2) Structure and functions in living organisms - nutrition Flashcards
Photosynthesis
Endothermic reaction in which energy from sunlight is transferred to the chloroplasts in green plants
-absorbed by chlorophyll
carbon dioxide + water –> oxygen + glucose
Glucose in plants
-source of energy in respiration
-Produce starch for storage
-Synthesise lipids for an energy source in seeds
-To form cellulose to make cell walls
-Produce amino acids (used to make proteins) when combined with nitrogen and other mineral ions absorbed by roots
Photosynthesis equation
Carbon dioxide + water –light–> glucose + oxygen
6CO2 + 6H2O –> C6H12O6 + 6O2
Limiting factors of photosynthesis
Something present in the environment in such short supply that it restricts life processes
-temperature
-light intensity
-carbon dioxide concentration
Limiting factors of photosynthesis - temperature
-lower - less kinetic energy particles have, fewer successful collisions occurring over a period of time
-higher - increases the kinetic energy of particles, increase likelihood of collisions between reactants and enzymes which results in the formation of products
-At higher temperatures - enzymes can be denatured – this reduces the overall rate of photosynthesis
Limiting factors of photosynthesis - light intensity
-required for photosynthesis
-more light - faster rate
-This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply
Limiting factors of photosynthesis - carbon dioxide concentration
-required for photosynthesis
-more carbon dioxide, the faster rate
-This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply
Structure of leaf
-waxy cuticle
-upper epidermis
-palisade mesophyll
-spongy mesophyll
-lower epidermis
-guard cell
-stomata
-vascular bundle
-xylem
-phloem
Waxy cuticle
Protective layer on top of leaf, prevents water from evaporating
Upper epidermis
Thin and transparent to allow light to enter palisade mesophyll layer underneath
Palisade mesophyll
Column shaped cells tightly packed with chloroplasts to absorb more light, maximising photosynthesis
Spongy mesophyll
Contains internal air spaces that increases the surface area to volume ratio for the diffusion of gases (mainly CO2)
Lower epidermis
Contains guard cells and stomata
Guard cell
Absorbs and loses water to open and close the stomata to allow carbon dioxide to diffuse in, oxygen to diffuse out
Stomata
Where gas exchange takes place
-opens during the day, closes at night
-evaporation of water takes place
-found in greater concentration on underside of leaf to reduce water loss
Vascular bundle
Contains xylem and phloem to transport substances to and from the leaf
Xylem
Transports water and dissolved minerals from the roots to the rest of the plant and also provides physical support.
Phloem
Transports sucrose and amino acids around the plant
Plant - adaptations for photosynthesis
-Large surface area of leaf - increase absorption of light
-epidermis is thin and transparent - more light to reach the palisade cells
-thin cuticle made of wax - protects the leaf without blocking sunlight
-palisade cell layer at the top of the leaf - maximizes absorption of light
Mineral ions - plants
-magnesium
-nitrate
Magnesium - plants
-needed to make chlorophyll
-deficiency - causes yellowing between the veins of leaves
Nitrates - plants
-source of nitrogen to make amino acids
-deficiency - causes stunted growth, yellowing of leaves
Practical - starch testing
-Destarch the plant by placing it in a dark cupboard for 24 hours
1. Heat a plant leaf in boiling water for 30 seconds - kill the leaf, stop any more chemical reactions
2. Add leaf to boiling ethanol in a water bath for a few minutes - turns it white
3. Dip into water bath again to soften
4. Spread onto a white tile
5. Add iodine solution from a pipette
6. Part of the leaf that contains starch will turn the iodine blue/ black
Practical: light and photosynthesis
- Destarch a plant
- Cover part of a leaf with a lightproof paper/ foil
- Place the plant in a bright light for several hours
- Test the leaf for starch using the 4 step starch test
- The area which was covered in foil will not turn blue-black
Practical: chlorophyll and photosynthesis
- Destarch a variegated plant (partly green and white)
- Place the plant in bright light for several hours
- Test the leaf for starch using the 4 step starch test
- The white part of the leaf will not turn blue-black