Photosynthesis

Energy & LifePhotosynthesis is the process of capturing and transforming the energy of sunlight into chemical energy. (What type of organisms can make their own food?)

a. Autotrophs – organisms that can make their own food

b. Heterotrophs – organisms that obtain energy from the food they

consume

Energy & LifeChemical Energy and ATP

a. ATP – energy molecule used by cells (Fig. 8-2)

b. Energy is stored in the bonds between phosphate

c. When these bonds are broken energy is released

Energy & Life

Energy & LifeUsing Biochemical Energy

a. Active Transporthttp://www.dnatube.com/video/359/Active-Transport

b. Motor proteins move organelles throughout the cellhttp://www.youtube.com/watch?v=tL99pwdvmhU c. Synthesize various molecules

Photosynthesis: An OverviewI. Understand the

significance of Helmont’s,

Priestley’s, and Ingenhousz’s experiments.

II. 6CO2 + 6H2 O C6 H12 O6 + O2

Photosynthesis: An OverviewIII.Light and Pigments (Fig. 8-5)

A. Wavelength – distance between crests; shorter wavelengths have higher energy than longer wavelengths

Photosynthesis: An OverviewIII.Light and Pigments (Fig. 8-5)

B. Photon – a particle of lightC. In photosynthetic organisms,

absorbed energy is used to make chemical energy (glucose)D. Photosynthetic pigment – molecule that absorbs light (color you see is the color being reflected)

1. chlorophyll a - primary pigment; converts light energy to chemical

energy

Photosynthesis: An OverviewIII.Light and Pigments (Fig. 8-5)

D. Photosynthetic pigment (con’t)

1. chlorophyll a - (con’t)a. reflects green lightb. absorbs red & blue

lightc. normally hides other pigments

2. Chlorophyll b – accessory pigment; absorbs light

andtransfers the energy tochlorophyll a

Photosynthesis: An OverviewIII.Light and Pigments (Fig. 8-5)

D. Photosynthetic pigment (con’t)

3. carotenes & xanthophylls –

accessory pigment; colors

can be seen in autumn when

chlorophylls start to break

downE. Absorption spectrum – the different

colors (wavelengths) of lightabsorbed by each pigment

Reactions of PhotosynthesisI. Inside a chloroplast – organelle

in which photosynthesis occurs

Reactions of PhotosynthesisI. Inside a chloroplast

A. Thylakoids – flattened sacs of photosynthetic membranes; pigments and proteins are organized into photosystems in order for light energy to be captured & stored as chemical energyB. grana – stacks of thylakoidsC. stroma – region between grana

Reactions of PhotosynthesisII. Electron Carriers – molecules

that can accept a pair of high-energy electrons and protons and transfer them to another molecule (NADP+)

Reactions of PhotosynthesisThere are two sets of reactions that take

place within the chloroplasts: The light dependent reactions & the Calvin Cycle (also know as the light independent or the dark cycle)

Reactions of PhotosynthesisIII.Light Dependent Reactions

A. Takes place only in the presence of lightB. Occurs on membranes of thylakoidsC. Produces high energy compounds that are used in the dark reaction: ATP and NADPHD. Photosystem II

1. pigments absorb light energy and electrons are boosted to a higher

energy level

Reactions of PhotosynthesisIII.Light Dependent Reactions

D. Photosystem II (con’t)2. lost electrons are

replaced by the splitting of H2O into 2 e- ,2 p+, and O2

a. electrons are picked up by NADP

b. protons (H+) are pumped into inner thylakoid space

Reactions of PhotosynthesisIII.Light Dependent Reactions

E. Photosystem I1. pigments use energy

from light to re- energize the elctrons from photosystem II

2. produces NADPH which also powers the Calvin Cycle

Reactions of PhotosynthesisIII.Light Dependent Reactions

http://www.youtube.com/watch?v=Oi2_n2wbB9o

Reactions of PhotosynthesisIV.The Calvin Cycle – (light

independent, dark reaction) – uses ATP and NADPH from the light dependent reactions to produce high energy sugars (Fig. 8-11)

A. Takes place with or without the presence of light as long as ATP and NADPH are availableB. Occurs in the stroma of chloroplastC. 6CO2 molecules enter the cycle from the atmosphere and combine with 6 five

carbon molecules

Reactions of PhotosynthesisIV.The Calvin Cycle (con’t)

D. The resulting 12 three carbon molecules use the energy from ATP and NADPH to produce 12 high energy three carbon moleculesE. 2 of these molecules are used to synthesize sugar and other compoundsF. The remaining 10 molecules are used to produce more of the “starting” 6 carbon molecule of the cycle

The Calvin Cyclehttp://www.youtube.com/watch?v=_NIhg1qa_L0

Reactions of PhotosynthesisV. Factors Affecting

PhotosynthesisA. Light intensity – as intensity increases the rate of photosynthesis increases (up to a point)B. Temperature – photosynthesis occurs rapidly at specific temp.; extreme temps. are damaging to enzymesC. H2O – decrease in water slows rate of photosynthesisD. Minerals – must be present in certain amounts