transportation in vascular plants

Question 1

why do vascular plants have specialised its of organisation?

Answer 1

Plants are too large to obtain and remove substances by diffusion.

Question 2

what make up vascular bundles?

Answer 2

Xylem vessels: water and nutrients to leaf from roots
Phloem vessels: sugars from photosynthesis in leaves to roots
A sheath of lignin strengthens and supports the tissue

Question 3

what are examples of vascular plants? what are they characterised by? what two main organs make up vascular plants?

Answer 3

ferns, cycads, conifers and flowering plants that usually grow in terrestrial environments.
vascular tissue which transports fluids. They have two main organs: roots and leaves and vascular tissues are in both of these regions.

Question 4

why is transportation needed?

Answer 4

Photosynthesis produces sugars in the leaves but it is needed all over the plant and for photosynthesis to occur, water absorbed by the roots needs to be in the leaves for photosynthesis so transportation is needed.
Vascular tissue transports mineral ions from the roots throughout the plant and sugars made in the leaves to the rest of the plant.

Question 5

what is xylem?

Answer 5

transports water and inorganic nutrients (mineral ions) absorbed from the soil up the plant.

Question 6

what is phloem?

Answer 6

transports dissolved sugars which are produced in the leaves by photosynthesis throughout the plant. Other organic substances such an amino acids are transported too.

Question 7

what are the xylem and phloem like in roots?

Answer 7

the central core is a star of cross shaped tube of xylem and the phloem are between the arms of the xylem.

Question 8

what are the xylem and phloem like in stems and leaves?

Answer 8

they are grouped into vascular bundles.

Question 9

what is xylem composed of?

Answer 9

xylem vessels and tracheids.

Question 10

what do mature xylem vessels have?

Answer 10

Cylindrical skeletons of dead cells, joined making tubes
Perforated or complete openings at the ends to form tubes
Pits (un-thickened areas) and perforations in the sidewalls that allows sideways movement of substances between neighbouring vascular vessels
No nucleus or cytoplasm

Question 11

how do xylem mature and what are they strengthen by?

Answer 11

Cytoplasm and nucleus disintegrate. Strengthened with lignin

Question 12

what are tracheids?

Answer 12

Single, large, tapering, water-filled cells that form part of the xylem tissue. Unlike xylem they are not connected end to end.
Their ends overlap and water is transferred horizontally through adjoining pits.

Question 13

what do mature tracheids have?

Answer 13

cylindrical skeletons of dead cells joined to form continuous tubes like xylem vessels
Pits and perforations in their lignified cell walls
No nucleus or cytoplasm

Question 14

What are phloem composed of? what are they like when mature? what is their structure like?

Answer 14

Composed of sieve tubes, companion cells, parenchyma cells and sclerenchyma cells.
When mature sieve tubes are living but have no nucleus and no lignin in their cell walls.
Sieve tubes form linear rows of elongated cells.
Perforated at the ends to form sieve plates, allowing fluid through.
Stands of cytoplasm (plasmodesmata) pass through, connecting cells.
Sieve tubes are closely associated with company cells, connected by plasmodesmata.
Both sieve tubes and companion cells have thin cell walls.
Companion cells have a nucleus which enables the sieve tubes to keep functioning.

Question 15

what are the three distinct layers of leaves?

Answer 15

upper epidermis
Mesophyll
Lower epidermis

Question 16

what is the epidermis layer? what do they secrete? what is their structure like?

Answer 16

the layer of cells covering the leaf.
The secrete waterproof waylayers called a cuticle.
Together these provide a barrier and protect the leaf from excessive water loss.
Epidermal cells lack chloroplasts but are transparent, allowing sunlight through to cells below.

Question 17

what are within the lower epidermis? what do these structures do?

Answer 17

Within the lower epidermis are stomata (stoma singular) which consist of specialised epidermal cells called guard cells.
Guard cells create an opening through the cuticle and epidermis and regulate water loss and gas exchange

Question 18

where are the mesophyll cells? what do they contain?

Answer 18

Between the epidermal cells are the mesophyll cells where photosynthesis occurs.

Question 19

what are the cells closest to the upper epidermis and what are they like?

Answer 19

The cells closest to the upper epidemic are the palisade mesophyll cells which have many chloroplasts and are tightly packed together.

Question 20

what are spongy mesophyll? where are they? what do they do?

Answer 20

Spongy mesophyll cells are below these cells and are loosely packed together, with air spaces between them that allow gas exchange. They have fewer chloroplasts.

