c3 c4 and stomata lab follow up questions

• What is the function of the palisade mesophyll?

• To do process most of the photosynthesis

• The cells are tightly packed together with chloroplasts so they can absorb plenty of sunlight

• Why is the spongy mesophyll loosely packed?

• To create air spaces

• This is so (CO₂ and O₂) can move easily through the leaf

• What role do vascular bundles (xylem + phloem) play?

• These are part of the transport system in plants

• Xylem move water and minerals up the plant

• Phloem move sugars (produces from photosynthesis) from the leaves to other parts of the plant

• What is the function of guard cells and stomata?

• Guard cells are responsible for opening and closing the stomata

• The stomata are pores that allow the gas exchange between CO₂, O₂, and water vapor out

How do C₃ and C₄ leaf structures differ?

C3:

Smaller bundle sheath cells

^^ Contains less chloroplasts

Calvin cycle takes place in the mesophyll cells

C4:

Kranz anatomy - large bundle sheath cells form a ring around the vascular bundles

Bundle sheath cells contain lots of chloroplasts

The initial carbon fixation occurs in the mesophyll cells, then the Calvin cycle occurs in the bundle sheath cells

• Why do C₄ plants have bundle sheath cells with many chloroplasts?

• That is because the Calvin cycle occurs in bundle sheath cells for C4 plants

• The chloroplasts increase the efficiency

• Why are C₄ plants more efficient in hot, dry climates?

• C4 plants go through a secondary pathway known as the C4 cycle

• This adaptation allows plants to survive and flourish in conditions that could kill other plants

• Minimizes photorespiration occuring

• Keeps the stomata closed, which saves water while fixing carbon

• What is Kranz anatomy and how does it relate to C₄ photosynthesis?

• This is a leaf structure

• Bundle sheath cells are enlarged compared to C3 plants, form a ring, and are full of chloroplasts

• The bundle sheaths are larger and contain more chloroplasts which is important for C4 plants photosynthesis because the Calvin cycle occurs there

• Which type (C₃ or C₄) has bundle sheath cells tightly packed with chloroplasts?

• C4 plants

• C3 plants have less chloroplasts contained in the bundle sheath cells as it is also smaller

• Which leaf type shows the palisade mesophyll right under the upper epidermis?

C3 plants

What causes stomata to open or close?

• Guard cells fill with water → open

• Guard cells lose water → close

• Describe the structure of guard cells in an open vs closed stomate.

• Open: guard cells are swollen/curved.

• Closed: guard cells are flat/shrunk.

• Why are stomata important for photosynthesis?

• They let CO₂ enter, which is needed to make glucose

• Allows O₂ to move out the leaf as it’s a product of photosynthesis

• When do plants close their stomata and why?

• At night, it closes to save water because photosynthesis does not occur without sunlight

• In hot/dry conditions to save water (water evaporates quick when it’s hot)

• As an exception, CAM plants adapt to hot and dry climate (like cacti), so their stomata open at night to take in CO2 and close it during the day to save water

  • It’s a survival mechanism to prevent dehydration

Photosynthesis: carbon dioxide + water + sunlight → glucose + oxygen

• Where do light-dependent reactions occur?

• Thylakoid membranes within chloroplasts of plant cells

  • Light energy is absorbed by chlorophyll and other pigments in this membrane

The energy is used to split water, release oxygen, and create ATP and NADPH molecules

• Where do light-independent reactions occur?

• In the stroma of the chloroplast

The enzymes in the stroma use the energy from ATP and NADPH to convert CO2 to glucose

• What are the inputs and outputs of the Calvin cycle?

• Inputs: CO₂ , ATP, NADPH

• Outputs: G3P, glucose, ADP, NADP

• Why is the Calvin cycle sometimes called “dark reactions” even though it doesn’t happen in darkness?

• Because it doesn’t require light directly

• It uses ATP and NADPH made in the light reactions.

Palisade Mesophyll

Purpose: maximize light absorption

Spongy Mesophyll

Function: gas exchange (CO₂ in, O₂ out)

Vascular Bundle (vein)

 Purpose: transport system

Bundle Sheath Cells (important in C₄ plants)

• Site of the Calvin cycle in C₄ plants

Purpose: prevent photorespiration and increase efficiency

Guard Cells

 Purpose: gas exchange and controlling water loss

Stomata

Function: allow CO₂ in and O₂ + water vapor out