Plants - Textbook

Question 1

Why do plants need a transport system?

Answer 1

Larger plants have a small SA:V = need specialised exchange surfaces and transport system
Plants are not very active , respiration rate is low therefore demand for oxygen is low and can be met by diffusion
Demand for water and sugars is high plants absorb minerals from roots can’t absorb sugars from soil The leaves can perform gaseous exchange and manufacture sugars by photosynthesis cannot absorb water from the air
Therefore plants need a transport system to move:
- water and minerals from roots up to leaves
- sugars from the leaves to rest of plant

Question 2

The vascular tissues

Answer 2

Transport system in plants consists of specialised vascular tissues:
- water and soluble mineral ions travel up in xylem tissue
- assimilates (molecules formed as a result of photosynthesis) such as sugars travel up and down in the phloem tissue
- both X and P are highly specialised for transport functions
Distribution of vascular tissue:
Dicotyledonous plants have two seed leaves, vascular tissue distributed throughout the plant. X + P are found together in vascular bundles may contain other tissues e.g. collenchyma and sclerenchyma give bundle strength and help support plant

Question 3

Xylem and phloem in the young root

Answer 3

Vascular bundle found at centre, central core of xylem (often) in shape of X phloem found in between arms of X shaped xylem = arrangement provides strength to withstand the pulling forces to which roots are exposed
Around vascular bundle is endodermis key role of getting water in xylem vessels
Just inside endodermis is layer of meristem cells called pericycle

Question 4

Xylem and phloem in the stem

Answer 4

Vascular bundles found near outer edge
Non woody plants bundles are separate and discrete
Woody plants bundles are separate in young stems but continuous ring in older = complete ring of vascular tissue just under the bark of a tree = arrangement provides strength and flexibility to withstands the bending forces to which stems and branches are exposed
Xylem found towards inside of each vascular bundle phloem towards outside in between X + P is layer of cambium layer of meristem that divide to produce new X + P

Question 5

Xylem and phloem in the leaf

Answer 5

A dicotyledonous leaf has a branching network of veins get smaller away from the midrib within each vein xylem is located at top of phloem

Question 6

Structure and function of xylem

Answer 6

Transport water and dissolved mineral ions from the roots to the leaves
- vessels carry water and dissolved mineral ions
- contain Flores that help support the plant
- contains parenchyma (living) cells which act as packing tissue separates and supports the vessels

Question 7

Xylem vessels

Answer 7

• Lignin impregnated in the walls = waterproof, this kills cells the end wall and contents decay leaving long column of dead cells with no contents - tube called xylem vessel lignin strengthens walls prevents collapse lignin thickening forms patterns in cell wall (spiral rings or reticulate (brokenrings)) prevents vessel from being rigid allows flexibility of stem/branch
• lignification= not complete = gaps in cell was = boarded pits → are aligned to allow water to leave one vessel and pass to other allow water to leave xylem and pass to living Parts of plant.

Question 8

Adaptations of xylem to its function

Answer 8

Carry H2O + mineral ions from roots to top of the plant because:
- made from dead cells aligned end to end to form a continuous column (cambium cells)
- tubes = narrow water column doesn’t break easily+ capillary action can be effective
- bordered pits in signified walls allow water to more sideways one vessel from to another
- lignin deposited in the walls in spirals + rings allow X to stretch as plant grows Charles stem/branch to bend

Question 9

Structure and function of phloem

Answer 9

-transport assimilates (sucrose and amino acids) around the plant
- sucrose in dissolved water = sap
- (sieve tubes) made up of sieve tube elements and companion cells

Companion cells:
- small cells with dense cytoplasm and (large) nucleus, (have numerous mitochondria) produces ATP for metabolic activity(processes) (needed to load assimilates actively in the sieve tubes)

Question 10

Sieve tube elements

Answer 10

Sieve tube elements:
- tubes (lined end to end) with very little cytoplasm and no nucleus, (leaving space for) mass flow of sap end of these tubes are perforated sieve plates perforations help cell sap move from one element to another (the sieve tubes have very thin walls transverse section =5 or 6 sided)

Question 11

Companion cells

Answer 11

Companion cells:
- small cells with dense cytoplasm and (large) nucleus, (have numerous mitochondria) produces ATP for metabolic activity(processes) (needed to load assimilates actively in the sieve tubes)

Question 12

Pathways taken by water

Answer 12

• Cellulose cell wall is fully permeable to water, (mang plant cells are joined) by cytoplasmic bridges the cytoplasm of one cell is connected to another through holes (gaps) in the cell wall called plasmodesmata therefore there is 3 pathways water can take

Question 13

Apoplast pathway

Answer 13

Water passes through the spaces In the cell walls and between the cell, does not go through plasma membranes into the cell therefore water moves by mass flow rather than osmosis I dissolved mineral ions and salts can be carried with water

Question 14

Symplast pathway

Answer 14

Water enters the cell cytoplasm through the plasmamemorane, can then pass through the plasmodesmata from one cell to the next.

