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  • Created on: 18-11-12 12:53
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Lecture 8: plant biology
Plants are ancestors of animals
Three version of the plantae kingdom
Embroyphytes ( plants with embryos- land
plants ), which included BRYOPHYTES,
Streptophyta ­ green
algae plants
Viridiplantae ­ chlorophytes ( noncharophycean)
Growth ­ `irreversible' increase in size.
Development ­ increase in number or organs, accompanied by differentiation.
Meristem ­ region of undifferentiated stem cells producing new tissues by cell division.
Basic plant organs ­ roots, stems, and leaves ­ contain several types of tissues
Roots ­ monocots like grass have FIBROUS ROOT SYSTEMS- extends plant's exposure to soil water
and mineral. ­ dicots have TAPROOT system ­ one large vertical root
Stems ­ alternating system of nodes ­ point at which leaves are attached. INTERCODES stem
segment between nodes.
AUXILLARY BUD ­ between leaf and stem. Has potential to form vegetative branch
Growth of a young shoot is usually concentrated at the apex tip ­ TERMAINAL BUD
APICAL DOMINACE - terminal bud responsible for inhibiting the growth of the auxiliary bud

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Leaves ­ consist of flattened blade and a stalk, the peptiode, which joins the leaf to a node of the
stem . monocots ­ parallel major veins , run length of the leaf blade. Dicot leaves ­ multibrancehed
network of major veins
Tissues systems include- dermal, vascular, ground
Plant growth and development
­ Cell division
­ cell expansion
­ cell specialization
­ Apoptosis
Development and maintenance of a distinctive architecture (bodyplan) throughout life.
Increase in length by the activity of primary meristems.…read more

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When does pattern formation occur? During embryogenesis
Embryos are polar structures
Between primary walls of adjacent cells is the middle lamellae- thin
layer rich in sticky polysaccharides called pectin
Middle lamellae glues the cells together. When cell matures and stops
growing, it strengthens its wall.…read more

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The shape of the plant embryo is determined by:
Plant cell expansion
Extension occurs when water enters the central vacuole by osmosis ­ this accounts for 90%
of cell expansion
Most of the water is packaged in the larg central vacuole- forms by the coalescence of
numerous smaller vacuoles
Orientation of cellulose micro fibrils in the inner most layers of cell wall causes this
differential growth
Microfibrils cannot
stretch- cell expands…read more

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Very fast life cycle
Smallest known genome
Complete DNA sequence
27,000 genes
International cooperation
Embryogenesis in Arabidopsis
A. Asymmetric first division:
B-D.…read more

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suspensor & embryo lineages
E-F GLOBULAR: protoderm forms
> future epidermis;
G. HEART: cotyledons initiated
& root meristem formed
axis extension > future hypocotyl
cotyledon greening, vascular tissues
Asymmetric first division is linked to cell polarity & cell fate
· The plane of division is thought to be determined by the asymmetric distribution of factors in
the zygote, that somehow direct the positioning process.…read more

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Evidence for the role of positional information in specifying cell fate
· Cells within differentiated tissues, such as leaf tissue can be induced to REDIFFERENTIATE into
a completely new embryo or plant, containing the FULL RANGE OF CELL TYPES- totipotency
· Involves a change in the relative position (local contacts) of cells.
· Steward 1964 > carrot root cells regenerated into whole plants
What does this mean for plants?
· 1. Differentiated plant cells are usually NOT irreversibly committed
· 2.…read more

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Lecture 9: Meristems & Organogenesis
Growth in organisms is irreversible as the organism
increases in size
There are two components in plant growth
Cell proliferation
Cell growth
-plant known as annuals complete their life
cycle from germination through flowering
and seed production to death in a single year
- biennial ­ if a plant's life generally spans
two years e.g. carrots
- perennials ­ plants thatlive many years e.g.…read more

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- stems
- Leaves
- Flowers
Apical meristems
Tips of roots and buds of shoots
Primary growth ­ elongation enables
roots to ramify throughout the soil and
shoot to increase their exposure to light
and co2
Restricted to the youngest parts of the
plant ­ tips of the roots and the shoots
Herbaceous ­ only primary growth
Secondary growth ­ progressive
thickening of the roots and shoots
Product of lateral meristems (older regions of
the roots and stem) - cylinders of dividing cells…read more

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cell elongate ­ ten times their of their original length.…read more


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