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PLANT FORM AND FUNCTION. UNIT SIX Chapters 35,36,37,38,39. Angiosperm Structure. Angiosperms are further divided into 4 major categories: Basal Angiosperms (older angiosperms like Water lilies) Magnoliids (newer like the Magnolia) Monocotyledons a.k.a. monocots (newer still)

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plant form and function



Chapters 35,36,37,38,39

angiosperm structure
Angiosperm Structure
  • Angiosperms are further divided into 4 major categories:
    • Basal Angiosperms (older angiosperms like Water lilies)
    • Magnoliids (newer like the Magnolia)
    • Monocotyledons a.k.a. monocots (newer still)

Have a single seed leaf

- Dicotyledons and/or Eudicotyledons a.k.a. eudicots (newest)

Have double seed leaves

palms and bananas are monocots
Palms and Bananas are Monocots

Rice, wheat, corn – all monocots

basic angiosperm morphology
Basic Angiosperm Morphology
  • Shoot system= stems and leaves
  • Root system= tap root and lateral roots
plant morphology
Plant Morphology
  • Stems consist of alternating “nodes”, the site of leaf attachment
  • The angle created where the leaf attaches to the stem is called the axil
  • The axil contains an axillary bud, which can give rise to a lateral shoot or a branch
  • The tip of the shoot is called the apex and holds the terminal bud
  • The terminal bud and the apex is where the elongation of the shoot occurs
  • The apical bud inhibits the growth of the axillary buds - therefore the advent of the practice of pruning
modified stems
Modified Stems
  • Bulb(e.g. onions)when sliced in half, will show concentric rings.
  • Clove bulblike structures (e.g. garlic) will separate into small pieces when broken apart.
  • Tuber (e.g. potatoes and daylilies) these structures are either on strings or in clusters underneath the parent plants.
  • Rhizomeare large creeping rootstock or underground stems and many plants arise from the "eyes" of these roots (e.g. ginger)
  • Stolons – Horizontal, aboveground stems (e.g. Strawberries)
  • Cormare similar to bulbs but are solid when cut rather than possessing rings.
  • Crown(e.g. the type of root structure found on plants such as asparagus) looks much like a mop head under the soil\'s surface.
  • A tuber is a solid, enlarged, horizontal, shortened stem; it\'s a storage area for reserve food. Note in the center of the picture the production of young tubers arising from the rhizome. On the tubers, the so-called "eyes" are the nodes, where new shoots arise at the axil of a scale (modified leaf); these new shoots can give rise to new plants.

Ginger, bamboo, many self-naturalizing perennials like lily of the valley


Bulblike structures (e.g. garlic) will separate into small segments when broken apart.


Solid bulb, without concentric segments

purpose of roots
Purpose of roots
  • The entire root structure serves to anchor the plant/tree in the soil
  • Absorption of water and nutrients from the soil actually occurs only at the tips of each root fiber
  • Millions of tiny roots hairs in these tip areas help absorption by increasing surface area
fibrous vs tap roots
Fibrous vs. Tap Roots
  • Seedless vascular plants (ferns) and Moncot angiosperms such as grasses have fibrous roots
  • Dicot angiosperm have tap roots
adventitious roots
Adventitious Roots

Roots that grow out of the stem or trunk - sometimes for extra support, sometimes for vegetative reproduction

other modified roots
Other modified roots
  • Aerating roots (or pneumatophores): roots rising above the ground, have a large number pores for exchange of gases.
  • Buttress roots are large roots on all sides of a tall or shallowly rooted tree. Typically they are found in rainforests where soils are poor so roots don\'t go deep. They prevent the tree from falling over and help gather more nutrients.
more modified roots
More modified roots
  • Storage Roots: Beets, radish, turnip, horseradish, sweet potato, and cassava (tapioca).
types of leaves
Types of leaves

Single and double compound leaves

Compound Leaves

Simple Leaves

modified leaves
Modified leaves
  • Spines on cacti are actually leaves. The photosynthesis is carried out by the green stems
  • Bracts on poinsettias are actually not petals, but leaves around the tiny yellow flowers

Tendrils for grasping



When guard cells take up water, they become turgid and this closes the stomata. Loss of water from the cells makes them flaccid and this opens the stomata.


In a C3 leaf the palisade mesophyll cells typically form a layer in the upper part of the leaf; the corresponding mesophyll cells in a C4 leaf are usually arranged in a ring around the bundle sheath cells. The bundle-sheath cells of C4 plants have chloroplasts (dark green), those of C3 leaves usually lack them.

