7. Transport in plant

why do plants need transport system?

they have small surface area to volume ratio

state the 3 types of plant tissues.

epidermis (outermost layer) , vascular tissues (xylem and phloem) and ground tissues (not epidermis nor ground)

state the sections .

leaf , stem , roots

state the function of parenchyma tissues.

they act as packing tissues to support the roots stem and leaves

state the parenchyma layers in root stem and leaves.

root cortex , stem cortex and pith , palisade and spongy cells

how do parenchyma cells support the plant?

by turgor pressure and photosynthesis (palisade and spongy)

what is the role of sclerenchyma.

provide support

state the properties of sclerenchyma cells.

dead tissues and lignified

where are sclerenchyma cells located?

in the stem , outermost part of vascular bundle

what are collenchyma cells?

makes cell wall thicker

where are collenchyma cells found?

in the leaf (midrib)

where is the endodermis found ?

found in the root and has a single layer

how the xylem vessel is formed?

lignin surrounds original vessels , the living cells are deprived of water and die , this creates a hollow vessel with dead cells and no end walls

why are there pits?

when the plasmodesmata died the pits were formed

what is the function of lignin in the xylem cell wall?

provides strength to xylem

what is the function of the pits?

allow lateral movement of water in case of air bubbles forming

what is the function of the phloem tissue?

to transport assimilates (organic compounds) from source (leaf) to sink (roots)

the organic compound are dissolved in water to form ____________.

sap

what does the phloem consist of ?

sieve tube elements and companion cells

outline the structure and function of each structure of the sieve tube elements.

1. sieve plates and sieve pores → allow for continuous movement of assimilates

2. cellulose cell wall → strengthen the wall to withstand hydrostatic pressure

3. thin cytoplasm → reduce friction to facilitate movement of assimilate

4. no organelles → facilitate movement of assimilates

outline the structure and function of companion cells.

1. has transport protein in plasma membrane → to move assimilates into and out of sieve tube elements

2. large number of mitochondria → more atp for active transport of assimilates

3. plasmodesmata → links companion cells and sieve tube element

state the 2 ways by which water moves in a plant.

apoplastic and symplastic pathway

explain the apoplastic pathway?

moving through the cell wall by diffusion

explain the symplastic pathway.

moves through the cytoplasm via osmosis

state the pathway to the xylem from the roots.

1. water and mineral uptake through the roots → via entering the cell membrane or active transport

2. apoplastic or symplastic pathway to reach endodermis

3. endodermal cells contain casparian strip which blocks the apoplastic pathway

4. symplastic pathway is taken and enter the xylem via the pit

explain the movement of water into the leaf to cause evaporation.

water evaporates at the surface of the mesophyll cells and diffuses into the atmosphere through the stomata

this lowers the water potential in adjacent cell and water is drawn from the xylem

what are the 2 properties of water important for transpiration.

it is polar and can form hydrogen bonds

what is meant by cohesion in water molecules.

the force of attraction between the water molecules

what is meant by the adhesion of water molecules.

the force of attraction between the water molecules and the wall of the xylem

what is the role of the cohesive and adhesive force?

cohesive force provides strong tensile strength and adhesive force prevent the stream from pulling away

how is the cohesion and adhesion mechanism called?

cohesion tension theory

what does the plant help the movement of water.

by secreting solutes to lower the water potential in xylem and increasing the pressure

what are xerophytic plants?

adapted to dry and arid conditions

what must the xerophytes do to survive?

maximise water conservation

state the adaptation of xerophytes.

1. fleshy succulent leaves → water storage

2. sunken stomata / covered in hairs → reduces diffusion gradient near stomata

3. leaves reduced to spines / curled → reduced surface area for transpiration

4. less stomata

5. thick waxy cuticle → water loss reduced

what is the process of transporting assimilate through the phloem?

translocation

assimilates is transported from __________ to ___________ .

source to sink

state some source of assimilate.

leaves , stems , tubers , tap roots , food stored in seed

state some examples of sinks.

meristem , roots

which carbohydrate is transported as assimilate? and why?

sucrose , because they are non reducing sugars

explain loading of assimilates?

apoplastic pathway is taken

modified companion cells pump hydrogen ions out of the cytoplasm into cell wall Via a Proton pump (ATP)

high concentration of hydrogen ions in cell wall of companion cell , it moves back to cytoplasm

hydrogen ions move by a cotransporter protein which also transport sucrose molecules into companion cell

moves to sieve tubes via plasmodesmata

explain the mass flow in the phloem.

a pressure difference is created by actively loading sucrose into the sieve elements at the source which lowers the water potential in the sap

water moves into the sieve elements

hydrostatic pressure increases at source

as solutes are being removed from the sieve , hydrostatic pressure decreases

this creates a hydrostatic pressure difference

this results in the mass flow