Question 21

where is the vascular tissue located?

Answer 21

The vascular tissue is located between the layers of epidermal cells and is often visible as veins.

Question 22

what do roots do? what is a feature that helps this?

Answer 22

Roots take up water (for photosynthesis and nutrient transfer and transpiration), mineral ions such as nitrogen, phosphorus and potassium (needed to manufacture organic compounds).
Roots are branched to increase surface to volume ratio.

Question 23

what are the two ways that water is absorbed by the roots?

Answer 23

Extracellular pathway: most water and some mineral ions pass in or between cell walls.
Cytoplasmic pathway: most mineral ions and some water pass through the cytoplasm of the living root. This involves the substances entering through the plasma membrane and then passing from cell to cell through plasmodesmata.

Question 24

what are the three ways that substances get into the cells for cytoplasmic pathway?

Answer 24

active transport: dissolved mineral ions are selectively taken in. Proteins in the membrane are used for this. Concentration is higher in the cell.
Osmosis: large amounts of ions in the cells causes water to move in.
Diffusion: some mineral ions such as potassium and phosphate enter the roots by diffusion. The uptake depends on the rate of water uptake.

Question 25

how does water enter the xylem?

Answer 25

Water must them reach the xylem tissue.
Between the roots and the xylem is a waterproof layer of cells called the Casparian strip.
At this barrier, water travelling through the extracellular pathways is forced into the cytoplasm.
In this way, Casparian strips ensure the regulation of the substances entering the xylem.

Question 26

what is transpiration? how much water is lost this way?

Answer 26

Transpiration is the passive movement of water through a plant from the roots, including its evaporation through the stomatal pores in the leaves. 99%

Question 27

how does transpiration occur?

Answer 27

Sunlight breaks cohesive bonds between water molecules, allowing evaporation.
Water molecules are very cohesive. They have a strong tendency to stick together. When water evaporates, cohesion between the water molecules remaining in the leaf draws water from nearby xylem to replace lost water.
In this way thousands of leaf cells drawing water from xylem create a differential pressure that pulls water up xylem vessel from roots.

Question 28

what is the transpiration stream?

Answer 28

flow from roots to leaves is called the transpiration stream.

Question 29

what does transpiration allow?

Answer 29

plants to absorb the water necessary for photosynthesis, transport mineral salts to leaf cells and fruits and cool down and not become overheated.

Question 30

What factors affect transpiration rate?

Answer 30

How open the stomata is.
Humidity- rate decreases because there is a lot of water vapour in the air because this reduces the water concentration gradient.
Temperature- rate increases a temperature increases because heat speeds up vaporisation.
Wind- air currents increase the rate of transpiration by moving water vapour away from the leaf and therefore removing humidity.

Question 31

what is translocation? why does this happen? where are the transported?

Answer 31

The transport of organic solutes from the leaves to other tissues in the plant is known as translocation Leaves produce carbohydrates in the form of sugars during photosynthesis but non-photosynthetic areas also need them and other organic molecules. These nutrients are transported from sources to sinks (where they are needed).

Question 32

what allows for translocation? what is transported? what is it? where is it produced? where does it travel?

Answer 32

These solutes move through phloem and the material that flows through is called phloem sap which is 90% sucrose.
Sucrose is a disaccharide that is easily dissolved in water.
It is produced in chlorenchyma cells (parenchyma with chloroplasts) and pumped into companion cells.
It then flows into the sieve tubes. Only one way in one tube but both in a bundle of tubes.

Question 33

is translocation active r passive?

Answer 33

Translocation is an active process that involves the flow of cytoplasm in sieve tubes driven by a pressure gradient.

Question 34

how does the pressure gradient occur for translocation? when does translocation stop?

Answer 34

The pressure gradient begins in the leaves, where sucrose is actively pumped into phloem Sieve tubes. This makes an osmotic gradient that draws water passively into the sieve cells.
As water enters, turgor pressure is made in the sieve cells which pushes fluid from these cells into adjacent sieve cells.
While this happens in the leaves, sucrose is being actively removed from sieve cells in roots, growing shoots and developing fruit. This causes an osmotic gradient that draws water out of sieve cells and lowers their burger pressure.
Fluid pressure is therefore high in sieve tube cells in leaves and low in sieve tube cells in roots and growing shoots.
A bulk flow of the contents of the sieve tubes occurs along this fluid pressure gradient, from sources to sinks.
Translocation stops if the cells in the stream die.