final: plant structures Flashcards
(29 cards)
Plasmodesmata:
- Pores in cell wall between adjacent cells, cytoplasm runs through plasmodesmata
- Routes for signalling substances to pass from cytoplasm of one cell to another
Pits
Communication between cells, transport of () molecules
Cell wall
Cellulose fibers support the cell, retain rigid structure
Middle lamella
Joins adjacent cell walls together, increasing strength and stability of the plant.
Chloroplasts
Contains chlorophyll which converts light energy to chemical energy by photosynthesis
Vacuole
Provide support, stores water/sugars/minerals/pigments
Cellulose
a) Hydrogen bonds between adjacent cellulose molecules
b) Layers of cellulose microfibrils
c) Criss-cross at different angles to form a mesh like structure, which increases strength
Describe structure of cellulose in plant cell walls
a) Cellulose is an unbranched polymer of B-glucose
b) Joined by 1,6-glycosidic bonds
c) Cellulose molecules are joined by strong hydrogen bonds into cellulose microfibrils
d) Layers of cellulose microfibrils criss cross at different angles, forming a mesh structure
Starch
a) Starch is a polymer of A-Glucose, consisting of amylose and amylopectin
b) Amylose consists of many A-Glucose molecules held together by 1,4-glycosidic bonds
c) Amylopectin consists of many A-Glucose molecules held together by 1,4 and some 1,6-glycosidic bonds.
Starch as a suitable storage molecule
a) Starch consists of many A-Glucose monomers, hence many energy can be stored
b) Amylose is helical, compact storage
c) Amylopectin is heavily branched, hydrolysed to release energy easily
d) Starch is insoluble, no osmotic effect
Why starch needs to be broken down before embryo plant can grow (2)
a) Starch is insoluble
b) Starch is broken down into glucose, which is soluble and can move into the embryo
c) The glucose is used in respiration to provide energy
Describe structure of cell wall of xylem vessel (4)
- Xylem vessel cell walls consists of cellulose and lignin
- Cellulose molecules are held by hydrogen bonds into cellulose microfibrils
- Layers of cellulose microfibrils criss cross at different angles, forming a mesh like structure
- Hemicellulose and lignin are deposited in the secondary cell wall
- Cell wall is lignified in helical or spiral manner
- Bordered pits, which are unlignified regions, are present between xylem vessels 1
*Rings, spirals: for strength/ flexibility
Cellulose molecule VS structure of starch
Similarity:
- Both made of glucose
- Both have 1,4- Glycosidic bonds
Difference:
- Starch made of A-Glucose, Cellulose B-Glucose
- Amylopectin has some 1,6- Glycosidic bonds
- Starch composed of amylose and amylopectin, more than one type of molecule
- Cellulose is unbranched, amylopectin is branched
- All monomers same direction in starch, every other one inverted in cellulose
Explain how structure of cell walls enables to be strong and flexible
- Cellulose molecules are held by strong hydrogen bonds as cellulose microfibrils
- Flexible: microfibrils parallel to each other in layers for flexibility
- Strong: layers of cellulose microfibrils criss cross at different angles into a mesh structure for strength.
- Cellulose microfibrils are embedded in pectin
Lignin
a) Lignin makes xylem cell walls waterproof
b) Lignin provides support and strengthens the cell walls
How secondary thickening in cell wall contributes to physical properties of xylem vessels (3)
a) Secondary thickening provides greater tensile strength
b) Secondary thickening provides extra rigidity/ reduced flexibility
c) Lignin provides waterproofing
d) Pits are present for lateral movement of water in and out of xylem
Less lignin contents and differences in plants
a) Plants cannot stay upright and are drooping
b) Because less lignin in cell walls
c) Less support to the plant leaves and stems
d) Hence xylem vessels collapse
e) Plant will not be supplied with sufficient water.
Sclerenchyma fibers VS Xylem vessels
Functions
Similarity:
- Both used for structural support
Difference:
- Xylem vessels transport water and mineral ions but sclerenchyma fibers do not.
Structure
Similarity:
- Both contain cellulose/ pits/ dead cells/ secondary walls
- Both are hollow and do not contain cytoplasm
Difference:
- Sclerenchyma has end walls but xylem does not.
How is the xylem adapted for its functions?
Transport
a) Hollow tubes, no end walls or cytoplasm: Allow for the movement of water, forming a continuous water column
b) Narrow: Aid capillary action
c) Contain pits which are non-lignified areas: Allow for the movement of water in and out of xylem
d) Lignin: Waterproofing, keeping water in the xylem
Support
a) Secondary thickening, lignin in cell wall: Providing strength
Explain how structure of xylem is related to its function (4)
a) Hollow tubes, waterproof
Allowing for the transport of water and minerals
b) Lignified, secondary thickening
Makes xylem strong, allowing it to provide support to the plant
c) DO NOT have end walls, hollow tubes
Allowing for uninterrupted transport of water, continuous water column
d) Pits, non-lignified areas
Allowing for lateral movement of water and minerals between xylem vessels
Parenchyma depends on functions of xylem vessels
a) Supply water for photosynthesis/ keep cells turgid
b) Supply Mg2+ for synthesis of chlorophyll
c) Supply NO3- for synthesis of amino acids/ protein/ DNA
d) Supply Ca2+ for synthesis of calcium pectate for cell walls structure
e) Supply PO43- for synthesis of ATP/ DNA
f) Support the leaves so they are exposed to sunlight
Phloem function
a) Transport sucrose and amino acids
b) From sources to sinks
Structure and function of phloem
- continous tube / hollow tube: flow of solution / movemenet of sucrose / translocation
- contain plasmodesmata: allow entry / exit of sucrose / water
- companion cells: move sucrose into sieve tube elements, provide ATP for active transport
- cellulose cell wall: withstand pressure
Phloem sieve tube VS Xylem vessel
Similarities:
- Contain cellulose in cell wall
- Tubular structure
- Do not have nucleus
Difference:
- Phloem sieve tubes have sieve plates and perforated end walls but xylem vessels do not
- Phloem sieve tubes do not have lignin/ secondary thickening
- Phloem have plasmodesmata, xylem has pits
