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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,
PTERIDOPHYTES,
GYMNOSPERMS and
ANGIOSPERMS



Streptophyta ­ green
algae plants




Viridiplantae ­ chlorophytes ( noncharophycean)
Growth ­ `irreversible' increase in size.

Development ­ increase in…

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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…

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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.

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The shape of the plant embryo is determined by:


> RATE OF CELL DIVISION

> PLANE OF CELL DIVISION

> DIRECTIONAL CELL EXPANSION



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…

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Very fast life cycle
Self-fertile
Smallest known genome
Complete DNA sequence
27,000 genes
International cooperation




FIRST (ZYGOTIC) DIVISION- asymmetric




Embryogenesis in Arabidopsis

A. Asymmetric first division:
B-D. Cells have different FATES

Suspensor > transverse divisions

Embryo > precise cell divisions

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D. OCTANT:

suspensor & embryo lineages

E-F GLOBULAR: protoderm forms

> future epidermis;

G. HEART: cotyledons initiated

& root meristem formed

H. TORPEDO:

axis extension > future hypocotyl

COTYLEDONARY:

cotyledon greening, vascular tissues




Asymmetric first division is linked to cell polarity & cell fate

· The plane of division is…

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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)…

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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




Meristems

-plant known as annuals complete their life
cycle from germination through flowering
and seed production to death in a single year

-…

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- Roots

- 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…

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zone of cell division blends into the ZONE OF ELONGATION
cell elongate ­ ten times their of their original length.
Even before they finish elongation the cells of the root begin to specialize in structure and
function, where this zones goes to the ZONE OF MATURATION (differentiation)

· SAM and…

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