transport in flowering plants

Question 1

what are the two major components a plant has?

Answer 1

the root system and the shoot system

Question 2

what does the root system do?

Answer 2

the root system primarily functions to anchor the plant firmly to the ground, absorb water and mineral salts, and serve as a carbohydrate reserve.

Question 3

what does the shoot system do?

Answer 3

the shoot system is designed to maximise light capture for photosynthesis, optimise growth, and facilitate the transport of materials through the plant.

Question 4

what do vascular plants do in order to survive?

Answer 4

vascular plants rely on both systems to survive the many cells that make up the large, multicellular organism are not always in contact with the nutrients they require. their relatively large size also makes it inefficient for the entire plant to directly absorb the nutrients they require due to their small surface area to volume ratio.

Question 5

what do non-vascular plants do in order to survive?

Answer 5

non-vascular plants like mosses are small enough and mostly in direct contact with the nutrients they require, allowing them to survive without a dedicated transport system.

Question 6

what does the vascular bundle do?

Answer 6

the xylem (water-carrying tubes) and phloem (food-carrying tubes) are highly specialised tissues adapted for transporting substances throughout the plant as efficiently as possible. together, the xylem and phloem are found in the vascular bundle that extend to all parts of the plant.

Question 7

what is the function of the xylem?

Answer 7

xylem transports water and dissolved mineral salts from the roots to all parts of the plant
-fully mature cells are dead- no organelles, no cytoplasm, no cross walls
-walls are reinforced with lignin to prevent vessel collapse as water flows through
-provides additional structural support to the stems and branches of non-woody plants

Question 8

what is the function of the phloem?

Answer 8

phloem transports sucrose and amino acids from the photosynthetic organs to all parts of the plant
-sucrose and amino acids are dissolved in a thin layer of cytoplasm to be transported
-cytoplasm flows within the sieve tubes elements-degenerate cells
-companion cells provide metabolic support for the sieve tube elements to function

Question 9

explain the vascular bundle when in the leaf

Answer 9

the vascular bundle is nestled within the spongy mesophyll layer, with the xylem closer to the upper epidermis and the phloem closer to the lower epidermis

Question 10

explain the vascular bundle when in the stem

Answer 10

the vascular bundles are arranged in a ring within the cortex of the stem, with the xylem closer to the pith (innermost section) and the phloem closer to the epidermis

Question 11

explain the vascular bundle in the root

Answer 11

the vascular bundle takes on a unique arrangement and structure in the roots. the xylem is spread out to form a star or cross shaped arranged in the middle of the root, and the phloem are found littered around the xylem

Question 12

in the root hair cell, what is the function of the elongated protrusion?

Answer 12

increases surface area to volume ratio of the cell
-greater rate of absorption via osmosis, diffusion, and active transport

Question 13

in the root hair cell, what is the function of the concentrated cell sap?

Answer 13

decreases water potential of the cell
-greater rate of osmosis

Question 14

in the root hair cell, what is the function of the numerous mitochondria?

Answer 14

greater rate of respiration to release more energy
-to absorb mineral salts via active transport, if needed

Question 15

explain transpiration

Answer 15

in the daytime when most of the stomata of a plant are fully open to allow for gaseous exchange to occur, water vapour is constantly lost. water evaporates from the thin film of moisture into water vapour in the intercellular air spaces, before diffusing through the stomata into the surrounding air.
basically, the loss of water vapour from the stomata

Question 16

what are the benefits of transpiration?

Answer 16

1) prevents the plant from overheating
-water gains heat from the plant to evaporate, cooling the plant down
2) maintains the turgidity of plant cells and rigidity in non-woody plants
-ensures that all cells have sufficient water to remain turgid
3) creates an upwards force to transport water from the roots to all parts of the plant
-this force is known as transpiration pull

Question 17

what are the disadvantages of transpiration?

Answer 17

1) water is lost from the plant

Question 18

what happens when the amount of water lost in a plant is more than the root can absorb?

