B8 Flashcards
Photosynthesis
Is photosynthesis an endothermic or exothermic reaction (and why) ?
- endothermic
- TAKES IN light energy in order to convert carbon (dioxide) and water into glucose (and oxygen)
Give the word and symbol equations for photosynthesis
carbon dioxide + water -> glucose + oxygen
6CO(2) + 6H(2)O -> C(6)H(12)O(6) + 6O(2)
Which adaptations do plant leaves have that make them well-suited to photosynthesis ?
- broad surface area
[] lots of lightfall on the leaf, absorbed for photosynthesis - are green due to presence of chlorophyll in chloroplasts
[] green is one of the most effective colours at absorbing light - increases efficiency of photosynthesis and allows it to happen at a faster rate - many stomata on the underside of the leaf
[] absorb carbon dioxide from the air and expel waste oxygen created as a by-product of photosynthesis (though some is used for respiration)
[] have guard cells to regulate gas exchange - contain vascular bundles in the veins of the leaf
[] good supply of water for photosynthesis via the xylem, and phloem transport glucose produced in photosynthesis away from the leaf and to areas of the plant where it can be used for respiration, synthesis of other forms of glucose and stored - leaves are thin, so short diffusion distance, making gas exchange in the leaf more efficient
[] also have air spaces, allowing gases to move through the leaf
How are algae adapted to photosynthesis ?
large surface area to more efficiently absorb dissolved carbon dioxide in the water via diffusion, as well as expelling unneeded oxygen in the same way
What are the four limiting factors of photosynthesis ?
- light intensity
- carbon dioxide concentration
- temperature
- chlorophyll levels in leaves
How does light intensity affect the rate of photosynthesis ?
- brighter light = more photosynthesis
- need light to carry out photosynthesis, so the more there is, the more photosynthesis can take place
[] energy is used to break bonds in carbon dioxide and water, then on a smaller level to make bonds to form glucose molecules
How does carbon dioxide concentration affect the rate of photosynthesis ?
- most common limiting factor due to scarcity in the atmosphere (0.04% of air)
[] becomes more available at night, when plants don’t photosynthesise due to the lack of light so instead respire, producing carbon dioxide - more carbon dioxide = more photosynthesis
How does temperature affect the rate of photosynthesis ?
- as temperature rises, molecules have more energy and collide more frequently, so reaction speeds up
- temperature too high = enzyme denatures
- temperature too low = reaction extremely slow
What does a plateau mean on a limiting factor graph ?
the graphed factor is no longer the limiting factor, and has increased to a point where any further increase has no exacerbation of its effects on photosynthesis
How do chlorophyll leaf levels affect the rate of photosynthesis ?
- limited chlorophyll means less light absorption and thus less photosynthesis can take place
[] limitations in chlorophyll levels are common in variegated plants or plants with mineral deficiencies (specifically magnesium deficiency) - not much can be done to increase chlorophyll levels in leaves, though providing soil/growing material with a lot of soluble magnesium ions is a good start
Describe a practical to investigate the effects of changing light intensity on the rate of photosynthesis
- gather equipment
[] aquatic plant, like pondweed
[] scissors
[] metre rule
[] boiling tube
[] sodium hydrogen carbonate solution (encourages photosynthesis)
[] clamp stand
[] LED light source (doesn’t give off heat (temp. = another limiting factor)) - set up clamp stand with boiling tube in it 10cm from the light source
- pour sodium hydrogen carbonate solution into the boiling tube so that it fills most of the tube
- place a piece of pondweed in the boiling tube so that it is fully submerged
[] whilst underneath the solution, cut the top of the stem at an angle so that the bubbles of gas produced by photosynthesis are more visible - turn off any room lights, then turn on the light source
[] leave for 5 minutes so that the plant can adjust to the light intensity and begin photosynthesising at a constant rate - set a timer for one minute and count the number of gas bubbles produced in one minute (only count bubbles produced from the cut stem)
- repeat this 2 more times, then calculate the mean number of bubbles produced per minute
- move the boiling tube 10 cm further from the light source (20cm total) and leave again for 5 minutes to adjust before repeating the counting process
- repeat the above 3 more times in total, so that you have mean bubbles produced for 10cm, 20cm, 30cm, 40cm and 50cm from the light source
Describe how to make the practical for investigating the effect of light intensity on rates of photosynthesis more accurate
- collect oxygen to see the exact volume produced within a time period
[] original method assumes that all bubbles of oxygen are of the same volume - collect the gas to prove that it is oxygen (relights glowing splint)
[] original method assumes that the gas produced from the stem is oxygen
What is the inverse square law (with formula) ?
