9.1 - Transport systems in dicotyledonous plants Flashcards
Why do multicellular plants need transport systems?
Plants need transport systems to move substances such as water, glucose, oxygen, mineral ions, nutrients, and hormones between leaves, stems, and roots.
How do the pressures in plant transport systems compare to other systems?
The pressure in the phloem, one of the main transport tissues in plants, is around 2,000 kPa, which is much higher than the 16 kPa pressure in human arteries but lower than the 4,000 kPa pressure in steam turbines of power stations.
How does the pressure in plant transport systems remain contained?
The high pressures in plants are confined to much smaller spaces than those in human arteries or steam turbines, allowing efficient transport without structural damage.
What are the three main reasons plants need transport systems?
1) Metabolic demands
2) Large size
3) Small surface area to volume ratio (SA:V).
How do metabolic demands create a need for transport systems in plants?
Some parts of the plant, like underground roots, cannot photosynthesize, so they rely on transport systems to receive glucose and oxygen. Waste products also need to be removed.
What role do mineral ions play in plant metabolism?
Mineral ions absorbed by roots are transported to all cells to help produce proteins necessary for enzyme function and cell structure.
Why do hormones need to be transported in plants?
Hormones made in one part of the plant must be transported to other areas where they regulate growth and development.
How does plant size affect the need for transport systems?
Many plants, especially perennial plants, grow to large sizes and need efficient transport systems to move substances between roots, stems, and leaves.
What are some of the tallest plant species in the world?
The Coastal Redwood and Giant Redwood in the USA (up to 115m tall) and the Mountain Ash in Australia (114m tall).
How does the surface area to volume ratio (SA:V) affect transport in plants?
Although leaves have a large SA:V ratio for gas exchange, the overall plant structure (including stems, trunks, and roots) has a relatively small SA:V ratio, limiting diffusion efficiency.
Why can’t plants rely on diffusion alone to transport substances?
Due to their large size and small SA:V ratio, diffusion alone is too slow to supply all cells with nutrients and remove waste effectively.
Where are the vascular bundles located in the stem of a young herbaceous plant?
The vascular bundles are arranged around the edge of the stem to provide strength and support.
What tissues are found in the vascular bundle of a plant stem?
The vascular bundle contains xylem, phloem, and parenchyma (packing and supporting tissue).
What is the function of parenchyma in the plant stem?
Parenchyma acts as packing and supporting tissue, helping maintain the plant’s structure.
How are the vascular bundles arranged in the root of a young herbaceous plant? Why?
They are centralized in the middle of the root to help withstand the tugging forces caused by wind and movement.
What are the key tissues found in a plant root cross-section?
Epidermis, exodermis, endodermis, cortex, xylem, and phloem.
What is the function of the endodermis in a plant root?
The endodermis regulates water and mineral uptake into the xylem via the Casparian strip.
What role do root hairs play in plant roots?
Root hairs increase surface area for efficient water and mineral absorption from the soil.
What is the main vascular structure in a dicot leaf?
The midrib, which contains the vascular bundle (xylem and phloem) and provides support.
How is the vascular bundle arranged in a dicot leaf?
Xylem is positioned on top, and phloem is positioned below within the vascular bundle.
What is the function of the palisade mesophyll in the leaf?
It is the main photosynthetic tissue, containing many chloroplasts for maximizing light absorption.
Why does a leaf need small branching veins?
Small veins help in transporting water, sugars, and nutrients while also providing structural support.
What are dicotyledonous plants (dicots)?
Dicots are plants that produce seeds with two cotyledons, which act as food stores for the developing embryo and form the first leaves during germination.
What are the two main types of dicotyledonous plants?
1) Herbaceous dicots – soft tissues, short life cycles.
2) Woody (arborescent) dicots – hard lignified tissues, long life cycles (some lasting hundreds of years).
What type of dicot plants are studied in this topic?
Herbaceous dicots, which have vascular bundles running through their stems, roots, and leaves.
What is the vascular system in dicots?
A network of transport vessels that run through the stem, roots, and leaves to move substances efficiently.
What are the two main transport vessels in dicot plants?
1) Xylem – transports water and minerals.
2) Phloem – transports organic substances like sugars (sucrose).
