lower secondary - photosynthesis
DESCRIPTION
This presentation is tailored for the Lower Secondary Science syllabus in Singapore.TRANSCRIPT
This presentation was produced by the Science department of Temasek Secondary School.
Redistribution or reproduction of this resource is prohibited by copyright regulations. This resource should be used for educational
purposes.
PhotosynthesisPhotosynthesis
Overview1. What is photosynthesis?
2. Testing the leaf for starch to see if photosynthesis has taken place.
3. Conditions and factors affecting photosynthesis.
4. Importance of photosynthesis.
Lesson objectivesAt the end of the lesson, you will be able to:1. define photosynthesis.
2. classify the various factors of photosynthesis into either raw materials or conditions required for photosynthesis.
3. state the word and chemical equation for photosynthesis.
Plants make their own food!
Food for plants:
•Energy-rich substances called carbohydrates (sugars)
PhotosynthesisPhotosynthesis
LightLightPutTogetherPutTogether
blue black blue-black
Raw materials
Conditions
Water Carbon dioxide
Glucose(Sugar)
Oxygen
Light,Chlorophyll,
Suitable temperature
+
+
WORD EQUATION FOR PHOTOSYNTHESIS
6H2O 6CO2
C6H12O6 6O2
Light,Chlorophyll,
Suitable temperature
+
+
CHEMICAL EQUATION FOR PHOTOSYNTHESIS
Process where light energy is absorbed by chlorophyll and
converted to chemical energy, which is used to synthesise
glucose from water and carbon dioxide, liberating oxygen
during the process.
Lesson objectivesYou are now able to:1. define photosynthesis.
2. classify the various factors of photosynthesis into either raw materials or conditions required for photosynthesis.
3. state the word and chemical equation for photosynthesis.
Video: The photosynthesis song
http://www.youtube.com/watch?v=C1_uez5WX1o
Video to recap the last lesson
http://www.youtube.com/watch?v=eJQxHoqIPIM&feature=related
Take note: The chemical equation is not balanced!
Lesson objectivesAt the end of the lesson, you will be able to:1. describe the steps involved in testing a leaf
for starch to see if photosynthesis has taken place.
2. state the reason behind each step in testing a leaf for starch.
Why do we test the leaf for starch instead of glucose?
Starch is a good storage molecule as it is– insoluble in water– used only when needed.
How do we tell if Photosynthesis has taken place?
•Test for Starch
Glucose + Oxygen
Light energy
chlorophyll(stored as
starch)
Carbon dioxide + Water
Use Iodine test
To Test for Starch in a Leaf1.Place leaf in boiling water.
To stop chemical reactions in the leaf so that enzymes will stop converting starch to glucose.
2.Place leaf in hot alcohol /ethanol. To remove the green chlorophyll
(decolourisation) so the final results can be clearly seen.
Bunsen burner
turned off
Alcohol turned green
3. Dip leaf into warm water To remove the alcohol on the leaf/
to soften the leaf
4. Spread leaf evenly on white tile. Cover leaf with iodine solution
to test for the presence of starch.
5. Leaf turns blue-black if starch is present.
Leaf turns light brown, starch is absent
Iodine test video
http://www.youtube.com/watch?v=VeU7ULL9Usw
Lesson objectivesYou are now able to:
1. describe the steps involved in testing a leaf for starch to see if photosynthesis has taken place.
2. state the reason behind each step in testing a leaf for starch.
Lesson objectivesAt the end of the lesson, you will be able to:
1. state the factors affecting the rate of photosynthesis and interpret related graphs.
2. describe the steps involved in testing how various factors can affect the rate of photosynthesis
Chlorophyll
Light Intensity Carbon
DioxideConcentration
Temperature
Factors affecting rate of photosynthesis
Experiments used to show how certain factors
can affect the rate of photosynthesis.
As future scientists, these are the things to look out for before we
carry out an experiment….
1. What is the result we are looking for?
2. What factor are we changing in the experiment?
•Keep in a dark place for 24-48 hours (1 to 2 days)
- any stored starch will be converted to sugars which are transported to other parts of the plant
How to destarch a plant?
•To ensure that starch is absent from the leaves at the beginning of an experiment, so that if any starch is formed, then photosynthesis must have taken place
Why destarch a plant?
As future scientists, these are the things to look out for before we
carry out an experiment….
1. What is the result we are looking for?
2. What factor are we changing in the experiment?
Lesson objectivesAt the end of the lesson, you will be able to:1. describe the steps involved in testing how various
factors can affect the rate of photosynthesis.
2. define respiration.
3. write the word and chemical equation for respiration.
