Plants Flashcards
Name four structure which are plant cells but are not found in animal cells
Chloroplast
Permanent vacuole
Cellulose cell wall
Plasmid such as amyloplast
Primary cell wall
Middle lamella
Middle lamella is first layer -when a plant cell divides into two new cells
Mainly consists of pectin (polysaccharides) which act as a glue and holds the cell walls of adajecent plant cell together
Pectin -negatively charged carboxyl group combine with positive calcium ion to make calcium pectate
Cellulose microfibrils and the matrix build up on both sides of the middle lamella
-walls are flexible with all microfibrils being arranged in the same direction
Secondary cell wall
Secondary cell walls build up with the microfibrils densly laid at different angles to each other which makes the composition much more rigid
Hemicellulose helps harden it further
Lignin is added to cell wall to produce wood makes it more
—> rigid
What are plasmodesmata?
Cytoplasmic bridges that connect the cytoplasm of neighbouring cells
The cell walls are thinner in the region of plasmodesmata
- channels of cytoplasm that pass between adjacent cells walls of plant cells that allows fast communication and exchange of substances between cells
What are symplast?
Interconnected cytoplasm of the cells
What is middle lamella
The first layer of the plant cell wall to be formed when a plant cell divides, made mainly of calcium pectate(pectin) that binds the layers of cellulose togther
What are pits
In secondary thickening, area around the plasmodesmata dont have secondary thickening in them which leave thin areas of the wall called pits
There is no cytoplasm in xylem cells, but pits allow water to move between the vessel which is essential in maintaining a flow of water at even pressure
Thin areas of cell wall in plant cells with secondary thickening , where plasmodesmata msintian contact with adjacent cells, simple holes which allows water move out into the surrounding cell
Describe the strcuture of the permanent vacuole found in plant cell
A membranous sac that contain cell sap -(dissolved sugar and salts)
—> which cause water to move inside the cell by osmosis, which keeps the cell turgid
Vacuole mainly maintain the shape of the cell, as well as store pigments which will prevent them from leaking to the cytoplasm unless it heated, they also store protein
Contain lytic enzyme and act similarit to lysosome and they also store waste product
What are chloroplast
A small flattened structure that contains a double membrane. The inner membrane is stacked into thylakoid . Contain chlorophyll which is green pigment that absorb light for photosynthesis
Similarities of chloroplast and mitochondria
Large organelle
- > diameter (4-10 um)
- > thick (2-3 um)
Contain their own DNA
Surrounded by an outer membrane
Have an enormously folded inner membrane that gives a greatly increased surface area where enzyme-controlled reaction take place
Difference of chloroplast and mitochondria
Site of photosynthesis
Contain chlorophyll
-green pigment that is largely responsible for trapping the energy from light , making it available for plant to use
Describe amyloplast
An organelle found in some plant cells that synthesises and stores starch molecule and breaks them down to glucose when the cell requires it
Primary function of stem
Stem is support to hold the leaves in the best position for obtaining sunlight for photosynthesis
Movement of material such as water and mineral ions
What is parenchyma
Relatively unspecialised plant cell that act as packing in stem and roots to give support
And can be modified suitabel for storage or photosynthesis
What is collenchyma
Plant cells with areas of cellulose thickening that gives mechnical strength and support to the tissue
Due to the thick primary cellulose walls
What are sclerenchyma
Plant cells that have very thick lignified cell walls and an empty lumen with no living content
Propterties of sclerenchyma
Provide support to the plant, much like xylem vessel
-made of bundle of dead cells that run vertically up the stem
Have strong secondary walls made of cellulose microfibrils positioned at right angle
Ligin deposited on the cell walls of fibres , makes the fibre strong but flexible
The strength of the fibre depend on their length , how much ligin it contains
When the fibre liginfied , the cell content dies because water cannot pass through and so fibre becomes a hollow tibe
The cell can no longer grow so plant growth has to be highher up in the stem
Structure of parenchyma
Consist of thin walled living cells
They are involed in food storage
Comprises a thin cell wall and made up of cellulose
Sturcutrw of collenchyma
Consist of thin walled living cells
Mechanical tissue in particulary dicot stems
Comprises an uneven thick primary cell wall and is made up of pectin and hemicellulose
Strucutre of sclerenchyma
Consists of dead cells
Mainly mechnical tissue
Comprises a hard and thick cell qall and is made up of lignin
Function of parenchyma
