1. Photosynthesis is
- a process that converts light energy into chemical energy
- initial substrates are carbon dioxide and water
- sunlight is required as energy source
- produces carbohydrates such as glucose or starch
- and releases oxygen to the surrounding
3. Leaf structure and its adaptation for photosynthesis.
- Take note of the Diagram-LEAF ....make sure you know how to label the structures well..and the drawing...
1. Leaf Lamina:
Thin and wide // (high TSA/V ratio) to enable
(i) Leaf absorb sunlight
(ii) Carbon dioxide diffuse into cells easily
Mosaic arrangement of leaves to enable
(i)leaves absorb light maximum.
2) Leaf veins
* Situated at the centre of the leaf and branched out to the side of the leaf
* Xylem and phloem are found in the veins.
*Xilem transports water and minerals from root to the leaf
*Phloem transports glucose (synthesized in the leaf ) to all part of the plant
3) Epidermis
· Consists of upper epidermis and lower epidermis . It serves a transparent single layer
· Epidermal cell has no chlorophyll and therefore permits light to penetrate into mesophyll tissues.
· Outer surface of epidermis is covered by cuticle which waterproof.It protects leaf from microb and excessive water loss
4) Stomata.(Relate its role when you discuss about TRANSPIRATION...)
Found abundantly at the lower surface of leaf.
- Its opening is controlled by guard cells .
- Exchange of oxygen and carbon dioxide gas during photosynthesis and respiration takes place through the opening
5) Palisade mesophyll
Elongated cells with many chloroplast inside ,
near to leaf surface for more and efficient light absorbed.
6) Spongy mesophyll
- Irregular shape,
- loosely arranged beneath the palisade mesophyll
- with many air sac It contains many chloroplast for photosynthesis.
Plant adaptation in favour of photosynthesis at different habitats.
1. Desert plants like cacti
2.Aquatic plant which could be Floating plants like water lilies OR submerged plants like Hydrilla sp.. (There was one question asked in SPM2005. Its about Eichhornia sp in its habitat...(It is pokok keladi bunting.)..
Question asked you to:
Explain the adaptations of the plant which enable it to float on the water surface. [4 marks]
3. Tropical land plants.
..Take note of their stomata and chloroplast distribution..There is one simple experiment to investigate the distribution of stomata and chloroplast on the epidermis of few sample of leaves....may be gotten from dofferent habitat...Just watch out..
..Next is...The mechanism of photosynthesis which consist of Lite and Dark reaction...It has been asked detail in Paper 2 SPM 2006..So I dont think it comes out again for 2009.
LIGHT REACTION:- Chlorophyll molecules absorb light energy,
- becomes excited and release high energy electrons (this occurs in grana ) which is later on converted to ATP.
· At the same time, water molecules in chlorophyll dissociates forming hydrogen ions and hydroxyl ions
· Hydrogen ions combine with electrons to form hydrogen atoms
· Hydrogen atoms thus formed later enters the dark reaction in stroma.
· Hydroxyl ions releases its electron to form hydroxyl molecule
· The electrons is accepted by chlorophyll molecules that had lost their electrons earlier.
· Hydroxyl groups finally form water and releases oxygen.
- DARK REACTION
- The reaction takes place in stroma.
- Hydrogen atoms produced during light reaction reduces carbon dioxide to form glucose.
- The reduction of carbon dioxide in stroma is catalysed by enzymes
- and requires energy from ATP ( produced during light reaction )
- Units of (CH2O) combine to form glucose.
- Glucose units are then condensed together to form starch which is stored in the leaves
The Factors affecting The rate of Photosynthesis...which I always consider have a greater chance to be asked...be it in Paper 2 or Paper 3..So you should be well versed about it.
In 2007 paper 3 Factor asked was Light intensity...And five years back, concentration of carbon dioxide has also being asked...But I wont eliminate the concentration of Carbon dioxide factor for this year...
The important factors are :
i. Carbon dioxide concentration
ii. Light intensity
iii. Temperature
...As for all graphs for the factors: You should be able to interpret each part of the graph with the meaningful sentences....It could be asked for Essay.
..As for paper 3, it could possibly be asked as Question 1 or Question 2: designing an experiment , which should be a bonus to you because it is quite straight forward as long as you know how to identify the THREE VARIABLES...and know how to operate them.....
- Take note for all these experiments, we must use Hydrilla sp or any suitable aquatic plant..
- and of course by counting bubbles in a fixed time ,are the best method...
- take note also the set up of apparatus...basically it is all the same for all factors..
1. To investigate the effect of light intensity on the rate of photosynthesis
- MV: Distance between the light source / bulb and Hydrilla sp // Light intensity
- RV: Number of bubbles released in 5 minutes //The rate of photosynthesis
- FV: Volume of sodium hydrogen carbonate solution
2. To investigate the effect of carbon dioxide concentration on the rate of photosynthesis.
- MV: Different concentration of sodium hydrogen bicarbonate.
- RV: Number of bubbles released in 5 minuted // the rate of photosynthesis
- FV: Light intensity/ distance between lite source and Hydrilla sp.
3. To investigate the effect of temperature on the rate of photosynthesis
- MV: Different temperature of water
- RV: Number of bubbles released in 5 minutes //the rate of photosynthesis
- FV:Concentration of carbon dioxide/sodium hydrogen bicarbonate....
If the question ask you:
Explain the differences in the rate of photosynthesis in plants throughout the day, could you write an essay???..
- Tips:
Look at marks allocated - Study the graph given (if any)
- Explain part by part: morning, afternoon, evening, night
- Relate the story....
Another Question:
What is the importance of photosynthesis?...[ 5 marks ]
Another question: Green houses related to photosynthesis..
Explain why provision of ‘ green houses ‘ are significant in four seasonal countries like those in Europe and northern America compared to tropical countries?
Suggested Answer:
- Greenhouse effect are significant in four seasonal countries which have different amount of light intensities throughout the year.
- During winter where light intensities is the least,
- so a greenhouse is designed to trap the sun’s energy.
- Sunlight can penetrate the glass roof of a greenhouse to warm the soil.
- However, the heat given off by the soil cannot pass through the glass, so it remains inside to warm the air.
- This means that the heat from the sun is trapped inside the greenhouse
- and this keeps the plants warm throughout the year.
...and its good for the plants...Mind you ..it is not the other effect of Greenhouse effect....
Lastly: Technology used in Food Production.
Just take note and be able to write a few reasons why is it necessary to improve the quality and quantity of foods..
..Read a bit about Hydroponic, aeroponics... WHAT, HOW, ADVANTAGE and one EXAMPLE...
- ..and methods involve in food processing such as:
pasteurisation - canning
- drying
- freezing
- prickling
...Usually only 2-4 marks to explain that...
- The basic guidelines are:
What is the method - How it is done
- Advantages/Disadvantages.
Happy Revising..
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