B7.1 Flashcards
What is the functions of: xylem
Transport water + minerals from roots -> stem, shoot, leaves
Only goes one direction
Cells are dead -> contain lignin (protein) to make walls (they also support the plant)
No end wall -> one long hollow tube -> old cell walls have broken down
No cytoplasm or nuclei, just water in tube
What is the function of: phloem
Transports sugar in leaves through the plant
-> rest of leaves
-> stem -> growing and storage tissue
Living cells -> sieve tubes -> small holes in cell wall -> flow between cells
Cytoplasm but no nuclei
End of cell wall -> sieve plate
What is a vascular bundle?
Two tubes found closely together:
Xylem and phloem -> main transport in plants
What is the location of the vascular bundle in:
Leaves
Stems
Roots
Leaves:
One on top of the other
Many small sections together
Stem:
Multiple pill-like shapes in a circle
Phloem outside, xylem inside
Root:
Xylem -> rounded cross in the middle
Phloem -> dots in the pockets of the cross
What are root hair cells?
They are single cell extensions of epidermis cells in root
Grow between soil particles to absorb water and minerals
Water enters via osmosis -> soil has higher water potential than cytoplasm
What do root hair cells look like under a light microscope?
A long tube coming from the root
How do root hair cells help increase the absorption of water?
Increase surface area -> increased rate of absorption and active transport
What is active transport?
Since the mineral concentration is lower in the soil, the plant uses:
Uses ATP energy
Root hair cells have specialised channel to take in minerals from the soil
Carrier protein moved mineral into plant across concentration gradient
Mineral ions transported into the xylem
Describe the pathway of water from the soil to the mesophyll cells
Osmosis cause water to pass into the root hair cell -> root cortex cells -> xylem -> leaf mesophyll cells
Describe an experiment that can show the pathway of water using appropriate stains
Experiment:
- Place plant (in this case celery) into beaker of water with a stain (food coloring)
- after few hours -> leaves of the celery are the same color as the stain
Shows water is taken up by the celery
Cross section:
If celery cut -> only certain areas would be stained -> water is being carried through specific vessel -> xylem vessels
What is transpiration?
The loss of water vapor from leaves -> evaporation of water at the surface of mesophyll cells followed by diffusion of water vapor through stomata
What are the functions of transpiration?
Transporting mineral ions
Providing water to keep cells turgid -> support plant
Providing water to leaf cells for photosynthesis
Keeping leaves cool (evaporation requires heat energy)
How does water move up the xylem vessel?
Transpiration pull:
- Water molecules attracted to each other (cohesion) -> continuous column of water up
- transpiration produces tension/pull on the water
- cohesive force keeps the stream going (each molecules pull on the one under it)
Increased rate of transpiration -> increased rate of water being pulled up
What is cohesion?
Particles of the same type are attracted to each other and stick together
What is adhesion?
Particles are attracted to other objects and stick to other things
How does the water potential gradient help transpiration (transpiration mechanism pt.2)?
Leaves have the lowest water potential -> caused by loss of water vapor by transpiration
Air spaces in leaves -> large surface area of wet cells -> increased rate of evaporation
Stomata open -> water vapor diffuse out -> more water evaporates
Root -> absorption of lot of water (helped by root hair cells)
Xylem provides easy pathway for water
High concentration in root and low concentration in leaves encourage movement of water to areas of lower concentration
Describe stomata movement
Underside of leaves -> holes called stomata (sing. Stoma)
Surrounded by 2 guard cells -> control opening and closing
CO2 low -> guard cells gain water and become turgid -> curves out
Allows gases in and out (because of concentration gradients), evaporates water
CO2 high-> guard cells lose water (evaporation) -> flaccid -> closes stomata
Also caused by low water levels -> prevent water loss
Describe an experiment that shows the effects of variation in heat and humidity on transpiration rates
Experiment:
1. Cut shoot underwater at an angle (prevent air entering xylem) place in tube
- Set up apparatus (see notes) and make sure it is air and water tight
- Dry the leaves of the shoot
- Remove the capillary tube from the beaker of water and allow a single air bubble to form
- Place the tube back into the water
- Set factors
- Allow plant to adapt for 5 min
- Record the starting position of the air bubble and leave for a set period of time
- After time record the position of the bubble
10: rinse and repeat to test other factors or variations
Variables:
Independent -> wind speed/temp
Dependent -> rate of transpiration
Control -> light, temp, wind speed, type of plant, surface area of leaves
What happens if there is too much transpiration?
Water evaporating > water available in the soil moving into the root via osmosis -> results in wilting
Cells are not full of water -> strength of cell wall cannot support plant -> collapse
What is the rate of transpiration?
The speed at which the plant loses water
How does variation in light intensity effect transpiration rates?
Rate of transpiration increase as light intensity increases
When sunny -> increased photosynthesis, plant uses more H2O and CO2
Stomata is open -> CO2 in and water evaporates out
How does variation in temp effect transpiration rates?
Rate of transpiration increases as temp increases
Higher temp -> heat leaves -> water evaporates quicker
Warm air absorbs more water vapor than cold air
How does variation in air movement/wind effect transpiration rates?
Rate of transpiration increases as wind increases
Saturated air replaced with dry air quicker
Water concentration in air is consistently lower -> increased rates of transpiration -> water potential gradient is more exaggerated
How does variation in humidity effect transpiration rates?
Rate of transpiration decreases as humidity increases
Humid -> already pretty saturated air -> water potential gradient is less exaggerated
What is translocation?
The movement of sucrose and amino acids in the phloem from regions of production (source) to regions of storage, utilisation or growth (sink)
Where do the phloem tubes transport the amino acids and sucrose?
Winter -> plants have no leaves -> transports from storage organs to other parts of the plant for respiration
Growth period (usually spring) -> storage organs would be the source, and the growing areas of the plant are the sinks
Summer -> plant has grown -> leaves are photosynthesizing and producing lots of sugars -> leaves are source and root are sinks -> stores sucrose as starch until needed
What is sucrose?
Glucose and fructose (fructose is used in nectar and flower use sucrose -> fructose)