How are xylem and phloem arranged in herbaceous dicots?
They are arranged together in vascular bundles, found in the stems, roots, and leaves.
How is the vascular tissue arranged in the stem of a dicot?
Vascular bundles are positioned around the edge to provide strength and support.
How is the vascular tissue arranged in the roots of a dicot?
Vascular bundles are in the center, helping the plant withstand pulling forces from wind and movement.
How is the vascular tissue arranged in the leaves of a dicot?
The midrib contains the main vascular bundle, with branching veins that help in transport and structural support.
What are the two main functions of the xylem?
1) Transport of water and mineral ions from roots to shoots and leaves.
2) Support to maintain plant structure.
In which direction does the xylem transport materials?
Upwards only – from the roots to the shoots and leaves.
Is xylem a living or non-living tissue?
Non-living – most xylem cells are dead when they are functional.
What are xylem vessels and how are they formed?
Long, hollow structures made by several columns of cells fusing together end-to-end.
What are the three other tissues associated with the xylem in herbaceous dicots?
1) Xylem parenchyma – stores food and contains tannin deposits (protection).
2) Xylem fibres – long, lignified cells providing mechanical strength (no transport).
3) Bordered pits – small unlignified areas where water leaves the xylem to enter other cells.
What is tannin, and what is its function in the xylem?
A bitter, astringent-tasting chemical that protects plant tissues from herbivore attacks.
What is lignin, and what is its function in the xylem?
A strong waterproof polymer that reinforces xylem walls, preventing collapse under pressure.
How can xylem vessels be observed in living plant tissue?
By placing plant material (e.g., celery sticks, gerbera flowers, or germinated seed roots) in water containing a strongly coloured dye for at least 24 hours.
What happens to the xylem vessels when plants are placed in dyed water?
The dye moves up the xylem due to transpiration, staining the xylem vessels.
How do you prepare a transverse section to observe xylem vessels?
Use a sharp blade to make clean transverse cuts across the stem on a white tile.
Observe the cut section – xylem vessels should appear as coloured spots where the dye is present.
Draw the position of the stained xylem vessels.
What should the xylem vessels look like in a transverse section?
They should appear as coloured circular spots where the dye has stained them.
How do you prepare a longitudinal section to observe xylem vessels?
Make a careful longitudinal cut through a region where xylem vessels are expected.
Observe the section – xylem vessels should appear as coloured lines where the dye has been absorbed.
Draw the stained xylem vessels.
What should the xylem vessels look like in a longitudinal section?
They should appear as long, continuous coloured lines, indicating the transport of dye through the plant.
What is the main function of the phloem?
The phloem is a living tissue that transports organic solutes (e.g., sugars and amino acids) from the leaves (where they are made in photosynthesis) to the rest of the plant.
What is the direction of transport in the phloem?
The flow of materials in the phloem can go both up and down the plant, unlike the unidirectional flow in the xylem.
What are sieve tube elements, and how do they form the main transport vessels in phloem?
Sieve tube elements are long, hollow structures formed by many cells joined end to end.
How do sieve tube elements differ from xylem vessels?
Sieve tube elements are living, while xylem vessels are dead.
Sieve tube elements are not lignified, whereas xylem vessels have lignin for structural support.
Phloem transports organic solutes (e.g., sugars), whereas xylem transports water and minerals.
What are sieve plates, and what is their function?
Sieve plates are perforated areas between sieve tube cells.
They allow the flow of phloem sap between cells.
What are companion cells, and why are they important? What structures do they contain to help this function?
Companion cells are living cells attached to sieve tube elements via plasmodesmata (microscopic channels).
They provide metabolic support to sieve tube elements, which lack nuclei and most organelles.
They contain a nucleus and organelles to maintain active transport of solutes in the phloem.
How are companion cells connected to sieve tube elements?
Through plasmodesmata, which are tiny cytoplasmic connections allowing communication and transfer of materials between cells.
What additional cells are found in phloem tissue, alongside the companion cells?
Fibres – provide mechanical support.
Sclereids – have extremely thick cell walls for extra strength.
What material do plants exchange and transport?
CO2 - photosynthesis
O2 - respiration
H2O - Perspiration
Organic nutrients - healthy growth
Inorganic ions - healthy growth
