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IGCSE Biology - PLANT NUTRITION

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Define Photosynthesis
The process of which plants manufacture carbohydrates from raw materials using energy from light
State the word equation for photosynthesis
carbon dioxide + water --> glucose + oxygen, in the presence of light and chlorophyll
State the balanced chemical equation of photosynthesis
6CO2 + 6H20 --> C6H1206 + 6O2
Describe the role of chlorophyll
Chlorophyll transfers light energy into chemical energy in molecules, for the synthesis of carbohydrates
Investigate the necessity for chlorophyll, using appropriate controls
1. Use a variegated leaf
2. Place the plant in sunlight for 6 hours
3. Test for starch:
- Submerge leaf in boiling water
- Turn off bunsen burners
- Put leaf into test tube w/ ethanol. (Chlorophyll is extracted)
- Put test tube in beaker of boiling water
-Wash leaf in cold water. (Removes ethanol and rehydrates)
- Spread leaf out flat on white surface and add drops of iodine
4. Green parts turn blue/black bc contains chlorophyll = photosynthesis = starch
White parts stay red/brown bc NO chlorophyll = NO photosynthesis = NO starch
Investigate the necessity for carbon dioxide, using appropriate controls
1. Enclose plant in plastic bag with a substance that absorbs carbon dioxide (e.g. Soda lime)
2. Leave the plant in light for a few hours
3. Set up a CONTROL experiment in exact way WITHOUT soda lime and not enclosed in plastic bag. (So ensure that absence of CO2 caused lack of starch)
4. Test for starch:
- Submerge leaf in boiling water
- Turn off bunsen burners
- Put leaf into test tube w/ ethanol. (Chlorophyll is extracted)
- Put test tube in beaker of boiling water
-Wash leaf in cold water. (Removes ethanol and rehydrates)
- Spread leaf out flat on white surface and add drops of iodine
5. Experiment 1 will have negative result for starch (red/brown) bc NO Carbon dioxide = NO photosynthesis = NO starch
Control will be opposite
Investigate the necessity for light, using appropriate controls
1. Take a de-starched plant. Cover parts of the plant w/ aluminium foil, so light won't pass thru
2. Leave plant in light for a few hours
3. Test for starch:
- Submerge leaf in boiling water
- Turn off bunsen burners
- Put leaf into test tube w/ ethanol. (Chlorophyll is extracted)
- Put test tube in beaker of boiling water
-Wash leaf in cold water. (Removes ethanol and rehydrates)
- Spread leaf out flat on white surface and add drops of iodine
4. Only the parts uncovered will turn blue/black
Investigate and describe the effects of varying light intensity on the rate of photosynthesis e.g. in submerged aquatic plants
1. Cut 5cm of pondweed
2. Attach paperclip to pondweed to stop floating
3. Put a lamp close to the plant and measure the distance between them
4. Count the number of bubbles released over 5 minutes. Repeat several times and count the average.
5. Repeat procedure with the lamp at different distances to the plant
6. The closer the lamp is to the plant, the higher the light intensity = gives more energy to the plant
*Above a certain conc. rate stays constant
Investigate and describe the effects of varying temperature on the rate of photosynthesis e.g. in submerged aquatic plants
1. Cut 5cm pieces of pondweed and place into test tubes, which are placed into beakers of water at diff. temps. Minimum of 5 diff temps from 10-40 degrees
2. The lamp is kept at one distance (constant light intensity)
3. Sodium hydrogen carbonate added to water in test tubes to maintain carbon dioxide conc.
4. Count the number of bubbles released over 5 minutes. Repeat several times and count the average.
6. The maximum rate of photosynthesis occurs at OPTIMUM TEMP.
Investigate and describe the effects of varying carbon dioxide on the rate of photosynthesis e.g. in submerged aquatic plants
1. Cut 5cm of 5 pieces of pondweed and place each into test tubes
2. Add diff. quantities of sodium hydrogen carbonate into water (increases conc.)
3. Light intensity and temp. must remain constant
4. Results: Increase in CO2 = increase in rate of photosynthesis
*Above a certain conc. rate stays constant
Outline the subsequent use and storage of the carbohydrates made in photosynthesis
Carbohydrates made during photosynthesis are stored as starch and are used for:
- Respiration
- Active transport
- Making cellulose
- Converted to sucrose and transported to diff. parts of plant thru Phloem

