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