3.4 Flashcards
Reducing respiration in stoned products.
Pre-cooling - reduction of temp. Done quickly by hydro cooling (immersion in water) or vacuum cooling or chilled air cooling at temps around 0 - 5 degrees, higher for tropical fruits. Superficial scald can be result of low temperatures.
Changes to gaseous atmosphere.
Decrease in oxygen.
Increase in Carbon dioxide.
Ethene is removed to control ripening.
Lemons for example maybe waxed to reduce water loss and reduce respiration.
Inert gasses maybe used to prevent build up of carbon dioxide eg cherries.
Plants maybe packed in plastic, oxygen used up, build up of carbon dioxide which slows respiration.
Balancing photosynthesis, transpiration and respiration in open ground.
Right plant, right place.
Light - reduce shading from extraneous plants, space crops correctly, remove some lower leaves, pruning.
Nutrient availability/ limiting pest and disease damage.
Temperature - choose correct location eg. against wall, correct aspect S or SW, provide shelter, cover or shelter plants.
Exposure - reduce strong air currents to reduce drying, provide shelter, choose less exposed area.
Competition - correct spacing
Anchorage - firm anchorage is necessary.
Balance between photosynthesis, respiration and transpiration.
Balancing photosynthesis, respiration and transpiration maximizes yield and quality of crops.
Photosynthesis captures carbon and energy.
Respiration releases energy needed for growth and reproduction.
The amount of carbon fixed in photosynthesis must exceed that lost in respiration for plant growth.
Loss of water through transpiration must be controlled to keep cells turgid so that they can expand fully and stomata remain open.
Sources and sinks: seasonal changes.
Spring - carbs produced by photosynthesis from new growth.
Carbs stored in dormant season as starch located in stems, roots, rhizomes and stolons. - sinks new spring plant growth until photosynthesis start and produces cabs for growth.
Summer - reproductive growth requires high levels of carbohydrates. Photosynthesis produces some of carbs required but stored reserves can be used.
Autumn - growth slows, in perennial plants build up of carbs for spring growth, source - photosynthesis leaves.
Winter - root growth continues. Small amounts of carbohydrates are used for root growth and bud formation > as spring starts, stored carbs are utilised to kickstart spring growth.
Sources and sinks.
Plant organs and seasonal changes.
Plant sinks and plant sources.
Plant sources (area in plant where sugars are produced and stored) - leaves, woody stems, storage organs that store starch.
Plant sinks (areas in plant where sugars are required) - meristems of stems and roots, flowers, fruits, seeds, storage organs and woody stems.
Translocation within the Phloem
Phloem involved in the movement of products of photosynthesis.
Organic materials (inc. starches and sugars) are moved from the tissue where they are produced to other areas of plant.
Some minerals and hormones are also transported.
Phloem tissues are in underside of vein, periphery of stem, centre of root surrounding xylem core.
Glucose and fructose are converted into sucrose for transport.
Phloem tissues of the leaf connect with phloem tissues in the stem.
Sucrose molecules move from the sieve cells of the phloem and are then transported out of the leaf.
Transport of sugars is ACTIVE TRANSPORT and requires energy.
Companion cells within phloem have organelles for creation of energy.
Uptake and movement of mineral nutrients.
Not all minerals are absorbed through the root.
Foliage feed are applied to leaves.
Mineral nutrients diffuse into the leaf across the cuticle and through stomata they are distributed through the apoplast and symplast, crossing cell membranes by active transport, s in root.
Phloem translocation and movement of sugars.
Theories.
Theory of phloem translocation has to explain:
Large amount of sugars are transported.
The rapid rate if movement of sugars - travels faster than simple diffusion or protoplasmic streaming.
Great distances travelled.
Bi-directional movement up and down.
Uptake and movement of mineral nutrients.
Mobile minerals
Mobile minerals are also redistributed in the phloem to areas in the plant where they are most needed.
Nitrogen is a mobile mineral - if it is in short supply it will move from old leaves to new leaves.
Iron and calcium are immobile leading deficiencies eg. Chlorosis or Blossom end rot.
Uptake and movement of mineral nutrients - translocation
Once minerals have entered the xylem are trans located to the rest of the plant.
Minerals move upwards through the plant in the transpiration stream.
Transpiration may be necessary for initial uptake.
At the end if the xylem mineral ions are delivered to shoots, flowers and leaves.
They are distributed through apoplast and symplast and taken up into cells by active transport.
Uptake and movement of mineral nutrients.
Active transport.
Mineral ions are dissolved in soil water.
Mineral ions are taken up from films of water surrounding the soil particles through root cortex, generally via apoplast pathway.
Carrier proteins are specialised proteins that are embedded in the cell membrane.
Mineral ions are taken into cells by ACTIVE TRANSPORT on carrier proteins at the endodermis.
Active transport requires energy supplied by ATP.
Movement is generally against CONCENTRATION GRADIENT.
Photosynthesis, respiration and transpiration - control in protected environments.
Hot/summer weather.
Shading reduces temperature and photosynthesis- can be automated, only use if necessary.
Humidity can be increased by damping down or misting, thus reducing respiration and lower temperature.
Ventilation - increase carbon dioxide supplies, reduces temperature next to leaf. Carbon dioxide may be supplemented.
Photosynthesis, respiration and transpiration - control in protected environments.
In winter/cooler weather.
Light needs to be maintained above compensation point for net growth.
Temperature needs to be increased, best at night when stomata are closed, transpiration is low and leaf has a supply of carbohydrate from previous day. Irrigation is important.
