Plant tissues Flashcards
All eukaryotic cells have…
(2)
- Crucial physiological, biochemical and molecular functions.
- Non-static cytoplasm.
Characteristics unique to plant cells.
(6)
- Different composition of plasma membrane
- Rigid cell wall.
- Middle lamella
- Presence of vacuole
- Absence of intermediate filaments.
- More extensive range of plastids and microbodies.
Composition of macromolecules in plasma membrane of plants.
- Lower concentrations of cholesterols
- Higher concentration of complex sterols.
- The range of sterols is much greater as they have to adapt to the environment rapidly.
Vacuole
Required for cell turgor.
Contains water and important solutes for cellular function.
Features of nuclei common to most eukaryotic cells
(6)
- One nucleus containg the cells DNA
- Double membrane of nuclear envelope is part of ER.
- nucleolus
- Heterochromatin
- similar cell cycle components and regulation stages.
- Nuclear pore complexes
Nucleolus
- Site of nuclear ribosome synthesis - where RNA is made.
- rRNA subunits come together to make up 80S ribosomes in all eukaryotes.
- Size of ribosomes is different in plastids
Heterochromatin
10%: multi-coiled, usually found at the periphery
Non-coding DNA
Nuclear Pore Complexes
- High order quaternary protein complex aggregates.
- supramolecular sieves that control export and import.
- Proteins require nuclear localisation in N-terminal sequences to gain entry.
A feature of the plasma membrane common to all living cells …
… are fluid-mosaic model holds.
This is the lipid bilayer with hydrophobic regions facing each other.
Fluid = things can move
Mosaic = things imbedded in that can also move.
Leaflets have different compositions of peripheral and anchored proteins, but share integral protein complexes.
Features of plasma membrane in plant cells
- Higher proportion of many types of sterols.
- Lower concentration of cholesterol.
- Contain galactolipids in the head groups of chloroplast membranes.
Galactolipids
allow phosphates to be used for other essential cellular processes.
More effecient process evolved in ancestral prokaryotes.
Features of vesicle transport common to eukaryotic cells
(3)
- Plasma membrane of living cells is never static
- Secretory pathways are mediated by COPII-coated vesicles.
- Endocytotic pathways are mediated by clathrin-coated and COPI-coated vesicles
Characteristics of vesicle transport unique to plants and fungi.
(2)
- More transport of sterols to plasma membran and glycoproteins
- Sterols make up a high proportion of the plasma membrane, particularly in the leaf epidermal cells and seed coat cells.
Features of the endomembrane system in eukaryotic cells.
(4)
- Forms close associations with different organelles
- Certain proteins are specific to each type of association
- Rough and smooth ER
- Produce microbodies such as peroxisomes and oil bodies.
Microbodies
- Small specialised organelles with no DNA or ribosomes.
- Have simple plasma membrane leaflets.
- Carry out specific and specialised enzymatic reactions.
- Known as semi-autonomous, because they can grow, divide, or fuse
Key characteristics unique to plant cells
(5)
- ER shared between cells.
- Transvascular strands
- Predominantly polygonal network structure in elongated plant types
- Cisternae
- Unique protein - plasma membrane associations
Cisternae
Used for processing proteins.
More flattened and very prevalent in young plant cells.
Microbodies in eukaryotic cells have a …
… single leaflet membrane. They carry out specialised functions of intermediate metabolites. They house compounds and contain no DNA or ribosomes.
Oil bodies
Store triglycerides in seeds
Peroxisomes
Contain catalase to quickly degrade hydrogen peroxide, which can be generated as a by-product of inefficient photosynthetic processes in leaves.
Glyoxysomes
specialised peroxisomes that are particularly found in large quantities in storage plant cells. They process fatty acids to make acetyl coenzyme A and sugars, which are needed for metabolic processes in mitochondria.
Features of plastids common to living cells
(6)
- Highly specialised organelles such as mitochondria
- Have complex double membrane (two leaflets) made up of galactolipids
- Have their own DNA and ribosomes
- Semi-autonomous, so can grow, divide, fuse and be degraded.
- Are moved around the cytosol via actin microfilaments.
- Highly dynamic - readily undergo fission or fusion
Plastids in plants
Chloroplasts - energy producing organelles with a third set of membranes called thylakoids, which are specialized to promote efficient photosynthesis.
More types of plastids are possible in different plant cells.