C3 Leaf

C4 Leaf

Bundle sheath cells surround vascular bundles – thus the name.

the protoplast the functional living part of a cell
The Protoplast – the functional, living part of a cell
  • All areas of a plant cell except the cell wall are considered the protoplast
    • Cell membrane
    • Cytosol,
    • All organelles
major plant cells
Major Plant Cells
  • Parenchyma cells
  • Collenchyma cells
  • Sclerenchyma cells
    • Fibers
    • Schlereids
  • Water-conducting cells of the Xylem
    • Tracheids
    • Vessel elements
  • Food-conducting cells of the Phloem
    • Sieve-tube members
    • Companion cells
parenchyma cells
Parenchyma cells
  • Typical plant cell – most abundant in plants
  • Thin walled (Walls contain cellulose, not lignin)
  • Unspecialized – can either photosynthesize, or store starch
    • Can be found in leaves – contain chloroplasts and carry out photosynthesis (mesophyll cells are an example)
    • Can also be found in roots and other non-photosynthesizing parts and store starch in amyloplasts (related to chloroplasts) – in stems they are called the pith



collenchyma cells
Collenchyma cells
  • These cells are usually just under the epidermis of leaves, stems and roots
  • Collenchyma cells are collectively also called the cortex
  • Cells are columnar in shape
  • Also lack lignin in their cell walls, but have thicker walls than parenchyma cells
  • Give younger plants or plant parts support

Because they have thick walls but lack lignin, they are able to provide support without restricting growth – hence found in young, growing parts






sclerenchyma cells
Sclerenchyma cells
  • Thick walls that are fortified with lignin (secondary wall) making them much more rigid than collenchyma walls
  • Mature sclerenchyma cells usually do not contain protoplasts and cannot grow/elongate, so these cells are located in regions of the plant that have stopped growing
sclerenchyma cont d
Sclerenchyma cont’d.
  • Two types of sclerenchyma cells:
    • Fibers - long and thin, exist in bundles in stems, right above above vascular tissue
    • Sclereids – shorter than fibers and give nutshells and seed coats their hardness. The gritty texture of certain fruit like pears is basically due to sclereids scattered among the parenchyma tissue
xylem cells
Xylem Cells
  • Water conducting
  • Elongated
  • Produce lignin-containing secondary walls
  • Lack protoplasts after maturity
  • Two types:
    • Tracheids – spindle-shape, with hole (pits) in them through which water passes
    • Vessel element cells are broader and lie end to end and form continuous hollow tubes for water to flow through
phloem cells
Phloem Cells
  • Food conducting – sugar, minerals and other organic compounds
  • Unlike xylem cells, phloem cells can contain protoplasts* (either complete or incomplete)
  • Two types:
    • Sieve-tube members – chains of cells that conduct food (partial protoplasts -lack nuclei and ribosomes)
    • Companion cells – connected to sieve-tube cells, contain nuclei and ribosomes, so help maintain sieve-tube cells

*see slide #31 for non-protoplast-containing phloem

three tissue system
Three Tissue System
  • The cells we have learned about in the past slides such as parenchyma, sieve tube cells, etc. can be placed into 3 main tissue categories or systems:
    • Dermal tissue system
    • Vascular tissue system
    • Ground tissue system


 Epidermis

 Collenchyma (also called the cortex – which is ground tissue between the epidermis and the vascular bundles)



Vascular bundle


A thin layer of cells called the vascular cambium separates the xylem and phloem

 Parenchyma or pith

Also known as the Pith in stems – stores food (amyloplasts) and water (central vacuoles)

summary of dicot monocot stems
Summary of dicot & monocot stems



root anatomy
Root Anatomy

Pith – a central core of parenchyma cells that store food – mostly in monocots

Stele – a vascular bundle that gives rise to both xylem and phloem

Pericycle – the outermost layer of the stele that sprouts the lateral roots

Casparian strip – a thin strip or coating that prevents water from seeping between cells

cross section of a monocot root


(Dermal tissue)



Cortex or schlerenchyma (ground tissue)



Endodermis (dermal)


(Parenchyma or Ground)

Pericycle (Parenchyma or

Ground tissue)

Stele (Entire central Vascular region)

