Plant Stems Flashcards
What do larger plants require to gain all needed nutrients and why?
- Specialised transport systems, those with are called vascular plants
- because they have a lower SA:V
What are examples of types of molecules exchanged by plants?
Carbon dioxide, oxygen, water, organic nutrients, inorganic ions (nitrate, potassium)
Describe structure and function of vascular bundles in plant stems
- Transports substances as well as providing support
- Distributed throughout plant, vascular tissue made up of xylem and phloem tissue (xylem larger section on inside, phloem smaller on outside)
Describe structure and function of the epidermis in plant stems
- Outer layer of the stem; protects cells beneath plant
- contains cutin (waxy substance secreted to reduce water loss)
- some plants produce hairs to trap warm air + keep plants warm
Describe structure and function of lignin in plant stems
- Protein which makes wood
- Produced by xylem vessel; lignin wraps itself in spiral pattern around xylem tube
- very strong + completely water proof —> strengthens xylem and prevents water leakage
- however kills xylem so means plants must produce more xylem cells
Describe structure and function of xylem and phloem in plant stems
- Water moves up stem in xylem tubes
- Sugar moves up and down stem in phloem tubes
- xylem + phloem form single stele in roots but run up stem in vascular bundles
- contain cambium between them
Describe structure and function of sclerenchyma in plant stems
- Provide support for plants without lignin
- may be either fibres (found in vascular bundles or bundles of cells) or sclereids
- cells are dead
- thick walls made of cellulose + lignin, make up 90% volume
Describe structure of phloem vessel in depth
- made up of sieve tube elements on top of one another
- these are living, contain thin cytoplasm but no nucleus + few organelles, walls made of cellulose
- connected to companion cells via plasmodesmata; carry out living functions for sieve tube elements
- contain lots of mitochondria fro active transport
- sieve tubes have sieve plates either end, have large pores to allow sap to move through sieve tube
Describe xylem structure and function
~ transports water and mineral ions
- long tubes of cells running up plant stem
- made up of dead cells
- no cell walls at end of each vessel element; creates continuous tube for water to flow
- walls lined with lignin, provides structural support
How does water move up the xylem?
1 Water evaporates from leaves via transpiration
2 This creates tension in the xylem = hydrogen bonds between water molecules and xylem vessel elements; pulls water upwards
3 Cohesion - water molecules hydrogen bonds to each other; continually moves water upwards
4 Osmosis - when water moves up stem, water diffuses into roots via osmosis as water potential has lowered
How does sugar move through the phloem?
Translocation
- sucrose actively transported into companion cells in phloem
- sucrose diffuses into sieve tube elements
- water diffuses via osmosis into
phloem as water potential in phloem is low
- sucrose diffuses out of phloem into sink cells at bottom phloem
- now water diffuses out of phloem via osmosis, allowing mass transport of sucrose
Describe the roles of water in plants
- Keeps plant cells turgid which supports plant
- Reactant in photosynthesis, vital for producing sugar in respiration
- Maintains a constant internal temp
- Transpiration
- Transports dissolved substances in xylem and phloem
Describe the role of nitrate ions in plants
- Used to synthesise amino acids and so proteins, also component of chlorophyll
Describe role of calcium ions in plants
- Play an important role in growth of new tissues such as root and shoot tips
- also present in cell walls, stabilise cell wall
Describe role of magnesium ions in plants
- Essential component in synthesising chlorophyll
- chlorophyll absorbs light used in photosynthesis
