Nutrition

2.17 Describe the process of photosynthesis and understand its importance in the conversion of light energy to chemical energy

Light energy from the sun is absorbed by the chlorophyll present in the chloroplasts present in plant leaves. This light energy is then used to convert carbon dioxide and water into glucose and oxygen. This is used in respiration.

So light energy from the sun is used to create chemical energy. This is called the conservation of energy. The energy is then passed down the food chain. The conversion of light energy to chemical energy is important as it allows starch to be created which can be stored in the plant, which can be later eaten by animals.

2.18 Write the word equation and the balanced chemical symbol equation for photosynthesis.


                                        light energy
carbon dioxide + water ààààààààglucose + oxygen

                                        chlorophyll

2.19 Understand how varying carbon dioxide concentration, light intensity and temperature affect the rate of photosynthesis.

Carbon dioxide concentration

As carbon dioxide concentration in the air rises, the rate of photosynthesis increases. However,the increase in rate of photosynthesis will stop after some time because another factor such as light intensity or temperature became a limiting factor- the graph looks like this.

Light intensity
As light intensity increases, rate of photosynthesis also increases up to a certain point. After this point it decreases as either temperature or carbon dioxide concentration become a limiting factor. However if light intensity is too high, plant cells may be damaged


Temperature
As temperature increases up to 40 degrees Celcius, rate of photosynthesis also increases. This is because an increase in temperature means that the collisions in the reactions ahve more energy. This leads to more number of successful reactions. However after 40 degrees Celcius the enzymes start to denature. This leads to a decrease in the rate of photosynthesis.

For the first part of each of these graphs (The straight line with positive gradient)- the label on the x-axis is the limiting factor.

For the second and last part of each of these graphs- every other factor that affects the rate of photosynthesis(carbon dioxide concentration, light intensity and temperature) excluding the  label at the x axis are the limiting factors.