transport in plants

what is the function of the xylem vessel

it transports water and mineral ions around plants. it also provides structural support

list some adaptations of the xylem vessels

• they are elongated, hollow tubes without end walls

• they lack organelles

• their walls are thickened with lignin for support

• they have non-lignified pits that allow movement of water and ions into and out of the vessels

what is the function of the phloem tissue

transports sugars and amino acids (assimilates) around plants.

list some adaptations of the sieve tube elements

• they are connected end-to-end to form sieve tubes

• they have sieve plates with pores at their ends to allow flow of sugars and amino acids

• they lack nuclai and most organelles

• they have only a thin layer of cytoplasm

give some adaptations of companion cells

• they are connected to sieve tube elements through pores (plasmodesmata)

• the cytoplasm contains a large nucleus, many mitochondria to release energy for the active transport of substances through the sieve tube elements, and many ribosomes for protein synthesis

give names of features in the xylem tissue

• elongated, hollow tubes

• non-lignified pits

• thick lignified wall

give names of features of the phloem tissue

• companion cell

• nucleus

• mitochondria

• ribosomes

• sieve plate

• sieve tube

• sieve tube element

• pores

• assimilates

• plasmodesmata

what are herbaceous dicotyledonous plants

plants with two seed leaves (cotyledons) in their seeds.

describe how the vascular tissues are distributed in the roots

• xylem forms central cylinder surrounded by phloem

how does the distribution of the vascular bundle in the roots aid the roots

it provides support as the root grows through the soil

describe the distribution of the vascular tissues in the stem

xylem and phloem are in the outer region, with phloem being closest to the outside of the root

how does the vascular tissue dustribution in the stem help the stem

it forms ‘scaffolding’ to resist bending

describe the distribution of the vascular tissues in the leaves

xylem and phloem form a network of veins

how does the structure of the vascular tissues help thin leaves

they provide support for thin leaves

briefly describe the pathway of water through a plant

1. water enters a plants root hair cells via osmosis

2. it moves through the cell cytoplasm or cell wall towards the xylem

3. the xylem transports water from the roots up to the leaves

4. water is used for photosynthesis

5. some water evaporates from leaf cells by transpiration and diffuses out of the plant

what are the two main pathways of water from the plant root to the xylem

apoplast and symplast

what happens in the apoplast pathway

• water moves through spaces in the cell walls and between cells

• once water meets the casparian strip, water if forced into the symplast pathway

what is the casparian strip made of that makes it waterproof

suberin

through what pathway does water mainly travel in from the xylem to leaf cells

apoplast pathway

what theory explains how water moves upwards through the xylem

the cohesion-tension theory

define cohesion

hydrogen bonding causes water molecules to stick together and move as one continuous column

define adhesion

hydrogen bonding between polar water molecules and non-polar cellulose in xylem vessel walls pulls water upwards through the xylem

define transpiration pull

evaporation of water at leaves creates the transpiration pull, and this tension is transmitted down the whole water column due to cohesion.

what factors cause the cohesion-tension theory

cohesion, tension, transpiration pull

what properties of water allow the apoplast pathway to take place

it occurs due to the cohesive and adhesive properties of water

what happens during the symplast pathway

water moves from cell to cell through the cytoplasm and plasmodesmata

in what pathway are water potential gradients used

symplast

what is the apoplast pathway blocked by

the casparian strip

where is the casparian strip located

the root endodermis/ endodermis cells

what evaporates from the moist surfaces of mesophyll cells

water

what leaf component opens so that it can absorb carbon dioxide for phosotynthesis

stomata

what is lost through the stomata when they open to absorb carbon dioxide

water vapour

what is transpiration a side effect of

gas exchange (watere vapour moving out of the stomata)

how does light intensity affect the transpiration rate

• at high light intensities, stomata open for maximum carbon dioxide absorption, increasing the amount of water vapour lost and increasig the transpiration rate

