Topic 6 Gas Exchange + Nutrition in Plants Flashcards
What is the word equation for photosynthesis?
Carbon dioxide + water -> glucose + oxygen
What is the chemical equation for photosynthesis?
6CO2 + 6H2O -> C6H12O6 + 6O2
What is the role of diffusion in gas exchange during photosynthesis?
- carbon dioxide diffuses DOWN concentration gradient from HIGH concentration (outside leaf) to LOW concentration (inside leaf)
- oxygen diffuses down concentration gradient from high concentration (inside leaf) to low concentration (outside leaf)
Why is the carbon dioxide concentration always low inside photosynthesising cells?
- cells use carbon dioxide in photosynthesis
- > conc always low
How is the structure of the leaf adapted for gas exchange?
- Stomata + guard cells allow diffusion of gases in and out of leaf
- Leaf shape = thin -> decreases diffusion distance
- Spongy mesophyll cells have large SA + moist surfaces for fast diffusion
- Air spaces increase SA
Why does a leaf have a waxy underside?
Prevents excess water loss
How is the structure of the leaf adapted for photosynthesis?
- maximum number of palisade cells packed in to absorb sunlight
What happens when guard cells gain H2O by osmosis?
- expand + curve out
- stomata opens -> allows for gas exchange
What happens when guard cells lose water via osmosis?
- stomata closes
- gas exchange can no longer occur
- water can’t be lost
What is the net exchange of carbon dioxide and oxygen during the day?
- depends on light intensity but higher rate of photosynthesis
- > net diffusion of carbon dioxide into plant + net diffusion of oxygen out of plant during day
What is the net exchange of carbon dioxide and oxygen during the night?
- plants only respire (no sunlight)
- > net diffusion of oxygen into plant + net diffusion carbon dioxide out of plant
Cormmss method for investigating effect of light on net gas exchange from leaf using hydrogen carbonate indicator
C - change availability of light for each boiling tube (foil, no foil etc)
O - plant used will be pondweed - same species age + length
R - repeat experiment 3 times to ensure reliability
M - observe change in hydrogen carbonate indicator
M - after 30 mins
S - control vol of hydrogen carbonate indicator / no of leaves / temp of environment
In a test tube containing a plant, what colour would the hydrogen carbonate indicator be after it was exposed to light?
Purple - low CO2 levels
Carbon dioxide + water -> oxygen + glucose
RELEASE of oxygen in photosynthesis
Why would a control test tube for the hydrogen carbonate experiment be included?
- measures baseline levels of co2 to compare to other results
- makes sure that pondweed was causing the colour changes
How would you know which test tube was kept in bright light?
- purple
- > higher levels of photosynthesis -> less co2 released
What colour is the test tube that was kept in the dark and why?
- yellow
- > higher levels of respiration -> co2 released
- photosynthesis could not be carried out
What test tube is at compensation point?
- orange
- > equal levels of co2 and o2 (remember however, that OXYGEN DOES NOT AFFECT the indicator)
- > thus rate of photosynthesis = rate of respiration
During photosynthesis what is light energy converted into?
Chemical energy
By chloroplasts
How does light intensity affect photosynthesis?
Increases the rate of photosynthesis -> more energy for reaction
Graph will be linear then level off (becoming constant) as another factor limits the rate
How does carbon dioxide concentration affect photosynthesis?
Increases the rate of photosynthesis -> more reactants
Graph will be linear then level off (becoming constant) as another factor limits the rate
How does temperature affect photosynthesis?
Increase in temp up to optimum -> increase rate of photosynthesis
After optimum -> decreases
Increase in kinetic energy -> more successful collisions between active site + substrates
After optimum -> enzymes denature -> active site changes shape + no longer complementary to substrate
Too hot -> too much water loss
Graph peaks at optimum and then decreases
What is a limiting factor?
Factor present in an environment that controls a process
How do chloroplasts affect photosynthesis?
More chloroplasts (contain chlorophyll which absorbs light energy) increases rate
Why can a starch test show whether the leaf is photosynthesising?
Starch is made from glucose -> a product of photosynthesis
Why do you put the leaf in boiling water and then ethanol and then water before the starch experiment?
- boiling water kills tissues + breaks down cell walls
- ethanol removes chlorophyll -> colour changes can be seen more clearly
- wash in water to soften leaf tissue -> more permeable + allows colour change to be observed more clearly
What would be the results for starch test on:
- leaf with strip of paper over it
- variegated leaf
- leaf covered by paper will turn orange brown -> starch not present -> no sunlight -> no photosynthesis occurring
- the rest would be blue black
- the green part of variegated leaf = blue black (starch present, chlorophyll present, photosynthesis is occurring)
- white part = orange brown (not present, not chlorophyll)
Cormms for light and starch test?
C - light / no light
O - leaves from same species, age, size of plant
R - repeat x 3 for reliability
M -observe colour change of leaf when iodine is applied
M - after 1 day collect results
S - control room temp
Method for investigating affect of carbon dioxide concentration with starch?
- Destarch two identical plants
- Place them in plastic bags
- Place saturated sodium hydrogen carbonate (gives out co2) in one bag
- Place soda lime (absorbs co2) in other bag
- Leave in bright light for a day
- Test a leaf from each plant with iodine
What are the results for the starch test for co2 conc?
Plant with sodium hydrogen carbonate turns blue / black -> starch in leaf -> photosynthesis -> glucose produced
Plant with soda lime turns orange / brown -> no starch in leaf -> photosynthesis not occurring (no co2 for it) -> glucose not produced
How do you investigate affect of light intensity on photosynthesis? By measuring carbon dioxide released?
- Fill boiling tube with water
- Add pondweed
- Place the lamp at fixed distance from tube, leave until bubbles can be seen
- Count number of bubbles released in 5 minutes at each distance
- Repeat + calculate a mean for each distance
How could you make the method more accurate for measuring carbon dioxide versus light intensity?
- measuring vol of gas released with an inverted measuring cylinder / gas syringe since bubbles = diff sizes
- may contain different vols of gas
What do plants do with glucose?
- Convert -> insoluble starch for storage
- Convert -> fat + oil for cytoplasm
- Makes cellulose for cell walls
- Combines w nitrates -> amino acids (to make proteins)
- Converted -> sucrose -> transport around plant in phloem
What are nitrates needed for?
Amino acids + proteins
-> lack of nitrates = poor plant growth
What is magnesium needed for?
Chlorophyll
-> lack of magnesium= yellow plant
What are phosphates for?
DNA = ATP
-> lack of phosphates = poor root growth + discoloured leaves
What is potassium for?
Helps photosynthesis + respiration enzymes function
-> lack of potassium : discoloured leaves, poor flower + fruit growth
