Plants And Food Flashcards
What is the equation for photosynthesis?
- carbon dioxide + water -> glucose + oxygen (light and chlorophyll over and under arrow)
6CO2 + 6H2O -> C6H12O6 + 6O2 - Importance in converting light energy to chemical energy
What is chlorophyll?
- A green pigment needed to absorb light energy
- Photosynthesis converts light energy into chemical energy
How are leaves adapted for photosynthesis? ππππππππππβοΈβοΈβοΈβοΈβοΈβοΈβοΈβοΈβοΈβοΈβοΈβοΈβοΈβοΈ
- LSF to absorb light efficiently.
- Chloroplasts (containing chlorophyll).
- Supply of water and carbon dioxide
- Systems to carry away products of photosynthesis to other parts of the plant.
- Thin flat structures supported by a lead stalk which can grow to allow the blade of the leaf to be angled to receive the maximum amount of sunlight.
- Leaves are broad so there is a large surface area for diffusion
How is the waxy cuticle adapted for its function?
- Reduces water loss by evaporation
- Prevents entry (barrier) to disease-causing microorganisms such as bacteria and fungi.
How is the palisade layer adapted to its function? π
-There are elongated palisade cells which are close to the source or light and filled with chloroplasts and so chlorophyll so main site of photosynthesis.
How is the upper epidermis adapted for its function?
-Relatively transport and contains few chloroplasts to allow sunlight through easily to the photosynthetic cells.
How is the spongy mesophyll layer adapted for its function?
- There a fewer chloroplasts (containing chlorophyll) to absorb any of the remaining sunlight
- This layer forms the main gas exchange surface by absorbing carbon dioxide and releasing oxygen and water vapour
- The air spaces increase the surface area for gas exchange allowing O2 and CO2 to diffuse in and out of cells in in and out of the mesophyll
How is the lower epidermis adapted for its function?
-Contains may pores called stomata, these allow oxygen and water vapour to diffuse out of the leaf and allows carbon dioxide to diffuse into the leaf to reach the photosynthetic cells
How are the guard cells adapted for its function?
- The guard cells are highly specialised cells, which can alter their shape to open or close the stomata
- At night the stomata close as there is no light, so no photosynthesis would be able to occur and so this prevent CO2 from entering and water from escaping and the plant drying out. Therefore as water is lost at night the guard cells move together closing the stomata
- At day the guard cells become turgid, as they take up water by osmosis
- In dry condition the stomata closes, this causes photosynthesis to stop (which is bad) but it prevents the plant from drying out and dying
What are the limiting factors of photosynthesis?
- Light intensity
- Temperature
- Carbon dioxide concentration
Why is light intensity a limiting factor?
- As light intensity increases, so does the rate of photosynthesis
- This is because light energy is needed to speed up the reaction
- However once the enzymatic reactions are carried out at a maximum velocity due to sufficient light, the rate plateaus
Why is carbon dioxide a limiting factor?
- Carbon dioxide is needed as a substrate for photosynthesis
- This is why an increase in its concentration increases the rate of the reaction
- However once every enzyme is occupied with carbon dioxide a further increase fails to increase the rate
- Ans therefore the graph plateaus
Why is temperature a limiting factor?
-As temperature increases so does the rate of the reaction until a certain temperature, after which a sudden drop is observed
-This is because initially the increase in temperature sped up the reaction as the particles were moving faster
-However beyond a certain temperature the enzymes become denatured which prevents further photosynthesis
(If there is cool temperature there is not enough kinetic energy for enzymes to carry out photosynthesis)
What is the plantβs use for glucose?
- Respiration
- Sucrose: transport as main sugar carried in the phloem
- Starch: for storage
- Cellulose: another polymer which forms plant walls
- Lipids: membranes of all cells and energy store in many seeds and fruits e.g. in peanuts and olives
- Chlorophyll (and magnesium ions from the soil)
- Proteins and DNA (and mineral ions from the soil e.g. nitrates and phosphates)
What is the use of magnesium ions for a plant and what is the deficiency?
Mg 2+
- Use: forms part of the chlorophyll molecule
- Deficiency: Chlorosis, leaves turn yellow
What is the use of nitrate ions for a plant and what is the deficiency?
NO 3- / NH4 +
- Use: making amino acids, proteins, chlorophyll, DNA and many other compounds
- Deficiency: stunted growth, weak stem, older leaves turn yellow
What is the use of potassium ions for a plant and what is the deficiency?
K+
- Use: needed for enzymes of respiration and photosynthesis to work
- Deficiency: leaves turn yellow with dead spots
What is the use of phosphate ions for a plant and what is the deficiency?
PO4 3-
- Use: making DNA and many other compounds, part of cell membranes
- Deficiency: poor root growth and the younger leaves turn purple
What is the result of a shortage of a particular mineral?
mineral deficiency disease
How are minerals absorbed from the soil?
In the form of an ion
How can you investigate if a particular plant is deficient?
- Plants can be grown in soil-free cultures (water cultures) as plants only take water and mineral ions from the soil for growth
- You could compare culture solution and so if you replace a mineral ion you would be deficient in that
- Hydroponics is growing plants in water culture solution
- Can determine by growing plants under selective conditions omitting single factors at a time and studying the plantβs growth characteristics
How do you investigate photosynthesis?
- Place a leaf in boiling water with forceps for 5-30 seconds, to arrest chemical reactions (i.e. as it denatures the enzymes) and to make the leaf permeable to iodine and ethanol
- TURN the bunsen burner off as ethanol is highly flammable
- Place the leaf in a boiling tube and boil it with ethanol and place it in a hot water bath for 5 minutes, the leaf should go pale yellow or colourless as the ethanol would have removed the green pigment, this allows the results of the iodine test to be seen more clearly
- Wash the leaf off with cold water
- Add iodine, and the areas where starch is present will go from brown iodine to bluey-black (dark)
How do you destarch a leaf?
- Place the plant in the dark for 2-3 days, and the plant will use up the starch stores in its leaves (since it was in the dark it would not have been able to photosynthesise and hence produce glucose and starch)
- Add iodine and the leaf will NOT turn blue-black
How do you test to see if a leaf needs carbon dioxide?
- Place a plant in a close container which contains a chemical called soda lime which absorbs carbon dioxide from the air around the plant and in the jar
- Add iodine to the leaf of the plant and it will not turn blue black as photosynthesis would not have been able to occur without carbon dioxide, so no starch produced even if there is a good light source, need CO2 for photosynthesis
(Temperature would be a control variable)
(The pot might be covered in a plastic bag because it stops bacteria and microorganisms from respiring)
(If you had another pot with no soda lime it would be an experimental control)