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A2 OCR Biology Practical - All ideas
As discussions on the forum about the looming A2 Biology Unifying Concepts Practical seem to be a bit sparse, thought I should post all my ideas down and we can all deliberate about what topics and information would be useful!
Post all your experiment ideas, diagrams, methods, and theory questions on this thread.
Topics: Stomata, Transpiration, Water use - from root to leaf, Photosynthesis, Cellular respiration
1) Stomata
- Tiny pores in the epidermal barrier, flanked by specialised epidermal cells -
Guard Cells. They are the means of contact between photosynthesising mesophyll cells and the external air.
- Stomata are mostly located on the abaxial (under surface) of a leaf. This in turn helps to reduce the water lost through transpiration.
- Open during the day, closed at night.
2) Guard Cells
- Help balance the need to conserve water with the requirement for photosynthesis.
- Equipped with chloroplasts.
- Have blue-light receptors within the membranes.
- Allows CO2 to diffuse to the photosynthetic cells of the mesophyll.
- Increases exposure to CO2.
- Abaxial surface receives less sunlight than the adaxial surface and therefore reduces losses by transpiration.
Opening:
1) The blue light in sunlight (has the more efficient frequency for usage by plants) causes proton pumps in the guard cell membrane to activate. Protons (H+ ions) are extruded from the cytoplasm using ATP. This creates an electro-chemical gradient and opens the voltage operated channels on the membrane.
2) Potassium (K+ ions) flow passively into the cell across the plasma membrane from the surrounding tissues. Chloride ions (Cl-) also enter, which offsets the influx of positive charge.
3) The cytoplasm of the guard cell now has a lower water potential than the surrounding abaxial epidermal tissue cells. Water is taken in by osmosis down a water potential gradient.
4) The guard cell becomes Turgid.
(Extra- Light may encourage stomtal opening by driving photosynthesis in guard cell chloroplasts, making ATP available for the active transport of H+ ions. The depletion of CO2 within mesophyll air spaces also triggers the opening of stomata)
Closing:
1) An exodus of K+ ions occurs, and maybe linked with falls in sucrose concentrations.
2) The water potential of the cell increases.
3) Water is lost by osmosis as the ion concentrations in the tissue cells are higher than within the guard cells.
4) The guard cell becomes flaccid and the stomatal apperture becomes smaller.
Plants (most Dicots and most Monocots) open and close their stomata in Circadian rhythms.
3) ABA - Abscisisc Acid
- Produced in the terminal bud of plants.
- Acts as a 'stress hormone'.
- Causes stomata to close.
- Reduces transpiration and further water loss in times of drought.
- Triggers K+ ion loss from guard cells.
4) Transpiration
(In relation to stomata)
- Water is lost via the stomata is replaced by water that is pulled out of the leaf system.
- The generation of negative pressure induces transpirational pull.
1. As water is lost from the film of moisture surrounding the mesophyll cells the remaining water retreats into the cell wall pores.
2. It does this due to the adhesion properties of water and its attraction to the hydrophillic walls.
3. But, the cohesive forces in the water resist the surface area of the water increasing.
4. So. Adhesion + Surface tension = formation of a Meniscus.
5. The water film has a negative pressure, one that is less than the atmospheric pressure.
6. The more concave the meniscus the greater the -ve pressure.
7. Water is drawn out of the xylem to replace transpirational loss by the stomata this way.
Possible Experiments
Photosynthesis -
The Hill Reaction - to show that chloroplasts have reducing power, liberation of oxygen from water in the presence of an oxidising agent.
http://www.northern.edu/ramsayj/Botany/hillrxn2.html
Transpiration-
Potometer experiments
Stomata-
http://www-saps.plantsci.cam.ac.uk/worksheets/scotland/stomata.htm
Useful websites:
www.schoolbiology.com/11/xi%20bio/CH%2011.htm
Good luck everybody!
Please comment back... look forward to seeing what everyone thinks
Post all your experiment ideas, diagrams, methods, and theory questions on this thread.
Written from my notes, feel free to debate my accuracy!
Topics: Stomata, Transpiration, Water use - from root to leaf, Photosynthesis, Cellular respiration
1) Stomata
- Tiny pores in the epidermal barrier, flanked by specialised epidermal cells -
Guard Cells. They are the means of contact between photosynthesising mesophyll cells and the external air.
