Transport Systems in Dicotyledonous Plants Flashcards
Explain why multicellular plants need transport systems in terms of surface area: volume ratio
- Due to having stems, trunks and roots, multicellular plants have a very small surface area: volume ratio.
- This means that they cannot rely on diffusion alone for the transport of substances
Explain why multicellular plants need transport systems in terms of metabolic demands
- Parts of multicellular plants cannot carry out photosynthesis (e.g. the roots) and so do not produce their own oxygen and glucose for aerobic respiration
- Due to this, they need oxygen and glucose transported to them and waste products of cell metabolism removed
- In addition, mineral ions absorbed by the roots need to be transported to other parts of the plant
Explain why multicellular plants need transport systems in terms of size
- Many multicellular plants are very large. For this reason they need very effective transport systems to move substances up and down them from their tips to the roots
What are the names of the transport vessels which make up the vascular bundle?
Xylem and Phloem
Draw a cross-section of a root plant showing the vascular bundle
An ‘X’ shape for the xylem and four sections around the ‘X’ for the phloem
Where is the vascluar bundle located in the root cell?
In the middle
Why is the vascular bundle located in the middle of the root cell?
The xylem vessels are strong and so they help to withstand tugging forces as the plant is being blown in the wind
Draw the arrangement of the vascular bundle in a stem cell
Vascular bundle in an outer ring in the cell
The phloem on the outside with lines in them
Xylem on the inside
Cambium in the middle
Why is the vascular bundle arranged in an outer ring in stem cells?
To allow the stem to withstand bending forces
What is cambium made of?
Merristem cells
What does the cambium in the stem cells do?
Differentiate to form new xylem and phloem cells
Where is the vascular bundle located in the leaf cell?
In the midrib of the leaf which provides support
Is the xylem at the top or the bottom of the leaf cell?
At the top
(to provide pallisade mesophyll with water and mineral ions quickly for photosynthesis)
ONLY IN DICOTYLEDONOUS PLANTS
Is the phloem at the top or the bottom of the leaf cell?
The bottom
What do the smaller branching veins do in the leaf cell?
They function as tranSPORT and supPORT
In which type of plants are the xylem are the top of the leaf cell?
Dicotyledonous plants
Why are the xylem at the top of the leaf cell in dicotyledonous plants?
The pallisade mesophyll are at the top of the leaf cell and this is mainly where photosynthesis take place. The xylem provides water to the pallisade mesophyl for photosynthesis.
Describe the structure of xylem vessel elements
- Dead cells stacked end-to-end to form a continuous hollow tube (lumen) containing no cytolasm.
- The walls of the xylem are strengthened by lignin
Describe the function of xylem vessel elements
- To transport water and absorbed mineral ions up the plant from the roots to the leaves
Describe the structure of xylem fibres
- Long and narrow cells containing lignin
What is the function of xylem fibres?
- To provide mechanical support to the plant
What is the difference between the function of the xylem vessel elements and the xylem fibres?
The xylem vessel elements transport water up the plant, whereas the xylem fibres don’t, they provide mechanical support to the plant
What is the function of the phloem?
To transport assimilates (e.g. sucrose) up and down the plant
Describe the structure and function of the sieve tube elements
Cells stacked end-to-end to form a hollow tube with thin walls, little cytoplasm and no nucleus. The end walls have holes in them to form sieve plates which allow the phloem contents through them.
What links the companion cells and sieve tube elements together?
Plasmodesmata
What two components make up the phloem?
Sieve tube elements+ Companion cells
What is the function of the companion cells?
To provide the sieve tube elements with essential molecules
Name three things that the companion cells contain
1) Dense cytoplasm
2) Large nucleus
3) Many mitochondria
