PHOTOSYNTHESISand its relationship to cellular respiration

Process by which plants and other autotrophs convert the energy of sunlight into sugars.

Requires sunlight, water, and carbon dioxide.

Overall equation:

6 CO2 + 6 H20 C6H12O6 + 6 O2

Occurs in the leaves of plants in organelles called chloroplasts.

PHOTOSYNTHESIS IN OVERVIEW

LEAF STRUCTURE Most photosynthesis occurs in the palisade layer. Gas exchange of CO2 and O2 occurs at openings

called stomata surrounded by guard cells on the lower leaf surface.

Palisade

Spongy

PHOTOSYNTHETIC ORGANISMS

Photosynthesis transforms solar energy

Organic molecules built by photosynthesis provide both the building blocks and energy for cells.

Plants use the raw materials: carbon dioxide and water

photosynthesis occurs in choloroplasts

CHLOROPLASTS

CHLOROPLAST STRUCTURE

Inner membrane called the thylakoid membrane.

Thickened regions called thylakoids. A stack of thylakoids is called a granum. (Plural – grana)

Stroma is a liquid surrounding the thylakoids.

CHLOROPLASTS

Chlorophylls and other pigments involved in absorption of solar energy reside within thylakoid membranes of chloroplasts

PIGMENTS Chlorophyll A is the most important

photosynthetic pigment. Other pigments called antenna or

accessory pigments are also present in the leaf.Chlorophyll BCarotenoids (orange / red)Xanthophylls (yellow / brown)

These pigments are embedded in the membranes of the chloroplast in groups called photosystems.

IT ALL STARTS WITH SUNLIGHT This shows the visible light spectrum Notice that different colors have different light

wavelengths. Pigments found in chlorophyll absorb various portions

of visible light as seen in this absorption spectrum.

IT ALL STARTS WITH SUNLIGHT

Two major photosynthetic pigments are chlorophyll a chlorophyll b.

Both chlorophylls absorb violet, blue, and red wavelengths best.

Very little green light is absorbed; most is reflected back; this is why leaves appear green.

AUTUMN COLORS

Carotenoids are yellow-orange pigments which absorb light in violet, blue, and green regions.

When chlorophyll breaks down in fall, the yellow-orange pigments in leaves show through.

TWO SETS OF REACTIONS Occurs in two main phases.

Light reactions Dark reactions (aka – the Calvin Cycle)

Light reactions are the “photo” part of photosynthesis. Light is absorbed by pigments.

Dark reactions are the “synthesis” part of photosynthesis. Trapped energy from the sun is converted to the chemical energy of sugars.

TWO SETS OF REACTIONS Light reactions cannot take place unless light is present. They are

the energy-capturing reactions.

LIGHT REACTIONS

Light-dependent reactions occur on the thylakoid membranes. Light and water are required for this process. Energy storage molecules are formed. (ATP

and NADPH) Oxygen gas is made as a waste product.

DARK REACTIONS

Dark reactions (light-independent; Calvin cycle) occur in the stroma. Carbon dioxide is “fixed” into the sugar

glucose. the ATP and NADPH molecules created

during the light reactions power the production of this glucose.

THIS IS PRETTY HARD TO VISUALIZE, BUT THROUGH THE MAGIC OF TECHNOLOGY, WE CAN WATCH THESE PROCESSES AS ANIMATIONSYouTube: The process of photosynthesis.

Forest biology – the overall process

McGraw Hill Animation