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LSU / Biological Sciences / BIOL 1001 / In biology, what is the chloroplast?

In biology, what is the chloroplast?

In biology, what is the chloroplast?

Description

School: Louisiana State University
Department: Biological Sciences
Course: General Biology
Professor: S. crousillac
Term: Fall 2018
Tags:
Cost: 25
Name: Biology, Week 6 Notes
Description: Week 6 Materials: Chapter 7 Notes - Photosynthesis
Uploaded: 09/30/2018
6 Pages 120 Views 6 Unlocks
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C H A P T E R 7 :


In biology, what is the chloroplast?



P H O T O S Y N T H E S I S  

7.1 What is Photosynthesis?

Energy

o Most organism acquire energy either directly,

through prosthesis, or indirectly, through

consumption

o Photosynthesis – the process of tapping

and storing solar energy as chemical

energy

 Chloroplast in leaves allow for this to

happen

Photosynthesis  

o Photo” refers to light reactions

o Chlorophyll and other pigment molecules embedded in thylakoid  membranes capture sunlight energy and convert some into chemical  energy stored in the energy-carrier molecules ATP and NADPH o “Synthesis” refers to Calvin Cycle


How is light energy converted to chemical energy?



o Enzymes in stroma use CO2 and chemical energy (from ATP and  NADPH) to synthesize a three-carbon sugar (will be used to make  glucose)

o Leaves are covered by the cuticle

o Transparent, waxy, waterproof covering that reduces evaporation of  water

o Leaves obtain CO2 for photosynthesis

from air through stomata (singular: Don't forget about the age old question of Why is the elasticity of demand always negative?

stoma)

o Carbon dioxide + water + sunlight 

glucose (sugar) and oxygen

Mesophyll

o Loosely packed layers of internal. Leaf Don't forget about the age old question of What are the types of dimensions?

cells where chloroplasts are located

o Features vascular bundles  

o Veins transporting water, minerals, and sugars throughout the plant o Surrounded by bundle sheath cells


What is the carbon fixation?



Chloroplasts  

o Chloroplast - organelle with a double membrane enclosing fluid called  stroma

o Embedded with  

o Disk-shaped membranous sacs, stacked into grana

o Light-dependent reactions of photosynthesis occur in and adjacent to  the membranes of the thylakoids

7.2 The Light Reactions: How is Light Energy Converted to Chemical Energy? Don't forget about the age old question of What are the symptoms of generalized anxiety disorder?

Electromagnetic Spectrum

o Electromagnetic spectrum - range of energy emitted from the sun ranting  from short-wavelength gamma rays through ultraviolet, visible, and infrared  light to long-wavelength radios wavesWe also discuss several other topics like What are the roles of advertising?

Light Energy

o Light is composed of photons

o Photons – packets of energy

o Visible light has wavelengths with energies strong enough to alter biological  pigment molecules such as chlorophyll

o Green light is reflected making leaves appear green

o Accessory pigments If you want to learn more check out What is the human leukocyte antigen complex?

o Absorb additional wavelengths of light energy and transfer them to  chlorophyll a

 Chlorophyll b absorbs blue and red-orange wavelengths missed  by chlorophyll a

 Carotenoids absorb blue and green light and reflect yellow and  orange (they appear yellow or orange)

∙ in autumn, chlorophyll breaks down before carotenoids do

, revealing their yellow color

Light Reactions

o Light reactions occur in association with thylakoid membranes, which contain  photosystems

o Clusters of chlorophyll and accessory pigments

o Photosystem II and photosystem I work together during light reactions o Each PS has a unique ETC located adjacent to it

o Electron-carrier molecules

o Reaction center – pair of specialized chlorophyll a molecules and  primary electron acceptor molecule embedded in a complex of proteins o Path of electrons:

o PS II  ETC II  PS I  ETC I  NADP+ 

Steps in Light Reactions

1. Photons of light are absorbed by pigment molecules

clustered in PS II

2. An energized electron is ejected from the reaction Don't forget about the age old question of What defines electrochemical gradient?

center

3. The primary electron acceptor captures the electron

4. The primary electron acceptor passes the electron to

the first molecule of ETC II, then it is passed from one

electron-carrier molecule to the next, releasing

energy as it goes

5. Some of the energy released is used to pump H+ across the thylakoid  membrane into the thylakoid space, leading to ATP synthesis

6. The low-energy electron leaves ETC II and enters the reaction the center of PS I, replacing the electron ejected when light strikes PS I

7. The primary electron acceptor of PS I captures the electron

8. The primary electron acceptor passes the electron to the first molecule of ETC I, passed along until it reaches NADP+

9. NADPH is formed when the NADP+ molecule picks up two energetic electrons,  along with H+ 

Electron Movement  

o Chemiosmosis – electron movement

through the thylakoid membrane creates an

H+ gradient that drives ATP synthesis

o During a light reaction, H+

concentration inside of the thylakoid

space builds  

o H+ flows down is concentration

gradient through thylakoid channel

protein called ATP synthase

generating ATP from ADP

7.3 The Calvin Cycle: How is Chemical Energy Stored in Sugar Molecules?

Calvin Cycle

o The Calvin cycle captures carbon dioxide 

o The ATP and NADPH created from light reactions power the creation of simple sugar

o Occurs in the stroma  

Carbon Fixation

o Carbon from CO2 is incorporated, or “fixed,” into a larger organic molecule o Enzyme rubisco combines three CO2 molecules with three  RuBP (ribulose bisphosphate) molecules

o molecules, forming three unstable six-carbon molecules that each quickly split in half, forming six molecules of phosphoglyceric acid (PGA)

o Because of generation of this three-carbon PGA molecule, the Calvin cycle is  often referred to as C3 pathway

o Carbon from CO2 is incorporated, or “fixed,” into a larger organic molecule o Enzyme combines three CO2 molecules with three RuBP (ribulose  bisphosphate) molecules

o molecules, forming three unstable six-carbon molecules that each quickly  split in half, forming six molecules of phosphoglyceric acid (PGA)

o Because of generation of this three-carbon PGA molecule, the Calvin cycle is  often referred to as C3 pathway

G3P

o Synthesis of G3P

o Energy donated by ATP and NADPH (generated by light reactions) is  used to convert six PGA molecules into six three-carbon G3P molecules o Regeneration of ribulose bisphosphate (RuBP)

o ATP from light reactions is used with five of the six G3P molecules  formed to regenerate five-carbon RuBP (three molecules) necessary to  repeat cycle

o Remaining G3P molecule exits cycle

Photorespiration

o Problem in hot environments and oxygen builds in the plant cells o Rubisco will then bind to O2 rather than CO2 especially when there are more  O2 than CO2

o Photosynthesis is not always 100% efficient

o About 33% less carbon fixed

o Some species have evolved and created alternatives pathways to avoid  wasteful photorespiration

o C4 Pathway  

o Crassulacean acid metabolism  

What do plants  do with

glucose?

o Broken down during cellular respiration so the plant’s cells get energy o Linked to form starch (a storage molecule)  

o Linked to form cellulose (a major component of plant cell walls) o Components may be used in amino acids, nucleic acids, nectar, fruit

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