Plant structure and growth and it occurs

1. BIO 304
Plant Structure and Physiology

2. Assessment
• 60 % exam 40% coursework
• CATs 2 = 20%
• Practical work 10%
• Individual task 10%
2

3. Bio 304
Contents
• Plant structure and growth
• Plant transport
• Plant nutrition
• Plant growth substances (hormones)
• Photosynthesis

4. BIO 304 Part 1
Objectives:Objectives: at the end of this section the
student will be able to:
Relate plant structure to functions
Describe the main stages of plant growth,
development

5. Plant growth
• Annuals –life cycle is complete in one year; it
germinates, flowers and dies.
• Biennials- life cycle takes 2 years. First year-
plant grows leaves, stems, and roots (vegetative
structures), then enters a period of dormancy
over the colder months- next season it flowers
and dies.
• Perennials- grows for more than 2 years
5

6. Ancient trees
4700+ Bristlecone pine Baobab - 6000 yrs old?
6

7. A1 Overview of primary and secondary
growth
A = in woody stems,
lateral meristems add
secondary growth,
increasing the girth of
roots and stems
B = Apical meristems
add primary growth in
length

8. A1 Overview of primary and secondary
growth (cont.)
C = The vascular
cambium adds
secondary xylem and
phloem
D = The cork cambium
adds secondary
dermal tissue

9. A 2A 2
Revision ofRevision of
importantimportant
plantplant
tissuestissues::
Dermal-,Dermal-,
ground- andground- and
vascular tissuesvascular tissues

10. A2 Overview of important plant structures

11. A 3 Examples of differentiated plant cells
Parenchyma cells
A relatively unspecialized plant
cell type that carries out most of
the metabolism, synthesizes and
stores organic products, and
develops into a more
differentiated cell type (see next
slides).

12. A 3 Examples of differentiated plant cells
Collenchyma cells
A flexible plant cell type that
occurs in strands or cylinders
that support young parts of the
plant without restraining
growth. They e.g. support
young parts of the plant shoot

13. A 3 Examples of differentiated plant cells
Sclerenchyma cells
A rigid, supportive plant cell
type usually lacking protoplasts
and possessing thick secondary
walls strengthened by lignin at
maturity.
In plant cells, the wall is
formed of cellulose
fibers embedded in a
polysaccharide-protein
matrix. The primary cell
wall is thin and flexible,
whereas the secondary
cell wall is stronger and
more rigid and is the
primary constituent of
wood.

14. A 3 Examples of differentiated plant cells
Xylem
The tube-shaped, nonliving
portion of the vascular
system in plants that carries
water and minerals from the
roots to the rest of the plant.
The water-conducting
cells of the xylem
Tracheid
A water-conducting and
supportive element of xylem
composed of long, thin cells
with tapered ends and walls
hardened with lignin.

15. A 3 Examples of differentiated plant cells
Sugar-conducting cells
of the phloem
Phloem
The portion of the vascular
system in plants consisting of
living cells arranged into
elongated tubes that transport
sugar and other organic
nutrients throughout the plant.

16. A 3
Primary
tissues
in young
roots

17. A 4 Secondary Growth
1 = Primary growth of the apical
meristem is nearing completion.
Vascular cambium has just formed.
2 = Primary growth continues in
apical bud. In this section only
secondary growth occurs. Stem
thickens as vascular cambium forms
secondary xylem to the inside and
secondary phloem to the outside.

18. A 4 Secondary Growth
3 = Some initials of the vascular
cambium give rise to vascular raysvascular rays
Cambium cells
that produce
radial lines of
parenchyma
cells known as
xylem rays
and phloem
rays.

19. A 4 Secondary Growth
4 = When cambium’s diameter
increases, the secondary phloem
and other tissues (including
epidermis) rupture because they no
longer divide and cannot keep
pace.
A second meristem, the cork
cambium, develops from
parenchyma cells in the cortex. The
cork cambium produces cork cells,
which replace the epidermis.

20. A 4 Secondary Growth
5 = In year 2 of secondary growth,
vascular cambium produces more
secondary xylem and phloem; cork
cambium produces more cork.
6 = Stem diameter increases, the
outermost tissues exterior to the cork
cambium rupture and are worn off.

21. A 4 Secondary Growth
6 = As the stem’s diameter increases,
the outermost tissues exterior to the
cork cambium rupture and are shed
7 = When none of the cortex is left,
the cambium develops from phloem
parenchyma cells
8 = The cork cambium and the
tissues it produces are called
periderm
9 = bark consists of tissues exterior to
the vascular cambium

22. A5 Growth rings in tropical trees
• May not have them unless the tree is growing in
areas which have definite wet and dry seasons
• Dry season would act like cold winter, and slow
growth.
• Start of wet season would promote growth
again, so rings may be visible
22

23. A 6 The role of the vascular cambium
A = Secondary xylem and
secondary phloem being added in
equal amounts. NOTE: cambial
initials produce much MORE Xylem.
B = A cambial initial can divide to
from a new initial (= undifferentiated
cell) and either a secondary xylem
cell (X) or secondary phloem (P)
C = A cambial initial (C) can divide
to form two cambial initials,
increasing the circumference of the
vascular cambium

24. A 6 The role of the vascular cambium
D = Most of the thickening is
from secondary xylem

25. A 7 The anatomy of a tree trunk
A = Secon-A = Secon-
dary xylemdary xylem
B = BarkB = Bark

26. 26

27. Morphogenesis in plants: control of organ development
• Development of flowers from meristem has
been studied in Arabidopsis thaliana (thale
cress)
• Easy because: small size, many seeds, rapid life
cycle, small genome, easy to cause mutations.
• Meristem cells are undifferentiated
• 3 organ identity genes code for proteins that
cause cells to differentiate into whorls of flower.
27

28. Arabidopsis thaliana
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29. A 8
29
If only A only sepals
If A and B sepals and
petals
If A and C sepals
and carpels
If only C only carpels

30. The ABC hypothesis
30

31. 31
Genes
(a) The four organs of a flower
—carpel (yellow), stamens
(green), petals (purple), and
sepals (pink)—grow in whorls
that develop from meristems.
Mutation in one of three
organ identity genes
occurs one type of organ
replaces another.
Mutations helped scientists
know the pattern of gene
expression that p
roduces normal flowers

32. Application: Two uses in horticulture/agriculture
A9
32
C genes control development of carpels
Carpels develop into grains we eat
More active C genes more carpels  more food
Transgenic orange trees containing leafy gene
produce flowers (therefore fruits) much earlier than
normal trees.