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Why do multicellular plants need transport systems
Metabolic demands, size and surface area to volume ratio
Metabolic demands
Nutrients obtain in one part of the plant need to be transported to other cells.
Surface area : volume ratio
Multicellular plants have a small SA:V ratio so they can’t rely on diffusion alone for transport.
Vascular system structure in the stem
Vascular bundles are found around the edge to give strength and support.
Vascular system structure in the roots
Vascular bundles are in the middle to help the plant withstand tugging strains.
Vascular system structure in dicot leaves
The midrib is the main vein carrying the vascular tissue and helps to support the structure of the leaf.
Xylem is always
Inside the phloem
Structure of xylem vessels
Long, hollow structures made by several columns of cells fusing together.
Xylem parenchyma
Thick walled cells pack around the xylem vessels, storing food and containing tannin deposits (chemical protection from predators).
Xylem fibres
Long cells with lignified secondary walls that provide extra mechanical strength.
Phloem structure
Living tissue with no organelles, containing phloem sap that transports organic solutes around the plant (up and down).
Sieve tube elements
The main transporting vessels of the phloem
Sieve plates
In the areas between cells, the walls become perforated to form sieve plates
Companion cells
Linked with sieve tube elements by plasmodesmata to perform cell functions.
Meristematic tissue
It is located between the the phloem and xylem tissues and produces stem cells for vascular growth.
Palisade cell specialisation
Contain many chloroplasts, rectangular, thin cell walls, large vacuole
Root hair cell specialisation
Increase surface area of the cell, thin cell wall, vacuole containing ions and sugars
Guard cell specialisation
Thick inner cell wall
Ribosomes
The site of protein synthesis
Rough endoplasmic reticulum
A network of membranes attached to the SER with ribosomes bound to the surface. It is responsible for the synthesis and transport of proteins.
Smooth endoplasmic reticulum
A network of membranes attached to the nucleus, not containing ribosomes. It is responsible for lipid and carbohydrates synthesis and storage.
Golgi apparatus
A structure formed of cisternae which puts proteins into vesicles (lysosomes or secretory)
Lysosome
A specialised vesicle that contains digestive enzymes to break down waste materials.
Mitochondria
Contain a double membrane with the inner membrane folded and containing enzymes to perform aerobic respiration.
Chloroplasts
They have a double membrane with the inner membrane forming a granum which contains chlorophyll for photosynthesis.
Vacuole
Membrane lines sacs containing cell sap to maintain cell turgor.
Peroxisome
Contains enzymes to break down hydrogen peroxide (protection against bacteria).
Nuclear envelope
A double membrane containing the DNA in the nucleus.
Magnification
The number of times bigger an image is than the actual object.
Resolution
The ability to distinguish between two points that are close together.
What is the difference in resolution between light and electron microscopes?
Electron microscopes have a higher resolution, as they used beams of electrons with short wavelengths. This makes it easier to distinguish between different structures.
Light microscopes (8)
Inexpensive, small, simple sample prep, no vacuum, colour, up to 2000x magnification, resolving power is 200nm, samples can be living
Transmission electron microscope
The beam is transmitted through the specimen - best resolution
Scanning electron microscope
The beam is sent across the surface and reflected electrons are collected - resolution is worse
Hydrogen bonding
Polar molecules (water) interact with each other as the positive and negative regions attract each other and form weak bonds.
High boiling point of water
It provides a constant environment for aquatic animals
Solid water is less dense than liquid
Ice floats, forming an insulating layer so that habitats don’t freeze.
Waters cohesive/adhesive properties
It is an efficient transport medium within living things because molecules stick together.
Water acts as a solvent
It is polar so can carry polar molecules dissolved in it and acts as a medium for chemical reactions (cytosol).
Water acts as a coolant
Maintains constant temperatures in cellular environments for enzyme activity.
Water absorption
Roots absorb water from the soil through root hairs with a high water potential by osmosis.
Movement up the stem
Water travels up the stem through xylem vessels by capillary action
Transpiration pull
As water evaporates from the leaves, it creates a suction force that pulls more water up the xylem.
Evaporation
Water reaches the leaves, where it evaporates from a mesophyll cell travels through air spaces and out of the stomata.
Apoplastic pathway
Water moves through cell walls and the spaces between cells - stops at the casparian strip.
Symplastic pathway
Water moves through the cytoplasm of cells through plasmodesmata.
Light as a limiting factor
Increasing light intensity gives increasing numbers of open stomata, increasing the rate of water vapour diffusing out.
Relative humidity as a limiting factor
A high relative humidity will lower the rate of transpiration because of the reduced water vapour potential gradient between the leaf and air.
Temperature as a limiting factor
Increase in kinetic energy of water molecules, increases rate of evaporation.
Air movement as a limiting factor
Wind increases the rate of transpiration because water vapour potential around stomata decreases, increasing diffusion gradient.
Soil-water availability
If it is very dry the plant will be under water stress so will close its stomata and the rate of transpiration will decrease.
Hydrophytes
Plants with adaptations that enable them to survive in wet habitats.
Xerophytes
Plants with adaptations that enable them to survive in dry habitats.
