Photosynthesis Flashcards
Site of photosynthesis
The leaf is the main photosynthetic structure in eukaryotic plants.
Chloroplasts are the organelles where it occurs.
Adaptations of the lead for photosynthesis
- large surface
- arrangement of leaves to minimise overlapping & therefore shadowing
- thin so most light is absorbed
- transparent cuticle and epidermis
- long, narrow upper mesophyll cells packed with chloroplasts
- lots of stomata so gas exchange and mesophyll cells are close
- stomata open and close in response to light intensity
- many air spaces for rapid diffusion
- network of xylem to bring water to leaf and phloem to carry it away
Equation for photosynthesis
6CO2 + 6H2O —> C6H12O6 + 602
Carbon dioxide + water -> glucose + oxygen
What is photosynthesis
A process of energy transferral
Light energy is conserved in chemical bonds
3 main stages of photosynthesis
1) capturing of light energy by chlorophyll
2) light dependent reaction
3) light independent reaction
Structure and role of chloroplasts in photosynthesis
Vary in shape and size. Usually disc shaped and 2-10um long and 1um diameter. Surrounded by double membrane.
- grana. Stacks of 100 discs called thylakoids. Thylakoids gave chlorophyll and some gave tubular extensions that join up thylakoids in adjacent to grana called intergranal lamelle
- stroma. Fluid filled matrix (LIR occurs)containing structures e.g. Starch grains
Where do light dependent reactions occur
In thylakoids membranes of chloroplasts
In membranes are light harvesting systems called photosystems
What is the aim of light dependent reactions
To produce ATP and reduced NADP to drive light independent reactions
Factors of oxidation
- gain of oxygen
- loss of electrons
- substance becomes oxidised
- loss if hydrogen(protons)
- energy given out
Factors of reduction
- loss of oxygen
- gain if electrons
- substance becomes reduced
- gain if hydrogen (protons)
- energy taken in
What is photoionisation
Electrons leave the chlorophyll molecule
Occurs because they become excited by the absorption of light energy
What is chemiosmosis
The theory of circulation of protons through thylakoids membrane (via ATP synthase) to produce ATP and reduced NADP
What is ATP synthase
An enzyme that makes ATP
What is photophosphorylation
Name of the way in which the ATP is being made
Photolysis
Occurs in thylakoids space
Uses up water
Products are protons, electrons and oxygen
The protons and electrons-> reduce NADP, oxygen - given off as a byproduct or used in respiration
Stages of the light dependent reaction
1) in the thylakoid membranes are proteins called electron carriers which are arranged in a chain in a sequence
2) electrons released from Chlorophyll pass down the carriers which is called the electron transfer chain
3) if the carrier has an electron it is said to be reduced. When the electron leaves the carrier, the carrier is said to be oxidised
4) as the electrons pass from one carrier to the next, some of the energy released is used to pump a proton(H+) into thylakoid space
5) the proton concentration in the thylakoid space is further increased by photolysis
6) a concentration gradient of protons is set up
7) protons can only move back through the thylakoid membrane by ATP synthase enzymes
8) as the protons move back through they generate the production of ATP from ADP plus a pi
9) NADP on the stroma side of the membrane combines with protons and electrons to form reduced NADP
Where does the light independent reaction take place
In the stroma of chloroplasts
What is the light independent reaction also called
Calvin cycle
Stages of the light independent reaction
1) CO2 from atmosphere diffuses into leaf through stroma and dissolves in water around walls of mesophyll cells. It then diffuses to cell surface membrane, cytoplasm and chloroplast membranes into stroma of chloroplasts.
2) in stroma, CO2 reacts with RuBP (catalysed by rubisco) to produce 2 molecules of 3-carbon GP
3) reduced NADP reduces GP to TP using energy from ATP
4) NADP is re-formed and goes back to LDR to be reduced again by accepting more protons
5) TP molecules are converted to organic substances that the plant requires such as starch, cellulose, lipids, glucose, amino acids and nucleotides
How many times must the LIR turn to make a whole molecule of glucose?
6
