5 - Photosynthesis

Photosynthesis

• What is the formula?

• Plants’ version of using glucose in cellular respiration.

• Photosynthesis

  • CO₂ + water (with sunlight and chlorophyll) → glucose + O₂

  • Plants’ version of using glucose in cellular respiration.

Leaf Structure

• In plants, photosynthesis occurs in the mesophyll cells of the leaves. 

  • __^_ cells contain many ___.

• Cuticle -

• Stomata/stoma -

Leaf Structure

• In plants, photosynthesis occurs in the mesophyll cells of the leaves. 

  • Mesophyll cells contain many chloroplasts.

• Cuticle - provides leafs protective barrier

• Stomata/stoma - allow oxygen, carbon dioxide, and water to pass in/out of the leaf, and prevent water loss

Chloroplasts –

• Thylakoids –

• Grana –

• Stroma –

Chloroplasts – where photosynthesis occurs.

• Thylakoids – the internal membranes in chloroplasts

  • Grana – Thylakoids stacked in columns

• Stroma – the semi liquid substance that surrounds the thylakoids.

Photosystem –

• The primary pigment in plants is _____.

  • — absorbs ____ light of the visible light.

• Accessory pigments –

  • These pigments give color to flowers, fruits, and vegetables.

Photosystem – a network of pigments (located in the thylakoid membrane) that, like antennas, capture sunlight energy.

• The primary pigment in plants is chlorophyll.

  • Chlorophyll absorbs blue and red light of the visible light

  • Chlorophyll is green because green light is reflected, not absorbed.

• Accessory pigments – other pigments in plants that absorb other light levels that chlorophyll doesn’t

  • These pigments give color to flowers, fruits, and vegetables.

Light is comprised of packets of energy called _____

• Electromagnetic Spectrum -

• Human eyes only perceive photons of intermediate energy levels, known as ____.

Light is comprised of packets of energy called photons

• Electromagnetic Spectrum - represents the range of energy levels

• Human eyes only perceive photons of intermediate energy levels, known as “visible light”.

Three Stages of Photosynthesis

Three Stages of Photosynthesis

1. Capturing sunlight energy.

2. Using the captured energy to produce ATP + NADPH.

3. Using the ATP + NADPH to make carbohydrates from CO₂

2 Types of Reactions

• Light-dependent reactions ___

  • Includes the stages (1) ___ and (2) ____

• Light-independent reactions ___

  • Known as the Calvin cycle

  • Includes the stage (3) ____

• Light-dependent reactions take place only in the presence of light and produce ATP and NADPH.

  • Includes the stages (1) Capturing energy from sunlight and (2) Using the captured energy to produce ATP and NADPH.

• Light-independent reactions do not need light to occur and use CO₂ to make organic molecules (glucose).

  • Known as the Calvin cycle

  • Includes the stage (3) Using the ATP and NADPH to make carbohydrates from CO₂ in the atmosphere.

Light-Dependent Reactions

2 photosystems are used:

• Photosystem II –

• Photosystem I –

2 photosystems are used:

• Photosystem II – Captures a photon of light and releases an electron to the Electron Transport System → produces ATP.

• Photosystem I – Captures a photon and releases an electron to the ETS → produces NADPH.

Light-Independent Reactions (Calvin Cycle)

• Cells use the _____ to build organic molecules.

 

• The Calvin cycle reactions occur in 3 stages: 

1. Carbon fixation –

2. Making sugars – 

3. Reforming RuBP –

The Calvin cycle must “turn” ____ in order to form a glucose molecule.

• The Calvin cycle recycles back their reactant (the products of the light-dependent reactions) to the ETS; returns ADP and NADP+ back to the ETS

Cells use the products of the light-dependent reactions to build organic molecules.

The Calvin cycle reactions occur in 3 stages: 

1. Carbon fixation – Carbon from CO₂ is attached to an organic molecule, RuBP.

2. Making sugars – The carbons goes through reactions to make sugars.

3. Reforming RuBP – remaining molecules are used to reform RuBP (ready to start another round in the Calvin cycle). 

The Calvin cycle must “turn” 6x in order to form a glucose molecule.

• The Calvin cycle also recycles their reactants to the light-dependent reactions; returns ADP and NADP+ back to the ETS

Other Photosynthetic Pathways (to avoid reduction in photosynthesis)

Many plants have trouble carrying out C3 photosynthesis (where light dependent and light independent reactions are occurring in the same cell simultaneously) when its ____.

• Plants close their stomata in order to ____.

  • Photorespiration ____.

C4 Photosynthesis

• Occur in sugarcane, corn, many grasses

  • What does this pathway do?

    • Bundle-sheath cells trap CO₂

CAM (crassulacean acid metabolism) Photosynthesis

• Occurs in succulent (water-storing) plants, like cacti and pineapples.

• C4 pathway at night (stomata opens to take in CO₂) and the C3 pathway during the day.

Many plants have trouble carrying out C3 photosynthesis (where light dependent and light independent reactions are occurring in the same cell simultaneously) when its hot.

• Plants close their stomata in order to prevent water loss.

  • Photorespiration reduces photosynthesis because O₂ levels are built up, causing the enzyme rubisco to use oxygen instead of CO₂, decreasing sugar production.
    

C4 Photosynthesis

• Occur in sugarcane, corn, many grasses

  • They fix carbon using different types of cells and reactions, so they don’t run out of CO₂

    • Bundle-sheath cells trap CO₂

CAM (crassulacean acid metabolism) Photosynthesis

• Occurs in succulent (water-storing) plants, like cacti and pineapples.

• C4 pathway at night (stomata opens to take in CO₂) and the C3 pathway during the day.