Hydrophyte adaptations (5)
Thin waxy cuticle, open stomata, wide flat leaves, small roots, air sacs
Xerophyte adaptations (5)
Thick waxy cuticle, sunken stomata/hairs, reduced stomata, long/wide roots, curled leaves (marram)
Properties of glucose (2)
Soluble, bonds store lots of energy
Alpha glucose structure
DUDD
Beta glucose structure
DUDU
Maltose structure
Glucose + glucose
Sucrose structure
Glucose + fructose
Lactose structure
Glucose + galactose
Condensation of sugars
Reaction between hydroxyl groups to form a glycosidic bond and water
Hydrolysis of sugars
Reaction between disaccharide and H20 to break glycosidic bond
Polysaccharides include: (2)
Starch (Amylose and amylopectin) and cellulose
Properties of starch
Made of a-glucose, insoluble, large, coiled
Amylose structure
Long, unbranched chain, 1,4-glycosidic bonds, helix
Amylopectin structure
Branched chain, 1,4 and 1,6 glycosidic bonds, easily broken down
Cellulose structure
B-glucose, 1,4-glycosidic bonds, monomers are flipped, long, unbranched chains, H-bonds between chains
Cellulose fibres
Chains form micro fibrils, micro fibrils form macro fibrils, macro fibrils form cellulose fibres
Adaptations/properties of cellulose
Long, unbranched chains, H-bonds add collective tensile strength, micro fibrils provide additional strength
Reducing sugars
Monosaccharides and some disaccharides
Non-reducing sugars
Disaccharides (sucrose) and all polysaccharides
Benedict’s test
Heat in gently boiling water for 5 mins, turns blue - brick red
Qualitative test for reducing sugars
Use a colorimeter to measure the absorbance of each solution
Testing non-reducing sugars
If results for Benedict’s test are blue, add HCl before heating and then sodium hydrogen carbonate before retesting
How does Benedict’s test work?
Reducing sugars react with Cu2+ ions in Benedict’s reagent, reducing them to brick-red Cu+ ions. For non-reducing sugars, the sugars are hydrolysed by the acid - turns sucrose to glucose and fructose.
Biosensors process
Protein interacts with molecule under investigation
Cause change in the transducer which produces a response
This produces a visible signal which can be read (colour/electrical)
Diffusion
The net movement of particles from a region of higher concentration to a region of lower concentration.
Facilitated diffusion
Diffusion across a membrane through protein channels
Active transport
The movement of molecules into or out of a cell from a region of lower concentration to a region or higher concentration requiring energy (ATP) and carrier proteins.
How does active transport work?
molecule being transported binds to receptors in the carrier protein
On the inside of the cell, ATP binds to the carrier protein and is hydrolysed into ADP and phosphate.
Binding of the phosphate molecule to the carrier protein causes the protein to change shape.
The molecule is released from the protein and recombined with ADP to from ATP
Bulk transport
Large molecules are too large to move through a channel or carrier protein so they are transported by endocytosis and exocytosis.
Endocytosis
The bulk transport of material into cells - the cell-surface membrane invaginates and enfolds the material to form a vesicle
Exocytosis
The reverse of endocytosis - vesicles formed by the Golgi apparatus move towards and fuse with
Translocation
Plants transport organic compounds by active transport in the phloem from sources to sinks
Assimilates
The products of photosynthesis that are transported in the phloem
Actively loading (phloem)
H+ ions are actively transported out of companion cells into surrounding source cells.
H+ is co-transported along its concentration gradient back into companion cells with sucrose.
Sucrose can then diffuse along its concentration gradient through plasmodesmata from companion cells to sieve tube elements.
Unloading (phloem)
when solutes are actively loaded into sieve tube elements (STE) from companion cells at the source, the water potential decreases
Water enters the STE from the xylem and companion cells by osmosis
This increases hydrostatic pressure in the STE at the source
At the sink solutes are actively removed from the STE
This increases the water potential in STE at the sink.
This creates a pressure gradient, pushing solutes from the source to areas of lower pressure at the sink
Communicable diseases in plants
Pathogens are spread directly - contact, pollen/seeds, spores in soil
Ring rot
bacteria - clavibacter michiganensis
Infects potatoes, tomatoes and aubergines
Damages leaves, tubers and fruit
No cure + lasts at least 2 years
tobacco mosaic virus
viral
Infects tobacco plants +
Damages leaves
Resistance crop strains
Potato blight
protoctist (fungus-like) - phytophthora infestans
Hyphae penetrate host cells
Destroys leaves, tubers and fruit
Resistant strains + chemical treatments
Black Sigatoka
fungus - mycosphaerella fijiensis
Banana disease
Attacks leaves (black)
Hyphae penetrate and digest cells
Resistant strains + fungicide treatment
How plants recognise attack
receptors in cell membrane recognise pathogen molecules
Stimulates release of signalling molecules
Causes nucleus to trigger cellular responses - defense chemicals + alarm signals
Physical defenses
Callose is a polysaccharide containing beta-1,3 linkages and beta-1,6 linkages between glucose monomers. Molecules act as barriers in cells walls + block sieve plates / plasmodesmata.
Insect repellents
Pine resin, citronella from lemon grass
Insecticides
Pyrethrins from chrysanthemums act as neurotoxins
Caffeine is toxic to insects and fungi
Antibacterial compounds
phenols
Cotton gossypol
Defensins (proteins)
Antifungal compounds
phenols
Defensins
Saponins against membranes
Chitinases break down chitin cell wall (fungi)
Anti-oomycetes
Glucanases break down glucans in cell walls (protoctists)