transport in flowering plants Flashcards
what are the two major components a plant has?
the root system and the shoot system
what does the root system do?
the root system primarily functions to anchor the plant firmly to the ground, absorb water and mineral salts, and serve as a carbohydrate reserve.
what does the shoot system do?
the shoot system is designed to maximise light capture for photosynthesis, optimise growth, and facilitate the transport of materials through the plant.
what do vascular plants do in order to survive?
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.
what do non-vascular plants do in order to survive?
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.
what does the vascular bundle do?
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.
what is the function of the xylem?
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
what is the function of the phloem?
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
explain the vascular bundle when in the leaf
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
explain the vascular bundle when in the stem
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
explain the vascular bundle in the root
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
in the root hair cell, what is the function of the elongated protrusion?
increases surface area to volume ratio of the cell
-greater rate of absorption via osmosis, diffusion, and active transport
in the root hair cell, what is the function of the concentrated cell sap?
decreases water potential of the cell
-greater rate of osmosis
in the root hair cell, what is the function of the numerous mitochondria?
greater rate of respiration to release more energy
-to absorb mineral salts via active transport, if needed
explain transpiration
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
what are the benefits of transpiration?
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
what are the disadvantages of transpiration?
1) water is lost from the plant
what happens when the amount of water lost in a plant is more than the root can absorb?
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
explain transpiration pull
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
explain the transpiration process
-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
how to use a bubble potometer to measure the rate of transpiration?
(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
how to measure the rate of transpiration using the mass potometer?
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
what is the effect of humidity?
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
what is the effect of wind or wind speed?
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.
