9.1&9.2 Flashcards
what is the function of a waxy cuticle
waterproof surface that prevents water loss
what is the function of the upper epidermis?
protects the upper surface of a leaf but allows light through
what is the function of the lower epidermis?
protects the under side of a lead
what is the function of spongy mesophyll cells
photosynthetic tissue with large air spaces to allow for gas exchange
what is the function of palisade mesophyll cells
tightly packed cells with many chloroplasts for photosynthesis
what is the function of the xylem
specialised vessels that transport water
what is the function of phloem
tubes that allow transport of organic solutes
what is the function of the cambium
cells divide into new xylem and phloem
what are vascular bundles
xylem, phloem and cambium
what is the function of guard cells
specialised cells that open and close the stomata
what is the function of a stomata pore
allows gas exchange
How are carbon dioxide absorbed and oxygen released from a leaf?
CO2 diffuses into a leaf and O2 diffuses out of a leaf through the stomata
they both go down their concentration gradients
What’s the problem for plants when stomata are open
layer of water in the cellulose cell walls of spongy mesophyll cells
this water is needed to dissolve CO2 into a solution
however, the water evaporates into the spongy mesophyll air spaces and diffuses out of the leaf by stomata
Define Transpiration
the loss of water vapour from leaves
consequence of having stomata open during the day
How do guard cells regulate the opening and closing of stomata
cells absorb water by osmosis and become turgid & expand which opens the stomata because one cell wall side is thicker than the other (kidney bean shape)
It closes once the water has been lost and the cells become flaccid
explain the transpiration stream
water is lost by evaporation and diffuses out of the leaf through the stomata- which creates negative pressure
water is drawn out xylem vessels by adhesion the cellulose cell walls in mesophyll cells
This creates a pulling force in the xylem in the stem but does not collapse due to lignin rings
Cohesion transmits this pulling force from one molecule to the next all the way down the water column
Adhesion also helps water to be drawn up xylem vessel by capillary action
Water enters root hair cells by osmosis, is then pulled across the cortex and enters the xylem vessels in the root
draw the structure of primary xylem vessels
XX
Identification of root and stem tissues in microscope images
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Explain how active uptake of mineral ions in the roots causes absorption of water by osmosis
active uptake of mineral ions causes a high concentration of solutes in the cytoplasm of root hair cells
water is passively absorbed by osmosis from an area of low solute concentration (soil) to high solute concentration (root hair cells cytoplasm) through a semi permeable membrane
Can be done by two routes; apoplast & symplast
apoplast:
- the movement of water through freely permeable cellulose cell walls & extracellular spaces by mass flow
- aided by adhesion to cellulose fibres
- main route for water across cortex
symplast:
- the movement of water through cell cytoplasm, b/w via plasmodesmata by diffusion
- to enter this route, water has to move across cell membrane by osmosis
What are xerophytes ans halophytes
xerophytes- plants that live in dry conditions
halophytes- plants that live in salty conditions
Name some adaptations to reduce water loss
fewer leaves or spires- reduces surface area over which water can be lost to transpiration
fewer stomata- reduces number of pores through which water can escape by transpiration
deep roots- can absorb water deep underground
shallow spreading roots- can cover large surface area to collect water rapidly during occasional rain
water storage structures- swollen leaves or stems can store water to be used during dry periods
Explain how active transport is used to load organic solutes into phloem sieve tube at the source
organic solutes are loaded up into phloem sieve tube cells by a co-transporter mechanism
first, H+ ions are actively transported out of companion cells using ATP
This creates a high concentration of H+ ions outside of the cell
The H+ ions then flow down their concentration gradient into sieve tube cells through a co-transporter protein
The energy from this is used to carry sucrose into phloem sieve tube cells
This creates an increase of sucrose concentration in sieve tube cells at the source
What is the consequence of high solute concentration in sources
High solute concentration in sieve tube cells decreases water concentration
water flows down its concentration gradient to enter sieve tube cells by osmosis
this generates high hydrostatic pressure in sieve tube cells at sources
What is the consequence of low solute concentration in sinks
solutes leave the sieve tube cells
water concentration increases, so it leaves the sieve tube cells by osmosis and enters the xylem
this generate low hydrostatic pressure in sieve tube cells at sinks
