Biology Edexcel Topic 6 (Photosynthesis)

6.1 to 6.6

What is photosynthesis

A chemical reaction that takes place inside photosynthetic organisms converting light energy into chemical energy

Write the word equation for photosynthesis

carbon dioxide + water -> oxygen + glucose

Write the symbol equation for photosynthesis

6 CO2 + 6 H2O --> C6H12O6 + 6 O2

Why is photosynthesis important

It produces glucose which has a wide range of uses

Why is glucose useful

It is used in respiration to release energy, it can be converted to starch and stored (and broken back down to glucose when the plant needs energy), and it can be used to make up complex organic molecules which are used for growth which makes up an organism's biomass

Where does photosynthesis take place

Within chloroplasts

What type of reaction is photosynthesis

An endothermic reaction as it takes in energy (in the form of light)

What is chlorophyll

A pigment found in chloroplasts that absorbs light

Describe the two main staged of photosynthesis

Chlorophyll first absorbs light energy which is used to split water into oxygen and hydrogen ions, carbon dioxide then combines with the hydrogen ions to form glucose

What factors affect the rate of photosynthesis

Temperature, light intensity, and carbon dioxide concentration

What is a limiting factor

A variable that limits the rate of a particular reaction

Explain how temperature affects the rate of photosynthesis

Higher temperature provides more kinetic energy to the enzymes involved in photosynthesis so the rate of enzyme substrate collisions increases as temperature rises, this continues until it reaches the optimum temperature (usually around 25 degrees), if the temperature goes past the optimum, enzymes begin to denature so become not complementary to the substrates, so less enzyme-substrate complexes are formed so the rate of photosynthesis decreases

Draw a graph to show the effect of increasing temperature on the rate of photosynthesis

Explain how light intensity affects the rate of photosynthesis

Rate of photosynthesis is directly proportional to light intensity because as light intensity increases, the plant can take in more light energy to use in photosynthesis, so as light intensity increases, the rate of photosynthesis increases

Why does the rate of photosynthesis eventually plateau even if light intensity continues to increase

Another factor (temperature or CO2 concentration) becomes limiting

Draw a graph to show the effect of light intensity on the rate of photosynthesis

How can the effect of light intensity on the rate of photosynthesis be measured in the lab

Using a light meter and using the inverse square law

What is the inverse square law

Light intensity = 1/distance^2

Why does the rate of photosynthesis decrease as the distance from a light source increases?

Light intensity is inversely proportional to the square of the distance from the light source so as distance increases, light intensity decreases and the rate of photosynthesis decreases

Explain how carbon dioxide concentration affects the rate of photosynthesis

As carbon dioxide concentration increases, more carbon dioxide can be used in photosynthesis so the rate of photosynthesis increases

Why does the rate of photosynthesis eventually plateau even if CO2 concentration continues to increase

Another factor (temperature or light intensity) becomes limiting

Draw a graph to show the effect of carbon dioxide concentration on the rate of photosynthesis