Movement of substances in and out of cells Flashcards
diffusion
net random movement of substances from an area of high to low concentration
osmosis
net random movement of water from an area of high to low water potential across a partially permeable membrane
active transport
movement of substances from an area of low to high concentration, using energy from ATP
What is the function of the transport system in plants?
leaves can receive water and
mineral ions, both for photosynthesis
What is the xylem?
tissue that transports water and mineral ions from the roots to the leaves
Describe the structure of the xylem
- made of thick walled dead cells without any cytoplasm
- cell wall with lignin
- upwards movement
- no end walls
Why doesn’t the xylem have organelles?
to prevent obstruction to flow of water and minerals
Why does the xylem have cell walls stiffened with lignin?
waterproof
strength
stops cell collapsing in
Why doesn’t the xylem have end walls?
cells join together form long tubes to make complete tissue
Give examples of mineral ions needed for photosynthesis
magnesium ions
nitrate ions
What is the use of magnesium ions in plants?
make chlorophyll for photosynthesis
What is the use of nitrate ions in plants?
make amino acids and proteins
What is the phloem?
tissue in plants that transports sugars and amino acids both up and down the plant from the leaves to respiring tissues
translocation
movement of sugars and amino acids through the phloem that uses energy
Describe the structure of the phloem
- companion cells
- sieve plates (thin layer of cytoplasm)
- cell walls of cellulose
Why does the phloem have companion cells?
keeps phloem alive
has ribosomes and cytoplasm to do this
Why does the phloem have sieve plates?
allows contents to flow through
How does translocation work?
- companion cells have mitochondria
- sucrose moved into sieve tubes by active transport
- low water potential in sieve tubes
- water moves via osmosis into sieve tubes
- high pressure created
- sucrose and water removed from phloem
Why is translocation called an active process?
energy needed
Why is the process of translocation so important?
sugars needed in growing points
- roots
- leaves
How is water transported around the plant?
- enters by root hair cells
- high surface areas
- short diffusion distance
- water potential outside plant is higher than inside cells
- via osmosis
- water moves from cell to cell down concentration gradient
- via osmosis
- water reaches xylem vessel - carried to all parts of plant
How are mineral ions transported around the plant?
- enters by root hair cells
- concentration of the solutes outside is lower than inside
- move into the roots from the soil
- via active transport
- reaches phloem vessel
- carried to all part of plant
Which direction does the water and mineral ions move in the xylem?
upwards towards leaves
Which direction do the amino acids and proteins move in the phloem?
upwards and downwards to leaves and roots
transpiration
water loss via evaporation through the stomata
What is the transpiration stream?
upwards movement of water through the xylem from roots to leaves
What are the functions of the transpiration stream?
- carry mineral ions
- keep turgor pressure high
- supplies water
- evaporation cools leaf
Describe the process of transpiration
- water leaves
cells of the mesophyll - evaporates
into air spaces in
spongy mesophyll - water diffuses out through stomata
- loss of water from mesophyll cells
makes lower
water potential - water moves into them by osmosis
- water leaves xylem to replace water lost
How does temperature affect transpiration?
- increase in kinetic energy
- faster rate at higher temps
- more transpiration
How does light intensity affect transpiration?
- more light
- more photosynthesis
- more co2 needed
- stomata open
- more transpiration
How does wind speed affect transpiration?
- water molecules blown away faster
- higher water potential in leaf
- more transpiration
How does humidity affect transpiration?
transpiration increases when humidity decreases
due to concentration gradient
How does water supply affect transpiration?
lower water supply is caused by more transpiration than supply
- plant wilts
- guard cells around stomata become turgid - stops transpiration
What is an isotonic solution?
solution outside cell has same water potential as inside cell - no net movement
What is a hypertonic solution?
solution outside cell has lower water potential then inside cell - net movement of water molecules out of cell
What is a hypotonic solution?
solution outside cell has higher water potential then inside cell - net movement of water molecules into cell
What happens to an animal cell in an hypotonic solution?
lysed
bursts - no cell wall
What happens to plant cell in an hypotonic solution?
turgid (normal)
What happens to an animal cell in an isotonic solution?
normal
What happens to a plant cell in an isotonic solution?
flaccid
What happens to an animal cell in an hypertonic solution?
shrivels
What happens to a plant cell in an hypertonic solution?
plasmolyzed
wilts - not enough water to fill cells
- cytoplasm shrinks
What are the stomata?
holes in the surface of the leaf, mainly on bottom
What is the function of the stomata?
gas exchange
CO2 in (photosynthesis)
O2 out (respiration)
What is the function of the guard cells in relation to stomata?
control the opening and closing of stomata
two guard cells on either side of a stomata
Describe the structure of a guard cell
thickened, inflexible inner cell wall
How do guard cells complete the function in relation to stomata?
- photosynthesise in light
- concentration of sugars increases
- water potential in guard cells lowers
- water moves into guard cells
- via osmosis
- become turgid and stomata open
(opposite to close ; dark etc.)
What is a potometer?
device used to measure rate of transpiration
How do you set up a potometer?
- cut stem of shoot
- put shoot stem into bung
- put bung into potometer
- make sure tap is closed and is full of water (no bubbles)
- lift potometer out of water
- leave end of capillary tube out of water until air bubble forms then put end
into beaker of water - measure transpiration rate as distance bubble travels in five minutes
What are some things to ensure when setting up a potometer?
- potometer set up under water - prevents air bubbles from entering
system and blocking xylem - grease joint with petroleum jelly - this prevents
water loss and air entry - take multiple readings to find average
Define translocation
movement of dissolved substances such as sucrose and amino acids, down the phloem towards the roots