Pericycle (Parenchyma or ground)

cross section of a dicot root


No pith or parenchyma in dicot roots

growth in plants
Growth in Plants
  • Animals undergo determinate growth – they stop growing after they reach a certain size.
  • Plants on the other hand have indeterminate growth – they continue to grow throughout their life.
annual biennials perennials
Annual, Biennials, Perennials
  • Botanically, an annual plant is a plant that usually germinates, flowers and dies in one year. (Impatiens, sunflower, gerbera daisies)
  • A perennial plant is a plant that lives for more than two years. Perennial plants are divided into two large groups, those that are woody and those that are Herbaceous.(Roses, sage, peonies)
  • A biennial plant is a flowering plant that takes between twelve and twenty-four months to complete its lifecycle.(Parsley, foxglove, sweet William)
how can plants have constant growth
How can plants have constant growth?
  • They can have indeterminate growth because they have perpetual embryonic tissues (like stem cells in animals)
  • These embryonic tissues are called Meristems or cambiums.
  • There are 2 main types of meristems (embryonic tissues):
    • Apical meristems – they are located in the terminal and axillary buds of shoots and root tips
      • Apical meristems give rise to primary growth which means that they make the plant grow in length – in the roots throughout the soil and in the shoots to increase surface area for photosynthesis.
      • Parenchyma cells, collenchyma cells and sclerenchyma cells all come from apical meristems
      • Herbaceous plants (non-woody) the entire plant develops due to primary growth from apical meristems
meristems cont d
Meristems, cont’d.
  • Lateral meristems (also called Cambiums) – are also located in shoots and roots, but are responsible for secondary growth or lateral growth – they make the stems and roots thicker by growing sideways Woody plants and trees grow in thickness in areas where primary growth has stopped.

There are 2 types of lateral meristems:

    • Vascular cambiums: this produces secondary xylem and phloems which are actually wood. The vascular cambium is the source of both the secondary xylem (grows inwards, towards the pith) and the secondary phloem (grows outwards), and is located between these tissues in the stem and root.
    • Cork cambiums – replace the epidermis with peridermis which is bark or cork in some trees
lateral growth
Lateral Growth
  • The phloem is constantly being pushed outward and crushed, only the innermost layers adjacent to the vascular bundle are functional phloem (Protoplast-containing and food-conducting). Also called the inner bark
  • The dead, protoplast-lacking phloem cells are called non-functional phloem, which becomes part of the outer bark (The bark of trees consists of cork, cork cambium, cortex, and phloem)
meristems cont d1
Meristems, cont’d.

Vertical growth

Lateral growth 

Vertical growth

transpiration vs translocation
Transpiration vs. Translocation
  • Xylem sap (water from the roots) is helped along by transpiration
  • Phloem sap (fluid rich in sugar and minerals) is moved by translocation
    • The predominant sugar in phloem sap is sucrose
    • Phloem sap always moves from a sugar source (such as leaves) to a sugar sink (cells that consume sugar – growing plant parts)
transpiration vs guttation
Transpiration vs. Guttation
  • Transpiration is the loss of water through the xylem cells, when stomata in leaves open for gas exchange
  • Transpiration is essential, because it provides the “sucking” effect for water to travel up the xylem tissues (although too much is bad)
  • Guttation is the water exuded from leaves as a result of root pressure (removing excess water due to low transpiration rates)
guttation vs condensation
Guttation vs. Condensation

Dew appears as many droplets and is caused by the condensation of atmospheric water vapor

