Chapter 7.1 Flashcards
Dicotyledonous (dicots) plants
-Dicotyledonous (dicots) plants have:
—-Seeds that contain two cotyledons (seed leaves)
—-Network of veins
—-Leaves that typically have broad blades (leaf surface) and petioles (stalks)
—-Tap root with lateral branches -Herbaceous dicots have a relatively short life cycle (one growing season) and non-woody tissue
Transport systems
- Plants need transport systems to meet their metabolic demands (glucose, hormones, mineral ions are required for various processes within plants), to efficiently move substances up and down and to compensate for their relatively small SA:V ratio (generally plants cannot rely on diffusion alone)
- The vascular system is comprised of two distinct types:
—-Xylem (transports water and mineral ions from the roots to the rest of the plant) -
—Phloem (transports substances from the source (eg. leaf) to the sink (eg.root)) -The xylem and phloem are arranged together in vascular bundles -The bundles are laid out differently in the leaves, stem and roots
When drawing tissue plan diagrams (which is common in the practical paper 3) you need to:
- Read the instructions carefully
- Draw a large diagram
- Use a sharp pencil and do not shade (including the nucleus)
- Use clear, continuous lines
When using an eye-piece graticule, use it to ensure you have correct proportions or if you are not using a microscope then endeavour to keep the proportions between tissues to scale -If drawing from a low-power image:
- Do not draw individual cells -Read the question carefully as you may only have to draw a portion of the image
- Include the magnification on the drawing
- If drawing from a high-power image:
- Draw only a few of the required cells
- Draw the cell wall of the plant cells -Include the magnification on the drawing -When labelling, remember:
- Use a ruler for label lines (and scale line if appropriate)
- Label-lines should stop exactly at the structure (do not use arrows)
- Don’t cross label-lines over each other
- Label all tissues and relevant structures (those requested)
Common tissues that can be found in stems, roots and leaves are:
- Epidermis
- Parenchyma
- Mesophyll
- Endodermis
- Pericycle
- Vascular tissue
Epidermis
- This is the outermost protective layer of the stem, roots and leaves and is one cell thick
- It is in the leaves and stem it is covered by a waterproof layer called the waxy cuticle
- The leaves have two epidermis (upper and lower). The lower epidermis contains pores called stomata (stoma – singular) which allow gaseous exchange
- The roots have many extensions that increase the surface area for absorption of water and mineral ions. These are called root hairs
Parenchyma
- These are the unspecialised packing tissue of the stem, roots and leaves
- The cells making up the tissue are thin-walled, are metabolically active and carry out many functions e.g. photosynthesis, storing starch, providing support (when turgid) and the air spaces within the cells aid diffusion of gases
- In the roots, the tissue forms the cortex; in the stems, it forms the cortex and pith; in the leaves, it forms the mesophyll layer
Mesophyll
- This is made of specialised parenchyma cells.
- They are specialised for photosynthesis and therefore contain chlorophyll within chloroplasts
- There are two types, palisade mesophyll and spongy mesophyll
Endodermis
- This is one cell thick and surrounds the vascular tissue in roots (and can be found in stems)
- In roots, the endodermis cells contain a structure called the casparian strip, which help regulate the movement of water and ions into the vascular tissue
Pericycle
- This is located between the endodermis and vascular tissue in the roots
- It can be one to several layers of cells thick
- In roots, new roots can grow from this layer
- In stems, this tissue is specialised sclerenchyma (which has dead, lignified cells for strength)
Vascular tissue
- Xylem and phloem tissue
- They are called vascular tissue as both tissues transport fluids
The functions of xylem tissue in a plant are:
- Vascular tissue that transports dissolved minerals and water around the plant
- Structural support
- Food storage
Xylem tissue is made up of four cell types that function together:
- Tracheids (long, narrow tapered cells with pits)
- Vessel elements (large with thickened cell walls and no end plates when mature)
- Xylem parenchyma
- Sclerenchyma cells (fibres and sclereids)
- Most of the xylem tissue is made up of tracheids and vessel elements, which are both types of water-conducting cell
structure & function in xylem vessel: lignified cell walls (mature cells)
Adds strength to withstand the hydrostatic pressure so the vessels do not collapse, impermeable to water
structure & function in xylem vessel: no end plates (mature)
Allows the mass flow of water and dissolve solutes as cohesive (between water molecules) and adhesive (between water and the walls) forces are not impeded
structure & function in xylem vessel: no protoplasm (cells are dead when mature)
doesn’t impede the mass flow of water and dissolve solutes (transpiration stream)
structure & function in xylem vessel: pits in wall (non-lignified sections)
lateral movement of water, allows continual flow in case of air bubbles forming in the vessels
structure & function in xylem vessel: small diameter of vessels (although they are larger than trcheids)
helps prevent the water column from breaking and assists with capillary action
The function of phloem tissue in a plant is to:
- transport organic compounds (assimilates), particularly sucrose, from the source (eg. leaf) to the sink (eg. roots).
- The transport of these compounds can occur up and down the plant
- The organic compounds are dissolved in water to form sap
- Phloem is a complex tissue made up of various cell types; its bulk is made up of sieve tube elements which are the main conducting cells and companion cells
- Other cell types of phloem tissue also include parenchyma for storage and strengthening fibres
- Mature phloem tissue contains living cells, unlike xylem tissue
Phloem sieve tube elements structure & function: sieve plates with sieve pores
allows for the continuous movement of the organic compounds
Phloem sieve tube elements structure & function: cellulose cell walls
strengthens the wall to withstand the hydrostatic pressures that move the assimilates
Phloem sieve tube elements structure & function: no nucleus, vacuole or ribosomes in mature cells (some ER and mitochondria are preset)
maximizes the space for the translocation of the assimilates
Phloem sieve tube elements structure & function: thin cytoplasm
reduces friction to facilitate the movement of the assimilates
Phloem companion cells structure & function: nucleus and other organelles present
provides metabolic support to sieve tube elements and helps with the loading and unloading of the assimilates
Phloem companion cells structure & function: transport proteins in the plasma membrane
moves assimilates into and out the sieve tube elements
Phloem companion cells structure & function: large numbers of mitochondria
to provide ATP for the active transport of assimilates into or out of the companion cells
Phloem companion cells structure & function: plasmodesmata (channels in the cell wall)
the link to sieve tube elements which allow organic compounds to move from the companion cells into the sieve tube elements
Comparison of xylem & phloem tissue table
