碳浓度最低,这意味着光合作用速率最高。但
实际上这样的概念是错的。

There are, in fact, two misconceptions here. The first
arises from the failure to distinguish an instantaneous
effect from a cumulative one. The rate of photosynthesis
is an instantaneous effect, but the level of carbon
dioxide is a cumulative one. To take the analogy of a
car, photosynthesis is equivalent to the speed of the
car whereas the level of carbon dioxide equates to the
distance it travels. It therefore follows that whatever the
speed of the car (i.e. even when it slows down) the total
distance it has covered always increases. In other words it
is cumulative, as in Figure 2. The total distance is indicated
by the shaded area which necessarily increases with time.
And the same is true for the level of carbon dioxide in the
greenhouse — provided that the rate of photosynthesis
(i.e. the absorption of CO2) remains higher than the rate of
respiration (i.e. the giving out of CO2) in the greenhouse,
the carbon dioxide level will progressively fall.
这里有两个概念上的错误。第一是对即时效果和累积效果
的混淆。可以用汽车的速度和行驶里程之间的关系来做个
类比说明。光合作用的速率可以比作汽车的速度,是一种
即时效果;二氧化碳的浓度则像汽车的总行驶旅程,是一
种累积效果。
To return to the car analogy, we can see what might have
been in the mind of the question setter here because it is
certainly true that the faster the car is going at any single
moment in time the longer is the distance it will travel per
unit of time, and conversely that the slower it is going the
shorter is the distance it will travel per unit of time. In the
case of the question, this means that the higher the rate
of photosynthesis the more carbon dioxide is absorbed
per unit of time. But the fact that 3 pm marked the
lowest level of carbon dioxide in the greenhouse does not
necessarily mean that this was the time at which the rate of
photosynthesis was at its highest, because as with the car

and the total distance it has covered, it might have been
slowing down for some time already. Indeed, 3 pm may
well have been the time when the rate of photosynthesis
was actually at its lowest in that, as implied by the gradient
in Figure 2, it could have been close to zero.
图2显示一辆汽车的速度与时间的变化关系。曲线包含的面
积是汽车的行驶里程(阴影部分)。无论任何时间,汽车
的速度是较大或较小,汽车的总行驶里程都随着时间的变
化持续增加。如图2所示,即使汽车的速度一直在降低,
总行驶里程仍不断增长。 正如汽车的速度是一种即时效
果一样,光合作用的速率也是一种即时效果。而二氧化碳
的浓度则像汽车的总行驶里程,是一种累积效果。如果光
合作用(吸入二氧化碳)的速率大于呼吸作用(放出二氧
化碳)的速率,那么二氧化碳的浓度就会随着时间一直下
降。光合作用的速率可以用图1中的曲线斜率求得。所以,
根据图1,下午3点的斜率几乎等于零,光合作用速率恰恰
是最低的。因此,最高的光合作用速率和最低的二氧化碳
浓度未必发生在同一时间。

Many schools believe that the levels of carbon dioxide and
oxygen change with the rate of photosynthesis. In other
words, when the rate of photosynthesis is high, they think
that the oxygen level is high and the carbon dioxide level
is low. However, as explained above, this is to mistake an
instantaneous effect for a cumulative one.
很多学校认为,二氧化碳和氧气的浓度都跟随光合作用的
速率而变化,光合作用的速率高,氧气浓度就高而二氧化
碳浓度就低。根据以上说明,这是混淆了即时效果和累积
效果而导致的结果。

The second misconception in the question is to think that
an answer can be arrived at when there are two variables
in operation. These are: the carbon dioxide level, and the
light intensity. Both of these factors will affect the rate
of photosynthesis and both will change over time. The
question setter would have done better to have made
one of these constant as in Figure 4.
另一个错误概念是,这个实验中有两个自变量:二氧化碳
浓度和光的强度。这两个量都随时间变化,而且都会影响
光合作用的速率。这不是一个公平的实验。只有在面对一
个自变量,比如光的强度随时间变化的时候,学生才能够
研究光合作用的速率,如图4.

Here we can see a graph that plots the changing rate
of photosynthesis against the changing light intensity
in an open field. Although the carbon dioxide levels
progressively reduce over time (and the oxygen levels

gradually increase) they are quite a stable element and
can therefore be treated as a constant for the purposes
of any question set.
Figure 1, however, shows significant changes in both
the carbon dioxide level and the light intensity inside the
greenhouse, which renders the question unfair.
图4显示了一个在开放空间(并非温室)的典型光合作用速
率(非二氧化碳和氧气浓度)随光强变化的图谱。在开放
空间里,虽然光强、二氧化碳浓度和氧气浓度都随时间而
变化,但二氧化碳和氧气浓度都相当稳定。因此,光强被
视为是唯一的自变量。相反,图1题目所示,在一个隔离的
温室,二氧化碳浓度和光强都有相当显著的变化,形成两
个自变量,导致实验不公平。

 

Conclusion 结论
The rate of photosynthesis is an instantaneous effect while
the level of carbon dioxide or oxygen is a cumulative effect.
光合作用速率是一种即时效果而二氧化碳浓度则是一种
累积效果。
The rate of photosynthesis in an open field is different
from that in a greenhouse. In an open field, there is only
one variable — the light intensity while in a greenhouse,
there are two variables — the light intensity and the
level of carbon dioxide. The test cannot be fair with two
variables.
开放空间里的光合作用速率和温室里不同。在开放空间
里,自变量只有光强一个;在隔离的温室里,光强和二氧
化碳浓度两个都是自变量。一个实验中有两个自变量,是
不公平的。

 

 

You may also find this article and other educational articles at www.edunationsg.com 

 

 

 

 

 

 

 

Your are currently browsing this site with Internet Explorer 6 (IE6).

Your current web browser must be updated to version 7 of Internet Explorer (IE7) to take advantage of all of template's capabilities.

Why should I upgrade to Internet Explorer 7? Microsoft has redesigned Internet Explorer from the ground up, with better security, new capabilities, and a whole new interface. Many changes resulted from the feedback of millions of users who tested prerelease versions of the new browser. The most compelling reason to upgrade is the improved security. The Internet of today is not the Internet of five years ago. There are dangers that simply didn't exist back in 2001, when Internet Explorer 6 was released to the world. Internet Explorer 7 makes surfing the web fundamentally safer by offering greater protection against viruses, spyware, and other online risks.

Get free downloads for Internet Explorer 7, including recommended updates as they become available. To download Internet Explorer 7 in the language of your choice, please visit the Internet Explorer 7 worldwide page.