organisation (in plants) Flashcards
xylem, phloem, transpiration, transpiration stream, measuring transpiration, stomata and guard cells, transport, adaptations of the leaf
what movement are xylem vessels involved in
they are involved in transpiration.
the movement of water through a plant from ROOTS —> LEAVES
what movement are phloem vessels involved in
they are involved in translocation.
the movement of food substances from stems to growing tissues + storage tissues
why do plants require a transport system
to move food, water and minerals
describe how translocation works
plants make their sugars through photosynthesis - this happens in the leaves. so to share the sugars with the rest of the plant, they have to be transported.
phloem cells are tubes arranged end to end forming a phloem tube.
in between adjacent cells, there are small pores which allow cell sap (mixture of water and sugar) - this means that the sugars made in the leave can be transported long distances through multiple cells
once the sugar has ended up wherever it needs to go, 1 of 2 things can happen:
- the sugar can be used directly for energy
- the sugar can be stored to be used for energy later
describe how transpiration works
stomata allows gas exchange between the leaf and the atmosphere.
when the stomata are open they let in carbon dioxide and also allow water vapour to leave the leaf through evaporation
this is what drives the movement of water up through the plant
describe how the transpiration stream works
water (by osmosis) and mineral ions (by active transport) are absorbed from the soil through root hair cells
(the transported water is needed for photosynthesis which mostly takes place in the leaves)
(the mineral ions are needed to make proteins and other molecules)
it is then transported through the xylem vessels UP the stem to the leaves
the water then evaporates from the leaves (transpiration)
how are root hair cells adapted for transpiration
they have a large surface area to increase the rate of absorption
all about xylem
- physical process
- transports water + minerals from roots to leaves via transpiration
- transports upwards (one way only)
- thick walls stiffened with lignin
- no end wall between cells (hollow)
all about phloem
- requires energy
- transports amino acids dissolved in water from the leaves to the rest of the plant and to storage organs via translocation
- transports upwards and downwards
- cells have end walls with perforations
features of a leaf (from top to bottom)
- waxy upper epidermis
- upper palisade mesophyll cells
- spongy mesophyll
- guard cell - stomata - guard cell
- waxy layer
- lower epidermis
upper epidermal tissue adaptation + function
- it is transparent
- it protects the plant from infection and water
palisade mesophyll adaptation + function
- packed with chloroplast
- absorbs light for photosynthesis
spongy mesophyll adaptation + function
- packed loosely
- diffusion of gases (CO2)
lower epidermal tissue adaptation + function
- lots of stomata to prevent excess transpiration
- allows CO2 to enter the leaf and O2 + excess water to exit
vascular bundles adaptation + function
- has xylem + phloem
- transport critical substances to plant
features of an OPEN stomata (6)
1 - stomatal pore
2 - inner thick wall
3 - nucleus, chloroplast, vacuole
4 - outer thin wall
5 - guard cells (from 2 - 4)
6 - epidermal cell
how do guard cells work
when the plant wants to open, ions are pumped into the guard cell
this creates a concentrated region and water moves into the guard cell - osmosis - causing them to become turgid (swollen/no more water can get in)
due to the different wall thickness, the outsides of the cell becomes longer than the insides and so the cells curve - this creates a space
when the stomata needs to close, the water moves out of the cells - osmosis - and they become flaccid (opposite of turgid/floppy)
the cell returns to normal shape and the space between them closes
what needs to be transported in plants (5)
WATER - taken in primarily at the roots and needs to get all the way around the plant
IONS AND NUTRIENTS - taken in by roots and needs to get all the way round the plant
GLUCOSE - made by chloroplast ; needs to be transported to all cells for respiration
CARBON DIOXIDE - diffuses in through stomata to be used in photosynthesis
OXYGEN - diffuses out through stomata
measuring transpiration
you use a potometer
–> this indicates how quickly transpiration occurs
–> how far the bubble moves shows how much water has been taken up
transpiration happens at different rates in different environmental conditions
what affects transpiration
light intensity -
the brighter the light intensity, the more photosynthesis can take place –> this means more stomata will have to be open to let in the CO2 (required for photosynthesis) so more water can evaporate resulting in a higher rate of transpiration
so when it is nighttime, there is no photosynthesis happening because is it dark –> closed stomata so little transpiration
temperature - the warmer it is the higher the rate of transpiration because the particles of water will have more energy –> more likely to evaporate and diffuse out of the stomata
FOR AIRFLOW AND HUMIDITY –>
because water is constantly being brought up from the roots, the inside of the leaf is going to have a much higher concentration of water than the outside
–> concentration gradient where the water can diffuse out the leaf SO rate of transpiration will depend on gradient
airflow - when airflow is high (windy) the water molecules that leave the leaf are quickly going to be blown away –> so the concentration gradient between inside and outside will stay high, increasing the rate of transpiration
humidity (how much water vapour is in the air) - more humid air will decrease the rate of transpiration because the large amount of water in the moist air will decrease the concentration gradient –> so less water will diffuse out so there will be less overall evaporation
