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Exam II Powerpoint II. PHOTOSYNTHESIS CO 2 + H 2 O sunlight energy > C 6 H 12 O 6 + O 2 + H 2 O. The Sun. is the ultimate source of biological energy for living organisms.

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CO2 + H2O sunlight energy>C6H12O6 + O2 + H2O

the sun
The Sun

is the ultimate source of biological energy for living organisms.

The light waves that come from the Sun include visible light that we see and shorter wavelengths (with more energy) and longer wavelengths that we cannot see.

primary producers
Primary Producers

Plants, some protists, and some prokaryotes capture sunlight energy with photosynthetic pigments

plant pigments
Plant Pigments

Chlorophyll which is found in chloroplasts is the most common pigment. It appears green because it absorbs light of colors other than green and allows green light to be reflected and thus detected by other organisms.

There are also accessory photosynthetic pigments that make plants appear yellow and orange

leaves and chloroplasts
Leaves and Chloroplasts

The primary photosynthetic organs of plants are leaves.

Plants and photosynthetic know thylakoids, stroma, granuum, and inner and outer membranes)

light dependent reactions
Light dependent reactions

the “photo part of photosynthesis” that occur in the thylakoids

light absorption
Light absorption

Photochemical reactions involve the trapping of light.

Light energy excites pigment molecules and causes an electron to be freed which begins moving through an ETS (next step).

There are two photosystems [Photosystem I (with chlorophyll a absorbing lightwaves of 700 most efficiently; P700) and Photosystem II (also with chlorophyll a but absorbing lightwaves of 680 most efficiently; P680)] that are involved in capturing the energy and the beginning of electron transfer

electron transfer
Electron transfer

The electron that is excited in Photosystem I is sent along the ETS to NADP+ and as another electron is passed to NADP+, the latter is reduced to NADPH (a coenzyme and energy intermediate) which carries electrons.

Now light energy absorbed by Photosystem II is transferred into an electron thus exciting it and causing it to be sent to P700 (of Photosystem I) which can now absorb more light energy because of the replaced electron (note that Photosystem II has electrons replaced from split water molecules which also results in the formation of O2).

chemiosmotic synthesis of atp
Chemiosmotic synthesis of ATP

This is the final phase of energy capture and involves the movement of the hydrogen ions through ATP synthase with the release of energy and finally the synthesis of ATP from ADP. In addition, NADP+ picks up the H+ producing NADPH.


Overall, the light dependent reactions provide energy (in the form of cpe in ATP and cpe in NADPH), and H ions to be used as building blocks for glucose (from the NADPHs). Oxygen is released as a byproduct.

light independent reactions
Light Independent Reactions

or Carbon fixation

the “synthesis part of photosynthesis” that occurs in the stroma of the chloroplast


Carbon fixation occurs when a gas (CO2) is incorporated into a solid (e.g., a carbohydrate)

During energy capture the energy and the hydrogen needed for carbon fixation are required.

Carbon fixation involving atmospheric CO2 occurs during the reactions of the Calvin Cycle


The battle against world hunger can use plants adapted to water scarcity pp. 140-142

Greenhouse Gases pp. 607-609




Genetic Information

genes and chromosomes
Genes and Chromosomes

Genes are portions of DNA molecules that contain genetic information which controls protein synthesis.

Each chromosome is made up of DNA and associated proteins. The DNA of each chromosome contains many genes.

gene expression
Gene Expression

the process whereby genes direct protein synthesis

The order of this process is

DNA > RNA > protein

DNA is transcribed into RNA

RNA is translated into proteins

dna structure
DNA structure

DNA is composed of subunits called nucleotides which consist of a 5Carbon sugar (deoxyribose), phosphate group(s), and nitrogenous bases (A, T, C, and G)

Nucleotides are linked by sugar-phosphate bond which basically form a backbone

The 3-D structure of DNA (from Franklin; Watson and Crick) is a twisted spiral (or more commonly called a helix) consisting of two strand of DNA, thus it is called a double helix

dna replication
DNA Replication

In addition to serving as the code for proteins, DNA also undergoes replication

Replication is the duplication of DNA within a cell prior to cell division (e.g., mitosis or meiosis I)

The original strands of the double helix serve as a template for the new strands (replication is semi-conservative)

Enzymes are involved in replication (e.g., helicase and DNA polymerase)


Mistakes may occur during replication or mutations may be induced by a variety of mutagens (substances or phenomena that cause changes in DNA). Mutagens include: UV radiation which causes thymine dimers, X-rays, nicotine, and many other drugs or man-made chemicals

mutations can be
Mutations can be:

beneficial - antibiotic resistance in bacteria is good for the bacteria (but not for us of course), sickle-cell anemia (actually a person with one gene for hemoglobin S, a carrier, is at an advantage to people with two normal hemoglobin genes in areas of the world where malaria is endemic), and mutations are a source of variation which is necessary for evolution to occur.

deleterious - many mutations are bad in that they result in serious conditions and possibly death, for example- UV light causes thymine dimers in bacteria which prevent replication and thus eventually the colony of bacteria will die.

Neutral or silent - some mutations do not change the protein that is coded for by that gene. This is because each amino acid has more than one triplet code