Plant anatomy Flashcards
Plant meristems
Plant growth and development
Perpetually young and generates new cells and tissues by mitotic cell division
New cells differentiate and form specific tissues with specific functions
Various types of meristems – apical, primary, intercalary, cambium, phellogen
Makes plant growth indeterminate
Apical meristem
Shoot and root are found at tips of all stems and roots that undergo extension growth
Group of cells composed of initials and derivatives
When an initial cell divides one cell remains a meristematic cell while the sister cell becomes a derivative or body cell
Apical meristem = forms primary tissue
Protoderm = epidermis
Ground meristem = ground tissues (parenchyma, collenchyma, sclerenchyma)
Procambium = primary xylem and primary phloem
Ground tissues
Parenchyma
- Found in cortex, pith mesophyll and in vascular rays
- Involved in photosynthesis, storage and secretion
- Alive at maturity (living protoplast) and do not usually have thickened walls
Collenchyma
- Living protoplast at maturity
- Unevenly thickened primary cell wall (cellulose)
- Great plasticity and ideal strengthening tissue for growing organs
- E.g found in stranfs or continuous cylinder below epidermis, bands next to vascular bundles, bordering veins of leaf
Sclerenchyma
- Primary cell wall of cellulose and secondary cell wall, usually with lignin (lignified) and thick
- Often dead at maturity (no chloroplast)
- Tissue is elastic, giving strength to mature organs that have stopped growing
- Two types = fibres and scelreids
- Wood contains a lot of fibres which are long and very elastic (trees bend but retain normal shape)
- Scelrids are short, isodiametric, in mass give hard protective coats = e.g walnut shell
Vascular tissue
Made up of xylem and phloem
Xylem is dead at maturity and responsible for water and mineral transport
Xylem is dead at maturity and responsible for water and mineral transport
Xylem also important in mechanical support
Phloem cells have living protoplast at maturity and are responsible for transport of photosynthate and other organic compounds
Primary meristem (procambium) gives rise to primary xylem and primary phloem
Xylem
- Made up of tracheids and vessel elements in angiosperms
- Other vascular plants have tracheids buy not vessels
- Tracheids and vessels alongated, empty cells with thick, lignified secondary walls
- Both have pits in their walls (thin areas where secondary wall is missing)
- Vessels also have perforations in their walls in areas called perforation plates
- Vessels are wider and usually shorter than tracheids
- Vessels and tracheids have various forms of secondary wall thickenings
- Water travelling through tracheid’s must pass through pit membranes
Phloem
- Principle conducting cells are sieve elements
- 2 types of sieve elements – sieve cells (gymnosperms), sieve-tube members (angiosperms)
- Sieve elements have clusters of pores called sieve areas which allow protoplastic connection between adjacent sieve elemetns
- Sieve-tube members are associated with companion cells
- Phloem tissue is not lignified and is easily crushed
Dermal tissue
Epidermis is the outermost cell layer of the primary plant body
Variable in structure and function
May contain guard cells which regulate the opening and closure of stomata
Often with appendages – i.e trchomes (hairs) and other specialised cells
Trichomes have many functions – protection, reflection, glandular secretion, absorption of water
In terrestrial plants the above ground epidermis is covered with a cuticle (cutin and wax)
During secondary growth, a periderm often replaces the epidermis of stems and roots
Function and structure of roots
Roots are organs specialised for anchorage, absorption, storage and conduction
In gymnosperms and dicotyledons there is usually a taproot system
In monocots the root system is usually fibrous
Not all root are found in soil – e.g aerial roots of epiphytic orchids and pneumatophores of mangrove trees
Mucigel sheath and root cap protect developing root
Many root hair increase surface area for absorption
Root tip
Can be divided into regions of cell division (in apical meristem), elongation and maturation
Root apical meristem gives rise to 3 primary meristems, protoderm, ground meristem and procambium
Apical meristem also gives rise to a root cap which protects the apical meristem
Mucigel which is produced by the outer root cap cells is also protective and aids root in passage through the soil
Epidermal cells in the maturation zone develop root hairs which increase absorbing surface of root
Root anatomy
Primary structure = epidermis, cortex, central stele
- Central stele made up of vascular tissue surrounded by a pericycles, separated from the cortex by endodermis (compact layer of cells)
- Most of cells in endodermis have casparian strip integrated into their primary wall and middle lamella which makes them impermeable
- Endodermis also contains a few unthickened passage cells
- Lateral roots develop in pericycle
Secondary structure = some dicots produce woody roots which result from secondary growth
- Meristematic activity of vascular cambium between xylem and phloem
- Pericycle opposite ridges of xylem also produces vascular cambium
- These meristems give rise to secondary xylem and phloem
- Cork cambium originates in the pericycle producing a periderm which cuts off cortex and epidermis from rest of root
Adventitious roots
Root system already in place in the seed, roots can also be formed later from other places during growth and development – e.g from nodes on stem, from rhizome, from leaves, from cutting = adventitious roots
The shoot
= stem, nodes, internodes, leaves, axillary buds, stem apex
Stems
Axillary buds are produced in angles between leaves and stem
Leaves produced at nodes
Buds are mini shoot with dormant apical meristem covered by bud scales
As well as the typical upright, above-ground stem rhizomes, corms, bulbs, tubers, stolon, tendrils, cladophyll are all stems
Anatomy of stem
Tissue systems continuous throughout plant
Dicot – vascular bundles around edge
Monocots – scattered vascular bundles
Hydrophytes – aerenchyma and central vascular area
Leaf structure and anatomy
Leaves consist of petiole (stalk) and lamina (blade)
Leaf size and shape is genotypically and phenotypically variable – vary shape and size according to environment
May be simple or compound
Usually photosynthetic
Sometimes modified – spines, pitchers, bladders
Made up of primary tissue although petioles may become woody in some species
Vascular tissue in the leaf (midrib and veins) is connected to the vascular tissue of the stem
Palisade mesophyll = elongate parallel cells – densely packed, neatly arranged
Spongy mesophyll = nonparallel cells with large intercellular spaces
Mesophyll = parenchyma cells
Stomata
Pores regulated by guard cells
Guard cells associated with subsidiary cells
May be present on one or both surfaces
Abscission
Leaf drop
Abscission zone comprises an abscission layer (where leaf breaks off) and a protective layer (to preserve stem)
