C3, C4, CAM plants

Mesophyll cells

Main photosynthesizing cells which contain large amounts of chloroplasts

Chloroplasts

Responsible for photosynthesis

Chlorophyll

A photosynthesis pigment that captures sunlight

Stomata

Pores on the surface of the leaf that open and close to allow for water/gas exchange

Xylem

Vascular tissue in plants that transport water

Phloem

Tissues in the plant that transport the sugar (glucose) that is made

Stroma

Internal space/fluid

Thylakoid

Disks

Thylakoid membrane

Membrane surrounding thylakoid, chlorophyll is located here

Grana

Stack of disks

Equation for photosynthesis

6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O

Stages of photosynthesis

Light dependent stage and light independent stage

Light dependent stage

• Occurs in thylakoid membrane

• Purpose is to split water into oxygen and hydrogen → creates the loaded energy carrying molecules needed for the light independent stage

• Occurs in the presence of light

What happens in the light dependent stage

• Chlorophyll in thylakoid absorbs light energy from the sun

• Light excites electrons, which move and help pump H⁺ ions.

• Water splits to replace electrons, making oxygen and more H⁺

• Oxygen is released into the air through stomata

• H⁺ and electrons help make NADPH and ATP.

• ATP and NADPH go to the next stage of photosynthesis.

Light independent stage

• Occurs in the stroma

• Does not require light

• The stage produces glucose from carbon dioxide

What happens in the light independent stage

• CO₂ enters the Calvin cycle.

• Each CO₂ combines with a 5-carbon molecule, forming two pyruvate molecules

• ATP and NADPH give energy to change these molecules, becoming ADP and NADP⁺ (low energy forms).

• One 3-carbon (G3P) leaves the cycle to help make glucose.

• The other 5 carbon molecules stay in the cycle to keep it going.

• Water is produced when leftover oxygen from CO₂ joins with H⁺ from NADPH.

Inputs and outputs for light dependent stage

Inputs : 12H2O, 12NADP+, 18ADP+Pi
Outputs : 12NAHPH, 18ATP, 6O2

Inputs and outputs for light dependent stage

Inputs : 6CO2, 12NADPH, 18ATP
Outputs : C6H12O7, 12NADP+, 18ADP+Pi, 6H2O

What is a Rubisco

• A key enzyme in the light independent stage

• Involved in the first step of the light independent stage - Uses 3 CO2 molecules and 3 5C molecules to produce 6 3C (3-PGA)

3 stages of Calvin cycle

Carbon fixation, reduction, regeneration

Carbon fixation

CO₂ is attached to a 5-carbon molecule (RuBP), forming 3-PGA

Reduction

ATP and NADPH provide energy and electrons to convert 3-PGA into G3P (a high-energy 3-carbon sugar).

Regeneration

Some G3P is used to remake RuBP, so the cycle can continue.

Explain the problem with Rubisco

• Rubisco is the enzyme that normally helps take in CO₂ during photosynthesis.

• But sometimes, Rubisco uses O₂ instead of CO₂ this is called photorespiration.

• This wastes energy and slows down photosynthesis

When does photorespiration happen?

• When there's not much CO₂ and too much O₂

• When it’s too hot, Rubisco is more likely to pick O₂.

Why is photorespiration bad?

Less photosynthesis → less glucose → less plant growth

Types of plants

C3, C4, CAM

C3 plants

• Most common type of plant

• Goes under normal photosynthesis

• No special way to stop photorespiration

• Struggle in hot/dry conditions

C4 plants

• Tropical grasses

• Special photosynthesis that separates the carbon fixation step from the rest of the Calvin cycle over space

CAM plants

• Succulents, pineapple, agave

• Special photosynthesis that separates the carbon fixation step from the rest of the Calvin cycle over time

Photosynthesis in C4 plants

• CO2 enters the plants and is stored in the mesophyll cell as malate

• The malate is then transported to the bundle sheath cell

• It then breaks down into CO2, so then it can enter the Calvin cycle

Photosynthesis in CAM plants

• At night, the stomata opens to bring in CO2

• The CO2 is converted into malate which is stored in the mesophyll

• During the day, the stomata remains closed

• The sunlight causes the release of malate which is then converted back into CO2 and the CO2 then goes under the Calvin cycle

Adaption of C4 plants

Able to withstand hot temperatures

Adaption of CAM plants

Withstand hot and dry conditions

Purpose of cellular respiration

involves the breakdown of organic molecules and the subsequential release of that energy - allowing the cell to perform ‘work’ at a cellular level

Mitochondria

• Double membrane (inner and outer membrane)

• Has its own DNA

Intermembrane space

Space between the inner and outer membranes

Mitrochondrial matrix

Space inside the inner membrane

Cristae

Folds of the inner membrane

3 stages of aerobic cellular respiration

Glycolysis, krebs cycle, electron transport chain

Glycolysis

Breaks down one molecule of glucose (6C) into two pyruvate molecules

Where does glycolysis happen

Cytosol

Where does the krebs cycle happen

Mitochondrial matrix

Where does the electron transport chain happen

Cristae

The krebs cycle

• Has 8 reactions that break down acetyl CoA

• The breaking down of acetyl CoA releases protons and high energy electrons

• They are loaded into NAD+ and FAD to generate NADH and FADH2

• A total of 2 ATP are produced

Electron transport chain

• NADH and FADH₂ are converted back to NAD+ and FAD forms

• This energy pumps H⁺ ions

• H⁺ flows back through ATP synthase, making ATP.

• 26 or 28 ATP are made (depends on the cell).

• Water is produced in the mitochondrial matrix