Answer 18

the leaves droop down and curl up
-reduces surface area exposed to the hot environment to reduce the rate of evaporation
the stomata closes
-reduces the rate of diffusion of water vapour out of the leaf
the plant wilts
-plants wilt to prevent themselves from losing too much water via transpiration but doing so also decreases its rate of photosynthesis. the drooping and curling of leaves have a smaller surface area, reducing the amount of light energy they can trap. less co2 is also absorbed by the leaves now that most the stomata are closed

Question 19

explain transpiration pull

Answer 19

with water being constantly lost in the form of water vapour diffusing through the stomata, the cells in the leaf draw water from the xylem to replace the water that was lost. this creates a suction force that pulls the water column (transpiration stream) in the xylem upwards, allowing the transpiration stream to rise to heights of more than 120m in the tallest trees

Question 20

explain the transpiration process

Answer 20

-water molecules are also pushed into the root xylem, creating more pressure for the upwards movement of the transpiration stream
-water molecules travel through the xylem in a continuous stream, pulled upwards by a suction force
-water vapour diffuses through the stomata and out of the leaf
-to replace the water lost, leaf cells absorb water from the xylem

Question 21

how to use a bubble potometer to measure the rate of transpiration?

Answer 21

(measuring the volume of water absorbed by a plant per unit time)
-in a carefully calibrated capillary tube, the distance travelled by the air bubble is equal to the volume of water absorbed by the shoot
-the reservoir allows water to enter the capillary tube after each experiment to reset the air bubble
-the cut shoot is attached via a rubber or cork stopper to prevent water in the set-up from evaporating directly
the farther the air bubble moves per unit time, the greater the rate of transpiration of the cut shoot

Question 22

how to measure the rate of transpiration using the mass potometer?

Answer 22

if placed in a closed system with no additional water source, the overall mass of a plant will decrease as it loses water vapour, which has mass, via transpiration. the rate of transpiration of a plant can be estimated by measuring the decrease in mass of the plant per unit time
the larger the decrease in mass per unit time, the greater the rate of transpiration of the plant

Question 23

what is the effect of humidity?

Answer 23

the speed of movement of water vapour from the intercellular air spaces of a leaf to the surrounding air occurs via diffusion, which depends on how steep the concentration gradient is between the two regions
(low humidity) when a plant is placed in a low humidity area, the concentration of water vapour in the leaf is much higher than that of the surrounding air, allowing water vapour to diffuse out of the leaf very quickly down a steep concentration gradient, resulting in a high rate of transpiration
(high humidity) when a plant is placed is a very humid area, the concentration of water vapour in the leaf is not much higher than that of the surrounding air, causing water vapour to diffuse out of the leaf very slowly down a gentle concentration gradient, resulting in a low rate of transpiration

Question 24

what is the effect of wind or wind speed?

Answer 24

when a breeze arrives or the wind starts moving faster, air surrounding the leaf gets blown away. any water vapour that had just exited the leaf will be moved away, resulting in a steeper concentration gradient of water between the air in the leaf and the surrounding air. the rate of transpiration is lowest in still air, which increases in the presence of wind. as the wind speed increases, the rate of transpiration also increases.

Question 25

what is the effect of temperature?

Answer 25

since transpiration is the loss of water vapour from the leaves of a plant through the stomata, and the formation of water vapour in the intercellular air spaces of the leaf is due to evaporation, factors that affect evaporation will also affect transpiration.
the higher the surrounding temperature, the greater the rate of evaporation of water from the thin film of moisture surrounding the spongy mesophyll cells. the concentration of water vapour in the intercellular air spaces will be so much higher than the surrounding air, creating a steep concentration gradient for water vapour to diffuse out of the leaf, which results in a high rate of transpiration. at lower temperatures, the decreased rate of evaporation results in a gentler concentration gradient of water vapour between the two regions . water vapour diffuses out of the leaf more slowly, resulting in a lower rate of transpiration.

Question 26

what is the effect of light intensity?

Answer 26

the wider the stomatal opening, the more easily water vapour can diffuse out of the leaf. guard cells control the diameter of the stomata based on the water potentials of the guard cells and the adjacent cells. when exposed to light, guard cells photosynthesise to produce glucose, increasing the concentration of the cell sap. this decreases the water potential of the guard cells until it is lower than that of the adjacent cells, causing water to enter the guard cells down the water potential gradient via osmosis. the entry of excess water cause the guard cells to swell and become turgid. guard cells have an uneven distribution of cellulose in the cell walls, with the inner cell wall being thicker and more rigid than the outer cell wall. the inner cell wall thus swells less than the outer cell wall, and the swollen guard cell curves to create an opening, the stoma. hence, at higher light intensities, more stomata are open (or open wider) and more water vapour can diffuse out of the leaf, resulting in a greater rate of transpiration.

Question 27

explain translocation

Answer 27

translocation is independent of gravity and transports phloem sap containing sucrose and amino acids throughout the plant in any direction from source cells to sink cells

Question 28

what are sink cells?

Answer 28

storage organs like the roots, stem and fruits