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 vessels on the inside (providing strength), phloem in middle and schlerenchyma fibres on the 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
- made up of long, dead cells
- 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 of sucrose
- 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 from root
- long hollow tubes of cells running up plant stem
- made up of dead cells
- no cell walls at end of each vessel element, no cytoplasm or organelles ; 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
How are inorganic ions taken into plants?
Via active transport as concentration in roots > than soil, root hair cells have carrier proteins on surface which pick up minerals and change shape