- Stomata are mostly located on the abaxial (under surface) of a leaf. This in turn helps to reduce the water lost through transpiration.
- Open during the day, closed at night.
2) Guard Cells
- Help balance the need to conserve water with the requirement for photosynthesis.
- Equipped with chloroplasts.
- Have blue-light receptors within the membranes.
- Allows CO2 to diffuse to the photosynthetic cells of the mesophyll.
- Increases exposure to CO2.
- Abaxial surface receives less sunlight than the adaxial surface and therefore reduces losses by transpiration.
Opening and Closing of Stomata
Opening:
1) The blue light in sunlight (has the more efficient frequency for usage by plants) causes proton pumps in the guard cell membrane to activate. Protons (H+ ions) are extruded from the cytoplasm using ATP. This creates an electro-chemical gradient and opens the voltage operated channels on the membrane.
2) Potassium (K+ ions) flow passively into the cell across the plasma membrane from the surrounding tissues. Chloride ions (Cl-) also enter, which offsets the influx of positive charge.
3) The cytoplasm of the guard cell now has a lower water potential than the surrounding abaxial epidermal tissue cells. Water is taken in by osmosis down a water potential gradient.
4) The guard cell becomes Turgid.
(Extra- Light may encourage stomtal opening by driving photosynthesis in guard cell chloroplasts, making ATP available for the active transport of H+ ions. The depletion of CO2 within mesophyll air spaces also triggers the opening of stomata)
Closing:
1) An exodus of K+ ions occurs, and maybe linked with falls in sucrose concentrations.
2) The water potential of the cell increases.
3) Water is lost by osmosis as the ion concentrations in the tissue cells are higher than within the guard cells.
4) The guard cell becomes flaccid and the stomatal apperture becomes smaller.
Plants (most Dicots and most Monocots) open and close their stomata in Circadian rhythms.
3) ABA - Abscisisc Acid
- Produced in the terminal bud of plants.
- Acts as a 'stress hormone'.
- Causes stomata to close.
- Reduces transpiration and further water loss in times of drought.
- Triggers K+ ion loss from guard cells.
4) Transpiration
(In relation to stomata)
- Water is lost via the stomata is replaced by water that is pulled out of the leaf system.
- The generation of negative pressure induces transpirational pull.
1. As water is lost from the film of moisture surrounding the mesophyll cells the remaining water retreats into the cell wall pores.
2. It does this due to the adhesion properties of water and its attraction to the hydrophillic walls.
3. But, the cohesive forces in the water resist the surface area of the water increasing.
4. So. Adhesion + Surface tension = formation of a Meniscus.
5. The water film has a negative pressure, one that is less than the atmospheric pressure.
6. The more concave the meniscus the greater the -ve pressure.
7. Water is drawn out of the xylem to replace transpirational loss by the stomata this way.
Possible Experiments
Photosynthesis -
The Hill Reaction - to show that chloroplasts have reducing power, liberation of oxygen from water in the presence of an oxidising agent.
http://www.northern.edu/ramsayj/Botany/hillrxn2.html
Transpiration-
Potometer experiments
Stomata-
http://www-saps.plantsci.cam.ac.uk/worksheets/scotland/stomata.htm
Useful websites:
www.schoolbiology.com/11/xi%20bio/CH%2011.htm
Good luck everybody!
Please comment back... look forward to seeing what everyone thinks
Scroll to see replies
thats amazing.. thanks!
do you have any ideas on what could be in the second part of the paper??
do you have any ideas on what could be in the second part of the paper??
wow thanks
i want to make sure you got that right. are you 100% sure about the blue light receptors in the membrane? i havent found that in many sources, and ive never seen a mark scheme give credit to detail such as that. aren't they far more likely to give credit to the fact that guard cells contain photosynthetic pigments e.g. chlorophyll a, which absorbs blue light anyway?
cowsgomoo
could the microscope slide be anything from AS biology e.g cross section of cortex/xylem vessels etc?
yes it could be... well we were told to know the structures within a dicot leaf
wow, thanks a lot
Hi again,
In reply to bahbahbah -
I have read from many sources; Biology Campbell Fourth edition (used by most University level students taking Biology) that the illumination of blue-light wavelengths stimulates the blue-light receptors in the guard cells which are built into the plasma membrane.