how does temperature affect the transpiration rate

• at high temperatures, evaporation of water molecules is faster due to higher kinetic energy, increasing the transpiration rate

how does humidity affect the transpiration rate

• low humidity increases the water vapour gradient between the leaf and the atmosphere, increasing the transpiration rate

how does wind speed affect the transpiration rate

• high wind speeds increase the water vapour gradient between the leaf and the atmosphere, increasing the transpiration rate

what instrument is useed to measure the rate of transpiration

potometer

when measuring rate of transpiration, why should you cut the plant shoot at a slant

to increase the surface area for water uptake

what is the equation for rate of transpiration

rate of transpiration= volume of water uptake/ time taken

list all the component names of a leaf

• waxy cuticle

• palisade mesophyll cell

• spongy mesophyll cell

• air spaces

• guard cell

• stoma/ stomata

• lower epidermis

• xylem and phloem

• upper epidermis

what part of the leaf reduces water loss from the lead surface

upper epidermis with waxy cuticle

what cells are located beneath the upper epidermis to carry out photosynthesis

palisade mesophyll cells

what cells are disperesed beneath the palisade mesophyll layer to carry out photosynthesis

spongy mesophyll cells

what are small pores surrounded by guard cells on the underside of leaves that can open and close

stomata

what is the name of the bottom layer of cells in a leaf that contains the stomata and guard cells

lower epidermis

how do air spaces help gas exchange in the leaf

they provide a network for gases to quickly diffuse in and out of the leaf and access photosynthesising cells

how do mesophyll cells help gas exchange in the leaf

they are disperesed throughout the leaf, which provides a large surface area across which gases can diffuse

how do stoma help gas exchange in the leaf

they open when conditions are suitable for photosynthesis, allowing inward diffusion of carbon dioxide and outward diffusion of oxygen, and close to minimise water loss

what are two ways that plants can limit water loss

• waterproof waxy cuticle

• guard cells can close stomata when needed

what are xerophytes and give examples of how they can redeuce water loss

xerophytes are plants adapted to living in dry environments with limited water availability

adaptations:

• thick waxy cuticle

• rolling or folding of leaves- encloses the stomata on the lower surface to reduce airflow and the evaporation of water

• hairs on leaves- these trap moist air against the leaf surface to reeduce the diffusion gradient of water vapour

• sunken stomata in pits- reduce airflow and evaporation of water

• small, needle-like leaves- reduce surface area across which water can be lost

• water storage organs- conserve water for when it is in low supply

what is the mass flow hypothesis

proposes that translocation occurs due to pressure gradients

what are the steps in the mass flow hypothesis

1. at the source, solutes like sucrose are actively loaded into sieve tube elements from companion cells

2. this decreases the water potential in sieve tube elements

3. water enters the sieve tube elements from the xylem and companion cells by osmosis

4. this increases hydrostatic pressure in the sieve tube elements at the source

5. at the sink, solutes are actively removed form the sieve tube elements

6. this increases the water potential in sieve tube elements at the sink

7. water leaves the phloem by osmosis, decreasing the hydrostatic pressure at the sink

8. this creates a pressure gradient, pushing solutes from the source to areas of lower pressure at the sink

what happens when solutes are actively unloaded at the sink

• solutes are actively unloaded from sieve tube elements into companion cells.

• they can then move into sink cells where solutes can be used, for example, in respiration, or stored.

how are assimilates actively loaded into the phloem

1. hydrogen ions are actively transported out of companion cells into surrounding source cells

2. hydrogen ions are co-transported along its concentration gradient back into companion cells with sucrose

3. sucrose can then diffuse along its concentration gradient through pasmodesmata from companion cells into sieve tube elements

what is translocation

the mass flow of assimilates from the source of the plant to the sink

what are assimilates

substances that have been manufactured or modified in the plant, such as sucrose and amino acids.

does translocation require energy

yes

what substance provides the medium for which substances are dissolved in during translocation

water