Plant nutrition Flashcards
What is photosynthesis?
the process by which plants synthesise carbohydrates from raw materials using energy from light
What is the word equation for photosynthesis?
carbon dioxide + water → glucose + oxygen
What is chlorophyll?
The protein found within chloroplasts that catalyses the reaction, it’s also what causes the plant to be green.
What does chlorophyll do?
transfers energy from light into energy in chemicals, for the synthesis of carbohydrates
What’s the balanced chemical equation for photosynthesis?
6CO2 + 6H2O → C6H12O6 + 6O2
What are the 5 uses and storage of the carbohydrates made in photosynthesis?
- Glucose is commonly stored in plants as starch (as an energy source)
- Glucose can be used to form cellulose to build cell walls
- Glucose can be used in respiration to provide energy
- Glucose can be converted to sucrose and transported through phloem vessels from source to sink
- Glucose can be converted into nectar and used to attract insects for pollination
What ions are needed in plants
- Magnesium
- Nitrate
Function of magnesium in plants
It’s needed to make chlorophyll
Function of nitrate in plants
A source of nitrogen needed to make amino acids (build proteins)
Deficiency of magnesium in plants
Yellowing between the veins of leaves (known as chlorosis) due to lack of chlorophyll production
Deficiency of nitrate in plants
Stunted growth, leaves (usually near growing tip) start to turn yellow, old leaves start to dry out
How do you test the parts of a leaf that are photosynthesising?
- though plants make glucose in photosynthesis,leaves cannot be tested for its presenceas the glucose is quickly used, converted into other substances and transported or stored as starch.
- Starch is stored in chloroplasts where photosynthesis occurs sotesting a leaf for starchis a reliable indicator of which parts of the leaf are photosynthesising.
Process to test a leaf for starch
- A leaf is dropped inboiling watertokill the cells and break down the cell membranes
- The leaf is left for 5-10 minutes in hotethanolin a boiling tube. Thisremoves the chlorophyllso colour changes from iodine can be seen more clearly
- The leaf is dipped in boiling water to soften it
- The leaf is spread out on a white tile and covered withiodine solution
- In a green leaf, the entire leaf will turnblue-blackas photosynthesis is occurring in all areas of the leaf
- This method can also be used to test whether chlorophyll is needed for photosynthesis by using avariegatedleaf (one that is partially green and partially white). The white areas of the leaf contain no chlorophyll and when the leaf is testedonly the areas that contain chlorophyll stain blue-black. The areas that had no chlorophyll remain orange-brown asno photosynthesis is occurring here and so no starch is stored
How to investigate the need for light in photosynthesis?
- Before starting the experiment the plant needs to bedestarchedby placing in a dark cupboard for 24 hours. This ensures thatany starch already present in the leaves will be used upand will not affect the results of the experiment
- Following destarching, a leaf of the plant can bepartially covered with aluminium foiland the plant placed in sunlight for a day. The leaf can then be removed and tested for starch using iodine
- The area of the leaf that was covered with aluminium foil willremain orange-brownas it did not receive any sunlight and could not photosynthesise, while the area exposed to sunlight will turnblue-black
- This proves that light is necessary for photosynthesis and the production of starch
How to investigate the need for carbon dioxide in photosynthesis?
- Destarch two plants by placing in the dark for a prolonged period of time
- Place one plant in a bell jar which contains a beaker ofsodium hydroxide(which willabsorb carbon dioxidefrom the surrounding air). Place the other plant in a bell jar which contains a beaker of water(control experiment), which willnot absorb carbon dioxidefrom the surrounding air
- Place both plants in bright light for several hours. Test both plants for starch using iodine
- The leaf from the plant placed near sodium hydroxide willremain orange-brownas it could not photosynthesise due to lack of carbon dioxide. The leaf from the plant placed near water should turn blue-black as it had all necessary requirements for photosynthesis
What is a limiting factor?
something that is in short supply that restricts a process. When a process depends on two or more variables, the rate of that process is determined by the factor that is in shortest supply.
Main limiting factors of photosynthesis
- Light intensity
- Carbon dioxide concentration
- Temperature
How does light intensity affect the rate of photosynthesis?
