B7.1 - Transport in Plants Flashcards
Xylem vessels
transport water and minerals from the roots to the stem and leaves
Phloem vessels
transport food materials (mainly sucrose and amino acids) made by the plant from photosynthesising leaves to non-photosynthesising regions in the roots and stem
Vascular bundles
a strand of conducting vessels in the stem or leaves of a plant, typically with phloem on the outside and xylem on the inside
Characteristics of xylem (name 3)
- long, hollow tube
- made of dead cells
- no end walls
- to withstand pressure, strengthened by lignin
- only in upward direction
Characteristics of phloem (name 3)
- active transportation
- made up of living cells
- sieve tube cells: no nucleus, perforated end walls, cytoplasm connects cells
- companion cells: provides energy for translocation (lot of mitochondria)
Lignin
substance in vascular plants that makes cell walls rigid
Source
Where a susbtance is made
Sink
Where a susbstance is stored or used
What happends to translocation during the winter, the spring and the summer?
- Winter (no leaves): phloem tubes may transport dissolved sucrose and amino acids from the storage organs to other parts of the plant so that respiration can continue
- Spring (growth period): storage organs (eg roots) would be the source and the many growing areas of the plant would be the sinks
- After growth period (summer): leaves are photosynthesising and producing large quantities of sugars; so they become the source and the roots become the sinks - storing sucrose as starch until it is needed again
Active transport
Energy-requiring process that moves material across a cell membrane against a concentration difference
Passive transport
The movement of materials through a cell membrane without using energy
Cortex cells
The tissue of unspecialised cells between the epidermis and the vascular bundle that transports water and nutrients absorbed by the root epidermis into the bundle and stores substances such as starch, resins, and essential oils
Collenchyma
Type of ground tissue cell with a strong, flexible cell wall; helps support larger plants
3 steps how water enters the plant
- From soil to root
- Into the stem of the leaves
- Into the leaf
How does water enter the plant and move from the soil to the roots?
- enters root hair cells by osmosis
- from the soil through the membrane (from higher water potential to lower water potential)
- diffuses cell to cell until it enters the xylem
How does water move through the stem to the leaves?
- in one continuous column due to transpiration pull
- continuous column is due to cohesion between water molecules and adhesion to the wall of the xylem
How does water move into the leaf?
- water diffuses out of the xylem to palisade mesophyll cells (for photosynthesis)
- also through the spongy mesophyll
- it evaporates into air spaces and moves out through the stomata
Transpiration pull
The force by which column of water is pulled up the xylem as a result of transpiration.
Cohesion
Attraction between molecules of the same substance
Adhesion
An attraction between molecules of different substances
Factors effecting transpiration (4)
- temperature
- humidity
- wind speed
- light intensity
Translocation
The transport of sucrose and amino acids in the phloem, from regions of production to regions of storage or use
Transpiration
The loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata
How does temperature effect the rate of transpiration?
As temperature increases the rate of transpiration increases because water molecules will diffuse from the surface of the leaf faster
How does humidity effect the rate of transpiration?
When the atmosphere is humid there will be a decrease in transpiration because there is less of a difference in the water concentration gradient between inside and outside the leaf
How does wind effect the rate of transpiration?
The faster the wind speed, the greater the transpiration rate because the movement of air across the surface of leaves causes evaporation of water from the mesophyll cells, and this loss of water must be replaced by water moving up the xylem from the roots
Root hair cells
Single-celled extensions of epidermis cells in the root
- water enters by osmosis because soil water has a higher water potential than the cytoplasm of the root hair cell
What are the functions of transpiration? (name 3)
- transporting mineral ions
- providing water to keep cells turgid in order to support the structure of the plant
- providing water to leaf cells for photosynthesis
- keeping the leaves cool
How does transpiration keep the leaf cool?
The conversion of water (liquid) into water vapour (gas) as it leaves the cells and enters the airspace requires heat energy. The using up of heat to convert water into water vapour helps to cool the plant down
Wilting
- If more water evaporates from the leaves of a plant than is available in the soil to move into the root by osmosis, then wilting will occur
- This is when all the cells of the plant are not full of water, so the strength of the cell walls cannot support the plant and it starts to collapse
Potometer experiment
- Cut a shoot underwater to prevent air entering the xylem and place in tube
- Set up the potometer - beaker with water connected by a capillary tube to test tube with plant shoot; covered by a bung; ruler beneath capillary tube
- Remove capillary tube to allow a single bubble to form
- Set up the environmental factor you are investigating
- Allow the plant to adapt to the new environment for 5 minutes
- Record the starting location of the air bubble
- Leave for a set period of time
- Record the end location of air bubble
- Change a factor
- Repeat the experiment
- The further the bubble travels in the same time period, the faster transpiration is occurring and vice versa
Potometer
Apparatus used to measure water uptake in a leaf shoot and so to estimate rate of transpiration
How can temperature be investigated using a potometer?
Change the temperature of the room (cold room, warm room)
How can humidity be investigated using a potometer?
Potometer experiment but spray water in plastic bag and wrap around plant
How can light intensity be investigated using a potometer?
Changing the distance of a light source (e.g. a lamp) from the potometer