Glucose can also be converted to other substances:
*Plants get nitrogen from nitrate ions in soil
- Glucose and nitrate are used to form AMINO ACIDS/PROTEIN
+ Protein is needed for growth and cell repair/making enzymes and hormones
- Sugars are converted to OILS (efficient way to store energy in seeds)
Define the term limiting factor
Something present in the environment in such short supply that it restricts life processes
Identify the limiting factors of photosynthesis in different environmental conditions
- Light intensity
- Temperature
- Carbon dioxide
Explain light intensity as a limiting factor of photosynthesis in different environmental conditions
- Light intensity determines the energy available to photosynthesis
- As light intensity increases = rate increases bc it is limiting factor
- Doesn't matter if temp, or CO2 conc. is high; if light is low = low energy = low rate of Photosynthesis
- Later the rate remains constant even tho light intensity increases BC it is no longer limiting factor. It might be CO2 or temp
Explain temperature as a limiting factor of photosynthesis in different environmental conditions
- Temperature increases rate of ENZYME-CATALYSED reactions
- Rate increases until reaches a maximum/optimum, then decreases
- The rate INCREASES bc the substrates and enzymes in the chloroplasts have more energy = collide more often
- Rate DECREASES bc enzymes in chloroplasts are DENATURED
Explain Carbon Dioxide as a limiting factor of photosynthesis in different environmental conditions
- Carbon Dioxide is a raw material for photosynthesis = so if increased = more available for chloroplast enzymes to use to make carbohydrates
Describe the use of carbon dioxide enrichment in glasshouses in temperate and tropical countries
- Growers can pump CO2 into glasshouses to increase conc.
- Can also burn BUTANE or NATURAL GAS which: provide CO2 and heat -> raise temp. in cold weather
Describe the use of optimum light in glasshouses in temperate and tropical countries
- Glass lets in sunlight
- ARTIFICAL LIGHTING for when light intensity is too low
- BLINDS keep out very strong light
- SHADING lowers temp. in tropical countries
Describe the use of optimum temperature in glasshouses in temperate and tropical countries
- Sunlight heats up inside of glasshouse
- Glass stops heat escaping
- ELECTRIC HEATERS used in cold weather
- VENTILATOR FLAPS are opened to cool the glasshouse on hot days
Describe the use of water in glasshouses in temperate and tropical countries
- AUTOMATIC WATERING SYSTEMS using SPRINKLERS and HUMIDIFIERS so plants always get enough water
Describe the use of carbon dioxide enrichment , optimum light, water, and optimum temperature in glasshouses in temperate and tropical countries
Allow plants to:
- Grow earlier in the year
- Grow in places where they would not normally grow well

All these conditions are monitored by:
- Sensors which detect changes in limiting factors
- Computers which collect data from sensors and control all heating, ventilation, lighting, and shading
Use hydrogen carbonate indicator solution to investigate the effect of gas exchange of an aquatic plant kept in the light and in the dark
*hydrogen carbonate indicator solution is RED
1. - 1st: Set up a test tube w/ 10 cm pondweed, TINFOIL (to prevent light passing) and hydrogen carbonate indicator
- 2nd: Set up a test tube with 10 cm pondweed and hydrogen carbonate indicator
- 3rd: CONTROL Set up a test tube with hydrogen carbonate indicator solution ONLY
2. Leave the test tubes near a light for 2-3 hours
*If carbon dioxide is added to the water by the plant the solution will turn YELLOW.
*If carbon dioxide is removed from the water by the plant the solution will turn PURPLE.
- 1st will turn yellow bc carbon dioxide was ADDED by PONDWEED bc of RESPIRATION (since there was no sunlight)
- 2nd will turn purple bc carbon dioxide was TAKEN IN by PONDWEED for PHOTOSYNTHESIS
- 3rd is red bc CONTROL
Identify chloroplasts, cuticle, guard cells and stomata, upper and lower epidermis, palisade mesophyll, spongy mesophyll, vascular bundles, xylem and phloem in leaves of a dicotyledonous plant
Explain how the internal structure of a leaf is adapted for photosynthesis
Palisade mesophyll:
- Are packed TIGHTLY together, NEAR THE UPPER SURFACE of the leaf to maximise absorption of light where its intensity is highest
- Has MANY CHLOROPLASTS to absorb as much light as possible

Stomata:
- Open to allow carbon dioxide to diffuse into the leaf. Carbon dioxide is a raw material for photosynthesis

Leaves:
- Are THIN so that carbon dioxide does not have to diffuse FAR from the atmosphere to the cells of the palisade and spongy mesophyll

Spongy mesophyll:
- Spaces in spongy mesophyll allow easy diffusion of carbon dioxide. Diffusion through air is faster than diffusion from cell to cell

Xylem:
- Bring water and ions to mesophyll cells. Water is a raw material for photosynthesis and magnesium ions are needed to make chlorophyll

Phloem:
- Sugar from photosynthesis is converted to sucrose and is transported away by phloem

Stomata:
- Open and closed by GUARD CELLS
- Open during the DAY (bc sunlight present = photosynthesis); water passes in through OSMOSIS --> they swell, bend and open
- CO2 diffuses into leaf, O2 and water vapour out
- At NIGHT water passes OUT by OSMOSIS--> guard cells STRAIGTEN --> stomata closes
+ Stomata also closes during extreme conditions such as drought to prevent water loss, and wilting
Describe the importance of nitrate ions
- Nitrate ions are important for making AMINO ACIDS, which are used to make PROTEINS
-> Proteins are required for GROWTH; low proteins = poor growth
Describe the importance magnesium ions
- Magnesium ions are used to make CHLOROPHYLL
Explain the effects of nitrate ion deficiency on plant growth
Plants that are deficient in nitrate:
- Less/stunted growth
Explain the effects of magnesium ion deficiency on plant growth
Plants that are deficient in magnesium:
- Make LESS CHLOROPHYLL
- LESS PHOTOSYNTHESIS
- Less SUCROSE available to plant (due to reduced photosynthesis; reduced sucrose transport)
= YELLOWING leaves (chlorosis)
= MORE SUGAR in leaves