Transport in plants Flashcards
Define Translocation [3]
Transport of sucrose and amino acids from the leaf to the other parts of the plant
via active transport in the phloem.
Describe the adaptations of the phloem vessel in translocation of nutrients [4]
Sieve tube cell / element:
Little protoplasm to minimise obstruction to flow [1]
Sieve tube plate with pores to facilitate efficient transport of sucrose and amino acids along the sieve tube element [1]
Companion cells
Abundant mitochondria – release E during aerobic respiration for active transport of sucrose and amino acids into phloem [1] and support sieve tube cell survival [1]
Compare and contrast between the functions of xylem and phloem [5]
Similarities:
Xylem and phloem both transport substances/materials to different parts of the plant. [1]
Xylem and phloem both transport substances as a dissolved solution to different parts of the plant. [1]
Differences:
Xylem transports water and dissolved mineral salts from the roots to the leaves while phloem transports sucrose and amino acids from the leaves to other parts of the plant. [1]
Xylem transports water and mineral salts in one direction up the plant while phloem transports sucrose and amino acids in both directions. [1]
Xylem transports water and mineral salts by root pressure, transpiration pull and capillary action while phloem transports sucrose and amino acids by active transport which requires energy released from the mitochondria of companion cells. [1]
Compare and contrast between the structures of xylem and phloem [4]
Similarity
Both are made up of cells forming a cylindrical tube [1]
Both lacks protoplasm for efficient transport of fluids without obstruction. [1]
Differences
Phloem is made up of two kinds of cells sieve tube cell and companion cell, whereas xylem is made up of one kind of cells
Xylem is dead tissue with long, narrow and hollow lumen whereas phloem still has some protoplasm present as it is a living tissue
Xylem has lignin deposit along its inner cellwall for mechanical support but phloem does not have.
Describe and explain how the carbon in an atmospheric CO2 can be found in the starch molecule of a potato tuber of the plant. [4] *summaries the steps
CO2 in the atmosphere diffuse into the leaf via stomata. CO2 is used during photosynthesis to form / synthesize glucose in the leaf
The glucose containing the carbon is converted to sucrose and loaded into phloem via active transport to be transported
Sucrose is transported to the roots where it is taken by the potato tuber and converted back to glucose for cellular activities.
Excess glucose is converted to starch to be stored in the potato tuber.
describe and explain the ‘ringing’ experiment for the function of phloem. [3/4]
The outer layer of bark is removed, which contains the phloem vessel. [1]
Sucrose and amino acids cannot be transported / obstructed / accumulate at the cut region, lowering water potential at that region. [1]
Net movement of water molecules from neighbouring xylem / tissue cells into the region down WP gradient via osmosis [1]
The obstructed region swell, forming a bulge. [1]
Describe how a molecule of water is transported from the roots to the leaf [5]
Net movement of water molecule from the soil into the cell sap of root hair cell down
water potential gradient [1] via osmosis [1]
Osmosis through adjacent cells down the water potential gradient into the root [1] Transport up the xylem via capillary action, root pressure and transpiration pull [1] Osmosis into mesophyll cells in leaf from xylem [1]
Describe how mineral salts / chemical compounds is transported from the roots to the leaf [5]
diffusion from the soil into cell sap of root hair cell down conc gradient OR Active transport into the root hair cell against conc gradient using energy released from aerobic respiration by mitochondria. [1]
Diffusion through adjacent cells into the root [1]
Dissolved in solution [1] and transport up the xylem via capillary action, root pressure and transpiration pull [1]
Diffusion into mesophyll cells in leaf from xylem [1]
Explain how potometer can be used to measure the rate of transpiration in a plant [4]
It is assumed that the rate of absorption of water by the plant is equal to the rate of transpiration from the plant. [1]
As the water is taken up by the plant, the air bubble moves towards the plant. [1]
By measuring the distance moved by the air bubble per unit time[1], we can measure the rate of water loss / transpiration from the leafy shoot. [1]
Describe and explain the process of transpiration in the leaf [5]
Water molecules move out of the mesophyll cells by osmosis [1] to form a thin film of moisture [1] around the mesophyll cells, before water evaporates into the intercellular air spaces in the spongy mesophyll as water vapour [1]; the loss of water by the cell due to evaporation creates a suction force which draws water from neighbouring cells closer to the xylem. The suction force is called transpiration pull.[1] water vapour from the intercellular air spaces in the leaf diffuse to the atmosphere down the concentration gradient through the stomata [1] on the lower epidermis
Explain how the following factors will affect rate of transpiration [4]
Wind
In moving air, the rate of water loss from the shoot is greater than in still air. [1] The movement of air removes water vapour around the leaf[1]. This sets up a steeper concentration gradient of water vapour between the leaf and the atmosphere [1] increasing the rate of diffusion of water vapour out of the stomata of the leaves into the surrounding air down the concentration gradient. [1]
Humidity
In high humidity, the rate of water loss from the shoot is lower. [1] high humidity indicated saturation of water vapour in the air [1]. This sets up a less steep concentration gradient of water vapour between the leaf and the atmosphere [1] decreasing the rate of diffusion of water vapour out of the stomata of the leaves into the surrounding air down the concentration gradient. [1]
Temperature
Increase in temperature increases the rate of evaporation of water from the layer of moisture on mesophyll cell into the intercellular spaces. [1] This increases the concentration of water vapour and causing steeper concentration gradient of water vapour between the intercellular spaces of the leaf and the air.[1] This increases the rate of diffusion of water vapour out of the stomata of leaf into the air[1], thus rate of transpiration increases. [1]
Light intensity
Increase light intensity increase rate of transpiration[1]. More photosynthesis in guard cells to pump in more K+ ions[1], more osmosis of water molecules into guard cells to swell turn more turgid[1], stomata open bigger allowing more water vapour to diffuse out [1] from intercellular space to environment.
Describe and explain the advantage and disadvantage of wilting in plants [4]
Definition of wilting:
Wilting is due to excessive water loss in plants via transpiration. It is the net water loss as rate of transpiration is higher than rate of water absorption from the roots
Advantages
Reduce excessive water loss through transpiration [1] by reducing surface area of leaf and closure of stomata[1]
Disadvantages
Reduced rate of photosynthesis [1] due to reduced surface area of leaf thus less light absorbed by chlorophyll [1]
OR closure of stomata [1] to reduce taking in of CO2 as raw material for photosynthesis, rate of photo drops [1]
Explain how plants support itself in the upright position. [5]
Xylem has lignin deposited along its wall / lignified wall to provide mechanical support. [1]
Xylem form bundles in stem to further strengthen its structure and provide mechanical support. [1]
The plant cells have concentrated cell sap to lower water potential [1] so net movement of water molecules will enter the cells via osmosis[1], causing the cell to swell and become turgid / maintain turgidity. Providing structural support. [1]
Explain why having stomata open in daylight is an advantage to plants [4]
take in CO2 as raw material via diffusion to increase rate of photosynthesis to synthesize glucose [1]
Diffusion of excess oxygen out as by product [1]
Promote transpiration allowing water vapour to diffuse out down the conc gradient to cool down the plant [1]
Increase transpiration promote transpiration pull to transport water up the xylem from the roots for constant supply of water in the leaves as raw material for photosynthesis to synthesize glucose [1]
Increase transpiration promoting transpiration pull to transport water up the xylem from the roots for constant supply of water in the leaves to maintain turgidity in mesophyll cells for mechanical /structural support and to prevent wilting of plant [1]
