Photosynthesis

Energy balance of Respiration and Photosynthesis Completely burning glucose yields 686 kcal per 180 g. That’s 4 kcal/g of sugar or carbohydrate that you eat. Building glucose from CO2 in the air and H2O takes 686 kcal per 180 g (2,840 KJ/180 g). Sunlight is converted into electrical energy in the leaf. The glucose is then further assembled into cellulose, lignin, and starches.

First, a brief review of plant cells

The ‘power plant’ of the cell: Animal cells have mitochondria Plant cells have chloroplasts

Leaf Structure vascular bundle (vein) xylem (water) phloem (sugar) cuticle epidermis palisades layer spongy layer epidermis stomate guard cells cuticle

Function of Leaf Structures Cuticle = ‘skin’ in Latin waxy coating reduces water loss Epidermis = ‘upon’ + ‘skin’ in Gk. skin protecting leaf tissues Palisades layer = ‘a fence of stakes’ in Latin high concentration of chloroplasts Spongy layer air spaces gas exchange CO2 in for sugar production, remove waste O2

Transpiration Xylem = ‘wood’ xylem (water) stomate guard cells O2 H2O CO2 stomate guard cells O2 H2O CO2

Transpiration Water evaporates from the stomates in the leaves pulls water up from roots water molecules stick to each other more water is pulled up tree from ground

Stomates & Guard Cells Stoma = mouth guard cell stomate Function of stomates CO2 in O2 out H2O out Function of guard cells open & close stomates guard cell stomate

Guard cells & Homeostasis Homeo = similar Stasis = standing still Guard cells & Homeostasis Homeostasis keeping the internal environment of the plant balanced Stomates open let CO2 in needed to make sugar let H2O out so it gets to leaves let O2 out get rid of waste product Stomates close if too much H2O evaporating

Xylem carry water up from roots Xylem = ‘wood’

Phloem: food-conducting cells “Phloem” means husk or bark carry sugars around the plant wherever they are needed new leaves fruit & seeds roots

Photosynthesis

The overall process has 2 phases – light dependent and light independent. Light phase: energy harvesting Dark phase: molecule building. The Calvin Cycle.

Stage 1. The light-dependent phase: energy conversion/ energy harvesting Takes place in the thylakoid membrane inside the chloroplast. Involves PS I and PS II systems.

‘Light reactions’: The simple view

The ‘less simple’ view

The complex view

The light reactions actually happen in 2 steps, with slightly different pigments

The ‘antenna’ pigments capture a range of wavelengths and channel the (now electrical) energy to chlorophyll A

Greens and yellows are emitted

Now on to Stage 2, the light-independent (dark) phase, also known as: ‘Glucose construction’ ‘Carbohydrate assembly’ ‘Carbon or CO2 fixation’ Takes place outside of the thylakoid membrane in the stroma inside the chloroplast

Again, the overall process

The Calvin Cycle. One of the greatest discoveries of modern science The Calvin Cycle. One of the greatest discoveries of modern science. Melvin Calvin awarded the 1961 Nobel Prize in Chemistry.

Alternate view

Energy molecules: ATP and NADPH Currency analogy ATP = $.25 Glucose = $10.00 (38 ATP’s to build 1 glucose) Battery analogy ATP phosphate bond stores 30 KJ/mol (7kcal/mol) NADPH/NADP+ stores ≈ 200 KJ/mol (50kcal/mol) Glucose C6H12O6 bond energy = 2,840 KJ/mol (686 kcal/mol) Each cell produces 10 million ATP molecules per second

ATP – the battery of the cell The 3rd phosphate bond contains 30 KJ/mol (7kcal/mol)

ATP = charged battery ADP = depleted battery This bond stores about 30KJ/mol

NADPH is the other energy molecule in photosynthesis.

NADP+ = oxidized form. Depleted battery. NADPH = reduced form. Charged battery. The extra electron carries ≈ 7X the energy as an ATP molecule. NADP+ = oxidized form. Depleted battery. This bond stores about 200KJ/mol

Photosynthesis pigments Discussion: which solvent, polar or non-polar, can be used to extract and dissolve each from leaves?

Chlorophyll B