Photosynthesis

Chloroplast Structure&

Reactants Products

Carbon dioxide

C6H12O6

Photosynthesis

H2OCO2 O2

Water

+ 66

Lightenergy

Oxygen gasGlucose

+ 6

Plant Cells Contain Chloroplast – the organelles that carry on photosynthesis converting light

energy into sugar!

Raw Materials

Simple Sugar

Gas Used Gas Released

Photosynthesis• Chloroplasts are

concentrated in mesophyll, the green tissue in the interior of a leaf

• Membranes in the chloroplast form the framework where many of the reactions of photosynthesis occur

Fig. 7-2a

CO2 O2Stoma

Mesophyll Cell

Vein

Chloroplast

Mesophyll

Leaf Cross Section

Leaf

The Chloroplast• A chloroplast contains two membranes (as do

mitochondria)• A thick fluid called the stroma fills the inner

compartment of the chloroplast• Suspended in the stroma are the thylakoids, a

system of interconnected individual membranous sacs, which enclose another compartment known as the thylakoid space

• The thylakoids are arranged in stacks called grana

Chloroplast

Outer and innermembranes

IntermembranespaceGranumStroma Thylakoid

space

Thylakoid

The Chloroplast

• Built into the thylakoid membranes are the chlorophyll molecules that capture light energy

• Photosynthesis occurs throughout a plant (all the green parts), but is concentrated in the leaves

• A plant will invest much of its energy into the production of its leaves in order to capture as much light energy as possible

Make like a tree and…

• Leaves are designed to capture light and increase the absorption of carbon dioxide

• Carbon dioxide enters the leaf (and oxygen exits the leaf) via the stomata, tiny pores protected by guard cells

• Water is supplied to the tree via its roots, but may exit the leaves when the stomata are open (a catch 22!); why stomata open at night in many plants

Pigments

• Pigments are light-absorbing molecules built into the thylakoid membranes

• Pigments absorb some wavelengths of light, but reflect others

• We do not see the absorbed wavelengths (because their energy has been absorbed by the pigment molecules); we see the wavelengths that the pigment reflects!

Pigments

• A leaf is green because chlorophyll absorbs colors other than green; absorbs light most strongly in the blue and red, but poorly in the green

• Different pigments absorb different wavelengths

• Chloroplasts contain different types of pigments

Pigments• Chlorophyll A (a

type of chlorophyll pigment) absorbs light mainly in the blue-violet (high energy) and Chlorophyll B red (low energy) wavelengths

Light

Chloroplast

Thylakoid

Absorbedlight

Transmittedlight

Reflectedlight

Pigments

Light

Chloroplast Absorbedlight

Transmittedlight

Reflectedlight

•In addition to chlorophyll, other pigments, known as accessory pigments are present in plants; these include carotene, and cyanins, colors like orange & brown.

Autumn color change

• Autumn leaf color is a phenomenon that affects the normally green leaves of deciduous trees and shrubs, changing to reds and yellows (and various shades in between)

• In late summer, the veins that carry fluids into and out of the leaf are gradually closed off, and chlorophyll decreases

Autumn color change

• When chlorophyll concentrations decrease at the end of summer, some of these other pigments – which are usually masked by chlorophyll – reveal their colors

• Carotene, for example, is especially long-lasting variations of orange color

http://ohad.me/?showimage=53

The Chloroplast Structure Cont.

Fig. 7-2b

Chloroplast

Outer and innermembranes

IntermembranespaceGranumStroma Thylakoid

space

Thylakoid

Fig. 7-2a

CO2 O2Stoma

Mesophyll Cell

Vein

Chloroplast

Mesophyll

Leaf Cross Section

Leaf

Fig. 7-6b

Light

Chloroplast

Thylakoid

Absorbedlight

Transmittedlight

Reflectedlight

Fig. 7-0c

Carbon dioxide

C6H12O6

Photosynthesis

H2OCO2 O2

Water

+ 66

Lightenergy

Oxygen gasGlucose

+ 6