chap 7 nutrition in plants Flashcards
conditions for photosynthesis (5)
occurs in chloroplasts
- Chlorophyll: green pigment found in the chloroplasts of a plant’s leaf cells
- Light energy: trapped by the chlorophyll found in chloroplasts to use in photosynthesis
- Carbon dioxide
- Water
- Optimum temperature
why is photosynthesis important (3)
- plants are producers which release and store chemical energy through p/s = plants eaten by other organisms and animals = chemical energy transferred to them (makes it available for them)
- Purifies air: plants take in carbon dioxide from the atmosphere and release oxygen as a product
- Provides fuel: energy in fossil fuels come from the Sun through photosynthesis = burning of fossil fuels release energy (fuel)
light dependent stage
- Chlorophyll in chloroplasts absorb light energy = converted into chemical energy
- Light energy used in photolysis of water - splitting of water molecules into oxygen and hydrogen atoms (present in glucose: C6H12O6)
light independent stage
- Enzymes catalyse the reduction of CO2 to glucose - CO2 gains hydrogen to form glucose
- Glucose converted to starch = stored as starch granules in leaves
- Glucose converted to sucrose and amino = translocated via phloem to other parts of the plants from leaves = used to build new plant cells or in storage
limiting factors for p/s i
light intensity, concentration of carbon dioxide, temperature
what can we use to measure rate of p/s of water plants
rate of bubble production, no of bubbles produced per min
(more bubbles produced, higher rate of p/s)
effect of low temp on rate of p/s
Low temp: enzymes are inactive due to low kinetic energy = low frequency of effective collisions between enzymes and substrates = low rate of p/s;
effect of increasing temp on rate of p/s
kinetic energy of enzymes and substrates increase
frequency of effective collisions between enzymes and substrates increase
more enzyme-substrate complexes (ESC) are formed per unit time
rate of p/s increases
effect of optimum temp on rate of p/s
KE of enzymes of substrates highest
highest frequency of effective collisions between enzymes and substrates
most number of enzyme-substrate complexes formed per unit time =
highest rate of p/s
effect of temp beyond optimum temp on rate of p/s
Enzymes denature
active site of enzymes altered
no ESC formed
rapid decrease in rate of p/s
what happens to glucose that is used immediately
- Used immediately in: cellular respiration = provide energy for cellular activities OR in forming cellulose cell wall
- Can be converted into sucrose immediately:
translocated to other parts of plant/storage organs –> converted to starch at storage organs
OR might be converted to glucose - Reacts with nitrates and mineral salts absorbed from soil: form amino acids in leaves
- excess amino acids transported away
- amino acids forms proteins = synthesis of new protoplasm in leav
what happens to glucose that is stored (2)
- conversion to starch in day: rate of p/s is so high = rate of glucose production exceeds rate of sugars being removed = excess glucose formed = converted into starch granules which is stored in leaves OR stored in storage organs -> for essential use of the plant (eg plant must always maintain a certain concentration of starch in plant)
- conversion to starch in darkness: photosynthesis does not occur = starch converted back into glucose
external adaptations of leaf (3 leaf parts)
Lamina
1. Broad: increases SAVR -> max light absorption = max rate of photosynthesis
2. Flat and thin: provides a shorter distance for diffusion of gases such as carbon dioxide = higher rate of diffusion
Petiole: holds the lamina away from the stem = lamina can obtain sufficient sunlight and carbon dioxide
Upper and lower epidermis (surface layer):
1. has waxy cuticle on both epidermis = reduces water loss through evaporation/prevent excessive water loss
2. transparent cuticle on the upper epidermis: allows maximum light to penetrate to the mesophyll cells = max rate of p/s
internal structure of leaf
- Upper epidermis: waxy and transparent
layer of upper epidermis cells -> have no chloroplasts at all - Palisade mesophyll cells: long and cylindrical in shape -> Have the most chloroplasts = most chlorophyll
- Spongy mesophyll cells: irregularly shaped -> have numerous air spaces in between SMC (intercellular air spaces - ICAS)
- Each cell covered by a thin film of moisture
- Have less chloroplasts than PMC
- Contains vascular bundle - Lower epidermis: covered by cuticle
Layer of lower epidermal cells -> have more stomata than UE - little chloroplasts present
internal adaptations of leaf
- Network of veins containing xylem and phloem: xylem carry water and dissolved mineral salts from roots to the cells in the lamina + phloem carry manufactured food from leaves to other parts of the plant
- Abundant chloroplasts in PMC: abundant chlorophyll = maximise light absorption = max rate of p/s
- PM layer is located directly below UE layer = receive max light energy
- ICAS in spongy mesophyll layer: allows gases such as carbon dioxide and oxygen to dissolve (thin film of moisture) and diffuse in and out of the cells = rapid rate of diffusion
- Stomata present in epidermal layers: open in presence of light to allow diffusion of CO2 and O2 in and out the leaf