From another source it states that:
"Blue-light wavelengths of daylight, are detected by zeaxanthin which is a carotenoid and this subsequently activates the proton pumps in the guard cells." Obviously, proceeding to extrude protons from the cytoplasm of the cell creating a proton motive force.
Hope this clarifies!
In reply to bahbahbah -
I have read from many sources; Biology Campbell Fourth edition (used by most University level students taking Biology) that the illumination of blue-light wavelengths stimulates the blue-light receptors in the guard cells which are built into the plasma membrane.
From another source it states that:
"Blue-light wavelengths of daylight, are detected by zeaxanthin which is a carotenoid and this subsequently activates the proton pumps in the guard cells." Obviously, proceeding to extrude protons from the cytoplasm of the cell creating a proton motive force.
Hope this clarifies!
Just to say, I don't actually know what the Practical is going to be on tomorrow!
A good revision list would be:
Ask yourself these questions? (Off the top of my head)
1)a) Plant cells
. Know the ultra-structure of a plant cell.
. Name all the components of a plant cell and its organelles.
(Nucleus, Nucleolus, Vacuole, Cell wall, Plasma membrane, Plasmodesmata, Lamella, Golgi apparatus, Rough endoplasmic reticulum, Ribosomes, Chloroplasts, Mitochondria, Storage molecules etc)
Label this diagram http://www.biologycorner.com/resources/plantcell.gif
. What is each feature used for? (write a simple definition)
. How darkly staining would each feature be, if seen under normal conditions of a light microscope?
b) Stomata
. What is the structure of a guard cell?
. What components do guard cells contain?
(Nucleus, Vacuole, Tonoplast, Mitochondria, Chloroplasts, Cell wall, Plasma membrane, Radially orientated cellulose microfibrils)?
. What is the function of each of these components?
. How darkly staining will each of these components be, if you can see them?
. What is the structure of the plasma membrane of a guard cell?
c) Opening and Closing
. What changes occur within a guard cell to change the appeture of the stomatal gap?
. Is the transport across the plasma membrane performed actively or passively? And for which substances, H+, K+, Cl- and H2O?
. What is needed in order for active transport to occur?
. List the changes that occur when stomata are needed to be closed.
. List the changes that occur when the stomata need to be open.
2)a)Plant tissues
. What is the Parenchyma and Chlorenchyma?
. Draw a simple (unsketchy/unshaded) diagram of a cell from each tissue.
2)b) Xylem and Phloem
. Explain the function and structure of Xylem. (Vessel elements, tracheids, lignified walls etc.
. Explain the function of Phloem. (Loading, Sink and Source - really not sure how relevant this will be, but you never know)
. How does water travel from root tip to the leaf?
. Explain the relevance of the Apoplast and Symplast pathways, Suberin in the Casparian strips, Completely suberised cells, the Cortex, Stele, Endodermis, the Pericycle etc.
. Explain how water travels through each of these parts?
Transpiration and Translocation
. Write down a defintion for each; Transpiration and Translocation.
. How do you compare rates of transpiration? Devise and simple experiment and explain briefly.
. What factors would increase and inhibit rates of transpiration? Explain each briefly.
. Draw a lateral section of a Dicot leaf and label each feature and layer. Palisade, Mesophyl etc.
. Explain briefly, what is transpirational pull?
. What is root pressure?
4) Photosynthesis
. What is the structure of a chloroplast? Name the features and functions.
. What are photosystems and where are they located?
. What are primary and accessory pigments?
. What are the absorption and action spectra?
. Explain cyclic and non-cyclic photophorylation?
. What is the 'z' scheme of electron flow?
. Explain the relevance of ATP, e-, NADP, reduced NADP and H+ in photophosphorylation and the photolysis of water?
. Why is ATP important for stomata and mitochondria?
. Draw the Calvin cycle.
. What factors (biotic) affect photosynthesis?
Respiration
. Structure and functions of mitochondria.
. Know Glycolysis, The Krebs cycle, ETC and where they occur, their products, yields and inputs.
Transport across the plasma membrane
. What is the fluid mosaic model?
. Explain the structure of phosopholipid bilayers?
. What are glycolipids and glycoproteins?
. What is the function of channel proteins and voltage operated gates?
. Know diffusion, facilitated diffusion, osmosis, active transport, pressure potential and plasmolysis.
. What is hydrophillic and hydrophobic?
