Transport systems in plants Flashcards
Name the 2 types of vascular tissue in a plant and what their function is.
- Xylem: transports water and soluble minerals upwards
- Phloem: transports sugars upwards and downwards
In the vascular bundle in the roots where is the xylem and phloem located, and name the other tissues located here.
- Xylem is in the centre of the bundle in an x shape
- Phloem is located in-between the arms of the x shape
- Endodermis surrounds the xylem and phloem
Describe the shape and different tissues in a vascular bundle in the the stem.
- The separate vascular bundles form a circular ring shape near the outside of the stem
- Xylem: on the inside
- Phloem: towards the outside
- Cambium cells: separate the xylem and phloem
- Medula: cells on the inside of the stem
- Cortex: cells on the outside
What is the reason for the circular arrangement of the vascular bundles in the stem?
Stems are exposed to bending forces, having the vascular bundles located towards the outside of the stem increases flexibility and thus allows it to withstand bending forces.
Describe the vascular bundle in a leaf.
- Bundles form the midrib (central vein) of the leaf
- Side veins (branches) get smaller the further from the midrib they get.
- The xylem is onto of the phloem.
What is the reason for the arrangement of the vascular bundles in the leaves?
- Short diffusion distance, efficient rate of diffusion of water, minerals and assimilates
- Provide support for thin leaf
Name the 3 different cells types in the xylem tissue.
- Vessel elements: dead
- Fibres: dead
- Parenchyma cells: living act as packing
In 5 stages describe the formation of the xylem vessels.
- Made from stem cells via differentiation and elongation
- Xylem elements mature by incorporating increasing elements of lignin into the cell walls
- Lignin: hard, strong water impermeable substance
- Cell wall becomes waterproof and the cell dies
- Endways and cell content (protoplast) decay leaving long columns of dead cells = xylem
Why is ligninification important?
- Waterproofs cell
- Strengthens walls and prevent collapse when water is low
- Not continuous and forms in patterns to allow plant to grow
- Increase flexibility of stem and branches
In 4 stages describe the formation of pits.
- Plant cells are connected via plasmodesmata
- Where the plasmodesmata the cells wall remains non-lignified
- This leaves pores in the wall called pits
- This allows water to move in and out of the xylem (sideways movement)
Describe the structure of the phloem tissue.
- Sieve tube element lined up to form long tubes
- Companion cells containing organelles connected via a plasmodesmata
Why is water important to plants?
- Hydrostatic pressure (turgor pressure) forms the hydroskeleton
- Turgor drives cell expansion
- Cooling of plant via evaporation
- Transport of mineral ions and products of PS
- Raw material for PS
Define these terms.
- Hypertonic
- Hypotonic
- Isotonic
- Hypertonic- Inside has a lower water potential than the outside so osmosis travels outwards down the WP Gradient
- Hypotonic- Inside has a higher water potential than the outside so osmosis travels inwards down the WP Gradient
- Isotonic- Inside and outside have the same water potential so there is no osmotic action
Define the terms
- Plasmolysed
- Turgid
- Flacid
- Plasmolysed: The vacuole and cytoplasm have shrunk due to lack of water
- Turgid: Pressure is exerted on the cell due to high water potential
- Flacid: Where the cell is isotonic
How do root hair cells intake mineral ions?
- Active transport requires ATP/ aerobic respiration
- Cell lowers Water Potential inside the cell increasing solute concentration
- Water and mineral ions move in via osmosis
