biology 3.3

Question 1

Why do Plants need water?

Answer 1

-Photosynthesis
-Structure and support-turgidity
-Transport dissolved nutrients
-Cooling

Question 2

Why do plants need transport systems?

Answer 2

-Plants grow throughout their lives so need effective tranport systems to transport nutrients
-Surface area to volume ratio
-Non green plants can’t photosynthesis so need glucose and oxygen transported to them

Question 3

What is transpiration and translocation?

Answer 3

-Transpiration is where water and mineral ions are transported in the xylem upwards, the process is passive
-Translocation is where sugar and amino acids are transported in the phloem bidirectionally and the process is active

Question 4

What is found in the vascular bundles?

Answer 4

Xylem, Phloem, Sclerenchyma, Collenchyma, and Parenchyma

Question 5

What are the functions of Sclerenchyma, Parenchyma and Collenchyma?

Answer 5

-Sclerenchyma provide support and structure
-Collenchyma are involved in growth and strength
-Parenchyma is a soft packing tissue

Question 6

What are the adaptations of the xylem vessels?

Answer 6

-Cell walls decay and don’t contain cytoplasm or organelles
-The end plates break down leaving a long hollow tube
-Cell walls are thicker than usual to withstand pressure of water
-Cell walls are lignified which makes the cells waterproof, strong and keeps the vessel open but kills the cells

Question 7

What are bordered pits?

Answer 7

-Non-lignified regions of the xylem vessel that allow water and mineral ions to move laterally between xylem vessels

Question 8

What are the adaptations of the phloem vessel? and why do they need companion cells?

Answer 8

-Elongated, no nucleus, very little cytoplasm
-The end walls form perforated plates
-Sieve tube elements can’t keep themselves alive so need companion cells to carry out their metabolic function

Question 9

What are the adaptations of companion cells?

Answer 9

-Large nucleus
-Dense cytoplasm
-Many mittochondria for ATP for active transport
-Infoldings on the cell surface membrane to increase surface area for active transport

Question 10

What are Cotyledons, Monocots and Dicots?

Answer 10

-Cotyledons= organs that act as food stores for a developing embryo plant
-Monocots= plants that make seeds containing one cotyledon
-Dicots= plants that make seeds containing two cotyledons

Question 11

What are the roles of water in plants?

Answer 11

-Photosynthesis
-Structure and support: vacuole presses cytoplasm against cell wall
-Transport of dissolved nutrients
-Cooling

Question 12

What are the adaptations of a root hair cell?

Answer 12

-Microscopic size: penetrate soil particles easily
-Large SA:V
-Thin surface layer: diffusion, osmosis and active transport can take place quickly
-High concentration of solutes to maintain a steep water concentration gradient

Question 13

What are the three ways water can move from the root hair to the xylem?

Answer 13

1.Apoplast pathway
2. Symplast pathway
3. Vacuolar pathway

Question 14

Describe the apoplast pathway?

Answer 14

-The continuous flow of water through the open structure of the cytoplasm due to the pull of water into the xylem and cohesive forces

Question 15

Describe the symplast pathway?

Answer 15

-Movement of water into the xylem through the continuous cytoplasm connected by plasmodesmata
-Water moves into root hair cell making it have a higher water potential than its neighbour cell so water moves in via osmosis all the way to the xylem.
-Water leaves the cell so there is a steep water potential again and water moves in from the soil.

Question 16

Describe the vacuolar Pathway?

Answer 16

-Same as the symplast pathway except water isn’t confined to cytoplasm and can travel through vacuoles
-Slower than Symplast pathway

Question 17

What is the Endodermis and Casparian strip and the importance of the Casparian strip?

Answer 17

-Endodermis: layer of cells surrounding the vascular tissue (xylem and phloem)
-Casparian strip= waterproof layer that runs around endodermal cells
-Its important because it forces water into the symplast pathway and therefore ensures it passes through a selectively permeable membrane

Question 18

What is root pressure and guttation?

Answer 18

-Root pressure= as water moves into medulla pressure builds up forcing water into xylem pushing water up xylem
-Guttation= loss of water from leaves when root pressure is high

Question 19

What is transpiration and a transpiration stream?

Answer 19

-Transpiration= loss of water from plants by evaporation
-Transpiration stream= constant movement of water from roots to the leaves. Driven by evaporation of leaves and capillary action

Question 20

Why do guard cells swell lengthways and not in width?

Answer 20

Cellulose hoops stop them from swelling in width

Question 21

What is capillary action and mass flow?

Answer 21

-Capillary action= process by which water can rise up a tube against gravity due to polarity of water and hydrogen bonds
-Mass flow= movement of fluids down a concentration gradient

Question 22

What would happen if there were breaks and bubbles in the xylem and how has it adapted to get around this?

Answer 22

-Any breaks or bubbles would break the cohesion between the water molecules preventing upwards motion
-Bordered pits allow water to move laterally and bypass bubbles and breaks

Question 23

What is evidence for Cohesion tension theory?

Answer 23

1. Cut flowers don’t leak water
2. Brocken xylems- they stop drawing water up as cohesion between water is stopped
3. Changes in tree diameter- at day during high transpiration rates diameter decreases due to tension

Question 24

What is the importance of transpiration?

Answer 24

-Tugor pressure= provide hydrostatic skeleton to support leaves
-Cell expansion= tugor drives cell expansion of roots
-Cooling
-Transportation of minerals and assimilates= transported in aqueous solution
-Photosynthesis

Question 25

How do plants control water loss?

Answer 25

-Waxy cuticle prevents water loss on top of leaf
-Wilting (leaves collapse exposing a smaller s/a for evaporation)
-Stomata on bottom of leaf
-Stomata close at night
-Lose leaves in winter- grounds frozen and temperature is too low for photosnythesis

Question 26

What are factors affecting transpiration?

Answer 26

-Light intensity, humidity, temperature, air movement, soil-water availability

Question 27

Describe phloem loading (Symplast route)?

Answer 27

-Assimilates diffuse through cytoplasm of mesophyll cells into sieve tubes
-Passive process
-Controlled by water potential

Question 28

Describe phloem loading (Apoplast route)?

Answer 28

-Active process controlled by H+ ions
-H+ ions are actively pumped out of companion cells and diffuse back in with assimilates through cotransporter protein, this increase of concentration in companion cells cause assimilates to diffuse into sieve tube elements through plasmodesmata

Question 29

Describe the mass flow hypothesis of translocation?

Answer 29

1. Assimilates are loaded into sieve tube elements at leaves causing an increase in hydrostatic pressure
   2.This pushes them down the concentration gradient and sieve tube elements
   3.Assimilates unload at a sink resulting in a decrease in hydrostatic pressure