Is to store and assimilate food. Hence , they are referrd to as food storage tissue
Stores waste product of plants
Serves as a packing tossie to fill the spaces between other tissues and maintian the plant shape and firmess
Function of collenchyma
Provides mechanical support and elascitt to the stems of dicot plants
Cells possess chloroplast the involved in manufacturing sugar and starch
Provides tensile strength and flexibility to the plant body
Function of sclerenchyma
Provides mechical strength to the plant
It makes the plant body rigid, flexible and elastic
Structure of xylem
Vessel are long tube like strucutre that are formed from dead cells, joined end to end but they have no end walls, making for an uninterrupted tube that allows water and minerals ion to pass up through it easily
Walls are thickened by ligin which helps support the plant
What is a protoxylem
Not fully ligified (can stretch and grow)
The cellulose microfibrils in the walls of the xylem vessel are arranged vertically in the stem
—> increasing strength of the tube
Allowing it to resist the compression force from the weight of the plant pressing down on it
What is Metaxylem
Increasing amount of lignin are incorporated into the cell walls as the stem ages and the cells stop growing
Means that the cells become impermeable to water and other substances
—> tissue becomes stronger and more supportive but the content of the cell dies
The end walls between the cells mostly break down so the xylem forms hollow tubes which go from the roots to the tip of the stems and leaves
What transport in xylem and system
Water and mineral ions are transported from the roots to the leaves and shoots in the transpiration stream
Water moves out of the xylem into the surrounding cells through the specialised pits in the walls of the xylem vessels
Where are xylem located
Located around stem and part of the vascular bundle
What does phloem transport and
Phloem is made of living tissue and transport food molecules around the plant, both up and down in active process - translocation
—> from leaves to tissue where needed
Structure of phloem
Phloem is made up of many cells that are joined togther to form very long tubes
Cells dont get lignifed and this the content remain living
As a result of the cell walls being pirced , specilaised sieve plates will form and the phloem sap flows through the holes in these plates
Mature phloem cells have no nucleus, tonoplasat and some other organelle as they break down while the gaps in the sieve plate are being made, filling the phloem sieve tube with phloem sap
The phloem surivial relies on the companion cells which are very active cells with orgnelles, they are connected to the phloem sieve tubws through the plasmodesmata
The cell membrane of the companion cells have many inner foldings that increase the surface area over which they transfer sucrose into the cell cytoplasm, as well as many mitochondria to provide the needed ATP
Similarities of plant stem
Both are plant transport tissue
Both have lot of water moving through them
Both found togther in vascular bundles in plants
Difference in xylen
Xylem
- water mineral ions are transported in the xylem
- xylem cells are living when first formed but become heavily lignified , so cell contents die
- comprises hollow tube running through plants
- water moves through xylem in transpiration stream carrying minerals with it
Water leaves xylem through pits
-provide important structural support for plant
Difference in phloem
Contains product of photosynthesis
Eg suvrose transported in the phloem in the solution in water
Phloem sieve tubes are made of many cells joined togther to form tubes with perforated sieve plates between them
Phloem sieve elemnts are not dead but have lost most their functions; they are a tube filled woth phloem sap - cell habe no nuclei
Phloem cells only survive because they are supoorted by companion cells which are very active and lunked to phloem cells by many plasmodesmata
Parenchyma structure
Found throughout the body
—> outer layers of parenchyma cells in the stem may contain chloroplast
—> stem is modified into collenchyma and schlerenchyma
Can differentiate into other kinds of cells
Alive;metabolically active
Functions in photosynthesis, storage, and secretion
Sclerenchyma
Specialised for strucutural support
- cells have primary walls and strong thick secondary walls
- pits allow exchange of substances between adjacent living sclerenchyma cells
-mature functioning cells are dead
What does sclerenchyma contain
Lignin deposited on the cell walls of these fibre in a spiral which makesthe fibre strong and flexible
Sclerenchyma how does the strength of the fibres depends what
Strength of the fibre
- length
- how much it is lignified ( how much lignin it contains)
Schlerenchyma what happens when the fibre is lignified
When it is lignified the cell content die because water cannot pass through lignin
—> fibres become hollow tube
-once this happen cell can no longer grow , so plants growth has to be higher up in the stem
