Chapter 10, Problem 1IQ

Summary Introduction

To label: The indicated parts of a chloroplast.

Introduction: Photosynthesis is a process in which the green plants and algae obtain their nutrients. This process takes place in the chloroplast where chlorophyll molecules are present. The chloroplast contains the thylakoid membrane where the light reaction takes place. The end product of the light reaction is the formation of ATP and NADPH, which together help in driving the Calvin cycle in the stroma of the chloroplast.

Answer to Problem 1IQ

Pictorial representation: Fig.1 shows the parts of chloroplast.

Fig.1: The parts of chloroplast

Explanation of Solution

The chloroplast is a double membrane bound organelle, which contains the chlorophyll pigments, stroma, grana, and thylakoid. The outer membrane of the chloroplast provides protection and permeability to small ions into the chloroplast. The thylakoid present in the inner membrane of the chloroplast contains chlorophyll, which absorbs the light energy and provides green color to the chloroplast. The thylakoid membrane separates the chloroplast into two separate compartments. The interior compartment is the thylakoid lumen. It is a continuous aqueous phase that plays an important role in photophosphorylation.

The exterior compartment, which consists of colorless fluid, surrounding the grana (stacks of thylakoids) is called chloroplast stroma. Thylakoid space present in the chloroplast mostly serves to provide structure and to build up a concentration gradient of protons during photosynthesis. As the molecules pass the electrons in the electron transport chain, they pump hydrogen ion from the stroma to the thylakoid lumen. In the chloroplasts, ATP synthase is embedded into the thylakoid membrane. The H⁺ ions are pumped into the inner thylakoid space (thylakoid lumen) in the chloroplast by increasing its concentration in the thylakoid lumen that can be used to make ATP. The ATP is synthesized in the chloroplast stroma.