Unit 5A: Photosynthesis Flashcards
(32 cards)
Adaptations of a leaf
- broad and thin for larger SA
- waxy cuticle and upper epidermis transparent for sunlight
- palisade mesophyll are tightly packed for more chlorophyll
- spongy mesophyll have air spaces for gas exchange
- stoma on bottom of leaf to minimise water loss
How do stomata open and close
- turgor pressure makes guard cells expand, forcing the tough inner walls to be convex, opening the stoma.
- close during day and open during night to maximise gas exchange and minimise water loss
Features of chloroplasts
- double membrane
- 70S ribosomes
- lipid droplets
- starch granules
- stroma
- integral lamella
- thylakoids (grana)
Permeability of double membrane
- outer membrane permeable to small molecules, e.g water, co2
- inner membrane regulates passage of large substances through channel proteins
What does stroma contain
- enzymes, starch granules, proteins, chloroplast DNA and ribosomes
What are thylakoids
Disk shaped, fluid filled sacs, hollow, containing photosynthetic pigments.
What is a photosynthetic pigment
Coloured biological compound present in chloroplasts and photosynthetic bacteria, capturing light energy for photosynthesis
Why do we need pigments?
To capture the frequencies of all of the waves, allowing us to see them as visible light
What happens to light after it strikes a leaf
12% is reflected
83% is absorbed
4% is used in photosynthesis
5% of light is transmitted
Photosystem notes
- Pigment + protein = photosystem
- PS1 and PS2 contain a chlorophyll molecule which absorbs red light
- PS1 found in lamellae, absorbs 700nm
- PS2 found in thylakoid, absorbs 680nm
Two types of photosynthetic pigments
- chlorophylls (primary)
- carotenoids (accessory)
What is chromatography
A method used to separate molecules in mixtures
How does chromatography work
Molecules are dissolved and move through the mobile stage (liquid solvent) and get fixed to a stationary phase: different molecules spend different amounts of time in the mobile phase, separating them.
The longer the compounds spend in mobile phase depends on:
1) solubility - the more soluble the pigment the further it will travel
2) affinity to stationary phase - molecules which interact more strongly with the plate will not travel as far
3) mass - the smaller the molecule the further it will travel
Why should you use a non-polar solvent in chromatography
A polar solvent does not compete well, making the compounds remain in the stationary phase, therefore they would not move as far as they would with a non-polar solvent.
Where does light dependent reaction happen, and why
Thylakoids, because light energy is absorbed by chlorophyll in photosystems
How is light converted into energy
- Light energy excites the electrons in the chlorophyll, giving them more energy.
- electrons are released from chlorophyll, making it positively charged
What are coenzymes
- aids the function of an enzyme
- transfer a chemical group from one molecule to another
NADP notes
- coenzyme used in photosynthesis
- transfers hydrogen from one molecule to another
- reduces a molecule by giving it a hydrogen atom
- or oxidise another molecule, by reducing itself to NADPH
What is the light independent reaction
- calvin cycle
- doesnt use light directly
- can take place in the dark but not for long, as it uses products from light-dependent reaction
- happens in the stroma
- ATP and NADPH supply energy
Stages of non-cyclic photophosphorylation
1) photoionisation of chlorophyll in PS2
2) photolysis of water
3) electron transport chain
4) photophosphorylation (chemiosmosis)
5) photoionisation of chlorophyll in PS1
6) reduction of NADP to NADPH
What us photoionisation of chlorophyll in PS2
Chlorophyll absorbs light energy and causes excitation of an electron. The electron is lost from the chlorophyll, and captured by an electron acceptor, moving along the electron transport chain. Chlorophyll is then oxidised and positively charged
What is photolysis of water
Photoionisation of chlorophyll results in photolysis (splitting of water using light energy) into oxygen, hydrogen ions and electrons. Electron lost from chlorophyll molecule can be replaced and chlorophyll is reduced.
What is electron transport chain
Electron is passed from carrier to carrier along ETC in a series of rapid redox reactions, energy is released at each stage. Energy is used to move hydrogen ions from the stroma into thylakoid space against conc. gradient, creating an electrochemical gradient.
