Chapter 9 - Plants Flashcards
Why do plants require specialised transport tissue?
To overcome the limitations of diffusion over large distances
A group of students wants to observe the position of xylem vessels in the leaf stalks of celery.
Describe a procedure they could use to do this.
Cut a thin cross section of the plant
Add a stain - toluidine blue
Observe with a microscope under a low power
State one similarity between the structure of xylem and phloem
Both are made up of cells joined end to end
State two differences between the structure of xylem and phloem
D1. Phloem has companion cells whereas Xylem do not
D2. Phloem tubes have cellulose cell walls, Xylem vessels have lignified cell wall
A student designed an investigation into the rate of transpiration in plants.
They use 8 leaves of the same size, age and species.
Why did the student take readings from 8 different leaves?
To assess the repeatability of their data
Water Starwort is a hydrophyte. It is an aquatic plant which has its stems fully submerged in water.
Cholla is a cactus. Growing over 4 metres tall.
Give one way in which you would expect the walls of the xylem vessels
Water Starwort - walls of the xylem vessels to be quite thin compared to deciduous plant; less lignin
Cholla - walls of the xylem vessels would be quite thick to preserve water; more lignified.
How do hydrogen ions move out of companion cell
active transport
How do sucrose move into companion cells
Facilitated diffusion
How do sucrose move out of companion cell
Diffusion
The use of cyanide prevents the change in pH occuring. What conclusion can be made
Cyanide prevents active transport as ATP cannot be produced
A scientist used an electron microscope to look for evidence in loading sucrose.
What evidence might the scientists see
It has a large mitochondria to proudce ATP.
Plasmodesmata between companion cell and sieve tube element
What is the pathway water is transported along the cells walls and between cells in plants
Apoplast pathway
What is the function of the pits in xylem tissue
Lateral movement of water
Xylem forms part of a plant’s transport system.
Explain why large multicellular plants need a transport system.
Small surface area to volume ratio
Long distance from external surface to cells
Simple diffusion is not enough to meet the demands
Suggest and explain 2 likely adaptations of the leaves of the plant with lots of air spacs
Large Surface area to maximise photosynthesis
Many stomata to increase gas exchange
What is the most common pathway of water
Apoplast
What is meant by the term resolution of a microscope
Resolution is the ability to differentiate between two things
Phloem sap mainly consists of carbohydrate in the form of sucrose
Suggest why it is beneficial to the plant for the carbohydrate to be transferred throughout the plant in the form of sucrose rather than an alternative carbohydrate
Sucrose is soluble so can be transported in sap.
It is metabolically inactive
How is the transport in the phloem similar to the transport in the xylem.
Both use mass flow generated by hydrostatic pressure
Explain with a suitable example how some parts of the plant can act as both a source and a sink
Certain parts can store and then release carbohydrates when needed.
Leaf can act as a sink or source at different times of year.
Explain the process of loading of sucrose into the phloem and its movement in the phloem
Sucrose is pumped from companion cell into phloem tube by active transport.
H+ is a co transporter for sucrose.
This reduce water potential in sieve tube
Water also enters from the companion cell to the sieve tube
Water also enters from the xylem this increases pressure so sap flows down the phloem and goes through the pores
How are meristems producing new plant tissues?
Meristems can generate new plant tissues.
Xylem tissue is formed, lignin impregnates the cell walls making them impermeable to water. Cytoplasm is lost.
Phloem tube is formed by the sieve tube elements becoming elongated and lost most of their cytoplasm
which macromolecule does a plant need both nitrogen and phosphorus.
DNA
How would flooding from sea water affect soil water potential?
It makes it more negative
How does casparian strip prevent ions such as Na+ and CL- from reaching the xylem of the plant by the apoplast pathway.
The phospholipid bilayer in the strip repels charged particles
It forces water to pass through plasma membrane
halophytes are plants that have the ability to live in soils with a very low water potential .
Suggest and explain how the root hairs of halophytes are able to absorb water by osmosis from the soil of the salt marsh
there is a lower water potential inside root hair cells
actively transport ions into root hairs
Explain how mass flow of the phloem sap occurs in plants with a vascular system.
sucrose enters the sieve tube which lowers the water potential
water enters by osmosis from xylem and the companion cell , this increases hydrostatic pressure.