Lesson objectivesAt the end of the lesson, you will be able to:1. describe the steps involved in testing how various
factors can affect the rate of photosynthesis.
2. define respiration.
3. write the word and chemical equation for respiration.
•To ensure that starch is absent from the leaves at the beginning of an experiment, so that if any starch is formed, then photosynthesis must have taken place
Why destarch a plant?
•Keep in a dark place for 24-48 hours (1 to 2 days)
- any stored starch will be converted to sugars which are transported to other parts of the plant
How to destarch a plant?
Chlorophyll
Light Intensity Carbon
DioxideConcentration
Temperature
To find out whether sunlight is necessary for
photosynthesis
With sunlight
Without sunlight
To find out whether carbon dioxide is necessary for photosynthesis
Soda lime to absorb CO2
Sodium hydroxide to absorb CO2
Without carbon dioxide
With carbon dioxide
White (without
chlorophyll)
Green
(with chlorophyll)
brown
Blue-black
To find out whether chlorophyll is essential for photosynthesis
Variegated leaf
To find out what gas is given off during photosynthesis
Oxygen gas released from the
cut end of the stem
To find out what gas is given off during photosynthesis
To provide
CO2
Why is Photosynthesis important?
Provides food and energy for animals (primary producers).
Produces oxygen and removes carbon dioxide from the air.
Respiration
Process by which food molecules are broken down to release energy.
• Energy is used for:– muscle movement, – maintain constant body temperature, – for growth etc.
Respiration
• Oxygen taken in, Carbon dioxide given out
• Takes place all the time in living organisms, be it in plants or in animals.
Respiration: Word equation
Glucose + Oxygen Carbon dioxide + Water + Energy
Aerobic respiration•Oxygen is
required
Lesson objectivesYou are now able to:1. describe the steps involved in testing how various
factors can affect the rate of photosynthesis.
2. define respiration.
3. write the word and chemical equation for respiration.
Lesson objectivesAt the end of the lesson, you will be able to:1. interpret graphs relating to photosynthesis and
respiration.
2. compare and contrast between photosynthesis and respiration.
blue black blue-black
Raw materials
Conditions
Net uptake/release of gasesRate of photosynthesis > rate of respirationNet uptake of CO2 > Net release of CO2
Net release of oxygen > Net uptake of oxygen
Rate of respiration > rate of photosynthesisNet release of CO2 > Net uptake of CO2
Net uptake of oxygen > Net release of oxygen
Photosynthesis/ RespirationN
et r
elea
se o
f o
xyg
enN
et u
pta
ke o
f o
xyg
en
6 am midday 6 pm midnight
X
Time of day
rate of photosynthesis=rate of respirationX
Yrate of photosynthesis>rate of respiration
Zrate of respiration > rate of photosynthesis
20-
15-
10-
5 -
0
5 -
10-
15-
20-
Q: Why should you not have any green plants in your bedroom at night?
At night, green plants do not photosynthesise due to the absence of light. Respiration takes place and the green plants will compete with you for oxygen.
Lesson objectivesYou are now able to:1. interpret graphs relating to
photosynthesis and respiration.
2. compare and contrast between photosynthesis and respiration.
DIFFERENCES BETWEEN• PHOTOSYNTHESIS • RESPIRATION
Can you differentiate between photosynthesis &
respiration?
Write on a foolscap paper!
Thinking time!
Why do some people say that plants form the ‘lungs’ of the earth?
Producers
Think of plants making their own food like…your parents making food for you
Parents preparing food for you
Plants making their own food
Process:
Ingredients used:
Cooking
Rice
Vegetables
Egg
Process:?
Ingredients used: ?
E-revision questions(To be completed)
Think about it…Instruction: Please revise through the chapter using the powerpoint slides provided and try this on your own before referring to the answer scheme which
will be uploaded tomorrow. Google is a good tool to use to research for the answers!
•1a. Do you think that red leaves contains chlorophyll? If yes, how do you explain the red colour of the leaf? If no, why not? •1b. Hence, do you think that the red leaf can photosynthesise? Why or why not?
To fill inInstruction: Please revise through the chapter using the powerpoint slides provided and try this on your own before referring to the answer scheme which
will be uploaded tomorrow.Similarities and differences between Photosynthesis and Respiration
Photosynthesis Respiration
Similarities
Differences
To complete (1)Instruction: Please revise through the chapter using the
powerpoint slides provided and try the following question (this question comprises of the next 3 slides) before referring
to the answer scheme which will be uploaded tomorrow.
Concept: Factors affecting photosynthesis
To complete (2)
Concept: Factors affecting photosynthesis
To complete (3)
Concept: Factors affecting photosynthesis