1. PLANT STRUCTURE & FUNCTION
AHL Topic 9.1
IB Biology
Miss Werba

2. TOPIC 9 – PLANT SCIENCE 9.1 PLANT STRUCTURE and GROWTH 9.3
9.2
TRANSPORT IN ANGIOSPERMS
9.3
REPRODUCTION IN ANGIOSPERMS
J WERBA – IB BIOLOGY 2

3. THINGS TO COVER Tissue distribution in stem & leaf of dicots
Difference between dicots & monocots
Tissue distribution & function in the leaf
Modification of roots, stems & leaves
Apical & lateral meristems of dicots
Role of auxin in phototropism
J WERBA – IB BIOLOGY 3

4. Let’s review…Kingdom Plantae
9.1
Let’s review…Kingdom Plantae
Structural features are used to classify plants:
eg. seeds, roots, stems, flowers & leaves
How many groups of plants are there?
4 or 5 groups
Mosses & liverworts  BRYOPHYTES
Conifers  CONIFEROPHYTES
Ferns  FILICINOPHYTES
Flowering plants  ANGIOSPERMOPHYTES
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5. Let’s review…Kingdom Plantae
9.1
Let’s review…Kingdom Plantae
Non-vascular: have no vessels, no roots, no stems or leaves.
eg. mosses & liverworts
Vascular: have vessels to transport food and water. They have roots, stems and leaves.
eg. grass, corn, trees, flowers, bushes
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6. Let’s review…Kingdom Plantae
9.1
Let’s review…Kingdom Plantae
Angiosperms:
have seeds enclosed in a fruit
are flowering plants with finite growing seasons
are mostly pollinated by birds & bees
eg. grasses, tulips, oaks, dandelions
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7. Let’s review…Kingdom Plantae
9.1
Let’s review…Kingdom Plantae
ALL GREEN PLANTS
contain vascular tissue (eg. phloem & xylem)
no vascular tissue
small delicate leaves
thick leathery leaves
seeds
no seeds
MOSSES
LIVERWORTS
no flowers, seeds in cones
flowers with seeds
CONIFERS
FLOWERING PLANTS
FERNS
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8. ANGIOSPERMS Command term: OUTLINE
9.1.2
ANGIOSPERMS Command term: OUTLINE
Angiosperms are divided into two main groups:
Monocots
& Dicots
The ‘cots’ refers to the cotyledons or seed leaves
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9. ANGIOSPERMS Command term: OUTLINE
9.1.2
ANGIOSPERMS Command term: OUTLINE
Structure
Monocotyledons
eg. onions and grasses
Dicotyledons
eg. oak trees and roses
Seed
one cotyledon
two cotyledons
Leaf
parallel veins
branched, net-like veins
Flower
floral parts in multiples of 3
floral parts in multiples of 4 or 5
Stem
vascular bundles scattered throughout the stem
vascular bundles arranged in a ring
Root
adventitious roots
(Fibrous, unbranched)
branched tap roots
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10. ANGIOSPERMS Command term: OUTLINE
9.1.2
ANGIOSPERMS Command term: OUTLINE
Monocotyledons
eg. onions and grasses
Dicotyledons
eg. oak trees and roses
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11. STEM STRUCTURE Command term: DRAW and LABEL
9.1.1
STEM STRUCTURE Command term: DRAW and LABEL
Surrounded by the epidermis
Contains vascular tissue in a system of veins or vascular bundles
Vascular bundles contain:
xylem for water transport
phloem for transport of solutes
Vascular bundles are arranged in a ring, positioned towards the outside of the stem
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12. STEM STRUCTURE Command term: DRAW and LABEL
9.1.1
STEM STRUCTURE Command term: DRAW and LABEL
Cambium
Epidermis
Xylem
Cortex
Phloem
Pith
Sclerenchyma
Tissue map of young sunflower stem in transverse section
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13. STEM STRUCTURE Command term: DRAW and LABEL
9.1.1
STEM STRUCTURE Command term: DRAW and LABEL
Epidermis:
Typically one cell thick
Protects the stem against invasion by pathogens & desiccation (drying out)
Xylem:
Transport of water and dissolved ions
Walls of tube are lignified (hardened with lignin) to resist the pressure to collapse inwards
Phloem:
Transport of solutes (eg. sucrose, amino acids)
Have companion cells that load/unload/maintain the sieve tube
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14. STEM STRUCTURE Command term: DRAW and LABEL
9.1.1
STEM STRUCTURE Command term: DRAW and LABEL
Cambium:
Acts as a lateral meristem (similar to stem cells)
Can divide & differentiate into phloem & xylem
Cortex:
Support stem
Pith:
Parenchyma cells that form the basic packaging tissue of the plant body
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15. LEAF STRUCTURE Command term: DRAW and LABEL
9.1.1
LEAF STRUCTURE Command term: DRAW and LABEL
Leaf structure is adapted for:
photosynthesis
gas exchange
Leaves are oriented towards the light to allow for optimum illumination
The large leaf surface area is held perpendicular to the light source
Leaves are thin so there are few cell layers to absorb light before it is received by photosynthetic cells
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16. LEAF STRUCTURE Command term: DRAW and LABEL
9.1.1
LEAF STRUCTURE Command term: DRAW and LABEL
phloem
xylem
vascular bundles of leaf
epidermis
palisade
spongy
mesophyll 
Tissue map of young sunflower stem in cross-section
stoma
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17. LEAF STRUCTURE Command term: DRAW and LABEL
9.1.1
LEAF STRUCTURE Command term: DRAW and LABEL
Upper Cuticle
Palisade mesophyll
Upper epidermis
Spongy mesophyll
Xylem
Phloem sieve tube
Lower epidermis
Stomatal
pore
Guard cells
Lower cuticle
J WERBA – IB BIOLOGY
Vertical section of dicotyledonous leaf 17
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18. LEAF STRUCTURE & FUNCTION Command term: EXPLAIN
9.1.3
LEAF STRUCTURE & FUNCTION Command term: EXPLAIN
Upper epidermis:
A single layer of cells found on the upper surface of the leaf.
It is covered by a thick waxy cuticle.
Main function is water conservation:
prevents water loss from the upper surface where the light intensity and heat are the greatest.
Upper epidermis
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19. LEAF STRUCTURE & FUNCTION Command term: EXPLAIN
9.1.3
LEAF STRUCTURE & FUNCTION Command term: EXPLAIN
Palisade mesophyll:
Consists of tightly packed cylindrical cells.
Main photosynthetic tissue containing many chloroplasts.
It is found on the upper half of the leaf (upper surface) where the light intensity is the greatest
Palisade mesophyll
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20. LEAF STRUCTURE & FUNCTION Command term: EXPLAIN
9.1.3
