Chapter 11 - Photosynthesis Flashcards
How does energy enter plants?
The energy in light is absorbed by chlorophyll and transferred into chemical energy during photosynthesis
Where does photosynthesis take place?
Chloroplasts
How are leaves adapted for photosynthesis?
A large SA to absorb sunlight
An arrangement that prevents overlapping and so shadowing of other leaves
Thin for a short diffusion pathway
Transparent cuticle to let light through to the palisade mesophyll cells
Upper mesophyll cells full of chloroplasts
Numerous stomata so mesophyll cells are never far from one
Xylem bringing water to leaf cells and phloem bringing food to roots
Air spaces in the spongy mesophyll for a large surface area
What is the overall equation for photosynthesis?
6CO2 + 6H2O -light-> C6H12O6 + 6O2
What are the three main stages of photosynthesis?
Capturing light energy
The light-dependent reaction
The light-independent reaction
What happens in the first stage of photosynthesis?
Light energy is captured in the chlorophyll of the chloroplasts to make ATP and photolyse water
What happens in the second stage of photosynthesis?
Light breaks the bonds in chlorophyll, causing water molecules to split by photolysis into protons, electrons and oxygen.
What are the products of the light-dependent reaction?
Reduced NADP, ATP and oxygen
What happens in the third stage of photosynthesis?
Protons are used to produce sugars and other organic molecules
How long are chloroplasts typically?
2-10 micrometres
What type of membrane can be found in chloroplasts?
A double membrane
What are the two distinct regions in a chloroplast?
The grana and the stroma
What is the stroma?
A fluid-filled matrix containing starch grains. Also where the light-independent stage takes place
What are grana?
Stacks of up to 100 thylakoid structures, which contain chlorophyll. Also where the light-dependent stage takes place
What happens when a substance is oxidised?
Gains oxygen, loses hydrogen or electrons
What happens when a substance is reduced?
Loses oxygen, gains hydrogen or electrons
What is the metabolic pathway?
A series of small reactions caused by enzymes
What is phosphorylation?
Adding phosphate to a molecule
What is photolysis?
A
What is photoionisation?
When light energy excited electrons, causing them to be released and move to a higher energy level
What is hydrolysis?
The splitting of a molecule using water
What is decarboxylation?
The removal of carbon dioxide from a molecule
What is dehydrogenation?
The removal of hydrogen from a molecule
What does NADP do?
NADP is a coenzyme - it transfers hydrogen from one molecule to another
At what wavelength does Pi best absorb light?
700 nm
At what wavelength does Pii best absorb light?
680 nm
What happens in the light-dependent reaction?
A chlorophyll molecule absorbs light energy, which excites the electrons in the chlorophyll and raises them to a higher energy level so they leave the chlorophyll. The chlorophyll has been photoionised. The electrons are taken up by an electron carrier molecule and passed along a chain of carriers via a series of redox reactions. Because each new carrier is at a slightly lower energy level, the electrons lose a bit of energy each time. This energy is used to combine a phosphate molecule with ADP to produce ATP
Describe chemiosmotic theory
Protons are pumped into the thylakoid membranes using protein carriers called protein pumps. The energy produced when water is photolysed is what fuels this movement. This creates a higher concentration of protons inside the thylakoid than in the stroma. Protons move down the concentration gradient into the stroma via the carrier protein ATP synthase. As they move through the protein, they change the shape of the enzyme, which catalyses the combination of ADP and Pi
What is the equation for the photolysis of water?
2H2O -> 4H+ + 4e- + O2
What happens to the protons produced when water is photolysed?
They pass out of the thylakoid via the ATP synthase protein, where they combine with electron carrier NADP, reducing it. This NADP enters the light-independent stage, taking with it the electrons created from the chlorophyll molecules
Where does the light-dependent reaction take place?
The thylakoids of chloroplasts
How are chloroplasts adapted for the light-dependent reaction?
The thylakoid membranes provide a large surface area
Proteins hold the chlorophyll in a precise manner that allows maximum absorption of light
Chloroplasts contain DNA and ribosomes so can quickly produce proteins required
The membranes have ATP synthase within them, which catalyses the formation of ATP
What is another name for the light-independent reaction?
The Calvin Cycle
Where does the light-independent reaction take place?
The stroma of the chloroplasts
What happens in the light-independent reaction?
CO2 diffuses into the leaf through the stomata and then into the stroma
Here, the CO2 combines with RuBP in a reaction catalysed by rubisco. This forms an unstable 6 carbon compound which quickly breaks down into two molecules of GP
The hydrolysis of ATP provides every and reduced NADP provides H+ ions to tun this GP into TP
The NADP goes back to the light-dependent reaction to accept more protons
Some TP is turned into glucose and the rest continues to regenerate RuBP
How many carbons are there in RuBP?
5
How many carbons are there in GP?
3
How many times does the Calvin Cycle need to occur to produce one hexose sugar?
6
How are the chloroplasts adapted for the light-independent reaction?
The matrix of the stroma contains all necessary enzymes
The stromal fluid surrounds the grana so products of the light-dependent reaction in the grana can diffuse into the stroma
Contains DNA and ribosomes so can easily make necessary proteins
What are the optimum conditions for photosynthesis?
High light intensity
Temperature at 25c
Carbon dioxide at 0.4%
Why is a high light intensity required for photosynthesis?
It provides the energy for the light-dependent reaction
Why is a temperature at 25c required for photosynthesis?
It is the optimum temperature for enzymes like rubisco
What is the saturation point?
Where the rate of respiration = rate of photosynthesis so there is no net movement of gas in the plant