Assimilates move from high to low down the pressure gradient .
Cells in the phloem are specialised so that translocation can occur.
What is meant by translocation?
The movement of assimilates from source to sink
State one adaptation that leaves might have to conserve water
Thick waxy cuticle to prevent water loss
Fewer Stomata
One environmental factor that affects the loss of water vapour from the leaves is air movement.
Explain how increased air movement increases the loss of water vapour from the leaves.
Water vapour around the stomata is blown away so a steeper water potential gradient
The leaves of moss plants are usually one cell thick and are attached to a thin stem. Neither the leaves nor the stem contain vascular tissue.
Suggest and explain how the absence of vascular tissue might affect the size to which moss plants can grow.
The plant will remain small as there is no support from vascular tissue.
The only transport is diffusion . Therefore for large plants diffusion would be too slow so the plant will remain small
Describe how the guard cells surrounding the leaf pores are adapted to their role.
They have an unevenly thickened cell wall. (Thick inner and thin outer walls).
This means they can change shape - bend when turgid.
Also contains chloroplasts to provide ATP
Name one other part of the leaf from which water may be lost.
Stomata
Cuticle
Why does a plant wilt
if there is a lot of water lost from the leaf cell, then turgidity is lost and the plant wilts.
The cohesion tension theory is often used to explain the mechanism by which water moves up the xylem from the roots to the leaves.
Use this theory to explain how water moves from the roots to the leaves.
Evaporation from the top of the plant causes tension in xylem.
Water molecules are cohesive and when pulled up the column by tension, the water molecules stick and followup the column to the leaves.
Name 2 types of cell that can be found in phloem tissue
Parenchyma
Sieve tube element
Companion cell
Multicellular organisms such as plants have evolved internal transport systems.
Explain the benefit to plants of internal transport systems.
Surface area to volume ratio is too small so diffusion is not fast enough therefore transport systems ensure molecules reach all tissues at a high metabolic rate.
Give an example of what substance root hair cells transport
Nitrate ions
Mosses are small plants with no true roots. Each plant is anchored by simple root-like structures which do not contain vascular tissue.
Although a moss plant has no vascular tissue, water still moves through the plant from the root-like structures to the leaves.
Use your knowledge of the mechanisms of water transport to explain the movement of water through the moss plant.
Water is lost by evaporation. It is transported by symplast and apoplast pathways.
Apoplast pathway is along cell walls.
Symplast partway, water is transported by osmosis from a high concentration to a low concentration
Leaves of dicotyledonous plants contain types of cells that are not found in the leaves of mosses
Other than the cells found in vascular tissues, name two types of cell found in the leaves of dicotyledonous plants that are not found in the leaves of mosses
Palisade cells
Spongy Mesophyll
How is transport in the phloem similar to and different from transport in the xylem?
Similar - Both use mass flow
Different -
transport in phloem can take place in different directions and transport in xylem only takes p
Explain the benefit to plants of internal transport systems.
ensures molecules / nutrients / sugars / water, reach all tissues at a high metabolic rate
Describe how potometer can be used to calculate a more accurate rate of transpiration
potometer airtight / watertight dry leaves cut shoot under water measure distance air bubble travels per time interval calculate volume of water uptake
maintain constant conditions - wind, temp, sunlight
Suggest why it might be considered better to use a capillary tube rather than a calibrated pipette to measure water uptake
capillary tube:
measures smaller volumes
Besides safety precautions, explain one practical precautions that should be taken when using a potometer
Keep abiotic factor (temp) constant as it affects rate of transpiration
They placed the leaves on graph paper and then counted squares to obtain an estimate of leaf area.
State two things the student would have to do to ensure that the estimate of leaf area was accurate
Flatten leaf on graph paper
Only count squares more than 50% covered
Neonicotinoid insecticide molecules are absorbed by the roots and leaves of maize plants.
Describe how once these molecules have been absorbed they may be transported to the fruits of the maize plant
in xylem (by),cohesion-tension / transpiration (stream); in phloem (by), translocation / mass flow;
