Biology II Exam 2 - Botany Part 2

The Plant Body

• two organ systems

  • The Shoot

  • The Root

The Shoot

• Aerial (above-ground) component of the plant

• The organs in this system are Stem (and its branches) and leaves

• Composed of repeating module called a phytomer

Phytomer

• consists of a leaf, the portion of the stem which the leaf is attached (node) and the surrounding stem (internode), and the bud

• Include Leaf, Stem and Bud

Node

the portion of the stem to which the leaf if attached

Leaf

primary organ of photosynthesis

Bud

contains shoot meristem cells

Stem

organ of support; vascular tissue

The Root

• the below-ground component of the plant. The organs in this system are the foots and repeating units called lateral roots

Root Functions

• Secures the plant in place

• Absorb water and minerals from the soil

• Store photosynthetic products

Parts of the Leaf

petiole and sheaths, blade, compound leaves

Taproot

• type of root system

• large trees need these for stability

Fibrous

• type of root system

• common in monocots esp. grasse

Adventitious

• type of root system

• roots that arise from tissue other than the radicle

How many tissue systems are there in plants?

• 3

• Dermal, Ground and Vascular

Dermal Tissue System

forms the outer covering of the plant

Ground tissue system

carries out photosynthesis, stores photosynthetic products, and helps support the plant

Vascular Tissue System

conducts water and solutes throughout the plant

Characteristics of plant cells

• cell walls - primary, secondary and middle lamella

• Plasma membrane

• Large Vacuoles

• Chloroplasts (plastids)

• Starch grains can be present

• Plasmodesmata

Primary Cell Wall

• flexible, cellulose

Secondary Cell Wall

• cellulose, lignin, other components

Middle Lamella

• Pectin-rich layer that cements together cell walls of adjacent cells

Plasmodesmata

• small tubes joining plant cells

• Cytoplasmic channels that pass through pores in primary and secondary cell walls

• Living bridges between cells allowing molecules to pass from cell to cell

• Provide cell to cell communication

Parenchyma

• least specialized plant cells ‘workhouse cells’

• Primary walls thin and flexible, no secondary walls

• Large vacuoles - water and solute storage

• ALIVE at functional maturity

• regeneration of more specialized cells in case of damage

• Functions: Metabolism, Photosynthesis, Starch Storage, in stems and roots, abundant in fleshy parts of fruit

Totipotent

stem cells of plants

Collenchyma

• Thick primary walls

• usually grouped in strands of cylinders

• can elongate and expand with stem and leaf growth

• ALIVE at functional maturity

• Function: flexible support for herbaceous and young woody plants

Sclerenchyma

• thick secondary walls

• two types (Fibers and Sclereids)

• strengthened by lignin

• cannot elongate with growth

• Function: support

• Often lack protoplasts at maturity

  • DEAD at functional maturity

Fibers

• Type of Sclerenchyma

• long slender and tapering in bundles (rope, flax)

Sclereids

• type of sclerenchyma

• (stone cells); short, irregular shape

• makes hard seed coat and nut shells

• Gritty texture in pears

Cells in Vascular Tissue

Xylem and Phloem (together in vascular bundles)

Xylem

• Tracheids and Vessel Elements; Sclerenchyma

• Water conducting cells - from roots to leaves

• Pits in secondary walls

• Dead at functional maturity

  • secondary walls often deposited in spiral or ring patterns

Tracheids

• type of Xylem

  • Angiosperms = Hardwood

  • Gymnosperms = Softwood

• Gymnosperms and Angiosperms

• Long thin cells with pits and tapered ends

• Water moves from tracheid to tracheid through the pits in the cell wall

Vessel Elements

• type of Xylem

• Angiosperms

• wider, shorter, less taper than tracheids

• end walls perforated - form long tubes or pipes constructed of vessel elements end to end

Phloem

• ‘Food’ conducting cells - from leaves to roots but also elsewhere in the plant

• In chains like pipes joined together

• Alive at maturity although sieve tube elements lack nucleus, ribosomes and vacuoles

