C3, C4 and CAM plants

Unit 3 AOS 2

What’s RubsiCO?

The main enzyme used in the light independent reaction of photosynthesis

When is RubsiCO most effective?

• When CO2 levels in the cell are high

• When Oxygen levels are low

• When temperature with within expected range

Where does RubsiCO preferably bind to?

Carbon dioxide

What does RubsiCO do?

RubsiCO attaches to CO2 to RuBP to catalyze the creation of 2 3PGA molecules

What then happens to the 3PGA molecules?

They are converted through chemical reactions involving ATP and HADPH to synthesize glucose

When does photorespiration occur?

When RubsiCO captures oxygen instead of carbon dioxide

Why is photorespiration not ideal?

Because it has a lower photosynthesize efficiency, doesn’t produce glucose but rather CO2

What are C4 plants?

Plants that have adapted to make photorespiration less frequent

What’s the same between C3 plants and C4 plants?

They both still use the light dependent reaction

What’s different for C4 plants compared to CAM and C3?

They use an extra 4-carbon molecule called Oxaloacetate

What’s the oxaloacetate do?

It’s transferred to the bundle sheath where the CO2 is released

Why is transferring the oxaloacetate to the bundle sheath for CO2 to be released good?

As it maintains high levels of CO2 in the cell

Why are these adaptations food for C4 plants?

As it enables them to live in hotter climates

What are CAM plants?

Plants that are hyper adapted to hard and dry climates

What do CAM plants do to reduce water loss via transpiration?

They close their stomata during the day and reopen them during the night to take up CO2

What do CAM plants do while they’re taking up CO2?

They’re synthesizing Oxalacetic acid and malic acid

What is the malic acid converted to and when?

It’s converted into CO2 during the day

RubisCO definition

An important enzyme involved in the carbon fixation process

C3 plants definition

Plants that carry out the original Calvin Cycle using RubisCO and are prone to photorespiration

What’s the immediate organic product made in the Calvin Cycle?

A 3-carbon molecule of phosphoglyceric acid (PGA)

What’s the optimal conditions for C3 plants?

Cool temperatures and moist conditions

What’s RubisCO role in C3 plants?

RubisCO fixes inorganic CO2 molecules from the air and enters into the Calvin Cycle, joined by a carrier molecule called RuBP

Where does the Calvin cycle take place?

In the mesophyll cell leaves of plants

C4 plant definition

Plants that carry out an adapted Calvin Cycle, in which carbon fixation and glucose product occurs in different cells of the plant

What’s the optimal conditions for C4 plants?

They thrive in warm temperature regions and tropical areas

What 2 cells do leaves in C4 plants have?

• Bundle sheath cells

• Mesophyll cells

What’s the immediate product of fixing CO2 in C4 plants?

An organic acid with 4-carbon atoms, mainly oxaloacetic acid (OAA)

What are the 2 steps to glucose production and where do they happen in C4 plants?

Carbon fixation happens in the mesophyll cells and glucose production happens via the Calvin cycle in bundle sheath cells

CAM plants definition

Plants that thrive in arid climates and have their 2 stages of the Calvin cycle occurring at different times of the day

What’s the optimal conditions for CAM plants?

They thrive in hot arid environments and regions exposed to drought

Photorespiration definition

The process which plants take up oxygen rather than CO2 in the light, resulting in photosynthesis being less effective

How does photorespiration happen?

It happens when RubisCO binds to oxygen instead of carbon dioxide

Why can RubisCO bind to both oxygen and carbon dioxide?

Because RubisCO’s active site can accommodate both carbon dioxide and oxygen so they’re in competition

What are the 2 situations where photorespiration can arise?

1. As temperature increases

2. As conditions dry out

Why can temperature increase result in photorespiration?

As temperature increases, its harder for RubisCO to differentiate between carbon dioxide and oxygen

Why can conditions drying out cause photorespiration?

As water availability declines, stomata wont open and this closure prevents carbon dioxide from entering. This then creates a high oxygen environment in mesophyll cells, making it more likely for RubisCO to bind to oxygen

When does RubisCO work most effectively?

• When CO2 levels are high

• When O2 levels are low

• When temperature is moderate

What does photorespiration produce instead of glucose?

it produces CO2 that’s then filtered into the external environment

Why is photorespiration inefficient?

Because 20 to 40% of the energy produced during photosynthesis doesn’t go to glucose production

What are the mechanisms that prevent photorespiration from happening in C4 plants?

• CO2 becomes malic acid and it takes place in the leaf mesophyll cells

• Glucose production via the Calvin cycle happens in the bundle sheath cells

What’s the process of CO2 becoming malic acid in C4 plants?

Instead of RubisCO being used in this stage, PEP carboxylase is used to catalyze the binding of CO2 to an acceptor molecule

Why is binding to PEP carboxylase beneficial for C4 plants?

PEP carboxylase can only bid to CO2

What’s the process of glucose production via the Calvin cycle in C4 plants?

Malic acid is broken down, creating a steady supply of CO2 which raises the CO2 concentration of CO2 in the leaf

Why is breaking down malic acid in C4 plants beneficial?

It enables RubisCO to ideal bind to CO2

What’s the end product of carbon fixation process in the mesophyll cells in C4 plants?

Malic acid

Why isn’t photorespiration an issue in CAM plants?

Carbon fixation happens at night when the stomata is open and the Calvin cycle only produces glucose during the day when the stomata is closed

Where does the mechanisms that prevent photorespiration in CAM plants occur?

In the mesophyll leaf cells

Why does the stomata in CAM plants open at night for carbon fixation?

They open at night to enable free passage of CO2 molecules into the leaves

What happens to the end product of carbon fixation in CAM plants?

The organic acids like malic acid are stored in the cell vacuoles until after sunrise

Why does the stomata in CAM plants closed at during the say for glucose production?

As the organic acids are transported out of the cells vacuole, malic acid is broken down, creating a high CO2 concentration which enables RubisCO to ideal bind to CO2