FACTORS THAT AFFECT THE RATE OF PHOTOSYNTHESIS

What does a faster rate of photosynthesis equal

• more glucose (and oxygen) produced in a shorter time frame

What does the rate of photosynthesis depend on

• The amount of light reaching leaves

• The temperature of the environment

• The availability of water

• The concentration of carbon dioxide

Other factors that can affect the rate of photosynthesis are…

• The amount of chlorophyll

• The availability of nutrients

• Phosphate and nitrates

What may any of the previous factors become

• limiting factors

What are limiting factors

• stops any further increase in the rate of photosynthesis

• the factor that restricts the rate

Photosynthesis and light availability relationship

• Photosynthesis rate increases as light intensity increases, until it reaches a maximum point (optimum temperature)

• Low light intensities = low rate of photosynthesis

What is a limiting factor of light availability

• Low light intensity in winter months are limiting factors on the rate of photosynthesis

Define optimal light intensity

• the one at which the rate of photosynthesis is the greatest

What occurs beyond the optimal light intensity? What is this called?

• Further increases in light intensity have no effect and the rate of photosynthesis stays constant

• This is called the light saturation point

What occurs when there is too little water in plants

• A plant can close their stomata within minutes to prevent water loss

• This prevents gas exchange

• Preventing the supply of CO2 to mesophyll cells stops the Calvin Cycle (stopping photosynthesis) (using water as an input)

What causes plant death (water context)

• Prolonged periods of water deficit

What occurs when there is too much water in plants

• Waterlogging

Explain waterlogging

• Roots require oxygen for growth

• Insufficient oxygen in the root zone results in root asphyxiation

• The air spaces that normally exist in soil to become filled with water

• The oxygen content of the soil decreases

• Plant root cells are not able to respire

What are the biochemical reactions in the light-independent Calvin Cycle catalysed by

• Several different enzymes

• Including rubisco

Chemical reactions depend on…

• collisions between reactants and enzymes

What do low temperatures result in

• Low collision rates (kinetic energy)

• Low rate of photosynthesis

What do high temperatures result in

•  the rate of photosynthesis initially increases as the rate of molecular collisions increases

• once the optimal temperatures of the enzymes involved are exceeded, the rate of photosynthesis decreases rapidly due to denaturation

What does an increasing carbon dioxide concentration result in

• the rate of photosynthesis will increase until it levels off due to limiting factors

What shape is the graph of carbon dioxide concentration generally within photosynthesis

• it plateaus

What is the plateau of the carbon concentration graph caused by

• Rubisco working at its maximum rate so that no further increase in rate if possible

• The availability of essential coenzymes such as NADPH, may have become a limiting factor

Various factors are constantly…

• influencing the rate of photosynthesis

• they do not operate in isolation

Carbon dioxide concentration limiting factor

• the amount of carbon dioxide is limiting the maximum rate of photosynthesis at higher light intensities

Temperature limiting factor

• on the rate of photosynthesis

• the interrelationship between the factors of light intensity, CO2 and temperature

What shape is the graph of temperature generally within photosynthesis

• gradually increases

• optimum

• decreases