LEAF STRUCTURE & FUNCTION Command term: EXPLAIN
Spongy mesophyll:
Made up of loosely packed cells.
This tissue is found in the lower half of the leaf (lower surface) and has few chloroplasts.
It provides gas exchange (CO2 uptake and O2 release) and therefore needs to be close to the stomata found in the lower epidermis.
Spongy mesophyll
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21. LEAF STRUCTURE & FUNCTION Command term: EXPLAIN
9.1.3
LEAF STRUCTURE & FUNCTION Command term: EXPLAIN
Vascular tissue:
Consists of xylem and phloem which are found in the veins of the leaf.
The veins are positioned in the middle of the leaf so that they are in close contact with all the cells.
Vascular bundle
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22. LEAF STRUCTURE & FUNCTION Command term: EXPLAIN
9.1.3
LEAF STRUCTURE & FUNCTION Command term: EXPLAIN
Vascular tissue:
Xylem – dead tissue; long and tubular and transport water into the leaf to replace the water that has been lost through transpiration
Phloem - living cells with pores in between them; transport the products of photosynthesis out of the leaf
Vascular bundle
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23. LEAF STRUCTURE & FUNCTION Command term: EXPLAIN
9.1.3
LEAF STRUCTURE & FUNCTION Command term: EXPLAIN
Lower epidermis:
Contains stomata
Stomata open/close to allow gas exchange but reduce water loss
Secretes cuticle
Barrier against infection
Lower epidermis
Guard cell
Stomata
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24. PLANT ADAPTATIONS Command term: IDENTIFY
9.1.4
PLANT ADAPTATIONS Command term: IDENTIFY
Geophytes are herbaceous plant with an underground storage organ
Storage organs are reserves of carbohydrates, nutrients and water.
They evolved as a mechanism for plant survival through adverse climatic conditions.
eg. bulbs, stem tubers, storage roots or tendrils
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25. PLANT ADAPTATIONS Command term: IDENTIFY
9.1.4
PLANT ADAPTATIONS Command term: IDENTIFY
Bulbs:
A stem that grows underground
Has modified leaves for storing food
Allows for growth after dormancy
Stem is shortened so that the leaves grow together
The leaves have no chloroplasts but are thickened to store food.
Only monocots form true bulbs.
eg. onion bulbs
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26. PLANT ADAPTATIONS Command term: IDENTIFY
9.1.4
PLANT ADAPTATIONS Command term: IDENTIFY
Stem tubers:
Stems modified for food storage
They can form roots
The stem contains a lot of parenchyma tissue for storing food.
Also serve as a means of asexual reproduction (vegetative propagation) as new plants develop from the stem tubers
eg. potato tubers
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27. PLANT ADAPTATIONS Command term: IDENTIFY
9.1.4
PLANT ADAPTATIONS Command term: IDENTIFY
Storage roots:
Modified roots for storing water or food.
These roots are typical of biennials (takes 2 years to complete life cycle)
eg. carrots
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28. PLANT ADAPTATIONS Command term: IDENTIFY
9.1.4
PLANT ADAPTATIONS Command term: IDENTIFY
Tendrils:
Modified stems or leaves
Provide attachment and support
This allows the plant to climb
When the tendril touches something, the other side will grow faster, making it wrap around the object.
eg. sweet pea, passion fruit, grape vines
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29. PLANT ADAPTATIONS Command term: IDENTIFY
9.1.4
PLANT ADAPTATIONS Command term: IDENTIFY
Tendrils:
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30. MERISTEMS Command term: STATE
9.1.5
MERISTEMS Command term: STATE
Dicotyledonous plants have apical and lateral meristems
Plants grow at their tips in regions called meristems
Meristems are undifferentiated tissue (stem cells)
There are 2 types: lateral and apical
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31. MERISTEMS Command term: STATE
9.1.5
MERISTEMS Command term: STATE
Dicotyledonous plants have apical and lateral meristems
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32. MERISTEMS Command term: COMPARE
9.1.6
MERISTEMS Command term: COMPARE
Apical meristem:
Found in buds and the tips of shoots/roots.
It is responsible for primary growth which makes a plant taller at roots and stems
Type of growth is herbaceous, non-woody stem/roots
Lateral meristem:
Found in the cambium.
It is responsible for secondary growth which makes a plant wider, or adds woody tissue
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33. AUXIN & PHOTOTROPISM Command term: EXPLAIN
9.1.7
AUXIN & PHOTOTROPISM Command term: EXPLAIN
Tropisms are a plant’s version of a taxis ie. movement response to directional external stimulus
Positive = towards stimuli; negative = away from stimuli
Stimuli = chemicals, gravity, light, touch, etc
Phototropism:
Growth response to directional light
Plants grow towards the light
= positive phototropism
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34. AUXIN & PHOTOTROPISM Command term: EXPLAIN
9.1.7
AUXIN & PHOTOTROPISM Command term: EXPLAIN
Auxins (plant hormones) cause positive phototropism in plant shoots and seedlings
Auxins are found in embryo of seeds, meristems of apical buds and young leaves
Promote cell elongation on one side of shoot to grow/bend towards light
Auxin moves away from light source (uneven spread) causing the elongation of cells on stem side away from light and therefore curvature towards light
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35. AUXIN & PHOTOTROPISM Command term: EXPLAIN
9.1.7
AUXIN & PHOTOTROPISM Command term: EXPLAIN
Dark
Blue light source
Foil cap
Foil cap 1 2 3 4 1 2 3 4
Mica
Agar
Mica
Agar
Shoot 1: Control
Shoot 2: Foil cap over tip – no light is able to pass
Shoot 3: Mica barrier placed between plant and tip. Mica is impermeable.
Shoot 4: Agar barrier placed between plant and tip. Agar is permeable.
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36. AUXIN & PHOTOTROPISM Command term: EXPLAIN
9.1.7
AUXIN & PHOTOTROPISM Command term: EXPLAIN
Dark
Blue light source
Foil cap
Foil cap 1 4
Mica
Agar
Mica
Agar 1 2 3 4 2 3
Shoot 1: Control
Shoot 2: Foil cap over tip – no light is able to pass
Shoot 3: Mica barrier placed between plant and tip. Mica is impermeable.
Shoot 4: Agar barrier placed between plant and tip. Agar is permeable.
J WERBA – IB BIOLOGY 36

