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STUDY GUIDE PLANT STRUCTURE & REPRODUCTION
CHAPTER 32
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Monocots – Dicots
Plant organs – root system is formed of roots, branches, root hair and root caps.
Shoot system is formed of stem and its branches, leaves, flowers and fruits.
Apical dominance is growth of only terminal bud and axillary buds remain dormant.
Meristems: retain the capacity to divide and result in plant growth. Apical meristems lie at the
apices of stems and roots and result in primary growth – increase in length. Lateral meristems
lie in mature roots and stems and result in formation vascular bundles.
6. Permanent tissues lose the capacity to divide and become specialized. 3 basic types of Plant
cells: most plant cells are Parenchyma – living cells perform storage and photosynthesis.
Collenchyma cells are with partially thickened walls and are present in growing stems and other
tissues. Schlerenchyma are dead cells with very thick walls provide mechanical strength. They
can be long, Fibers or branched, Sclereids.
7. Plant Tissues: Dermal tissue – covers plant surface, epidermis is one layer of parenchyma in
young / primary tissues. It is covered with waxy cuticle to prevent water loss. Cork replaces it in
secondary tissues. Ground tissue – is specialized for storage and is present between dermal and
vascular tissues. For example Mesophyll of leaves. Vascular tissue – Xylem is the tubes formed
of dead cells and conduct sap (water and minerals). Phloem is the tubes of living cells and
conducts the organic foods like sugars between leaves and roots. Xylem and Pholem are
arranged in Vascular Bundles.
8. Xylem has 2 main types of tubes, vessels and tracheids.
Vessels
Tracheids
1. Wide and multicellular formed of vessel elements
1. Narrow and unicellular
2. No end walls between vessel elements
2. Tracheids have end walls
3. Present in angiosperms
3. Present in all seeded plants
9. Phloem: Angiosperms have Sieve tubes formed of a row of sieve tube members and companion
cells. Seedless vascular plants and most gymnosperms have sieve cells. Sieve cells have smaller
pores than sieve tube members. Sieve tube members are arranged end to end to form sieve
tubes.
Anatomy of roots and stems:
Root
Stem
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Root has a root cap and root hair
Vascular bundle has either xylem or phloem
o
o
Stem has nodes and internodes
Both xylem and phloem present
in vascular bundle
•
Xylem and phloem bundles alternate with
each other
o
Xylem is internal and phloem is
external in same bundle
•
Protoxylem, first formed xylem is external.
o
Protoxylem is internal.
10. Primary Growth: leads to increase in the length of shoots and roots due to Apical Meristems .
11. Secondary Growth: is the increase in girth = thickness of shoots and roots. It usually takes place
in dicot plants. It takes place in 2 regions. 1st is from Vascular Cambium and secondary xylem =
wood is added on inner side of cambium. Secondary phloem is added on outer side of cambium.
Wood in secondary growth of stems often displays Annual Rings due to different thickness and
quantity of vessels formed in spring/summer versus fall/winter seasons.
12. Old wood, dark in color, is accumulated at center, stops conducting sap and is called Heartwood.
Younger wood is outer, light in color, conducts sap and is called Sapwood. 2nd is from Cork
Cambium and adds dead cells of Cork, the dermal tissue. Bark refers to all tissues of a mature
root or stem outside vascular cambium.
Leaf Anatomy
13. Leaf has upper and lower epidermis. Most leaves have stomata in lower epidermis. Each stoma
is guarded by a pair of Guard Cells.
14. Plants lose water by evaporation from stomata – Transpiration. Stomata also used for gas
exchange.
15. Vascular Bundle: Xylem and phloem surrounded by a bundle sheath lie in veins. Veins bring
water and minerals and take away sugars.
16. Mesophyll – Parenchyma cells with large # of chloroplasts lie around the bundle sheath.
Mesophyll performs photosynthesis. In dicot leaves it has 2 distinct regions Palisade layer below
upper epidermis and Spongy Parenchyma around bundle sheath.
Ascent of Sap – water movement
17. Root Pressure: Water enters roots due to osmosis, it leads to Root Pressure.
18. Adhesion: walls of vessels and tracheids pull water up. It leads to Capillary action.
19. Transpiration is loss of water by evaporation mostly through stomata. It leads to upward pull –
tension.
20. Cohesion keeps water molecules together due to H-bonds. Narrow vessels/tracheids have
greater cohesion.
21. Cohesion-Adhesion-Tension theory of ascent of sap: This combined force is enough to carry
water up in the tallest trees.
