Module 5: Photosynthesis Flashcards
Label the leaf parts
How are palisade cells adapted to help photosynthesis?
Palisade cells are parallel to the direction of light entering the leaf. This means there are less cell walls to cross so more light is absorbed.
- Contain many chloroplasts – large amount of chlorophyll;
- Closely packed columnar cells arranged with long axis perpendicular to surface – reduces number of light absorbing cross walls and increases surface area;
- Chloroplasts moved by cytoskeleton (cyclosis) - to absorb maximum light or to protect from excessive light
- Thin cell walls – reduces diffusion pathway; efficient light penetration
- Chloroplasts at periphery of cell – short diffusion pathway
- Non pigmented vacuole – allow light penetration
How are leaves adapted to their function?
• Flat – large surface area - maximum light absorption. • Thin – short diffusion distance between palisade mesophyll cells & external environment (for CO2, H2O and O2); palisade mesoophyll cells are near the upper surface – maximises light absorption; upper epidermal cells are transparent –allows light to reach the palisade mesophyll cell. • Waxy transparent cuticle – allows light to enter; prevents loss of water for photosynthesis. • Lower epidermis contain stomata (pores) – allows gas exchange – intake of CO2 and release of O2.
How are spongey mesophyll cells adapted to their function?
• Spherical cells; less chloroplasts; larger intercellular air spaces for movement of gases and H2O vapour); store carbohydrates (and other organic substances) made by photosynthesis – which are taken into the phloem.
What is the difference between a heterotroph and autotroph?–
An autotroph is an organism that makes complex organic compounds (food) from inorganic molecules using energy (chemical or light). A photoautotroph makes its own food using light energy and inorganic materials. A heterotroph is an organism that cannot make organic compounds from inorganic sources. It needs a ready made supply of organic compounds (carbon compounds).Heterotrophs obtain their organic compounds by consuming other organisms. Almost all animals, fungi and some Protista and bacteria.
What is the chemical formula for respiration and photosynthesis?
Photosynthesis: 6CO2 + 6H20 –> C6H12O6 + 6O2 Respiration: 6O2 + C6H12O6 –> 6CO2 + 6H2O+ energy (ATP)
Explain the relationship between respiration and photosynthesis
Light –> photosynthesis in chloroplasts –> organic molecules + O2 –> respiration in mitochondria –> CO2 + H2O used in photosynthesis
Describe the structure of a chloroplast
Describe the size and shape of a chloroplast
• Usually between 2-10µm in length • Usually disc shaped
Describe the structure of a chloroplast membrane
• Chloroplasts are surrounded by a double membrane (known as the envelope). • The outer membrane is highly permeable. • The inner membrane is less permeable and has transport proteins embedded in it. • The inter-membrane space is 10-20nm wide between the inner and outer membrane.
Describe the structure of thylakoids and lamellae
• The inner membrane is folded into lamellae (thin plates) also called thylakoids. • Thylakoids are staked in piles called granum (pl. grana). • Intergranal lamellae (or stroma lamellae) link different stacks of thylakoids or grana. • One granum may contain up to 100 thylakoids.
Describe the structure of grana
• Grana are where the first stage of photosynthesis takes place - the light-dependent stage. • Create a huge surface area for: > Distribution of photosystems that contain photosynthetic pigments that trap sunlight > Electron carriers and ATP synthase enzymes needed to convert light energy into ATP. • Proteins embedded in the thylakoid membrane hold the photosystems in place
Describe the structure of the stroma
• Is a fluid filled matrix • Contains enzymes needed for the second stage of photosynthesis - the light-independent stage • Also contains starch grains, oil droplets, small ribosomes (similar to prokaryotic cells) and a loop of DNA
How are chloroplasts adapted?
Define the term photosynthetic pigements
- Absorb certain wavelengths of light
- Reflect other wavelengths
- Arranged in photosystems in thylakoid memrbane
Describe the absorbtion spectrum
Wavelengths of light around 430nm to 500nm are absorbed well (blue light). Wavelengths of 530nm to 620nm are not absorbed (green light). Wavelengths of 670nm to 700nm are absorbed well (red light)
What is a photosystem?
- A photosystem is a funnel shaped light-harvesting cluster of photosynthetic pigments.
- Accessory pigments absorb different wavelengths of light to maximise the amount of sunlight that can be utilised.
- Accessory pigments funnel energy associated with light wavelengths to the primary pigment reaction centre (chlorophyll a)
Describe the steps involved in the light-independent stage
1) A photon strikes Photo System II
2) The light energy excites a pair of electrons inside chlorphyll 3) The energised electrons are captured by an electron carrier 4) The electrons are passed along the electron transport chain, releasing energy at each step
5) The energy released is used to create ATP
6) Eventually the electrons are captured by chlorophyll in PSI, replacing those lost from PSI.
7) Electrons energised from PSI are captured by another electron carrier and pass along another electron transport chain.
8) Electrons and protons are accepted by NADP which becomes reduced.
Explain the importance of water in the LDS
• In PSII there is an enzyme that splits water in the presence of light
• This reaction is called photolysis
3H20 –> 4H+ + 4e - + 02
• Some oxygen produced is used by plants in aerobic respiration
Cyclic phosphorylation
• ATP is produced
- No photolysis
- No reduced NADP
- Guard cells contain PSI only, producing ATP to pump K+ into the cells.
- This causes guard cells to swell and open the stomata.
Describe how light intensity affects the rate of photosynthesis
Light: Light provides the energy to power the first stage of photosynthesis and prdouce ATP and reduced NADP needed for the next stage. Light also causes stomata to open so that gaseous exchange can occur. When light intendity is low, the rate of photosynthesis is low. As the light intensity increases, the rate of photsynthesis increases. At a certain point, even when light intensity increases, the rate of photosynthesis does not increase. Now a factor other than light intensity is the limiting factor
Describe the effect of changing the light intensity on the calvins cycle
1) GP cannot be reduced to TP
2) TP levels fall and GP accumulates
3) If TP falls, RuBP cannot be regenerated
Describe the effects of changing CO2 concentration on the Calvin cycle
If the concentration of carbon dioxide falls below 0.01%:
- RuBP cannot accept it, and accumulates
- GP cannot be made
- Therefore, TP cannot be made
Describe the steps involved in the light-independent stage of photosynthesis
1) Carbon dioxide combines with a carbon dioxide acceptor, a five carbon compund called ribulose bisphosphate (RuBP). This reaction is catalysed by the enzyme RuBisCO.
2) RuBP becomes carboxylated by accepting the carboxyl group, forming an unstable intermediate 6 carbon compound that immediatley breaks down.
3) The product is 2 molecules of a 3-carbon compund, GP. The carbon dioxide has now been fixed.
4) GP is then reduced, using hydrogens from recued NADP from the LDS, to triose phosphate (TP). Energy from ATP, also made during the LDS is used at this tsage at the rate of two molecules of ATP for every molecule of carbon dioxide fixed during stage 3.
5) In 10 of every 12 TP molecules, the atoms are rearranged to regenerate 6 molecules of RuBP. This process requires phosphate groups. Chloroplasts contain only low levels of RuBP, as it is contiually being converted to GP, but is also continually being regenrated. The remaining 2 of the 12 molecules of TP are the product.