Right! Better make sure I know all of this! Ha! Its easier writing the questions than answering your own.
A good revision list would be:
Ask yourself these questions? (Off the top of my head)
1)a) Plant cells
. Know the ultra-structure of a plant cell.
. Name all the components of a plant cell and its organelles.
(Nucleus, Nucleolus, Vacuole, Cell wall, Plasma membrane, Plasmodesmata, Lamella, Golgi apparatus, Rough endoplasmic reticulum, Ribosomes, Chloroplasts, Mitochondria, Storage molecules etc)
Label this diagram http://www.biologycorner.com/resources/plantcell.gif
. What is each feature used for? (write a simple definition)
. How darkly staining would each feature be, if seen under normal conditions of a light microscope?
b) Stomata
. What is the structure of a guard cell?
. What components do guard cells contain?
(Nucleus, Vacuole, Tonoplast, Mitochondria, Chloroplasts, Cell wall, Plasma membrane, Radially orientated cellulose microfibrils)?
. What is the function of each of these components?
. How darkly staining will each of these components be, if you can see them?
. What is the structure of the plasma membrane of a guard cell?
c) Opening and Closing
. What changes occur within a guard cell to change the appeture of the stomatal gap?
. Is the transport across the plasma membrane performed actively or passively? And for which substances, H+, K+, Cl- and H2O?
. What is needed in order for active transport to occur?
. List the changes that occur when stomata are needed to be closed.
. List the changes that occur when the stomata need to be open.
2)a)Plant tissues
. What is the Parenchyma and Chlorenchyma?
. Draw a simple (unsketchy/unshaded) diagram of a cell from each tissue.
2)b) Xylem and Phloem
. Explain the function and structure of Xylem. (Vessel elements, tracheids, lignified walls etc.
. Explain the function of Phloem. (Loading, Sink and Source - really not sure how relevant this will be, but you never know)
. How does water travel from root tip to the leaf?
. Explain the relevance of the Apoplast and Symplast pathways, Suberin in the Casparian strips, Completely suberised cells, the Cortex, Stele, Endodermis, the Pericycle etc.
. Explain how water travels through each of these parts?
Transpiration and Translocation
. Write down a defintion for each; Transpiration and Translocation.
. How do you compare rates of transpiration? Devise and simple experiment and explain briefly.
. What factors would increase and inhibit rates of transpiration? Explain each briefly.
. Draw a lateral section of a Dicot leaf and label each feature and layer. Palisade, Mesophyl etc.
. Explain briefly, what is transpirational pull?
. What is root pressure?
4) Photosynthesis
. What is the structure of a chloroplast? Name the features and functions.
. What are photosystems and where are they located?
. What are primary and accessory pigments?
. What are the absorption and action spectra?
. Explain cyclic and non-cyclic photophorylation?
. What is the 'z' scheme of electron flow?
. Explain the relevance of ATP, e-, NADP, reduced NADP and H+ in photophosphorylation and the photolysis of water?
. Why is ATP important for stomata and mitochondria?
. Draw the Calvin cycle.
. What factors (biotic) affect photosynthesis?
Respiration
. Structure and functions of mitochondria.
. Know Glycolysis, The Krebs cycle, ETC and where they occur, their products, yields and inputs.
Transport across the plasma membrane
. What is the fluid mosaic model?
. Explain the structure of phosopholipid bilayers?
. What are glycolipids and glycoproteins?
. What is the function of channel proteins and voltage operated gates?
. Know diffusion, facilitated diffusion, osmosis, active transport, pressure potential and plasmolysis.
. What is hydrophillic and hydrophobic?
Right! Better make sure I know all of this! Ha! Its easier writing the questions than answering your own.
... another fairy told me the same...
This is the OCR practical.
And I believe kidneys and the like came up last year so I doubt they'll be here this year
And I believe kidneys and the like came up last year so I doubt they'll be here this year
cheeers for the list tc_13 and thnx for the hint jay!!
toffeegal
sorry to sound stupid but is this practical OCR? or another board
the title specifies OCR, and it matches the likely practicles from what i've had in lessons, (for OCR) and it matches all the other forums for OCR (edexcel people seem to think will be human based)
i'd say its pretty definitely OCR, have you heard anything to contradict it being OCR atall? i'm all ears for anything that will help tomorrow.
Regards
Will
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