Proplastids
Predominantly found in meristem cells.
Membrane is rudimentary and internal grana are missing
Etioplasts
internal lattice of rudimentary membranes which will develop into grana
Leucoplasts
Contain no pigments
Cell walls of fungi
Fungi have chitin-based cell walls
Soluble proteins are important for …
… cell-cell signalling
Secondary cell wall
Present in the vascular tissue of many plant groups and all woody plants.
Also present in tissues that are water-impermeable,
Ligin is important in the walls of water-conducting plant tissue.
Intercellular junctions in animal cells
Animals are mobile.
Cells only have a plasma membrane, so junctions are needed for adhesion and cohesion.
* Tight junctions
* Desmosomes
* Gap junctions
Intercellular junctions of plants
Plants have a sessile lifestyle.
They have a partially permeable primary cell walls stuck together with a gel-like middle lamella for organism flexibility. Specialised tissues have additional impermeable secondary cell walls for organism ridigity.
Only have one type of junction - plasmosdesmata
Plasmodesmata
Used for osmotic control and communication.
Desmotubules link to the ER and contribute to biomechanical sensing and signalling.
Can have a complex architecture to maintain cell wall integrity.
Cells
- Usually all perform housekeeping functions
- Can be specialized. Form often relates to function.
- They also often have unique biochemical profiles.
- In plants, 40 different cell types that fall into three main types/groups
Tissue
- Uniform-looking group of cells which perform a specialized function.
- Three main types/groups in vegetative phase
Organ
Different tissues made up of groups of different cell types
Plants have two phases in their life cycle…
… vegetative and reproductive.
The three types of plant cells/tissues
- Dermal
- Ground (cortex)
- Vascular
Dermal cells/tissues
May form several protective layers
May also have additional associated cells:
* Epidermis.
* Guard cells.
* Trichromes
* Periderm
Epidermis
Non woody plants and non-woody parts
Single layer, often has a cutic.e to prevent water loss.
Guard cells
Control water loss and affect gaseous exchanges
Trichomes
On leaves and stems
Additional physical barrier or may have a secretory function.
Periderm
Roots and stems of woody plants.
secondary cell walls of dermal tissue are reinforced with lignin and suberin.
These cell layers exposed to the environment are dead.
Ground/cortext cells/tissues
- Three types of tissues:
1. Parenchyma
2. Collenchyma
3. Sclerenchyma - Supportive and connective
- Carry out most of the housekeeping biochemical functions in plants
- Longitudinal.
- Only primary cell walls, so reduced rigidity.
Parenchyma cells
(5)
- Most common type of ground cell
- Least specialized but perform key metabolic functions
- Have thin and flexible primary walls and lack secondary (lignified) walls
- In roots, they contain colourless plastids that store starch (amyloplasts)
- They also retain the ability to differentiate into other types of cells
Collencyma cells
(5)
- Differentiated (adapted) parenchyma cells.
- Collenchyma cells are grouped in strands and help support young parts of the plant shoot.
- They have thicker and uneven cell walls – layering of primary cell wall.
- They lack secondary walls.
- This ensures that these cells provide flexible support without restraining growth
Sclerenchyma cells
(3)
- Differentiated (adapted) parenchyma cells which die once secondary walls are laid down.
- Sclereids: short and irregular in shape and have thick lignified secondary walls. Found in seed coats, nut shells, and the texture to pear fruits.
- Fibers: long and slender and arranged in threads
The xylem and phloem are examples of _ cells/tissues
Vascular
Xylem cells
- Conduct water
- Tracheids
- Vessel elements
Tracheids
- Type of xylem cell
- common to most plants
- Long, thin, tapered ends
- promote lateral movement of water
Vessel elements
- Type of xylem cell
- Tall trees
- more robust (lignified) vascular tissue
- Perforated end walls or no end plates:
- promotes upward movement
Phloem cells
(6)
- sucrose conducting
- Sieve-tube elements.
- Non-conducting companion cell: Nucleus and ribosomes serve both cells.
- In some plants, companion cells load sucroseinto the sieve-tube elements.
- P-protein are active in transport - controls how nutrients move through sieve.
- Is associated throughout the endomembrane system.
Sieve-tube elements
- Only type of phloem cells.
- Alive at functional maturity
- No nucleus, ribosomes, vacuole and cytoskeleton
- Porous end sieve plants
- Can conduct nutrients