37. AUXIN & PHOTOTROPISM Command term: EXPLAIN
9.1.7
AUXIN & PHOTOTROPISM Command term: EXPLAIN
Shoot 1: Auxin moved to dark side of shoot in blue light, causing these cells to elongate & shoot to grow towards the light.
Shoot 2: Foil removed external stimulus from shoot therefore auxin was evenly spread throughout stem & it grew straight.
Shoot 3: Mica stopped auxin flowing down from the tip of the shoot, so the plant grew straight.
Shoot 4: Auxin was able to diffuse through agar and move to dark side of shoot, causing the shoot to bend.
J WERBA – IB BIOLOGY 37

38. PRACTICE QUESTION
Which structure is shown in the following image? [Source: Ohio State University at Lima]
A dicotyledon stem

39. PRACTICE QUESTION The diagram below shows a cross section of a stem.
What is the structure labelled Y and one of its functions?
Xylem
mechanical support
transport of water and ions

40. PRACTICE QUESTION How do terrestrial plants support themselves? 3 ways
cellulose cell wall
turgor pressure
lignin / lignified xylem

41. PRACTICE QUESTION Explain the role of auxin in phototropism. [8 marks]
auxin is a plant hormone; produced by the tip of the stem/shoot tip/apical meristem;
transported to zone of cell growth;
lateral transport of auxin to cells on shade side/with least light;
makes cell walls flexible/softens cell walls; auxin makes cells enlarge/grow; results in cell expansion;
gene expression also altered by auxin to promote cell growth; (positive) phototropism is growth towards light; causes cells on dark side to elongate/grow faster;