UNIT 3: Nutrition In The Flowering Plant Flashcards
Transpiration stream
The movement of water through a plant
transpiration stream is maintained by
- osmosis
- root pressure
- transpiration
osmosis
the movement of water from high water concentration to low water concentration across a semi-permeable membrane
root pressure
the force exerted by water within the xylem tissue of the roots
transpiration
the loss of water from the aerial parts of the plants
water and mineral uptake
- water enters the root hairs by osmosis, moving from high water concentration to low water concentration.
- minerals dissolve easily in water and move into the root by diffusion - either by passive transport or by active transport (requires ATP)
- water moves across the ground tissue and into the xylem tissue.
- water is then transported up the plant.
cohesion-tension model of water transport
- john joly & henry dixon = two irish scientists who first proposed the cohesion-tension model.
- water moving into the xylem tissue of the root causes a pressure build up - this is called root pressure.
- root pressure contributes to the upward movement of water molecules.
- water molecules also tend to stick easily to the sides of the xylem vessels - this is called adhesion of the water molecules.
- transpiration of the water molecules occurs mainly from the leaves - this pulls the column of water molecules upwards through the xylem, creating a tension in the water molecules.
control of transpiration
- waxy cuticle - prevents direct water loss from the surface of the leaves
- stomata - controls the rate of transpiration by opening and closing.
- lenticles - allows a small amount of transpiration but also allows oxygen in (for respiration) and carbon dioxide out (excretion).
carbon dioxide uptake
carbon dioxide is mostly taken in from the atmosphere, but can be taken from the mitochondria in the leaf (via respiration)
stomatal opening and closing
- stomata open during the day and close during the night, in general.
- high levels of water can cause the stomata to open- the plant tries to get rid of excess water.
- low levels of water cause stomata to close - plant tries to conserve water.
- windy conditions cause the stomata to close - plant tries to conserve water.
- guard cells are the structures that control the opening- when they become turgid they curve away from eachother - opening the stoma; when they lose water (become flaccid) they remain together and stoma closes.
- carbon dioxide levels are the main controlling factor in whether stomata open or close - high CO2 levels cause the stomata to close and low levels of CO2 cause them to open.
transport of oxygen & glucose (the products of) in photosynthesis
- OXYGEN - it is a by-product of photosynthesis and is either released into the atmosphere or is used by the leaf cells in respiration.
- GLUCOSE - the main product of photosynthesis, can be used immediately in respiration, stored in the cell as starch or converted to sucrose and transported to another area of the plant
root storage organ
tap roots, such as the carrot and parsnip are root storage organs where a lot of starch is stored.
stem storage organ
potatoes and asparagus
leaf storage organ
onions and garlic store food in modified leaves - in the form of a tightly packed ‘bulb’.
petiole storage organ
celery and rhubarb