22. 2 Guard cells regulate transpiration by closing or opening the stomata
Transport of sugars
23. Translocation: It takes place in Phloem tubes and is done by Pressure-flow mechanism.
24. Sugar from the leaves (source) is actively loaded in phloem tubes.
25. Water enters from the xylem.
26. The combination creates a pressure. This pressure pushes the sugar towards Root (sink).
27. Water returns through xylem.
28. In early spring source and sink can be reverse.
Essential Plant Nutrients:
29. Plants need many mineral nutrients from soil. But N-P-K are 3 most critical plant nutrients.
Symbol K stands for potassium.
30. Nitrogen – part of proteins and nucleic acids
31. Phosphorus – part of ATP and nucleic acids.
32. Potassium – helps guard cells to regulate opening and closing stomata
33. Calcium – part of cell walls
34. Magnesium – part of Chlorophyll
35. Sulfur – part of amino acids
Chapter 33
36. Life Cycle of an angiosperm: Adult plant is a Sporophyte, diploid and has true roots, stem,
leaves, flowers, fruits and seeds. Gametophytes are separate and more reduced than in any
other plant group. Pollen is male gametophyte produces 2 sperms in pollen tube. Female
gametophyte is embryo sac, formed of 7 cells and 8 nuclei. It has a single egg. Embryo sac is
present inside Ovule. Ovule is present in ovary part of Carpel. Besides ovary carpel has style and
stigma to receive pollen. Fig 34.2
37. Pollination: is the transfer of pollen to stigma of carpel. If pollen and stigma belong to same
flower the pollination is called Self-pollination. For example in Pea. If the pollen of one flower
reaches the stigma of other flower, pollination is called Cross-Pollination. Cross-pollination
increases variations and plants possess higher strength called Hybrid vigor.
38. Double Fertilization: in angiosperms pollen tube bring 2 sperms to embryo sac, the female
gametophyte. One sperm fuses with the egg and forms Zygote. The zygote produces embryo.
The 2nd sperm fuses with 2 polar nuclei and form a triploid Endosperm Nucleus. It produces the
reserve food material of seed called Endosperm. There are 2 fusions and the process is referred
as double fertilization, a unique feature of flowering plants.
39. Seed: ovule ripens to form seed. Seed has an embryo and reserve food endosperm which may
be absorbed by cotyledons. It is covered with 2 seed coats. It has a small opening, micropyle.
40. Seed Germination: requires water and 1st part to come out is root. Then shoot grows. Some
seeds do not germinate even if water is available – the condition is called Seed Dormancy.
41. Fruit: ovary ripens to form ovule. The fruit is Simple when formed from one simple or fused
ovary of a flower. If the pericarp (wall of ovary in fruit) is thin and non-juicy, the fruit is called
Dry (Nuts, pods). If the pericarp grows and becomes juicy and swollen, the fruit is called Fleshy
simple fruit (Tomato, apple). If the fruit develops from many free pistils of one flower, the fruit
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is called Aggregate (Strawberry). When many pistils of many flowers develop into a single fruit,
fruit is called Multiple (Pineapple).
Plant Hormones: are chemical messengers and can bring dramatic changes. Fig in review.
Auxin: helps in cell elongation, apical dominance and phototropism.
Ethylene: helps in fruit ripening and leaf-fall.
Cytokinins: promote cell division and are produced in growing tissues like roots, germinating
seeds etc.
Gibberellins: promote seed germination and elongation of intact stems.
Abscissic Acid = ABA: is inhibitor, promotes seed dormancy and closes stomata during water
stress. It is stress hormone of plants.
Tropisms: are growth responses toward or away from a stimulus like light, touch or gravity. The
bending of shoots toward light of a plant placed on a windowsill is Phototropism. The response
of stem or root towards gravity is Gravitropism. The growth of tendrils around a support on
contact is Thigmotropism. These are caused due to accumulation of plant hormone mostly auxin
more on one side. It causes the elongation of cells on that side. More auxin collects on dark side
in case of Phototropism.
Photoperiod: is effect of relative length of day and night on the physiology of a plant. Plants can
determine the season or time of year by determining photoperiod. Long night plants flower only
if the nights are longer than a critical period. Whereas short night plants flower when the night
is shorter than a critical period. Plants have pigment phytochrome that determines the ratio of
day light and UV light to measure photoperiod. A plant is called Day-neutral if its flowering is not
affected by photoperiod. Many other processes like seed germination are controlled by
photoperiod.