- inverse relationship between light intensity and distance from light source
light intensity is indirectly proportional to (1/distance^2)
Describe the key uses of glucose in plants
- some is used for respiration
- converted to starch for storage
[] starch is insoluble in water, whilst glucose is soluble
[] if stored as simple glucose, would affect osmosis in the plant
[] is the main energy store for night time/when it is dark, and is found in all cells of the plant
[] special storage areas for starch often exist in plants, like tubers and bulbs (humans tend to take advantage of these though) - converted into cellulose to build up cell walls and strengthen the plant
[] cellulose has a very similar chemical structure to starch (so won’t get two marks if mentioning both) - synthesis of amino acids
[] sugars are combined with nitrates from soil to make amino acids
[] these amino acids are then used to make proteins (uses energy from respiration)
[] vital to digestion in carnivorous plants, which eat protein-rich organisms to replace nitrates that cannot be found/are scarce in their soil - used to make fats and oils (lipids)
[] these often surround new seeds so that the seeds have a food source when planted and can grow into a new plant more easily
[] some algal cells also rich in oils - considered for future biofuels
Describe a practical to test for starch in a variegated leaf
- gather equipment
[] variegated leaf
[] ethanol
[] beaker
[] bunsen burner
[] tripod
[] gauze
[] water
[] iodine
[] boiling tube
[] tweezers
[] spotting tile - set up bunsen burner with tripod and gauze
[] place beaker with water on gauze - light bunsen burner and set to roaring flame
- wait for water to reach rolling boil
- switch off bunsen burner and place boiling tube with ethanol and the variegated leaf submerged in the ethanol inside of the beaker
- leave until the leaf turns white (mostly)
[] boiled in ethanol so that the waxy cuticle is destroyed, allowing iodine to react with the cells of the plant, and also to bleach the chlorophyll from the leaf so that colour changes are clearer - remove leaf carefully with tweezers (don’t burn yourself) and place on a spotting tile
- put a few drops of iodine solution on the leaf
[] areas that have a colour change of orange-brown to blue-black are positive for starch presence, whilst other areas without the colour change are starch negative
[] shows how starch builds up in photosynthetic cells of the plant, as opposed to areas with no chlorophyll
[] demonstrates that roots of plant would not contain starch due to not photosynthesising (hence why tubers and bulbs are stored underground)
Why is the artificial control of limiting factors of photosynthesis important to farmers ?
more photosynthesis = faster growth = bigger plants that can be sold more quickly for bigger profits
How do farmers use commercial greenhouses to maximise rates of photosynthesis and plant growth ?
- complex computer software used to control carbon dioxide levels in the air, light intensity and temperature
- hydroponics systems are used to give plants the exact nutrients they need in the right quantities
What are the economic advantages and disadvantages of the techniques used by commercial greenhouses to grow plants ?
advantages:
- turnover is very quick due to maximising and perfecting growing conditions, so more profit can be made
- plants are cleaner (when using hydroponics) and larger
[] reduces cost of cleaning plants, ploughing fields and maintaining land + soil quality, making more room for profit
[] bigger plants are priced higher and bought more often - more profit
- monitoring and controlling conditions via computer systems means less money can be spent on employing in-person staff, meaning higher profits
- hydroponics means that even areas with poor soil quality can make profits off of agriculture, improving overall economy
disadvantages:
- complex computer systems are expensive and require a lot of maintenance
- due to lack of in-person staff, sufficient alarm systems and emergency measures must be put in place in the greenhouse itself - expensive
