Ch. 8.1: Photosynthesis Overview

Plants use sunlight to make food (glucose).

Plants and Photosynthesis Plants are autotrophs (producers) - make their

own food. Plant cells have chloroplasts which can capture

light energy and convert it into chemical energy – stored in glucose.

PhotosynthesisPhotosynthesis

HH22OO COCO22

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Light Light ReactionReaction

Dark ReactionDark Reaction

Light is AdsorbedLight is AdsorbedBy By

ChlorophyllChlorophyll

Which splitsWhich splitswaterwater

ChloroplastChloroplast

ATP andATP andNADPHNADPH22

ADPADPNADPNADP

Calvin CycleCalvin Cycle

EnergyEnergy

Used Energy and is Used Energy and is recycled.recycled.

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Chemical Equation for Photosynthesis

Chloroplast – the Photosynthetic Organelle in Plant Cells

Chloroplast

site of photosynthesis. Chloroplasts are concentrated in the

mesophyll tissue found in the leaf.

Mesophyll tissue is present right under the epidermis of the leaf and consists of Palisade tissue + spongy tissue.

Gases: Where Does the O2 Come From?

CO2 is taken into the leaf through stomata for photosynthesis.

O2 is released out of the leaf through stomata as a product of photosynthesis.

In order to determine whether the O2 gas product came from the reactant CO2 or from H2O, scientists used tracer (radio-isotopic) Oxygen, first in CO2 and then in H2O as follows:

Fate of Atoms in Photosynthesis CO2 becomes part of glucose (C6H12O6) H2O is split into H and O; O2 is

released as a gas; H’s become part of glucose.

Two Stages of Photosynthesis Photosynthesis occurs in two stages.

Light reactions (during day-time only, in the thylakoid membrane)

Calvin Cycle (both day and night, in the stroma), which are linked together by NADPH and ATP.

Light Reaction Light reaction – is dependent on light and

occurs only during the day in nature. Where: thylakoid membrane of the

chloroplast.Light reactions involve: a) Splitting of water to produce O2 gas and

H for glucose. b) Production of

ATP = chem. Energy NADPH (carries H, also energy).

Calvin Cycle independent of light and occurs during

the day and the night. Where: stroma of the chloroplast. Calvin Cycle involves the production

of ‘food’ as glucose, by using CO2, ATP energy and NADPH.

Light Used in Photosynthesis Chlorophyll pigments can absorb only some

wavelengths of the visible light from the electromagnetic spectrum.

Visible light consists of the following colors or wavelengths in order of increasing wavelengths / decreasing energy: Violet Blue Green Yellow Orange

Red. Chloroplasts absorb mainly blue-violet and red-

orange lights. Green light is reflected and transmitted by green

plants – hence, they appear green.

Light

Photon = a discrete packet of light energy. The shorter the wavelength, the greater the

energy….and vice-versa.

PhotosynthesisPhotosynthesis

HH22OO COCO22

OO22 CC66HH1212OO66

Light Light ReactionReaction

““Dark” ReactionDark” Reaction

Light is AdsorbedLight is AdsorbedBy By

ChlorophyllChlorophyll

Which splitsWhich splitswaterwater

ChloroplastChloroplast

ATP andATP andNADPHNADPH22

ADPADPNADPNADP

Calvin CycleCalvin Cycle

EnergyEnergy

Used Energy and is Used Energy and is recycled.recycled.

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ATP = chemical energy

NADPH – carries Hydrogen(NADP + H)

Photosynthesis and Cellular Respiration Both Photosynthesis and Cellular Respiration

are reverse of each other. Photosynthesis is an endergonic reaction

(energy required for rxn) Cellular Respiration is an exergonic reaction

(energy released during rxn)

The Flow Of Biological Energy

Photosynthesis cellular respiration

carbohydrates/

energy rich O2

chloroplast mitochondria

CO2 + H2O ATP for:

(energy poor)movement/cell activity