plant transport 🍃

Question 1

identify the xylem and the phloem in the cross-section of a stem/root

Answer 1

stem:
xylem is the inner layer while phloem is the outer layer!

root:
xylem is the star ⭐ while phloem is the parts that make the star a circle

Question 2

identify the xylem and phloem in the cross-section of a leaf

Answer 2

xylem is bigger, closer to the top of the leaf (palisade mesophyll)
phloem is smaller, closer to the bottom of the leaf (spongy mesophyll)

Question 3

structure of xylem

Answer 3

• consist of dead cells with their cross wall removed
• cell membrane and organelles break down, forming long, continuous and hollow tubes
• inner walls of vessels are strengthened by lignin deposits

Question 4

structural adaptations to function of xylem

Answer 4

1) empty lumen consisting of dead cells reduces resistance to the flow of water, to transport water and mineral salts
2) lignin deposits prevents the collapse of the vessel and allows it to provide mechanical support to the plant

Question 5

structure of phloem

Answer 5

• composed of sieve tubes made of sieve tube cells
• each sieve tube cell is separated by perforated walls called sieve plates
• reduced quantities of cytoplasm and no nucleus
• each sieve tube cell has a companion cell <3<3

Question 6

WHat is translocation and how is it carried out?

Answer 6

translocation is the transport of organic compounds (sucrose and amino acid) throughout the plant (bidirectional)
- sucrose is transported as it is not readily metabolised during transport
- phloem links sources to sinks

Question 7

structural adaptations of phloem

Answer 7

1) sieve tube cells need to be alive as translocation is an active process
2) sieve plates + reduced cytoplasm + no nucleus reduces resistance to flow of substances
3) companion cells perform many genetic and metabolic functions of sieve tube cells, keeping them alive
- companion cells contain many mitochondria to provide the energy for translocation + active transport to load organic compounds into phloem at roots

Question 8

structural adaptations of root hair cells

Answer 8

1) long narrow extensions to increase SA:VR, increase rate of osmosis of water and diffusion of mineral salts
2) cell sap has a lower water potential than the soil solution, ensuring water continuously enters root hair cell via osmosis
3) root hair cell contains mitochondria to provide energy for active transport of mineral salts into the cell

Question 9

how does water enter the plant via the roots?

Answer 9

1) cell sap of root hair cells are concentrated with sugars and mineral salts, lower water potential than soil solution. water enters the root hair cells via osmosis
2) this increases the water potential of the root hair cell, hence water moves from root hair cell to neighbouring cells via osmosis
3) water travels cell by cell via osmosis until it reaches the xylem

Question 10

what is transpiration?

Answer 10

transpiration is the loss of water vapour from the leaves through the stomata

Question 11

what are the processes through which water is transported from the roots to the leaves via xylem?

Answer 11

1) root pressure
2) capillary action
3) transpiration pull (main)

Question 12

how does root pressure work?

Answer 12

• respiring cells around the xylem vessels in the roots use active transport to pump mineral salts into the xylem, lowering the water potential in the xylem vessels
• water moves into the xylem vessels via osmosis

Question 13

how does capillary action work?

Answer 13

• cohesion is the forces of attraction between water molecules
• adhesion is the forces of attraction between water molecules and the inner walls of the tube
• water can hence be pulled up in a continuous stream

Question 14

how does transpiration pull work? ****************

Answer 14

1) water continuously moves out of mesophyll cells by osmosis to form the thin film of moisture
2) water evaporates from the thin film of moisture surrounding the mesophyll cells into the intercellular air space
3) water vapour diffuses out of the leaf via the stomata by transpiration
4) water leaves the mesophyll cells to replenish the thin film of moisture, decreasing the water potential of these cells
5) water moves from neighbouring cells into these cells via osmosis
6) the neighbouring cells draw water from cells deeper inside the leaf. these cells then draw water from the xylem, resulting in transpiration pull !

Question 15

what is the importance of transpiration?

Answer 15

1) creates transpiration pull
2) removes latent heat which helps cool the plant, preventing it from being scorched

Question 16

factors affecting rate of transpiration

Answer 16

1) humidity
2) wind speed
3) temperature of surrounding air
4) light intensity

Question 17

how does humidity and wind speed affect the rate of transpiration?

Answer 17

they affect the concentration gradient of water vapour outside the leaf, affecting rate of diffusion out of leaf and hence rate of transpiration

Question 18

how does temperature affect the rate of transpiration?

Answer 18

higher temperature increases the rate of evaporation, increasing concentration of water vapour in intercellular air spaces, INCREASING (omg JAIMIE THIS WAS DECREASING) water vapour concentration gradient, increasing rate of diffusion and transpiration.
however at very high temperatures, stomata close to prevent excessive transpiration

Question 19

how does light intensity affect the rate of transpiration?

Answer 19

higher light intensity causes stomata to open and become wider, increasing the rate of transpiration (not evaporation u stupid idot jerald)

Question 20

advantage and disadvantage of wilting

Answer 20

advantage: leaves fold up, reducing surface area exposed to sunlight, causing guard cells to become flaccid and stomata to close, reducing rate of transpiration
disadvantage: leaves droop and less surface area exposed to the sun, hence rate of photosynthesis decreases

Question 21

i am not doing the experiments! go check it out theres nothing

Answer 21

people make me cry. but you dont