Guttation appears as single droplets of water

and is the plant’s way of removing water

opening and closing of stomata
Opening and Closing of Stomata
  • Located throughout the epidermis are paired, guard cells, and between each pair is a small opening, called a stoma (plural: stomata). Guard cells contain chloroplasts, but other epidermal cells do not.
  • When the two guard cells are turgid (swollen with water), the stoma is open
  • The increase in osmotic pressure in the guard cells is caused by an uptake of potassium ions (K+).
  • Abscisic acid (ABA) is the hormone that triggers closing of the stomata when there is a danger of excessive water loss (hot midday)
plant control systems
Plant Control Systems
  • Many hormones are involved in controlling plant systems:
    • Auxins
    • Cytokinins
    • Gibberellins
    • Abscisic acid
    • Ethylene
auxin and elongation
Auxin and elongation
  • Auxins promote primary and secondary growth
  • They promote growth of adventitious roots from cuttings
  • They control phototropism, gravitropism
  • They control the release of ethylene – another plant hormone
  • Auxin is made in apical meristems, young leaves and seed embryos
Ehtylene promotes
    • fruit ripening
    • Promotes apoptosis
    • leaf and flower aging
    • leaf abscission or the intentional shedding of leaves, flowers and fruit
    • Made in aging flowers and leaves, ripening fruits and stems
abscisic acid
Abscisic Acid
  • Causes stomata to close
  • Inhibits growth in plant parts
  • Maintains dormancy in plants
  • Made in leaves, stems and unripe (green) fruit
  • Promote cytokinesis during plant mitosis
  • Delay senescence in leaves and other parts of a plant
  • Made in roots and delivered to other parts of the plant
  • Fruit growth
  • Germination of seeds
  • Stem elongation or - the growth of an elongated stalk with flowers grown from within the main stem of a plant. This condition occurs in plants that are grown for their leaves, such as cabbage, lettuce, spinach, and other leafy greens.
plant movement
Plant Movement
  • Phototropism – movement toward light – caused by photoreceptors on shoot tips and auxins
  • Gravitropism – response to gravity (seeds always germinate in the right direction) – caused by plastids called statoliths that contain dense grains of starch, in root tips and auxins
  • Thigmotropism – response to touch (ivy grasping supports), caused by ethylene
  • When a plant responds to amount to light available - e.g. by flowering
  • Controlled by proteins called phytochromes
  • Phytochrome is a photoreceptor, a pigment that plants use to detect light. It is sensitive to light in the red and far-red region of the visible spectrum. Many flowering plants use it to regulate the time of flowering based on the length of day and night (photoperiodism) and to set circadian rhythms. It also regulates other responses including the
    • germination of seeds,
    • elongation of seedlings,
    • the size, shape and number of leaves, and
    • the synthesis of chlorophyll.
  • Plants make several different phytochromes
red light blue light
Red Light Blue Light
  • Blue light inhibits seed germination and shoot elongation and red light promotes it
  • This is due to phytochromes – non-photosynthetic plant pigments and photoreceptors
sustainable agriculture soil conservation
Sustainable Agriculture &Soil Conservation
  • Irrigation – primary source is underground water sources called aquifers. Overuse can cause ground to sink.
  • Fertilization – crops deplete soil nutrients, so nutrients must be added to soil – chemicals or organic materials such as compost, manure, etc.
  • Crop Rotation – alternating types of plants grown, to prevent depletion of nitrogenous nutrients (alternating grains and legumes).
    • Crop rotation also prevents the accumulation of pathogens specific to a crop
sustainable agriculture soil conservation1
Sustainable Agriculture &Soil Conservation
  • Phytoremediation – using certain plants to absorb soil toxins such as zinc, lead, etc.

Alpine Pennycress is used to absorb

Zinc from agricultural soil

soil free agriculture
Soil-free agriculture
  • Hydroponics – plants are grown without soil, in a solution of water and nutrients.


  • Nutrients readily available
  • Plants grow better, mature faster
  • Less space needed since roots do not need to grow far in search of nutrients.
  • No weeds – no competition and no need for weed killers, healthier harvest.
  • No soil-based insects or pests, so no pesticides needed


  • Plants that attach to other plants
  • Epiphytes usually derive only physical support and not nutrition from their host, though they may sometimes damage the host. Hence, they are NOT parasitic
  • They do this to get more light and rain water in a rainforest canopy



parasitic plants
Parasitic Plants
  • Derive all or some nutrients from host plant
  • Parasitic plants have a modified root, the haustorium, that penetrates the host plant and connects to the xylem, phloem, or both, in stems or roots of the host plant.
  • Examples: Mistletoe, Dodder, Rafflesia
carnivorous plants
Carnivorous Plants
  • Grow in nutrient poor soil such as bogs.
  • High acidity in bogs prevents growth of much-needed nitrogen cycle bacteria
  • Most plants cannot grow in such soil
  • Carnivorous plants evolved a mechanism to trap and digest insects
  • This adaptation helped them overcome the nitrate dilemma
  • Examples: Pitcher plants, sundews, Venus fly-trap
carnivorous plants1
Carnivorous Plants

Venus Flytrap


Pitcher Plant

plant and fungal symbiosis
Plant and Fungal Symbiosis
  • Fungal mycorrhizae penetrate plant tissues
  • The fungus derives nutrients from the plant
  • The plant gets: More water-absorbing surface area, minerals that fungus absorbs, antibiotics to prevent infections (many fungi produce antibiotics)


    • Hyphae form a mantle around roots
  • Endomycorrhizae (arbuscular mycorrhizae)
    • Hyphae are not visible
    • Tiny vesicles called arbuscules are formed between root cells