• Companion Cells

Companion Cells

• alongside each sieve tube member

• Plasmodesmata connect sieve tube member to companion cell, companion nucleus serves sieve tube member

Dermal Tissue

comprised of epidermis, cuticle and root hairs

Epidermis

single layer of tightly packed cells

Root Hairs

specialized epidermal cells for water and mineral absorption

Meristems

• specialized bundles of undifferentiated cells

• can give rise to any and all of the cell types in plants

• tissue found in both shoot and the root

  • two types; apical and lateral

Apical Meristem

• Dome shaped

• all types of tissues (epidermal, ground vascular) are derived from ______

• Axillary buds develop from meristematic tissues at base of leaf primordia

Lateral Meristems

• responsible for secondary (outwards) growth

• 2 types

  • Vascular Cambium

  • Cork Cambium

Vascular Cambium

• in stems and roots of perennials and woody trees

• increase tree girth

• form xylem to inside, phloem to outside

Cork Cambium

Produced Bark

Primary Growth in Roots 3 Regions plus Root Cap

1) Zone of Differentiation (Maturation) - root hairs. vascular tissue

2) Zone of Elongation

3) Zone of Division - Meristem produces cells to either side

4) Root Cap - protective layer of cells, continuously sloughed off

The Leaf

• primary organ of photosynthesis

  • occur in any tissue or organ where chloroplasts are present, but are in HIGHEST concentration in the leaf

The Veins

• a bundle of vascular tissue that deliver water and nutrients to the leaf cells (xylem), and remove sugars to distribute throughout the body of the plant (phloem)

Tricomes

are specialized hair-like extensions of the epidermis that reduce air flow around the leaf, helping to reduce water loss throughout the stomata

Epidermis

• secrete waxy cuticle

• Stomata, and trichomes are usually on the lowest

Stomata

• pores in a leaf, mostly on the undersurface

• each pore is surrounded by a pair of guard cells

• pores that regular gas exchange

• Take in CO2 and releasing O2

• Close to prevent water loss

Guard Cells

• change shape to open or close the stoma

Mesophyll

• ground tissue in plant leaves

• two layers

  • the upper/palisade

  • lower/spongy

Palisade Mesophyll

• is made up of elongate cells with a high density of chloroplasts

• this layer performs most of the photosynthesis in the leaf

Spongy mesophyll

• made up of smaller, irregularly shaped, loosely packed cells

• The loose packing of these cells helps with both gas exchange and catching any photons the palisade miss

Vascular Bundles

• continuous with stem and roots

• contain both xylem and phloem

• structural support and transport

Chloroplasts

• cellular organelles that conduct photosynthesis

• circular genome (endosymbiotic origin)

• outer and inner membrane

• Contain stroma, thylakoid and granum

Stroma

dense fluid

Granum

stack of thylakoids

Thylakoid

• light-dependent reactions take place

• Contain chlorophyll

Chlorophyll A

• absorbs blue and red light

• Accounts for most of the photon capture by chloroplasts

Chlorophyll B

• absorbs aqua and orange light

Carotenoids, Xanthophylls and Anthocyanins

• absorb other wave lengths

  • Overall photosynthetic efficiency of the plant

Chlorophylls

• reflect green wavelength

• that’s why ‘grass is green’

Absorption Spectrum

plot of light energy absorbed against wavelength

Action spectrum

plot of the biological activity of an organism against wavelength

First step of Photosynthesis

• Light dependent reaction

• Captures light energy as chemical energy; produces oxygen, splits water oxygen

• In those photons of specific wavelengths are absorbed by photosynthetic pigments are used to create ATP and NADPH

• One photon = 3ATP, 2NADPH and 1 O2

Second Step of Photosynthesis

• The calvin cycle

• can occur in light or in the dark

• energy from the light reaction is used to create an organic (sugar) colecule

• Photosynthetic products → sugars are usually stored in plants as starch

Photosynthesis

• Occurs in Chloroplasts

• Uses CO2 and H2O

• Produces O2 and Glucose

• Requires energy input

Respiration

• occurs in mitochondria

• uses O2 and Glucose

• Produces CO2 and H2O

• Produces Energy (ATP)