Question 15

Vacuolar pathway

Answer 15

Similar to simplest, water is not confined to the cytoplasm of the cells able t0 enter and pass through the vacuoles as well

Question 16

Movement from cell to cell - water potential

Answer 16

• measure of the tendency of water molecules to move from one place to another
• water always moves from a region of high w. p. (Less negative) To a region of low w.p. (More negative), pure water = w. p. 0
• plants cytoplasm contains mineral ions and sugars which lowers w.p. As fewer free water molecules = w.p. Of plants is-ve

Question 17

Water uptake

Answer 17

Place plant cell in water, water moves in by osmosis as plant has more -ve w.p. Than water
- water molecules more down a water potential gradient into the cell
- will not continue to absorb water until it bursts. = cellulose cell walls are strong
- once cell is full = turgid
- water exerts pressure onto cell wall = pressure potential

Question 18

Water loss

Answer 18

• Place cell in salt solution with more -ve w. p. Water moves out by osmosis, moves down w.p. Gradient and out of the cell, cytoplasm and vacuole shrink, cytoplasm loses contact with cell wall = plasmolysis, cell is flaccid

Question 19

Movement of water between cells

Answer 19

Cells next to each other = water can move between them, moves from less negative (higher) w.p. To more negative (lower) w.p.

Question 20

Transpiration

Answer 20

Loss of water vapour from top of the plant particularly leaves top of leaf is restricted due to waxy cuticle mainly leaves through open stomata → gas exchange for photosynthesis
1. Water enters the leaf through the xylem, moves by osmosis into the cells of spongy measophyll .it may pass along the cell walls via apoplast pathway
2. Water is evaporated of the cell wall of spongy measophyll
3. Water vapour moves out of leaf by diffusion through open stomata, relies on difference in the concentration of water vapour molecules in the leaf compared with outside = water vapour potential gradient (must be less - ve (higher) w.p. Inside than out or leaf)

Question 21

Importance of transpiration

Answer 21

• Plants survival
• supplies usefull nutrients up the plant
• supplies water for growth, cell elongation and photosynthesis
• supplies water that evaporates to keep cool when hot

Question 22

Environmental factors- transpiration

Answer 22

Light intensity: in the light stomata open allow gaseous exchange for photosynthesis higher light intensity increases transpiration rate
Temperature:
- increases rate of evaporation = water vapour potential in the leaf ↑
- increases rate of diffusion through stomata as water molecules have more kinetic energy
- decreases relative water vapour potential of the air = allows more rapid diffusion of molecules out of the leaf
Relative humidity:
- higher relative humidity reduces rate of water loss as smaller water vapour potential gradient between the airspace’s of leaf than air outside
Air movement:
- air moving outside of leat will carry away water vapour that has Just been diffused out of leat = maintains high water vapour potential gradient
Water availability: plant can’t replace lost water, insufficient = stomata close and leaves wilt

Question 23

Investigation - rate of transpiration

Question 24

Transpiration stream - water uptake + movement across the root

Answer 24

• Outermost layer (epidermis) of root contains root hair cells = Î S.A., absorbs water + mineral ions from the soil the water moves across the root cortex down a concentration gradient to the vascular bundle water may travel through the apoplast pathway then symplast apoplast is blocked by casparian strip

Question 25

Role of endodermis

Answer 25

• Movement of water across the root is driven by an active process that occurs at endodermis, layer or cells surrounding xylem and medulla also called starch sheath = contains starch granules
• casparian strip blocks the apoplast pathway between xylem and medulla
• this ensures the water and mineral ions move into the cytoplasm through the plasma membrane
• plasma membrane contains transport proteins which actively pump mineral ions into cytoplasm of cortex which moves into the medulla and xylem
• this means water potential of m + x more negative = water moves in by osmosis,
  -water entered medulla = can’t pass back into cortex as casparian strip blocks A pathway

Question 26

Movement of water up the stem

Answer 26

Moves up xylem by mass flow- flow of water and mineral ions in the same direction

Question 27

Root pressure - process that helps move water up stem

Answer 27

• Water produces pressure on the roots, pressure in root medulla builds up pushing water up xylem, helps water move up a few metres not accountable for top of tallest trees

Question 28

Transpiration pull - process that helps move water up stem

Answer 28

Water molecules attracted to other by cohesive forces = strong enough that water moves in column/chain, when water is lost at top of collumn = pulled up as one chain = creates tension on xylem = why lignin is important for strength
- cohesion + tension = cohesion tension theory = xylem maintains unbroken collumn of water = if broken can be maintained In another vessel through bordered pits

Question 29

Capillary action - process that helps move water up stem

Question 30

Now water leaves the leaf

Question 31

Adaptation of plants to the availability of water - terrestrial plants

Question 32

Marram grass

Question 33

Cacti

Question 34

Xerophytic features

Question 35

Hydrophytes

Question 36

Translocation

Question 37

Translocation- active loading

Question 38

Translocation - movement of sucrose

Question 39

Translocation - the source

Question 40

Translocation - the sink

Question 41

Translocation - along the phloem