Chapter 17 photosynthesis Flashcards
Describe the structure of chloroplasts.
Chloroplasts are double membrane organelles, so there is an outer membrane and inner membrane. The liquid that makes up the chloroplast is called the stroma. Freely flowing in the stroma is strands of ‘naked’ DNA. As well as this, there are ribosomes and starch grains (as glucose is a product of photosynthesis, it is stored in the chloroplasts in the form of starch). Thylakoids are structures that are in the shape of disks. The thylakoids are stacked on one another to make a structure called a granum. Numerous grana are joined together by intergranular lamella. The function of thylakoids in the chloroplasts is that it is involved in the first stage of photosynthesis- the light dependent stage. The thylakoid membrane contains photosystems, which contains photosynthetic pigments that absorbs the light energy needed for photosynthesis to occur.
How are chloroplasts adapted for photosynthesis?
Thylakoid membranes are stacked- This gives a larger surface area for which more light dependent reactions can occur.
Photosynthetic pigments are organised into photosystems- The efficiency of light absorption is maximised.
Grana are surrounded by stroma- Products of the light dependent stage can pass directly to enzymes in the stroma to initiate the light independent stage.
Chloroplasts have their own DNA and ribosomes- Photosynthetic proteins can be produced within the chloroplasts rather than being imported from the cell.
Where does the light dependent stage of photosynthesis occur?
The light dependent stage of photosynthesis occurs in the thylakoid membrane.
Where does the light independent stage occur?
Occurs in the stroma.
Describe the arrangement of different pigments in the photosystem.
Primary pigments are the pigments that mainly absorbs the light energy. It is found in the main area of absorption- the reaction centre.
Accessory pigments also assists with absorbing light energy, and they funnel this energy to the reaction centre (hence, they themselves do not exist in the reaction centre).
Give examples of primary pigment.
Chlorophyll a
Give examples of accessory pigments.
Chlorophyll b, carotenoids, xanthophyll.
The process of chemiosmosis, in any organism (and any part within the organism), must occur where?
The process of chemiosmosis must occur over a membrane.
At the start of chemiosmosis, electrons become ‘excited’. What does this mean?
The electrons are raised to a higher energy level.
Describe the process of chemiosmosis.
> High energy electrons pas through an electron transport chain (series of electron carriers).
Energy is released as electrons are passed down to lower energy levels.
Energy released is used to pump hydrogen ions across the membrane (through proton pumps).
A proton gradient is established across the membrane.
Protons move down the concentration gradient through channel proteins linked to ATP synthase (a protein).
The flow of proteins provides kinetic energy to enable ATP synthase to make ATP, by driving an ADP and Pi closer together.
In the light dependent stage, electrons, oxygen and hydrogen ions are produced. How does this occur?
This occurs firstly when light hits the first photosystem in the thylakoid membrane- Photosystem II. Through this process, light also hit water molecules (this water is drawn up from the roots). This process breaks down the water molecule, and is called photolysis. The products of photolysis is 2 electrons, 2 hydrogen ions and half an oxygen molecule.
In the light dependent stage, after photolysis, the electrons produced becomes ‘excited’. How?
The electrons absorbs some of the light energy that hit Photosystem II.
