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Photosynthesis: Chapter 2.16 to 2.20

A brief student-made presentation reviewing photosynthesis, part of the IGCSE Biology Syllabus

MK Kas

on 7 February 2014

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Transcript of Photosynthesis: Chapter 2.16 to 2.20

Photosynthesis by Muriel Kasanga What is photosynthesis? Every living organism requires food, but animals and plants acquire their food in different ways. On the other hand, plants need raw materials to build up tissues and to use as a source of energy. They are autotrophs (meaning self-feeding) and carry out photosynthesis using compounds from the environment around them. Animals digest "ready-made" food and use the digested food for energy, and the building up of new tissues and cells. The process where light energy from the sun is absorbed by chlorophyll and is used to convert carbon dioxide and water into glucose and oxygen. Photosynthesis Plants need energy and enzymes which are obtained from sunlight and the plant's cells. Carbon dioxide from the atmosphere Oxygen waste is released into the atmosphere, where it's breathed in by humans. Water and minerals (including nitrate, phosphate & magnesium) come from the soil. Light energy from the sun. The plant makes the following compounds, which are used for energy, growth, repair and reproduction. - Glucose, starch (containing Carbon, Hydrogen and Oxygen).
- Amino acids and proteins (which all contain Carbon, Hydrogen, Oxygen and Nitrogen)
- Nucleic acids (which contain phosphorus and Carbon, Hydrogen, Oxygen and Nitrogen and:
- Lipids (which contain Carbon, Hydrogen and Oxygen. How do plants absorb light energy? ...and use it for photosynthesis? Plant cells contain chloroplasts (which contain chlorophyll). The green pigments help the plant to absorb and make use of light energy. The chloroplasts convert the absorbed light energy into chemical energy. So just how does a plant manage to absorb light energy from the sun... The word and balanced symbol equation for photosynthesis are:

Carbon dioxide + water → glucose + oxygen
6CO2 + 6H2O → 6C6H12O6 + 6O2 When glucose is produced, some of it can be stored in the plant's cells as starch.
Testing for the presence of starch is useful to tell if photosynthesis has taken place. How can you tell if photosynthesis has taken place? But, the iodine test measure for the presence, and doesn't give an idea of how much starch is present. It's a qualitative test. Instead, testing for oxygen can give a quantative result. Variables In an experiment where you want to measure the speed of photosynthesis, there would be many different variables. Plant Nutrition (and Megha, the clicker) Because light intensity can be changed by the experimenter, it is independant Temperature of the water is also independant and continuous The volume of oxygen released is what the results of the experiment depend on, so it is the dependent (outcome) variable. Starch Test Procedure First, the plant must be left in the dark for 48 hours. This will destarch it, so that we can tell if a factor is needed for photosynthesis. The leaf is then boiled in water, to allow the enzyme action to stop. Then the leaf is placed a test tube filled with ethanol and placed in a beaker of warm water. Since chlorophyll needs to be removed and is only dissolvable in ethanol. The leaf can be dipped in warm water very quickly to soften the leave and let iodine solution in better. Finally, the leaf is put on a white tile and iodine solution is added. If starch is present, then the iodine will turn blue-black. If not, the iodine remains orange-brown. When it comes to an experiment measuring the effect of light on the rate of photosynthesis, there are many variables. Efficient photosynthesis For photosynthesis to be effective, a leaf needs a method of gaseous exchange, a water delivery system, a system for removing glucose to transport to the rest of the plant and a way of absorbing light energy. The upper epidermis is transparent, allowing light to pass freely. It is one cell thick to prevent disease causing bacteria and fungi. The Palisade cells are long and thin and close together. They contain a lot of chloroplasts allowing for the maximum absorption of light energy. The waxy cuticle is thicker on the upper side of the leafe because it is the surface most exposed to the sunlight. The spongy mesophyll are not closely packed and have spaces between them to allow for the diffusion of gases through the leaf. The stoma are pores allowing for carbon dioxide to be enter the leaf and oxygen to leave it. They are contained on the bottom of the leaf because the lowe surface is less exposed to the sun and there is not as much water loss.When there is a water shortage the stomata close. Control of photosynthesis Photosynthesis depends on:
Light availability
Chlorophyll pigment for light absorption
Carbon dioxide and water supply
And a optimum temperature for enzyme activity. There are limiting factors which stop photosynthesis which vary they are:
-Carbon dioxide concentration
-Lack of light
-Low or high temperature Respiration Respiration is the process by which cells obtain energy.
The formula for respiration is

Glucose + oxygen = carbon dioxide + water

Green plants carry out respiration and photosynthesis at the same time

If there is more photosynthesis taking place than respiration in the day then carbon dioxide will be removed from the plant while oxygen will be taken in.

When the level of photosynthesis is less than respiration (like when it's dark) then the plant will remove oxygen and intake carbon dioxide Questions What is the meaning of autotrophic? Self-feeding Name two of three minerals that plants obtain from the soil Nitrate, phosphate and magnesium Why should a leaf be warmed in ethanol when carrying out a starch test? To remove all chlorophyll from the plant, because chlorophyll cannot dissolve in water, but it can in ethanol. Why is an iodine starch test not useful to show how much photosynthesis is taking place? It's a qualitative test, not quantitative. Which variable can be changed by the experimenter? The independant (input) variable. Name one part of the leaf and its adaptation(s) eg.Upper epidermis, transparent to allow free passage of light. The balanced equation for photosynthesis? Name an example of a limiting factor for a plant Carbon dioxide concentration, light or temperature.
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