- Themore lighta plant receives, thefaster the rateof photosynthesis
- At low light intensities, increasing the intensity will initially increase the rate of photosynthesis. At a certain point, increasing the light intensity stops increasing the rate. The rate becomes constant regardless of how much light intensity increases as something else is limiting the rate
How does carbon dioxide concentration affect the rate of photosynthesis?
- Carbon dioxide is one of the raw materials required for photosynthesis
- This means themore carbon dioxidethat is present, thefaster the reactioncan occur
- This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply
How does temperature affect the rate of photosynthesis?
- As temperature increases the rate of photosynthesis increases as the reaction iscontrolled by enzymes
- However, as the reaction is controlled by enzymes, this trend only continues up to the optimum temperature beyond there the enzymes begin todenatureand the rate of reactiondecreases
What gas exchange do plants do in the day?
Plantsphotosynthesise during daylighthours, for which they need totake in carbon dioxide and release the oxygenmade in photosynthesis. Plants respire all the time
What gas exchange do plants do in the night?
At night, plants do not photosynthesise but they continue to respire, meaning theytake in oxygen and give out carbon dioxide
What is the net effect of the carbon dioxide in plants during the day and night?
During the day, especially when the sun is bright,plants are photosynthesising at a faster rate than they are respiring, so there is anet intake of carbon dioxide and a net output of oxygen. During the night, plants respire more than they photosynthesise so there is a net release of carbon dioxide
What is hydrogen carbonate indicator?
- a pH indicator that changes colour depending on the pH of a solution
- Carbon dioxide is acidic, meaning a higher carbon dioxide concentration is more acidic
What does yellow and orange colour of hydrogen carbonate indicator mean?
Highest and high concentration of carbon dioxide, respectively. More respiration>photosynthesis (lower pH, more acidic)
What does red colour of hydrogen carbonate indicator mean?
Concentration of carbon dioxide is atmospheric level. Photosynthesis=respiration
What does purple and magenta colour of hydrogen carbonate indicator mean?
Lowest and low concentration of carbon dioxide, respectively. More photosynthesis>respiration (higher pH, more alkaline)
What does a waxy cuticle do in a leaf?
Protective layer on top of the leaf that prevents water from evaporating. It also allows light to pass through whilst protecting the leaf’s surface
What does upper epidermis do in a leaf?
Offer protection but thin and transparent to allow light to enter the palisade mesophyll layer
What does palisade mesophyll do in a leaf?
Column shaped cells tightly packed together with many chloroplasts to absorb more light, maximising photosynthesis
What does spongey mesophyll do in a leaf?
Irregular shape, fewer chloroplasts and contain internal air spaces to increase the surface area to volume ratio for the diffusion of gases
What does lower epidermis do in a leaf?
Contains guard cells and stomata
What do guard cells do in a leaf?
Absorbs and loses water to open and close the stomata to allow carbon dioxide to diffuse in and oxygen to diffuse out
What do the stomata do in a leaf?
Where gas exchange takes place; opens during the day and closes during the night. Evaporation of water also takes place here. In most plants they are located on the underside of the lead to reduce water loss.
What does the vascular bundle do in a leaf?
Contains xylem and phloem to transport substances to and from the leaf. Xylem transports water into the leaf for mesophyll cells to use in photosynthesis and for transpiration from the stomata. Phloem transports sucrose and amino acids around the plant
Why does a large surface area adapt a leaf for photosynthesis?
Increases surface area for the diffusion of carbon dioxide and absorption of light for photosynthesis
Why does the leaf being thin adapt a leaf for photosynthesis?
Allows carbon dioxide to diffuse to palisade mesophyll cells quickly
How does chlorophyll adapt a leaf for photosynthesis?
Absorbs light energy so photosynthesis can take place
How do the epidermal cells adapt a leaf for photosynthesis?
They are thin and transparent which allows more light to reach the palisade cells
How does the waxy cuticle adapt a leaf for photosynthesis?
It protects the leaf without blocking sunlight
How does the spongey mesophyll layer adapt a leaf for photosynthesis?
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How does the vascular bundle adapt a leaf for photosynthesis?
Thick cell walls of the tissue in the bundles help to support the stem and leaf
Why is the palisade mesophyll layer at the top of the leaf?
It maximises the absorption of light as it will hit chloroplasts in the cell directly
