Concept 8.1 Summary

Photosynthesis uses light energy to make food.

The Stucture of Chloroplasts
chloroplast
: organelle found in some plant cells and certain unicellular organisms where photosynthesis takes place
chlorophylls
: pigment that gives a chloroplast its green color; uses light energy to split water molecules during photosynthesis
- leaves contain the most chloroplasts = major sites of photosynthesis
- chloroplasts are concentrated in the cells of the mesophyll
- tiny pores, stomata, are found on the surface of the leaf
- stomata is where CO2 enters leaf and O2 exits
- veins carry water and nutriendts from the plant's roots to the leaves
- also transport organic molecules produced in leaves to other parts of the plant
- chloroplast's structure is key to its function
- thylakoids arranged in stacks = grana
- the various structures within th chloroplast organize the complex series of chemical reactions that make the process of photosynthesis
- some in thylakoid membranes and some in stroma

Overview of Photosynthesis
- opposite of cellular respiration occures in photosynthesis
- electrons go "uphill"
-occurs in two main stages

The Light Reactions
light reactions
: chemical reactions that convert the sun's energy to chemical energy; take place in the membranes of thylakoids in the chloroplast

1. chlorophyll molecules capture light energy
2. chloroplasts use energy to remove electrons from wateR
3. water splits into oxygen and hydogen ions (oxygen=waste product in photosynthesis)
4. oxygen leaves through the stomata of leaves
5. electrons and hydrogen ions are used by chloroplasts to make NADPH (a energy-rich molecule)
6. chloroplasts also use captured light energy to make ATP

- OVERALL: conversion of light energy to chemical energy stored in two compounds -> NADPH and ATP

The Calvin Cycle
Calvin cycle
: cycle in plants that makes sugar from carbon dioxide, H+ ions, and high-energy electrons carried by NADPH
- enzymes are located outside the thylakoids and dissolved in the stroma
- ATP made by light reactions provides energy to make sugar
- also referred to as "light-independent reactions"
- does not directly require light to begin, but cannot run in a plant left in the dark - requires ATP and NADPH both from light reaction

Concept Check

1. Draw and label a simple diagram of a chloroplast that includes the following structures: outer and inner membranes, stroma, thylakoids.
   


2. What are the reactants for photosynthesis? What are the products?
   The reactants for photosynthesis are carbon dioxide and water. The products are glucose and oxygen.
3. Name the two main stages of photosynthesis. How are the two stages related?
   The two main stages of photosynthesis are light reactions and the Calvin cycle. They are related because the Calvin cycle's inputs are the results of light reactions.