Topic 4: Plant stems Flashcards
In the stem, what provides support? (2 things)
- Sclerenchyma fibres
2. Xylem
Why is support needed in the plant stems? (3 points)
- to hold leaves in best position for photosynthesis
- allows effective flower pollination
- to withstand the {wind/rain}
What provides transport within the stem? (2 things)
- Xylem
2. Phloem
What does the xylem transport? (2 things)
- Water
2. Mineral ions
What does the phloem transport? (1 point)
- organic solutes (e.g. sucrose)
In a cross section of a plant stem, name the parts of a vascular bundle from the part furthest away from the centre.
(4 parts)
- Sclerenchyma
- Phloem
- Cambium (cells that divide the xylem and the phloem)
- Xylem
NOTE:
From Outside of stem
Outside Sclerenchyma Phloem Xylem = OSPX
How can sclerenchyma fibres be identified under a microscope? (1 point)
- They have the thickest walls
How can xylem vessels be identified under a microscope? (1 point)
- They have the largest cross-sectional area
NOTE: biggest circles with slightly thicker walls than the rest of the stem
Name all the parts of a plant stem (8 parts)
- Xylem vessels
- Phloem vessels
- Epidermis
- Collenchyma
- Parenchyma
- Cambium
- Sclerenchyma fibres
- Stoma
What flow do xylem vessels have? (1 point)
- Upward (the flow is always upward)
What flow do the phloem vessels have? (1 point)
- Two-way flow
What is the epidermis? (1 point)
- The cells at the very outside of the stem
What are the collenchyma? (2 points)
- The cells found around the outside of the stem, underneath the epidermis, to give strength
- They stretch as the plant grows
What is the cambium? (2 points)
- Layer of unspecialised cells
2. which divide giving rise to specialised xylem and phloem.
Key Summary: What are the similarities between the position of xylem, phloem and sclerenchyma fibres?
(1 point)
- All 3 tissues are located towards the outside of the stem (in the region of the vascular bundle)
Key Summary: What are the differences between the position of xylem, phloem and sclerenchyma fibres?
(3 points)
- Xylem vessels are nearest the centre of the stem
- Sclerenchyma fibres are nearest outside of the stem
- Phloem vessels are between the xylem and sclerenchyma
Key Summary: Describe the structure of the xylem (5 points)
- Cellulose in cell walls
- Lignin in walls (often in rings/spirals)
- Continuous column made of hollow DEAD cells, with no end walls and no cell contents/cytoplasm
- Open ended
- Pits in walls
Key Summary: Describe the structure of sclerenchyma fibres (4 points)
- long {narrow cells/narrow lumen}, usually POINTED AT BOTH ENDS
- have cellulose cell walls, which are THICKLY LIGNIFIED
- DEAD, hollow cells when mature
- often have PITS in their walls
Key Summary: Describe the structure of the phloem (4 points)
- living tissue.
- sieve tube elements have NO NUCLEUS and thin layer of peripheral cytoplasm (containing a few organelles).
- sieve tubes have a fluid filled lumen and sieve plates which have sieve pores.
- a sieve tube element is connected to a companion cell (has normal cell structure) by PLASMODESMATA.
Key Summary: What are the structural SIMILARITIES of xylem vessels and sclerenchyma fibres (3 points)
- Dead, hollow tubes with no cell contents
- Have lignified cellulose cell walls
- Pits in cell wall
Key Summary: What are the structural DIFFERENCES of xylem vessels and sclerenchyma fibres (2 points)
- Sclerenchyma fibres have pointed ends but xylem vessels have open/blunt ends
- Sclerenchyma fibre walls are more thickly lignified than xylem vessel walls
Key Summary: What are the functions of the xylem vessels in the plant stem? (2 functions)
- Transport of water and mineral ions up the plant
2. {Structural/mechanical} support
Key Summary: What is the function of the sclerenchyma fibres in the plant stem? (1 function)
- {Structural/mechanical} support
Key Summary: What is the function of the phloem sieve tubes in the plant stem? (1 function)
- Transport (translocation) of organic solutes (eg. sucrose, amino acids), produced by sources (eg. leaves), to {other parts of the plant/sinks}.
